Method and controller for turn coordination of an aircraft, and an aircraft with turn coordination

Abstract

A method for controlling a aircraft with a plurality of drive units, in particular a plurality of electrical drive units, and a controller for flight control. At least one lateral control signal is entered into the controller for flight control in order to initiate a lateral movement of the aircraft. The significant point is that a speed (V) of the aircraft is ascertained through a speed estimation (6) and, depending on the estimated airspeed (V), a commanded roll angle (?.sub.C) and a commanded pitch angle (?.sub.c), a rate of turn ({dot over (?)}) is calculated. The lateral movement is automatically initiated with the calculated rate of turn ({dot over (?)}) through input of the lateral control signal.

Claims

1. A method for controlling an aircraft (1) with a plurality of drive units (2) and a controller for flight control (3), the method comprising: entering at least one lateral control signal into the controller (3) in order to initiate a lateral movement of the aircraft (1); ascertaining a speed of the aircraft through an airspeed estimation (6) based on a commanded pitch angle (?.sub.C) and in dependence on a drag coefficient (c.sub.W, c.sub.w); depending on the estimated airspeed (V) and a commanded roll angle (?.sub.C), calculating a rate of turn ({dot over (?)}); and automatically initiating the lateral movement with the calculated rate of turn ({dot over (?)}) through input of the at least one lateral control signal, wherein the calculated rate of turn ({dot over (?)}) is zero below a first threshold speed (V.sub.0) for the airspeed (V), so that an exclusively translatory movement is initiated.

2. The method as claimed in claim 1, further comprising, at the airspeed (V) between the first threshold speed (V.sub.0) and a second threshold speed (Vcoor), ascertaining a reduced rate of turn ({dot over (?)}) for a coordinated turning flight depending on the first threshold speed (V.sub.0) and the second threshold speed (Vcoor) in order not to exceed a permitted rate of turn threshold of the aircraft.

3. The method as claimed in claim 2, further comprising initiating the lateral movement of the aircraft in coordinated turning flight with the calculated rate of turn ({dot over (?)}) when the airspeed (V) exceeds the second threshold speed (Vcoor).

4. The method as claimed in claim 2, wherein the calculated rate of turn ({dot over (?)}) is calculated based on the following formula $\stackrel{?}{?}=c\frac{g\tan \left({?}_c\right)}{V\cos \left({?}_c\right)},c=\{\begin{array}{cc}0& \mathrm{if}V<V_0\\ \frac{V-V_0}{V_{coor}-V_0}& \mathrm{else}\mathrm{if}V<V_{\mathrm{coor}}\\ 1& \mathrm{else}\end{array}$ wherein ?.sub.c is a commanded pitch angle, ?.sub.c is the commanded roll angle, g is a specific vertical thrust force, and c is a rate of turn coefficient that is ascertained depending on the estimated airspeed V.

5. The method as claimed claim 1, further comprising changing the calculated rate of turn through offsetting with an external input ({dot over (?)}.sub.c).

6. The method as claimed claim 5, wherein the external input ({dot over (?)}.sub.c) is at least one of a manual input by a pilot (8) of a rate of turn correction or a target value for the rate of turn.

7. A controller (3) for the flight control of an aircraft (1) with a plurality of drive units (2), the controller (3) being configured to receive at least one lateral control signal in order to initiate a lateral movement of the aircraft (1), and the controller (3) being further configured to ascertain a speed (V) of the aircraft through a speed estimation based on a commanded pitch angle (?.sub.C) and in dependence on a drag coefficient (c.sub.W, c.sub.w), to calculate a calculated rate of turn ({dot over (?)}) depending on the estimated airspeed (V) and a commanded roll angle (?.sub.C), and to automatically initiate the lateral movement with the ascertained, calculated rate of turn through the input of the lateral control signal, wherein the calculated rate of turn ({dot over (?)}) is zero below a first threshold speed (V.sub.0) for the airspeed (V), so that an exclusively translatory movement is initiated.

8. The controller as claimed in claim 7, wherein the controller is configured such that at least one of a rate of turn correction and/or a target value for the rate of turn ({dot over (?)}.sub.c) is enterable through manual input in order to change the calculated rate of turn ({dot over (?)}).

9. The controller as claimed in claim 7, wherein the controller (3) is configured without sensors for measuring the speed.

10. A vertical takeoff and landing aircraft (1), comprising a controller as claimed in claim 7.

11. The vertical takeoff and landing aircraft (1) of claim 10, further comprising a plurality of electrical drive units.

12. The vertical takeoff and landing aircraft (1) of claim 11, wherein the plurality of electrical drive units are connected to a plurality of rotors.

13. The vertical takeoff and landing aircraft (1) of claim 12, wherein the rotors are essentially arranged in one plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further preferred features and forms of embodiment of the method according to the invention and of the controller according to the invention, as well as of the aircraft according to the invention, are explained below with reference to exemplary embodiments and to the figures. The exemplary embodiments and the quoted dimensions are merely advantageous embodiments of the invention, and are not restrictive.

(2) Here:

(3) FIG. 1 shows a side view of a multicopter;

(4) FIG. 2 shows a front view of the multicopter during the turning flight;

(5) FIG. 3 shows a plan view of the multicopter during a turning flight;

(6) FIG. 4 shows a graph of the curve of a calculated rate of turn depending on an estimated airspeed and a roll angle of the aircraft; and

(7) FIG. 5 shows a flow diagram for performing the method for lateral control of the aircraft.

DETAILED DESCRIPTION

(8) FIG. 1 shows an aircraft, in the present case a multicopter 1, with electrical drive units 2, of which, for the sake of clarity, only two are given corresponding reference signs. The multicopter 1 comprises a flight control computer (FCC) 3 that is connected for signaling with the drive units 2 and an input device (not shown).

(9) With a commanded pilot input for maneuvering the multicopter 2 entered in the input device, the pilot input is communicated as a control signal to the FCC 3. On the basis of the control signal, the FCC 3 ascertains a thrust distribution for the drive units 2, so that the multicopter 1 performs a movement corresponding to the commanded pilot input.

(10) To set a forward flight with a speed vector V, the pilot commands a negative pitch angle ?? to the FCC 3. By setting a corresponding thrust distribution at the drive units 2, the multicopter pitches. As a result, a total thrust generated by the drive units 2 is split in terms of its angular components into a specific vertical thrust component g and a horizontal component ?g tan(?). The specific vertical thrust component g is aligned against a weight (not shown).

(11) The air drag is opposed to the speed vector of the aircraft, and leads to the multicopter 1 being braked. c.sub.wV.sup.2 is an approximation for the air drag, wherein c.sub.w is an individual, specific, air drag coefficient, and V corresponds to the amplitude of the speed vector. By balancing the forces in the horizontal direction according to the dAlembert principle, the following movement equation results for the multicopter:

(12) $\stackrel{?}{V}=-g\tan \left({?}_c\right)-{\stackrel{?}{c}}_{W}V.Math.V.Math.\mathrm{where}-\frac{?}{2}<{?}_c<\frac{?}{2}$

(13) {dot over (V)} here corresponds to the estimated acceleration, V to the estimated airspeed, c.sub.w to the specific air drag coefficient, g to the specific vertical thrust component, and ?.sub.c to the commanded pitch angle. The solution of the equation is found in the FCC 3 through a numerical solution method in order to ascertain the estimated airspeed V.

(14) FIG. 2 shows the multicopter 1 viewed from the front during a turning flight. The multicopter 1 is the same one as is also shown in FIG. 1.

(15) In order to carry out a lateral movement, a lateral signal in the form of a commanded roll angle ?.sub.c (not shown) is entered into the FCC of the multicopter 1 by the pilot (not shown). On the basis of the commanded roll angle ?.sub.c, a shift distribution for the drive units 2 is ascertained in the FCC, through which the actual roll angle ? of the multicopter 1 is changed, and thereby also the direction along which a specific total thrust S=g/cos(?)/cos(?) of the multicopter 1 acts. Taking the vertical thrust component into account, the horizontal component of the total thrust S is then g tan(?)/cos(?).

(16) The centrifugal force {dot over (?)}V is opposed to the horizontal component g tan(?)/cos(?). {dot over (?)} here is the rate of turn of the multicopter 1 when flying the curve through an angle of turn ?.

(17) The following equation, which describes the force relationship in coordinated turning flight, results from balancing the forces in the horizontal direction.

(18) $\stackrel{?}{?}V=\frac{g\tan \left(?\right)}{\cos \left(?\right)}$

(19) FIG. 3 shows a plan view of the multicopter 1 during a turning flight. The multicopter 1 is the same one as is also shown in FIGS. 1 and 2.

(20) A curved path 5 is flown along by adjusting a roll angle in accordance with FIG. 2. A part of an angle ? is passed through here by the multicopter 1, wherein the movement of the multicopter 1 is described by the rate of turn {dot over (?)}. The centrifugal force {dot over (?)} V results from the rate of turn ? and from the speed V, which is oriented tangentially to the flight curve 5.

(21) A known effect during turning flight is known as slipping, wherein the multicopter 1 is pushed out of the flight curve 5. Slipping arises as a result of transverse forces which, in the illustrated exemplary embodiment, are compensated for through an appropriate control of the drive units of the multicopter 1. In the multicopter 1 shown, the regulation takes place through adjusting the rate of turn of the aircraft. This cannot, however, be changed arbitrarily, since the multicopter 1 has a rate of turn threshold. This maximum permissible rate of turn is stored as a threshold value in the FCC and is taken into account during flight when adjusting permissible orientations of the multicopter.

(22) If equation

(23) $\stackrel{?}{?}V=\frac{g\tan \left(?\right)}{\cos \left(?\right)}$

(24) is rearranged for {dot over (?)}, it will be seen that the rate of turn {dot over (?)} at low airspeeds V rises correspondingly, and during slow turning flights therefore cannot necessarily always be readjusted quickly enough taking the rate of turn threshold into account. Threshold values are therefore stored in the FCC of the multicopter 1, with which the coordination of the turning flight takes place giving consideration to the airspeed.

(25) The calculation of the rate of turn {dot over (?)}.sub.coor takes place on this basis with:

(26) $\stackrel{?}{?}=c\frac{g\tan \left({?}_c\right)}{V\cos \left({?}_c\right)},c=\{\begin{array}{cc}0& \mathrm{if}V<V_0\\ \frac{V-V_0}{V_{coor}-V_0}& \mathrm{else}\mathrm{if}V<V_{\mathrm{coor}}\\ 1& \mathrm{else}\end{array}$

(27) V.sub.0 here is a lower first threshold speed, below which the aircraft does not carry out a turning movement, but a purely lateral translational movement. In the calculation of the rate of turn, this is reflected by the coefficient c, which is set to zero when the speed falls below the first threshold speed, as stated. V.sub.coor is an upper second threshold speed.

(28) If the estimated airspeed V.sub.est lies between the first threshold speed V.sub.0 and the second threshold speed V.sub.coor, the required rate of turn in the coordinated turning flight {dot over (?)} is calculated in such a way that the maximum permissible rate of turn threshold is not exceeded. The difference between the estimated airspeed V.sub.est and the first threshold speed V.sub.0 is set in relation to the difference between the second threshold speed V.sub.coor and the first threshold speed V.sub.0 to calculate the coefficient c. As a result, the rate of turn {dot over (?)} is reduced in such a way that the rate of turn threshold, and thereby a yaw rate threshold that may correspond to it, is not exceeded. The magnitudes of the first threshold speed V.sub.0 and the second threshold speed V.sub.coor are ascertained for the multicopter through experiment and simulation.

(29) If, however, a rate of turn is calculated during the turning flight at which the rate of turn lies below the permissible rate of turn threshold, it is possible to offset the ascertained rate of turn with a directional pilot specification {dot over (?)}.sub.c. The reference variable resulting from this is {dot over (?)}.sub.des={dot over (?)}.sub.c+{dot over (?)}.

(30) The way in which the coordination of the flight is realized depending on the airspeed Vis shown with reference to a graph according to FIG. 4.

(31) The estimated airspeed V is plotted on the horizontal axis of the illustrated graph, while the vertical axis indicates the rate of turn {dot over (?)} to be ascertained. The first threshold speed V.sub.0 and the second threshold speed V.sub.coor divide the region of the horizontal axis into a first speed region I, a second speed region II and a third speed region III.

(32) If one of five exemplary roll angles ?.sub.1, ?.sub.2, ?.sub.3, ?.sub.4, ?.sub.5 is commanded for a turning flight, where ?.sub.1<?.sub.2<?.sub.3<?.sub.4<?.sub.5 applies, then the equation

(33) $\stackrel{?}{?}=c\frac{g\tan \left({?}_c\right)}{V\cos \left({?}_c\right)},c=\{\begin{array}{cc}0& \mathrm{if}V<V_0\\ \frac{V-V_0}{V_{coor}-V_0}& \mathrm{else}\mathrm{if}V<V_{\mathrm{coor}}\\ 1& \mathrm{else}\end{array}$

(34) yields the automatically calculated rate of turn {dot over (?)}, which is used both for a pure translatory movement as well as for a coordinated turning flight. If the calculated rate of turn {dot over (?)}.sub.coor lies below a maximum rate of turn threshold {dot over (?)}.sub.max, at which the rate of turn threshold of the aircraft is not exceeded, the rate of turn can be increased by changing the roll angle, in that the roll angle is increased, for example, from ?.sub.1 to ?.sub.2.

(35) FIG. 5 shows an exemplary embodiment of a schematic method flow for lateral control of the aircraft, according to which the controller is implemented in the FCC of the multicopter according to FIGS. 1-3. The exemplary embodiment shown contains a speed estimation 6 that is obtained on the basis of the solution to the differential equation of motion

(36) 0$\stackrel{?}{V}=-g\tan \left({?}_c\right)-{\stackrel{?}{c}}_{W}V.Math.V.Math.\mathrm{where}-\frac{?}{2}<{?}_c<\frac{?}{2}.$

(37) The speed is ascertained for this purpose on the basis of the air drag coefficient c.sub.w and the commanded pitch angle ?.sub.c. The estimated airspeed V resulting from this is used to calculate the rate of turn in a rate of turn calculation 7 that corresponds to the description of FIG. 4. A rate of turn {dot over (?)}, which can be adjusted by a directional input {dot over (?)}.sub.c of a pilot 8, is yielded by this. An overwritten rate of turn {dot over (?)}.sub.des, with which the multicopter is controlled, is found as a result.