Propeller device

Abstract

To provide an apparatus for a vertical takeoff and landing (VTOL) aircraft.SOLUTION: A VTOL aircraft includes a plurality of lift propellers configured to be rotated by lift motors to provide vertical thrust during takeoff, landing and hovering operations. The lift propellers are configured to generate a cooling airflow to cool the lift motors during use. During a cruise operation when the VTOL aircraft is in forward motion, the lift propellers may be stowed in a stationary position. Therefore, the cooling airflow may be reduced or eliminated when it is not needed.SELECTED DRAWING: Figure 4A

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims priority to and benefit of U.S. patent application Ser. No. 18 / 163,372, filed February 2, 2023, entitled "SYSTEMS AND METHODS FOR LIFTER MOTOR COOLING IN EVTOL AIRCRAFT" (Attorney Docket No. 16163.0005-01000), which claims priority to and benefit of U.S. patent application Ser. No. 18 / 055,268, filed November 14, 2022, entitled "SYSTEMS AND METHODS FOR LIFTER MOTOR COOLING IN EVTOL AIRCRAFT" (Attorney Docket No. 16163.0005-0 ... This application claims priority to and benefit of U.S. Provisional Patent Application No. 63 / 378,680, filed October 7, 2022, entitled "Aircraft" (Attorney Docket No. 16163.6002-00000), the entire contents of which are incorporated herein by reference in their entirety for all purposes.

[0002] The present disclosure relates generally to the field of powered aerial vehicles. More specifically, but not by way of limitation, the present disclosure relates to innovations in eVTOL aircraft that use electric propulsion systems. Certain aspects of the present disclosure generally relate to cooling paths for motors, such as lift motors, in powered aerial vehicles. Other aspects of the present disclosure generally relate to motor improvements that may be used in other types of vehicles but provide particular advantages in aerial vehicles. Summary of the Invention

[0003] Some embodiments of the present disclosure provide an apparatus for a vertical take-off and landing (VTOL) aircraft, the apparatus may include: a propeller; a support structure for the VTOL aircraft; an electric engine mounted to the support structure and configured to rotate the propeller, the electric engine located within an enclosure; a first heat transfer element thermally coupled to the electric engine, at least a portion of the first heat transfer element located outside the enclosure; an air inlet located on an upper side of the support structure, the air inlet configured to receive downwash from the propeller during a climb phase; a first cooling path configured to direct a first portion of the downwash from the air inlet to the first heat transfer element; and a first air outlet configured to exhaust the first portion of the downwash from the first heat transfer element.

[0004] Some embodiments of the present disclosure provide an apparatus for a VTOL aircraft, which may include a propeller, a support structure for the VTOL aircraft, an electric engine mounted to the support structure and configured to rotate the propeller, an air inlet located on an upper side of the support structure and configured to receive downwash from the propeller during a climb phase, a first cooling path configured to direct a first portion of the downwash from the air inlet to a first portion of the electric engine, and a second cooling path configured to direct a second portion of the downwash from the air inlet to a second portion of the electric engine.

[0005] Some embodiments of the present disclosure provide a lift apparatus for a VTOL craft, the lift apparatus may include a lift propeller, a propeller controller electrically coupled to the lift propeller, the propeller controller located within a controller enclosure, a heat exchanger with fins located outside the controller enclosure, the heat exchanger fins thermally coupled to the propeller controller by oil passages, a boom, a fairing, an air inlet located on an upper side of the fairing, the air inlet configured to receive downwash from the lift propeller during a climb phase, cooling passages configured to direct the downwash to cool the heat exchanger fins, and an air outlet configured to exhaust the downwash from the heat exchanger fins. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram illustrating an exemplary VTOL aircraft, consistent with disclosed embodiments.

[0007] [Figure 2] FIG. 1 is a schematic diagram illustrating an exemplary VTOL aircraft, consistent with an embodiment of the present disclosure.

[0008] [Figure 3] FIG. 1 is a schematic diagram illustrating an exemplary VTOL aircraft, consistent with an embodiment of the present disclosure.

[0009] [Figure 4A] FIG. 1 is a schematic diagram illustrating an exemplary lift propeller and motor assembly on a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 4B] FIG. 1 is a schematic diagram illustrating an exemplary lift propeller and motor assembly on a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 4C] FIG. 1 is a schematic diagram illustrating an exemplary lift propeller and motor assembly on a VTOL aircraft, consistent with an embodiment of the present disclosure.

[0010] [Figure 5A] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5B] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5C] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5D] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5E] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5F] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5G] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5H] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5I] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5J] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5K]FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5L] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5M] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 5N] FIG. 1 is a schematic diagram illustrating exemplary oil and air flow paths in a motor assembly and surrounding area of ​​a VTOL aircraft, consistent with an embodiment of the present disclosure.

[0011] [Figure 6A] FIG. 1 is a schematic diagram illustrating an exemplary airflow path arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 6B] FIG. 1 is a schematic diagram illustrating an exemplary airflow path arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 6C] FIG. 1 is a schematic diagram illustrating an exemplary airflow path arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 6D] FIG. 1 is a schematic diagram illustrating an exemplary airflow path arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 6E] FIG. 1 is a schematic diagram illustrating an exemplary airflow path arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure.

[0012] [Figure 7A] FIG. 1 is a schematic diagram illustrating an example door arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 7B] FIG. 1 is a schematic diagram illustrating an example door arrangement in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure.

[0013] [Figure 8] FIG. 1 is a schematic diagram illustrating auxiliary features in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure.

[0014] [Figure 9A] FIG. 1 is a schematic diagram illustrating auxiliary features in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. [Figure 9B] FIG. 1 is a schematic diagram illustrating auxiliary features in a portion of a VTOL aircraft, consistent with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present disclosure primarily addresses components of electric vertical take-off and landing (eVTOL) aircraft for use with non-traditional aircraft. For example, an eVTOL aircraft of the present disclosure may be intended for frequent (e.g., more than 50 flights per working day), short-duration flights (e.g., less than 100 miles per flight) into and out of densely populated areas. The aircraft may be intended to carry four to six passengers or commuters who expect low noise and vibration. Therefore, it may be desirable for the components to be configured and designed to withstand frequent use without wear, to generate less heat and vibration, and for the aircraft to include mechanisms for effectively controlling and managing the heat or vibration generated by the components. Furthermore, some of these aircraft may be intended to operate in close proximity to each other over congested metropolitan areas. Therefore, it may be desirable for the components to be configured and designed to generate low levels of noise both inside and outside the aircraft and to have various safety and backup mechanisms. For example, for safety reasons, it may be desirable for an aircraft to be propelled by a distributed propulsion system, avoiding the risk of a single point of failure, and capable of conventional takeoff and landing on a runway. Furthermore, it may be desirable for the aircraft to be able to safely take off and land vertically from and in relatively restricted spaces (e.g., vertiports, parking lots, or driveways) compared to conventional airport runways, while carrying approximately four to six passengers or commuters, along with their associated baggage. These operational requirements may impose design constraints on the size, weight, and operational efficiency (e.g., drag, energy use) of the aircraft, which may affect the design and configuration of aircraft components.

[0016] The disclosed embodiments provide new and improved configurations of aircraft components not observed in conventional aircraft and / or identified design criteria for components that differ from conventional aircraft components. Such alternative configurations and design criteria have resulted in the disclosed embodiments herein for various configurations and designs of eVTOL aircraft components, in combination to address shortcomings and challenges of conventional components.

[0017] In some embodiments, the disclosed eVTOL aircraft may be designed to be capable of both vertical and conventional takeoff and landing with a distributed electric propulsion system that enables vertical flight, forward flight, and transition. Thrust may be generated by supplying high-voltage power to the distributed electric propulsion system's electric engines, each of which may convert the high-voltage power into mechanical shaft power to rotate a propeller. The embodiments disclosed herein may involve optimizing the energy density of the electric propulsion system. The embodiments may include an electric engine connected to an onboard power source, which may include a device capable of storing energy, such as a battery or capacitor, or one or more systems for harnessing or generating electricity, such as a fuel-powered generator or a solar panel array. Some disclosed embodiments provide for reduced component weight and space within the aircraft, thereby increasing the aircraft's efficiency and performance. With an eye toward safety in passenger transportation, the disclosed embodiments implement new and improved safety protocols and system redundancies in the event of a failure to minimize any single point of failure in the aircraft's propulsion system. Some disclosed embodiments also provide new and improved approaches to meeting aviation and transportation laws and regulations. For example, the Federal Aviation Administration implements federal laws and regulations that require safety components, such as fire barriers, adjacent to engines that use oil or other flammable materials in amounts above a threshold.

[0018] In a preferred embodiment, the distributed electric propulsion system may include 12 electric engines that may be mounted on forward and aft booms of the aircraft's wings. The forward electric engines may be tiltable in flight between a horizontal position (e.g., generating forward thrust) and a vertical position (e.g., generating vertical lift). The forward electric engines may be clockwise or counterclockwise with respect to the direction of propeller rotation. The aft electric engines may be fixed in a vertical position (e.g., generating vertical lift). They may also be clockwise or counterclockwise with respect to the direction of propeller rotation. In some embodiments, the aircraft may possess various combinations of forward and aft electric engines. For example, the aircraft may possess six forward and six aft electric engines, four forward and four aft electric engines, or any other combination of forward and aft electric engines, including embodiments in which the number of forward and aft electric engines is unequal. In some embodiments, the aircraft may possess four forward propellers and four aft propellers, at least four of which include tiltable propellers.

[0019] In a preferred embodiment, for vertical take-off and landing (VTOL) missions, the forward and aft electric engines can provide vertical thrust during take-off and landing. During flight phases when the aircraft is in forward flight mode, the forward electric engine can provide horizontal thrust, while the propeller of the aft electric engine can be retracted in a fixed position to minimize drag. The aft electric engine can be actively retracted with position monitoring. Transition from vertical to horizontal flight and vice versa can be achieved via a tilt propeller subsystem. The tilt propeller subsystem can redirect thrust from a primarily vertical direction during vertical flight mode to a generally horizontal direction during forward flight mode. A variable pitch mechanism can vary the collective angle of the propeller-hub assembly blades of the forward electric engine for operation during hover, transition, and cruise phases.

[0020] In some embodiments, for conventional take-off and landing (CTOL) missions, the forward electric engine may provide horizontal thrust for fixed-wing take-off, cruise, and landing. In some embodiments, the aft electric engine may not be used to generate thrust during CTOL missions, and the aft propeller may be stowed in place.

[0021] In some embodiments, the electric engine may be housed in or connected to the boom of the aircraft and may include a motor, an inverter, and a gearbox. In some embodiments, the motor, inverter, and gearbox may be interfaced such that they share a central axis. In some embodiments, torque resulting from the motor may be sent to the gearbox, away from the propeller of the propulsion system. In some embodiments, the gearbox may provide gear reduction and then send torque back to the propeller via the main shaft through bearings located inside the motor. In some embodiments, the inverter may be mounted to the rear of the gearbox so that the main shaft does not travel through the inverter when outputting torque to the propeller. In some embodiments, the motor, gearbox, and inverter may be interfaced such that a coolant, such as oil, may be used to service the motor, inverter, and / or gearbox while sharing a common heat exchanger. In some embodiments, the amount of oil used to lubricate and cool the electric engine may vary, including less than 1 quart, 2 quarts, 3 quarts, or any other measured amount of oil.

[0022] In some embodiments, the tilting propeller system may 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 may be changed as a function of the orientation of the propulsion system. In some embodiments, the rotary actuator may include a motor, an inverter, and a gearbox. In some embodiments, the gearbox may include various types of gears that interface to provide a gear reduction that can orient the propulsion system. In some embodiments, the tilting propeller system may include a redundant configuration in which multiple motors, inverters, and gearboxes are present and interface using gears. In some embodiments, a configuration utilizing multiple motors, gearboxes, and inverters may allow a failed portion of the redundant configuration to be driven by a motor, inverter, and gearbox of another portion of the configuration. In some embodiments, the gearbox configuration may also allow the tilting propeller system to maintain the orientation of the propulsion system with or without additional power assistance provided by the system.

[0023] In some embodiments, the electric propulsion systems described herein may generate thrust by supplying high-voltage (HV) power to an electric engine, which in turn converts the HV power into mechanical shaft power used to rotate a propeller. As noted above, the aircraft described herein may possess multiple electric engines mounted on booms at the front and rear of the wings. The amount of thrust generated by each electric engine may be controlled by torque commands from a flight control system (FCS) via a digital communication interface to each electric engine. Embodiments may include forward electric engines, which may be capable of changing their orientation, or tilt. Additional embodiments include forward engines, which may be clockwise (CW) or counterclockwise (CCW) types. The forward electric engine propulsion subsystem may consist of a multi-blade adjustable pitch propeller as well as a variable pitch subsystem.

[0024] In some embodiments, the aircraft may include an aft engine or lifter that may be of the clockwise (CW) or counterclockwise (CCW) type. Additional embodiments may include an aft electric engine that utilizes a multi-blade fixed pitch propeller.

[0025] As described herein, the orientation and use of the electric propulsion systems may vary throughout the operation of the aircraft. In some embodiments, during vertical takeoff and landing, the forward propulsion system and the aft propulsion system may provide vertical thrust during takeoff and landing. During flight phases in which the aircraft is in forward flight mode, the forward propulsion system may provide horizontal thrust, while the aft propulsion system propellers may be retracted in a fixed position to minimize drag. The aft electric propulsion system may be actively retracted while providing position monitoring. Some embodiments may include transitioning from vertical flight to horizontal flight and vice versa. In some embodiments, the transition may be achieved via a tilt propeller system (TPS). The TPS redirects thrust from a primarily vertical direction during vertical flight mode to a generally horizontal direction during forward flight mode. Additional embodiments may include a variable pitch mechanism that can change the collective angle of the forward propulsion system's propeller-hub assembly blades for operation during hover, cruise, and transition phases. Some embodiments may include a conventional takeoff and landing (CTOL) configuration, with the tilter providing horizontal thrust for fixed-wing takeoff, cruise, and landing. The aft electric engine does not need to be used to generate thrust during CTOL missions, and the aft propeller can be stowed in place.

[0026] In some embodiments, the electric engine described herein may possess design features that mitigate and protect against uncontained fires, such as utilizing a non-hazardous amount of flammable fluid contained in both the tilt engine and the lift engine, having no nominal ignition source within the electric engine, having an engine that exceeds temperature operating limits that may be more than 50°C below the flammable fluid auto-ignition temperature, overheat detection and protection, overvoltage detection and protection, and overcurrent detection and protection. In some embodiments, the design features of the electric engine may deem it not a designated fire zone. In some embodiments, the flammable fluid may include oil, and the non-hazardous amount may be less than 1 quart, or 2 quarts, or 3 quarts, or 4 quarts, or 5 quarts, or 10 quarts, as determined based on factors such as the size of the aircraft, the number of propellers, or the payload.

[0027] As disclosed herein, an electric engine may include an inverter and a motor, or an inverter, gearbox, and motor in various configurations, such as the exemplary configurations described herein. For example, an electric engine may include an electric motor, gearbox, and inverter that all share the same central axis. Additionally, the central axis may be configured along the axis of the output shaft that extends to the aircraft's propeller. In such an exemplary configuration, the motor, gearbox, and inverter all share the output shaft as the central axis and are oriented circularly around the output shaft. Additional embodiments may include a motor, gearbox, and inverter that are mounted together in sequence, or may include configurations in which some of the components, such as the motor and gearbox, are mounted together and other components, such as the inverter, are located elsewhere, but wiring is used to connect the electric engine.

[0028] As noted above, the electric engines for 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 motor's output shaft directly provides the speed and torque of the propeller shaft. Additional embodiments of the electric engine may include a motor, an inverter, and a gearbox, where the motor's output may travel through the gearbox connected to an output shaft for the propeller, and a motor, an inverter, and a gearbox, where the output from the motor travels through the gearbox away from the propeller and the output shaft for the propeller travels through the gearbox and motor back to the propeller. As described herein, the electric engine may occupy any combination or orientation of some or all of the motor, inverter, and gearbox. Additionally, each configuration or orientation of the electric engine disclosed herein may include cooling via air cooling, a coolant liquid, or a mixture of both.

[0029] For example, an electric engine configuration may include a motor and an inverter, with the motor being between the aircraft's propeller and the inverter. Additionally, the motor may include a gearbox. Furthermore, the inverter may share the same central axis as the motor, with the inverter being located in an enclosure that is cantilevered from the rear of the motor and may be air-cooled. It is recognized that such an inverter orientation may not be an optimal configuration in terms of the enclosure required to achieve such a cantilevered orientation. Additionally, a motor in this configuration utilizing air cooling may include potting material, and air fins to assist in cooling the motor may result in a further significant increase in system mass.

[0030] Some embodiments may include an electric engine, where the inverter module may be mounted outside the motor enclosure. Additional embodiments may include an electric engine where the inverter may be mounted above the electric motor, such that the inverter's air cooling fins are below the propeller. Further embodiments may include the inverter mounted on the back of the motor with the air cooling fins facing radially, the inverter mounted on the front of the motor with the air cooling fins facing radially, the inverter mounted on the motor where the inverter is cooled by a liquid such as oil, or any other location of the inverter relative to the motor.

[0031] Embodiments of the electric motor may include a stator enclosure, a winding stator assembly, a rotor, various bearings, and any additional components to help transfer the speed and torque generated by the motor to the propeller.

[0032] It is understood that electric engines may generate heat during operation and may include thermal management systems to ensure that components of the electric engine do not fail during operation. In some embodiments, a coolant may be used and circulated throughout individual components of the engine, such as the inverter, gearbox, or motor, through some of the components, or through all of the engine's components, to help manage the heat present within the engine. Additional embodiments may include using air-cooling methods to cool the electric engine, or using a mixture of coolant and air to manage the heat generated by the electric engine during operation. In some embodiments, the coolant used may also be the same liquid used as a lubricant throughout the inverter, gearbox, or motor. For example, the inverter, gearbox, and motor may use a mixture of air and liquid cooling, such as using liquid or air to cool the motor and liquid cooling in the inverter and gearbox, or any other combination of air and liquid cooling throughout the inverter, gearbox, and motor, or a subset of their components.

[0033] In some embodiments, oil may be used as a lubricant throughout the electric engine and as a coolant fluid to help manage heat generated by the engine during operation. Further to this example, different amounts of oil may be used to function as both a lubricant and a coolant fluid within the electric engine, such as in combination with 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 assistance of air cooling. As disclosed herein, the electric engine may have different primary functions, such as being used only for ascent and landing and thus only in one orientation, or being used during all phases of flight, such as ascent, landing, and flight. An engine used during all phases of flight may experience various orientations throughout flight and may contain more lubricant and coolant than an engine used only in one orientation. As such, all engines on an aircraft may not contain the same amount of lubricant and coolant. For example, an ascent and landing engine may require less than one quart of oil, while an engine operating during all phases of flight may require more than one quart of oil. It should be understood that the exemplary embodiments as referred to herein are representative and do not determine the limits of the amounts of lubricant and coolant that may be used in an electric engine.

[0034] It should be understood that by using oil not only to lubricate but also to cool the electric engine rather than a separate coolant, additional oil is added to the system, but oil eliminates traditional components that may be used to cool such an electric engine. For example, if the electric engine were cooled by a separate liquid, such as glycol, the engine may include separate heat exchangers for both the lubricant fluid and the coolant fluid. Thus, in embodiments where a single fluid is used for both lubrication and cooling, such as oil, there would be an increase in oil, but only the need for one heat exchanger, so the overall system may have a reduced mass due to using fewer heat exchangers and potentially other components not being needed, and there may be a more attractive drag profile. Furthermore, using one material to lubricate and cool the engine may increase the efficiency of the system due to the reduced mass and the benefits of cooling the engine with a material rather than relying on air cooling, which can be problematic to manage throughout the engine.

[0035] Additional embodiments of the electric engine may include various components to ensure that any flammable fluids are monitored and prevented from entering certain sections of the electric engine. Some embodiments may include an electric engine with a wet zone enclosure, which may be defined by the gearbox, motor, and / or heat exchanger. In some embodiments, the electric engine may have up to 4 liters or more of air in contact with the engine oil within the motor gearbox enclosure. For example, the electric engine may have up to 5 liters, 6 liters, 8 liters, 10 liters, or 20 liters of air in contact with the engine oil within the motor gearbox enclosure, based on factors such as the size of the aircraft, the number of propellers, or the payload. Embodiments of the motor gearbox enclosure may use a breather to equalize internal and external pressures. Breather embodiments may include a breather that protrudes above a nearby design feature to prevent the inadvertent intrusion of external fluids. Additional embodiments may include a breather with a screen and bypass entry path to prevent the intrusion of external debris. An embodiment may include sight glasses present on both the tilt and lift electric engines to ensure the oil is not overfilled or underfilled during maintenance.

[0036] Additional embodiments of the electric engine may include active protection features in the front and rear electric engines, such as monitoring internal temperatures during engine operation, including oil temperature, stator winding sets, inverter bulk capacitors, power modules, control board power modules, control board control processors, control board monitor processors, internal hot spots, and various other locations throughout the engine. Embodiments may include over-temperature limits that take into account known fault temperatures and operating limits related to fluid auto-ignition temperatures. Some embodiments may include a high-voltage power system that may have fuses at the high-voltage battery terminals that can irreversibly and quickly disconnect the engine electrical connections to mitigate an over-current event. This over-current protection may be activated when the current draw of the electric engine is greater than the over-current operation. Thus, in some embodiments, a fault condition that leads to an over-current may only result in a temporary overheat, arc, or spark fault. 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 within the electric engine and is opened by an engine fuse. In some embodiments, the inverter will detect AC overcurrents and isolate faulty phases and / or will continuously monitor the input DC voltage and apply protective actions to maintain the voltage below the overvoltage operating limit.

[0037] During takeoff, landing, hovering, and cruising, the motors and associated control components of a VTOL aircraft may generate heat. The heat must be dissipated to prevent degradation or damage to the motors, control components, and other elements of the VTOL aircraft. In some types of VTOL aircraft, such as electric VTOL (eVTOL) aircraft, thermal control is also important, for example, to maintain optimal energy efficiency of battery-powered components.

[0038] Some elements may generate high heat loads only during certain periods of operation. For example, some lift propellers may be used only during takeoff, landing, and hovering and may be shut off during cruise. Thus, such lift propellers may generate high heat loads during takeoff, landing, and hovering, but generate little or no heat during cruise.

[0039] Reference will now be made in detail to the 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. Instead, they are merely examples of apparatus and methods consistent with aspects related to the subject matter set forth in the appended claims.

[0040] In some embodiments, the VTOL aircraft described herein includes at least one fixed wing, multiple lift propellers fixed to provide lift during takeoff, landing, and hovering, and multiple tilt propellers tiltable from a lift configuration to provide lift to a cruise configuration to provide the forward thrust necessary for the at least one fixed wing to provide lift to the aircraft. By configuring the VTOL aircraft so that a portion of the propulsion system is dedicated to lift and a portion of the propulsion system is used for both lift and forward flight, the aircraft can be lighter and have lower drag than VTOL aircraft with separate lift and propulsion systems, and VTOL aircraft that use all propulsion for both lift and forward flight. Wing-type VTOL aircraft with separate propulsion systems for vertical and forward propulsion essentially waste the forward propulsion system during vertical takeoff, landing, and hovering. In contrast, aircraft according to the principles described herein utilize a forward propulsion system during vertical takeoff and landing, which may result in an overall relatively light propulsion system. All tilting propeller wing-type VTOL aircraft have limited locations for positioning the propellers (the propellers must be positioned in front of or behind the center of gravity, but their location is restricted by other propellers and the wing), which often results in relatively few, and therefore larger, propellers. In contrast, propulsion systems according to the principles described herein can have relatively smaller, lighter weight, and lower drag propellers. Thus, in some embodiments described herein, the aircraft has an ideal balance between a dedicated lift propulsion system and a tiltable propulsion system.

[0041] As used herein, the term "tilt propeller" refers to a variable-pitch propeller configured to provide thrust for vertical lift and forward propulsion by varying the pitch of the propeller. The term "lift propeller" may refer to a fixed-pitch propeller configured to provide thrust for vertical lift.

[0042] 1 and 2 illustrate a VTOL aircraft 100 in a cruise configuration and a vertical takeoff, landing, and hovering configuration (also referred to herein as a "climb" configuration), respectively, consistent with an embodiment of the present disclosure. The aircraft 100 may include a fuselage 102, wings 104 attached to the fuselage 102, and one or more aft stabilizers 106 attached to the rear of the fuselage 102. A plurality of lift propellers 112 may be attached to the wings 104 and configured to provide lift for vertical takeoff, landing, and hovering. A plurality of tilt propellers 114 may be attached to the wings 104 and may be tiltable between a climb configuration, which provides a portion of the lift required for vertical takeoff, landing, and hovering, as shown in FIG. 2, and a cruise configuration, which provides forward thrust to the aircraft 100 for horizontal flight, as shown in FIG. 1. As used herein, tilt propeller climb configuration refers to any tilt propeller orientation in which the tilt propeller thrust is primarily providing lift to the aircraft, and tilt propeller cruise configuration refers to any tilt propeller orientation in which the tilt propeller thrust is primarily providing forward thrust to the aircraft.

[0043] In some embodiments, lift propellers 112 may be configured to provide only lift, with all propulsion provided by tilt propellers. Thus, lift propellers 112 may be in a fixed position and generate thrust only during takeoff, landing, and hovering, while tilt propellers 114 may be tilted into a lift configuration in which their thrust is directed downward to provide additional lift.

[0044] For forward flight, tilt propellers 114 may tilt from their climb configuration to their cruise configuration. In other words, the pitch of tilt propellers 114 may change from a pitch where tilt propeller thrust is directed downward (to provide lift during vertical takeoff, landing, and hovering) to a pitch where tilt propeller thrust is directed rearward (to provide forward thrust to aircraft 100). The tilt propellers may tilt about axis 118, which may be perpendicular to the forward direction of aircraft 100. When aircraft 100 is in full forward flight, lift may be provided entirely by wings 104. Meanwhile, in the cruise configuration, lift propellers 112 may be shut off. Blades 120 of lift propellers 112 may be locked in a low-drag position for aircraft cruise. In some embodiments, lift propellers 112 may each have two blades 120 that can be locked for cruising in a minimum-drag position with one blade immediately ahead of the other, as illustrated in FIG. 1. In some embodiments, lift propellers 112 have three or more blades. In some embodiments, tilt propellers 114 include more blades 116 than lift propellers 112. For example, as illustrated in FIGS. 1 and 2, lift propellers 112 may each include, for example, two blades, while tilt propellers 114 may each include, for example, five blades. In some embodiments, tilt propellers 114 may have, for example, two to five blades.

[0045] In some embodiments, the aircraft may include only one wing 104 on each side of the fuselage 102 (or a single wing extending across the entire aircraft), and at least a portion of the lift propellers 112 may be located aft of the wing 104 and at least a portion of the tilt propellers 114 may be located forward of the wing 104. In some embodiments, all of the lift propellers 112 may be located aft of the wing 104 and all of the tilt propellers 114 may be located forward of the wing 104. According to some embodiments, all of the lift propellers 112 and tilt propellers 114 may be mounted on the wing, i.e., no lift propellers or tilt propellers may be mounted on the fuselage. In some embodiments, all of the lift propellers 112 may be located aft of the wing 104 and all of the tilt propellers 114 may be located forward of the wing 104. According to some embodiments, all of the lift propellers 112 and tilt propellers 114 may be positioned inboard of the wing tips 109 .

[0046] In some embodiments, the lift propellers 112 and tilt propellers 114 may be attached to the wing 104 by a boom 122. The boom 122 may be attached below the wing 104, above the wing, and / or integrated into the wing profile. In some embodiments, one lift propeller 112 and one tilt propeller 114 may be attached to each boom 122. The lift propeller 112 may be attached to the aft end of the boom 122, and the tilt propeller 114 may be attached to the forward end of the boom 122. In some embodiments, the lift propeller 112 may be attached in a fixed position on the boom 122. In some embodiments, the tilt propeller 114 may be attached to the forward end of the boom 122 via a hinge 124. The tilt propeller 114 may be mounted to the boom 122 such that when in its cruising configuration, the tilt propeller 114 is aligned with the body of the boom 122 and forms a continuous extension of the forward end of the boom 122 that minimizes drag for forward flight.

[0047] In some embodiments, the aircraft 100 may include, for example, one wing on each side of the fuselage 102 or a single wing extending across the aircraft. According to some embodiments, at least one wing 104 is a high wing mounted on 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 may have curved wing tips 109 to reduce drag during forward flight.

[0048] In some embodiments, the aft stabilizer 106 includes control surfaces such as one or more rudders, one or more elevators, and / or one or more combined rudder-elevators. The wing(s) may have any suitable design. In some embodiments, the wing has a tapered leading edge 123, for example, as shown in the embodiment of FIG. 1. In some embodiments, the wing has a tapered trailing edge, as shown in the embodiment of FIG. 3. In the embodiment of FIG. 3, the wing may have a substantially straight leading edge 127 in the center section of the wing 104.

[0049] The aircraft 100 may include at least one door 110 for passenger ingress and egress. In some embodiments, the door 110 may be located under and in front of the wing 104, as seen in FIG.

[0050] In some embodiments, a lift propeller 112 or tilt propeller 114 may cant relative to at least one other lift propeller 112 or tilt propeller 114. As used herein, canting refers to the relative orientation of the lift propeller / tilt propeller's axis of rotation about a line parallel to the longitudinal direction, similar to the roll degree of freedom of an aircraft. Tilting of a lift propeller and / or tilt propeller may help minimize damage from propeller rupture and may provide enhanced yaw control during flight by orienting the plane of rotation of the lift propeller / tilt propeller disk (the blades and the propeller portion to which they are attached) so as not to intersect critical parts of the aircraft (areas of the fuselage where personnel may be positioned, critical flight control systems, batteries, adjacent propellers, etc.) or other propeller disks.

[0051] The lift propellers 112 may be tilted in any suitable manner and combination. In some embodiments, the lift propellers 112 may be tilted in accordance with the corresponding tilt propellers. For example, as seen in FIG. 3, the innermost lift propeller 112a may be tilted the same amount and in the same direction as the innermost tilt propeller 114a. Similarly, lift propellers 112b and 112c may be tilted similarly to the corresponding tilt propellers 114b and 114c, respectively. Any suitable combination of tilting and / or non-tilting of the lift propellers relative to each other and to the tilt propellers may be used to achieve desired performance characteristics.

[0052] Further discussion of VTOL aircraft can be found in U.S. Patent Publication No. 2021 / 0362849, which is incorporated by reference in its entirety.

[0053] As discussed above, the motors and associated control components of a VTOL aircraft may generate heat during operation. Dissipation of heat is necessary to prevent deterioration or damage to the motors, control components, and other elements of the VTOL aircraft. For example, cooling may be achieved by directing airflow over heated components. The heated components may be, for example, motors or other heat-generating components, or may be, for example, heat exchangers configured to accept heat from heat-generating components via a liquid heat exchange medium. However, diverting constant airflow from outside the VTOL may create undesirable drag and other forces that could slow the aircraft. For example, the boom may be configured with scoops or large openings to collect enough air to meet maximum cooling requirements. Such scoops or large openings may generate drag. Additionally, large or other openings may create weak points within the VTOL structure, weakening its overall structural integrity. This may increase the risk of damage or failure or impose requirements for structural reinforcement in other locations, which may increase the weight of the VTOL aircraft.

[0054] Furthermore, some components may generate high heat loads only during their operation. For example, a lift propeller may only operate in climb configuration during the climb phase and therefore only require large amounts of cooling. The climb configuration may be a period during which drag is not a major consideration for the lift propeller. However, during the cruise configuration, the situation may be reversed: drag may be a significant issue and cooling of the lift propeller may not.

[0055] Finally, air-cooled components may be exposed to dirt, debris, and other contamination from the airflow. This contamination can degrade the components, cause malfunctions, and shorten their lifespan. Therefore, it may be desirable to provide a lift motor cooling path and motor configuration that allows for efficient cooling during ascent without incurring an unacceptable drag penalty during cruise and without contaminating or damaging sensitive components of the VTOL aircraft.

[0056] 4A-4C illustrate portions of a VTOL aircraft 400 consistent with embodiments of the present disclosure. VTOL aircraft 400 may be similar to, for example, VTOL aircraft 100 of FIGS. 1-3. Elements in FIGS. 4A-4C that are similar to those in FIGS. 1-3 may be labeled with a corresponding number using a 4 as the leading digit. For example, in some embodiments, boom 422 of FIG. 4A may be similar to boom 122 of FIGS. 1-3.

[0057] In Figure 4A, two booms 422 are depicted on the wing 404, with the lower boom shown in an exploded view with the motor assembly 430 exposed. The upper boom 422 is shown as it would appear in operation, with a fairing 425 covering its motor assembly. The motor assembly 430 may be coupled to the boom 422 by a mount 434 (as seen in Figure 4B). Each motor assembly 430 may be configured to drive its lift propeller 412, which includes blades 420 fixed to a hub 431.

[0058] Boom 422 is a structural component in that it may contribute significantly to the structural integrity of VTOL air vehicle 400 and may provide structural support to motor assembly 430 and lift propeller 412. Stated another way, boom 422 is an elongated support structure for motor assembly 430, lift propeller 412, fairing 425, or other components of VTOL air vehicle 400. Fairing 425 is an aerodynamic component. For example, fairing 425 may be shaped to provide an aerodynamic advantage, such as reduced drag, but does not contribute significantly to the structural integrity of VTOL air vehicle 400 or provide structural support to motor assembly 430 or lift propeller 412.

[0059] Fairing 425 may be further configured to channel cooling air to motor assembly 430. For example, fairing 425 may include air inlet 440 on its upper side. Air inlet 440 may be an opening positioned in a strategic area on fairing 425 to receive a large amount of cooling air from downwash (i.e., the flow of air pushed down by the rotation of blades 420) from lift propeller 412 during operation. For example, inlet 440 may be positioned below the path of blades 420 at a radial distance from hub 431 where the pressure or flow from the downwash is high. Furthermore, inlet 440 may have a substantially elongated slot shape along the longitudinal axis of boom 422 to span a range of radial distances from hub 431 and capture a larger amount of downwash from lift propeller 412. Finally, as discussed further below with respect to FIG. 6D, the air inlet 440 may be laterally offset from the longitudinal axis of the boom 422 to place the inlet in an area of ​​locally highest downwash pressure or mass flow.

[0060] Inlet 440 may have certain aerodynamic design advantages over traditional scoops or other openings because it does not need to face the forward direction of flight to collect sufficient airflow. For example, inlet 440 may be located on the downwardly sloping surface of fairing 425, for example, aft of lift propeller 412. Additionally, a bump, lip, or other aerodynamic feature may be formed on the forward side of air inlet 440 to reduce drag during cruise configuration without interfering with the cooling function of air inlet 440 during climb configuration.

[0061] In addition to the location and shape of air inlet 440, its size may be advantageously increased by not having air inlet 440 located on a structural component of VTOL 400. For example, when large openings or other openings are cut into a structural component such as boom 422, they may raise concerns about the structural integrity of VTOL air vehicle 400. This may not be a significant issue when cutting large openings into a non-structural surface such as fairing 425, but other considerations (e.g., drag) may remain. Nevertheless, in some embodiments, boom 422 may include air inlet 440, or may include an inlet instead of or in addition to inlet 440.

[0062] FIG. 4B illustrates an exemplary close-up view of motor assembly 430 of FIG. 4A , consistent with an embodiment of the present disclosure. Motor assembly 430 may be attached to and supported by boom 422 via mounting bracket 434. Motor assembly 430 may be further coupled to hub 431 and blades 420 of lift propeller 412 via shaft 432 (as seen in FIG. 4A , not shown in FIG. 4B ). Motor assembly 430 may be configured to rotate shaft 432 at a variable speed to generate vertical thrust with lift propeller 412 in a climb configuration during a climb phase of VTOL air vehicle 400. Motor assembly 430 may be configured to position blades 420 in a fixed, low-drag cruise configuration during a cruise phase of VTOL air vehicle 400 (e.g., as seen in FIG. 4A ).

[0063] Motor assembly 430 may include, for example, motor 435, gearbox 436, and inverter 437. Motor assembly 430 may further include enclosure 426 around motor 435, gearbox 436, and inverter 437. For example, enclosure 426 may include a substantially form-fitting casing around components 435-437 of motor assembly 430. Because motor 435, gearbox 436, and inverter 437 are housed within enclosure 426, the internal workings of those components are not shown here. Enclosure 426 may prevent dust, debris, or other contaminants contained in the cooling airflow from adversely affecting components 435-437. Motor assembly 430 may further include, for example, heat transfer elements 433 and 438 disposed outside enclosure 426 to thermally couple components 435-437 of motor assembly 430 to the cooling airflow. For example, cooling fins 438 may be coupled to enclosure 426 to surround motor 435 at an upper portion of motor assembly 430. Additionally, heat exchanger 433 may be coupled to enclosure 426 near inverter 437 at a lower portion of motor assembly 430. Thus, in some embodiments, the motor assembly may include a hybrid-cooled electric engine having first and second portions that may be cooled separately. In some embodiments, portions of heat exchanger 433 or cooling fins 438 may extend inside enclosure 426 in a manner that maintains a substantial seal against the outside air.

[0064] 4B , it should be understood that the spatial relationships between the different components of the motor assembly 430 are shown by way of example and need not always be so arranged. For example, in some embodiments, the gearbox 436 may not be located below the motor 435, or neither component may necessarily be located above or below the other. In general, the various components of the motor assembly 430 may be arranged in multiple configurations, as will be understood by those skilled in the art. Furthermore, the motor assembly may include additional components or omit one or more of the components discussed herein.

[0065] Furthermore, not all components need to be symmetrically arranged. For example, motor 435 and gearbox 436 may be configured to share the same longitudinal axis. For example, the longitudinal axis may correspond to the rotational axis of their propellers (not shown in FIG. 4B ). On the other hand, inverter 437 may not share a longitudinal axis with motor 435 and gearbox 436. For example, inverter 437 may be positioned offset from other components of motor assembly 430 or may be positioned to the side of motor assembly 430. In general, inverter 437 may be positioned in any suitable arrangement within enclosure 426.

[0066] Additionally, motor assembly 430 may include redundancy to ensure proper operation in the event of failure of one or more components. For example, motor 435 may include a rotor surrounded by multiple redundant stators. The multiple stators may be configured to operate simultaneously in conjunction with one another and to operate on their own in the event of a failure. Similarly, inverter 437 may include multiple stages. In some embodiments, inverter 437 may include a dual-stage inverter, or may include three or more stages.

[0067] The heat exchanger 433 may be configured to receive a circulating heat exchange medium from the interior of the motor assembly 430. For example, the heat exchange medium may comprise oil, which may be used to lubricate and cool components of the motor assembly 430. The oil may circulate through a lubrication heat exchange flow path that includes one or more components of the motor assembly 430, such as the motor 435, the gearbox 436, the inverter 437, and the heat exchanger 433. The lubrication heat exchange flow path may be advantageously minimized by locating the heat exchanger 433 adjacent to the enclosure 426, thereby minimizing the volume (and weight) of material required to achieve the cooling and lubrication functions. Furthermore, the lubrication heat exchange flow path may reduce the need for hoses, connections, and other elements that may increase complexity and weight and increase the risk of failure. Thus, the motor assembly 430 may include a substantially sealed hybrid cooling system configured to target multiple heat-generating portions of the motor assembly 430 with one or more cooling airflow paths, as described further below.

[0068] 4C illustrates an example close-up view of the enclosure 426 of the motor assembly 430 of FIG. 4A or 4B, consistent with an embodiment of the present disclosure. The enclosure 426 may include a motor enclosure 427, a divider plate 428, and an inverter or controller enclosure 429.

[0069] Motor enclosure 427 may surround and seal the upper components of motor assembly 430, such as motor 435 and gearbox 436. A coolant, such as oil, may circulate through motor enclosure 427 to lubricate and cool the components of motor 435 and gearbox 436. The lower surface of motor enclosure 427 may be sealed by dividing plate 428. For example, dividing plate 428 may include end bell plates that help close motor enclosure 427.

[0070] The inverter enclosure 429 may enclose and seal the lower components of the motor assembly 430, such as the inverter 437. The inverter 437 may include, for example, electronic circuit boards and other control components configured to control the operation of the motor assembly 430. Thus, the inverter may include a lift propeller controller, and the inverter enclosure 429 may alternatively be referred to as a controller enclosure 429. The controller enclosure 429 may be isolated from the oil or other coolant of the motor enclosure by a dividing plate 428. For example, the dividing plate 428 may include a thermal plate that serves to close the controller enclosure 429 and thermally couple it to the oil or other coolant.

[0071] Dividing plate 428 may comprise one or more plates sandwiched together and disposed between motor enclosure 427 and controller enclosure 429. For example, in some embodiments, dividing plate 428 may comprise end bells and thermal plates sandwiched together between motor and controller enclosures 427 and 429, as discussed above. Dividing plate 428 may isolate the interior spaces of motor enclosure 427 and controller enclosure 429 from each other and from the external environment outside enclosure 426. In some embodiments, one or more of the sandwiched plates of dividing plate 428 may comprise grooves, bores, or other conduits configured to distribute oil or other coolant in the plane of dividing plate 428.

[0072] In some embodiments, the dividing plate 428 may include an integral mounting bracket for supporting the heat exchanger 433. The heat exchanger 433 may include, for example, a folded-fin or other type of heat exchanger. Oil or other coolant heated by the motor 435, gearbox 436, or inverter 437 may be circulated through the fins of the heat exchanger 433 by internal conduits of the heat exchanger 433. The inlet and outlet for the internal conduits may be coupled to the outlet and inlet of the bore or groove, respectively, in the dividing plate 428. In this way, the heated oil (or other coolant) may carry heat from the enclosure 426 to the fins of the heat exchanger 433, where the heat may pass to the cooling airflow traveling through the fins. Thus, the entire motor assembly may be efficiently cooled without exposing sensitive components to the external environment.

[0073] The motor enclosure 427, the divider plate 428, and the inverter enclosure 429 may be formed, for example, from a lightweight, rigid material with high thermal conductivity, such as a metal such as aluminum or copper, a ceramic such as silicon carbide, or another suitable material.

[0074] 5A-5N provide schematic illustrations of example oil and airflow paths in a motor assembly and surrounding area of ​​a VTOL aircraft consistent with embodiments of the present disclosure. The VTOL aircraft may be similar to, for example, VTOL aircraft 100 of FIGS. 1-3 or VTOL aircraft 400 of FIGS. 4A-4C. Elements in FIGS. 5A-5N that are similar to those in FIGS. 1-4C may be labeled with corresponding numerals, using 5 as the leading digit and ending with the corresponding figure letter. For example, in some embodiments, fairing 525a in FIG. 5A may be similar to fairing 425 of FIG. 4A or fairing 525b of FIG. 5B. The solid arrowed lines in FIGS. 5A-5N may represent oil (or other heat exchange medium) flow paths, and the dashed arrowed lines may represent cooling airflow paths.

[0075] FIG. 5A schematically depicts a motor assembly 530a and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Motor assembly 530a may include components such as a motor 535a, a gearbox 536a, and an inverter 537a housed within an enclosure 526a. Enclosure 526a may include a motor enclosure 527a, a divider plate 528a, and a controller enclosure 529a. Motor enclosure 527a may surround and seal components such as motor 535a and gearbox 536a. Controller enclosure 529a may surround and seal inverter 537a. Motor assembly 530a may further include a heat exchanger 533a thermally coupled to components 535a-537a via lubricating heat exchange oil flow paths (shown with solid lines). In some embodiments, heat exchanger 533 may be supported by a mounting bracket or other extension of divider plate 528a. Divider plate 528a may extend beyond motor enclosure 527a / controller enclosure 529a so that divider plate 428a can support heat exchanger 533a and seal motor enclosure 527a and controller enclosure 529a. Divider plate 528a may further include bores, grooves, or other conduits for circulating oil (or other coolant) from motor enclosure 527a to heat exchanger 533a. Central portion 528a may further thermally couple controller enclosure 529a to the oil via thermal conduction. Thus, the lubricating heat exchange oil flow path may lubricate components 535a-537a and / or absorb heat generated by the components. Heat absorbed by the oil may be transported to heat exchanger 533a, where it may be transferred to incoming air (shown in dashed lines). For example, air may pass through fins or other passages within heat exchanger 533a. The fins or other channels may be configured to maximize the surface contact area between the heat exchanger and the airflow while maintaining an acceptable limit on the air pressure drop across the heat exchanger. The airflow may enter the interior chamber through inlets 540a in the surface of fairing 525a.The interior chamber may be formed by a fairing 525a, which may enclose the motor assembly 530a in cooperation with, for example, the end of a boom (not shown) to which the fairing 525a is attached. Airflow may be forced into the inlet as, for example, downwash from propeller blades (not shown) above the inlet 540a. The air may be exhausted from the heat exchanger 533a and leave the chamber by one or more air outlets (not shown), for example, without entering or passing through the enclosure 526a.

[0076] The lubrication and heat exchange oil flow path is illustrated at a high level of generality as a simple loop. However, it should be understood that the oil flow path may comprise branches, sub-loops, or other segmented paths. In general, oil may be circulated in any manner that effectively lubricates and cools the various components of the motor assembly.

[0077] FIG. 5B schematically illustrates a motor assembly 530b and surrounding elements of a VTOL aircraft consistent with an embodiment of the present disclosure. Elements corresponding to those in FIG. 5A may have similar numerals, and their descriptions may be omitted here. In FIG. 5B, the motor assembly 530b may further include an additional heat-transfer element 538b coupled to the enclosure 526b. For example, the heat-transfer element 538b may include cooling fins attached to the exterior of the motor enclosure 527b, similar to the configuration illustrated in FIG. 4B. The airflow from the inlet 540b may be split into bifurcated airflow paths, with a first airflow path passing through the heat-transfer element 538b and a second airflow path passing through the heat exchanger 533b. The first airflow path may exit through an outlet (not shown) without passing through the heat exchanger 533a. As seen in FIG. 5B, the first airflow path is shown passing behind the heat exchanger 533b. However, this is merely a schematic illustration to demonstrate that the two airflow paths are not collinear. The second airflow path may exit through the same outlet or a different outlet without passing through the heat-transfer element 538a. The bifurcated flow paths may allow the cooling airflow to target the section of the motor assembly 530b with the highest heat load. Furthermore, providing different flow paths may allow each section of the motor assembly 530b to be cooled regardless of the heat load applied to the different flow paths in the different sections. For example, if the motor 535b is very hot and transfers a large amount of heat to the first flow path through the heat-transfer element 538b, the heat exchanger 533b may continue to receive a relatively cool airflow from the second flow path because that airflow does not encounter the heat-transfer element 538b.

[0078] FIG. 5C schematically depicts a motor assembly 530c and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 5A-5B may have similar numerals, and their descriptions may be omitted here. In FIG. 5C, the branched flow paths may recombine before entering the heat exchanger 533c. This may have the advantage of providing a larger airflow to the heat exchanger 533c, at the expense of risking heat transfer between the heat transfer element 538c and the heat exchanger 533c. In some embodiments, various parameters (e.g., expected mass flow rate and temperature of the incoming air, expected heat load from the heat transfer element 538c and the heat exchanger 533c, etc.) may make such a risk acceptable.

[0079] FIG. 5D schematically depicts motor assembly 530d and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 5A-5C may have similar numerals, and their descriptions may be omitted here. FIG. 5D depicts a single airflow path through both heat transfer element 533d and heat exchanger 538d. This arrangement may provide a complete flow of cooling air to both elements 533d and 538d and may provide a simpler internal structure for the chamber within fairing 525d.

[0080] FIG. 5E schematically illustrates a motor assembly 530e and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 5A-5D may have similar numerals, and their descriptions may be omitted here. FIG. 5E illustrates bifurcated airflow paths, where a first airflow path may exit through a first inlet on a first side of the chamber and a second airflow path may exit through a second inlet on a second side of the chamber. For example, as discussed below, the first airflow path may pass, for example, through cooling fins of heat transfer element 538e to remove heat transferred from an upper portion of motor assembly 530e, such as from motor 535e. The first airflow path may then exit, for example, through the upper side of fairing 525e, in a region of relatively lower pressure than the pressure value found at inlet 540e. Meanwhile, the second airflow path may pass through, for example, a heat exchanger 533e to remove heat transferred from the lower portion of the motor assembly 530e, such as the inverter 537e, or from all components 535e-537e via heated oil. The second airflow path may then exit, for example, through the bottom of the fairing 525e. The arrangement of FIG. 5E may provide improved thermal isolation between the two flow paths and may provide a shorter stretch within each airflow path so that heated air can be more quickly exhausted from the chamber. Additionally, the arrangement of FIG. 5E may allow the system to utilize multiple low-pressure outlet areas to improve overall airflow through the chamber.

[0081] FIG. 5F schematically depicts a motor assembly 530f and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 5A-5E may have similar numerals, and their descriptions may be omitted here. FIG. 5F depicts a general case in which a controller 537f of the motor assembly 530f is located in a sealed enclosure 526f and thermally coupled to an external heat exchanger 533f. In some embodiments, the enclosure 526f may also house other elements, such as other components of the motor assembly 530f. Heat from the controller 537f may be transferred to oil or other coolant circulating within the enclosure 526f and then transferred by the heat exchanger 533f to a cooling airflow.

[0082] FIG. 5G schematically depicts a motor assembly 530g and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 5A-5F may have similar numerals, and their descriptions may be omitted here. FIG. 5G depicts an embodiment similar to FIG. 5A in which a cooling airflow path is constrained within a channel 545g. For example, the channel 545g may comprise a baffle or duct configured to define a channel surrounding the airflow cooling path between the inlet 540g and the inlet side of the heat exchanger 533g. Further, the channel 545g may continue from the outlet side of the heat exchanger 533g to an air outlet (not shown) within the fairing 525g. In some embodiments, the channel 545g may partially or completely enclose the cooling airflow path and further isolate downwash within the airflow path from the enclosed components of the motor assembly inside the enclosure 526g. The arrangement of FIG. 5G may advantageously provide improved flow rate and reduced intracavity pressure loss, as discussed further below with respect to FIG. 6E.

[0083] 5H-5N schematically depict further configurations of the motor assembly and surrounding elements of a VTOL aircraft consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 5A-5G may have similar numerals, and their descriptions may be omitted here. The arrangements of FIGS. 5H-5N substantially correspond to the arrangements of FIGS. 5A-5G, respectively. However, in each of FIGS. 5H-5N, inlet 540 may be located in boom 522 rather than fairing 525. Thus, FIG. 5H substantially corresponds to FIG. 5A, with inlet 540h located in boom 522h rather than the fairing. FIG. 51 substantially corresponds to FIG. 5B, with inlet 540i located in boom 522i rather than the fairing. FIG. 5J substantially corresponds to FIG. 5C, with inlet 540j located in boom 522j rather than the fairing. FIG. 5K substantially corresponds to FIG. 5D, with inlet 540k located in boom 522k rather than the fairing. Figure 5L substantially corresponds to Figure 5E, with inlet 540l located in boom 522l rather than in the fairing. Figure 5M substantially corresponds to Figure 5F, with inlet 540m located in boom 522m rather than in the fairing. Figure 5N substantially corresponds to Figure 5G, with inlet 540n located in boom 522n rather than in the fairing.

[0084] In some embodiments, the surface of the boom 522h-n in FIGS. 5H-5N may substitute for the fairing 525, and the inlets 540h-n may be located in substantially the same location as they would otherwise be. For example, the aft profile region including the inlets 540h-n, which in some embodiments may be a fairing (e.g., fairing 425 as seen in FIG. 4A), may instead form part of the boom and may contribute to the structural integrity of the VTOL aircraft or be part of a structural surface supporting the motor assembly 530. Alternatively, the inlets 540h-n may be located in a different location away from the fairing. For example, the arrangement of FIGS. 5H-5N may still include a fairing in the aft profile region, but the inlets 540h-n may be located elsewhere on the surface of the boom 522h-n. In some embodiments, the fairing may occupy more or less of the total surface profile formed by the combination of the boom and fairing, and the inlets / outlets may be formed in the fairing, the boom, or both. In some embodiments, the inlet or outlet may straddle the boundary between the boom and the fairing.

[0085] 6A-6E illustrate example airflow path arrangements for portions of VTOL air vehicles 600a-e consistent with embodiments of the present disclosure. VTOL air vehicles 600a-e may be similar to, for example, any of VTOL air vehicles 100, 400, or 500 of FIGS. 1-5N, respectively. Elements in FIGS. 6A-6E that are similar to those in FIGS. 1-5N may be labeled with a corresponding numeral using a 6 as the leading digit. For example, in some embodiments, inlet 640 of FIG. 6A may be similar to inlet 440 of FIG. 4A.

[0086] 6A illustrates an example bifurcated airflow path arrangement for a portion of a VTOL air vehicle 600a consistent with embodiments of the present disclosure. For example, airflow from the downwash of a lift propeller blade (not shown) may enter fairing 625 through inlet 640, as indicated by the arrows. Inlet 640 may be located in an area of ​​relatively high pressure due to the downwash. Baffle 645 may split the airflow into upper and lower flow paths 643 and 644. Alternatively, separate inlets may be provided for each of the motor and lower flow paths.

[0087] Air in the lower flow path 644 may be guided by a baffle 645 through a heat exchanger 633. The heat exchanger 633 may receive heat from components of the motor assembly 630, such as the motor 635, gearbox 636, or inverter 637, for example, via an oil flow path as discussed with respect to FIGS. 5A-5N. The cooling air in the lower flow path 644 may absorb heat from the heat exchanger 633 and exit the fairing 625 at a lower outlet 642. In this way, a source of cool air may be constantly supplied to the target heat load during the ascent phase, when heat generation is greatest. Meanwhile, sensitive components in the motor assembly 630 may be protected from impurities in the airflow by an enclosure.

[0088] As viewed from above in the lower view of FIG. 6A , inlet 640 and outlet 642 may have different shapes and orientations. For example, inlet 641 may be elongated substantially parallel to the longitudinal axis of boom 622, e.g., spanning a range of radial distances from hub 631, to capture a large amount of downwash from the lift propeller blades. In some embodiments, inlet 640 may have an asymmetry. For example, inlet 640 may be offset from the longitudinal axis, elongated at a substantial angle relative to the longitudinal axis, or have a shape that is not symmetrical relative to the longitudinal axis. The asymmetry may depend on the unique downwash distribution expected for the particular boom to which inlet 640 belongs. For example, the lift propeller may be configured to rotate in one of two rotational directions, creating an asymmetry in the downwash distribution on the upper surface of fairing 625. Furthermore, as seen in FIG. 3 , the lift propeller may be tilted at a different angle. Thus, the location, shape, and orientation of the inlet 640 may be selected to accommodate these asymmetries and their resulting expected downwash distribution.

[0089] In some embodiments, the outlet 642 can be elongated substantially perpendicular to the longitudinal axis. The outlet 642 can be positioned to allow heated air to easily escape from the heat exchanger 633. For example, the outlet 642 can be shaped and oriented to substantially match the outlet path of the heat exchanger 633. In some embodiments, the outlet 642 may not exactly correspond to the shape or size of the outlet side of the heat exchanger 633.

[0090] In some embodiments, such as those discussed below with respect to FIG. 6E , the baffle 645 may define a channel configured to direct air between differently sized or oriented inlets and outlets. For example, instead of forming an open chamber in the lower passage 644, the baffle 645 may define a channel that matches the right portion of the inlet 640 (as viewed from above in FIG. 6A ) at the location of the inlet 640. The channel may conform to the shape of the inlet side of the heat exchanger 633 at the location of the inlet side of the heat exchanger 633. The channel may continue from the outlet side of the heat exchanger 633 and conform to the shape of the outlet side at that location. Finally, the channel may extend to the outlet 642 and substantially match the shape and orientation of the outlet 642 at that location.

[0091] The air in the upper flow passage 643 may be directed by a baffle 645 through heat transfer elements 638, such as cooling fins. The cooling fins 638 may transfer heat to the air from an upper portion of the motor assembly, such as the motor 635. As seen in the lower view of FIG. 6A, the air in the upper flow passage 643 may be channeled to surround the cooling fins 638 and the motor 635 to optimize heat transfer. The heated air may then be exhausted from the fairing 625 by an upper outlet 641.

[0092] The upper outlet 641 may surround the shaft 632 and exit the fairing 625 in a region of relatively low pressure compared to the inlet 640. Downwash from the propeller blades above the fairing may vary with radial distance from the hub 631, with the downward pressure in the central region of the upper outlet 641 being significantly lower than the region of the inlet 640. This may be particularly true in the region directly below the hub 631, which may not generate direct downwash from rotation. Thus, in some embodiments, the outlet 641 may be located wholly or partially below the hub 631. Furthermore, the use of an upper outlet may allow the flow path to utilize convection generated by air heated by the cooling fins 638 to increase the upward flow at the upper outlet 641. In this way, the two flow paths may be kept completely separate from the inlet to the outlet. The flow path arrangement according to FIG. 6A may allow the ascent configuration to fully utilize multiple low-pressure regions during the ascent phase.

[0093] Additionally, the inlet and outlet contours may be optimized for reduced drag during the cruise phase without significantly penalizing airflow during the climb phase. For example, the outlet 641 may be configured to surround the shaft 632 or hub 631, e.g., with a tapered elliptical shape. The outlet 641 may have a larger opening aft of the shaft 632 than forward, or may include a lip or other aerodynamic feature on its forward side to minimize cruise drag while allowing heated air to easily exit during the climb phase.

[0094] FIG. 6B illustrates an exemplary single flow path in a VTOL aircraft 600b consistent with embodiments of the present disclosure. Elements corresponding to those in FIG. 6A may have similar numerals, and their descriptions may be omitted here. In FIG. 6B, the entire airflow from inlet 640 may be channeled through multiple heat load sources within motor assembly 630. Thus, the airflow may traverse upper flow path 643 and lower flow path 644 without branching. For example, as seen in the upper and lower views of FIG. 6B, baffle 645 may extend beyond the aft side of inlet 640 so that the entire inlet is not split. This arrangement may beneficially provide more cooling airflow to each component. Furthermore, eliminating upper outlet 641 may allow for greater conveyance of airflow through fairing 625 to heat exchanger 633. In some embodiments, outlet 641 may instead be configured as a secondary inlet. For example, as discussed below with respect to FIGS. 8-9B, lift propellers may be provided with auxiliary features configured to direct additional cooling air to the secondary inlet around shaft 632.

[0095] FIG. 6C illustrates a further variation of the exemplary flow path arrangement similar to FIG. 6B in a VTOL aircraft 600c consistent with embodiments of the present disclosure. Elements corresponding to those described above may have similar numerals, and their descriptions may be omitted here. In FIG. 6C , the upper flow path may be restricted to direct airflow to the upper portion of the cooling fins 638. A baffle 645 may be configured with a manifold or other opening to direct air to the cooling fins 638. For example, as illustrated by the radially inward arrows in the lower view of FIG. 6C , airflow from the upper passage 643 may surround the cooling fins 638 and flow downward along the cooling fins into the lower flow path 644. The airflow may then pass around the exterior of the motor assembly as it proceeds to the heat exchanger 633 and lower outlet 642. In this manner, cooling air may be in close and sustained contact with the heat-generating areas of the motor assembly 630 for efficient heat transfer. In some embodiments, as seen in FIG. 6C, the width of the air inlet 640 at the cross section of the fairing may be more than 50% of the width of the fairing.

[0096] 6D illustrates an example inlet arrangement in a portion of a VTOL aircraft 600d consistent with embodiments of the present disclosure. Inlet 640 may comprise multiple inlets 640a and 640b. Inlets 640a-b may correspond to the same or different flow paths. For example, in some embodiments, first inlet 640a may direct airflow to a first flow path, and second inlet 640b may direct air to a second flow path. In some embodiments, both inlets 640a and 640b may direct air to one or more flow paths. In some embodiments, there may be more than two inlets.

[0097] The multiple inlets 640a-b may be positioned to correspond to the downwash distribution of the particular boom 622 to which the inlets 640a-b belong. For example, as indicated by the arrows, downwash from a propeller (not shown) above the boom 622 and fairing 625 may have a swirl component given their direction of rotation. This swirl component may result in a downwash distribution that is better collected by asymmetric placement of one or more inlets 640a-b relative to the longitudinal axis LA of the boom 622. For example, the inlets 640a-b may be offset from the longitudinal axis LA to be located in an area of ​​maximum downwash or to take advantage of the swirl component. The inlets 640a-b may be offset to different sides of the longitudinal axis LA. For example, the downwash distribution may have a complex or curved shape along the upper surface of the fairing 625. A first inlet 640a may be located at a first radial distance from the hub 631.

[0098] The swirl component may be further utilized, for example, to create a desired flow direction within the fairing 625 or to operate louver doors, as discussed below. The offset or other asymmetry may vary depending on characteristics of each boom 622, such as the direction of blade rotation or tilt angle. For example, a first boom may include a first lift propeller configured to rotate in a first direction. One or more inlets on the first boom may be offset from its longitudinal axis in the first direction. A second boom may include a second lift propeller configured to rotate in a second direction. One or more inlets on the second boom may be offset from its longitudinal axis in the second direction.

[0099] FIG. 6E illustrates an exemplary single flow path in VTOL aircraft 600e consistent with embodiments of the present disclosure. Elements corresponding to those in FIGS. 6A-6D may have similar numerals, and their descriptions may be omitted here. In FIG. 6E, baffle 645 may define a channel for directing airflow to heat exchanger 633. For example, baffle 645 may comprise a funnel-shaped channel. The channel may have a curved inner surface or may have flat sides. In some embodiments, the shape of the channel may generally conform to the shapes of the various inlets and outlets it connects. For example, the channel formed by baffle 645 may substantially conform to the contours of inlet 640 at the location of inlet 640 and outlet 642 at the location of outlet 642. Furthermore, the channel formed by baffle 645 may substantially conform to the contours of the inlet and outlet sides of heat exchanger 633 at the inlet and outlet locations of heat exchanger 633. Thus, large airflows may be captured by arranging the inlets 640 in any desired size, shape, and orientation. Regardless of the selected size, shape, and orientation, the airflow may flow efficiently into the fins of the heat exchanger 633 with little turbulence and minimal intracavity pressure loss. Thus, configuring the baffles 645 as form-conforming channels may allow greater design freedom for other elements of the cooling path.

[0100] In some embodiments, the arrangement of Figure 6E may illustrate one component of a branched flow path, for example, Figure 6E may illustrate an example of the lower flow path 644 seen in Figure 6A, as discussed above.

[0101] 7A-7B illustrate example arrangements of portions of VTOL aircraft 700a-b consistent with embodiments of the present disclosure. VTOL aircraft 700a-b may be similar to, for example, any of VTOL aircraft 100, 400, 500, or 600 of FIGS. 1-6E, respectively. Elements in FIGS. 7A-7B that are similar to those in FIGS. 1-6E may be labeled with a corresponding number using a 7 as the leading digit. For example, in some embodiments, entrance 740 of FIG. 7A may be similar to entrance 440 of FIG. 4A.

[0102] In FIG. 7A , the inlet 740 may include a door 746 configured to optimize aerodynamic needs between the climb and cruise configurations. For example, the door 746 may be configured to open during the climb configuration to allow air to enter the inlet 740 and close during the cruise configuration to reduce drag. The door 746 may include a lip or other feature that allows the swirl component of the downwash from the blades 720 to force the door 746 open. The hinge 747 may be positioned substantially perpendicular to the swirl component to enable opening and closing. The doors 746 may include a spring or other biasing mechanism to hold them tightly closed during the cruise configuration when the blades 720 are blocked. The doors 746 may be closed by gravity during cruise or forced into a closed position by air. The door 746 may also be actuated into open and closed positions by active control. Alternatively, the door 746 may be fixed in place at an angle that captures sufficient airflow from the swirl component of the downwash. The fixed door may be configured to reduce drag from what would otherwise be a fully exposed opening at inlet 740. For example, door 746 may have an angled opening that is wider on the aft side than the forward side, or may include other contours designed to reduce drag. For example, the opening created by door 746 may be angled to at least partially face the aft side of fairing 725 to prevent air from being blown into fairing 725 during forward motion during cruise.

[0103] FIG. 7B illustrates a further variation of an exemplary door 746 arrangement in a VTOL aircraft 700b, similar to FIG. 7A in a VTOL aircraft 700a, consistent with an embodiment of the present disclosure. Elements corresponding to those described above may have similar numerals, and their descriptions may be omitted here. In FIG. 7B , the door 746 may be forced inward by downwash during the climb phase. The door 746 may comprise a majority of the upper surface of the fairing 725 so that the flow path receives a large amount of airflow when in the climb configuration. For example, in a cross-sectional direction of the boom 722 or fairing 725 perpendicular to the longitudinal axis of the boom 722, the width of the door 746 or air inlet 740 may occupy 50%, 75%, 85%, or 90% of the width of the upper surface of the fairing 725. Furthermore, as seen in FIG. 7B , the length of the door 746 in the longitudinal axis direction of the boom 722 may be greater than the width of the door. The door 746 can then be biased or actuated to a closed position during cruise to reduce drag. The hinge 747 can be located, for example, at the rear end of the door 746 as shown, or along one side as seen in FIG. 7A.

[0104] Figure 8 illustrates exemplary auxiliary features on a lift propeller in a portion of a VTOL aircraft 800, consistent with embodiments of the present disclosure. VTOL aircraft 800 may be similar to, for example, any of VTOL aircraft 100, 400, 500, 600, or 700 of Figures 1-7B, respectively. Elements in Figure 8 that are similar to those in Figures 1-7B may be labeled with a corresponding numeral using 8 as the leading digit. For example, in some embodiments, blade 820 of Figure 8 may be similar to blade 420 of Figure 4A.

[0105] In FIG. 8 , blade 820 may include internal channels 850 for directing additional cooling air to the secondary inlets. For example, as discussed above with respect to FIG. 6B , in some embodiments, the secondary inlets may be located around hub 831 or shaft 832. Rotation of blade 820 may force air through blade channel 850 to blade outlet 852 at blade inlet 851, as indicated by the dashed arrow. The blade outlet may be located within hub 831 as shown, or may be formed elsewhere, such as at the root of blade 820 near hub 831. Alternatively, one or more blade outlets 852 may be positioned midway through blade 820 to be aligned with another inlet, such as inlet 640 of FIGS. 6A-6E .

[0106] 9A-9B illustrate additional exemplary auxiliary features on a lift propeller in a portion of VTOL aircraft 900, consistent with embodiments of the present disclosure. VTOL aircraft 900 may be similar to, for example, any of VTOL aircraft 100, 400, 500, 600, 700, or 800 of FIGS. 1-8, respectively. Elements in FIGS. 9A-9B that are similar to those in FIGS. 1-8 may be labeled with a corresponding numeral using a 9 as the leading digit. For example, in some embodiments, blade 920 of FIG. 9A may be similar to blade 420 of FIG. 4A.

[0107] FIG. 9A illustrates multiple integrated cooling blades 953 consistent with embodiments of the present disclosure. The cooling blades 953 may be located, for example, on the spinner or hub 932 below the lift propeller blades 920. The cooling blades may direct the flow of cooling air through secondary inlets, for example, to the stator of the motor assembly. For example, as discussed above with respect to FIG. 6B, in some embodiments, the secondary inlets may be located around the hub 831 or shaft 832. The cooling air flow rate may be proportional to the rotational speed of the lift propeller and, therefore, proportional to the rate of heat generation within the lift propeller motor assembly. This results in a cooling system design that passively increases flow rate as needed when the lift propeller is generating more heat. The cooling blade configuration may be added without requiring additional failure-prone components such as dedicated motors, wiring, or controls.

[0108] 9B illustrates a further configuration of multiple integrated cooling blades 953 consistent with embodiments of the present disclosure. In FIG. 9B, the cooling blades 953 may be disposed about the shaft 931 and surrounded by a fan cowling 954. The fan cowling 954 may be configured to channel cooling airflow through the cooling blades 953 to improve airflow to the motor assembly.

[0109] Some embodiments of the present disclosure, such as in Figures 6A-7B, are described with respect to an inlet located on a fairing. However, embodiments of the present disclosure are not limited thereto. As discussed in Figures 5A-5N, embodiments of the present disclosure may alternatively locate the inlet or outlet on the boom instead of the fairing, for reasons discussed above. Similarly, elements illustrated in some figures as fairings may alternatively be formed as part of the boom.

[0110] The embodiments may be further described using the following clauses. Clause Set A: 1. A lift device for a vertical take-off and landing (VTOL) aircraft, comprising: Lift propellers and a motor assembly coupled to the lift propeller; a boom supporting the motor assembly; a fairing coupled to the boom and surrounding the motor assembly; an air inlet located on an upper side of the fairing, the air inlet configured to receive lift propeller downwash during a climb phase of the VTOL craft; a cooling passage configured to direct downwash toward the motor assembly; an air outlet configured to discharge downwash from the cooling path. 2. A lifting device as described in clause A1, wherein the center of the air inlet is aligned with the longitudinal axis of the boom. 3. A lifting device as described in clause A1 or A2, wherein the center of the air inlet is offset from the longitudinal axis of the boom. 4. A lifting device as described in clause A3, wherein the offset of the air inlet corresponds to the area of ​​maximum downwash pressure from the lifting propeller in a direction perpendicular to the longitudinal axis of the boom. 5. The lifting device of any one of clauses A1-A4, wherein the air inlet comprises a plurality of air inlets. 6. The plurality of air inlets are offset from one another in the direction of the longitudinal axis of the boom; the plurality of air inlets are offset from one another in a direction perpendicular to the longitudinal axis of the boom; The lifting apparatus of clause A5, wherein for each of the plurality of air inlets, the offset in a direction perpendicular to the longitudinal axis of the boom corresponds to a vertical area of ​​maximum downwash pressure from the lifting propeller. 7. A lifting device as described in any one of clauses A1 to A6, wherein in a cross section of the fairing, the width of the air inlet is more than 50% of the width of the fairing. 8. A lifting device as described in clause A7, in which the width of the air inlet in the cross section of the fairing is more than 75% of the width of the fairing. 9. A second lift propeller; a second motor assembly coupled to the second lift propeller; a second boom supporting a second motor assembly; a second fairing coupled to the second boom and surrounding the second motor assembly; a second air inlet located on an upper side of the second fairing, the second air inlet configured to receive a second downwash of the second lift propeller during an ascent phase of the VTOL craft; a second cooling path configured to direct the second downwash to the second motor assembly; The lifting device of any one of clauses A1 to A8, further comprising a second air outlet, the second air outlet configured to discharge the second downwash from the second cooling path. 10. A motor assembly is configured to rotate the lift propeller in a first rotational direction; a second motor assembly configured to rotate the second propeller in a second rotational direction opposite the first rotational direction; a center of the air inlet is offset from a longitudinal axis of the boom in a first offset direction; The lifting apparatus of clause A9, wherein the center of the second air inlet is offset from the longitudinal axis of the second boom in a second offset direction opposite the first offset direction. 11. A lifting device as described in any one of clauses A1 to A10, wherein the air outlet is located within the fairing. 12. A lifting device according to any one of clauses A1 to A11, wherein the air outlet is located on the bottom side of the fairing. 13. A lifting device as described in clause A12, wherein the air outlet is located below the heat exchanger of the motor assembly. 14. A lifting device according to any one of clauses A1 to A12, wherein the air outlet is located on the upper side of the fairing. 15. The lifting device of clause A14, further comprising a second air outlet located on the bottom side of the fairing. 16. A lifting device according to clause A14 or A15, wherein the air outlet surrounds the shaft of the lifting propeller. 17. The lifting device of clause A16, wherein the air outlet comprises an elliptical shape. 18. A lifting device as described in any one of clauses A14 to A17, wherein the air outlet is located below the hub of the lifting propeller. 19. A lifting device as described in clause A18, in which a segment of the outer boundary of the air outlet is located below the hub of the lifting propeller. 20. A first downwash flow path directed toward an upper portion of the motor assembly; The lifting apparatus of any one of clauses A1-A18, further comprising: a second downwash flow path directed toward a lower portion of the motor assembly. 21. The air inlet comprises a first air sub-inlet and a second air sub-inlet; a first air sub-inlet configured to direct a first portion of the downwash to the first downwash flowpath; The lift device of clause A20, wherein the second air sub-inlet is configured to direct a second portion of the downwash to a second downwash flow path. 22. The lift device of clause A20 or A21, further comprising a baffle configured to bifurcate the downwash into a first downwash flow path and a second downwash flow path. 23. The motor assembly includes a hybrid cooled motor assembly having a first motor assembly portion and a second motor assembly portion; the first motor assembly portion is configured to be directly air-cooled by a first portion of the downwash in the first downwash flow path; A lifting device as described in any one of clauses A1 to A22, wherein the second motor assembly portion is configured to be indirectly air-cooled via a fluid heat exchange medium in the second portion of the downwash within the second downwash flow path. 24. The lifting apparatus of any one of clauses A1-A23, further comprising a manifold configured to distribute downwash around the motor assembly. 25. Opens during the ascent phase of a VTOL aircraft to expose the air inlet to downwash, The lifting apparatus of any one of clauses A1-A24, further comprising a door configured to close during a cruise phase of the VTOL aircraft to cover the air inlet. 26. The lifting device of clause A25, further comprising a control actuator configured to operate the door. 27. The lifting apparatus of clause A25 or A26, further comprising a biasing mechanism configured to bias the door to a closed position. 28. The lift device described in clause A27, wherein the biasing force of the biasing mechanism is configured to be higher than the opposing force from the air during a cruise phase of the VTOL craft and lower than the opposing force from the air during an ascent phase of the VTOL craft. 29. A lifting device according to any one of clauses A25 to A28, wherein the door is configured to open by the swirling component of the downwash. 30. A lifting device according to any one of clauses A25 to A29, wherein the door is hinged within the fairing. 31. A lifting device according to any one of clauses A1 to A30, wherein the motor assembly comprises a motor, a gearbox, and an inverter. 32. The motor and gearbox share the same longitudinal axis; A lifting apparatus as described in clause A31, wherein an axis of the inverter is offset from a longitudinal axis of the motor and gearbox. 33. A lifting device according to clause A31 or A32, wherein the motor assembly comprises redundant components. 34. The lifting apparatus of clause A33, wherein the redundant components comprise at least one of: a redundant stator of the motor; and a redundant inverter stage of the inverter. 35. A vertical take-off and landing (VTOL) aircraft comprising a lift device according to any one of clauses A1 to A35. Clause Set B: 1. A lift device for a vertical take-off and landing (VTOL) aircraft, comprising: Lift propellers and a motor assembly coupled to the lift propeller, the motor assembly being located within the enclosure; a heat exchanger located outside the enclosure and thermally coupled to the motor assembly by a coolant flow path; Boom and Fairing and an air inlet located above either the boom or the fairing, the air inlet configured to receive lift propeller downwash during the ascent phase of the VTOL craft; a cooling passage configured to direct the downwash to a heat exchanger; an air outlet configured to discharge downwash from the heat exchanger. 2. A lifting device as described in clause B1, wherein the center of the air inlet is aligned with the longitudinal axis of the boom. 3. A lifting device as described in clause B1 or B2, wherein the center of the air inlet is offset from the longitudinal axis of the boom. 4. A lifting device as described in clause B3, wherein the air inlet is offset from the lifting propeller relative to the side of the longitudinal axis having the highest downwash pressure. 5. The lifting device of any one of clauses B1-B4, wherein the air inlet comprises a plurality of air inlets. 6. Multiple air inlets are located at different radial distances from the hub of the lift propeller; the plurality of air inlets are offset from one another in a direction perpendicular to the longitudinal axis of the boom; The lifting apparatus of clause B5, wherein for each of the plurality of air inlets, the offset in a direction perpendicular to the longitudinal axis of the boom corresponds to a side at a radial distance from the longitudinal axis having a highest downwash pressure from the lifting propeller. 7. A lifting device as described in any one of clauses B1 to B6, wherein in a cross section of the boom, the width of the air inlet is more than 50% of the width of the boom. 8. A lifting device as described in clause B7, wherein in the cross section of the boom the width of the air inlet is more than 75% of the width of the boom. 9. A second lift propeller; a second motor assembly coupled to the second lift propeller, the second motor assembly being located within the second enclosure; a second heat exchanger located outside the second enclosure, the second heat exchanger being thermally coupled to the motor assembly by a second coolant flow path; The second boom and a second fairing; a second air inlet located above the second boom or the second fairing, the second air inlet configured to receive a second downwash of the second lift propeller during a climb phase of the VTOL craft; a second cooling path configured to direct the second downwash to a second heat exchanger; The lifting device of any one of clauses B1 to B8, further comprising a second air outlet, the second air outlet configured to discharge the second downwash from the second heat exchanger. 10. A motor assembly is configured to rotate the lift propeller in a first rotational direction; a second motor assembly configured to rotate the second propeller in a second rotational direction opposite the first rotational direction; a center of the air inlet is offset from a longitudinal axis of the boom in a first offset direction; The lifting apparatus of clause B9, wherein the center of the second air inlet is offset from the longitudinal axis of the second boom in a second offset direction opposite the first offset direction. 11. A lifting device as described in any one of clauses B1 to B10, wherein the air outlet is located within the boom. 12. A lifting device according to any one of clauses B1 to B11, wherein the air outlet is located on the bottom side of the fairing. 13. A lifting device as described in clause B12, wherein the air outlet is located below the heat exchanger. 14. A lifting device according to any one of clauses B1 to B13, wherein the air outlet is located on the upper side of the fairing. 15. The lifting device of clause B14, further comprising a second air outlet located on the bottom side of the fairing. 16. A lifting device according to clause B14 or B15, wherein the air outlet surrounds the shaft of the lifting propeller. 17. The lifting device of clause B16, wherein the air outlet comprises an elliptical shape. 18. A lifting device according to any one of clauses B14 to B17, wherein the air outlet is located below the hub of the lifting propeller. 19. A lifting device as described in clause B18, in which a segment of the outer boundary of the air outlet is located below the hub of the lifting propeller. 20. A first downwash flow path directed toward an upper portion of the motor assembly; The lifting apparatus of any one of clauses B1-B19, further comprising: a second downwash flow path directed toward a lower portion of the motor assembly. 21. The air inlet comprises a first air sub-inlet and a second air sub-inlet; a first air sub-inlet configured to direct a first portion of the downwash to the first downwash flowpath; The lift device of clause B20, wherein the second air sub-inlet is configured to direct a second portion of the downwash to a second downwash flow path. 22. The lift device of clause B20 or B21, further comprising a baffle configured to bifurcate the downwash into a first downwash flow path and a second downwash flow path. 23. The motor assembly includes a hybrid cooled motor assembly having a first motor assembly portion and a second motor assembly portion; the first motor assembly portion is configured to be directly air-cooled by a first portion of the downwash in the first downwash flow path; A lifting device as described in any one of clauses B1 to B22, wherein the second motor assembly portion is configured to be indirectly air-cooled via a fluid heat exchange medium in the second portion of the downwash within the second downwash flow path. 24. The lifting apparatus of any one of clauses B1-B23, further comprising a manifold configured to distribute downwash around the motor assembly. 25. Opens during the ascent phase of a VTOL aircraft to expose the air inlet to downwash, The lifting apparatus of any one of clauses B1-B24, further comprising a door configured to close to cover the air inlet during a cruise phase of the VTOL aircraft. 26. The lifting device of clause B25, further comprising a control actuator configured to operate the door. 27. The lifting apparatus of clause B25 or B26, further comprising a biasing mechanism configured to bias the door to a closed position. 28. The lift device described in clause B27, wherein the biasing force of the biasing mechanism is configured to be higher than the opposing force from the air during the cruise phase of the VTOL craft and lower than the opposing force from the air during the ascent phase of the VTOL craft. 29. A lifting device according to any one of clauses B25 to B28, wherein the door is configured to open by the swirling component of the downwash. 30. A lifting device according to any one of clauses B25 to B29, wherein the door is hinged within the fairing. 31. The lifting device of any one of clauses B1-B30, wherein the coolant flow path includes a lubrication flow path, and the coolant is configured to lubricate components of the motor assembly. 32. A lifting device according to any one of clauses B1 to B31, wherein the motor assembly comprises a motor, a gearbox, and an inverter. 33. The motor and gearbox share the same longitudinal axis; A lifting apparatus as described in clause B32, wherein an axis of the inverter is offset from a longitudinal axis of the motor and gearbox. 34. A lifting device according to clause B32 or B33, wherein the motor assembly comprises redundant components. 35. The lifting device of clause B34, wherein the redundant components include at least one of a redundant stator of the motor and a redundant inverter stage of the inverter. 36. A vertical take-off and landing (VTOL) aircraft comprising a lift device according to any one of clauses B1 to B35. Clause Set C: 1. A lift device for a vertical take-off and landing (VTOL) aircraft, comprising: Lift propellers and a motor assembly coupled to the lift propeller, the motor assembly being located within the enclosure; a heat exchanger located outside the enclosure and thermally coupled to the motor assembly by a coolant flow path; Boom and Fairing and an air inlet located above either the boom or the fairing, the air inlet configured to receive lift propeller downwash during the ascent phase of the VTOL craft; a first cooling path configured to direct a first portion of the downwash to cool a portion of the enclosure around the motor assembly; a second cooling path configured to direct a second portion of the downwash to cool the heat exchanger; an air outlet configured to discharge downwash from the first cooling path or the second cooling path. 2. A lifting device as described in clause C1, wherein the center of the air inlet is aligned with the longitudinal axis of the boom. 3. A lifting device as described in clause C1 or C2, wherein the center of the air inlet is offset from the longitudinal axis of the boom. 4. A lifting device as described in clause C3, wherein the air inlet is offset from the lifting propeller relative to the side of the longitudinal axis having the highest downwash pressure. 5. The lifting device of any one of clauses C1-C4, wherein the air inlet comprises a plurality of air inlets. 6. Multiple air inlets are located at different radial distances from the hub of the lift propeller; the plurality of air inlets are offset from one another in a direction perpendicular to the longitudinal axis of the boom; The lifting apparatus of clause C5, wherein for each of the plurality of air inlets, the offset in a direction perpendicular to the longitudinal axis of the boom corresponds to a side at a radial distance from the longitudinal axis having a highest downwash pressure from the lifting propeller. 7. A lifting device as described in any one of clauses C1 to C6, wherein in the cross section of the boom, the width of the air inlet is more than 50% of the width of the boom. 8. A lifting device as described in clause C7, wherein in the cross section of the boom the width of the air inlet is more than 75% of the width of the boom. 9. A second lift propeller; a second motor assembly coupled to the second lift propeller, the second motor assembly being located within the second enclosure; a second heat exchanger located outside the second enclosure, the second heat exchanger being thermally coupled to the motor assembly by a second coolant flow path; The second boom and a second fairing; a second air inlet located above the second boom or the second fairing, the second air inlet configured to receive a second downwash of the second lift propeller during a climb phase of the VTOL craft; a third cooling passage configured to direct a first portion of the second downwash to cool an exterior upper portion of the second motor assembly; a fourth cooling path configured to direct a second portion of the second downwash to cool the heat exchanger; The lifting device of any one of clauses C1 to C8, further comprising a second air outlet, the second air outlet configured to discharge the second downwash from the third cooling path or the fourth cooling path. 10. A motor assembly is configured to rotate the lift propeller in a first rotational direction; a second motor assembly configured to rotate the second propeller in a second rotational direction opposite the first rotational direction; a center of the air inlet is offset from a longitudinal axis of the boom in a first offset direction; The lifting apparatus of clause C9, wherein the center of the second air inlet is offset from the longitudinal axis of the second boom in a second offset direction opposite the first offset direction. 11. A lifting device as described in any one of clauses C1 to C10, wherein the air outlet is located within the boom. 12. A lifting device according to any one of clauses C1 to C11, wherein the air outlet is located on the bottom side of the fairing. 13. A lifting device as described in clause C12, wherein the air outlet is located below the heat exchanger. 14. A lifting device according to any one of clauses C1 to C13, wherein the air outlet is located on the upper side of the fairing. 15. The lifting device of clause C14, further comprising a second air outlet located on the bottom side of the fairing. 16. A lifting device as described in clause C14 or C15, wherein the air outlet surrounds the shaft of the lifting propeller. 17. A lifting device as described in clause C16, wherein the air outlet comprises an elliptical shape. 18. A lifting device as described in any one of clauses C14 to C17, wherein the air outlet is located below the hub of the lifting propeller. 19. A lifting device as described in clause C18, in which a segment of the outer boundary of the air outlet is located below the hub of the lifting propeller. 20. The air inlet comprises a first air inlet and a second air inlet; a first air inlet configured to direct a first portion of the downwash to the first cooling path; The lifting device of any one of clauses C1-C19, wherein the second air inlet is configured to direct a second portion of the downwash to the second cooling path. 21. The lifting device of clause C20, further comprising a baffle configured to bifurcate the downwash into the first cooling path and the second cooling path. 22. The lifting apparatus of any one of clauses C1-C21, further comprising a manifold configured to distribute downwash around the motor assembly. 23. Opens during the ascent phase of a VTOL aircraft to expose the air inlet to downwash, The lifting apparatus of any one of clauses C1-C22, further comprising a door configured to close to cover the air inlet during a cruise phase of the VTOL aircraft. 24. The lifting device according to clause C23, further comprising a control actuator configured to operate the door. 25. The lifting apparatus of clause C23 or C24, further comprising a biasing mechanism configured to bias the door to a closed position. 26. The lift device described in clause C25, wherein the biasing force of the biasing mechanism is configured to be higher than the opposing force from the air during a cruise phase of the VTOL craft and lower than the opposing force from the air during an ascent phase of the VTOL craft. 27. A lifting device as described in any one of clauses C23 to C26, wherein the door is configured to open by the swirling component of the downwash. 28. A lifting device according to any one of clauses C23 to C27, wherein the door is hinged within the fairing. 29. A lifting device as described in any one of clauses C1 to C28, wherein the coolant flow path includes a lubrication flow path and the coolant is configured to lubricate components of the motor assembly. 30. A lifting device according to any one of clauses C1 to C29, wherein the motor assembly comprises a motor, a gearbox, and an inverter. 31. The motor and gearbox share the same longitudinal axis; A lifting apparatus as described in clause C30, wherein an axis of the inverter is offset from a longitudinal axis of the motor and gearbox. 32. A lifting device as described in clause C30 or C31, wherein the motor assembly comprises redundant components. 33. The lifting device of clause C32, wherein the redundant components comprise at least one of a redundant stator of the motor and a redundant inverter stage of the inverter. 34. A vertical take-off and landing (VTOL) aircraft comprising a lift device according to any one of clauses C1 to C33. Clause Set D: 1. An apparatus for a vertical take-off and landing (VTOL) aircraft, comprising: Propeller and a support structure for the VTOL aircraft; an electric engine mounted to the support structure and configured to rotate a propeller, the electric engine located within the enclosure; a first heat transfer element thermally coupled to the electric engine, at least a portion of the first heat transfer element located outside the enclosure; an air inlet located above the support structure, the air inlet configured to receive downwash from the propeller during a climb phase; a first cooling path configured to direct a first portion of downwash from the air inlet to a first heat transfer element; a first air outlet configured to discharge a first portion of the downwash from the first heat transfer element. 2. The apparatus of clause D1, wherein the first heat transfer element comprises a heat exchanger. 3. The apparatus of clause D2, further comprising an oil flow path, wherein the heat exchanger is thermally coupled to the electric engine by the oil flow path. 4. The electric engine comprises a motor; the enclosure comprises a motor enclosure surrounding the motor; The apparatus of clause D3, wherein the oil flow path is configured to circulate oil within the motor enclosure. 5. The electric engine further comprises an inverter; the enclosure includes an inverter enclosure surrounding the inverter, and a dividing plate between the motor enclosure and the inverter enclosure; The apparatus of clause D4, wherein the divider plate is configured to thermally couple the inverter to the oil flow path. 6. The electric engine is equipped with a gearbox; the enclosure comprises a gearbox enclosure surrounding the gearbox; The apparatus of clause D4 or D5, wherein the oil flow path is configured to circulate oil within the gearbox enclosure. 7. A second heat transfer element thermally coupled to the electric engine, wherein at least a portion of the second heat transfer element is located outside the enclosure; and The apparatus of any one of clauses D1-D6, further comprising: a second cooling path configured to direct a second portion of the downwash from the air inlet to a second heat transfer element. 8. The apparatus of clause D7, further comprising a baffle configured to divide downwash from the air inlet into the first cooling path and the second cooling path. 9. The inlet comprises a first air inlet and a second air inlet; a first cooling path configured to receive a first portion of the downwash from the first air inlet; The apparatus of clause D7 or D8, wherein the second cooling path is configured to receive a second portion of the downwash from the second air inlet. 10. The apparatus of any one of clauses D7-D9, wherein the first air outlet is configured to discharge a second portion of the downwash from the second heat transfer element. 11. The apparatus of any one of clauses D7-D10, further comprising a second air outlet, the second air outlet configured to discharge a second portion of the downwash from the second heat transfer element. 12. The apparatus of clause D11, wherein the second air outlet is located on an upper side of the support structure. 13. Further comprising an oil flow path; the electric engine includes a hybrid cooled electric engine having a first portion and a second portion; the first heat transfer element comprises a heat exchanger thermally coupled to the first portion of the electric engine via the oil flow path; The apparatus of any one of clauses D7-D12, wherein the second heat transfer element comprises an air-cooled fin thermally coupled to the second portion of the electric engine. 14. One of the first part of the electric engine or the second part of the electric engine comprises a motor; The apparatus of clause D13, wherein the other of the first part of the electric engine or the second part of the electric engine comprises an inverter. 15. Further comprising a second heat transfer element thermally coupled to the electric engine, wherein at least a portion of the second heat transfer element is located outside the enclosure; The apparatus of any one of clauses D1-D14, wherein the first cooling path is configured to direct downwash from the first heat transfer element to the second heat transfer element. 16. Opens during the ascent phase of a VTOL aircraft to expose the air inlet to downwash, The apparatus of any one of clauses D1-D15, further comprising a door configured to close during a cruise phase of the VTOL aircraft to cover the air inlet. 17. The apparatus of clause D16, further comprising a biasing mechanism configured to bias the door to a closed position, wherein the biasing force of the biasing mechanism is configured to be greater than a first opposing force from the air during a cruise phase of the VTOL aircraft and less than a second opposing force from the air during an ascent phase of the VTOL aircraft. 18. An apparatus as described in clause D16 or D17, wherein the door is configured to open by the swirling component of the downwash. 19. An apparatus as described in any one of clauses D16 to D18, wherein the door is configured to be forced open inwardly into the support structure by downwash. 20. An apparatus according to any one of clauses D16 to D19, wherein the width of the door in a cross-sectional direction of the support structure perpendicular to the longitudinal axis of the support structure is at least 75% of the width of the support structure. 21. A device according to clause D20, in which the length of the door in the longitudinal axis direction is greater than the width of the door. 22. The apparatus of any one of clauses D1-D21, further comprising a boom, and wherein the support structure comprises one of the boom or a fairing coupled to the boom. 23. A method of operating a vertical take-off and landing (VTOL) aircraft, comprising: rotating a propeller with an electric engine in an ascent configuration of the VTOL aircraft, the electric engine being located within an enclosure and mounted to a support structure of the VTOL aircraft; directing downwash from the propeller through an air inlet located above the support structure; receiving a portion of the downwash in a cooling path via an air inlet; directing a portion of the downwash through a cooling path to a heat transfer element, at least a portion of the heat transfer element being located outside the enclosure and thermally coupled to the electric engine; and discharging a portion of the downwash from the heat transfer element via the air outlet. 24. An apparatus for a vertical take-off and landing (VTOL) aircraft, comprising: Propeller and a support structure for the VTOL aircraft; an electric engine mounted to the support structure and configured to rotate a propeller; an air inlet located above the support structure, the air inlet configured to receive downwash from the propeller during a climb phase; a first cooling path configured to direct a first portion of downwash from the air inlet to a first portion of the electric engine; a second cooling path configured to direct a second portion of the downwash from the air inlet to a second portion of the electric engine. 25. A first heat transfer element thermally coupled to a first portion of the electric engine; The apparatus of clause D24, further comprising: a second heat transfer element thermally coupled to a second portion of the electric engine. 26. Further comprising an oil flow path; the electric engine includes a hybrid cooled electric engine having a first portion and a second portion; the first heat transfer element comprises a heat exchanger thermally coupled to the first portion of the electric engine via the oil flow path; The apparatus of clause D25, wherein the second heat transfer element comprises an air-cooled fin thermally coupled to the second portion of the electric engine. 27. The apparatus of any one of clauses D24 to D26, further comprising an enclosure around the electric engine, wherein at least a portion of the first heat transfer element and at least a portion of the second heat transfer element are located outside the enclosure. 28. One of the first part of the electric engine or the second part of the electric engine comprises a motor; The apparatus of any one of clauses D24 to D27, wherein the other of the first part of the electric engine or the second part of the electric engine comprises an inverter. 29. Opens during the ascent phase of a VTOL aircraft to expose the air inlet to downwash, a door configured to close to cover the air inlet during a cruise phase of the VTOL aircraft; The apparatus of any one of clauses D24-D28, wherein the door is configured to open due to a swirling component of downwash. 30. The apparatus of any one of clauses D24-D29, further comprising a boom, and wherein the support structure comprises one of the boom or a fairing coupled to the boom.

[0111] The foregoing description has been presented for purposes of illustration. It is not exhaustive and is not intended to limit the invention to the precise form or embodiment disclosed. Modifications and adaptations of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments of the invention disclosed herein.

Claims

1. 1. A propeller system for a vertical take-off and landing (VTOL) aircraft, comprising: Propeller and a support structure for the VTOL aircraft; an electric engine mounted to the support structure and configured to rotate the propeller, the electric engine located within an enclosure; a first heat transfer element thermally coupled to the electric engine, at least a portion of the first heat transfer element located outside the enclosure; and a first air inlet for a first cooling path and a second air inlet for a second cooling path located above the support structure, the first air inlet and the second air inlet each configured to receive downwash from the propeller during a climb phase, the first cooling path configured to direct a first portion of the downwash from the first air inlet to the first heat transfer element, and the second cooling path configured to direct a second portion of the downwash from the second air inlet to a second heat transfer element thermally coupled to the electric engine; a first air outlet configured to discharge the first portion of the downwash from the first heat transfer element.

2. the first heat transfer element comprises a heat exchanger; The propeller device of claim 1 , further comprising an oil flow path, the heat exchanger being thermally coupled to the electric engine by the oil flow path.

3. the electric engine comprises a motor; the enclosure comprises a motor enclosure surrounding the motor; The propeller device of claim 2 , wherein the oil passage is configured to circulate oil within the motor enclosure.

4. the electric engine further comprises an inverter; 4. The propeller device of claim 3, wherein the enclosure comprises an inverter enclosure that encloses the inverter, and a dividing plate between the motor enclosure and the inverter enclosure, the dividing plate being configured to thermally couple the inverter to the oil flow path.

5. the electric engine comprises a gearbox; The propeller device of claim 3 , wherein the enclosure comprises a gearbox enclosure surrounding the gearbox, and the oil flow passage is configured to circulate oil within the gearbox enclosure.

6. 2. The propeller device of claim 1, further comprising a second air outlet configured to discharge the second portion of the downwash from the second heat transfer element.

7. The propeller assembly of claim 6 , wherein the second air outlet is located above the support structure.

8. Further comprising an oil flow path; the electric engine includes a hybrid cooled electric engine having a first portion and a second portion; the first heat transfer element comprises a heat exchanger thermally coupled to the first portion of the electric engine via the oil flow path; The propeller device of claim 1 , wherein the second heat transfer element comprises an air-cooled fin thermally coupled to the second portion of the electric engine.

9. one of the first portion of the electric engine and the second portion of the electric engine comprises a motor; The propeller device of claim 8 , wherein the other of the first portion of the electric engine and the second portion of the electric engine includes an inverter.

10. 10. The propeller device of claim 1, further comprising a door configured to open during the climb phase of the VTOL aircraft to expose at least one of the first air inlet or the second air inlet to the downwash and to close during a cruise phase of the VTOL aircraft to cover at least one of the first air inlet or the second air inlet.

11. 11. The propeller system of claim 10, further comprising a biasing mechanism configured to bias the door to a closed position, the biasing force of the biasing mechanism configured to be greater than a first opposing force from the air during the cruise phase of the VTOL aircraft and less than a second opposing force from the air during the climb phase of the VTOL aircraft.

12. The propeller device of claim 10 , wherein the doors are configured to open due to a swirling component of the downwash.

13. The propeller device of claim 10 , wherein the doors are configured to be forced open inwardly into the support structure by the downwash.

14. 11. The propeller device of claim 10, wherein the width of the door in a cross-sectional direction of the support structure perpendicular to the longitudinal axis of the support structure is at least 75% of the width of the support structure.

15. The propeller device of claim 10 , wherein the length of the door along the longitudinal axis of the support structure is greater than the width of the door.

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