Patent Description:
"<NPL>, discloses a flight control arrangement for a hybrid aircraft.

There is provided a flight control arrangement for a hybrid aircraft according to claim <NUM>.

A flight control arrangement for a hybrid aircraft includes a fixed-wing (F/W) flight control module and vertical takeoff/landing flight (VTOL) control module. The F/W control module is an integrated component fully capable of independently controlling F/W flight, and it has a respective network interface connected to an aircraft data network via which it provides fixed-wing control output to network-connected fixed-wing flight components including one or more horizontal-thrust components. The VTOL control module is also an integrated component and has a respective network interface to the aircraft data network via which the VTOL control module (<NUM>) passively observes flight status as reflected in network messages originated by the fixed-wing flight control module, and (<NUM>) based on the observed flight status, generates VTOL control output to network-connected VTOL flight components including one or more vertical-thrust components, to control VTOL flight as well as transitions to and from fixed-wing flight, which is executed by the F/W controller without logical or supervisory control of the VTOL controller functions.

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

In certain operating scenarios for fixed-wing aircraft, including unmanned "drone" aircraft as generally known, transition to/from fixed wing flight has been accomplished via rolling take-off/landing or using energetic assistance through catapult/launcher with recovery performed on runway, net, or other capture device. Hybrid solutions with separated lift and thrust capabilities (quad-planes) have emerged as a means to provide runway independence and enable point take-off and recovery without the need for supplemental ground support equipment. These hybrid systems leverage multi-rotor lifting capability to lift/recover fixed wing aircraft by enabling transition to/from fixed wing flight.

Prior methods of implementing flight control for such hybrid aircraft required implementing unique hybrid quadrotor software code applied as part of an integrated device (autopilot). While the implementation approach has differed in levels of architectural modularity within these devices, prior methods involved singular autopilot device solutions that were closely coupled with defined quad-plane aircraft characterization, sensing and inner/outer loop controls to provide VTOL, transition, and fixed wing flight.

A presently disclosed technique augments a fixed wing aircraft flight control and management solution to enable vertical take-off and landing capability without modification to the existing fixed wing controller. The system utilizes a federated VTOL flight controller loosely coupled with the fixed wing controller via an aircraft network and distributed interface modules. The VTOL flight controller provides for transition to and from fixed wing flight by asserting control to VTOL lift propulsion systems based upon fixed wing control and aircraft configuration parameters. During fixed wing flight, the VTOL controller is maintained in a quiescent state. The VTOL flight controller asserts control based upon high level observable state/mode and other criteria of the fixed wing controller, while remaining loosely coupled to the fixed wing controller via a network interface.

The F/W controller operates as an independent agent without knowledge of the presence and involvement of the VTOL controller beyond indirect inertial observations (i.e. inertial sensors perceive VTOL motion but F/W controller has no logical understanding or relationship). In effect, the F/W controller is simply flying a F/W aircraft in a conventional manner, while the VTOL controller is the steward of entering and transitioning to/from viable fixed wing flight regimes.

More particularly, the disclosed technique may be differentiated from known aircraft control arrangements by one or more of the following:.

<FIG> shows an unmanned aircraft system (UAS) <NUM>, also referred to as an unmanned aerial vehicle (UAV). The basic structure is that of a fixed-wing (F/W) aircraft having an elongated fuselage <NUM> and fixed wings <NUM>, with propulsion provided by a rear-mounted engine and propeller <NUM> for horizontal fixed-wing flight. The UAS <NUM> is also configured for vertical takeoff and landing (VTOL) through the use of booms <NUM>, each attached to the underside of a respective wing <NUM> and carrying respective upward-facing rotors <NUM>. The rotors <NUM> are powered by respective small engines/motors within the booms <NUM>, not visible in this view. With the addition of the VTOL structure and capability as described, the UAS <NUM> may be referred to as a "hybrid" UAS <NUM>. Another term that is commonly used is "hybrid-quad", referring to the use of four VTOL rotors <NUM>.

In operation, the UAS <NUM> is launched vertically, typically from a ground position, then flown in a conventional fixed-wing manner, and then landed, which may be a vertical landing. During launch and landing, the rotors <NUM> are used to provide vertical thrust and horizontal translation, while the engine and propeller <NUM> are either inactive, actively assisting longitudinal translation, or at idle. During fixed-wing flight, the engine and propeller <NUM> provide horizontal thrust, and the VTOL rotors <NUM> are inactive. Although the booms <NUM> represent undesirable weight and drag for fixed-wing flight, there are applications in which this drawback is outweighed by the desired VTOL capability.

In one embodiment the rotors <NUM> have fixed upward orientation, while in alternative embodiments some or all rotors <NUM> may be articulable in one or more directions, e.g., about a roll axis and/or pitch axis.

<FIG> illustrates certain components of the aircraft <NUM> in schematic form, in particular in relation to an aircraft network <NUM> used within the aircraft <NUM> to convey operating commands and data among the components. The components include longitudinal (horizontal) thrust components <NUM> (e.g., engine and propeller <NUM>), fixed wing control surfaces <NUM>, vertical thrust components <NUM> (e.g., VTOL rotors <NUM>), and Other functional components <NUM>, examples of which are given below. Additionally, the arrangement includes a flight management and fixed-wing control module <NUM> and a separate VTOL control module <NUM>. The flight management and F/W control module <NUM>, also referred to herein as the F/W control module <NUM>, has external communications links to a ground system <NUM> and to a global navigation satellite system (GNSS) <NUM>. Generally in operation, the F/W control module <NUM> serves as the overall flight controller and in particular as the controller for fixed-wing flight, thus providing control commands and data to the longitudinal/horizontal thrust components <NUM> and F/W control surfaces <NUM>. In one embodiment, the F/W control module <NUM> may be realized using a Piccolo™ autopilot module, which is a separately housed component with integrated flight control functionality. The VTOL control module <NUM> serves as the controller for VTOL flight, providing control commands and data to the vertical thrust components <NUM>. The VTOL control module <NUM> may likewise be separately housed, and it incorporates integrated VTOL control functionality as described herein.

In one embodiment the aircraft network <NUM> may be realized as a collection of one or more physical networks, some or all of which may utilize the so-called CAN Bus (Controller Area Network Bus) standard. In the present description, the acronym CAN is used to refer to one of these physical buses.

The Other functional components <NUM> generally include components of a variety of types, including aircraft power system components (e.g., generators, batteries, distribution), payload/mission-related components (e.g., weapon), network-connected sensors, transponder/IFF, navigation/anti-collision lighting, etc. Details of the flight management and F/W control module <NUM> and VTOL control module <NUM> in illustrative embodiments are provided below.

The VTOL control module <NUM> augments the F/W flight control of the F/W control module <NUM> to independently manage VTOL and transitions. Aircraft control is exchanged between the loosely coupled F/W control module <NUM> and the VTOL control module <NUM> based on state/mode transitions of the F/W control module <NUM>, as described more below. The CANbus architecture provides access to the VTOL control module <NUM>, which has its own dedicated IMU in at least one embodiment. In operation, a fixed wing waypoint launch and landing plan may be used that is unmodified from standard fixed wing operations/logic. Standard Flight Status Utility (FSU) widgets can be used at the ground controller to facilitate the VTOL augmentation.

<FIG> shows details of the flight management and F/W control module <NUM>. The main component is a processor-based flight management and F/W controller <NUM> having its own inertial measurement unit (IMU) <NUM>. The flight management and F/W controller <NUM>, also referred to herein as the F/W controller <NUM>, is connected to the aircraft network <NUM> by a network interface module <NUM>, and has connections to air data ports <NUM>, an aircraft command/control (CMD/CNTL) data link system <NUM>, and a GNSS receiver <NUM> as shown. The F/W controller <NUM> includes processing circuitry and specialized firmware/software that is executed to realize the flight management and F/W control operation. As briefly mentioned above, one important aspect of the present arrangement is the ability to utilize a flight management and F/W control module <NUM> that has no knowledge of or adaptation to the presence of the separate VTOL control module <NUM>, providing benefits such as relative ease of retrofit for incorporating VTOL operation into existing fixed-wing aircraft. As described more below, the VTOL control module <NUM> observes traffic on the aircraft network <NUM> to identify operational state of the aircraft and exert VTOL control accordingly.

<FIG> illustrates details of the VTOL control module <NUM>. It includes a processor-based VTOL controller <NUM>, which in the illustrated embodiment includes its own IMU <NUM>, and a network interface module <NUM> providing connection to the aircraft network <NUM>. The VTOL controller <NUM> includes processing circuitry and specialized firmware/software that is executed to realize VTOL operations as described herein. In one embodiment the VTOL controller <NUM> may be realized using certain open-source hardware known as Pixhawk®.

Although both the F/W controller <NUM> and VTOL controller <NUM> are shown as including respective IMUs <NUM>, <NUM>, in alternative embodiments the system may include a separate IMU providing navigation data to one or both controllers <NUM>, <NUM>. Alternatively, the VTOL controller <NUM> may use the F/W controller IMU <NUM>.

<FIG> shows a more particular arrangement of the general scheme of <FIG>. The aircraft network <NUM> is realized by a collection of CAN Buses shown as CAN1 and CAN2, with connections as shown. In particular, the F/W controller <NUM> and the VTOL controller <NUM> are both connected to the same buses CAN1 and CAN2, and the components <NUM>, <NUM> and <NUM> are reachable via CAN1 and CAN2 and a set of network interface modules <NUM> (e.g., hatch interface modules, wing interface modules). The VTOL controller <NUM> observes traffic on both CAN1 and CAN2, and also generates its own traffic on these buses as well. In one embodiment, these four different types of network traffic include the following:.

In the above, the indication "insofar as supported" refers to the possibility of the F/W controller <NUM> having awareness of the VTOL controller <NUM> and incorporating its presence into the overall flight management and control functionality. As noted, however, one benefit of the present arrangement is the ability to incorporate VTOL functionality into an existing F/W control scheme without requiring modification of the F/W controller <NUM>.

<FIG> is a schematic illustration of takeoff/launch, showing the transition or "hand-off" between VTOL control controller <NUM> and F/W controller <NUM>. The VTOL controller <NUM> may be viewed as providing a "virtual launcher" to bring the aircraft <NUM> to fixed wing transition speed and then hand off to the F/W controller <NUM> once transition has been achieved. In particular, the VTOL controller <NUM> receives a discrete "launch" command and performs forward transition operation to cruise speed. When cruise speed is confirmed the VTOL controller <NUM> stows the lift kit motors. During the pre-launch period, the F/W controller <NUM> is commanding control surfaces to maintain level flight.

<FIG> is a schematic illustration of landing/recovery. Here the VTOL controller <NUM> may be viewed as providing a "virtual net" to capture the aircraft <NUM> at the end of horizontal flight, shown here as including a final approach to a decision/wave-off point, followed by a short final. Operation transitions from the F/W controller <NUM> to the VTOL controller <NUM> at the moment of the "net" intercept, and the VTOL controller <NUM> manages the actual landing to a touch-down point (TDP). In typical use, the F/W controller <NUM> idles or completely cuts the horizontal engine <NUM> at the point of capture, but in some cases, such as testing or in connection with rolling landing/launch or touch-and-go maneuvers, the engine may be left running.

The landing/recovery operation depicted in <FIG> may be particularly useful for certain operating scenarios, such as a shipboard landing for example, whereas for other scenarios it may not be necessary. Thus in some embodiments a landing/recovery operation such as depicted in <FIG> may be altered to suit recovery location geometry and constraints or not be supported.

Claim 1:
A flight control arrangement for a hybrid aircraft capable of horizontal fixed-wing flight, vertical takeoff and landing (VTOL) flight, and transitions therebetween, comprising:
a fixed-wing flight control module (<NUM>) configured and operative to control the horizontal fixed-wing flight, the fixed-wing flight control module being an integrated component having a respective first network interface (<NUM>) connected to an aircraft data network (<NUM>) via which the fixed-wing flight control module obtains sensory input and generates fixed-wing control output to network-connected fixed-wing flight components including one or more horizontal-thrust components (<NUM>); and
a VTOL flight control module (<NUM>) configured and operative to control the VTOL flight, the VTOL flight control module also being an integrated component having a respective second network interface (<NUM>) connected to the aircraft data network via which the VTOL flight control module (<NUM>) observes flight status as reflected in network messages originated by the fixed-wing flight control module, and (<NUM>) based on the observed flight status, generates VTOL control output to network-connected VTOL flight components (<NUM>) including one or more vertical-thrust components, wherein the aircraft data network includes a plurality of controller area network (CAN) buses each carrying respective network messages originated by the fixed-wing flight control module and VTOL flight control module, and wherein the VTOL flight control module monitors and acts upon states, modes, and observable/sensors reporting of the fixed-wing flight control module as reflected in the network messages originated thereby.