Hybrid power system for different flight modes

Abstract

A first power source, a second power source, and a power controller are provided, where a vehicle including the first power source, the second power source, and the power controller is capable of flying in a transition mode between a hover mode and a forward flight mode. The power controller selects one or more of the first power source and the second power source to power a rotor included in the vehicle during the transition mode.

Description

[0001] Cross-references to other applications This application claims priority to U.S. Provisional Patent Application No. 62 / 912,872, filed on October 9, 2019, entitled “FIXED WING AIRCRAFT WITH TILT ROTORS,” which is incorporated herein by reference for all purposes. Background Art

[0002] New aircraft are being developed that can take off and land in dense urban areas, opening up new transportation corridors and avoiding congestion on the road. For example, Kitty Hawk is developing a new electric vertical take-off and landing (eVTOL) tiltrotor aircraft that can take off and land in a footprint of approximately 30 feet by 30 feet. Early prototypes have been built and tested, and further improvements in the performance of the vehicle (e.g., improved range) would be desirable. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Various embodiments of the invention are disclosed in the following detailed description and accompanying drawings.

[0004] Figure 1A is a perspective view showing an embodiment of a forward-swept fixed-wing vehicle with tilt-rotors.

[0005] Figure 1B is a top view showing an embodiment of a forward-swept fixed-wing vehicle with tilt-rotors.

[0006] Figure 2A is a bottom view of an embodiment showing boundary layer thickness with the motor turned off.

[0007] Figure 2B is a bottom view of an embodiment showing boundary layer thickness with the motor turned on.

[0008] Figure 3A is a diagram illustrating an example of a tilt-wing configuration with corresponding lift vector, thrust vector, and drag.

[0009] Figure 3B is a diagram illustrating an example of a fixed wing configuration with a leading edge mounted tilt rotor and corresponding lift vector, thrust vector, and drag.

[0010] Figure 3C is a diagram illustrating an embodiment of a fixed wing configuration with a trailing edge mounted tilt rotor and corresponding lift vector, thrust vector, and drag.

[0011] Figure 4 is a diagram showing an embodiment of the airflow generated when a trailing edge mounted tilt rotor on a main wing is closed.

[0012] Figure 5 is a diagram showing an embodiment of a forward swept and tapered wing and a straight wing for comparison.

[0013] Fig. 6A is a diagram showing an embodiment of a takeoff tilt transition from a hovering position to a cruise position.

[0014] Figure 6B is a diagram showing an embodiment of a landing tilt transition from a cruise position to a hovering position.

[0015] Figure 7 is a diagram showing an embodiment of a velocity tilt map.

[0016] Figure 8 is a diagram illustrating an embodiment of a vehicle having a hybrid power system including two battery subsystems.

[0017] Fig. 9 is a diagram illustrating an embodiment of a vehicle having a hybrid power system including a battery subsystem and an internal combustion engine.

[0018] Fig.10 A diagram of an embodiment of a vehicle is shown having dedicated propellers for cruise and dedicated tiltrotors for hover and transition, and a hybrid power system including a battery subsystem and an internal combustion engine. DETAILED DESCRIPTION

[0019] The present invention can be implemented in a variety of ways, including as: a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer-readable storage medium; and / or a processor, for example, a processor configured to execute instructions stored on a memory connected to the processor and / or provided by the memory. In this specification, these embodiments or any other form that the present invention may take may be referred to as technology. In general, within the scope of the present invention, the order of the steps of the disclosed process may be changed. Unless otherwise stated, a component described as being configured to perform a task (such as a processor or memory) may be implemented as a general component temporarily configured to perform a task at a given time or as a specific component manufactured to perform the task. As used herein, the term "processor" refers to one or more devices, circuits, and / or processing cores configured to process data (such as computer program instructions).

[0020] A detailed description of one or more embodiments of the present invention is provided below together with the accompanying drawings that illustrate the principles of the present invention. The present invention is described in conjunction with such embodiments, but the present invention is not limited to any embodiment. The scope of the present invention is limited only by the claims, and the present invention encompasses many alternatives, variations and equivalents. Many specific details are set forth in the following description in order to thoroughly understand the present invention. These details are provided for the purpose of example, and the present invention can be implemented according to the claims without some or all of these specific details. For the sake of clarity, technical materials known in the technical field related to the present invention are not described in detail so that the present invention is not unnecessarily concealed.

[0021] Various embodiments of electric vertical take-off and landing (eVTOL) tiltrotors with hybrid power systems are described herein. For context and background, it may be helpful to first describe an early version of the vehicle that uses a single type of cell and / or power train in all power systems (e.g., all batteries have the same design with the same type of cell). Then, various embodiments of exemplary eVTOL tiltrotors with hybrid power systems are described along with example applications and / or benefits. Of course, the hybrid power systems described herein can be used for other vehicles.

[0022] Figure 1A is a perspective view showing an embodiment of a forward-swept fixed-wing vehicle with tilt-rotors. Figure 1B 1 is a top view showing an embodiment of a forward-swept fixed-wing vehicle with tilt-rotors. In the example shown, the main wings (100a and 100b) are fixed wings that are attached to the fuselage (102a and 102b) in a fixed manner or position. In other words, the main wings are not tilt-rotors that can rotate. The main wings (100a and 100b) are also forward-swept (e.g., relative to the pitch axis). For example, for an aircraft embodiment with canard wings (as shown here), the forward sweep angle can be between about 14° and 16°. 掠 , or for an aircraft embodiment without canards, the forward sweep angle can be as high as 35°.

[0023] In this example, the main wings (100a and 100b) have six rotors (104a and 104b) attached to the trailing edge of the main wings. Rotors or propellers in this configuration are sometimes referred to as pusher propellers (e.g., because at least when the propellers are in their forward flight position, the propellers are behind the wings and "push" the vehicle forward). The forward flight mode is sometimes referred to as the cruise mode in this article. For clarity, these rotors on the main wings are sometimes referred to as main wing rotors (e.g., to distinguish them from rotors attached to canards). Of course, the number of rotors shown here is merely exemplary and is not meant to be limiting.

[0024] In addition to the six main wing rotors, there are two rotors (106a and 106b) attached to the canards (108a and 108b). These rotors are sometimes called canard rotors. The canards are thinner than the main wings, so unlike the main wing rotors, the canard rotors are attached to the far end of the canards, rather than to the trailing edge of the canards.

[0025] All rotors in this example are tilt-rotors, which means that they can tilt or otherwise rotate between two positions. In the accompanying drawings shown here, the rotors are in a cruising (e.g., forward flight, backward facing, etc.) position. In this position, the rotors rotate around (e.g., substantially) a longitudinal axis of rotation so that they provide (substantially) backward thrust. When the rotors are in this position, the lift that keeps the tilt-rotor vehicle in the air comes from the airflow above the main wing (100a and 100b) and the canard (108a and 108b). In this particular example, the rotation range of the tilt-rotor range has a minimum angular position of approximately 0°-5° and a maximum angular position of approximately 90°-95°. This range is specific to the design and / or implementation.

[0026] The rotors can also be tilted downward to be in a hovering (e.g., vertical takeoff and landing, downward facing, etc.) position (not shown). In this second position, the rotors rotate about a (e.g., substantially) vertical axis of rotation so that they provide (substantially) downward thrust. In this configuration, the lift that keeps the tilt-rotor vehicle airborne comes from the downward airflow of the rotors.

[0027] Generally speaking, the tiltrotors, when oriented to output thrust substantially downward, allow the aircraft to perform vertical takeoff and landing (VTOL). This mode or configuration (e.g., in terms of the manner in which the aircraft as a whole flies and / or in terms of the position of the tiltrotors specifically) is sometimes referred to as hovering. The ability to perform vertical takeoff and landing allows the aircraft to take off and land in areas without airports and / or runways. Once airborne, the tiltrotors (if desired) change position to output thrust (substantially) backward instead of downward. This allows the aircraft to fly in a more efficient manner for forward flight; this mode or configuration is sometimes referred to as cruising.

[0028] Canards are useful because they can stall first (e.g., before the main wings), thereby generating a large pitching moment and not losing much lift when stalled, whereas a main wing stall loses a large amount of lift for each change in pitch moment (e.g., causing the entire aircraft to drop or fall). Therefore, a stall with a canard may be more benign than without it. Canard stall behavior is particularly beneficial in conjunction with a forward-swept wing, because a stall of the main wing can generate an adverse pitching moment if at the wing root, and a large and dangerous rolling moment if at the wing tip. In addition, the canard can generate lift at low airspeeds and increase CL 最大(ie, maximum lift coefficient), and struts are provided to hold or otherwise attach the canard motors.

[0029] In some embodiments, the pylons (110a and 110b) for attaching the rotor to the canard and / or main wing include some hinges and / or rotation mechanisms so that the tilt rotor can rotate between the two positions shown. Any suitable hinge mechanism can be used. For example, for ultralight aircraft, there are very strict weight requirements, and therefore a lightweight solution may be desired. Alternatively, a fixed tilt solution can also be used to meet very strict weight requirements.

[0030] In some embodiments, the aircraft is designed so that the main wings (100a and 100b) and canards (108a and 108b) can provide sufficient lift to perform a glider-style landing if needed during an emergency. For example, some ultralight standards or specifications require the ability to land safely in the event of one or more rotor failures, and the ability to perform a glider-style landing would satisfy that requirement. One benefit of using a fixed wing for the main wing (e.g., as compared to a tilt-rotor wing) is that there is no danger of the wing getting stuck in the wrong position (e.g., a hovering position) where a glider-style landing is not possible because the wing position is not suitable for a glider-style landing.

[0031] Another benefit of a fixed wing with a trailing edge mounted tiltrotor is the stalling behavior (or lack thereof) during the transition from a hover position to a cruise position (or vice versa). With a tiltwing, during the transition, the angle of attack of the tiltwing changes, which increases the risk of stalling. A fixed wing with a trailing edge mounted tiltrotor does not change the wing angle of attack (e.g., even if the rotor is turned off / on or the tiltrotor is displaced). In addition, this configuration increases the dynamic pressure and circulation over the main wing, which greatly improves the behavior during the transition (e.g., from a hover position to a cruise position or vice versa). In other words, a fixed wing with a trailing edge mounted tiltrotor can perform transitions more quickly and / or more efficiently than a tiltwing (as an example).

[0032] Another benefit associated with a fixed-wing vehicle with a tiltrotor (e.g., compared to a tiltwing) is that a smaller fraction of mass is used for the tilt actuator(s). That is, the multiple actuators for the multiple tiltrotors (still) comprise a smaller fraction of mass than a single heavy actuator for the tiltwing. The tiltrotor also has fewer points of failure because there are multiple actuators compared to a single (and heavy) actuator for the tiltwing. Another benefit is that the fixed wing makes transitions (e.g., between a cruise mode or position and a hover mode or position) more stable and / or faster than a tiltwing design.

[0033] In some embodiments, the rotor is a variable pitch propeller having different blade pitches when the rotor is in a hovering position and a cruise position. For example, different blade pitches (ranges) can achieve more efficient operation or flight when in a cruise position and a hovering position. When the rotor is in a cruise position, adjusting the blade pitch to a "cruise pitch" (e.g., approximately 26°) achieves a lower frontal area (e.g., lower drag) that is beneficial to cruising. When the rotor is in a hovering position, adjusting the blade pitch to a "hover pitch" (e.g., approximately 6°) achieves a higher rotor disc area that is beneficial to hovering. In other words, one blade pitch may be very suitable for a cruise mode, but not for a hover mode, and vice versa. The use of a variable pitch propeller achieves better (e.g., overall) efficiency, resulting in less power consumption and / or increased flight range.

[0034] The following figure shows the Figure 1A and 1B Various benefits are associated with the exemplary aircraft shown in FIG.

[0035] Figure 2A 2 is a bottom view of an embodiment showing boundary layer thickness with the motor off. In this example, laminar flow extension lines 200a, 202a, and 204a show the extension of laminar flow at different regions of the main wing. In this example, it is assumed that the aircraft is cruising (e.g., flying in a substantially forward direction). Figure 1A and 1B As shown in , in this embodiment, the main wing rotor (206) is attached to the trailing edge of the main wing (208). The figure below shows the boundary layer thickness when the rotor is turned on.

[0036] Figure 2B is a bottom view of an embodiment showing boundary layer thickness with the motor on. In this example, the motor is on and the rotor has an exit air velocity of 30 m / s. With the motor on, a low pressure area is formed toward the rear of the wing, which increases the laminar extension over the main wing. For example, see the corresponding Figure 2A 200a, 202a and 204a in FIG. 200b, 202b and 204b. Comparison of the two groups shows that the laminar flow stretch increases in the first two positions (i.e., at 200a / 200b and 202a / 202b). The last position (i.e., 204a / 204b) has only a slightly longer laminar flow stretch due to interference from the canard rotor (210).

[0037] The drag from the main wing rotor (or more precisely, the drag from the pylons used to attach the main wing rotor to the main wing) is hidden in the wake of the airflow from the main wing. See, for example, Figure 2A, which more clearly shows that the pylon (220) is connected or otherwise attached to the rear of most of the laminar flow extension (222). For the embodiment shown here, the pylon is also able to remain away from some of the boundary layer thickness of the main wing, which means that the pylon has lower drag per unit surface area. This improves drag compared to some other alternative designs or configurations. The following figures describe this in more detail.

[0038] Figure 3A is a diagram showing an example of a tilt-wing configuration with corresponding lift vectors, thrust vectors, and drag. In this example, a fixed rotor (300) is attached to a tilt-wing (302) at a fixed position or angle. This is an alternative arrangement to the above-described aircraft embodiment(s). In order to direct the airflow generated by the fixed rotor (300) rearward or downward, the tilt-wing (302) rotates. As shown here, for this configuration, there is drag (304) at the trailing edge of the tilt-wing, which is undesirable.

[0039] Also shown here is the lift (306) and thrust (308) for this configuration, with the tilt-wing shown in the middle of a transition (e.g., between a cruise position and a hover position). As shown here, the lift (306) and thrust (308) are substantially orthogonal to each other, which is inefficient. In other words, the tilt-wing is inefficient during its transition.

[0040] Figure 3B is a diagram showing an example of a fixed wing configuration with a leading edge mounted tiltrotor and corresponding lift vector, thrust vector and drag. In this example, the tiltrotor (320) is attached to the leading edge of the fixed wing (322). This is another alternative arrangement for the above-described aircraft embodiment(s). The corresponding drag (324) and thrust (326) for this arrangement are also shown. No useful lift is generated with this configuration, and therefore the lift vector is not shown here.

[0041] Figure 3C is a diagram showing an embodiment of a fixed wing configuration with a trailing edge mounted tiltrotor and corresponding lift vectors, thrust vectors, and drag. In this example, the tiltrotor (340) is attached to the trailing edge of a fixed wing (342). In this configuration, the drag due to the trailing edge mounted tiltrotor (e.g., primarily due to its pylon, not shown) is hidden in the wake of the airflow from the main wing. Thus, there is no drag (at least due to the tiltrotor (340)).

[0042] The position of the trailing edge mounted tilt-rotor (340) relative to the fixed wing (342) also draws air (344) over the fixed wing, after which the air turns or bends through the rotor and downward. This flow turning over the wing creates a relatively large induced lift (346), as shown here. Also shown here is the thrust vector (348) generated by the rotor. It should be noted that the induced lift (346) and the thrust (348) are substantially in the same direction (i.e., both are pointed substantially upward), which is a more efficient arrangement, including during transition. In other words, using a fixed wing with a trailing edge mounted tilt-rotor creates less drag and improved efficiency during transition (e.g., because the lift and thrust vectors are now pointed substantially in the same direction) compared to other rotor and wing arrangements. For example, please note that respectively Figure 3A and Figure 3B Resistance 304 and resistance 324, and Figure 3A The orthogonal positions of lift 306 and thrust 308 in FIG.

[0043] The following figures illustrate embodiments of flow diversion in more detail.

[0044] Figure 4 is a diagram showing an embodiment of airflow generated when a trailing edge mounted tiltrotor on a main wing is closed. In this example, a tiltrotor aircraft (400) is shown, but for comparison purposes, the main wing rotor is closed. With the rotor closed, the airflow inflow (402) and the airflow outflow (404) move substantially in the same direction. That is, the airflow does not turn (e.g., downward) as it passes over the rotor.

[0045] Tiltrotor 420 shows the same vehicle as tiltrotor 400, except that the rotors are open. In this example, the airflow inflow (422) and the airflow outflow (424) have significantly different directions, and there is a significant turn or bend in the airflow as it passes over the rotors of the exemplary tiltrotor shown. As described above, this causes significant lift, which is desirable because less power is consumed and / or the range of the tiltrotor is increased.

[0046] In this example, the main wing rotors (426) are in a hovering position. As shown here, these rotors are slightly pitched or otherwise tilted (e.g., with the top of the main wing rotor pointing slightly forward and the bottom pointing slightly backward). In this figure, the amount of tilt is shown as θ 俯仰(428), and in some embodiments is approximately a 90° range of rotation or movement (e.g., ~3° upward from horizontal when in the cruise position (e.g., for minimum drag) and ~93° downward from horizontal when in the hover position, which yields a ~96° range of rotation). Although such canting or pitching of the rotors is not absolutely necessary for flow steering to occur, in some embodiments, the main wing rotors are canted or otherwise pitched to some extent to increase or otherwise optimize the amount of flow steering. In some embodiments, the canard rotors are similarly pitched. It should be noted that the tiltrotor 420 is shown in a nose-up position, and thus the vertical axis (e.g., relative to the tiltrotor) is not perpendicular to the ground and / or reference frame.

[0047] In some embodiments, when the rotor is in the hovering position, the rotor (e.g., main wing rotor and / or canard rotor) is slightly turned outward away from the fuselage or otherwise tilted. In some embodiments, the turning (e.g., outward) is about 10° to obtain greater yaw authority.

[0048] In some embodiments, the main wing, in addition to being forward swept, is also tapered (eg, the wing narrows outwardly toward the wing tip). The following figures describe various wing and / or tail embodiments.

[0049] Figure 5 5 is a diagram showing an embodiment of a swept and tapered wing and a straight wing for comparison. In the example shown, wing 500 is a straight wing without tapering (e.g., the wing is the same width from center to wing tip). An exemplary rotor (502) is shown at the trailing edge of the straight wing (500).

[0050] The center of thrust (504), indicated by the dashed line, is determined by the location or arrangement of the rotors and extends through the center of the main wing rotor (502). For simplicity, the canard rotors are ignored in this example. The center of lift is based on the shape of the wing. For a rectangular wing such as wing 500, the center of lift (506), indicated by the solid line, extends along the center of the wing. The calculation of the aerodynamic center is more complex (e.g., the aerodynamic center depends on the cross-section of the wing, etc.), and the aerodynamic center 508, indicated by the dashed line, is exemplary and / or typical for this type of wing.

[0051] As shown here, the arrangement of a straight wing (500) and its corresponding main wing rotor (502) creates a center of thrust (504) that is relatively far from both the center of lift (506) and the aerodynamic center. This separation is undesirable. More specifically, when the main wing rotor (502) is in a hovering position, if the center of thrust (504) is far from the center of lift (506), then the transition (e.g., in the context of the aircraft moving as a whole, such as switching from substantially upward flight to substantially forward flight, or vice versa) will produce very large moments and may capsize the vehicle or prevent acceleration or stability and / or require a bulky and / or non-optimal propulsion system. In cruise, if the center of thrust (504) is far from the center of lift (506), it is less important (e.g., because the thrust moment is smaller and more easily balanced by the aerodynamic moment), but it is still undesirable.

[0052] In contrast, the arrangement of a forward-swept and tapered wing (520) and its corresponding rotor (522) along the trailing edge produces a center of thrust (524), center of lift (526), ​​and aerodynamic center (528) that are closer to one another. For example, the forward sweep of the wing moves the rotor forward to varying degrees. This causes the center of thrust to move forward (e.g., toward the leading edge and toward the other centers). The tapering of the wing prevents the aerodynamic center and the center of lift from being displaced too far forward (and, more importantly, away from the center of thrust) due to the forward sweep. For example, for a forward-swept wing (not shown) without tapering, the center of thrust would move forward by approximately the same amount as the aerodynamic center and the center of lift, and would result in a greater separation between the three centers than is shown here in wing 520.

[0053] Some other benefits of a forward-swept and tapered wing include better visibility for the pilot, and a better location for the fuselage to main wing junction (e.g., allowing the main spar to pass behind the pilot's seat, rather than through the pilot). In addition, the taper reduces wing moments and brings the motor's center of thrust closer to the wing-to-fuselage attachment when referenced to the direction of flight, so there is less moment carried from the wing to the fuselage, a shorter tail boom (e.g., which reduces the weight of the aircraft), and improved pitch stability.

[0054] The following figures describe exemplary tilt transitions of the rotor between the cruise position and the hover position.

[0055] Fig. 6Ais a diagram illustrating an embodiment of a takeoff tilt transition from a hover position to a cruise position. In some embodiments, an exemplary tiltrotor aircraft performs this transition shortly after takeoff (e.g., substantially vertically). It should be noted that this tilt transition is optional, and the aircraft can be flown entirely with the rotors in the hover position (although not at optimal performance). This may be done, for example, if a tilt maneuver is risky and is best performed at a higher altitude.

[0056] Tilt rotor 600 shows an exemplary aircraft after it performs a vertical takeoff. In this state shown here, the main wing rotor and the canard rotor are in a hovering position (e.g., rotating around a substantially vertical axis of rotation so that the rotor generates substantially downward thrust).

[0057] The tiltrotor then transitions from a completely upward direction of movement to a direction of movement with at least some forward motion, wherein the rotors continue in a hovering position until the tiltrotor reaches a certain desired altitude at which to begin the transition (602). In other words, the vehicle transitions first, and then changes the tilt of the rotors. In one example, the altitude at which the tiltrotor begins the change in rotor tilt from the hovering position to the cruise position is a sufficiently high altitude so that there is time to recover in the event of a problem during the transition. Switching the rotors between the hovering position and the cruise position is a riskier time, where the likelihood of problems (e.g., rotor failure, rotor jamming, etc.) is higher. Although the tiltrotor may have systems and / or techniques for recovery (e.g., compensating for rotor failure by causing the remaining rotors to output more thrust, deploying a parachute, etc.), these systems and / or techniques require time (i.e., sufficient altitude) to work.

[0058] From position 602, the tiltrotor aircraft flies substantially forward and moves the tiltrotors from a hovering position (e.g., wherein thrust is substantially output downward) to a cruise position. Once in cruise position 604, the rotors rotate about a substantially longitudinal axis so that they output rearward thrust.

[0059] Figure 6B is a diagram illustrating an embodiment of a landing tilt transition from a cruise position to a hover position. For example, an exemplary tiltrotor aircraft may perform this transition prior to a vertical landing. As with the previous transitions, this transition is optional. For example, if desired, an exemplary tiltrotor aircraft may maintain the tiltrotor in a cruise position and perform a glider-style landing instead of a vertical landing.

[0060] Tiltrotor 610 shows the rotor in a cruise position. When flying in a substantially forward direction, the tiltrotor moves from the cruise position shown at 610 to a hovering position shown at 612. With the tiltrotor in the hovering position (612), the tiltrotor descends to position 614 (at least in this example) with some forward movement, thereby keeping power usage (much) lower and retaining better options in the event of a motor or other component failure (e.g., the tiltrotor can add power to the rotor and exit the landing process or path) until it finally lands on the ground.

[0061] Figure 7 700 is a diagram illustrating an embodiment of a velocity-tilt graph. In the illustrated diagram, the x-axis illustrates the forward velocity of the aircraft, and the y-axis illustrates the tilt (e.g., the position or angle of the tilt-wing or tilt-rotor) ranging from a (e.g., minimum) cruise position (700) to a (e.g., maximum) hover position (702).

[0062] The first operational envelope (704), shown with a solid line border and filled with a grid pattern, is associated with a tilt-rotor aircraft. Figure 4 The tiltrotor 400 and Figure 3A 302 and fixed rotor 300 in FIG. 2. A second operational envelope (706), shown with a dashed border and gray fill, is associated with a (e.g., similar) aircraft having a forward-swept and fixed wing with a trailing-edge mounted tilt-rotor. See, for example, the above embodiments.

[0063] In the diagram shown here, the tiltrotor operating envelope (706) is a superset of the tiltrotor operating envelope (704), indicating that the former aircraft configuration is safer and / or more airworthy than the latter, and is also able to fly faster and slower at similar tilt positions. For fixed wings, the wings are already (and / or always) pointed in the (forward) direction of travel. When the tiltrotor is in or near the (e.g., maximum) hover position (702), the vehicle can fly almost all the way to the stall speed (e.g., V2) without having to tilt the motor up to the cruise position. It should be noted that, for example, the tiltrotor operating envelope (706) can stay in the (e.g., maximum) hover position (702) until V2. This greatly increases the operating states of the tiltrotor operating envelope (706) compared to the tiltrotor operating envelope (704). For example, please note all the gray areas above the tiltrotor operating envelope (704).

[0064] Another effect that may contribute to the extended operating envelope of a tiltrotor configuration in or near a hover position includes flow steering (see, e.g., Figure 4). The flow turning over the main wing causes some additional lift. In some embodiments, this flow turning and the lift it produces is amplified or optimized by tilting the main wing rotors from directly downward to a slightly backward angle when in normal hover (e.g., in the minimum tilt position 700).

[0065] In contrast, the tilt-wing presents a larger frontal area when it is tilted upward in the (e.g., maximum) hover position (702). Therefore, the tilt-wing cannot fly forward at any suitable speed until it is in or near the full (e.g., minimum) cruise position (700) or nearly so.

[0066] Temporarily return to Figure 1A and 1B Early prototypes of tiltrotor vehicles used battery systems with a single type of battery cell to simplify the design. For example, lithium battery cells tend to be either high discharge rate (i.e., capable of outputting high current levels) or high energy, but not both (e.g., because energy capacity generally decreases as discharge rate capacity increases). For example, batteries and / or cells with an energy density less than or equal to 190Wh / kg are generally able to support high current draw and are accordingly considered or classified as high discharge rate, while those with an energy density greater than or equal to 235Wh / kg are considered or classified as high energy. The battery cells used by early prototypes were a compromise between the two in order to use a single type of cell, which reduced design complexity. Since the rest of the vehicle is more different from existing vehicles, it is desirable to keep the design as simple as possible in early prototypes.

[0067] For subsequent versions and / or prototypes of the vehicle, increasing the range of the vehicle is a desired performance improvement. A hybrid power system (e.g., including two or more different power systems that are used at different times or modes during flight) is more complex than a battery system using a single type of cell (e.g., because a vehicle with a hybrid power system needs to turn the various power systems on and off in a safe manner during flight, among other design considerations), but the increase in range makes the tradeoff worthwhile.

[0068] The following figures describe various embodiments of hybrid power systems that can be used with the tiltrotor vehicle described above. First, an embodiment of a hybrid power system with two types of batteries is described. Then, an embodiment of a hybrid power system with a battery and an internal combustion engine is described. It should be noted that the hybrid power systems described herein can be applicable to other types of vehicles, not just the exemplary tiltrotor vehicle described herein.

[0069] Figure 8is a diagram showing an embodiment of a vehicle having a hybrid power system including two battery subsystems. In the example shown, the tiltrotor vehicle includes one high discharge rate battery (800) and five high energy batteries (802). In this example, the high discharge rate battery (800) has an energy density of ~180Wh / kg and accounts for ~15% of the total battery weight, while the high energy batteries (802) have an energy density of ~270Wh / kg. The high energy batteries are more limited in their discharge rate, but are suitable for the power requirements of cruise flight.

[0070] For example, consider Fig. 6A The flight sequence shown in . For the hover state ( Fig. 6A 600) and the transition state ( Fig. 6A 602 in FIG. 604 ) require relatively high discharge rates because greater thrust from the rotors is required during these flight modes (e.g., because there is little or no lift on the wing such that all or most of the lift comes from the rotors). In contrast, during cruise ( Fig. 6A 604), the power required is much lower, about 30% of the power required during hovering. For this reason, during vertical takeoff (i.e., Fig. 6A 600) and when the vehicle transitions from hover mode to forward flight ( Fig. 6A 602), the high discharge rate battery (800) is used to supply power to the tilt rotor. In forward flight or cruising mode ( Fig. 6A In 604), a high energy battery (802) is used to supply power.

[0071] The benefit of the exemplary hybrid power system shown here is that it increases (e.g., cruise) range compared to the early non-hybrid power systems (e.g., having a single type of battery cell) that were initially used for early prototypes. For example, the initial battery system used a single type of cell with an energy density of ~200Wh / kg, which was a compromise. This resulted in more cells being required to obtain the overall current levels required for the energy-consuming hovering and transition phases of flight. The end result of this compromise strategy is that the (e.g., cruise) range is lower than the range provided by the exemplary hybrid power system. For example, the exemplary hybrid power system shown here can produce a cruise battery capacity and cruise range increase of ~15% over the early non-hybrid power system.

[0072] As shown in this example, in some embodiments, the first power source (e.g., in a hybrid power system) includes a high discharge rate battery having an energy density less than or equal to 190Wh / kg, and the second power source (e.g., in a hybrid power system) includes a high energy battery having an energy density greater than or equal to 235Wh / kg. In some embodiments, during the transition mode, the power controller is configured to select the high discharge rate battery to power the rotors in the vehicle and select the high energy battery to power the rotors. In some embodiments, the weight of the high discharge rate battery is less than or equal to 20% of the total weight of the battery.

[0073] One consideration when using a hybrid power system is deciding when to change the power subsystems supplying power to the tiltrotor. In one example, after vertical takeoff, a current sensor monitors the bus current, and when the vehicle is in cruise mode, as the current draw from the motors drops and stabilizes, the power source is switched from the high discharge (800) to the high energy (802) battery. That is, the test for switching during the takeoff sequence can be based on which flight mode or state the vehicle is in (e.g., a flight computer or controller can have a flight state variable with a value of HOVER_ST, TRANS_ST, or FF_ST) and whether the average current draw (e.g., over a time window of movement) is less than or equal to a certain threshold.

[0074] In some cases, the threshold or state that triggers a change in the power subsystem used to provide power to the tilt rotor is different for the takeoff sequence (e.g., hover, transition, and forward flight sequence) and the landing sequence (e.g., forward flight, transition, and hover sequence). For example, a current sensor as described above can be used to determine when to switch from high discharge to high energy during takeoff. However, during landing, especially in the final approach phase, the current consumption remains low as the aircraft is descending, even if the rotor is tilted to hover mode. As the vehicle approaches the ground, the power consumption will suddenly increase, requiring a power source switch very close to the ground, and leaving no room in the event of a failure of the switching transmission. In this case, regardless of the current consumption, it may be desirable to switch the power source at the beginning of the release transition phase (e.g., the flight state variable transitions from FF_ST to TRANS_ST), rather than waiting until the power demand increases when approaching the ground.

[0075] An important consideration in aircraft hybrid power systems is how to safely switch between different power sources. In one example, for safety, switching is performed by using more than one electronically activated mechanical or semiconductor-based switch that is sized so that the system will operate even if any one switch fails. Additionally, for safety, the switches can be selected so that they fail in an open position for one power source, but closed for the other, thereby preventing situations where both battery packs are connected to the bus at the same time or where neither battery pack is connected to the bus.

[0076] In some embodiments, the hybrid power system includes a battery and an internal combustion engine. The following figures describe various examples of this. As will be described in more detail below, in some embodiments, there are one or more cruise-dedicated (i.e., fixed) propellers that are used in forward flight mode (and possibly to some extent during transition mode), but not in hover mode.

[0077] Fig. 9 is a diagram showing an embodiment of a vehicle having a hybrid power system including a battery subsystem and an internal combustion engine. In the example shown, during a cruise mode, an internal combustion engine (e.g., including a fuel tank (900) and an engine with a gearbox (902)) drives a generator (904) via an engine-generator shaft (906), wherein power electronics (908) control the generation of electrical power by the internal combustion engine for an electric tilt rotor. During a hover mode, the electrical power supplied by the internal combustion engine is supplemented by a battery (910).

[0078] In some embodiments, the generator (904) is used to charge the batteries (910) (e.g., slowly) during the cruise phase. For example, since the batteries are only used during the hover mode (e.g., for takeoff and landing), the batteries can be charged during the cruise mode because they are not discharged during this period. This can increase the available hover time of the vehicle during landing (which may be attractive if the landing zone is occupied and the vehicle needs to hover while the landing zone is cleared) and / or allow the use of smaller capacity (and therefore lighter) batteries.

[0079] For comparison purposes, it is assumed that an early prototype of the vehicle is equipped with a 100 kg battery pack (e.g., a non-hybrid battery system having a single type of cell). For the exemplary hybrid system shown here, it is assumed that Figure 8The high discharge rate batteries in the hybrid are used for the battery (910). If so, the battery portion (910) in this hybrid example would weigh ~16kg. The internal combustion engine portion of the hybrid power (e.g., including the fuel tank (900) and the engine (902) with a gearbox) together with its fluids and support systems accounts for ~38kg of weight. The generator (904) and power electronics (908) account for ~16kg. This leaves ~30kg for fuel, which increases the cruising range by 50% compared to a comparable non-hybrid battery configuration. Despite the increased complexity, safety challenges (e.g., due to flammable liquids), noise and vibration issues, the increased range may make the trade-off worthwhile for longer range applications. Additionally, compared to Figure 8 Unlike the hybrid example shown in , in this embodiment, one of the power subsystems (internal combustion engine) is always on. For safety reasons, this may be attractive because there is no chance that the first power subsystem is turned off and the second power subsystem cannot be turned on.

[0080] As shown in this example, in some embodiments, the first power source (e.g., in a hybrid system) includes an internal combustion engine and the second power source includes a (e.g., high discharge rate) battery; during the transition mode, the power controller is configured to select the internal combustion engine to provide power to the rotor and deselect the battery so that the battery does not provide power to the rotor; during the hover mode, the power controller is configured to select the internal combustion engine to provide power to the rotor and select the battery to provide power to the rotor. In some embodiments, when the battery is deselected and not providing power to the rotor, the internal combustion engine is used to charge the battery at least some of the time.

[0081] Fig.10 A diagram of an embodiment of a vehicle is shown having dedicated propellers for cruise and dedicated tiltrotors for hover and transition, and a hybrid power system including a battery subsystem and an internal combustion engine. In the example shown, the battery subsystem (1000) drives the (electric) tiltrotors during hover and transition (shown here in a tilted-down position for hover). In some embodiments, the battery subsystem (1000) includes multiple types of cells (e.g., high energy batteries and high discharge rate batteries) that are switched on and off during the various flight modes described above (e.g., see Figure 8 ).

[0082] The hybrid power system further includes an internal combustion engine that drives a cruise-only propeller (1002). In this example, the cruise-only propeller is mounted to the nose of the aircraft, but such a propeller may be located in a variety of places (e.g., a pusher propeller on a tail cone). During cruise (i.e., forward flight) mode, the engine (1004) turns a gearbox (1006), which in turn turns the cruise-only propeller (1002) via a propeller shaft (1008). Fuel is stored in a fuel tank (1010).

[0083] For comparison purposes, assume that an early prototype of the vehicle is equipped with a 100 kg battery pack (e.g., a non-hybrid battery system with a single type of cell). In this comparison, it is assumed that the battery portion (1000) in this example uses high discharge rate batteries, and that the battery portion weighs a weight of ~16 kg in this hybrid example. The internal combustion engine, along with its fluids and support systems, as well as the gearbox and attached propeller (1002) account for a weight of ~45 kg. This leaves approximately 39 kg for fuel, which increases the cruising range by almost 100% compared to the compared configuration. In some long-range applications, the range increase provided makes any trade-offs in complexity, safety issues (e.g., related to flammable liquids on board), noise and vibration worthwhile.

[0084] As shown in this example, in some embodiments, the first power source (e.g., in a hybrid power system) includes an internal combustion engine and the second power source includes a battery, wherein the rotor included in the vehicle includes a tilt rotor and the vehicle also includes a cruise-only rotor. The power controller is configured to: during the forward flight mode, select the internal combustion engine to provide power to the cruise-only rotor, and during the hover mode and the transition mode, deselect the internal combustion engine so that the internal combustion engine does not provide power to the cruise-only rotor.

[0085] In this example, the tilt propellers are used for hover and transition and are turned off during the cruise portion of the flight. In some embodiments, to reduce drag, the tilt propellers are foldable so that during the cruise mode the propeller blades can be folded (e.g., backwards) to reduce drag during cruise.

[0086] In some embodiments, the cruise-only rotor comprises a cruise-only pusher rotor located behind the tail of the vehicle (e.g., so that the wake generated by the cruise-only rotor does not interfere with the airflow over the canard or main wing). In some embodiments, the second power source comprises a high-discharge rate battery with an energy density less than or equal to 190Wh / kg and a high-energy battery with an energy density greater than or equal to 235Wh / kg (i.e., the battery subsystem itself is a hybrid system, such as Figure 8 ).

[0087] As described above, hybrid power systems can be useful in increasing range. In some embodiments, the batteries provide the additional thrust needed during hover and / or transition modes, but the internal combustion engine and generator provide the lower power needed for cruise flight. For a given vehicle weight, this will greatly increase range because the energy density of liquid fuels is much higher than batteries.

[0088] In another embodiment, a hybrid power system uses two electric (i.e., battery) systems, one utilizing high power output cells for hover and / or transition modes and the other utilizing high energy density cells (e.g., which typically have lower current output capability) to provide cruise power, thereby extending range compared to a single electric system (i.e., having a battery of a single composition type).

[0089] Although the foregoing embodiments have been described in detail for the purpose of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways to implement the invention. The disclosed embodiments are illustrative rather than restrictive.

Claims

1. A hybrid power system, comprising: a first power source comprising an internal combustion engine; a second power source comprising a battery; as well as A power controller, wherein: The hybrid powertrain is included in a vertical take-off and landing (VTOL) vehicle that is flown in a transition mode that occurs: (1) after a hovering mode and before a forward flight mode during a vertical take-off, or (2) after a forward flight mode and before a hovering mode during a vertical landing; and The power controller selects one or more of the first power source and the second power source to provide power to a VTOL vehicle including a rotor, including by: receiving a current consumption associated with the VTOL vehicle; receiving one or more flight state variables associated with a flight computer, the flight state variables indicating whether the VTOL vehicle is in a hover mode, a forward flight mode, or a transition mode; During vertical landing, the power controller performs power source switching so that the second power source provides power to the rotor, including, in a transition mode occurring after a forward flight mode and before a hover mode during vertical landing, supplementing power provided to the rotor by the first power source, independent of the current consumption and in response to one or more flight state variables associated with the flight computer; and During vertical takeoff, the power controller selects one or more of the first power source and the second power source to provide power to the rotor based at least in part on the current draw.

2. The hybrid power system according to claim 1, wherein: The VTOL vehicle also includes a plurality of pusher tilt-rotors.

3. The hybrid power system according to claim 1, wherein: The internal combustion engine charges the battery at least some of the time during the forward flight mode.

4. The hybrid power system according to claim 1, wherein: The VTOL vehicle also includes a plurality of propulsion tilt-rotors and cruise-specific propellers.

5. The hybrid power system according to claim 1, wherein: The VTOL vehicle further comprises a plurality of propulsion tilt-rotors and cruise-only propellers, wherein the plurality of propulsion tilt-rotors are only used for hovering and transition.

6. The hybrid powertrain system of claim 1 , wherein the power controller determines to have the second power source provide power to the rotor in response to a change from a flight state variable associated with the forward flight mode to a flight state variable associated with the transition mode.

7. A method for managing a hybrid powertrain system, comprising: providing a first power source including an internal combustion engine, included in a hybrid power system; providing a second power source including a battery, included in the hybrid system; and A power controller is provided, included in a hybrid power system, wherein: The hybrid powertrain is included in a vertical take-off and landing (VTOL) vehicle that is flown in a transition mode that occurs: (1) after a hovering mode and before a forward flight mode during a vertical take-off, or (2) after a forward flight mode and before a hovering mode during a vertical landing; and The power controller selects one or more of the first power source and the second power source to provide power to a rotor included in the VTOL vehicle, including by: receiving a current consumption associated with the VTOL vehicle; receiving one or more flight state variables associated with a flight computer, the flight state variables indicating whether the VTOL vehicle is in a hover mode, a forward flight mode, or a transition mode; During vertical landing, the power controller performs power source switching so that the second power source provides power to the rotor, including, in a transition mode occurring after a forward flight mode and before a hover mode during vertical landing, supplementing power provided to the rotor by the first power source, independent of the current consumption and in response to one or more flight state variables associated with the flight computer; and During vertical takeoff, the power controller selects one or more of the first power source and the second power source to provide power to the rotor based at least in part on the current draw.

8. The method for managing a hybrid powertrain system according to claim 7, wherein: The VTOL vehicle also includes a plurality of pusher tilt-rotors.

9. The method for managing a hybrid powertrain system according to claim 7, wherein: The internal combustion engine charges the battery at least some of the time during the forward flight mode.

10. The method for managing a hybrid powertrain system according to claim 7, wherein: The VTOL vehicle also includes a plurality of propulsion tilt-rotors and cruise-specific propellers.

11. The method for managing a hybrid powertrain system according to claim 7, wherein: The VTOL vehicle further comprises a plurality of propulsion-type tilt-rotors and a propeller dedicated to cruising, wherein the plurality of propulsion-type tilt-rotors are only used for hovering and transition.

12. The method for managing a hybrid powertrain system according to claim 7, wherein: In response to a change from a flight state variable associated with the forward flight mode to a flight state variable associated with the transition mode, the power controller determines to have the second power source provide power to the rotor.

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