Method for controlling rotorcraft airfoil to minimize auxiliary rotor noise and enhance rotorcraft performance

Abstract

A rotorcraft extends longitudinally along a first anteroposterior plane separating a first side from a second side of the rotorcraft. The rotorcraft includes at least one main rotor, an auxiliary rotor, and at least one steerable airfoil. The rotorcraft further includes a processor unit connected to a first measurement system configured to measure a current value of a speed parameter (V) of the rotorcraft and to a second measurement system configured to measure a current value of a power parameter (W) of a power plant of the rotorcraft. The processor unit is configured to adjust the deflection angle of the airfoil as a function of the current speed and power parameter values (V, W) to cause the auxiliary rotor to move towards at least one predetermined operating point which optimizes performance of the rotorcraft and minimizes noise generated by the auxiliary rotor.

Claims

1. A method for a rotorcraft, the rotorcraft extending longitudinally along a first anteroposterior plane (P1) separating a first side from a second side of the rotorcraft, the rotorcraft including a main rotor, an auxiliary rotor, and a power plant configured to drive the main rotor and the auxiliary rotor in rotation, wherein the auxiliary rotor is configured to exert lateral thrust in order to control yaw movement of the rotorcraft, the lateral thrust being directed towards the second side in order to counter torque generated by the main rotor on a fuselage of the rotorcraft, the rotorcraft further including a tail fin extending in elevation, wherein the tail fin is provided at least in part with a deflectable airfoil, wherein the airfoil is configured to generate transverse lift as a function of a deflection angle of the airfoil, wherein the airfoil has a trailing edge, wherein the deflection angle of the airfoil is at 0° when the trailing edge is present in a second plane (P2), wherein the deflection angle of the airfoil is negative relative to the second plane (P2) when the trailing edge is directed towards the second side, wherein the deflection angle of the airfoil is positive relative to the second plane (P2) when the trailing edge is directed towards the first side, wherein the deflection angle of the airfoil is controllable at least as a function of a current value of a speed parameter (V) of the rotorcraft and of a current value of a power parameter (W) of the power plant so as to enable the auxiliary rotor to be operated at a predetermined operating point in order to satisfy at least one of a performance target for the rotorcraft and an acoustic target for the auxiliary rotor, the method comprising: receiving a first power threshold (W1) and a second power threshold (W2), wherein the second power threshold (W2) is greater than the first power threshold (W1); receiving a first speed threshold (V1), a second speed threshold (V2), a third speed threshold (V3), and a fourth speed threshold (V4), wherein the second speed threshold (V2) is greater than the first speed threshold (V1) which is greater than the fourth speed threshold (V4) which is greater than the third speed threshold (V3); controlling the deflection angle of the airfoil to reach a first zone (Z1) for which the deflection angle of the airfoil is at a maximum positive threshold angle (δmax) relative to the second plane (P2), the first zone (Z1) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is lower than the third speed threshold (V3); controlling the deflection angle of the airfoil to reach a second zone (Z2) for which the deflection angle of the airfoil is at the maximum positive threshold angle (δmax) relative to the second plane (P2), the second zone (Z2) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is greater than the fourth speed threshold (V4) and lesser than the first speed threshold (V1) and the current value of the power parameter (W) of the power plant is greater than the second power threshold (W2); controlling the deflection angle of the airfoil to reach a third zone (Z3) for which the deflection angle of the airfoil is substantially 0° relative to the second plane (P2), the third zone (Z3) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is greater than the second speed threshold (V2) and the current value of the power parameter (W) of the power plant is greater than the second power threshold (W2); and controlling the deflection angle of the airfoil to reach a fourth zone (Z4) for which the deflection angle of the airfoil is at the minimum negative threshold angle (δmin) relative to the second plane (P2), the fourth zone (Z4) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is greater than the fourth speed threshold (V4) and the current value of the power parameter (W) of the power plant is lower than the first power threshold (W1).

2. The method according to claim 1, wherein the speed parameter (V) is selected from a list comprising an air speed and a ground speed.

3. The method according to claim 1, wherein the power plant includes at least one engine and a main gearbox interposed between the at least one engine and the main rotor, the method further comprising: selecting the power parameter from a list comprising: total power developed by the at least one engine; total torque generated by the at least one engine; power transmitted to the main gearbox; torque transmitted to the main gearbox; and torque exerted on a mast driving the main rotor.

4. The method according to claim 1, wherein the second plane (P2) is inclined relative to the first anteroposterior plane (P1) so that the second plane (P2) presents a positive angle relative to the first anteroposterior plane (P1), the trailing edge being directed towards the first side when the airfoil is present in the second plane (P2).

5. The method according to claim 1, further comprising using a relationship (L) in controlling the deflection of the airfoil, the relationship (L) providing a target angle (δ) for the deflection angle of the airfoil as a function of the speed parameter (V) of the rotorcraft and of the power parameter (W) of the power plant.

6. The method according to claim 5, wherein the auxiliary rotor has a plurality of blades, wherein the first zone (Z1), the second zone (Z2), the third zone (Z3) and the fourth zone (Z4) define a first sheet, the method further comprising: determining a maximum angle for the target angle in the application of the relationship (L) to define an upper sheet that is different from the first sheet; determining a minimum angle for the target angle in the application of the relationship (L) to define a lower sheet that is different from the first sheet and the upper sheet; measuring the current collective pitch of the blades of the auxiliary rotor; increasing the deflection angle of the airfoil by causing the deflection angle of the airfoil to move towards the maximum angle so long as the collective pitch is greater than a predetermined setpoint collective pitch, the deflection angle of the airfoil being limited to be less than or equal to the maximum angle; decreasing the deflection angle of the airfoil by causing the deflection angle of the airfoil to move towards the minimum angle so long as the collective pitch is less than the predetermined setpoint collective pitch, the deflection angle of the airfoil being limited to be greater than or equal to the minimum angle; and automatically modifying the collective pitch in parallel with modifying the deflection angle of the airfoil.

7. The method according to claim 6, wherein the rotorcraft includes means for controlling the collective pitch manually, and modification to the deflection angle of the airfoil is inhibited whenever a pilot is operating the control means.

8. A rotorcraft comprising: a fuselage extending longitudinally along a first anteroposterior plane (P1) separating a first side from a second side of the rotorcraft; a main rotor; an auxiliary rotor; a power plant configured to drive the main rotor and the auxiliary rotor in rotation; wherein the auxiliary rotor is configured to exert lateral thrust that is controllable in order to control yaw movement of the rotorcraft, the lateral thrust being directed towards the second side in order to counter torque generated by the main rotor on the fuselage of the rotorcraft; a tail fin extending in elevation and provided at least in part with a deflectable airfoil of controllable deflection, wherein the airfoil is configured to generate transverse lift as a function of a deflection angle of the airfoil, wherein the airfoil has a trailing edge, wherein the deflection angle of the airfoil is at 0° when the trailing edge is present in a second plane (P2), negative relative to the second plane (P2) when the trailing edge is directed towards the second side, and positive relative to the second plane (P2) when the trailing edge is directed towards the first side; a processor unit configured receive a first power threshold (W1) and a second power threshold (W2), wherein the second power threshold (W2) is greater than the first power threshold (W1); the processor unit configured to receive a first speed threshold (V1), a second speed threshold (V2), a third speed threshold (V3), and a fourth speed threshold (V4), wherein the second speed threshold (V2) is greater than the first speed threshold (V1) which is greater than the fourth speed threshold (V4) which is greater than the third speed threshold (V3); the processor unit connected to mover means for causing the airfoil to pivot, the processor unit being connected to a first measurement system configured to measure a current value of a speed parameter (V) of the rotorcraft and to a second measurement system configured to measure a current value of a power parameter (W) of the power plant, the processor unit configured to cause the airfoil to pivot to: a first zone (Z1) for which the deflection angle of the airfoil is at a maximum positive threshold angle (δmax) relative to the second plane (P2), the first zone (Z1) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is lower than the third speed threshold (V3); a second zone (Z2) for which the deflection angle of the airfoil is at the maximum positive threshold angle (δmax) relative to the second plane (P2), the second zone (Z2) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is greater than the fourth speed threshold (V4) and lesser than the first speed threshold (V1) and the current value of the power parameter (W) of the power plant is greater than the second power threshold (W2); a third zone (Z3) for which the deflection angle of the airfoil is substantially 0° relative to the second plane (P2), the third zone (Z3) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is greater than the second speed threshold (V2) and the current value of the power parameter (W) of the power plant is greater than the high second power threshold (W2); and a fourth zone (Z4) for which the deflection angle of the airfoil is at the minimum negative threshold angle (δmin) relative to the second plane (P2), the fourth zone (Z4) being reached by the deflection angle of the airfoil when the current value of the speed parameter (V) of the rotorcraft is greater than the fourth speed threshold (V4) and the current value of the power parameter (W) of the power plant is lower than the first power threshold (W1).

9. The rotorcraft according to claim 8, wherein the tail fin is one of a tail fin constituted entirely by the airfoil, a stationary tail fin provided with at least one movable control surface representing the airfoil, or a movable tail fin having at least one movable control surface together representing the airfoil.

10. The rotorcraft according to claim 8, wherein the second plane (P2) presents a positive angle relative to the first anteroposterior plane, the trailing edge being directed towards the first side when the airfoil is present in the second plane.

11. The rotorcraft according to claim 8, wherein the airfoil has a positive camber presenting a cambered face directed towards the second side.

12. The rotorcraft according to claim 8, wherein the auxiliary rotor includes a plurality of blades, wherein the rotorcraft includes manual control means for controlling the collective pitch of the blades of the auxiliary rotor, and the control means are in communication with the processor unit.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the following description of embodiments given by way of illustration and with reference to the accompanying figures, in which:

(2) FIG. 1 is a diagram of an aircraft of the invention;

(3) FIG. 2 is a diagram showing a stationary tail fin carrying a movable airfoil;

(4) FIG. 3 is a diagram showing a movable tail fin;

(5) FIG. 4 is a diagram showing a cambered airfoil;

(6) FIG. 5 is a diagram explaining the positioning of a movable airfoil having a positive deflection angle or a negative deflection angle;

(7) FIG. 6 is a diagram showing a first implementation; and

(8) FIG. 7 is a diagram showing a second implementation.

DETAILED DESCRIPTION OF THE INVENTION

(9) Elements present in more than one of the figures are given the same references in each of them.

(10) FIG. 1 shows a rotorcraft 1 having a fuselage 2. The fuselage 2 extends longitudinally along an anteroposterior plane of symmetry P1 from a nose 3 to a tail 4. The fuselage 2 also extends transversely from a first side 6 to a second side 7.

(11) The fuselage 2 also has at least one main rotor 5 providing at least part of the lift and possibly also the propulsion of the rotorcraft 1.

(12) The main rotor 5 has a plurality of blades performing rotary motion in a first direction S1. During this movement, one blade usually referred to as a “retreating” blade moves from the first side 6 towards the second side 7. Conversely, a blade usually referred to as the “advancing” blade moves from the second side 7 towards the first side 6.

(13) This rotary motion of the main rotor gives rise to rotor torque in yaw on the fuselage 2 in a second direction S2 opposite to the first direction S1. The rotor torque then tends to change the yaw angle of the rotorcraft.

(14) Under such conditions, the rotorcraft has at least one auxiliary rotor 10 for controlling the yaw movements of the rotorcraft.

(15) The auxiliary rotor 10 is usually arranged at one of the longitudinal ends of the rotorcraft. Thus, the auxiliary rotor is arranged at the tail 4 of the rotorcraft, and in particular in a tail fin 20.

(16) The auxiliary rotor may be an unducted rotor as shown in FIG. 1, or it may be a ducted rotor.

(17) The auxiliary rotor 10 then generates lateral thrust 100. This lateral thrust 100 may be controlled using conventional control means 50, such as pedals.

(18) In order to oppose the rotor torque, the lateral thrust is referred to as “positive” thrust 101, this positive thrust being directed towards the second side 7. The auxiliary rotor may also exert negative thrust 102 directed towards the first side 6.

(19) In order to drive the main rotor 5 and the auxiliary rotor 10, the rotorcraft includes a power plant 90. The power plant 90 has at least one engine 91 and a main gearbox 92 that is interposed between the main rotor 5 and at least one engine 91.

(20) The rotorcraft 1 also has a tail fin comprising at least in part a movable airfoil 25 that can be pivoted to generate adjustable transverse thrust 111, 112.

(21) This airfoil 25 extends in elevation in a substantially vertical plane that presents an angle relative to the first plane P1.

(22) In the variant of FIGS. 1 and 2, the rotorcraft 1 presents a stationary tail fin 20. The airfoil 25 then comprises a control surface 26 hinged to the stationary tail fin in order to represent said airfoil.

(23) In the variant of FIG. 3, the rotorcraft has an airfoil comprising a movable tail fin. The tail fin is movable as a whole and represents said airfoil.

(24) In a variant that is not shown, the rotorcraft has an airfoil including a movable tail fin, itself carrying a movable control surface.

(25) In addition, and with reference to FIG. 4, the airfoil 25 may optionally include positive camber, the airfoil 25 presenting a cambered face 29 facing the second side 7.

(26) Independently of the variant and with reference to FIG. 1, the airfoil 25 presents a deflection angle 200 that is zero when a reference chord of the airfoil 25 lies in a second plane P2. The airfoil is then in a middle position, and it may be deflected on either side of this middle position.

(27) It can be understood that the manufacturer can perform tests or simulations to determine the appropriate amount of lift to be delivered when the airfoil is in the middle position so as to be located in the second plane P2.

(28) The deflection angle is measured relative to a second plane P2. This second plane P2 may coincide with the first plane P1. Nevertheless, the second plane P2 may present a positive angle 300 relative to the first plane P1, as in the variant shown.

(29) The airfoil may then be moved in order to present a deflection angle relative to the second plane P2.

(30) By convention, the airfoil 25 presents a positive deflection angle when its trailing edge 27 moves away from the second plane P2 so as to be situated on the first side 6 of the rotorcraft, i.e. on the right-hand side of the second plane in FIG. 1. Conversely, the airfoil 25 presents a negative deflection angle when its trailing edge 27 moves away from the second plane P2 so as to be situated on the second side 7 of the rotorcraft, i.e. on the left-hand side of the second plane in FIG. 1.

(31) In order to control the deflection angle, the rotorcraft 1 has a processor unit 30 that is connected to mover means 35 for causing the airfoil 25 to pivot.

(32) The mover means 35 may comprise a hydraulic valve 36 communicating with the processor unit, and a hydraulic actuator 37 connected to the hydraulic valve 36 and to the airfoil 25. Alternatively, and by way of example, the mover means may comprise an electronic controller controlling an electromechanical actuator.

(33) The processor unit 30 may include a processor 31 executing information stored in a non-volatile memory 32 for controlling the mover means.

(34) Consequently, the processor unit 30 is connected to a first measurement system 41 for measuring a current value of a speed parameter V of the rotorcraft 1 and to a second measurement system 42 for measuring a current value of a power parameter W of the power plant 90.

(35) The speed parameter V is selected from a list comprising at least: an air speed and a ground speed.

(36) Furthermore, the power parameter is selected from a list comprising at least: total power developed by the engines 91 of the power plant; total torque generated by the engines 91 of the power plant; power transmitted to the main gearbox 92; torque transmitted to the main gearbox 92; and torque exerted on a mast 93 for driving the main rotor.

(37) Depending on the method applied, the deflection angle of the airfoil is controlled with the help of the processor unit 30 and the mover means 35 as a function of a current value of a speed parameter V measured using the first measurement system and of a current value of a power parameter W measured using the second measurement system.

(38) FIG. 5 explains the operation of the rotorcraft and the method that is applied.

(39) According to the invention, the airfoil 25 is placed at a large negative deflection angle, e.g. during a stage of descending flight with the rotorcraft flying at high speed or in auto-rotation. A negative deflection angle is represented by the airfoil drawn in dashed lines.

(40) With a negative deflection angle, the airfoil tends to reduce the lateral lift generated by the tail fin, as represented by vector 111″. The vector 111″ of this lateral thrust is directed towards the second side 7 and is short in length, and it may potentially be directed towards the first side in the event of thrust becoming negative. Conversely, the airfoil 25 is placed at a positive deflection angle 200 during a climbing stage of flight. A positive deflection angle is represented by the airfoil drawn in continuous lines.

(41) With a positive deflection angle, the airfoil tends to increase the lateral lift generated by the tail fin by directing it towards the second side 7 in order to counter the rotor torque. More precisely, the vector 111′ of this lateral thrust is directed towards the second side 7 and presents a length that is considerable. It is also possible to position the airfoil 25 at a small negative deflection angle during a stage of descending flight with the rotorcraft at low speed.

(42) Furthermore, a first adjustment zone Z1 is defined in which the deflection angle is at a maximum and reaches a positive threshold angle δmax. This first zone Z1 is reached at a forward speed less than a speed referred to as a “third” speed V3.

(43) In addition, a second zone Z2 is defined at which the deflection angle 200 is at a maximum and reaches a positive threshold angle δmax. This second zone Z2 is reached when the following two conditions are satisfied:

(44) the forward speed of the rotorcraft is an intermediate forward speed lying between the third speed V3 and a “first” speed V1 that is greater than the third speed V3; and

(45) the power developed by the power plant is high, being greater than a “second” power W2.

(46) The processor unit then positions the airfoil at this positive threshold angle δmax when the rotorcraft is flying in the first zone Z1 or the second zone Z2.

(47) A third zone Z3 is also defined in which the deflection angle 200 is equal to a medium deflection, this third zone Z3 being reached at a high forward speed at high power. This medium deflection is close to zero, e.g. lying in the range minus 5 degrees to plus 5 degrees, and may possibly be equal to zero.

(48) The processor unit then positions the airfoil at a medium orientation close to zero when the following two conditions are satisfied:

(49) the forward speed of the rotorcraft is faster than a second speed V2 that is faster than the first speed V1; and

(50) the power developed by the power plant is greater than the second power W2.

(51) A fourth zone Z4 is also defined in which the deflection angle 200 is small, reaching a negative threshold value δmin. This fourth zone Z4 is reached at a high forward speed and at low power developed by the power plant.

(52) The processor unit then positions, the airfoil at a negative threshold value δmin when the following two conditions are satisfied:

(53) the forward speed of the rotorcraft is faster than a fourth speed V4 lying between the first speed V1 and the third speed V3; and

(54) the power developed by the power plant is less than the first power W1.

(55) By way of example, the processor unit controls the deflection of the airfoil 25 using a relationship L giving a target angle for the airfoil 25 as a function of the speed parameter V of the rotorcraft 1 and of the power parameter W. This relationship L may possibly correspond to the following equations:

(56) ${\delta }_1=\{\begin{array}{c}V<V_1->{\delta }_{\mathrm{ma}x}\\ \begin{array}{c}{V}_1\le V<V_2->\left[\mathrm{sw}\right].Math.\left(A.Math.V+B\right)+\\ \left[{\delta }_{\mathrm{ma}x}-\left[\mathrm{sw}\right].Math.\left(A.Math.V+B\right)\right].Math.\left\{1-{\left[\sin \left(\frac{\pi }{2}.Math.\frac{V-V_1}{V_2-V_1}\right)\right]}^2\right\}\end{array}\\ V_2\le V->\left[\mathrm{sw}\right].Math.\left(A.Math.V+B\right)\end{array}{\delta }_2=\{\begin{array}{c}W<W_1->{\delta }_{min}\\ W_1\le W<W_2->{\delta }_1-\left[{\delta }_1-{\delta }_{min}\right].Math.\left\{{\left[\sin \left(\frac{\pi }{2}.Math.\frac{W-W_2}{W_2-W_1}\right)\right]}^2\right\}\\ W_2\le W->{\delta }_1\end{array}\delta =\{\begin{array}{c}V>V_4->{\delta }_2\\ \begin{array}{c}{V}_3<V\le V_4->{\delta }_{\mathrm{ma}x}-\\ \left[{\delta }_{\mathrm{ma}x}-{\delta }_2\right].Math.\left\{{\left[\sin \left(\frac{\pi }{2}.Math.\frac{V-V_3}{V_4-V_3}\right)\right]}^2\right\}\end{array}\\ V\le V_3->{\delta }_{\mathrm{ma}x}\end{array}$
where:

(57) “δ” represents the target angle;

(58) “δ1” and “δ2” represent calculation parameters;

(59) “δmax” and “δmin” represent respectively the predetermined positive threshold angle and negative threshold angle;

(60) “V1”, “V2”, “V3”, and “V4” respectively represent first, second, third, and fourth speeds predetermined by the manufacturer;

(61) “V” represents the current value of the speed parameter;

(62) “W1” and “W2” respectively represent the first and the second predetermined powers;

(63) “W” represents the current value of the power parameter;

(64) “sw” represents a predetermined adjustment parameter; and

(65) “A” and “B” represent variables that are functions of said adjustment parameter.

(66) In the implementation of FIG. 6, the adjustment parameter sw is equal to a predetermined value, e.g. 0. The deflection angle 200 is then equal to the target angle δ.

(67) The relationship L then serves to define a sheet presenting the deflection angle plotted along a vertical first axis AX1, the power parameter W plotted along a horizontal second axis AX2, and the speed parameter plotted along a third axis AX3.

(68) This sheet makes it possible to reach the first zone Z1, the second zone Z2, the third zone Z3, and the fourth zone Z4, together with transition areas between these zones.

(69) The processor unit then applies the relationship L directly in order to determine the deflection angle.

(70) FIG. 7 shows a second implementation.

(71) In this second implementation, the processor unit determines a maximum angle 400 equal to the target angle in applying the relationship L while giving a first value to the adjustment parameter sw. The maximum angle 400 is then in the form of an upper sheet in FIG. 7.

(72) Furthermore, the processor unit determines a minimum angle 500 equal to the target angle by applying the relationship L and giving a second value to the adjustment parameter sw. The minimum angle 500 then gives a sheet having the lower shape in FIG. 7.

(73) These lower and upper sheets put limits on the deflection angle.

(74) Under such circumstances, the current collective pitch of the blades 11 of the auxiliary rotor 10 is measured using a conventional pitch measurement device that is connected to the processor unit.

(75) Thereafter, the processor unit controls means for modifying the pitch of the blades 11, such as an autopilot system. The processor unit then requests an increase in the deflection angle 200 of the airfoil 25 so as to cause it to tend towards the maximum angle 400 so long as said pitch is greater than a predetermined setpoint pitch.

(76) Conversely, the processor unit requests a decrease in the deflection angle 200 of the airfoil 25 by causing it to tend towards the minimum angle 500 so long as said pitch is less than the predetermined setpoint pitch.

(77) In parallel, the autopilot system automatically modifies said pitch in parallel with modification to the deflection angle 200, in order to compensate for the modification in the deflection angle.

(78) The processor unit may optionally inhibit any modification to the deflection angle 200 whenever the pilot is operating the control means 50.

(79) This implementation enables the airfoil to be controlled in a manner that is transparent for the pilot. Pilot action on the control means 50 then stops this implementation being performed so as to leave full authority to the pilot.

(80) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several implementations are described, it will readily be understood that it is not conceivable to identify exhaustively all possible implementations. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.