Separate lift-thrust VTOL aircraft with a multi-joint rotor

Abstract

A separated lift-thrust (SLT) aircraft includes longitudinal thrust engines and articulated electric rotors, at least some of which are variable-position rotors that can be oriented based on rotor position signals. A control circuit independently controls the thrust of the longitudinal thrust engines and the thrust and direction of each variable-position rotor for the aircraft's lift surfaces and longitudinal thrust engines to provide commanded thrust vector steering of the aircraft during VTOL, fixed-wing flight, and intermediate transition conditions, including maintaining a desired lift surface attitude independent of rotor orientation when hovering the aircraft in windy conditions. A flight and navigation control system automates flight maneuvers and maintains a desired aircraft attitude and position relative to static or dynamic coordinates during stationkeeping, tracking, avoidance, and convergence maneuvers.

Description

Technical Field

[0001] The present invention generally relates to the field of aircraft propulsion, and more specifically, to a separable lift-thrust, fixed-wing aircraft capable of vertical takeoff and landing (VTOL).

Background Art

[0002] Known separable lift-thrust VTOL-capable fixed-wing aircraft rely on vertical thrust engines / motors for control during VTOL operation. The ability of the system to control effectively is limited by the aircraft's ability to maintain the attitude or orientation of the lift surface (wing). Typical thrust engines have limitations in vertical thrust during VTOL operation and cannot utilize a higher-output VTOL lift system during operation when the lift wing is not aerodynamically viable. As a result, separable lift-thrust systems are slower to control in VTOL compared to conventional multi-rotor systems, require additional onboard stored energy, and a larger egress / ingress footprint / volume, and performing accurate relative position control and convergence to static and dynamic targets can be limited by environmental conditions.

[0003] More specifically, the fixed-wing surface can have a profound adverse effect on the flight control of such a hybrid-type aircraft when it is operating in VTOL mode. A typical quad-rotor uses the pitch and roll of the platform to generate lateral forces, resist the wind, and create functions of rotation and translation. If such an approach is taken with a quad-rotor equipped with large appendages such as wings, the wind can interact with the wings to generate competing horizontal and vertical forces, overwhelming the VTOL control function. Therefore, in VTOL with wings, it is necessary to limit the pitch angle and roll angle to control flight when the wind is strong, and in such situations, the flight control of the aircraft may be greatly restricted.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] German Published Patent Application DE10 2014 000640 [Patent Document 2] US Published Patent Application 2009 / 008499 [Patent Document 3] US Published Patent Application 2018 / 265191 [Summary of the Invention] [Means for Solving the Problems]

[0005] Disclosed herein is a separable lift-thrust fixed-wing aircraft capable of vertical takeoff and landing (VTOL), which uses vector thrust propulsion by a multi-joint rotor to manipulate dynamic poses and relative positions. By utilizing a multi-joint lift rotor assembly, the aircraft can utilize additional thrust control to manipulate the attitude of the aircraft during flight. More specifically, the ability to independently generate vertical and lateral forces with a VTOL system while keeping the wings horizontal is an important ability of the disclosed aircraft. The lift rotor assembly operates about one or more axes of rotation, independently controls each rotor, and in conjunction with a vertical thrust engine / motor, actively manipulates the flight profile and the attitude of the aircraft while ultimately providing a control vector.

[0006] Generally, the disclosed aircraft includes the following: A fuselage having a lifting surface; One or more vertical thrust engines (usually including an internal combustion engine or an electric motor / propeller); A plurality of modular multi-joint electric rotors attached to the fuselage, at least some of the rotors being position-variable rotors having variable directions based on rotor position signals supplied thereto; A power source for supplying power to the electric rotors; To provide commanded thrust vector control of an aircraft during intermediate transition states, including maintaining a desired attitude of a lift surface regardless of the rotor orientation when VTOL, fixed-wing flight, and hovering the aircraft in windy conditions, a control circuit configured and operable to independently control the thrust of a vertical thrust engine and the rotor thrust and rotor direction of each position-variable rotor with respect to the lift surface of the aircraft and the vertical thrust engine; and, A flight and navigation control system that automates flight control through autonomous or human-assisted augmentation and can maintain the desired attitude and position of a desired aircraft system with respect to static or dynamic global coordinates defined autonomously or by an operator when the aircraft is performing station-keeping, tracking, avoidance, or convergence maneuvers.

[0007] According to some embodiments, each modular articulated electric rotor includes a propeller, a motor configured and arranged to rotate the propeller, and a vector control assembly (e.g., a set of actuators or servos) coupled to the motor. The vector control assembly receives control signals from the control circuit and controls the angular displacement or tilt of the motor with respect to the airframe.

[0008] During operation, the aircraft (e.g., an unmanned aerial vehicle or UAV) can fly horizontally in response to the propulsive force from a set of vertical thrust engines and the lift provided by a lift surface of the airframe (e.g., a set of fixed wings). During horizontal flight, one or more of the modular articulated electric rotors can contribute by providing a vector thrust having a horizontal component (e.g., due to the angular displacement of the motor axis). Alternatively, one or more of the modular articulated electric rotors can be configured not to provide thrust (e.g., to conserve power).

[0009] Furthermore, the aircraft can perform hovering control according to the lift provided by one or more modular articulated electric rotors. Here, the vertical thrust engine may provide little or no propulsive force. Instead, the modular articulated electric rotor provides a vector thrust having an important vertical component for maintaining the aircraft at a desired hovering position.

[0010] Furthermore, during such hovering control, each modular articulated electric rotor can move independently in response to a control signal from the control circuit to provide effective and efficient position control (e.g., pitch, roll, yaw, other position-holding maneuvers, etc.). For example, a first subset of the modular articulated electric rotors can be slightly oriented into the wind direction, and another second subset of the modular articulated electric rotors can remain substantially vertical (perpendicular to the fuselage) to maintain the aircraft in a horizontal hovering position. If necessary, the aircraft can maintain a horizontal hovering position even in a dynamically changing wind environment such as a strong but changing headwind situation.

[0011] During such operations, a set of vertical thrust engines can provide propulsive force for additional position control and / or maneuvers. For example, with the propulsive force from a set of vertical thrust engines, the aircraft can perform gradually scanning or creeping maneuvers, weather vane maneuvers (e.g., turning the nose or other aircraft components into the wind), takeoff / landing maneuvers, etc.

[0012] The foregoing and other objects, features, and advantages will be apparent from the following description of specific embodiments of the invention, and as shown in the accompanying drawings, like reference characters refer to the same parts throughout different figures.

Brief Description of the Drawings

[0013]

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DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 shows an unmanned aircraft system (UAS) 10 having a known arrangement, also referred to as an unmanned aerial vehicle (UAV). The basic structure is that of a fixed-wing aircraft having an elongated fuselage 12 and fixed wings 14, with horizontal thrust provided by an engine and propeller 16 attached to the rear. The UAS 10 is also configured for vertical takeoff and landing (VTOL) using booms 18, each of which is attached to the underside of its respective wing 14 and carries a respective direction-fixed upward-facing propeller 20. The propellers 20 are powered by respective small engines or motors within the booms 18, which are not visible in this figure. With the addition of the VTOL structure and capabilities as described, the UAS 10 may be referred to as a “hybrid” UAS 10.

[0015] During operation, the UAS 10 is typically launched vertically from a ground position, then flies in a conventional fixed-wing manner and can also land vertically. During takeoff and landing, the propeller 20 is used to obtain vertical thrust, and the engine and propeller 16 mounted at the rear are either in operation or in an idle state. During fixed-wing flight, the engine and propeller 16 mounted at the rear provide horizontal thrust, and the VTOL propeller 20 is typically in an idle state. The boom 18 represents an undesirable weight and drag for fixed-wing flight, but there are applications where this drawback is outweighed by the desired VTOL capabilities. In one embodiment, the boom 18 has the same structure even though it is used on the opposite side of the UAS 10. The left-right dependency can be addressed by using an adapter as needed, such as for connection to a V-shaped tail.

[0016] Depending on the dynamic environment, there may be significant limitations to the performance of a hybrid UAV such as the aircraft 10 shown in FIG. 1. Fixed-wing aircraft that employ direction-fixed, separate lift-thrust multi-rotor lift solutions (such as hybrid quads) limit the aircraft's attitude during hover and translational movement operations and need to impose limitations on the control rate. Constraints are necessary to prevent the aerodynamic adverse effects caused by exposing the fixed-wing lift surfaces (wings, tails, etc.) to the surrounding free airflow (wind).

[0017] FIGS. 2A and 2B are diagrams for schematically explaining this problem. FIG. 2A shows a front view of a hybrid quad aircraft 30 (which may be realized as the aircraft 10, etc.) in both a calm state (upper image) and a windy state (lower image). FIG. 2B is a corresponding side view. The results of the above-described constraints in the operation of a conventional hybrid quad 30 or a similar separate lift-thrust aircraft are as follows: · It is necessary to keep the pitch attitude of the aircraft positive to maintain the effective angle of attack (AoA) of the lift surface a. Limit the vertical translational movement to the range achievable by a vertical thrust propulsion system generally designed considering the efficiency of the fixed wing b. As a result, the forward / backward translation rate is restricted. · Limit the roll attitude and control speed of the aircraft so as not to impart a crosswind component to the lifting surface. a. The lateral translation rate and response are restricted. · The yaw attitude and control rate of the aircraft are restricted within the range of the rotor's moment of inertia. a. The aircraft must weathervane into the prevailing wind so as not to exceed the control authority. b. The yaw response rate is limited to that provided by differential moment of inertia. c. The scalability of the solution is restricted due to an increase in the moment of inertia and adverse effects due to environmental conditions. · The VTOL lift solution needs to maintain a thrust margin to overcome the adverse effects caused by the fixed-wing during hovering / translation. a. Provide size, weight, and power allocation. · Degradation of maneuverability or loss of control under dynamic or difficult environmental wind conditions. · Difficulty in tracking a fixed or moving relative position to support dynamic recovery under mission-related conditions.

[0018] As disclosed herein, a general solution to the above problems is to use vectorized thrust for attitude and relative position control. In addition to its vertical thrust engines, the aircraft has an independently controlled tilt propulsion assembly with one or more rotating axes with controllable positions relative to the aircraft body. The vector thrust applied to a separable lift-thrust fixed-wing aircraft can provide the following: - Control of the aerodynamic pose of the fixed-wing lifting surface during VTOL and fixed-wing flight; - Provide extended lateral and vertical thrust; and, - Active relative position control and convergence to a defined static or dynamic landing point.

[0019] Figure 3 shows an aircraft 40 according to an embodiment of the present invention. The aircraft 40 has a central body or fuselage 42, a rear horizontal thrust engine 44, and laterally extending wings 46. Four motor / rotor assemblies 48 are attached to respective ends of two support booms 50, each extending longitudinally and attached to the underside of the wing 46 as shown. The assemblies 48 are also referred to herein as "rotors" and "propulsion pods" or "pods". In the illustrated embodiment, the front rotors 48 are directed upward, the rear rotors 48 are directed downward, and at least some of the rotors 48 are articulated or position-variable (e.g., all rotors, only the front rotors, only the rear rotors). In the illustrated embodiment, the front and rear pairs of rotors are in line on a line parallel to the longitudinal axis of the aircraft 40 as shown. The opposite up and down rotor directions utilize a rear propulsion propeller and a front traction propeller. A typical arrangement includes four rotors 48 as shown, but other arrangements are possible. In some embodiments, some or all of the rotors 48 include a variable pitch mechanism in which the pitch of the rotor blades is dynamically adjusted to provide another aspect of flight control.

[0020] Figures 4A and 4B schematically show again the operation of the articulated rotor separated lift thrust (SLT) aircraft 60 under the same conditions as Figures 2A and 2B, and the aircraft 60 can be realized as the aircraft 40 (Figure 3) or the like. In the case of the lateral movement in Figure 4A, the lift rotors roll to assist while maintaining the attitude of the wing (substantially horizontal), reducing the adverse and fluctuating effects of the lift component due to the wind, and maintaining control authority during VTOL operation. In the case of the vertical movement in Figure 4B, the lift rotors pitch to assist while maintaining the attitude of the wing (again substantially horizontally), reducing the adverse and fluctuating effects of the lift component due to the wind, and maintaining control authority during VTOL operation.

[0021] Figures 5A and 5B illustrate certain operational advantages obtained. Figure 5A shows the transition from VTOL hover to fixed-wing flight. Conventional hybrid aircraft such as aircraft 10 have a relatively large transition range, which is the distance from the takeoff point to the fixed-wing transition point (right end), while the aircraft disclosed herein can enjoy a shorter transition range and a faster / shorter transition to fixed-wing flight. As shown in Figure 5B, the characteristics of the reverse transition (from fixed-wing to hover / VTOL) are similar.

[0022] Figure 6 shows the nature of thrust vector propulsion. For the vertical thrust engine 44, there are two controls (RPM and blade pitch), and for the rotors 48, there are four controls (longitudinal (pitch) tilt angle θ of the rotor assembly, lateral (roll) tilt angle φ of the rotor assembly, rotor RPM ω, rotor blade pitch φ) in six dimensions. T represents the resulting thrust vector, and the subscripted numbers indicate four separate rotors 48. In general, each rotor 48 may be controlled independently, but as will be described in detail below, there may also be configurations where some rotors are fixed or restricted relative to other rotors. Also, in this figure, the tilt of the rear rotors 48-3, 48-4 is assumed to be in only one axis, but as will be described later, the tilt can be performed in multiple axes to obtain even higher maneuverability.

[0023] More specifically, each resulting thrust vector (T1, T2, T3, T4) may be independently controlled as a function of the coordinated operation of the vertical pod tilt angle (pitch), the lateral pod tilt angle (roll), the rotor RPM, and the rotor blade variable pitch angle. Each degree of freedom is separated and managed via a central flight control processor (described in detail below) to achieve stable coordinated flight with closed-loop control. The ability to vary the tilt angle of the rotor about separate axes, such as both vertical (pitch) and lateral (roll) tilts, is sometimes referred to as a compound articulation. In the embodiment of FIG. 6, the degrees of freedom of the rear vertical thrust rotors (48-3, 48-4) can be extended to include vertical tilt (θ) and rotor variable pitch (Ψ). To increase the range of motion of this rotor, alternative aircraft tail / tailboom configurations that reduce and mitigate mechanical interference are conceivable.

[0024] FIG. 7 shows the main components involved in flight control, including: - Energy and power related components 70, including energy generation (e.g., solar panels), energy storage (e.g., batteries), energy distribution and monitoring, and associated management functions. - Navigation and related components 72, including data links for external communication, payload, flight control, navigation, navigation sensing, and inertial measurement.

[0025] FIG. 8 provides details of flight control including a computer implemented flight control device 80 that interacts with the aircraft plant dynamics 82. The flight control device 80, as described above, generates a control output that includes signals representing the values θ, ω, φ, Ψ, whereby the physical aircraft interacts with its environment. As shown, the flight control device 80 may be implemented as a model based controller that incorporates a model of the aircraft physical plant for predictive control. The sensed effects are provided to the control device 80 for state estimation, and altitude and trajectory estimation, as well as airspeed and direction estimation, and these estimations are fed back to the flight control device 80 along with other inputs to update the control output. As previously mentioned, in contrast to other aircraft that rely on control surfaces such as flaps, the control method is based on vector thrust.

[0026] FIG. 9 shows the deployment and use of the aircraft 40, including the characteristics of conventional fixed wing operation, along with VTOL and attendant enhanced operational flexibility. 90 are pre-flight operations such as transportation and pre-flight maintenance and inspection. The operation proceeds to a transition 92 to vertical takeoff and horizontal flight, followed by flight execution at 94. This may simply be conventional fixed wing flight (e.g., from one point to another), and / or may include one or more periods of VTOL hovering called "station keeping". After flight execution at 94, it returns to VTOL operation for landing at 96. Note that in the case of a mission spanning a series of locations, steps 92-96 can be repeated. 98 are post-flight operations such as post-flight maintenance and transportation.

[0027] One advantage of the aircraft 40 is that, in addition to the lift from the rotors 48, lift can be generated in the airflow by the action of the wings 46. Conventional rotary wing aircraft generally experience a decrease in durability when performing station keeping in the air, whereas the durability of the aircraft may increase when performing station keeping in the air.

[0028] Figures 10 to 11 show the rotor 48 and its joints in more detail. This arrangement employs parallel tandem servo control, that is, as best seen in FIG. 11, two individual servo mechanisms 100 are arranged in parallel. In this arrangement, the axis of rotation 102 extends through the center of gravity of the rotor 48, as best seen in FIG. 10. Other mechanisms can also be employed, such as direct-on-axis servo, series tandem servo, non-centroid rotation, pneumatic / hydraulic mechanisms, belt or gear drive. As described above, the variable positioning may be limited to one axis or may be multi-axis such as tilt / yaw.

[0029] Figures 12 to 14 show examples of different propulsion configurations as briefly described above. FIG. 12 shows a symmetrical configuration with a position-variable front pod (rotor) and a position-variable rear pod, where "position" refers to the angular joint. FIG. 13 shows an asymmetrical configuration with a position-variable front pod and a semi-fixed (limited variable) position rear pod. FIG. 14 shows another asymmetrical configuration with a position-variable front pod and a fixed position rear pod.

[0030] The following table shows the details of the functions of the various configurations of FIGS. 12 to 14 at different stages of flight. JPEG0007709976000001.jpg115128

[0031] In the case of the symmetric arrangement of FIG. 12, all the propulsion pods have an equal range of motion, and the basic condition is that they are used in all stages of flight. However, the system can operate with only a pair / set of propulsion systems that operate to provide all flight control, and the rest operate with a limited or no thrust vectoring function on one or more axes, for example, in the configurations of FIGS. 13 and 14. In an embodiment with four rotors, this can be achieved with a front pair of rotors or a rear pair of rotors. Assuming that the front rotor pair is prioritized in fixed-wing flight to achieve the most efficient propeller state during cruising, the rear motor is housed in a defined position and becomes inactive during the fixed-wing flight stage, increasing the electrical efficiency of the system and reducing the acoustic signal. Also, during fixed-wing flight, it is possible to reactivate the rear rotor to increase dash speed and lift, and transition to VTOL for recovery at the end of the flight. Furthermore, this asymmetric control function allows the system to adopt a rotor pair / set with a limited range of motion or no tilt / yaw thrust vectoring function, reducing the weight and complexity of the installed propulsion system. In embodiments with more than four propulsion pods, the specification of the alternative / limiting joint function can be applied between the front and rear propulsion systems, and the front and rear sets can have a combination of constrained / fixed propulsion pods and fully capable joint functions. The selection of these alternative control modalities can be done by replacing or swapping the propulsion modules of the aircraft. In all modalities, the presence of a fixed vertical engine that provides thrust in fixed-wing flight can reinforce or replace the function of the propulsion pods.

[0032] Figures 15 and 16 illustrate the particular modularity of system components that enable the use of a thrust vectoring approach common to various different types of aircraft, as will be described in detail below. A rotor 48 having associated actuators and a propulsion system including components of a vectorized thrust motion and actuation control system 110 (including energy storage, energy distribution, and other components shown) can be adapted to other airframe types, including the modification of existing fixed-wing systems.

[0033] Figures 17 - 22 are examples of applications to other airframe types. Figures 17 - 19 are a top view, a front view, and a side view of a conventional small fixed-wing airframe 120 of a type typically employing a single combustion engine, composed of a rotor 48 and a boom 50 attached to the lower surface of the wing 46, similar to the aircraft 40 (Figure 3). Figures 20 - 22 are a top view, a front view, and a side view of a second type of fixed-wing aircraft 130 similarly configured using a boom-mounted rotor.

[0034] Figure 23 is a schematic diagram of the various propulsion pod shapes (configurations of boom-mounted rotors) that can be used. Five configurations from 140-1 to 140-5 are shown. For each configuration 140, three views are shown: a top view, a front view, and a side view (downward in Figure 23). Different embodiments of the placement of the propulsion pod and its attachment to the airframe include variations such as offsets and lateral supports.

[0035] Figures 24 - 25 illustrate additional aspects of the modularity that can be employed. Figure 24 shows the modular attachment of the boom 50 and the rotor 48. Figure 25 shows the use of an alternative boom and tail configuration 150.

[0036] Scalability In general, the disclosed aircraft can be parametrically scaled in both the size and number of rotor assemblies. In one embodiment, the aircraft can provide for the attachment of additional booms 50 and corresponding rotors 48, for example, at more distal locations of the wing 46. This can provide additional lift / thrust.

[0037] Although various embodiments of the present invention have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. An aircraft comprising: An airframe having a lifting surface; A vertical thrust engine that supplies thrust in the longitudinal axis direction of the aircraft; A plurality of electric rotors attached to the airframe, wherein at least some of the rotors are variable-direction rotors that are variable in direction based on a rotor direction signal supplied thereto; A power source for supplying power to the electric rotors; A control circuit configured and operable to independently control the thrust of the vertical thrust engine and the rotor thrust and rotor direction of each variable-direction rotor to provide commanded thrust vector control of the aircraft during an intermediate transition state, including maintaining a desired attitude of the lifting surface when performing vertical takeoff and landing (VTOL), fixed-wing flight, and hovering the aircraft in a strong wind condition regardless of the rotor orientation; and, Navigation components that provide external communication, flight control, navigation, navigation sensing, and inertial measurement, Including, The variable-direction rotor is a compound-joint electric rotor having a variable orientation in both pitch and roll based on the rotor position, and the control circuit provides independent control of the compound-joint electric rotor to maintain the desired attitude of the lifting surface regardless of the rotor orientation when hovering the aircraft in a crosswind condition, Configured for both lateral movement operations and vertical movement operations, in the lateral movement operation, the variable-direction rotor rolls to assist while maintaining a substantially horizontal attitude of the lifting surface to reduce the adverse and fluctuating effects of lift due to wind, and in the vertical movement operation, the variable-direction rotor pitches to assist while maintaining the substantially horizontal attitude of the lifting surface to reduce the adverse and fluctuating effects of the lift component due to wind, and, The control circuit includes a model-based controller incorporating a physical plant model of the aircraft considering the aerodynamic forces experienced by the aircraft, including forces caused by wind from the environment, including (1) in the case of lateral movement caused by airflow across the lifting surface in the lateral and longitudinal directions, and (2) in the case of vertical movement caused by airflow across the lifting surface, the model-based controller uses the physical plant model to determine the response of the rotors, thereby reducing the energy requirements and time required for transition to and from fixed-wing flight, Aircraft.

2. The control circuit and the navigation components cooperate to provide thrust vector propulsion by six-dimensional control including (a) the rotational speed and blade pitch of the vertical thrust engine, and (b) the rotor assembly vertical tilt angle, rotor assembly lateral tilt angle, rotor rotational speed, and rotor blade pitch of the rotor. The aircraft according to claim 1.

3. The aircraft according to claim 2, wherein each rotor is independently controlled.

4. The aircraft according to claim 1, wherein the lift surface is formed by wings extending laterally from a central fuselage.

5. The aircraft according to claim 4, wherein the vertical thrust engine is disposed on the fuselage and arranged to supply rearward horizontal thrust.

6. The aircraft according to claim 4, further comprising two elongated booms attached to the wings, and the rotors are attached to respective ends of the booms.

7. The aircraft according to claim 1, wherein the rotor includes a front rotor having an upward traction propeller and a rear rotor having a downward propulsion propeller.

8. The aircraft according to claim 1, wherein the rotor has a symmetric propulsion configuration including a variable-direction front rotor and a variable-direction rear rotor.

9. The aircraft according to claim 1, wherein the rotor has an asymmetric propulsion configuration including a variable-direction front rotor and a direction-limited rear rotor.

10. The aircraft according to claim 1, wherein the rotor has an asymmetric propulsion configuration including a variable-direction front rotor and a direction-fixed rear rotor.

11. The aircraft according to claim 1, wherein at least some of the rotors include a variable pitch mechanism in which the pitch of the rotor propeller is dynamically adjusted as part of flight control for the aircraft.

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