Patent Application
20200393851
The present disclosure relates generally to multi-rotor aircraft, and more particularly, but not by way of limitation to systems and methods for high-performance descent of multi-rotor aircraft.
This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Some rotor aircraft use rotor systems having rotors of fixed pitch. Thrust provided by fixed-pitch rotor systems is controlled by changing rotor speed. For example, to produce more thrust, rotor system speed is increased. To produce less thrust, rotor system speed is decreased. In order to maintain stable flight characteristics, fixed-pitch rotor systems must maintain a minimum operating speed. If the speed of the rotor system falls below the minimum operating speed, control authority from the rotor systems can become insufficient and the aircraft becomes unstable. As a result of the necessary minimum operating speed, there exists a minimum amount of thrust that the aircraft is capable of generating during flight. The minimum amount of thrust generated affects a maximum descent rate for the aircraft. In some situations, the minimum amount of thrust generated can make it so that the aircraft is unable to descend. For example, updrafts, such as warm air streams or thermals, can overcome the rate of descent of the aircraft and prevent the aircraft from losing altitude. In some situations, aircraft have been lost because the aircraft was unable to descend to the ground to land before running out of fuel or battery.
An additional consideration regarding the maximum descent rate is a phenomenon known as the vortex ring state (VRS). The VRS is a known phenomenon that can affect VTOL aircraft. In short, a VTOL aircraft that descends too quickly can suddenly experience a loss in lift generated by the rotor system. The sudden loss in lift is the result of a vortex ring system engulfing the rotor system, which essentially causes the rotor system to stall. VRS can be quite dangerous and, if not handled properly, can result in crashing the aircraft.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it to be used as an aid in limiting the scope of the claimed subject matter.
An illustrative high-performance descent method for a multi-rotor aircraft includes preparing the multi-rotor aircraft for a high-performance descent, instructing, via a flight control system, a first proprotor to tilt, tilting the proprotor away from a vertical axis; and wherein, responsive to the tilting, an altitude of the multi-rotor aircraft is reduced.
An illustrative high-performance descent system for a multi-rotor aircraft includes a flight control computer comprising a processor, a propulsion system communicatively coupled to the flight control computer and configured to allow a direction of thrust relative to a vertical z-axis to be selected by the flight control computer. The processor is operable to implement a method including preparing the multi-rotor aircraft for a high-performance descent, instructing, via a flight control system, a proprotor to reduce an amount of vertical thrust produced by the proprotor by tilting the proprotor away from a vertical axis, and reducing an altitude of the multi-rotor aircraft.
The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.
Various embodiments will now be described more fully with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
Unlike fixed-wing aircraft, vertical takeoff and landing (VTOL) aircraft do not require runways. Instead, VTOL aircraft are capable of taking off, hovering, and landing vertically. Drones are one example of a VTOL aircraft. VTOL drones typically have multiple rotors that provide lift to allow the aircraft to fly. A wide variety of drones exist. Exemplary drones include, for example, traditional multi-rotor aircraft (e.g., aircraft having two or more rotor systems that are capable of VTOL and translating horizontally similar to a helicopter) and tail-sitter aircraft (e.g., see
The descent-related problems identified above (e.g., inability to descend and VRS) can be mitigated using the systems and methods discussed herein. For example, the maximum descent rate of a multi-rotor aircraft can be increased by changing thrust vectors of the rotor systems of the multi-rotor aircraft. Changing the thrust vectors of the rotor systems changes the amount of vertical thrust generated by the aircraft, but maintains the minimum operating speed of the rotor systems to prevent the aircraft from losing differential control authority and becoming unstable. The minimum operating speed is the operating speed at which the aircraft can exhibit stable and predictable flying characteristics while closely following reference states (rates, attitudes, accelerations, etc.) without extra effort from either the pilot or the computer. In some aspects, the minimum operating speed might be limited in order to avoid resonance with a structural or rotor system natural frequency. Changing the thrust vectors of the rotor systems not only allows for a faster maximum descent rate, but further reduces the likelihood that the aircraft will suffer from VRS related problems because air from the rotor systems can be directed horizontally away from the aircraft.
Referring to
Truss structures or pylons 18, 20 extend generally perpendicularly between wings 14, 16. Pylons 18, 20 are preferably formed from high strength and lightweight materials such as fiberglass fabric, carbon fabric, fiberglass tape, carbon tape and combinations thereof that may be formed by curing together a plurality of material layers. Pylons 18, 20 and/or wings 14, 16 may support various components of aircraft 10, such as flight control system 40. Wings 14, 16 and pylons 18, 20 are securably attached together at the respective intersections by bolting, bonding and/or other suitable technique such that airframe 12 becomes a unitary member. Wings 14, 16 may include central passageways operable to contain energy sources and communication lines.
Aircraft 10 includes a plurality of propulsion systems 26a-26d attached to airframe 12. Each propulsion system 26a-26d is independently controllable. It will be appreciated that aircraft 10 could be configured with any number of propulsion systems 26, including two, three, five, six, eight, twelve, sixteen or other numbers of propulsion systems. Each propulsion system 26a-26d may include a nacelle 28 that houses various components, such as a power source, an engine or motor, a drive system, a rotor hub, actuators and an electronics node including, for example, controllers, sensors and communications elements as well as other components suitable for use in the operation of a propulsion system (best seen in
In some aspects, aircraft 10 can be powered via a liquid fuel, wherein energy is provided to each of the propulsion assemblies from combustion of the liquid fuel. For example, in this configuration, each of the propulsion systems 26a-26d may be represented by propulsion system 26a of
In some aspects, aircraft 10 can be powered by electricity, wherein energy is provided to each of the propulsion systems 26a-26d from an electric power source. For example, in this configuration, each of the propulsion assemblies may be represented by propulsion system 26b of
The rotor assemblies of each propulsion system 26a-26d are preferably lightweight, rigid members that may optionally include swashyoke mechanisms operable for collective pitch control and thrust vectoring. Proprotors 38 include a plurality of proprotor blades that are securably attached to spindle grips of the respective rotor hub. In some aspects, the proprotor blades are operable for collective pitch control and may additionally be operable for cyclic pitch control. In some aspects, the pitch of the proprotor blades is fixed, in which case thrust is determined by changes in the rotational velocity of the proprotors. In the illustrated embodiment, the rotor hubs have a tilting degree of freedom to enable thrust vectoring.
To accommodate the tilting degree of freedom of the rotor hubs, wings 14, 16 have a unique swept wing design, which is referred to herein as an M-wing design. For example, as best seen in
Even though the propulsion assemblies of the present disclosure have been described as having certain nacelles, power sources, engines, drive systems, rotor hubs, proprotors and tail assemblies, it is to be understood by those having ordinary skill in the art that propulsion assemblies having other components or combinations of components suitable for use in a versatile propulsion system are also possible and are considered to be within the scope of the present disclosure.
Each tail assembly 46 includes an active aerosurface 48 that is controlled by an active aerosurface control module of a flight control system 40. During various flight operations, active aerosurfaces 48 of propulsion systems 26a-26d may operate as vertical stabilizers, horizontal stabilizers, rudders and/or elevators to selectively provide pitch control and yaw control to aircraft 10.
Flight control system 40 of aircraft 10, such as a digital flight control system, may be located within a central passageway of wing 14 (e.g., see
Flight control system 40 communicates with electronics nodes 41 of each propulsion system 26a-26d, respectively. Flight control system 40 receives sensor data from and sends flight command information to each electronics node 41 of each propulsion system 26a-26d such that each propulsion system 26a-26d may be individually and independently controlled and operated. In both manned and unmanned missions, flight control system 40 may autonomously control some or all aspects of flight operation for aircraft 10. Flight control system 40 is also operable to communicate with remote systems, such as a transportation services provider system via a wireless communications protocol. The remote system may be operable to receive flight data from and provide commands to flight control system 40 to enable remote flight control over some or all aspects of flight operation for aircraft 10, in both manned and unmanned missions.
Flight control system 40 is operable to independently control each propulsion system 26a-26d. For example, flight control system 40 can control collective pitch (when aircraft 10 is so equipped) and adjust the thrust vector of each propulsion system 26a-26d, which can be beneficial in stabilizing aircraft 10 during vertical takeoff, vertical landing and hover. Adjusting the thrust vector each propulsion system 26a-26d also enables aircraft 10 to perform a high-performance or rapid descent maneuver. The high-performance descent maneuver will be discussed in more detail below.
As discussed herein, flight control system 40 is operable to independently control each of the propulsion systems 26 including tilting each rotor assembly 60. For each propulsion system 26, flight control system 40 is operable to tilt rotor assembly 60 relative to mast axis 42. When propulsion systems 26a-26d are being operated and rotor assemblies 60 are tilted relative to mast axis 42, the thrust vectors generated by rotor assemblies 60 have a vertical component and a horizontal component. When rotor assemblies 60 are not tilted, the horizontal component of thrust for each rotor assembly 60 is zero.
Each propulsion system 26a-26d includes a thrust vectoring system depicted as a dual actuated thrust vectoring control assembly 50. As illustrated, IC engine 32′ or electric motor 32″, drive system 34, rotor hub 36 and proprotor 38 are mounted to a pivotable plate 52 operable to pivot about a pivot axis defined by pin 54. In some aspects, pivotable plate 52 is also operable to rotate about mast axis 42 to control the azimuth within the thrust vectoring system. Rotation of pivotable plate 52 is accomplished with an electromechanical rotary actuator 56, but other suitable rotary actuator could alternatively be used. The elevation of pivotable plate 52 is controlled with a linear actuator 58 that pulls and/or pushes pivotable plate 52 about the pivot axis. As illustrated in
The thrust vectoring of each of the propulsion systems 26a-26d is independently controlled by flight control system 40. In some aspects, flight control system 40 is operated autonomously. In some aspects, flight control system 40 may be controlled by a pilot onboard the aircraft or remote from the aircraft. In addition to allowing the aircraft to perform a high-performance descent, changing the thrust vector of propulsion systems 26a-26d enables differential yaw control during hover, as well as an unlimited combination of differential horizontal thrust coupled with net horizontal thrust to allow positioning over a stationary target, for example when crosswinds are present. Even though a particular thrust vectoring system having a particular maximum pitch angle has been depicted and described, it will be understood by those skilled in the art that other thrust vectoring systems, such as a gimbaling system or a teetering rotor that has the ability to tilt the thrust axis relative to a mast of the rotorcraft, having other maximum pitch angles, either greater than or less than 20 degrees, may alternatively be used on flying frames of the present disclosure. Additional tilting rotor hub configurations are illustrated in U.S. Pat. No. 10,220,944 and U.S. Patent Pub. Nos. 2019/0031331 and 2018/0002026, each of which is incorporated in its entirety as if fully set forth herein.
Method 100 begins at step 102. In step 102, aircraft 200 prepares for a high-performance descent. Preparations for high-performance descent can include transitioning to helicopter mode if aircraft 200 was flying in airplane mode. In some aspects, preparations include reducing a speed of the proprotors of aircraft 200, for example to a minimum operating speed. The minimum operating speed is the slowest speed at which control of aircraft 200 can be safely maintained. The minimum operating speed could be the speed where the aircraft can exhibit stable and predictable flying characteristics while closely following reference states (rates, attitudes, accelerations, etc.) without extra effort from either pilot or the computer. In addition, a minimum operating speed might be limited by avoiding resonance with a structural or rotor system natural frequency. Method 100 then proceeds to step 104.
In step 104, vertical thrust generated by aircraft 200 is reduced. Vertical thrust is reduced by altering a thrust vector of one or more of proprotors 204a-204d. In some aspects, the thrust vector of proprotors 204a-204d may be altered by tilting rotor hubs 202a-202d away from the z-axis, which reduces a vertical component of the thrust vectors (i.e., the component parallel to the z-axis) of proprotors 204a-204d.
The configurations of
Referring now to
The flight control system of aircraft 200 controls the amount of vertical thrust generated by rotor hubs 202a-202d by increasing the amount of tilt of rotor hubs 202a-202d. Vertical thrust decreases as tilt angle relative to the z-axis increases. Reducing the vertical thrust of rotor hubs 202a-202d allows aircraft 200 to perform a high-performance descent as aircraft 200 descends faster than a similar aircraft that cannot reduce vertical thrust by tilting its rotor hubs. Importantly, even though vertical thrust is reduced, the minimum operating speed of each rotor hub 202a-202d of aircraft 200 is maintained. An added benefit of tilting rotor hubs 202a-202d is that the air exhausted by the proprotors is directed away from aircraft 200 to reduce the likelihood of inducing the VRS phenomenon. Thus, unlike conventional multi-rotor aircraft, aircraft 200 can perform a high-performance descent.
In addition to the configurations of
After step 104, method 100 proceeds to step 106. In step 106, aircraft 200 performs a high-performance descent. High-performance descent is used herein to describe a descent in which at least the minimum operating speed of the proprotors is maintained, but the total vertical thrust generated by aircraft 200 is reduced compared to a configuration in which rotor hubs 202a-202d are not tilted. Tilting rotor hubs 202a-202d to reduce the total vertical thrust of aircraft 200 allows aircraft 200 to descend faster than if rotor hubs 202a-202d were not tilted.
In step 108, aircraft 200 lands. In some aspects, step 108 is optional. For example, it may be desirable for aircraft 200 to make a high-performance descent maneuver to a lower altitude without landing. For example, to avoid being detected by radar or to evade an oncoming aircraft while in VTOL mode, aircraft 200 may need to make a rapid descent to drop its altitude. Aircraft 200 can make such a descent utilizing step 102-106 discussed above. After performing the high-performance descent, each rotor hub 202a-202d may be returned to its non-tilted position to resuming normal flight. After landing in step 108, method 100 ends.
Referring now to
Processor 310 executes instructions, codes, computer programs, or scripts that it might access from the network connectivity devices 320, RAM 330, ROM 340, or secondary storage 350 (which might include various disk-based systems such as hard disk, floppy disk, optical disk, or other drive). While only one processor 310 is shown, multiple processors 310 may be present. Thus, while instructions may be discussed as being executed by processor 310, the instructions may be executed simultaneously, serially, or otherwise by one or multiple processors 310. Processor 310 may be implemented as one or more CPU chips and/or application specific integrated chips (ASICs).
The network connectivity devices 320 may take the form of modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, global system for mobile communications (GSM) radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to networks. These network connectivity devices 320 may enable processor 310 to communicate with the Internet or one or more telecommunications networks or other networks from which processor 310 might receive information or to which the processor 310 might output information.
The network connectivity devices 320 might also include one or more transceiver components 325 capable of transmitting and/or receiving data wirelessly in the form of electromagnetic waves, such as radio frequency signals or microwave frequency signals. Alternatively, the data may propagate in or on the surface of electrical conductors, in coaxial cables, in waveguides, in optical media such as optical fiber, or in other media. Transceiver component 325 might include separate receiving and transmitting units or a single transceiver. Information transmitted or received by transceiver 325 may include data that has been processed by processor 310 or instructions that are to be executed by processor 310. Such information may be received from and outputted to a network in the form, for example, of a computer data baseband signal or signal embodied in a carrier wave. The data may be ordered according to different sequences as may be desirable for either processing or generating the data or transmitting or receiving the data. The baseband signal, the signal embedded in the carrier wave, or other types of signals currently used or hereafter developed may be referred to as the transmission medium and may be generated according to several methods well known to one skilled in the art.
RAM 330 might be used to store volatile data and perhaps to store instructions that are executed by processor 310. ROM 340 is a non-volatile memory device that typically has a smaller memory capacity than the memory capacity of the secondary storage 350. ROM 340 might be used to store instructions and perhaps data that are read during execution of the instructions. Access to both RAM 330 and ROM 340 is typically faster than to secondary storage 350. Secondary storage 350 is typically comprised of one or more disk drives or tape drives and might be used for non-volatile storage of data or as an over-flow data storage device if RAM 330 is not large enough to hold all working data. Secondary storage 350 may be used to store programs or instructions that are loaded into RAM 330 when such programs are selected for execution or information is needed.
I/O devices 360 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, printers, video monitors, transducers, sensors, or other well-known input or output devices. Also, transceiver 325 might be considered to be a component of I/O devices 360 instead of or in addition to being a component of the network connectivity devices 320. Some or all of the I/O devices 360 may be substantially similar to various components disclosed herein and/or may be components of any of flight control system 130 and/or other electronic systems of aircraft 10.
Depending on the embodiment, certain acts, events, or functions of any of the algorithms, methods, or processes described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms, methods, or processes). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. Although certain computer-implemented tasks are described as being performed by a particular entity, other embodiments are possible in which these tasks are performed by a different entity.
Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.
The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degreesand substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately,” “generally,” “generally in the range of,” and “about” may be substituted with “within [a percentage] of” what is specified, as understood by a person of ordinary skill in the art. For example, within 1%, 2%, 3%, 5%, and 10% of what is specified herein.
While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
