Systems and methods for slipper motor cooling

Abstract

A VTOL aircraft includes a plurality of tilt propellers configured to rotate between a forward cruise configuration and a vertical lift configuration. A nacelle or other structure may include a variable inlet configured to expand in the lift configuration to maximize the amount of slip flow captured by the inlet. The variable inlet may contract in the cruise configuration to reduce drag. The variable inlet may be passively actuated as the tilt angle of the tilt propeller varies.

Description

[0001] Cross - Reference to Related Applications

[0002] This disclosure claims priority and the benefit of U.S. Patent Application No. 18 / 311,288, filed on May 3, 2023, entitled "SYSTEMS AND METHODS FOR TILTER MOTOR COOLING" (Attorney Docket No.: 16163.0014-01000), which in turn claims priority and the benefit of U.S. Patent Application No. 18 / 064,538, filed on Dec. 12, 2022, entitled "TILTER MOTOR COOLING APPARATUS FOR VERTICAL TAKEOFF AND LANDING AIRCRAFT AND OPERATING METHOD OF THE SAME" (Attorney Docket No. 16163.0014-00000). The foregoing applications are hereby incorporated by reference in their entirety for all purposes. TECHNICAL FIELD

[0003] This disclosure generally relates to the field of powered aerial vehicles. More specifically, but not limited thereto, this disclosure relates to innovations in tilt-rotor aircraft using an electric propulsion system. Certain aspects of this disclosure generally relate to cooling systems for tilter motors. Other aspects of this disclosure generally relate to improvements in cooling paths that can be used in other types of vehicles but provide specific advantages in aerial vehicles. SUMMARY OF THE INVENTION

[0004] Some embodiments of this disclosure provide a tilting device for a vertical takeoff and landing (VTOL) aircraft, the tilting device including: a propeller configured to be tiltable between a lift configuration and a cruise configuration; a motor assembly coupled to the propeller; and a nacelle including an air inlet and an air outlet for a heat transfer device configured to be thermally coupled to the motor assembly; wherein the air inlet is configured to receive a portion of the slipstream from the propeller when the propeller is operating in the lift configuration; and wherein the air outlet is configured to cause the air pressure at the air outlet to be less than the air pressure at the air inlet when the propeller is operating in the lift configuration.

[0005] Some embodiments of the present disclosure provide a method of operating antilt device of a vertical takeoff and landing (VTOL) aircraft. The method may include: tilting a propeller to a lift configuration, the propeller being coupled to a motor assembly; directing slipstream from the tilted propeller above an exterior of a nacelle, the nacelle including an air inlet and an air outlet for a heat transfer device, the heat transfer device being configured to be thermally coupled to the motor assembly; and generating a negative pressure zone at the air outlet by directing the slipstream above the exterior of the nacelle, the negative pressure zone causing air to flow from the air inlet to the air outlet. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figures 1A - 1B is a schematic diagram showing an exemplary VTOL aircraft consistent with the disclosed embodiments.

[0007] Figures 2A - 2I is a schematic diagram showing an exemplary tilted propeller in a VTOL aircraft consistent with embodiments of the present disclosure.

[0008] Figures 3A - 3B is a schematic diagram showing an exemplary motor assembly in a VTOL aircraft consistent with embodiments of the present disclosure.

[0009] Figures 4A - 4E is a schematic diagram showing an exemplary cooling flow path in antilt motor assembly of a VTOL aircraft consistent with embodiments of the present disclosure.

[0010] Figures 5A - 5D is a schematic diagram showing an exemplary tilted propeller in a VTOL aircraft consistent with embodiments of the present disclosure.

[0011] Figures 6A - 6I is a schematic diagram showing an exemplary tilted propeller in a VTOL aircraft consistent with embodiments of the present disclosure.

[0012] Figures 7A - 7I is a schematic diagram showing an exemplary tilted propeller in a VTOL aircraft consistent with embodiments of the present disclosure. DETAILED DESCRIPTION

[0013] The present disclosure presents components of an electric vertical takeoff and landing (eVTOL) aircraft mainly for use in unconventional aircraft. For example, the eVTOL aircraft of the present disclosure may be intended for frequent (e.g., more than 50 flights per weekday), short-duration flights (e.g., less than 100 miles per flight) over, into, and out of populated areas. The aircraft may be intended to carry 4 to 6 passengers or commuters who desire a low-noise and low-vibration experience. Accordingly, it may be required that their components be configured and designed to withstand frequent use without wear, that they generate less heat and vibration, and that the aircraft include mechanisms for effectively controlling and managing the heat or vibration generated by the components. Additionally, it may be expected that several of these aircraft operate close to each other over crowded metropolitan areas. Accordingly, it may be required that their components be configured and designed to generate low levels of noise both inside and outside the aircraft and be configured and designed to have various safety and backup mechanisms. For example, for safety reasons, it may be required that the aircraft be propelled by a distributed propulsion system to avoid the risk of a single point of failure and that they be capable of conventional takeoff and landing on a runway. Further, it may be required that the aircraft be able to safely vertically take off from and safely vertically land in a relatively restricted space (e.g., a vertical takeoff and landing airport, a helipad, or a driveway) compared to a conventional airport runway while transporting approximately 4 to 6 passengers or commuters with accompanying luggage. These usage requirements can impose design constraints on the aircraft size, weight, operational efficiency (e.g., drag, energy use), which can affect the design and configuration of the aircraft components.

[0014] The disclosed embodiments provide new and improved configurations of aircraft components not observed in conventional aircraft, and / or design criteria for the identification of components different from those of conventional aircraft. Such alternative configurations and design criteria, in combination with addressing the drawbacks and challenges of conventional components, result in the embodiments of the various configurations and designs for eVTOL aircraft components disclosed herein.

[0015] In some embodiments, the eVTOL aircraft of the present disclosure can be designed to be capable of both vertical takeoff and landing and conventional takeoff and landing, where a distributed electric propulsion system enables vertical flight, forward flight, and transitions. Thrust can be generated by supplying high-voltage electrical power to the electric motors of the distributed electric propulsion system, each of which can convert the high-voltage electrical power into mechanical shaft power to rotate a propeller. Embodiments disclosed herein can relate to optimizing the energy density of the electric propulsion system. Embodiments can include electric motors connected to an on-board electrical power source, which can include devices capable of storing energy, such as batteries or capacitors, or can include one or more systems for harnessing or generating electrical power, such as fuel-powered generators or solar panel arrays. Some disclosed embodiments provide a weight reduction and space reduction of components in the aircraft, thereby improving aircraft efficiency and performance. Given the concern for safety in passenger transportation, the disclosed embodiments implement new and improved safety protocols and system redundancy in the event of a failure to minimize any single point of failure in the aircraft propulsion system. Some disclosed embodiments also provide new and improved methods to meet aviation and traffic laws and regulations. For example, the Federal Aviation Administration of the United States enforces federal laws and regulations that require safety components, such as fire barriers, to be close to engines that use more than a threshold amount of oil or other combustible materials.

[0016] In a preferred embodiment, the distributed electric propulsion system can include twelve electric motors, which can be mounted on booms at the front and rear of the main wing of the aircraft. The front electric motors can be tilted between a horizontal orientation (e.g., to generate forward thrust) and a vertical orientation (e.g., to generate vertical lift) during flight. In terms of the direction of propeller rotation, the front electric motors can be of the clockwise type. The rear electric motors can be fixed in a vertical orientation (e.g., to generate vertical lift). In terms of the direction of propeller rotation, the rear electric motors can be of the clockwise type or the counterclockwise type. In some embodiments, the aircraft can have various combinations of front and rear electric motors. For example, the aircraft can have six front electric motors and six rear electric motors, four front electric motors and four rear electric motors, or any other combination of front and rear motors, including embodiments where the number of front and rear electric motors is not equal. In some embodiments, the aircraft can have four front propellers and four rear propellers, where at least four of these propellers include tiltable propellers.

[0017] In a preferred embodiment, for vertical takeoff and landing (VTOL) missions, the front electric engine and the rear electric engine can provide vertical thrust during takeoff and landing. During the flight phase when the aircraft is in the forward flight mode, the front electric engine can provide horizontal thrust, while the propellers of the rear electric engine can be retracted to a fixed position to minimize drag. The rear electric engine can be actively retracted using position monitoring. The transition from vertical flight to horizontal flight and vice versa can be achieved by tilting the propeller subsystem. The tilting propeller subsystem can redirect the thrust between the primary vertical direction during the vertical flight mode and the primary horizontal direction during the forward flight mode. A variable pitch mechanism can change the blade collective angle of the propeller-hub assembly of the front electric engine for operation during the hover phase, transition phase, and cruise phase.

[0018] In some embodiments, for conventional takeoff and landing (CTOL) missions, the front electric engine can provide horizontal thrust for wing-borne takeoff, cruise, and landing. In some embodiments, the rear electric engine may not be used to generate thrust during CTOL missions, and the rear propeller can be retracted to a suitable position.

[0019] In some embodiments, the electric engine can be housed or attached to a pylon of the aircraft and includes a motor, an inverter, and a gearbox. In some embodiments, the motor, inverter, and gearbox can be interfaced such that they share a central axis. In some embodiments, the torque originating in the motor can be sent away from the propeller of the propulsion system and sent to the gearbox. In some embodiments, the gearbox can provide gear reduction and then send the torque back to the propeller via a main shaft through a bearing located inside the motor. In some embodiments, the inverter can be mounted at the rear of the gearbox such that the main shaft does not travel through the inverter when outputting torque to the propeller. In some embodiments, the motor, gearbox, and inverter can be interfaced such that a coolant (such as oil) can be used to maintain the motor, inverter, and / or gearbox while sharing a common heat exchanger. In some embodiments, the amount of oil used for lubricating and cooling the electric engine can vary, including any other measured amount of two or more oils less than one quart, two quarts, three quarts.

[0020] In some embodiments, the tilt propeller system can include a linear or rotary actuator for changing the orientation of the propulsion system during operation. In some embodiments, the pitch of the propulsion system can change as the orientation of the propulsion system changes. In some embodiments, the rotary actuator can include a motor, an inverter, and a gearbox. In some embodiments, the gearbox can include various types of gears that interface to provide a gear reduction capable of orienting the propulsion system. In some embodiments, the tilt propeller system can include a redundant configuration such that there are multiple motors, inverters, and gearboxes and gear interfacing is used. In some embodiments, a configuration utilizing multiple motors, gearboxes, and inverters can enable a faulty portion of the redundant configuration to be driven by the motors, inverters, and gearboxes of another portion of the configuration. In some embodiments, the gearbox configuration can also allow the tilt propeller system to maintain the propulsion system orientation with or without additional power provided by the system.

[0021] In some embodiments, the electric propulsion system described herein can generate thrust by supplying high voltage (HV) power to an electric engine, which in turn converts the HV power into mechanical shaft power that is used to rotate a propeller. As mentioned above, the aircraft described herein can have multiple electric engines that are mounted in a pylon manner at the front and rear of the wings. The magnitude of the thrust generated by each electric engine can be managed by a torque command that arrives at each electric engine from a flight control system (FCS) via a digital communication interface. Embodiments can include a front electric engine that is capable of changing its orientation or tilting. Additional embodiments include a front engine that can be of a clockwise (CW) type or a counterclockwise (CCW) type. The front electric engine propulsion subsystem can consist of a multi-blade adjustable pitch propeller and a variable pitch subsystem.

[0022] In some embodiments, the aircraft can include a tail engine or a lift device, which can be of a clockwise (CW) type or a counterclockwise (CCW) type. Further embodiments can include a tail electric engine that uses a multi-blade fixed pitch propeller.

[0023] As described herein, the orientation and use of an electric propulsion system may change throughout the operation of an aircraft. In some embodiments, during vertical takeoff and landing, a front propulsion system as well as a tail propulsion system may provide vertical thrust during takeoff and landing. During the flight phase when the aircraft is in forward flight mode, the front propulsion system may provide horizontal thrust while the tail propulsion system propellers may be retracted in a fixed position to minimize drag. The tail electric propulsion system may be actively retracted by position monitoring. Some embodiments may include transitioning from vertical flight to horizontal flight and vice versa. In some embodiments, the transition may be accomplished by tilting a propeller system (TPS). The TPS redirects thrust between a primarily vertical direction during vertical flight mode and a primarily horizontal direction during forward flight mode. Additional embodiments may include a variable pitch mechanism that may change the total blade angle of the front propulsion system propeller-hub assembly for operation during hover, cruise, and transition phases. Some embodiments may include a conventional takeoff and landing (CTOL) configuration such that the tilter provides horizontal thrust for wingborne takeoff, cruise, and landing. The tail electric engine is not used to generate thrust during CTOL missions and the tail propellers are retracted in a suitable position.

[0024] In some embodiments, the electric engines described herein may have design features to mitigate and prevent uncontrolled fires, such as using less than one quart or other non-hazardous amounts of combustible fluid contained in both the tilt engine and the lift engine, having no nominal ignition source within the electric engine, having an engine over-temperature operating limit that may be 50 °C or more below the auto-ignition temperature of the combustible fluid, over-temperature detection and protection, over-pressure detection and protection, and over-current detection and protection. In some embodiments, the design features of the electric engine may cause it to be considered not a designated fire protection area.

[0025] As disclosed herein, within various configurations such as the representative configurations described herein, an electric engine may include an inverter and a motor; or an inverter, a gearbox, and a motor. For example, an electric engine may include an electric motor, a gearbox, and an inverter that share the same central axis. Additionally, the central axis may be configured along the axis of an output shaft leading to a propeller of the aircraft. In such an exemplary configuration, the motor, the gearbox, and the inverter will all share the output shaft as the central axis and will be oriented annularly around the output shaft. Additional embodiments may include a motor, a gearbox, and an inverter mounted together in sequence, or a configuration where some components are mounted together (such as the motor and the gearbox) and another component is located elsewhere (such as the inverter) but uses a wiring system to connect the electric engine.

[0026] As mentioned above, the electric engine of the aircraft described herein may include some or all of a motor, an inverter, and a gearbox. Various configurations may include an inverter and a motor such that the output shaft of the motor directly provides speed and torque to the propeller shaft. Additional embodiments of the electric engine may include a motor, an inverter, and a gearbox, in which case the output of the motor may travel through the gearbox, which is connected to the output shaft of the propeller; a motor, an inverter, and a gearbox, in which case the output travels away from the propeller from the motor, through the gearbox, where the output shaft of the propeller travels back through the gearbox and the motor to the propeller. As described herein, the electric engine may contemplate any combination or orientation of some or all of the motor, the inverter, and the gearbox. Additionally, each configuration or orientation of the electric engine disclosed herein may include cooling by air cooling, coolant fluid, or a mixture of both.

[0027] For example, a configuration of the electric engine may include a motor and an inverter, where the motor is located between the propeller of the aircraft and the inverter. Additionally, the motor may include a gearbox. Further, the inverter may share the same central axis as the motor, in which case the inverter may be located in a housing and may be air-cooled, and the housing projects cantileveredly from the rear of the motor. It is recognized that this inverter orientation may not be an optimal configuration in terms of the housing required to achieve such a cantilevered orientation. Additionally, the motor utilizing air cooling in such a configuration may include potting material, and air fins assisting in motor cooling may cause an even greater increase in the mass of the system.

[0028] Some embodiments may include an electric engine in which the inverter module may be mounted externally to the motor housing. Additional embodiments may include an electric engine in which the inverter may be mounted on top of the electric motor such that the air-cooling fins of the inverter are located below the propeller. Further embodiments may include the inverter mounted to the back of the motor, where the air-cooling fins face radially outward; the inverter mounted to the front of the motor, where the air-cooling fins face radially outward; the inverter mounted to the motor, in which case the inverter is cooled by a liquid (such as oil); or any other positioning of the inverter relative to the motor.

[0029] Embodiments of the electric motor may include a stator housing, a wound stator assembly, a rotor, various bearings, and any additional components such that it helps transfer the speed and torque generated by the motor to the propeller.

[0030] It should be understood that the electric engine can generate heat during operation and can include a thermal management system to ensure that the components of the electric engine do not malfunction during operation. In some embodiments, a coolant can be used, and the coolant can circulate through individual components of the engine (such as an inverter, a gearbox, or a motor), through some of the components, or through all of the components of the engine to help manage the heat present in the engine. Additional embodiments can include using an air cooling method to cool the electric engine, or using a mixture of coolant and air to manage the heat generated during operation in the electric engine. In some embodiments, throughout the inverter, gearbox, or motor, the coolant used can also be the same liquid as the liquid used as a lubricant. For example, the inverter, gearbox, and motor can be cooled using liquid or air, or a mixture of air cooling and liquid cooling can be used, such as using air cooling to cool the motor and liquid cooling in the inverter and gearbox, or any other combination of air cooling and liquid cooling throughout the inverter, gearbox, and motor or even a subset of these components.

[0031] In some embodiments, oil can be used as a lubricant for the entire electric engine and can also be used as a coolant to help manage the heat generated during operation of the engine. Further for this example, different amounts of oil can be used to act as both a lubricant and a coolant fluid in the electric engine, such as less than one quart, less than two quarts, or any other amount of oil required to lubricate and cool the electric engine with or without the aid of air cooling. As has been disclosed herein, the electric engine can have different primary functions, such as being used only for lift and landing and thus being used in only one orientation, or being used during all flight phases such as lift, landing, and flight. An engine used during all phases of flight can experience various orientations throughout the flight and can include more lubricant and coolant than an engine used in only one orientation. Thus, all engines on an aircraft may not contain the same amount of lubricant and coolant. For example, a lift engine and a landing engine may only require less than one quart of oil, while an engine operating during all flight phases may require more than one quart of oil. It should be understood that the exemplary embodiments mentioned herein are representative and do not prescribe a limit on the amount of lubricant and coolant that can be used in the electric engine.

[0032] It can be understood that by using oil not only to lubricate the electric engine but also to cool the electric engine instead of another coolant, additional oil will be added to the system, but the oil will remove traditional components that may be used to cool such an electric engine. For example, if the electric engine is cooled by another liquid such as ethylene glycol, the engine may include separate heat exchangers for both the lubricant fluid and the coolant fluid. Thus, in embodiments where a single fluid (such as oil) is used for both lubrication and cooling, there will be an increase in oil, but only one heat exchanger will be required, so the overall mass of the system may be reduced due to the use of fewer heat exchangers and the possible elimination of other components, and there may be a more attractive drag curve. Additionally, due to the reduction in mass and the benefits of cooling the engine with one substance rather than relying on air cooling which may have issues traveling throughout the engine, using one substance to lubricate and cool the engine can improve the efficiency of the system.

[0033] Additional embodiments of the electric engine can have various components to ensure that any combustible fluid is monitored and prevented from entering certain sections of the electric engine. Some embodiments can include an electric engine having a wet zone housing that can be defined by a gearbox, a motor, and / or a heat exchanger. In some embodiments, the electric engine can have up to 4 liters of air within a motor-gearbox housing that is in contact with engine oil. Embodiments of the motor-gearbox housing can use a breather to balance the internal pressure with the external pressure. Embodiments of the breather can include a breather that protrudes above nearby design features to prevent accidental entry of external fluids. Additional embodiments can include a breather having a screen and a tortuous entry path to prevent entry of external debris. Embodiments can include an observation window on an inclined electric engine and a lift electric engine to check for overfilling or underfilling of oil during maintenance.

[0034] Additional embodiments of the electric engine may include active protection features in the front and rear electric engines, such as monitoring internal temperatures throughout engine operation, including oil temperature, stator windings, inverter bulk capacitors, power modules, control board power modules, control board control processors, control board monitoring processors, internal hot spots, and various other locations throughout the engine. Embodiments may include over-temperature limits considering known failure temperatures and operating limits related to the auto-ignition temperature of the fluid. Some embodiments may include a high-voltage power system that may have a fuse at the high-voltage battery terminals, which can quickly and irreversibly disconnect the engine electrical connections to mitigate overcurrent events. This overcurrent protection may be activated when the electric engine current consumption is greater than the operating overcurrent. Thus, in some embodiments, a fault condition that causes overcurrent may only result in transient overheating, arcing, or spark faults. Some embodiments may include a fire threat characterization test ignition source that may be selected to be a more severe ignition source than a short circuit that occurs in the electric engine and is disconnected by the engine fuse. In some embodiments, the inverter will detect AC overcurrent and isolate the faulty phase and / or will continuously monitor the input DC voltage and will take protective measures to keep the voltage below the overvoltage operating limit.

[0035] During takeoff, landing, hover, and cruise, the motors and associated control components of a VTOL aircraft may generate heat. Heat dissipation must occur to prevent degradation or damage to the motors, control components, and other elements of the VTOL aircraft.

[0036] Some components may generate different heat loads during different operation time periods. For example, in a "lift" configuration, during takeoff, landing, and hover, the tilt propellers may generate heat loads in a first range. During forward flight in a "cruise" configuration, the tilt propellers may generate heat loads in a second range. In some embodiments, the first range and the second range may overlap or may be substantially the same. In some embodiments, the midpoint of the first range may be higher than the second range. In some embodiments, the midpoint of the second range may be higher than the first range. However, due to the power requirements during takeoff, landing, and hover, some tilt propellers may generate a higher heat load when operating in the lift configuration than when operating in the cruise configuration.

[0037] The problem of different cooling requirements between lift and cruise may be complicated by different amounts of available cooling air. For example, in some embodiments, the motor assembly of the tilt propeller can be air cooled by bringing a cooling air flow into contact with a heat transfer device such as a cooling fin or a heat exchanger. The air flow can enter the nacelle or other enclosure around the motor assembly through an air inlet. For example, air can be directed into the air inlet by the movement of the VTOL aircraft, or it can be forced into the air inlet as a slipstream from the tilt propeller blades. As used herein, "slipstream" can refer to the air flow that is forced away by the propeller blades when the propeller blades rotate. In the cruise configuration, the VTOL aircraft will move forward at a high speed such that sufficient air flow is directed into the air inlet. However, this is not the case in all situations in the lift configuration. The VTOL aircraft can ascend or descend slowly, or it can even hover in mid-air, essentially motionless. Therefore, when operating in the lift configuration, the speed of the VTOL aircraft cannot be relied upon to generate a cooling air flow. Additionally, in the lift configuration, it may be difficult to direct sufficient slipstream into the air inlet because the slipstream intensity may be relatively weak near the axis of rotation where the motor assembly is located.

[0038] Embodiments of the present disclosure provide an improved system and method for generating a cooling air flow in the lift configuration of a VTOL aircraft. In some embodiments, the VTOL aircraft can be designed to utilize the stronger slipstream at the periphery of the tilt propeller blades to create a low-pressure wake region at the exit side of the nacelle by using the stronger slipstream. This low-pressure wake region can allow the weaker central slipstream to flow through the air inlet and cool the motor assembly, as further described below.

[0039] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which like numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present disclosure. Rather, they are merely examples of devices and methods consistent with aspects related to the subject matter recited in the appended claims.

[0040] As used herein, the term "tilt propeller" refers to a variable pitch propeller configured to provide thrust for vertical lift and forward propulsion by changing the pitch of the propeller. The term "lift propeller" can refer to a fixed pitch propeller configured to provide thrust for vertical lift.

[0041] Figures 1A - 1BVTOL aircraft 100 in a cruise configuration and a vertical takeoff, landing, and hover configuration (also referred to herein as a "lift" configuration) consistent with embodiments of the present disclosure are shown, respectively. The aircraft 100 may include a fuselage 102, wings 104 mounted to the fuselage 102, and one or more rear stabilizers 106 mounted to the rear of the fuselage 102. A plurality of lift propellers 112 may be mounted to the wings 104 and may be configured to provide lift for vertical takeoff, landing, and hovering. A plurality of tilt propellers 114 may be mounted to the wings 104 and may be tilted between the cruise configuration and the lift configuration, in which the plurality of tilt propellers provide forward thrust for horizontal flight of the aircraft 100, as Figure 1A shown, and in which the plurality of tilt propellers provide a portion of the lift required for vertical takeoff, landing, and hovering, as Figure 1B shown. As used herein, the lift configuration may refer to a tilt propeller orientation in which the tilt propeller thrust primarily provides lift for the aircraft. The cruise configuration may refer to a tilt propeller orientation in which the tilt propeller thrust primarily provides forward thrust for the aircraft.

[0042] In some embodiments, the lift propellers 112 may be configured to provide only lift, with all propulsion provided by the tilt propellers. Thus, the lift propellers 112 may be in a fixed position and may generate thrust only during takeoff, landing, and hovering. At the same time, the tilt propellers 114 may be tilted to the lift configuration, in which the thrust of the tilt propellers is downward to provide additional lift.

[0043] For forward flight, the tilt propellers 114 may be tilted from their lift configuration to their cruise configuration. In other words, the pitch of the tilt propellers 114 may vary from a pitch in which the tilt propeller thrust is downward (to provide lift during vertical takeoff, landing, and hovering) to a pitch in which the tilt propeller thrust is rearward (to provide forward thrust to the aircraft 100). The tilt propellers may be tilted about an axis that may be perpendicular to the forward direction of the aircraft 100. When the aircraft 100 is in full forward flight during the cruise configuration, the lift may be provided entirely by the wings 104. At the same time, the lift propellers 112 may be turned off. The blades 120 of the lift propellers 112 may be locked in a low-drag position for aircraft cruising. In some embodiments, the lift propellers 112 may each have two blades 120, and the two blades may be locked to cruise in a minimum-drag position in which one blade is directly in front of the other blade, as Figure 1A shown. In some embodiments, the lift propellers 112 have more than two blades. In some embodiments, the tilt propellers 114 include more blades 118 than the blades of the lift propellers 112. For example, asFigures 1A - 1B As shown, the lift propellers 112 can each include, for example, two blades, and the tilt propellers 114 can each include, for example, five blades. In some embodiments, the tilt propellers 114 can have, for example, from 2 to 5 blades.

[0044] In some embodiments, the aircraft can include only one wing 104 on each side of the fuselage 102 (or have a single wing across the entire aircraft), and at least a portion of the lift propellers 112 can be located behind the wing 104, and at least a portion of the tilt propellers 114 can be located in front of the wing 104. In some embodiments, all of the lift propellers 112 can be located behind the wing 104, and all of the tilt propellers 114 can be located in front of the wing 104. According to some embodiments, all of the lift propellers 112 and tilt propellers 114 can be mounted to the wing, i.e., no lift propellers or tilt propellers can be mounted to the fuselage. In some embodiments, all of the lift propellers 112 can be located behind the wing 104, and all of the tilt propellers 114 can be located in front of the wing 104. According to some embodiments, all of the lift propellers 112 and tilt propellers 114 can be positioned inside the wing tips 109.

[0045] In some embodiments, the lift propellers 112 and tilt propellers 114 can be mounted to the wing 104 by struts 122. The struts 122 can be mounted below the wing 104, on top of the wing, and / or can be integrated into the wing profile. In some embodiments, one lift propeller 112 and one tilt propeller 114 can be mounted to each strut 122. The lift propeller 112 can be mounted at the rear end of the strut 122, and the tilt propeller 114 can be mounted at the front end of the strut 122. In some embodiments, the lift propeller 112 can be mounted on the strut 122 in a fixed position. In some embodiments, the tilt propeller 114 can be mounted to the front end of the strut 122 by a hinge. The tilt propeller 114 can be mounted to the strut 122 such that when in a cruise configuration, the tilt propeller 114 is aligned with the body of the strut 122, thereby forming a continuous extension of the front end of the strut 122, which minimizes drag during forward flight.

[0046] In some embodiments, the aircraft 100 can include, for example, one wing on each side of the fuselage 102 or can include a single wing extending across the aircraft. According to some embodiments, at least one wing 104 is a high wing mounted to the upper side of the fuselage 102. According to some embodiments, the wing includes control surfaces such as flaps and / or ailerons. According to some embodiments, the wing can have a curved wing tip 109 to reduce drag during forward flight.

[0047] In some embodiments, the rear stabilizer 106 includes control surfaces, such as one or more rudders, one or more elevators, and / or one or more combined rudder-elevators. The wings can have any suitable design. For example, the wings have a narrowed leading edge or a narrowed trailing edge. In some embodiments, in the central section of the wing 104, the wing can have a substantially straight leading edge.

[0048] The aircraft 100 can include at least one door 110 for passengers to enter and exit. In some embodiments, the door 110 can be located below and in front of the wing 104, as Figures 1A - 1B seen in.

[0049] In some embodiments, the lift propellers 112 or tilt propellers 114 can be deflected relative to at least one other lift propeller 112 or tilt propeller 114. As used herein, deflection refers to the relative orientation of the axis of rotation of the lift propeller / tilt propeller with respect to a line parallel to the forward-backward direction, similar to the roll degree of freedom of an aircraft. Deflection of the lift propellers and / or tilt propellers can be achieved by orienting the plane of rotation of the lift propeller / tilt propeller disk (blades plus the propeller portion to which the blades are attached) so as not to intersect critical parts of the aircraft (such body regions where personnel may be located, critical flight control systems, batteries, adjacent propellers, etc.) or other propeller disks, thereby assisting in minimizing damage caused by propeller burst and can provide enhanced yaw control during flight.

[0050] The lift propellers 112 can be deflected in any suitable manner and combination. For example, the lift propellers 112 can be deflected away from the fuselage 102 such that the lift propellers on the first side of the fuselage are deflected in a first direction and the lift propellers on the second side of the fuselage are deflected in a second direction. In some embodiments, the lift propellers 112 can be deflected in accordance with the corresponding tilt propellers. Any suitable combination of deflection and / or non-deflection of the lift propellers relative to each other and relative to the tilt propellers can be used to achieve the desired performance characteristics.

[0051] Further discussion of VTOL aircraft can be found in U.S. Patent Publication No. 2021 / 0362849, which is incorporated herein by reference in its entirety.

[0052] As discussed above, the motors and associated control components of a VTOL aircraft can generate heat during operation. Heat dissipation must be effected to prevent degradation or damage to the motors, control components, and other elements of the VTOL aircraft. For example, cooling can be achieved by directing an air flow to the heated components. The heated components can be, for example, a motor or other heat-generating component, or it can be, for example, a heat exchanger configured to receive heat from the heat-generating component via a liquid heat exchange medium. However, in a lift configuration, due to the reasons discussed above, it may be difficult to obtain an air flow sufficient to cool the tilting motors. Accordingly, it may be desirable to provide a tilting motor cooling system that can generate a sufficient air flow even when the VTOL aircraft is operating in a lift configuration.

[0053] A. Example Tilt Propeller Embodiment

[0054] Figures 2A - 2I A portion of a VTOL aircraft 200 consistent with an embodiment of the present disclosure is shown. For example, the VTOL aircraft 200 can be similar to the VTOL aircraft 100 in Figures 1A - 1B . Figures 2A - 2I Elements similar to those in Figures 1A - 1B can be labeled with corresponding numbers using 2 as the leading digit. For example, in some embodiments, the boom 222 in Figures 2A - 2I can be similar to the boom 122 in Figures 1A - 1B .

[0055] Figure 2A Tilt propellers in a lift configuration (top figure) and a cruise configuration (bottom figure) consistent with an embodiment of the present disclosure are shown. The tilt propeller 214 can be coupled to the boom 222 and can be tilted between a lift configuration and a cruise configuration by a tilt actuator 238. The tilt propeller can include: a plurality of propeller blades 218 that are coupled to a hub 231 at blade roots 219; a nacelle 225 that surrounds a motor assembly 230 and a heat exchanger 233; a boom baffle 227; a nacelle baffle 228; and a tilt actuator 238. The nacelle 225 can further include an air inlet 240 and an extension 226. The extension 226 can be configured to increase the size of the air outlet 241 of the nacelle 225 and the wake region 243 at the heat exchanger 233.

[0056] The propeller blades 218 can direct the slipstream substantially downward in the lift configuration, as in Figure 2AThe downward-pointing arrow at the top of the [description] is shown schematically. The air inlet 240 can receive the slipstream or other airflows, as indicated by the thin arrow pointing downward from the blade root 219. The slipstream can flow through the nacelle 225 and into the heat exchanger (or other heat transfer device, such as cooling fins) 233. The slipstream can be directed to the heat exchanger 233 by the nacelle baffle 228 or other guiding structures. For example, in some embodiments, the baffle function within the nacelle 225 can be at least partially performed by the housing covering the outer surface of the motor assembly 230. The heat exchanger 233 can transfer heat to the slipstream as the slipstream passes through the air outlet side of the nacelle 225 and the heat exchanger 233, thereby cooling the motor assembly 230.

[0057] The air inlet 240 is shown as having a substantially arcuate shape, but this is merely exemplary. In fact, the air inlet 240 can have any suitable shape, including circular, oval, rectangular, slot-shaped, or any other suitable design. The air inlet can include a scoop or notch within the nacelle 225 having any suitable size or shape. The air inlet 240 can include multiple air inlets that are arranged together or at different positions on the nacelle 225. For example, the air inlet 240 can include a series of slits within the nacelle 225. Further, the air inlet 240 does not need to be a completely open orifice, but can include a mesh or grid covering, or can have a lid that can be actuated passively or actively.

[0058] The air inlet 240 can be located at a certain radial distance from the center of the hub 231, which allows a desired amount of airflow to enter. In some embodiments, the center of the air inlet 240 can be located at a certain radial distance from the hub 231, which is between 20% and 25% of the radius of the propeller blade 218. For example, if the propeller blade 218 extends outward, such as to 40" from the center of the hub 231, then the center of the air inlet 240 can be located between 8" and 10" from the center of the hub 231. In some embodiments, the center of the air inlet 240 can be located at a certain radial distance from the hub 231, which is at least, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or more of the radius of the propeller blade 218.

[0059] Note that in Figure 2A and other figures, dashed lines are used for clarity, for example, to indicate that the heat exchanger 233 is located inside the nacelle 225 and to show the internal airflow. However, not all internal components are depicted using dashed lines. In some cases, internal components can be depicted using solid lines, or can be omitted.

[0060] The strength of the slipstream may be non-uniform along the blade 218 at all radial distances from the hub 231. For example, the thin arrows entering the air inlet 240 may represent a relatively weak slipstream, while the thick arrows passing along the exterior of the nacelle 225 may represent a relatively strong slipstream. The slipstream strength may be characterized by various factors such as air pressure, velocity, mass flow rate, etc. The slipstream strength may vary along the length of the blade 218 for a variety of reasons. For example, the circumferential velocity at a point on the blade 218 increases with increasing radial distance from the axis of rotation at the hub 231. Additionally, the profile, width, and angular orientation of the blade 218 may vary along the blade length. Thus, for example, a narrow blade root 219 located very close to the hub 231 may produce a slipstream that is significantly weaker than the slipstream produced by the wider portion of the blade 218 located farther away. As a further example, the blade 218 may not include a narrowed blade root 219 at the hub 231, and the slipstream at that location may be weak given the short radial distance from the axis of rotation. In some embodiments, as discussed further below, the propeller blade 218 may be wider near its root than at its periphery, or the blade root 219 may include a cylindrical shaft. In general, blade designs may vary widely. However, in some embodiments, the blade may be optimized primarily for flight rather than for generating a cooling air flow. Thus, it may be advantageous to optimize the nacelle 225 and other components of the tilt propeller 214 to increase the air flow reaching the heat exchanger 233 through the air inlet 240.

[0061] To increase the air flow, the nacelle 225 may include an extension portion 226 that is configured to increase the size of the wake region 243 at the outlet side of the nacelle 225 and at the heat exchanger 233. For example, the extension portion may increase the size of the wake region 243 by shielding the open air volume at the outlet side of the nacelle 225 from the high-pressure air flow surrounding the exterior of the nacelle 225. Thereby, a large and relatively low-pressure region is created by the strong slipstream flowing around the exterior of the nacelle 225 and through the end of the extension portion 226. The air pressure in the wake region 243 may be significantly lower than the air pressure in the surrounding regions, including the region containing the air inlet 240. Thus, even a moderate pressure at the air inlet 240 will produce a cooling air flow through the interior of the nacelle 225. The moderate pressure at the air inlet 240 may correspond to a weak slipstream near the hub 231, or it may simply correspond to the ambient air pressure near the VTOL aircraft 200. The open air volume created in the lift configuration may be occupied, for example, by the strut 222 and the strut baffle 227 in the cruise configuration. Thus, the open air volume at the outlet side of the nacelle 225 is larger in the lift configuration than in the cruise configuration.

[0062] The size and shape of the extension 226 can depend on the desired size of the wake region 243. This, in turn, can depend on a number of factors for the particular VTOL aircraft implementing the tilt propeller 214. For example, the extension can be designed taking into account the following factors: the cooling requirements of the tilt motor assembly 230; the size and layout of the air inlet 240; the air flow from the relatively weak slipstream at the inner portion of the blade 218 or the blade root 219 (if any); and the air flow from the relatively strong slipstream at the outer portion of the blade 218. Factors that can limit the size of the extension 226 can include: the weight of the nacelle 225; the drag that would be generated by an unnecessarily large extension; mechanical considerations such as the need to actuate the tilt propeller 214 unobstructed between the lift orientation and the cruise orientation; and the vertical distance for the strong slipstream from the outer portion of the blade 218 to remain coherent or available as air flow.

[0063] In some embodiments, the extension 226 can include a depth parallel to the axis of rotation of the tilt propeller 214. The depth can be represented as the distance from the bottom surface of the motor assembly 230 (when vertically oriented in the lift configuration) or the outlet side of the heat exchanger 233 to the end of the extension 226. The depth of the extension 226 can be selected based on, for example, the factors discussed above or other design considerations. In some exemplary embodiments, the extension 226 can include a depth of at least 4", 8", 12", 16", 20" or greater. In some exemplary embodiments, the extension 226 can include a depth of no greater than 24", 20", 16", 12" or 8".

[0064] In some embodiments, the extension 226 can substantially or completely surround the axis of rotation of the tilt propeller 214 in a plane perpendicular to the axis of rotation. In some embodiments, the extension 226 can almost surround the axis of rotation while leaving room to accommodate mechanical features such as the tilt actuator 238. In some embodiments, the extension 226 can only partially surround the axis of rotation. In still further embodiments, a complete section 226a of the extension 226 can surround the axis of rotation while a partial section 226b of the extension 226 only partially surrounds the axis of rotation (see the lower figure in Figure 2A . The dimension of the extension 226 in the circumferential direction around the axis of rotation can be referred to as the arc length and can be expressed in angular terms. For example, an extension 226 with an arc length of 180° will extend halfway around the axis of rotation of the tilt propeller 214. Note that terms such as "arc length" and "circumference" are not intended to imply that the cross-sectional shape of the nacelle 225 must be circular.

[0065] As Figure 2AAs shown in the exemplary embodiments, the arc length of the complete section 226a can be substantially 360°, while the arc length of the partial section 226b can be adjacent to 160°. However, this is only given as an example. The arc length can be expressed as, for example, the minimum arc length, the maximum arc length, or the average arc length in the depth direction along the extension part 226. For example, the minimum arc length of the extension part 226 or the partial section 226b of the extension part 226 can be 30°, 60°, 90°, 120°, 150°, or 180°. The maximum arc length of the extension part 226 or the partial section 226b of the extension part 226 can be, for example, 300°, 270°, 240°, 210°, or 180°. In addition, as Figure 2A shown, the arc length can substantially correspond to the arc length of the heat exchanger 233 or the arc length of another air flow path through the nacelle 225. For example, when the arc length at the outlet side of the heat exchanger 233 is, for example, 120°, 90°, or 45°, etc., the extension part 226 can be configured to have a similar arc length so that the wake region 243 extends near the outlet side of the heat exchanger 233.

[0066] In some embodiments, the nacelle 225 can be movably mounted on the first part of the boom 222, and the boom baffle 227 can be mounted on the second part of the boom 222 in a fixed position. When operating in the cruise configuration as shown in the lower figure in Figure 2A below, the tilt propeller 214 can be rotated by the tilt actuator 238 to align with the boom 222 (the blades 218 are omitted for clarity). In the cruise configuration, the nacelle 225 can be combined with the boom baffle 227 to form the discharge channel 242. For example, the nacelle baffle 228 can form the first part of the discharge channel 242, which guides the slipstream to the inlet side of the heat exchanger 233. The boom baffle 227 can be used for the second part of the discharge channel 242, which guides the slipstream from the heat exchanger 233 to the air outlet 241. Generally, the boom baffle 227 and the nacelle baffle 228 can be regarded as parts of an integral baffle structure that can be configured to optimize the air flow in both the lift configuration and the cruise configuration. The discharge channel 242 can guide the air flow from the air outlet 241 to the discharge outlet 244. The discharge outlet 244 can also be formed by the combination of the nacelle 225 and the boom baffle 227. The boom baffle 227 can further engage or abut against the lower surface of the motor assembly 230 or the heat exchanger 233. In this way, the boom baffle 227 can substantially seal the discharge channel 242 from the rest of the internal space of the nacelle 225, so that air flows smoothly from the air inlet 240 to the discharge outlet 244 without generating excessive resistance inside the nacelle 225.

[0067] Since the VTOL aircraft 200 moves at high speeds during cruise, there is sufficient cooling airflow available without relying on the wake region 243 as in the lift configuration. Thus, Figure 2A Embodiments of Figure 2A achieve sufficient cooling airflow in both the lift and cruise configurations.

[0068] Figure 2B Additional tilting propellers 214 in the lift and cruise configurations consistent with embodiments of the present disclosure are shown. In Figure 2B , the extension portion 226 is not divided into full and partial segments but substantially surrounds the entire axis of rotation along its full depth. This configuration can be beneficial for generating a wider wake region 243 by shielding a greater volume of space from the strong slipstream of the blade 218.

[0069] In some embodiments, the heat exchanger 233 can be larger than the heat exchanger described in Figure 2A . For example, at the upper figure of Figure 2B , the arc length of the heat exchanger 233 can be commensurate with the increased size of the wake region 243. In some embodiments, as shown in the lower figure of Figure 2B , the boom baffle 227 can be configured to enclose the entire heat exchanger 233 within the discharge passage 242. Alternatively, the boom baffle 227 can be configured to enclose only a portion of the heat exchanger 233 to maintain a narrow discharge passage 242 similar to Figure 2A , or the size of the heat exchanger 233 can be the same as the exchanger shown in Figure 2A , although the extension portion 226 is larger. Similarly, the nacelle baffle 228 can at least partially wrap around the motor assembly 230 to enclose the entire heat exchanger 233 within the discharge passage 241.

[0070] In some embodiments, to accommodate the 360° extension portion 226 in the cruise configuration, the motor assembly can be spaced from the boom 222 by an extended mount 223. The extended mount 223 can space the motor assembly 230 away from the boom 222 by a distance slightly less than the depth of the extension portion 226. This allows the nacelle 225 to slightly overlap the boom 222 when operating in the cruise configuration. Alternatively, the extended mount can space the motor assembly 230 away from the boom 222 by a distance substantially equal to the depth of the extension portion 226.

[0071] Figure 2C Additional tilting propellers 214 in the lift and cruise configurations consistent with embodiments of the present disclosure are shown. Figure 2C As with Figure 2AThe difference is that the air inlet 240 is located at the top of the nacelle 225, facing the propeller blades 218 or the blade roots 219, rather than on one side of the nacelle 225. Configuring the air inlet 240 to be closer to the propeller blades 218 can generate an improved air flow. Additionally, as explained above with respect to Figure 2A the air inlet 240 does not need to have the Figure 2B arc shape described in

[0072] but can include any number of different shapes, sizes, or other configurations. Figure 2D For example, Figure 2D shows additional tilting propellers 214 in lift configuration and cruise configuration consistent with embodiments of the present disclosure, the tilting propellers including additional annular air inlets 246 around the hub 231. The annular air inlets 246 can allow for better distribution of cooling air over the motor assembly 230. As seen in the lower figure of Figure 2D the discharge passage 242 can direct the air flow on a first cooling path, through the heat exchanger 233, and then exit through the discharge outlet 244. At the same time, the cooling air flow can also be directed on a second cooling path, through the annular air inlet 246 into the cooling fins 239, and leave through the second discharge outlet 247. Thus, the cooling air flow can target multiple heat generating locations to more efficiently cool the motor assembly 230. For example, the cooling fins 239 can surround the outer surface of the motor assembly 230 such that the entire annular air flow is transferred from the air inlet 240 past the cooling fins 239 and then exits at the second discharge outlet 247.

[0073] In some embodiments, the annular air inlet 246 can be used in place of the air inlet 240, rather than in addition to the air inlet. The annular shape can allow for a larger inlet size to allow more air to enter the nacelle 225. Additionally, the annular shape can space the opening area at a greater distance such that the surface area of the air inlet 240 can be better distributed. For example, configuring the air inlet 240 to have an annular shape can optimize the placement of the opening with respect to both the blades 218 and the motor assembly 230. At a location close to the hub 231, even a slight difference in the radial distance of the air inlet 240 can create a measurable difference in the air flow of the slipstream from the blades 218. For example, compared to the Figure 2C embodiment of

[0074] Figure 2E shows an additional baffle arrangement for an alternative flow path of the tilting propeller 214 in cruise configuration consistent with embodiments of the present disclosure. Figure 2E The upper figure of Figure 2Dvariants, in the figures, a second cooling path starting from the annular air inlet 246 merges with the first cooling path at the discharge channel 241. In Figure 2E In the embodiment of the upper figure of, the nacelle 225 may include a plurality of baffle portions 228. For example, a first nacelle baffle 228a may direct air from the cooling fins 239 to the inlet side of the heat exchanger 233. A second nacelle baffle 228b may direct air from the air inlet 240 along the discharge channel 242 to the heat exchanger 233. In such a configuration, the air flow from multiple parts of the motor assembly 230 can be discharged through a single discharge outlet 244. Further, the heat exchanger 233 can also receive a larger flow of cooling air by feeding air to the heat exchanger from both the second cooling path and the first cooling path.

[0075] Figure 2E The lower figure of shows an alternative arrangement of the two cooling paths. In this case, the first nacelle baffle may be arranged similarly to that shown in the Figure 2E upper figure of, but the annular air inlet 246 may not be present. Instead, all air flow can enter through the air inlet 240, and bifurcate through the second nacelle baffle 228b, where the air inlet 240 is shown to be configured as a scoop. The first cooling path may be along the discharge channel 242, as discussed above. The second cooling path may be formed by the first nacelle baffle 228a and the second nacelle baffle 228b. The second cooling path may include a meandering path along the cooling fins 239 to increase the thermal contact with the air.

[0076] In some embodiments, the nacelle baffle 228 and the pylon baffle 227 may include complementary shapes, such as toothed segments of a continuous baffle surface. Figure 2F is a view seen from below the tilted propeller 214 consistent with an embodiment of the present disclosure, which shows such a segmented baffle structure herein, corresponding to Figures 2A - 2E the elements of the pylon baffle 227 in as Figure 2F shown may include a first segment 227a and a second segment 227b of a multi-segment pylon baffle structure. The nacelle baffle 228 may be formed on the inner surface of the nacelle 225 as an additional segment to the complete discharge channel 242 from the air inlet 240 to the discharge outlet 244. The nacelle baffle 228 may be shaped to cooperate with the first pylon baffle segment 227a and the second pylon baffle segment 227b when operating in the cruise configuration. When tilted to the lift configuration, the nacelle baffle 228 may separate from the first pylon baffle segment 227a and the second pylon baffle segment 227b to expose the air outlet 241 to the wake region 243. In some embodiments, as described below with respect to Figure 2GFurther discussed, the nacelle baffle 228 may include an orifice configured to couple a region on the air inlet side of the nacelle baffle 228 to the wake region 243 on the opposite side. Thus, in the lift configuration, the baffle segments may be separated from each other to better expose the central portion of the wake region 243. Since the central region between the segments 227a and 227b is removed in the lift configuration, the airflow can pass through the nacelle 225 without obstruction caused by the protruding baffle.

[0077] Figure 2G Additional tilting propellers 214 in lift and cruise configurations consistent with embodiments of the present disclosure are shown. As Figure 2G shown, the entire baffle may be mounted inside the nacelle 225. In this case, discharge channels may be formed both in the lift and cruise configurations. In some embodiments, the nacelle baffle 228 may include an orifice for coupling a region within the discharge channel 242 to the wake region 243 outside the discharge channel 242. This may allow air to be drawn from the air inlet 240 into the discharge channel 242 due to the low pressure region in the wake region 243. The size, shape, number, and placement of the orifices are sufficient to achieve this coupling effect in the lift configuration while still guiding sufficient airflow through the discharge channel when operating in the cruise configuration. Alternatively, the orifice may include a cover that can be actuated passively or actively such that it opens in the lift configuration and closes in the cruise configuration. For example, in some embodiments, the nacelle 225 may include a sliding cover 248 (as Figure 2G seen in the lower figure), which moves in an inclined manner in cooperation with the tilting actuator 238. In the lift configuration, the sliding cover may expose the orifice 245. When tilted to the cruise configuration, the sliding cover may slide over the orifice 245, closing the orifice and sealing the discharge channel 242.

[0078] Further, other components of the nacelle 225 may also be actuated to optimize the airflow. Figure 2H Additional tilting propellers 214 in lift and cruise configurations consistent with embodiments of the present disclosure are shown. The top of the nacelle 225 may include clamshell segments 224 configured to open in the lift configuration. For example, the segments may be actuated by mechanical coupling to the tilting actuator 238. When opened, the clamshell segments 224 may create a funnel or other opening to direct a larger volume of airflow into the nacelle 225. When tilted back to the cruise configuration, the clamshell segments may be configured to form a streamlined nacelle 225.

[0079] Although the clamshell segments 224 are shown as having a gap therebetween in the lift configuration, this need not be the case. The clamshell segments can be configured to overlap each other such that they form a continuous funnel or other orifice shape. In some embodiments, there can be as few as one clamshell segment. For example, the clamshell segment 224 can include louvers that are configured to open in the lift configuration and close in the cruise configuration.

[0080] Further, although in Figures 2A - 2H , the blade 218 has been depicted as being narrower at the blade root 219, the blade 218 can also take other forms. For example, as Figure 2I shows, the blade 218 can be wider at the root 219 than at its peripheral region. This design can also additionally provide better air flow during lift by increasing the slipstream intensity near the hub 231. In some embodiments, the profile of the blade 218 can be selected such that the wide portion of the root 219 is located above the air inlet 240.

[0081] Although Figures 2A - 2I certain features can be described with respect to one embodiment or less than all embodiments, it should be understood that other combinations of the various disclosed features are also contemplated within the scope of the present disclosure, as would be understood by a person of ordinary skill in the art. For example, the various embodiments of the air inlet 240, baffles 227 - 228, heat exchanger 233, and extension portion 226 can be combined with each other in various ways, such as to achieve the various advantages of different configurations of each component.

[0082] B. Example motor assembly embodiments

[0083] Figures 3A - 3B An example close - up view of antilt motor assembly 330 in a VTOL aircraft vehicle consistent with an embodiment of the present disclosure is shown. The motor assembly 330 can be similar to, for example, the motor assembly 230 in Figures 2A - 2I . Figure 3A - B elements similar to the elements in FIGS. 1 - Figure 2I can be marked with corresponding numbers using 3 as a leading digit. For example, in some embodiments, Figure 3A 's heat transfer device 333 can be similar to Figure 2A 's heat exchanger 233.

[0084] The motor assembly 330 can be mounted to a boom (such as the boom 222 in Figures 2A - 2F ). The motor assembly 330 can be further coupled to the hub and blades of antilt propeller (such as the antilt propeller 214 in Figures 2A - 2I ) via a shaft 332. The motor assembly 330 can be configured to rotate the shaft 332 at a variable speed to be in the cruise configuration of the VTOL aircraft (e.g., asFigure 1A generate forward thrust at the tilting propeller in the situation (as seen in Figure 1B ). The motor assembly 330 can be further configured to generate vertical thrust at the tilting propeller during the lift phase of the VTOL aircraft (e.g., as seen in Figure 3B ). For example, the motor assembly 330 can include, for example, a motor 335, a gearbox 336, and an inverter 337 (represented by a dashed box). The motor assembly 330 can further include a housing 326 surrounding the motor 335, the gearbox 336, and the inverter 337. The motor assembly 330 can further include a heat transfer device 333 placed outside the housing 326 to thermally couple the components 335 - 337 of the motor assembly 330 to, for example, a cooling air flow. For example, the heat transfer device 333 can include a heat exchanger. In some embodiments as seen in

[0085] It should be understood that Figures 3A - 3B the spatial relationships between the different components of the motor assembly 330 shown in

[0086] are given by way of example and do not necessarily need to be arranged in this way always. For example, in some embodiments, the gearbox 336 may not be located below the motor 335, and neither component necessarily has to be located above or below the other. Generally, the various components of the motor assembly 330 can be arranged in a variety of configurations that would be understood by a person of ordinary skill in the art. Additionally, the motor assembly can include additional components or one or more of the components discussed herein can be omitted. Figure 4C ). Also, not all components need to be symmetrically arranged. For example, the motor 335 and the gearbox 336 can be configured to share the same longitudinal axis. For example, the longitudinal axis can correspond to the rotational axis of its associated propeller. Meanwhile, the inverter 337 may not share the longitudinal axis with the motor 335 and the gearbox 336. For example, the inverter 337 can be arranged to be offset relative to the other components of the motor assembly 330 or can be placed on one side of the motor assembly 330 (e.g., as seen in

[0087] Additionally, the motor assembly 330 may include redundancies to ensure proper operation in the event of failure of one or more components. For example, the motor 335 may include a rotor surrounded by multiple redundant stators. The multiple stators may be configured to operate in combination with each other simultaneously and to operate independently in the event of a failure. Similarly, the inverter 337 may include stages. In some embodiments, the inverter 337 may include a two-stage inverter, or may include more than two stages.

[0088] The heat exchanger 333 may be configured to receive a circulating heat exchange medium from within the motor assembly 330. For example, the heat exchange medium may include oil, and the oil may be used to lubricate and cool the components of the motor assembly 330. The oil may be circulated through a lubrication heat exchange flow path that includes one or more components of the motor assembly 330, such as the motor 335, the gearbox 336, the inverter 337, and the heat exchanger 333. The lubrication heat exchange flow path may be advantageously minimized by positioning the heat exchanger 333 near the housing 326, thereby minimizing the volume (and weight) of materials required to achieve the cooling and lubrication functions. Further, the lubrication heat exchange flow path may reduce the need for hoses, connectors, and other elements that may increase complexity and weight and increase the risk of failure. Thus, the motor assembly 330 may include a substantially sealed oil-cooled or hybrid-cooled system that is configured for one or more heat-generating portions of the motor assembly 330, as further described below with respect to Figures 4A - 4E Further described.

[0089] The housing 326 may include a substantially form-fitting sleeve surrounding the components 335-337 of the motor assembly 330. The housing 326 may prevent dust, debris, or other contaminants contained in the cooling air stream from negatively affecting the components 335-337. The housing 326 may include a motor housing 327, a dividing plate 328, and an inverter housing or controller housing 329.

[0090] The motor housing 327 may surround and seal the upper components of the motor assembly 330, such as the motor 335 and the gearbox 336. A coolant, such as oil, may be circulated to the motor housing 327 to lubricate and cool the components of the motor 335 and the gearbox 336. The lower portion of the motor housing 327 may be sealed by the dividing plate 328. For example, the dividing plate 328 may include an end bell plate that is used to enclose the motor housing 327.

[0091] The inverter housing 329 can surround and seal the lower components of the motor assembly 330, such as the inverter 337. The inverter 337 can include, for example, an electronic circuit board and other control components configured to control the operation of the motor assembly 330. Thus, the inverter 337 can include antilock propeller controllers, and the inverter housing 329 can alternatively be referred to as the controller housing 329. The controller housing 329 can be isolated from the oil or other coolant of the motor housing by a partition plate 328. For example, the partition plate 328 can include a heat plate for enclosing the controller housing 329 and thermally coupling the controller housing to the oil or other coolant.

[0092] The partition plate 328 can include one or more plates sandwiched together and disposed between the motor housing 327 and the controller housing 329. For example, in some embodiments, the partition plate 328 can include the end bell plate and the heat plate discussed above, which are sandwiched together between the motor housing 327 and the controller housing 329. The partition plate 328 can isolate the internal spaces of the motor housing 327 and the controller housing 329 from each other and from the external environment outside the housing 326. In some embodiments, one or more of the sandwiched plates of the partition plate 328 can include grooves, holes, or other conduits configured to distribute oil or other coolant in the plane direction of the partition plate 328.

[0093] In some embodiments, the partition plate 328 can include an integral mounting bracket for supporting the heat exchanger 333. The heat exchanger 333 can include, for example, folded fins or other types of heat exchangers. Oil or other coolant that has been heated by the motor 335, the gearbox 336, or the inverter 337 can circulate through the fins of the heat exchanger 333 via internal conduits of the heat exchanger 333. Separately, the inlets and outlets of the internal conduits can be coupled to the outlets and inlets of the holes or grooves of the partition plate 328. In this way, the heated oil (or other coolant) can carry heat from the housing 326 to the fins of the heat exchanger 333, where the heat can be transferred to the cooling air flow passing through the fins. Thus, the entire motor assembly can be efficiently cooled without exposing sensitive components to the external environment.

[0094] The motor housing 327, the partition plate 328, and the inverter housing 329 can be formed of, for example, a lightweight and rigid material having high thermal conductivity. For example, the material can include metals such as aluminum or copper, ceramics such as silicon carbide, or other suitable materials.

[0095] C. Example Coolant and Airflow Path Embodiments

[0096] Figures 4A - 4ESchematic illustrations of an example oil and air flow path in a motor assembly 430 and surrounding area of a VTOL aircraft consistent with embodiments of the present disclosure are provided. The VTOL aircraft can be similar to, for example, Figures 1A - 1B the VTOL aircraft 100 or Figures 2A - 2I the VTOL aircraft 200. The motor assembly 430 can be similar to, for example, Figures 2A - 3B the motor assemblies 230 or 330. Figures 4A - 4E Elements similar to those in Figure 3B Figure 1 - Figure 4A can be labeled with corresponding numbers using 4 as a leading digit. For example, in some embodiments, Figure 2A the air inlet 440 of Figures 4A - 4E can be similar to the air inlet 240 of

[0097] Figure 4ASchematically depicts a motor assembly 430 of a VTOL aircraft and surrounding components consistent with embodiments of the present disclosure. The motor assembly 430 may include components such as a motor 435, a gearbox 436, and an inverter 437 housed within a housing 426. The housing 426 may include a motor housing 427, a partition plate 428, and a controller housing 429. The motor housing 427 may surround and seal components such as the motor 435 and the gearbox 436. The controller housing 429 may surround and seal the inverter 437. The motor assembly 430 may further include a heat exchanger 433 that is thermally coupled to components 435 - 437 via a lubricating heat exchange oil flow path (represented by solid lines). In some embodiments, the heat exchanger 433 may be supported by a mounting bracket or other extensions of the partition plate 428. The partition plate 428 may extend beyond the motor housing 427 and the controller housing 429 such that the partition plate 428 can support the heat exchanger 433 and seal the motor housing 427 and the controller housing 429. The partition plate 428 may further include holes, grooves, or other conduits for circulating oil (or other coolant) from the motor housing 427 to the heat exchanger 433. The partition plate 428 may further thermally couple the controller housing 429 to the oil via heat conduction. Thus, the lubricating heat exchange oil flow path may lubricate components 435 - 437 and / or absorb heat generated by the components. The heat absorbed by the oil may be carried to the heat exchanger 433 where the heat may be transferred to incoming air (represented by dashed lines). For example, air may pass through fins or other passages in the heat exchanger 433. The fins or other passages may be configured to maximize the surface contact area between the heat exchanger and the air flow while maintaining an acceptable air pressure drop limit across the heat exchanger. The air flow may enter the cabin 425 through an air inlet 440. Due to a low pressure zone at the air outlet 441 side of the heat exchanger 433, the air flow may be drawn into the air inlet 440. For example, the low pressure zone may include a wake region generated by slipstream flowing past the exterior of the cabin 425. The cabin 425 may include an extension (not shown) configured to increase the size of the wake region to create a pressure differential between the air inlet 440 and the air outlet 441. In some embodiments, air may further be forced into the air inlet 440 as slipstream from a region of the propeller blade near the air inlet 440. The air may exit the heat exchanger 433 and leave the cabin 425 through the air outlet 441 without entering or passing through the housing 426.

[0098] The lubricating heat exchange oil flow path is shown as a simple circuit with a high level of generality. However, it should be understood that the oil flow path can include branches, sub-circuits, or other segmented paths. Generally, the oil can be circulated in any manner such that the various components of the motor assembly 430 are effectively lubricated and the components are cooled. Further, other elements are also shown in a highly schematic form. For example, the inlet 440 is depicted as a cutout in the nacelle 425. However, it should be understood that the air inlet 440 can take any suitable form or position, including any form or position disclosed regarding Figures 2A - 2I the air inlets 240 or 246 in

[0099] Figure 4B The motor assembly 430 and surrounding elements of a VTOL aircraft consistent with an embodiment of the present disclosure are schematically depicted. Except for the relative positioning of the gearbox 436 and the motor 435, Figure 4B the embodiments of Figure 4A can be similar to the embodiments of Figure 4B The oil flow path of

[0100] Figure 4C The motor assembly 430 and surrounding elements of a VTOL aircraft consistent with an embodiment of the present disclosure are schematically depicted. Except for the arrangement of the inverter 437 and the dividing plate 428, Figure 4C the embodiments of Figure 4A can be similar to the embodiments of Figure 4C Since the mechanical alignment constraints of the inverter 437 are not the same as those of the motor 435 and the gearbox 436, the arrangement of the inverter 437 can allow for more design freedom. For example, as seen in Figure 4C the oil flow path of

[0101] Figure 4D Schematically depicts the motor assembly 430 of a VTOL aircraft and surrounding components consistent with embodiments of the present disclosure. Figure 4D Embodiments of can be similar to Figure 4A embodiments of, but add a second heat transfer device in the form of cooling fins 439. The cooling fins 439 can extend around the exterior of the housing 426, which is similar to Figure 3B embodiments of. Alternatively, the cooling fins 439 can be shaped and arranged to conform to the specific airflow path of the VTOL aircraft in which they are implemented. In some embodiments, the cooling fins 439 can serve as an alternative form of the heat exchanger 433. In some embodiments, the element 439 can include an alternative heat exchanger 433 or a heat exchanger in addition to the heat exchanger. In the case of two heat exchangers, the two heat exchangers can share a common oil flow path, or can operate on two different oil flow paths. Alternatively, one flow path can include oil that lubricates and cools the components of the motor assembly 430, while the other flow path includes a coolant that is optimized for cooling only without any lubrication function.

[0102] Figure 4E Schematically describes the motor assembly 430 of a VTOL aircraft and surrounding components consistent with embodiments of the present disclosure. Figure 4E Embodiments of can include an additional annular air inlet 446. In addition to air entering from the air inlet 440 into the first cooling path, the annular air inlet 446 can also allow air to enter into a second cooling path. For example, the second cooling path can direct air through the cooling fins 439 and to an additional outlet 447, which is similar to the arrangement shown in Figure 2D . Alternatively, the second cooling path can direct air to that outlet 441. For example, the second cooling path can merge with the first cooling path, which is similar to the configuration shown in Figure 2E or any other suitable arrangement. The cooling fins 439 can surround the motor housing 427 (as shown in the cross-section at Figure 4E ) to increase the thermal contact between the airflow and the motor assembly 230.

[0103] D. Additional Example Tilt Rotor Embodiments

[0104] Figures 5A - 5D Shows an example portion of a VTOL aircraft 500 consistent with embodiments of the present disclosure. The example portion of the VTOL aircraft 500 can be similar to, for example, the portion described above with respect to Figures 1A - 4E . Figures 5A - 5D in with Figures 1A - 4E Elements similar to the elements in can be labeled with corresponding numbers using 5 as a leading digit. For example, in some embodiments, Figure 5AThe nacelle 525 can be similar to Figure 2A the nacelle 225.

[0105] Figure 5A Shown are tilt rotors in a lift configuration (top figure) and a cruise configuration (bottom figure) consistent with embodiments of the present disclosure. For clarity, some of the blades 518 are omitted. The tilt rotor 514 can be coupled to the pylon 522 or another body of the VTOL aircraft via a first frame 523 and can be tilted between the lift configuration and the cruise configuration via a tilt actuator 538. For example, a motor assembly 530 can be mounted to a second frame 529, which can be tilted relative to the first frame 523 via the tilt actuator 538. In the illustrated configuration, the tilt actuator 538 includes a rotary actuator that is coupled to a pivot 550 connecting the first frame 523 and the second frame 529. In some embodiments, the tilt actuator includes, for example, a linear actuator coupled to the pylon 522 or another body of the VTOL aircraft. The tilt rotor 514 can include: a plurality of propeller blades 518 that are coupled to a hub 531; a nacelle 525 that surrounds the motor assembly 530 and a heat transfer device 533; and a tilt actuator 238. The nacelle 525 can further include a first air inlet 540 and a nacelle segment 524.

[0106] As Figure 5A indicated by the arrow in, the nacelle segment 524 can be configured to separate from the nacelle 525 and translate rearward when the tilt rotor rotates into the lift configuration. For example, the nacelle segment 524 can be coupled to the nacelle 525, the motor assembly 530, the second frame 529, or another tilting component of the tilt rotor 514 via a mechanical coupling 551. For example, the mechanical coupling 551 can include a linkage, a track, a crank, a cam, a gear, a cable, a spring, a chain, a shaft, a hinge, or other mechanical means configured to actuate the nacelle segment as the tilt angle of the tilt rotor 514 changes. In some embodiments, the nacelle segment can be coupled to the pivot 550 or the tilt actuator 538 to actuate the nacelle segment 524 as the tilt angle of the tilt rotor changes. In some embodiments, the nacelle segment can be coupled to the pylon 522 or another body of the VTOL aircraft to obtain additional support and guidance for movement. In some embodiments, the nacelle segment 524 can be configured such that it translates away from the nacelle 525 along the pylon 522 when the tilt rotor tilts upward, for example, to allow a greater range of tilting motion without causing a collision between the nacelle 525 and the pylon 522.

[0107] In some embodiments, the nacelle segment 524 can be configured to improve the cooling efficiency of the motor assembly 530. For example, as Figure 5BAs shown, the nacelle segment 524 can be configured as a door or clamshell segment that can be opened via mechanical coupler 551 by, for example, hinging or other rotational movement. Thus, in some embodiments, nacelle segment 524 may alternatively be referred to as door 524. In some embodiments, in lift configuration, door 524 can be opened to expose a second air inlet 541 on the dorsal side of nacelle 525. Door 524 can be configured to direct slipstream from propeller blades 518 to, for example, motor assembly 530 or heat transfer device 539 (such as cooling fins or heat exchanger). Heat transfer device 539 can be located at second air inlet 541, such as on the dorsal side of nacelle 524, to provide additional cooling for motor assembly 530 in lift configuration.

[0108] In some embodiments, door 524 can be located on the dorsal side of nacelle 525. "Dorsal side" herein refers to the side opposite the front of the VTOL aircraft when the nacelle is tilted to lift configuration. For example, in Figures 5A - 5D the embodiment shown, the dorsal side of nacelle 525 in lift configuration can correspond to the top side of nacelle 525 when oriented in cruise configuration. By positioning door 524 on the dorsal side of nacelle 525, any drag created by opening the door can be minimized when the VTOL aircraft is moving forward (such as in an intermediate or transition configuration between cruise and lift configurations). In some embodiments, door 524 can be opened from the front or side of nacelle 525, similar to Figure 2H the embodiment of Figure 2H In some embodiments, similar to Figure 2H the embodiment of Figure 2H multiple nacelle segments 524 can be configured to open. In addition to providing more cooling, the airflow through second air inlet 541 strengthens the airflow through wake region 543 at the outlet side of heat exchanger 533, thereby improving the airflow through first air inlet 540.

[0109] In some embodiments, mechanical coupler 551 can be configured to begin opening nacelle segment 524 only when tilt propeller 514 tilts beyond a predetermined angle relative to the horizontal axis HA of the VTOL aircraft. For example, it can be determined that when tilt propeller 514 tilts below the predetermined angle, the VTOL aircraft is typically moving at a high enough speed to generate sufficient cooling airflow through first air inlet 540. Additionally, since drag may be proportional to the square of the speed, it may be desirable to keep nacelle segment 524 in a more streamlined closed position during higher speeds associated with lower tilt angles. Finally, at lower tilt angles, nacelle segment 524 can provide less shielding to the incoming air. Thus, in some embodiments, mechanical coupler 551 can be configured to begin opening nacelle segment 524 after tilt propeller 514 tilts beyond a predetermined angle (such as 20 degrees, 30 degrees, or 45 degrees).

[0110] In some embodiments, the heat transfer device 539 may include a device separate from the heat transfer device 533 used in the cruise configuration. For example, the heat transfer device may include a set of cooling fins located on the side of the motor assembly 530 opposite to the heat exchanger 533. In some embodiments, a single heat transfer device may capture cooling airflows from both the first air inlet 540 and the second air inlet 541. For example, the heat exchanger (or cooling fins, etc.) 533 may surround the motor assembly 530. In some embodiments, the distribution of the cooling fins or heat exchange ducts around the motor assembly may be non-uniform. For example, the concentration in the airflow path area of the first air inlet 540 or the second air inlet 541 may be higher than that in another area located away from the airflow path. In some embodiments, an internal baffle (similar to, for example Figure 2A the nacelle baffle 228 of Figure 5C or the baffle 528 of Figure 2D may direct a portion of the airflow from the first air inlet 540 to the second discharge outlet 547 (similar to the airflow through the second discharge outlet 247 in the configuration of

[0111] In some embodiments, as Figure 5C shown in, the airflow can be directed from the second air inlet 541 to the heat exchanger (or cooling fins, etc.) 533 through the baffle 528. This configuration can avoid redundancy of the heat transfer device, thereby minimizing the weight of the tilt propeller. For example, it can be determined that for either the cruise configuration or the lift configuration, at any given time, the airflow through only one of the first air inlet 540 or the second air inlet 541 will be strong. Therefore, a single heat transfer device 533 can have sufficient capacity to transfer heat in either configuration. Thus, the baffle 528 can allow the airflow from both the first air inlet 540 and the second air inlet 541 to be directed to the single heat transfer device 533.

[0112] In some embodiments, as Figure 5D shown in, the nacelle segment may rotate in a direction opposite to that of the embodiments of Figure 5B and Figure 5C . For example, Figure 5AThe backward translation motion described in [reference] causes the nacelle segment 524 to tilt toward the nacelle 524 rather than away from it. Thus, in some embodiments, the nacelle segment 524 can be configured to translate and rotate as the nacelle tilts between a lift configuration and a cruise configuration. Such an arrangement can be preferred, for example, for accommodating the mechanical couplings required to actuate the nacelle segment 524. Additionally, by sliding the nacelle segment 524 away from the propeller blades before (or simultaneously with) tilting the propeller blades upward, the size of the nacelle segment 524 can be increased without the risk of collision between the nacelle segment 524 and the propeller blades 518.

[0113] Figures 6A - 6I An example portion of a VTOL aircraft 600 consistent with embodiments of the present disclosure is shown. The example portion of the VTOL aircraft 600 can be similar to, for example, the portion described above with respect to Figures 1A - 5D the description. Figures 6A - 6I Elements similar to those in Figures 1A - 5D can be labeled with corresponding numbers using 6 as a leading digit. For example, in some embodiments, Figure 6A the nacelle 625 of Figure 2A can be similar to the nacelle 225 of

[0114] Figure 6A An example of a tilt propeller 614 in a lift configuration (right figure) and a cruise configuration (left figure) consistent with embodiments of the present disclosure is shown. Figure 6B An example front view of the hub 631 of a tilt propeller in a lift configuration (right figure) and a cruise configuration (left figure) facing an embodiment consistent with the present disclosure is shown. Figure 6A the tilt propeller in Figure 6C An example of a tilt propeller in a lift configuration (right figure) and a cruise configuration (left figure) consistent with embodiments of the present disclosure is shown. Figure 6AExample front view of an inclined propeller. For clarity, some of the blades 618 are omitted. The first air inlet 640 of the nacelle 625 may include a variable inlet having a variable portion 660. The variable portion 660 may be actuated such that the opening size of the air inlet 640 is larger in the lift configuration than in the cruise configuration. For example, the variable portion 660 may be actuated to a first position such that the air inlet 640 has a first opening size in the lift configuration, and actuated to a second position such that the air inlet has a second opening size in the cruise configuration, where the first opening size is larger than the second opening size. Thus, the air inlet 640 may be configured to direct an air flow to the heat transfer device 633 when the propeller is operating in the cruise configuration; and to direct a portion of the slipstream through the air inlet 640 to the heat transfer device 633 when the propeller is operating in the lift configuration. For example, in some embodiments, the variable portion 660 may be coupled to the nacelle 625, the motor assembly 630, the second frame 629, or another inclined component of the inclined propeller 614, and may be configured to open as the tilt angle of the inclined propeller 614 changes. In some embodiments, the variable portion 660 may be coupled to the pivot 650 or the tilt actuator 638 to actuate the variable portion 660 as the tilt angle of the inclined propeller 614 changes. In some embodiments, the variable portion 660 may be coupled to the first frame 623. For example, the variable portion 660 may be directly coupled to the first frame 623 or a boom (or other support structure) 622 or other components of the VTOL aircraft 600 that remain stationary relative to the first frame 623. Figures 6A - 6H Shows various example configurations of the variable portion 660, and Figures 7A - 7I shows various examples of mechanical couplings 751 for actuating the variable portion 660 as the tilt angle of the inclined propeller 614 changes.

[0115] For example, in Figures 6A - 6CIn [the figure], the variable portion 660 may include a flap, such as a door, damper, or other flap configuration. The flap may be configured to rotate, for example, about a hinge 662 along a hinge line HL. In a cruise configuration, a large amount of air flow can be obtained due to high speed. In this case, the variable portion 660 may be actuated to limit the opening size of the first air inlet 640 to a predetermined amount of, for example, the fully open size. By limiting the opening size to a predetermined amount, drag can be reduced while still providing an adequate amount of cooling air flow to the heat transfer device 633. In some embodiments, the predetermined amount may be, for example, 80%, 70%, 60%, 50%, or 40% of the fully open size. For example, in some embodiments, the second opening size may be 80%, 70%, 60%, 50%, or 40% of the first opening size. When the tilt propeller is tilted to a lift configuration, the variable portion 660 may be actuated to expand the opening size of the first air inlet 640 to, for example, the maximum opening size or 100% of the fully open size. This can enable the first air inlet 640 to increase the amount of slipstream captured in the lift configuration while maximizing drag in the cruise configuration.

[0116] In some embodiments, the variable portion may be biased to one of a restricted opening size in the cruise configuration, a fully open size in the lift configuration, or an intermediate size between the two. For example, a biasing member 661, such as a tension spring or a compression spring, may be provided to apply a biasing force to the variable portion 660. In some embodiments, the biasing member 661 may serve as a backup actuation system in case of a failure of a mechanical coupling or other actuator of the variable portion 660. For example, it may be determined that, for safety reasons, ensuring an adequate cooling air flow is more important than reducing drag. Thus, in some embodiments, the variable portion 660 may be biased towards the open position by the biasing member 661 to ensure a safe cooling level even in the event of a failure of a mechanical coupling or actuator. In some embodiments, the variable portion 660 may be biased towards the restricted position by the biasing member 661 to ensure a minimum drag even in the event of a failure of a mechanical coupling or actuator. In some embodiments, the variable portion 660 may be biased towards an intermediate position located between the fully open position and the restricted position by the biasing member 661 to strive for a balance between cooling efficiency and drag. In some embodiments, as Figures 7A - 7I further discussed below, the biasing member 661 may include a part of the mechanical coupling and may be configured to provide emergency actuation in the case of a mechanical failure or, in addition to providing emergency actuation, perform normal actuation.

[0117] As Figure 6BAs seen, in some embodiments, the flap-type variable portion 660 may be configured as a damper located inside the first air inlet 640. The damper may be actuated to increase or decrease while allowing the outer mold line of the nacelle to remain rigid and unchanged. In some embodiments, as Figure 6C seen, the flap-type variable portion 660 may be configured as the outer surface of the first air inlet 640.

[0118] As Figure 6D seen, the variable portion 660 may include a hinge or other connecting member 662 located on the upper side of the first air inlet 640 (as seen in the cruise configuration). This configuration may allow adjustment of the opening size of the first air inlet 640 while allowing the outer mold line of the nacelle to remain rigid and unchanged. Figure 6C This configuration may also provide easier routing of any mechanical or electrical connecting members required to actuate the variable portion 660.

[0119] In some embodiments, the variable portion 660 may alternatively or additionally be located in an area other than the first air inlet 640. For example, as Figure 6E seen, the variable portion 660 may be arranged at the discharge outlet 644. The variable portion 660 located at the discharge outlet may allow adjustment of the amount of air flow through the nacelle 625 without placing the variable portion 660 on a forward-facing surface where the variable portion 660 is more susceptible to, for example, ice accumulation or incoming objects. Similar to Figure 6D this, Figure 6E this arrangement may also provide easier routing of any mechanical or electrical connecting members required to actuate the variable portion 660.

[0120] In some embodiments, the variable portion 660 may take a form other than a simple flap. For example, as seen in Figures 6F - 6G this, the variable portion 660 may include a jaw structure having a bottom 663 and side walls 664. In some embodiments, the first side wall 664 of the variable portion 660 may be configured to slide along the second side wall 665 of the nacelle between a first position and a second position to change the opening size of the first air inlet 640 between a first opening size and a second opening size. For example, in some embodiments, the variable portion 660 may be configured to rotate about a hinge line HL on the hinge 662, as shown in the drawings. In some embodiments, instead of rotating or in addition to rotating, the variable portion 660 may be configured to translate linearly towards or away from the motor assembly 630, for example. Compared to the flap-type variable portion 660, the jaw-type variable portion 660 may achieve a more streamlined shape in the cruise configuration.

[0121] In some embodiments, as Figures 6H - 6I seen in, by configuring the variable portion 660 as a variable form surface of the nacelle 625, the variable portion 660 can be further streamlined. The variable form surface 660 can include a durable elastic structure formed at the outer surface of the nacelle 625 and containing internal linkages, cables, or actuators (not shown) configured to deform between a first position and a second position to vary, for example, between a restricted opening size and a full opening size.

[0122] Any of the above example designs of the variable portion 660 can be actuated actively or passively to change the air inlet opening size between a lift configuration and a cruise configuration. "Actively" can refer to independently controlled actuation, such as by a dedicated actuator configured to adjust the variable portion 660 to select the opening size of the first air inlet 640. "Passively" can refer to actuation that depends on another control or environment such that actuation of the variable portion 660 occurs automatically when specified conditions are met. For example, a counterweight system that uses the relative direction of gravity to control the variable portion such that the air inlet 640 is larger when the tilt propeller 614 points upward would be an example of a passive system. In some embodiments, the passive system can include a biasing member 661 as discussed above. In some embodiments, as described below, the passive system can include a mechanical coupling configured to actuate the variable portion 660 as the tilt angle of the tilt propeller 614 changes. In this way, the variable portion can be driven passively due to, for example, the tilting actuation of the tilt actuator 638.

[0123] Figures 7A - 7I An example portion of a VTOL aircraft 700 consistent with embodiments of the present disclosure is shown. The example portion of the VTOL aircraft 700 can be similar to, for example, the portion described above with respect to Figures 1A - 6I described. Figures 7A - 7I Elements similar to those in Figures 1A - 6I can be labeled with corresponding numbers using 7 as a leading digit. For example, in some embodiments, Figure 7A the nacelle 725 of Figure 2A can be similar to the nacelle 225 of Figures 7A - 7I Note that an example of the variable portion 760 can be shown as a flap in Figures 6A - 6I However, it should be understood that the variable portion 760 can take other forms, such as the form shown in

[0124] Figure 7AShows a tilt propeller 614 in a lift configuration (right figure) and a cruise configuration (left figure) consistent with embodiments of the present disclosure. For clarity, some blades 718 are omitted. The tilt propeller 714 may include a mechanical coupling 751, the flap of which is configured to actuate a variable portion 760 as the tilt angle of the tilt propeller 614 changes. For example, the mechanical coupling 751 may include a rigid link 757 connected by a bell crank or other pivoting connector 756. The mechanical coupling 751 may be coupled to a first frame 723 at a connector 758. In some embodiments, the bell crank 756 and the connector 758 may become closer to each other in the lift configuration than in the cruise configuration. Thus, as the tilt propeller 714 tilts upward, the first link 757a may push against the bell crank 756, which in turn may press the second link 757b to actuate the variable portion 760. The amount of actuation occurring over the entire range of the tilt motion may be set by, for example, selecting an appropriate distance between the hinge 762 and the point where the second link 757b is connected to the variable portion 760. Additionally, the direction of actuation may be reversed by connecting the second link 757b to the variable portion 760 on the side of the hinge 762 opposite to the side Figure 7A shown. Further, the total amount of actuation or the propeller tilt angle at which actuation begins may be set by incorporating a spring or other damping device into the mechanical coupling 751. For example, by arranging a spring system on the first link 757a and the connector 758, the initial tilt motion may be absorbed before the actuation of the variable portion 760 begins. In this way, the mechanical coupling 751 may be configured to begin actuating the variable portion only when the tilt propeller 714 tilts beyond a predetermined angle relative to the horizontal axis HA of the VTOL aircraft. For example, the predetermined angle may be, for example, 20 degrees, 30 degrees, or 45 degrees.

[0125] In some embodiments, as Figure 7B seen, the bell crank 756 and the connector 758 may become farther from each other in the lift configuration than in the cruise configuration. For example, in this case, the bell actuation of the crank 756 may be reversed relative to the Figure 7A actuation shown. Thus, as the tilt propeller 714 tilts upward, the first link 757a may pull against the bell crank 756, which in turn may press the second link 757b to actuate the variable portion 760. Additionally, as Figures 7C - 7D shown, the mechanical coupling 751 may be configured to actuate other variable portion 760 arrangements, such as the arrangements Figures 6C - 6D shown respectively.

[0126] In some embodiments, as Figure 7EAs seen in, the mechanical coupling 751 can be coupled to the pivot 750 between the first frame 723 and the second frame 729. For example, the mechanical coupling 751 can include a gear 759 that is coupled to a shaft (not shown) passing through the pivot 750. The gear 759 can be coupled to the variable portion 760 through, for example, a link 757 at a certain gear ratio that is configured to actuate the variable portion 760 by a predetermined amount within a range of tilting motion between the cruise configuration and the lift configuration. Alternatively or additionally, as Figure 7F shown, the gear 759 can be coupled to the pivot 750 and the hinge 762 through a chain 755 as an additional gear. The chain 755 can include, for example, a chain or a belt that is configured to actuate the variable portion 760 as the tilt angle of the tilt propeller 714 changes (such as by rotating the hinge 762).

[0127] In some embodiments, as Figure 7G seen in, the mechanical coupling 751 can include a cable 753. In some embodiments, the cable 753 can include a push-pull cable having a push rod 754. For example, the mechanical coupling 751 can include a cable 753 that is coupled to the first frame 723 at a first end through a first push rod 754a at a connection member 758. The mechanical coupling 751 can be further coupled to the variable portion 660 at a second end through a second push rod 754b. As the tilt propeller 714 tilts between the lift configuration and the cruise configuration, the first push rod 754a and the second push rod 754b can push and pull the cable 753 to actuate the variable portion 760. Alternatively, as Figure 7H shown in, the mechanical coupling 751 can include a pull cable 753 and a biasing member 761. In some embodiments, the pull cable 753 can be connected to the variable portion 760 and the connection member 758 at the first frame 723. The pull cable 753 can be guided by, for example, a pulley 775. In some embodiments, as the tilt propeller 714 tilts from the lift configuration to the cruise configuration, the pull cable 753 can allow the variable portion 760 to be actuated by the biasing member 761 to increase the opening size of the first air inlet 740. During reverse operation, the pull cable 753 can pull the variable portion 760 against the biasing member 761 to decrease the opening size of the first air inlet 740. In some embodiments, the functions of the pull cable 753 and the biasing member 761 can be opposite.

[0128] Generally, the example mechanical couplings discussed above can be configured in a variety of ways. For example, as discussed above, the mechanical coupling can be coupled to the first frame 723, the second frame 729, or the pivot 750 connecting the two frames. Additionally, as Figure 7IAs shown, a mechanical coupling (not shown) can be coupled to a pitch control system 770. For example, the pitch control system can include a pitch control lever 774 that can be actuated along the axis of rotation of the lift propeller as indicated by the double arrow to change the pitch angle of the propeller blades 718 ( Figure 7I not shown in Figure 7I ). In some embodiments, such actuation can be passively controlled by a linkage pitch system. The linkage pitch system can be configured to automatically adjust the blade pitch as the tilt angle of the lift propeller changes. For example, as the second frame 729 tilts about the pivot 750, a cam or other device can be coupled to and rotate with the shaft. The cam can then push against a roller 772 coupled to a slider 773 to push against the pitch control lever 774. By selecting an appropriately shaped cam 771, the blade pitch can be made to be related to the propeller tilt angle as needed. Further, the actuation of the variable portion 760 can also be related to the tilt angle using the mechanical coupling 751 discussed above. For example, a linkage, push rod, cable, or other element discussed above can be coupled to another linearly moving component such as the slider 773, the pitch control lever 774, or the pitch control system 770. In some embodiments, the mechanical coupling can be actuated by the cam 771. For example, the push rod 754 can be coupled to the cam 771 through an additional roller 772. Alternatively or additionally, a dedicated gear 759 coupled to the pivot 750 can be used to actuate the mechanical coupling. In this way, a single actuator can actively control the tilt angle of the tilt propeller 714 and can passively control the blade pitch angle and the opening size of the air inlet 740. Further, even when using a dedicated actuator (such as instead of the cam 771) to implement pitch control, nonetheless the variable portion 760 can be passively controlled in a similar manner by coupling it to the slider 773 or other elements of the pitch control system 770.

[0129] Further, it should be understood that the above example embodiments can be used in combination with each other. For example, the mechanical coupling can include a combination of one or more of a hinge, a rigid linkage, a bell crank, a cable, a chain, a spring, or a gear, as discussed above with respect to Figures 7A - 7I discussed. Further, the variable portion can include a combination of a flap, a sidewall, a variable form surface, etc., as discussed above with respect to Figures 6A - 6I discussed.

[0130] Embodiments of the present disclosure can be further described using the following clauses:

[0131] 1. A tilt device for a vertical takeoff and landing (VTOL) aircraft, comprising:

[0132] A first frame;

[0133] A second frame;

[0134] Propeller;

[0135] A motor assembly coupled to the propeller;

[0136] A heat transfer device configured to be thermally coupled to the motor assembly;

[0137] A nacelle coupled to the motor assembly, the nacelle including a variable portion; and

[0138] An inclination actuator configured to incline the second frame, the nacelle, the motor assembly, and the propeller relative to the first frame between a lift configuration and a cruise configuration,

[0139] Wherein:

[0140] The variable portion is configured to be actuated to a first position such that the air inlet of the nacelle has a first opening size in the lift configuration, and to a second position such that the air inlet has a second opening size in the cruise configuration, wherein the first opening size is larger than the second opening size;

[0141] The air inlet is configured to direct an air flow to the heat transfer device when the propeller operates in the cruise configuration, and

[0142] The air inlet is configured to direct a portion of the slipstream through the air inlet to the heat transfer device when the propeller operates in the lift configuration.

[0143] 2. The inclination device according to clause 1, further comprising a biasing mechanism configured to bias the variable portion towards one of the first position and the second position.

[0144] 3. The inclination device according to clause 1 or 2, wherein the variable portion is configured to rotate between the first position and the second position.

[0145] 4. The inclination device according to any one of clauses 1 to 3, wherein the variable portion is configured to translate between the first position and the second position.

[0146] 5. The inclination device according to any one of clauses 1 to 4, wherein the variable portion includes a flap.

[0147] 6. The inclination device according to any one of clauses 1 to 5, wherein the variable portion includes a damper.

[0148] 7. The tilting device according to any one of clauses 1 to 6, wherein the variable part includes a first side wall configured to slide along a second side wall of the nacelle between the first position and the second position.

[0149] 8. The tilting device according to any one of clauses 1 to 7, wherein the variable part includes a variable form surface configured to deform between the first position and the second position.

[0150] 9. The tilting device according to any one of clauses 1 to 8, further comprising:

[0151] A mechanical coupling configured to actuate the variable part as the tilt angle of the second frame changes.

[0152] 10. The tilting device according to clause 9, wherein the mechanical coupling is coupled to the first frame.

[0153] 11. The tilting device according to clause 9 or 10, wherein the mechanical coupling is coupled to the second frame.

[0154] 12. The tilting device according to clause 11, wherein the mechanical coupling is mounted on one of the motor assembly or the nacelle.

[0155] 13. The tilting device according to any one of clauses 9 to 12, wherein the mechanical coupling is coupled to a pivot connecting the first frame and the second frame.

[0156] 14. The tilting device according to any one of clauses 9 to 13, wherein the mechanical coupling includes a rigid link.

[0157] 15. The tilting device according to any one of clauses 9 to 14, wherein the mechanical coupling includes a bell crank.

[0158] 16. The tilting device according to any one of clauses 9 to 15, wherein the mechanical coupling includes a gear coupled to a pivot connecting the first frame and the second frame.

[0159] 17. The tilting device according to any one of clauses 9 to 16, wherein the mechanical coupling includes one of a chain or a belt.

[0160] 18. The tilting device according to any one of clauses 9 to 17, wherein the mechanical coupling includes a push-pull cable including a cable and a push rod.

[0161] 19. The tilting device according to any one of clauses 9 to 18, wherein the mechanical coupling includes a pulling cable, and the pulling cable includes a cable and a biasing mechanism.

[0162] 20. The tilting device according to any one of clauses 9 to 19, further comprising:

[0163] A pitch control system configured to control the pitch angle of the propeller blades of the propeller,

[0164] wherein the mechanical coupling is coupled to the pitch control system.

[0165] 21. The tilting device according to clause 20, wherein the pitch control system includes a linkage tilting pitch system configured to adjust the pitch angle as the tilt angle of the second frame changes.

[0166] 22. A vertical takeoff and landing (VTOL) aircraft tilting device, comprising:

[0167] A first frame;

[0168] A second frame;

[0169] A propeller;

[0170] A motor assembly coupled to the propeller;

[0171] A heat transfer device configured to be thermally coupled to the motor assembly;

[0172] A cabin coupled to the motor assembly, the cabin including a variable part; and

[0173] A tilting actuator configured to tilt the second frame, the cabin, the motor assembly, and the propeller relative to the first frame between a lift configuration and a cruise configuration,

[0174] wherein:

[0175] The variable part is configured to be actuated to a first position such that the discharge outlet of the cabin has a first opening size in the lift configuration, and to a second position such that the discharge outlet has a second opening size in the cruise configuration, wherein the first opening size is larger than the second opening size;

[0176] The discharge outlet is configured to receive an air flow from the heat transfer device when the propeller operates in the cruise configuration, and

[0177] The discharge outlet is configured to receive a portion of the slipstream from the heat transfer device when the propeller is operating in the lift configuration.

[0178] 23. A method of operating antilt equipment of a vertical takeoff and landing (VTOL) aircraft, the method comprising:

[0179] Tilting a second frame, a motor assembly, a nacelle, and a propeller of the tilt equipment relative to a first frame of the tilt equipment to a lift configuration via a tilt actuator of the tilt equipment, the nacelle including a variable portion;

[0180] Actuating the variable portion to a first position such that an air inlet of the nacelle has a first opening size in the lift configuration;

[0181] Guiding a slipstream from the propeller to the air inlet of the nacelle and further to a heat transfer device thermally coupled to the motor assembly when the propeller is in the lift configuration;

[0182] Tilting the motor assembly, the nacelle, and the propeller from the lift configuration to a cruise configuration; and

[0183] Actuating the variable portion to a second position such that the air inlet has a second opening size in the cruise configuration, wherein the first opening size is larger than the second opening size, and

[0184] Guiding an air flow through the air inlet to the heat transfer device when the propeller is in the lift configuration.

[0185] 24. A vertical takeoff and landing (VTOL) aircraft tilt equipment, comprising:

[0186] A propeller configured to be tiltable between a lift configuration and a cruise configuration;

[0187] A motor assembly coupled to the propeller; and

[0188] A nacelle including an air inlet and an air outlet for a heat transfer device, the heat transfer device being configured to be thermally coupled to the motor assembly;

[0189] Wherein the air inlet is positioned to receive a portion of the slipstream from the propeller when the propeller is operating in the lift configuration;

[0190] Wherein the air outlet is configured such that when the propeller is operating in the lift configuration, the air pressure at the air outlet is less than the air pressure at the air inlet.

[0191] 25. The tilting device according to clause 24, wherein the air inlet is a cutout in the nacelle.

[0192] 26. The tilting device according to clause 24 or 25, wherein the nacelle includes an extension portion that extends from the air outlet.

[0193] 27. The tilting device according to clause 26, further comprising a baffle;

[0194] wherein the extension portion and the baffle are configured to form an exhaust passage when the propeller operates in the cruise configuration.

[0195] 28. The tilting device according to clause 27, wherein the extension portion and the baffle are configured to form the exhaust passage both when the propeller operates in the lift configuration and when the propeller operates in the cruise configuration.

[0196] 29. The tilting device according to clause 27 or 28, further comprising an orifice located in the baffle, the orifice being configured to couple a region inside the exhaust passage with a wake region generated by the propeller outside the exhaust passage.

[0197] 30. The tilting device according to clause 29, wherein the orifice is configured to be closed in the cruise configuration.

[0198] 31. The tilting device according to any one of clauses 27 to 30, wherein the extension portion and the baffle are configured to form the exhaust passage by tilting the nacelle from the lift configuration to the cruise configuration.

[0199] 32. The tilting device according to any one of clauses 27 to 31, further comprising a boom, the nacelle being tiltable relative to the boom, wherein:

[0200] a first portion of the baffle is mounted to the nacelle;

[0201] a second portion of the baffle is mounted to the boom;

[0202] the first portion and the second portion are configured to separate in the lift configuration; and

[0203] the first portion and the second portion are configured to be substantially joined in the cruise configuration.

[0204] 33. The tilting device according to any one of clauses 27 to 31, further comprising a boom, wherein:

[0205] the nacelle is movably mounted to a first portion of the boom; and

[0206] The baffle is mounted to the second part of the boom in a fixed position.

[0207] 34. The tilting device according to any one of clauses 27 to 33, wherein the baffle and the extension are separated in the lift configuration such that the discharge channel is not formed in the lift configuration.

[0208] 35. The tilting device according to any one of clauses 27 to 34, wherein the area of the wake region in the lift configuration is larger than the area of the discharge channel in the cruise configuration.

[0209] 36. The tilting device according to any one of clauses 27 to 35, wherein the discharge channel includes a discharge outlet configured to discharge air from the air outlet to the outside of the tilting device, and the discharge outlet is formed by the extension and the baffle.

[0210] 37. The tilting device according to any one of clauses 26 to 36, wherein when the propeller operates in the lift configuration, the extension forms an extended negative pressure zone at the air outlet.

[0211] 38. The tilting device according to any one of clauses 26 to 37, wherein the depth of the extension is at least four inches.

[0212] 39. The tilting device according to any one of clauses 26 to 38, wherein the depth of the extension is not more than 20 inches.

[0213] 40. The tilting device according to any one of clauses 26 to 39, wherein the arc length of the extension around the rotation axis of the propeller is at least 45 degrees.

[0214] 41. The tilting device according to any one of clauses 26 to 40, wherein the arc length of the extension around the rotation axis of the propeller is not more than 270 degrees.

[0215] 42. The tilting device according to any one of clauses 24 to 41, wherein the air outlet is configured to be in a low pressure zone formed by another part of the slipstream passing along the outside of the nacelle.

[0216] 43. The tilting device according to any one of clauses 24 to 42, wherein, relative to the air inlet, another part of the propeller slipstream creates a negative pressure zone at the air outlet.

[0217] 44. The tilting device according to any one of clauses 24 to 43, wherein the heat transfer device includes a heat exchanger.

[0218] 45. The tilting device according to any one of clauses 24 to 44, wherein the air inlet is configured to face the propeller.

[0219] 46. The tilting device according to any one of clauses 24 to 45, wherein the distance between the air inlet and the rotational axis of the propeller is within 15% of the propeller radius.

[0220] 47. The tilting device according to any one of clauses 24 to 46, wherein the distance between the air inlet and the rotational axis of the propeller is within 25% of the propeller radius.

[0221] 48. The tilting device according to any one of clauses 24 to 47, wherein the distance between the air inlet and the rotational axis of the propeller is within 50% of the propeller radius.

[0222] 49. The tilting device according to any one of clauses 24 to 48, further comprising a baffle configured to direct air from the air outlet when the propeller is in the cruise configuration.

[0223] 50. The tilting device according to clause 49, further comprising:

[0224] A boom;

[0225] wherein the nacelle is movably mounted on a first portion of the boom, and the baffle is mounted on a second portion of the boom in a fixed position.

[0226] 51. The tilting device according to any one of clauses 24 to 50, wherein the open air volume at the air outlet is greater in the lift configuration than in the cruise configuration.

[0227] 52. The tilting device according to any one of clauses 24 to 51, wherein the propeller is configured to direct air into the air inlet.

[0228] 53. The tilting device according to any one of clauses 24 to 52, wherein in the cruise configuration, the air inlet is located at the lower side of the nacelle.

[0229] 54. The tilting device according to any one of clauses 24 to 53, further comprising:

[0230] A tilting actuator,

[0231] wherein the tilting actuator is configured to move the propeller, the motor assembly, and the nacelle between the lift configuration and the cruise configuration.

[0232] 55. The tilting device according to any one of clauses 24 to 54, further comprising an annular air inlet located at the top portion of the nacelle.

[0233] 56. The tilting device according to any one of clauses 24 to 55, wherein the nacelle includes a clamshell segment configured to open in the lift configuration.

[0234] 57. A method of operating a tilt device of a vertical takeoff and landing (VTOL) aircraft, the method comprising:

[0235] Tilting a propeller of the tilting device to a lift configuration, the propeller being coupled to a motor assembly;

[0236] Directing slipstream from the tilted propeller over the exterior of a nacelle of the tilting device, the nacelle including an air inlet and an air outlet for a heat transfer device configured to be thermally coupled to the motor assembly; and

[0237] Creating a negative pressure zone at the air outlet by the slipstream directed over the exterior of the nacelle, the negative pressure zone causing air to flow from the air inlet to the air outlet.

[0238] 58. The method according to clause 57, further comprising:

[0239] Tilting the propeller from the lift configuration to a cruise configuration;

[0240] Forming an exhaust passage of the air outlet in the cruise configuration, the exhaust passage including an extension portion and a baffle of the nacelle; and

[0241] Discharging air through the exhaust passage from the air outlet.

[0242] 59. A vertical takeoff and landing (VTOL) aircraft tilting device, comprising:

[0243] A body;

[0244] A propeller;

[0245] A motor assembly coupled to the propeller;

[0246] A heat transfer device configured to be thermally coupled to the motor assembly;

[0247] A nacelle coupled to the motor assembly, the nacelle including a door; and

[0248] An inclination actuator configured to incline the nacelle, the motor assembly, and the propeller relative to the body between a lift configuration and a cruise configuration.

[0249] Wherein:

[0250] The door is configured to be actuated such that the opening size of the air inlet of the nacelle is larger in the lift configuration than in the cruise configuration; and

[0251] The propeller is configured to direct a portion of the slipstream through the air inlet to the heat transfer device when the propeller operates in the lift configuration.

[0252] 60. The inclination device according to clause 59, wherein the door is configured to be actuated using a mechanical coupling between the door and the inclination actuator.

[0253] 61. The inclination device according to clause 59 or 60, wherein the door is configured to be closed in the cruise configuration to close the air inlet.

[0254] 62. The inclination device according to clause 61, wherein the door includes a cutout as an additional air inlet of the nacelle.

[0255] 63. The inclination device according to any one of clauses 59 to 62, wherein as seen in the cruise configuration, the door is located at the top portion of the nacelle.

[0256] 64. The inclination device according to clause 63, further comprising a baffle configured to direct the portion of the slipstream from the top portion of the nacelle to the heat transfer device.

[0257] 65. The inclination device according to clause 63 or 64, further comprising:

[0258] An additional air inlet located in the nacelle,

[0259] wherein the heat transfer device is configured to receive an air flow from the additional air inlet when the propeller operates in the cruise configuration.

[0260] 66. The inclination device according to any one of clauses 59 to 62, wherein as seen in the cruise configuration, the door is located at the side portion of the nacelle.

[0261] 67. The inclination device according to clause 66, further comprising a baffle configured to direct the portion of the slipstream from the side portion to the heat transfer device.

[0262] 68. The tilting device according to any one of clauses 59 to 67, wherein the heat transfer device includes cooling fins.

[0263] 69. The tilting device according to any one of clauses 59 to 68, wherein the heat transfer device includes a heat exchanger.

[0264] 70. The tilting device according to clause 69, further comprising:

[0265] An oil flow path, wherein the heat exchanger is thermally coupled to the motor assembly through the oil flow path.

[0266] 71. The tilting device according to any one of clauses 59 to 70, wherein:

[0267] The nacelle further includes a plurality of clamshell segments; and

[0268] The door includes one of the clamshell segments.

[0269] 72. The tilting device according to clause 71, wherein each of the plurality of clamshell segments is configured to be actuated using a mechanical coupling to the tilting actuator.

[0270] 73. The tilting device according to clause 71 or 72, wherein at least two of the plurality of clamshell segments are configured to overlap when the propeller is operating in the lift configuration.

[0271] 74. The tilting device according to any one of clauses 59 to 74, wherein the door is configured to translate and rotate as the nacelle tilts between the lift configuration and the cruise configuration.

[0272] 75. A method of operating a tilting device of a vertical takeoff and landing (VTOL) aircraft, the method comprising:

[0273] Tilting, by a tilting actuator, a motor assembly, a nacelle, and a propeller of the tilting device relative to a body to a lift configuration, the motor assembly being coupled to the propeller and the nacelle, the nacelle including a door;

[0274] Actuating the door to a first position as the nacelle and the propeller are tilted to the lift configuration;

[0275] When the propeller is in the lift configuration, directing slipstream from the propeller to an air inlet of the nacelle and further to a heat transfer device thermally coupled to the motor assembly;

[0276] Tilting the motor assembly, the nacelle, and the propeller from the lift configuration to a cruise configuration; and

[0277] Actuating the door to a second position as the nacelle and the propeller are tilted to the cruise configuration;

[0278] Wherein actuating the door to the first position or the second position causes the opening size of the air inlet of the nacelle to be greater in the first position than in the second position.

[0279] 76. The method according to clause 75, further comprising:

[0280] Actuating the door between the first position and the second position by a mechanical coupling between the door and the tilt actuator.

[0281] 77. The method according to clause 75 or 76, wherein the door is closed in the second position.

[0282] 78. The method according to any one of clauses 75 to 77, wherein as seen in the cruise configuration, the door is located at the top portion of the nacelle.

[0283] 79. The method according to any one of clauses 75 to 78, wherein the heat transfer device includes a heat exchanger that is thermally coupled to the motor assembly through an oil flow path.

[0284] 80. A vertical takeoff and landing (VTOL) aircraft comprising a tilt device according to any one of clauses 1 to 22, 24 to 56, or 59 to 74.

[0285] 81. A method of operating a vertical takeoff and landing (VTOL) aircraft, the method comprising: operating a VTOL aircraft tilt device according to the method of any one of claims 23, 57, 58, or 75 to 79.

[0286] The foregoing description has been presented for purposes of illustration. The description is not exhaustive and does not limit the invention to the precise forms or embodiments disclosed. Modifications and adaptations of the invention will be apparent to those skilled in the art by considering the specification and practice of the disclosed embodiments of the invention herein.

Claims

1. A tilt device for a vertical take-off and landing (VTOL) aircraft, comprising: A first frame; A second frame; A propeller; A motor assembly coupled to the propeller; A heat transfer device configured to be thermally coupled to the motor assembly; A cabin coupled to the motor assembly, the cabin including a variable part; And A tilt actuator configured to tilt the second frame, the cabin, the motor assembly, and the propeller relative to the first frame between a lift configuration and a cruise configuration, Wherein: The variable part is configured to be actuated to a first position such that the air inlet of the cabin has a first opening size in the lift configuration, and to a second position such that the air inlet has a second opening size in the cruise configuration, wherein the first opening size is larger than the second opening size; The air inlet is configured to direct an air flow to the heat transfer device when the propeller operates in the cruise configuration, and The air inlet is configured to direct a portion of the slipstream through the air inlet to the heat transfer device when the propeller operates in the lift configuration.

2. The tilt device according to claim 1, further comprising a biasing mechanism configured to bias the variable part towards one of the first position and the second position.

3. The tilt device according to claim 1 or 2, wherein the variable part is configured to rotate between the first position and the second position.

4. The tilt device according to any one of claims 1 to 3, wherein the variable part is configured to translate between the first position and the second position.

5. The tilt device according to any one of claims 1 to 4, wherein the variable part includes a flap.

6. The tilt device according to any one of claims 1 to 5, wherein the variable part includes a damper.

7. The tilt device according to any one of claims 1 to 6, wherein the variable part includes a first side wall configured to slide along a second side wall of the cabin between the first position and the second position.

8. The tilt device according to any one of claims 1 to 7, wherein the variable part includes a variable form surface configured to deform between the first position and the second position.

9. The tilt device according to any one of claims 1 to 8, further comprising: A mechanical coupling configured to actuate the variable part as the tilt angle of the second frame changes.

10. The tilt device according to claim 9, wherein the mechanical coupling is coupled to the first frame.

11. The tilt device according to claim 9 or 10, wherein the mechanical coupling is coupled to the second frame.

12. The tilt device according to claim 11, wherein the mechanical coupling is mounted to one of the motor assembly or the cabin.

13. The tilting device according to any one of claims 9 to 12, wherein the mechanical coupling is pivotally coupled to a pivot connecting the first frame and the second frame.

14. The tilting device according to any one of claims 9 to 13, wherein the mechanical coupling comprises a rigid link.

15. The tilting device according to any one of claims 9 to 14, wherein the mechanical coupling comprises a bell crank.

16. The tilting device according to any one of claims 9 to 15, wherein the mechanical coupling comprises a gear, the gear being pivotally coupled to a pivot connecting the first frame and the second frame.

17. The tilting device according to any one of claims 9 to 16, wherein the mechanical coupling comprises one of a chain or a belt.

18. The tilting device according to any one of claims 9 to 17, wherein the mechanical coupling comprises a push-pull cable, the push-pull cable comprising a cable and a push rod.

19. The tilting device according to any one of claims 9 to 18, wherein the mechanical coupling comprises a pull cable, the pull cable comprising a cable and a biasing mechanism.

20. The tilting device according to any one of claims 9 to 19, further comprising: A pitch control system configured to control the pitch angle of the propeller blades of the propeller, wherein the mechanical coupling is coupled to the pitch control system.

21. The tilting device according to claim 20, wherein the pitch control system comprises a linkage tilting pitch system configured to adjust the pitch angle as the tilt angle of the second frame changes.

22. A vertical takeoff and landing (VTOL) aircraft tilting device, comprising: A first frame; A second frame; A propeller; A motor assembly coupled to the propeller; A heat transfer device configured to be thermally coupled to the motor assembly; A cabin coupled to the motor assembly, the cabin including a variable portion; And A tilting actuator configured to tilt the second frame, the cabin, the motor assembly, and the propeller relative to the first frame between a lift configuration and a cruise configuration, wherein: The variable portion is configured to be actuated to a first position such that an exhaust outlet of the cabin has a first opening size in the lift configuration, and to a second position such that the exhaust outlet has a second opening size in the cruise configuration, wherein the first opening size is larger than the second opening size; The exhaust outlet is configured to receive an air flow from the heat transfer device when the propeller is operating in the cruise configuration, and The exhaust outlet is configured to receive a portion of the slipstream from the heat transfer device when the propeller is operating in the lift configuration.

23. A method of operating a vertical takeoff and landing (VTOL) aircraft tilting device, the method comprising: Tilting the second frame, motor assembly, nacelle, and propeller of the tilting device relative to the first frame to a lift configuration by a tilting actuator of the tilting device, the nacelle including a variable portion; Actuating the variable portion to a first position such that an air inlet of the nacelle has a first opening size in the lift configuration; When the propeller is in the lift configuration, guiding slipstream from the propeller to the air inlet of the nacelle and further to a heat transfer device thermally coupled to the motor assembly; Tilting the motor assembly, the nacelle, and the propeller from the lift configuration to a cruise configuration; And Actuating the variable portion to a second position such that the air inlet has a second opening size in the cruise configuration, wherein the first opening size is larger than the second opening size, and When the propeller is in the lift configuration, guiding an air flow through the air inlet to the heat transfer device.

24. A tilting device for a vertical takeoff and landing (VTOL) aircraft, comprising: A propeller configured to tilt between a lift configuration and a cruise configuration; A motor assembly coupled to the propeller; And A nacelle including an air inlet and an air outlet for a heat transfer device, the heat transfer device being configured to be thermally coupled to the motor assembly; Wherein the air inlet is positioned to receive a portion of the slipstream from the propeller when the propeller operates in the lift configuration; Wherein the air outlet is configured such that when the propeller operates in the lift configuration, the air pressure at the air outlet is less than the air pressure at the air inlet.

25. The tilting device according to claim 24, wherein the air inlet is a cutout in the nacelle.

26. The tilting device according to claim 24 or 25, wherein the nacelle includes an extension portion extending from the air outlet.

27. The tilting device according to claim 26, further comprising a baffle; Wherein the extension portion and the baffle are configured to form an exhaust passage when the propeller operates in the cruise configuration.

28. The tilting device according to claim 27, wherein the extension portion and the baffle are configured to form the exhaust passage both when the propeller operates in the lift configuration and when the propeller operates in the cruise configuration.

29. The tilting device according to claim 27 or 28, further comprising an orifice in the baffle, the orifice being configured to couple a region inside the exhaust passage to a wake region generated by the propeller outside the exhaust passage.

30. The tilting device according to claim 29, wherein the orifice is configured to be closed in the cruise configuration.

31. The tilting device according to any one of claims 27 to 30, wherein the extension portion and the baffle are configured to form the exhaust passage by tilting the nacelle from the lift configuration to the cruise configuration.

32. The tilting device according to any one of claims 27 to 31, further comprising a boom, wherein the nacelle is tiltable relative to the boom, and wherein: The first part of the baffle is mounted to the nacelle; The second part of the baffle is mounted to the boom; The first part and the second part are configured to separate in the lift configuration; and The first part and the second part are configured to join in the cruise configuration.

33. The tilting device according to any one of claims 27 to 31, further comprising a boom, wherein: The nacelle is movably mounted to the first part of the boom; and The baffle is mounted to the second part of the boom in a fixed position.

34. The tilting device according to any one of claims 27 to 33, wherein the baffle and the extension part are separated in the lift configuration such that the discharge channel is not formed in the lift configuration.

35. The tilting device according to any one of claims 27 to 34, wherein the area of the wake region in the lift configuration is larger than the area of the discharge channel in the cruise configuration.

36. The tilting device according to any one of claims 27 to 35, wherein the discharge channel includes a discharge outlet configured to discharge air from the air outlet to the outside of the tilting device, and the discharge outlet is formed by the extension part and the baffle.

37. The tilting device according to any one of claims 26 to 36, wherein when the propeller operates in the lift configuration, the extension part forms an extended negative pressure region at the air outlet.

38. The tilting device according to any one of claims 26 to 37, wherein the depth of the extension part is at least four inches.

39. The tilting device according to any one of claims 26 to 38, wherein the depth of the extension part is not more than 20 inches.

40. The tilting device according to any one of claims 26 to 39, wherein the arc length of the extension part around the rotation axis of the propeller is at least 45 degrees.

41. The tilting device according to any one of claims 26 to 40, wherein the arc length of the extension part around the rotation axis of the propeller is not more than 270 degrees.

42. The tilting device according to any one of claims 24 to 41, wherein the air outlet is located in a low pressure region formed by another part of the slipstream passing along the outside of the nacelle.

43. The tilting device according to any one of claims 24 to 42, wherein relative to the air inlet, another part of the slipstream generates a negative pressure region at the air outlet.

44. The tilting device according to any one of claims 24 to 43, wherein the heat transfer device includes a heat exchanger.

45. The tilting device according to any one of claims 24 to 44, wherein the air inlet is configured to face the propeller.

46. The tilting device according to any one of claims 24 to 45, wherein the distance between the air inlet and the rotational axis of the propeller is within 15% of the propeller radius.

47. The tilting device according to any one of claims 24 to 46, wherein the distance between the air inlet and the rotational axis of the propeller is within 25% of the propeller radius.

48. The tilting device according to any one of claims 24 to 47, wherein the distance between the air inlet and the rotational axis of the propeller is within 50% of the propeller radius.

49. The tilting device according to any one of claims 24 to 48, further comprising a baffle configured to direct air from the air outlet when the propeller is in the cruise configuration.

50. The tilting device according to claim 49, further comprising: a boom; wherein the nacelle is movably mounted to a first portion of the boom, and the baffle is mounted to a second portion of the boom in a fixed position.

51. The tilting device according to any one of claims 24 to 50, wherein the open air volume at the air outlet is greater in the lift configuration than in the cruise configuration.

52. The tilting device according to any one of claims 24 to 51, wherein the propeller is configured to direct air into the air inlet.

53. The tilting device according to any one of claims 24 to 52, wherein in the cruise configuration, the air inlet is located at the lower side of the nacelle.

54. The tilting device according to any one of claims 24 to 53, further comprising: a tilt actuator, wherein the tilt actuator is configured to move the propeller, the motor assembly, and the nacelle between the lift configuration and the cruise configuration.

55. The tilting device according to any one of claims 24 to 54, further comprising an annular air inlet located at the top portion of the nacelle.

56. The tilting device according to any one of claims 24 to 55, wherein the nacelle includes clamshell segments configured to open in the lift configuration.

57. A method of operating a tilt device of a vertical takeoff and landing (VTOL) aircraft, comprising: tilting a propeller of the tilt device to a lift configuration, the propeller being coupled to a motor assembly; directing slipstream above the exterior of a nacelle of the tilt device, the nacelle including an air inlet and an air outlet for a heat transfer device configured to be thermally coupled to the motor assembly; and creating a negative pressure zone at the air outlet by directing the slipstream above the exterior of the nacelle, the negative pressure zone causing air to flow from the air inlet to the air outlet.

58. The method according to claim 57, further comprising: tilting the propeller from the lift configuration to a cruise configuration; forming an exhaust passage for the air outlet in the cruise configuration, the exhaust passage including an extension of the nacelle and a baffle; and Air is discharged from the air outlet through the discharge channel.

59. A tilt device for a vertical takeoff and landing (VTOL) aircraft, comprising: A main body; A propeller; A motor assembly coupled to the propeller; A heat transfer device configured to be thermally coupled to the motor assembly; A nacelle coupled to the motor assembly, the nacelle including a door; and A tilt actuator configured to tilt the nacelle, the motor assembly, and the propeller relative to the main body between a lift configuration and a cruise configuration, wherein: The door is configured to be actuated such that the opening size of the air inlet of the nacelle is larger in the lift configuration than in the cruise configuration; And The propeller is configured to direct a portion of the slipstream through the air inlet to the heat transfer device when the propeller operates in the lift configuration.

60. The tilt device according to claim 59, wherein the door is configured to be actuated using a mechanical coupling between the door and the tilt actuator.

61. The tilt device according to claim 59 or 60, wherein the door is configured to be closed in the cruise configuration to close the air inlet.

62. The tilt device according to claim 61, wherein the door includes a cutout as an additional air inlet of the nacelle.

63. The tilt device according to any one of claims 59 to 62, wherein as seen in the cruise configuration, the door is located at the top portion of the nacelle.

64. The tilt device according to claim 63, further comprising a baffle configured to direct the portion of the slipstream from the top portion of the nacelle to the heat transfer device.

65. The tilt device according to claim 63 or 64, further comprising: An additional air inlet located in the nacelle, wherein the heat transfer device is configured to receive an air flow from the additional air inlet when the propeller operates in the cruise configuration.

66. The tilt device according to any one of claims 59 to 62, wherein as seen in the cruise configuration, the door is located at the side portion of the nacelle.

67. The tilt device according to claim 66, further comprising a baffle configured to direct the portion of the slipstream from the side portion to the heat transfer device.

68. The tilt device according to any one of claims 59 to 67, wherein the heat transfer device includes cooling fins.

69. The tilt device according to any one of claims 59 to 68, wherein the heat transfer device includes a heat exchanger.

70. The tilt device according to claim 69, further comprising: An oil flow path, wherein the heat exchanger is thermally coupled to the motor assembly through the oil flow path.

71. The tilt device according to any one of claims 59 to 70, wherein: The nacelle further includes a plurality of clamshell segments; and The door includes one of the clamshell segments.

72. The tilting device according to claim 71, wherein each of the plurality of clamshell segments is configured to be actuated using a mechanical coupling to the tilting actuator.

73. The tilting device according to claim 71 or 72, wherein at least two of the plurality of clamshell segments are configured to overlap when the propeller is operating in the lift configuration.

74. The tilting device according to any one of claims 59 to 74, wherein the door is configured to translate and rotate as the nacelle tilts between the lift configuration and the cruise configuration.

75. A method of operating a tilt device of a vertical takeoff and landing (VTOL) aircraft, the method comprising: Tilting, by a tilting actuator of the tilting device, a motor assembly, a nacelle, and a propeller of the tilting device relative to a body of the tilting device to a lift configuration, the motor assembly being coupled to the propeller and the nacelle, the nacelle including a door; Actuating the door to a first position as the nacelle and the propeller are tilted to the lift configuration; Guiding slipstream from the propeller to an air inlet of the nacelle and further to a heat transfer device thermally coupled to the motor assembly when the propeller is in the lift configuration; Tilting the motor assembly, the nacelle, and the propeller from the lift configuration to a cruise configuration; And Actuating the door to a second position as the nacelle and the propeller are tilted to the cruise configuration; Wherein actuating the door to the first position or the second position causes an opening size of the air inlet of the nacelle to be greater in the first position than in the second position.

76. The method according to claim 75, further comprising: Actuating the door between the first position and the second position using a mechanical coupling between the door and the tilting actuator.

77. The method according to claim 75 or 76, wherein the door is closed in the second position.

78. The method according to any one of claims 75 to 77, wherein the door is located at a top portion of the nacelle as seen in the cruise configuration.

79. The method according to any one of claims 75 to 78, wherein the heat transfer device includes a heat exchanger that is thermally coupled to the motor assembly through an oil flow path.

80. A vertical takeoff and landing (VTOL) aircraft comprising a tilting device according to any one of claims 1 to 22, 24 to 56, or 59 to 74.

81. A method of operating a vertical takeoff and landing (VTOL) aircraft, the method comprising: Operating a VTOL aircraft tilting device according to the method of any one of claims 23, 57, 58, or 75 to 79.

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