Separated lift-thrust vtol aircraft with articulated rotor

Abstract

To provide a flight and navigation control system that automates flight maneuvers and maintains desired aircraft pose and position relative to static or dynamic coordinates during station keeping, tracking, avoidance, or convergence maneuvers.SOLUTION: A separated lift-thrust aircraft includes a longitudinal-thrust engine and articulated electric rotors, some of which are variable-position rotors having variable orientations based on rotor position signals. Control circuitry independently controls the thrust of the longitudinal-thrust engine and the thrust and orientation of each of the variable-position rotors, relative to an aircraft lifting surface and the longitudinal thrust engine, to provide for commanded thrust-vectoring maneuvering of the aircraft during intermediate transitional states, including maintenance of a desired pose of the lifting surface independent of the rotor orientations when hovering the aircraft.SELECTED DRAWING: Figure 23

Description

[Technical Field]

[0001] The present invention relates generally to the field of aircraft propulsion, and more specifically to vertical take-off and landing (VTOL) capable, separated lift and thrust, fixed-wing aircraft. Summary of the Invention

[0002] Known separated lift-thrust VTOL-capable fixed-wing aircraft rely on longitudinal thrust engines / motors to maneuver during VTOL operations. The system's ability to maneuver effectively is limited by the aircraft's ability to maintain the attitude or orientation of its lifting surfaces (wings). Typical thrust engines have longitudinal thrust limitations for VTOL operations, preventing the more powerful VTOL lift system from being utilized during maneuvers while lifting wings are aerodynamically infeasible. As a result, separated lift-thrust systems slow VTOL maneuvers compared to traditional multirotor systems, require additional onboard stored energy and larger egress / ingress footprints / volumes, and can be limited by environmental conditions in their ability to perform precise relative position control and convergence on static and dynamic targets.

[0003] More specifically, fixed-wing surfaces can have a severely adverse effect on aircraft maneuverability and control when such hybrid aircraft are operating in VTOL mode. A typical quadrotor uses the platform's pitch and roll to generate lateral forces, resist wind, and create rotational and translational capabilities. If this approach were taken with a quadrotor equipped with large appendages such as wings, the wind would interact with the wings to generate competing horizontal and vertical forces that could overwhelm VTOL control. As a result, winged VTOLs would need to limit their pitch and roll angles for controlled flight in high winds, which can severely limit the aircraft's maneuverability in such conditions. [Means for solving the problem]

[0004] Disclosed herein is a vertical take-off and landing (VTOL) capable, separate lift-thrust fixed-wing aircraft that utilizes vectored thrust propulsion from articulated rotors to steer its dynamic pose and relative position. Utilizing articulated lift rotor assemblies, the aircraft leverages additional thrust control to steer the aircraft's attitude during maneuvers. More specifically, the ability to independently generate longitudinal and lateral forces in a VTOL system while maintaining the wings horizontal is a key capability of the disclosed aircraft. The lift rotor assemblies operate about one or more axes of rotation, independently controlling each rotor and, in conjunction with longitudinal thrust engines / motors, actively steer the flight profile and aircraft attitude, resulting in a steering vector.

[0005] Generally, the aircraft disclosed include: Airframe with lifting surfaces; one or more longitudinal thrust engines (usually including an internal combustion engine or electric motor / propeller); a plurality of modular articulated electric rotors mounted on the airframe, at least some of the rotors being variable position rotors having variable orientation based on rotor position signals provided thereto; a power source for powering the electric rotor; a control circuit configured and operated to independently control the thrust of the longitudinal thrust engines and the rotor thrust and rotor orientation of each variable position rotor for the lifting surfaces and longitudinal thrust engines of the aircraft to provide commanded thrust vector steering of the aircraft during intermediate transition conditions, including maintaining a desired lifting surface attitude independent of rotor orientation during VTOL, fixed wing flight, and hovering the aircraft in windy conditions; and A flight and navigation control system capable of automating flight maneuvers, either autonomously or with human-in-the-loop augmentation, and maintaining a desired aircraft system attitude and position relative to static or dynamic global coordinates defined autonomously or by an operator, while the aircraft is performing stationkeeping, pursuit, avoidance, or convergence maneuvers.

[0006] According to some embodiments, each modular articulated electric rotor includes a propeller, a motor constructed and arranged to rotate the propeller, and a vector control assembly (e.g., a set of actuators or servos) coupled to the motor, which receives control signals from the control circuitry to control the angular displacement or tilt of the motor relative to the vehicle.

[0007] During operation, an aircraft (e.g., an unmanned aerial vehicle or UAV) can fly horizontally in response to thrust from a set of longitudinal thrust engines and lift provided by lifting surfaces on 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 vector thrust having a horizontal component (e.g., due to angular displacement of the motor shafts). Alternatively, one or more of the modular articulated electric rotors can provide no thrust (e.g., to conserve power).

[0008] Additionally, the aircraft can perform hover maneuvers relying on lift provided by one or more of the modular articulated electric rotors, where the vertical thrust engines may provide little or no thrust. Rather, the modular articulated electric rotors provide vector thrust with a significant vertical component to maintain the aircraft in a desired hover position.

[0009] Furthermore, during such hover maneuvers, each modular articulated electric rotor can independently articulate in response to control signals from the control circuitry to provide effective and efficient position control (e.g., pitch, roll, yaw, other station-keeping maneuvers, etc.). For example, a first subset of the modular articulated electric rotors can be angled slightly into the wind direction while another second subset of the modular articulated electric rotors remains substantially vertical (perpendicular to the airframe) to maintain the air vehicle in a horizontal hover position. If desired, the air vehicle can maintain a horizontal hover position even in dynamically changing wind environments, such as in strong but varying headwind conditions.

[0010] During such maneuvers, the set of longitudinal thrust engines can provide thrust to perform additional positional control and / or maneuvers. For example, thrust from the set of longitudinal thrust engines can enable the aircraft to perform gradual scanning or creeping maneuvers, weather vane maneuvers (e.g., pointing the nose or other aircraft components into the wind), takeoff / landing maneuvers, etc.

[0011] The foregoing and other objects, features, and advantages will be apparent from the following description of specific embodiments of the present invention, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an isometric view of a VTOL aircraft known in the art. [Figure 2A] FIG. 2A is a schematic diagram of the hovering maneuver of the aircraft of FIG. [Figure 2B] FIG. 2B is a schematic diagram of the hovering maneuver of the aircraft of FIG. 1. [Figure 3] FIG. 3 is an isometric view of a VTOL aircraft in accordance with the present invention. [Figure 4A] FIG. 4A is a schematic diagram of the hovering maneuver of the aircraft of FIG. 3. [Figure 4B] FIG. 4B is a schematic diagram of the hovering maneuver of the aircraft of FIG. 3. [Figure 5A] FIG. 5A is a schematic diagram of aircraft operations showing egress (takeoff) and ingress (landing) volumes. [Figure 5B] FIG. 5B is a schematic diagram of aircraft operations showing egress (takeoff) and ingress (landing) volumes. [Figure 6] FIG. 6 is an isometric view of an aircraft illustrating thrust vector propulsion. [Figure 7] FIG. 7 is a block diagram of the flight control system. [Figure 8] Figure 8 is a block diagram of flight control at a detailed level. [Figure 9] FIG. 9 is a flow chart diagram of the deployment and use of the aircraft. [Figure 10] Figure 10 is a diagram of the rotor and its articulations. [Figure 11] Figure 11 is a diagram of the rotor and its articulations. [Figure 12] FIG. 12 is a side view of an aircraft with various propulsion configurations. [Figure 13] FIG. 13 is a side view of an aircraft with various propulsion configurations. [Figure 14] FIG. 14 is a side view of an aircraft with various propulsion configurations. [Figure 15] FIG. 15 is a diagram of the aircraft with exposed payload / battery compartments. [Figure 16] FIG. 16 is a schematic diagram of the arrangement of the payload and battery sections of the payload / battery compartment. [Figure 17] FIG. 17 shows top, front, and side views, respectively, of an aircraft employing an alternative fuselage type. [Figure 18] FIG. 18 shows top, front, and side views, respectively, of an aircraft employing an alternative fuselage type. [Figure 19] FIG. 19 shows top, front, and side views, respectively, of an aircraft employing an alternative fuselage type. [Figure 20] FIG. 20 shows top, front, and side views, respectively, of another aircraft employing an alternative fuselage type. [Figure 21] FIG. 21 shows top, front, and side views, respectively, of another aircraft employing an alternative fuselage type. [Figure 22] FIG. 22 shows top, front, and side views, respectively, of another aircraft employing an alternative fuselage type. [Figure 23] FIG. 23 is a semi-schematic view of various propulsion pod configurations. [Figure 24] FIG. 24 shows a modular side view of the aircraft. [Figure 25] FIG. 25 shows a modular side view of the aircraft. DETAILED DESCRIPTION OF THE INVENTION

[0013] FIG. 1 illustrates an unmanned aircraft system (UAS) 10, also referred to as an unmanned aerial vehicle (UAV), having a known configuration. The basic structure is that of a fixed-wing aircraft, having an elongated fuselage 12 and fixed wings 14, with horizontal propulsion provided by a rear-mounted engine and propeller 16. The UAS 10 is also configured for vertical takeoff and landing (VTOL) using booms 18, each mounted on the underside of a respective wing 14 and carrying a respective fixed-direction upward-facing propeller 20. The propellers 20 are powered by respective small engines or motors within the booms 18, not visible in this view. With the addition of the described VTOL structure and capabilities, the UAS 10 may be referred to as a “hybrid” UAS 10.

[0014] During operation, the UAS 10 is typically launched vertically from a ground location, then flies in a conventional fixed-wing manner and can also land vertically. During launch and landing, the propeller 20 is used to provide vertical thrust, while the rear-mounted engine and propeller 16 are active or idle. During fixed-wing flight, the rear-mounted engine and propeller 16 provide horizontal thrust, and the VTOL propeller 20 is typically idle. While the boom 18 presents undesirable weight and drag for fixed-wing flight, there are applications where this drawback is outweighed by the desired VTOL capabilities. In one embodiment, the boom 18 is identical in structure, even though it is used on opposite sides of the UAS 10. Side-to-side dependency can be accommodated by the use of adapters, such as a V-tail connection, as needed.

[0015] Dynamic environments can significantly limit the performance of hybrid UAVs, such as the aircraft 10 shown in Figure 1. Fixed-wing aircraft employing fixed-direction, separated lift-thrust multirotor lift solutions (e.g., hybrid quads) must constrain aircraft attitude and maneuver rate during hover-translation maneuvers. Constraints are necessary to prevent adverse aerodynamic effects caused by exposure of fixed-wing lifting surfaces (e.g., wings, tails) to the surrounding free airstream (wind).

[0016] 2A and 2B are diagrams for illustrating this problem. FIG. 2A shows a front view of a hybrid quad aircraft 30 (which may be embodied as aircraft 10, etc.) in both calm conditions (top image) and windy conditions (bottom image). FIG. 2B shows the corresponding side view. The consequences of the above constraints on the operation of a conventional hybrid quad 30 or similar separated lift-thrust aircraft are as follows: The aircraft must maintain a positive pitch attitude to maintain the effective angle of attack (AoA) of the lifting surfaces. a. Limit longitudinal translation to that achievable with longitudinal thrust propulsion systems typically designed for fixed-wing efficiency b. As a result, the rate of forward / backward translation is limited -Limiting the aircraft's roll attitude and control speed to avoid applying crosswind components to the lifting surface a. Lateral translation rate and response are limited The aircraft yaw attitude and control rate are limited within the range of the rotor's rotational inertia. a. Aircraft must weathervane into the prevailing wind without exceeding control authority b. Yaw response rate is limited by differential rotational inertia c. The increased moment of inertia and adverse effects of environmental conditions limit the scalability of the solution VTOL lift solutions must maintain thrust margin to overcome the negative effects caused by fixed wing impacts during hover / translation a. Provides size, weight, and power allocation Reduced maneuverability or loss of control under dynamic or difficult environmental wind conditions Difficulty tracking fixed or moving relative positions to support dynamic recovery under mission-relevant conditions

[0017] As disclosed herein, a common solution to the above problem is to use vectored thrust for attitude and relative position control. In addition to its longitudinal thrust engines, the aircraft has independently controlled tilt propulsion assemblies with one or more rotational axes with controllable positions relative to the aircraft body. Vectored thrust applied to separated lift-thrust fixed-wing aircraft can provide: -Control of the aerodynamic pose of fixed-wing lifting surfaces during VTOL and fixed-wing flight; -Provides enhanced lateral and longitudinal thrust; and - Active relative position control and convergence to defined static or dynamic landing points.

[0018] FIG. 3 illustrates an aircraft 40 according to one embodiment of the present invention. The aircraft 40 has a centerbody or fuselage 42, a rear horizontal thrust engine 44, and laterally extending wings 46. Four motor / rotor assemblies 48 are attached to the respective ends of two support booms 50, each extending longitudinally and attached to the underside of the wings 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 oriented upward and the rear rotors 48 are oriented downward, with at least some of the rotors 48 being articulated or variable-position (e.g., all rotors, only the front rotors, or only the rear rotors). In the illustrated embodiment, the front and rear pairs of rotors 48 are collinear on a line parallel to the longitudinal axis of the aircraft 40, as shown. Opposite top-to-bottom rotor orientation utilizes rear pusher propellers and front traction propellers. A typical arrangement includes four rotors 48 as shown, although other arrangements are possible. In some embodiments, some or all of the rotors 48 include variable pitch mechanisms that dynamically adjust the pitch of the rotor blades to provide additional aspects of flight control.

[0019] 4A and 4B again schematically illustrate operation of an articulated rotor separated lift-thrust (SLT) aircraft 60 under the same conditions as FIGS. 2A and 2B, where aircraft 60 may be realized as aircraft 40 (FIG. 3), or the like. For the lateral movement of FIG. 4A, the lift rotors roll to assist in maintaining wing attitude (substantially horizontal) to mitigate adverse or fluctuating effects of wind-induced lift components and maintain control authority during VTOL operations. For the longitudinal movement of FIG. 4B, the lift rotors pitch to assist in maintaining wing attitude (again substantially horizontal) to mitigate adverse or fluctuating effects of wind-induced lift components and maintain control authority during VTOL operations.

[0020] Figures 5A and 5B illustrate certain operational advantages that can be achieved. Figure 5A illustrates the transition from VTOL hover to fixed-wing flight. While 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 (far right), the aircraft disclosed herein may enjoy a shorter transition range and a faster / shorter transition to fixed-wing flight. The characteristics of the reverse transition (fixed-wing to hover / VTOL) are similar, as shown in Figure 5B.

[0021] FIG. 6 illustrates the nature of thrust vector propulsion, controlling six dimensions: two for the longitudinal thrust engines 44 (RPM and blade pitch) and four for the rotors 48 (rotor assembly longitudinal (pitch) tilt angle θ, rotor assembly lateral (roll) tilt angle φ, rotor RPM ω, and rotor blade pitch φ). T indicates the resulting thrust vector, and the numerical subscripts indicate the four separate rotors 48. Generally, each rotor 48 may be independently controlled, although, as described in more detail below, configurations are possible in which some rotors are fixed or constrained relative to other rotors. Also, while this illustration assumes tilt of the rear rotors 48-3 and 48-4 on only one axis, as described below, tilt can be achieved on multiple axes to achieve even greater maneuverability.

[0022] More specifically, each resulting thrust vector (T1, T2, T3, T4) may be independently controlled as a function of the coordinated actuation of longitudinal pod tilt angle (pitch), lateral pod tilt angle (roll), rotor RPM, and variable rotor blade pitch. Each degree of freedom is isolated and managed via a central flight control processor (described in more detail below) to achieve stable, coordinated flight through closed-loop control. The ability to vary rotor tilt angle around separate axes, such as both longitudinal tilt (pitch) and lateral tilt (roll), is sometimes referred to as a compound joint. In the embodiment of FIG. 6, the degrees of freedom of the rear vertical thrust rotors (48-3, 48-4) can be expanded to include longitudinal tilt (θ) and variable rotor pitch (Ψ). To increase this rotor range of motion, alternative aircraft tail / empennage configurations with reduced or mitigated mechanical interference are contemplated.

[0023] Figure 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 related management functions. - Navigation and related components 72, including data links for external communications, payload, flight control, navigation, navigation sensing, and inertial measurements.

[0024] FIG. 8 provides details of the flight control, including a computer-implemented flight control device 80 interacting with aircraft plant dynamics 82. The flight control device 80, as described above, generates control outputs, including signals representing the values ​​θ, ω, φ, and Ψ, by which the physical aircraft interacts with its environment. As shown, the flight control device 80 may be implemented as a model-based controller incorporating a model of the aircraft's physical plant for predictive control. Sensed effects are provided to the controller 80 for state estimation, as well as altitude and trajectory estimation, and airspeed and direction estimation, which are returned to the flight control device 80 along with other inputs to update the control outputs. As previously described, the control method is based on vector thrust, in contrast to other aircraft that rely on control surfaces such as flaps.

[0025] FIG. 9 illustrates the deployment and use of aircraft 40, including features of traditional fixed-wing operations along with VTOL and its associated enhanced operational flexibility. 90 represents pre-flight operations such as transport and pre-flight maintenance and inspection. Operations proceed with vertical takeoff and transition to horizontal flight at 92, followed by flight execution at 94. This may simply be traditional fixed-wing flight (e.g., from one point to another) and / or may include one or more periods of VTOL hovering, known as "stationkeeping." After flight execution at 94, the aircraft returns to VTOL operations for landing at 96. Note that steps 92-96 can be repeated for missions spanning a series of locations. 98 represents post-flight operations such as post-flight maintenance and transport.

[0026] One advantage of aircraft 40 is that it can generate lift on the airflow through the action of wings 46 in addition to the lift from rotors 48. Conventional rotorcraft generally have reduced endurance when stationkeeping in the air, whereas an aircraft may have increased endurance when stationkeeping in the air.

[0027] Figures 10-11 show the rotor 48 and its articulations in further detail. This arrangement employs parallel tandem servo control, i.e., two separate servo mechanisms 100 arranged in parallel, as best seen in Figure 11. In this arrangement, the axis of rotation 102 extends through the center of gravity of the rotor 48, as best seen in Figure 10. Alternative mechanisms can be employed, such as direct on-axis servos, serial tandem servos, off-center rotation, pneumatic / hydraulic mechanisms, belt or gear drives, etc. As noted above, variable positioning can be limited to one axis or can include multiple axes, such as tilt / yaw.

[0028] Figures 12-14 show examples of different propulsion configurations as briefly described above. Figure 12 shows a symmetric configuration with a variable position front pod (rotor) and a variable position rear pod, where "position" refers to angular articulation. Figure 13 shows an asymmetric configuration with a variable position front pod and a semi-fixed (limitedly variable) position rear pod. Figure 14 shows another asymmetric configuration with a variable position front pod and a fixed position rear pod.

[0029] The table below details the function of the various configurations of Figures 12-14 during various stages of flight. [Table 1]

[0030] In the symmetrical configuration of Figure 12, the baseline requirement is that all propulsion pods have equal range of motion and are used throughout all phases of flight. However, the system can operate with only one pair / set of propulsion systems active to provide full flight control, while the remaining ones operate with limited or no thrust vectoring capability in one or more axes, as in the configurations of Figures 13 and 14. In four-rotor embodiments, this can be achieved with either the front pair of rotors or the rear pair of rotors. Assuming that the front rotor pair is prioritized for fixed-wing flight to achieve the most efficient propeller configuration during cruise, the rear motors can be retracted and deactivated during fixed-wing flight, increasing the system's electrical efficiency and reducing its acoustic signature. Additionally, the rear / rear rotors can be reactivated during fixed-wing flight to increase sprint speed or climb, and then transition to VTOL for recovery at the end of the flight. Furthermore, this asymmetric control capability allows the system to employ rotor pairs / sets with limited range of motion or no tilt / yaw thrust vectoring capability, reducing the weight and complexity of the onboard propulsion systems. In embodiments with four or more propulsion pods, alternate / restricted joint function designations can be applied between the forward and aft propulsion systems, allowing the forward and aft sets to have a combination of restricted / fixed propulsion pods and fully capable joint functions. Selection of these alternate control modalities can be achieved by swapping or interchanging the aircraft's propulsion modules. In all modalities, the presence of fixed longitudinal engines providing thrust in fixed-wing flight can augment or replace the function of the propulsion pods.

[0031] 15 and 16 illustrate the particular modularity of the system components that allows a generic thrust vectoring approach to be used for a variety of different types of aircraft, as described in more detail below. The propulsion system, including rotors 48 with associated actuators and vectored thrust motion and actuation control system 110 components (including energy storage, energy distribution, and other components as shown), can be adapted to other airframe types, including retrofitting existing fixed-wing systems.

[0032] Figures 17-22 show examples of application to other types of aircraft. Figures 17-19 are top, front, and side views of a conventional small fixed-wing airframe 120, typically employing a single combustion engine, configured with a rotor 48 attached to the underside of a wing 46 and a boom 50, similar to aircraft 40 (Figure 3). Figures 20-22 are top, front, and side views of a second type of fixed-wing airframe 130 similarly configured using a boom-mounted rotor.

[0033] FIG. 23 is a semi-schematic diagram of various propulsion pod configurations (boom-mounted rotor configurations) that can be used. Five configurations are shown, 140-1 through 140-5. For each configuration 140, three views are shown: top, front, and side (progressing downward in FIG. 23). Different implementations of propulsion pod placement and attachment to the vehicle include variations such as offset and lateral support.

[0034] Figures 24-25 illustrate additional aspects of modularity that may be employed. Figure 24 illustrates modular mounting of the boom 50 and rotor 48. Figure 25 illustrates the use of an alternative boom and tail configuration 150.

[0035] (Scalability) In general, the disclosed aircraft may be parametrically scaled in both size and number of rotor assemblies. In one embodiment, the aircraft may provide for the attachment of additional booms 50 and corresponding rotors 48, for example, at more distal locations on the wings 46, thereby providing additional lift / thrust.

[0036] While 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

[Claim 1] 1. An aircraft comprising: an airframe having a lifting surface; Longitudinal thrust engines; a plurality of modular articulated electric rotors mounted on the airframe, at least some of the rotors being variable position rotors whose direction can be varied based on rotor position signals provided thereto; a power source for powering the electric rotor; a control circuit configured and operated to independently control the thrust of the longitudinal thrust engines and the rotor thrust and rotor orientation of each variable position rotor for the lifting surfaces and the longitudinal thrust engines of the aircraft to provide commanded thrust vector steering of the aircraft during vertical take-off and landing (VTOL), fixed-wing flight, and intermediate transition conditions, including maintaining a desired lifting surface attitude when hovering the aircraft in windy conditions, independent of rotor orientation; and a flight and navigation control system capable of automating flight maneuvers, either autonomously or with human-in-the-loop augmentation, and maintaining a desired aircraft system attitude and position relative to autonomously or operator-defined static or dynamic global coordinates while said aircraft is performing stationkeeping, tracking, avoidance, or convergence maneuvers; Including, aircraft.

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