There is a coupling between airspeed and climb-rate during longitudinal motion of an aircraft, wherein changes in one flight characteristic impacts the other characteristic. In other words, a change in airspeed indirectly causes a change in climb-rate and vice versa. Single rotary wing aircraft use the main rotor assembly to provide both altitude adjustment and airspeed adjustment. Co-axial rotary wing aircraft with a pusher-propeller, however, can also use the separate pusher-propeller to adjust airspeed. Accordingly, this type of aircraft often includes separate airspeed and climb-rate controllers. In this type of configuration, the aircraft may use the pitch altitude to control airspeed and main rotor thrust to control altitude when traveling at low speeds and may use the pusher-propeller to control air speed and the main rotor thrust to control altitude when traveling at high speeds. This separate single-input, single output control functionality, however, ignores the coupling between air speed and climb-rate, which can impact tight response control needed for many high-speed aircraft maneuvers, such as, for example, terrain masking through Nap-of-the-Earth (NOE) flight (e.g., flight at less than approximately 10 meters above ground level).
Accordingly, embodiments described herein provide a dynamic-inversion based technique to simultaneously control airspeed and climb-rate of a co-axial rotary wing aircraft with a pusher-propeller. The multi-input, multi-output control law can be designed independent of inner-loop dynamics (e.g., as long as sufficient time-scale separation exists between the inner-loop (controlling pitch, roll, and yaw of the aircraft) and the outer-loop (see, e.g.,
For example, some embodiments provide, among other things, a system for controlling an aircraft including a co-axial main rotor assembly and a pusher-propeller. The system includes an electronic controller configured to receive a reference velocity of the aircraft and receive a reference flight path angle of the aircraft. The electronic controller is also configured to simultaneously control the co-axial main rotor assembly and the pusher-propeller based on the reference velocity of the aircraft and the reference flight path angle of the aircraft, by simultaneously generating a commanded thrust of the pusher-propeller and a commanded thrust of the co-axial main rotor assembly using a multiple input, multiple output algorithm applying dynamic inversion.
Another embodiment provides a method of controlling an aircraft including a co-axial main rotor assembly and a pusher-propeller. The method includes receiving, with an electronic controller, a reference velocity of the aircraft, and receiving, with the electronic controller, a reference flight path angle of the aircraft. The method further includes simultaneously controlling, with the electronic controller, the co-axial main rotor assembly and the pusher-propeller based on the reference velocity of the aircraft and the reference flight path angle of the aircraft by simultaneously generating a commanded thrust of the pusher-propeller and a commanded thrust of the co-axial main rotor assembly using a multiple input, multiple output algorithm applying dynamic inversion.
A further embodiment provides non-transitory computer readable medium storing instructions, executable by an electronic processor, to perform a set of functions. The set of functions including simultaneously controlling a co-axial main rotor assembly and a pusher-propeller of an aircraft based on a reference velocity of the aircraft and a reference flight path angle of the aircraft using a multiple input, multiple output algorithm applying dynamic inversion. Simultaneously controlling the co-axial main rotor assembly and the pusher-propeller can include applying a reference model to the reference velocity and the reference flight path angle to generate a commanded velocity of the aircraft and a commanded flight path angle of the aircraft, applying desired dynamics to the commanded velocity of the aircraft and the commanded flight path angle of the aircraft to generate a rate of change of a desired velocity of the aircraft and a rate of change of a desired flight path angle of the aircraft, and applying dynamic inversion to the rate of change of the desired velocity of the aircraft and the rate of change of the desired flight path angle of the aircraft to generate a commanded thrust of pusher-propeller and a commanded thrust of the co-axial main rotor assembly.
Other aspects and embodiments will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments are explained in detail, it is to be understood that the disclosure is not intended to be limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. Embodiments are capable of other configurations and of being practiced or of being carried out in various ways.
A plurality of hardware and software-based devices, as well as a plurality of different structural components may be used to implement various embodiments. In addition, embodiments may include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if most of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software (for example, stored on non-transitory computer-readable medium) executable by one or more electronic processors. For example, “control units” and “controllers” described in the specification can include one or more electronic processors, one or more memory modules including non-transitory computer-readable medium, one or more input/output interfaces, one or more application specific integrated circuits (ASICs), and various connections (for example, a system bus) connecting the various components.
It also should be understood that although certain drawings illustrate hardware and software located within particular devices, these depictions are for illustrative purposes only. In some embodiments, the illustrated components may be combined or divided into separate software, firmware and/or hardware. For example, instead of being located within and performed by a single electronic processor, logic and processing may be distributed among multiple electronic processors. Regardless of how they are combined or divided, hardware and software components may be located on the same computing device or may be distributed among different computing devices connected by one or more networks or other suitable communication links.
Referring now to the figures,
The main rotor assembly 18 is driven by a power source, such as, for example, one or more motors 24 via a main rotor gearbox 26. The one or more motors 24 can include an electric motor, a piston engine, a gas turbine, or other device for providing motion.
The main rotor assembly 18 includes an upper rotor assembly 28 driven in a first direction (e.g., counter-clockwise) about the main rotor axis A, and a lower rotor assembly 32 driven in a second direction (e.g., clockwise) about the main rotor axis A, wherein the second direction is opposite to the first direction (i.e., to provide two counter rotating rotors). The upper rotor assembly 28 includes a first plurality of rotor blades 38 supported by a first rotor hub 39. The lower rotor assembly 32 includes a second plurality of rotor blades 34 supported by a second rotor hub 36. As illustrated in
In some embodiments, the pusher-propeller 40 (i.e., the propeller 42) is connected to and driven by the one or more motors 24 via a propeller gearbox 46. In some embodiments, the propeller gearbox 46 is driven by the main rotor gearbox 26, and the propeller gearbox 46 can be configured to change a gear ratio between the main rotor gearbox 26 and the propeller gearbox 46 to vary, on command, the relative speeds between the main rotor gearbox 26 and the propeller gearbox 46. In such embodiments, the variable gear ratio of the propeller gearbox 46 controls power transmitted from the main rotor gearbox 26 to the propeller gearbox 46. Other configurations for controlling the pusher-propeller 40 are possible, such as, for example, using an engine or power source to drive the pusher-propeller 40 that is separate from the engine or power source used to power the main rotary assembly 18.
As also illustrated in
The electronic processor 72 is communicatively connected to the memory 74 and the input-output interface 76. In some embodiments, the memory 74 stores software 75 executable by the electronic processor 72 to perform the control functionality and associated methods described herein. It should be understood that the electronic controller 70 can include other components, and the configuration illustrated in
In some embodiments, the aircraft 10 also includes a plurality of sensors (not shown). Each sensor generates a signal representing a measured operating characteristic of the aircraft 10 (e.g., altitude, airspeed, etc.) and transmits the signal to the electronic controller 70 (directly or indirectly). The electronic controller 70 receives such signals via the input-output interface 76 and these signals can be used as part of the control functionality performed by the electronic processor 72 (through execution of the software 75). These received signals (or data derived therefrom) can also be stored in the memory 74.
As noted above, the electronic controller 70 applies a multivariate (i.e., multi-input, multi-output) control law to simultaneously control airspeed (i.e. velocity) and climb-rate (i.e., flight path angle) of the aircraft 10. This control law is developed using flight path dynamics. For example, the dynamics of the flight path using a point mass model of the aircraft 10 can be expressed as Equations (1), (2), and (3):
Where V is the airspeed, χ is the course angle (defined in degrees from north), γ is the flight path angle, θ is the pitch angle, μ is the aerodynamic roll angle, D is the drag force, g is gravity, and m is the mass of the aircraft 10. Tp is the pusher-propeller thrust and Tr is the main rotor thrust as illustrated in
Variables Tx and Tz can be defined in Equations (4) and (5) below to simplify the above equations:
Tx=Tp cos(θ−γ)−Tr sin(θ−γ) (4)
Tz=Tp sin(θ−γ)+Tr cos(θ−γ) (5)
In particular, Equations (4) and (5) allow Equations (1), (2), and (3) to be written as Equations (6), (7), and (8) below:
Under the assumption that time-scale separation exists between the path dynamics and the roll and pitch inner-loop dynamics, Equations (6), (7), and (8) illustrate that velocity and flight path angle dynamics are highly coupled. Accordingly, as described below, the electronic controller 70 uses this coupling to provide a multivariate control law for the aircraft 10.
For example, the electronic controller 70, as part of the dynamic inversion module 350, determines a thrust of main rotor assembly 18 and a thrust of the pusher-propeller 40 by inverting the path dynamics equations. In particular, Tz (Equation 9) can be obtained by inverting Equations (7) and (16) (defined below):
Similarly, Tx (Equation 10) can be obtained by inverting Equation (6):
Tx=m({dot over (V)}des+g sin γ) (10)
Drag force has been omitted from the above dynamic inversion. Aerodynamic drag is typically difficult to model. Thus, drag has been treated as a disturbance force and, for this simplification, the drag disturbance force is removed by the electronic controller 70 via an augmented integrator described below with respect to the desired dynamics module 322.
After Tx and Tz are determined by the electronic processor 72, the electronic processor 72 determines a thrust Tr of the main rotor assembly 18 and a thrust Tp of the pusher-propeller 40 (Equation 11) using an inverse of Equation (5):
To obtain the desired variables {dot over (V)}des and {dot over (γ)}des via the desired dynamics module 322 (see
{dot over (y)}des=Kf{dot over (y)}ref+Kb(fcyref−y+z) (12)
ż=fiKb(yref−y) (13)
Where Kf is feedforward gain, Kb is feedback gain or bandwidth gain, fc is command gain, and fi is integral gain.
To obtain the commanded values Vcmd and γcmd via the reference model module 302, which is the input into the desired dynamics module 322, the electronic controller 70 uses a reference model. Since the path dynamics have a relative degree of one, the electronic controller 70 uses a first order reference model. Assuming ycmd the commanded signal, the reference model dynamics applied by the electronic controller 70 is defined by Equation (14) below:
{dot over (y)}Kref(ycmd−yref)−vh (14)
Where vh is a hedge signal described below and Kref is the reference model bandwidth.
With respect to the PCH module 360, PCH is used in adaptive control systems to slow down or speed up the reference model in case of input saturation. PCH can also be viewed as an anti-wind up mechanism that, instead of reducing the integrator gain, attempts to slow down the reference model in case of actuator saturation. In other words, PCH can be described conceptually as moving the reference mode backward (hedging) by an estimate of the amount the plant 355 did not move due to a saturated or rate-limited actuator. The hedge signal vh used in Equation (14) above slows down the first order reference model to the expected reaction deficit.
The equations for the hedge signals vh for flight path angle and velocity may be derived as shown below. It is to be noted that the main rotor thrust and pusher-propeller thrust is a known value which is measured, for example, directly via a sensor or obtained via a look-up table (e.g., stored by the memory 74) that relates collective and pedal commands to thrust. For example, the hedge signal for flight path angle is given by Equation (15):
{dot over (γ)}hedge={dot over (γ)}meas−{dot over ({circumflex over (γ)})} (15)
Where {dot over (γ)}meas is the measured or estimated {dot over (γ)}. Given the measured Tz (i.e., Tz,meas) the expected value for {dot over (γ)}) (i.e., {dot over ({circumflex over (γ)})}) based on the model is given by Equation (16):
Similarly, the hedge signal for velocity is set forth below by Equation (17):
{dot over (V)}hedge={dot over (V)}meas−{dot over ({circumflex over (V)})} (17)
Where {dot over (V)}meas is a measured or estimated {dot over (V)}. Given the measured Tx (i.e., Tx,meas), the expected value for {dot over (V)} (i.e., {dot over ({circumflex over (V)})}) based on the model is given by Equation (18):
Accordingly, using the above control logic and the configuration illustrated in
The flight path angle commanded signal γcmd and the velocity commanded signal Vcmd are received as input to the desired dynamics module 322, where the flight path angle commanded signal γcmd (i.e., the error signal) is multiplied by fiKb,γ and the velocity commanded signal Vcmd is multiplied by fiKb,V as described above with respect to Equations (12) and (13) (at 325). The result of this multiplication (at 325) is integrated (at 330). As illustrated in
As also illustrated in
At the dynamic inversion module 350, dynamic inversion is performed on the desired flight path angle {dot over (γ)}des and a desired velocity {dot over (V)}des. As described above with respect to Equations (9), (10), and (11), the dynamic inversion module 350 generates a commanded thrust Tr of the main rotor assembly 18 and a commanded thrust Tp of the pusher-propeller 40.
As illustrated in
In some embodiments, the actual thrust of the main rotor assembly 18, the actual thrust of the pusher-propeller 40, the actual flight path angle γ, the actual velocity V of the aircraft 10, or a combination thereof is measured at various points within the processing illustrated in
The electronic controller 70 uses the received reference velocity Vref and the reference flight path angle γref to simultaneously control the co-axial main rotor assembly 18 and the pusher-propeller 40 by generating a commanded thrust Tp of the pusher-propeller 40 and a commanded thrust Tr of the co-axial main rotor assembly 18 using a multiple input, multiple output algorithm applying dynamic inversion. As described above and illustrated in
As described above, the reference model can include a first order reference model and applying the reference model to the reference velocity and the reference flight path angle can includes applying the reference model based on a hedge signal (e.g., a hedge signal for velocity and a hedge signal for flight path angle). As also described above, the hedge signal can be generated based on a measured thrust of the co-axial main rotor assembly 18 and a measured thrust of the pusher-propeller 40, wherein the measured thrusts can be directly measured or generated via a one or more look-up tables. As also described above, the hedge signal can slow down the reference model in case of actuator saturation. As also described above with respect to the desired dynamics module 322, the desired dynamics module 322 can apply integral compensation using various gains (e.g., feedforward gain, feedback gain, bandwidth gain, command gain, integral gain, or a combination thereof).
Accordingly, embodiments described herein provide a multi-input, multi-output control logic and architecture that, using first principle modeling, simultaneously obtains main rotor assembly thrust and pusher-propeller thrust by inverting path dynamics equations. This simultaneous control provides tight altitude and airspeed response, such as for NOE flight, contour flight, and low level flight, by recognizing the coupling between airspeed (velocity) and climb-rate (flight path angle). In other words, simultaneously controlling airspeed and flight path angle via the above dynamic inversion equations by making use of both the pusher-propeller and the main rotor represents a novel control algorithm for an aircraft as compared traditional approaches where the main rotor and the pusher-propeller separately control altitude and speed, respectively.
Various features and advantages are set forth in the following claims.
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