Aircraft flight control system and method.

Abstract

Aircraft flight control system and method. The flight control system (10) includes at least one aircraft flight control computer (16) intended to control an aircraft elevator (5). The at least one flight control computer is configured to perform the following steps repeatedly during an aircraft acceleration phase while taxiing on the ground for takeoff: - determination (30) of an elevator deflection angle (5), corresponding to a load (Fz) to be applied to a nose landing gear of the aircraft such that said load is within a predetermined load range ([Fzmin; Fzmax]); - control (40) of an elevator actuator (18) so as to apply said elevator deflection angle to the elevator. Figure for the abstract: Fig. 2

Description

Title of the invention: System and method for flight control of an aircraft.

[0001] The invention relates to the field of aircraft flight controls. During the takeoff phase of an aircraft on an airport runway, the pilot first commands the aircraft to taxi down the runway, accelerating until the aircraft reaches a predetermined speed known as the rotation speed. At this rotation speed, the pilot commands the aircraft to pitch up by acting on a control in the cockpit, such as a control stick or a mini-stick. This command induces a deflection of at least one of the aircraft's elevators. As a result, the nose landing gear of the aircraft rises, and the aircraft then rolls on its main landing gear in a nose-up position. The elevator is also called a lift.The aircraft's pitch-up rotation, when the pilot acts on the control system, is more or less rapid depending on the load applied by the aircraft to the nose landing gear due to its weight. This load is primarily a function of the aircraft's center of gravity, and therefore particularly of the aircraft's load (number and distribution of passengers, amount of cargo, etc.), which can vary between flights. The greater this load, the longer the time required to raise the nose landing gear. When the load on the nose landing gear is very high, the initial part of the elevator deflection only serves to relieve the nose landing gear of the load previously applied by the aircraft. This requires a longer time as the initial load on the nose landing gear increases.Next, a second part of the elevator deflection raises the nose gear, thus pitching the aircraft up. Only this second part of the elevator deflection is truly useful for the aircraft's pitch-up rotation. Consequently, the response time between a pilot input on the control system and the aircraft's pitch-up rotation varies depending on the load applied by the aircraft to the nose gear. It would be desirable to have consistent rotations regardless of the aircraft's nose gear load, in order to improve the aircraft's takeoff performance and flight characteristics during the takeoff phase. Description of the invention

[0002] The present invention aims in particular to provide a solution to this problem. It relates to an aircraft flight control system comprising at least one aircraft flight control computer intended to control a control surface of aircraft depth. The flight control system is notable in that at least one flight control computer is configured to implement the following steps repeatedly during an aircraft acceleration phase while taxiing on the ground in preparation for takeoff:

[0003] - determination of a deflection angle of the elevator, corresponding to a load to be applied to a front landing gear of the aircraft such that said load is within a predetermined load range;

[0004] - control of a pitch control actuator so as to apply said steering angle at the elevator.

[0005] Thus, the flight control system allows control of the load applied by the aircraft to its nose landing gear during the acceleration phase for takeoff, and therefore in particular when a pilot commands a nose-up roll. As a result, the response time between a pilot input on the control device and the aircraft's nose-up roll is substantially independent of the initial load applied by the aircraft to the nose landing gear, which allows for consistent nose-up rolls regardless of the initial load applied by the aircraft to the nose landing gear.

[0006] In one embodiment, the elevator being part of an aircraft elevator assembly, the flight control computer is configured such that the elevator deflection angle determination step comprises the following substeps:

[0007] - estimation of a total moment around a pitch axis of the aircraft;

[0008] - estimation of a moment, around the pitch axis, induced by the control surfaces depth of the entire elevator assembly; and

[0009] - calculation of the elevator steering angle as a function of the moment total, of the moment induced by the elevators, of said load to be applied on the nose landing gear and of a distance between the center of gravity of the aircraft and the nose landing gear.

[0010] In one embodiment, at least one flight control computer is further configured to acquire a current speed value of the aircraft and to implement the steps of determining the elevator deflection angle and controlling the elevator actuator so as to apply said deflection angle to the elevator only if the current speed value is at least equal to a predetermined speed threshold.

[0011] In one embodiment, the flight control computer is configured such that the step of determining the elevator deflection angle includes a substep of limiting said deflection angle of the elevator between a minimum steering angle value and a maximum steering angle value.

[0012] The invention also relates to a method for controlling an aircraft elevator, the aircraft comprising a flight control system including at least one flight control computer intended to control the elevator. The method is notable in that it comprises the following steps implemented repeatedly by at least one flight control computer during an acceleration phase of the aircraft during its ground taxiing in preparation for takeoff:

[0013] - determination of a deflection angle of the elevator, corresponding to a load to be applied to a front landing gear of the aircraft such that said load is within a predetermined load range;

[0014] - control of a pitch control actuator so as to apply said steering angle at the elevator.

[0015] In one embodiment, the elevator being part of an aircraft elevator assembly, the step of determining the elevator deflection angle comprises the following substeps:

[0016] - estimation of a total moment around a pitch axis of the aircraft;

[0017] - estimation of a moment, around the pitch axis, induced by the control surfaces depth of the entire elevator assembly; and

[0018] - calculation of the elevator deflection angle as a function of the moment total, of the moment induced by the elevators, of said load to be applied on the nose landing gear and of a distance between the center of gravity of the aircraft and the nose landing gear.

[0019] In one embodiment, the method further includes a step of acquiring a current speed value of the aircraft, and the steps of determining the elevator steering angle and of controlling the elevator actuator so as to apply said steering angle to the elevator are only implemented if the current speed value is at least equal to a predetermined speed threshold.

[0020] In one embodiment, the step of determining the elevator steering angle includes a substep of limiting said elevator steering angle between a minimum steering angle value and a maximum steering angle value.

[0021] The invention also relates to an aircraft comprising such a flight control system. Description of the implementation methods

[0022] The invention will be better understood upon reading the following description and examining the accompanying figures.

[0023] Fig. 1 is a view of an aircraft comprising a flight control system according to an embodiment of the invention.

[0024] Figure 2 schematically illustrates a flight control system according to one embodiment of the invention.

[0025] Figure 3 illustrates a method of flight control of an aircraft according to an embodiment of the invention.

[0026] The aircraft 1 shown in [Fig. 1] comprises a set of elevators 5, referred to hereafter as "the elevators". In the example shown in the figure, each elevator 5 is hinged to a horizontal plane 4 of the aircraft's tail assembly. At least one elevator 5 is hinged to each horizontal plane 4. In the example shown in the figure, the tail assembly comprises two horizontal planes 4 arranged in the lower part of the tail assembly, symmetrically with respect to a vertical fin 6. In other aircraft, one or more horizontal planes may be arranged in the upper part of the vertical fin 6.

[0027] The aircraft 1 comprises a flight control system such as the flight control system 10 illustrated in [Fig. 2]. This flight control system comprises a set 14 of flight control computers, of which at least one flight control computer 16 is connected at its output to an actuator 18 of an elevator 5 forming part of the aircraft's elevator assembly. The flight control computer 16 is also connected at its input to a flight control device 12 of the aircraft, such as a joystick or a mini-joystick installed in a cockpit 3 of the aircraft. The flight control computer 16 is configured to control the elevator actuator 18, in particular according to piloting commands received from the flight control device 12. For clarity, this description relates to the control of a single elevator actuator 18.However, without departing from the scope of the invention, the flight control computer 16 can also be connected at its output to other actuators not shown in the figure, these other actuators being intended to actuate said elevator 5 and / or other elevators of the elevator assembly, not shown in the figure. Thus, the flight control computer 16 is intended to control at least one elevator 5 of the aircraft. In the following description, the term "elevator" refers to this at least one elevator, that is to say, said elevator 5 illustrated in the figure or any elevator of the elevator assembly of which at least one is shown. The actuator is controlled by the flight control computer 16. The flight control computer 16 is also connected as input to a set of information sources 13 of the aircraft. The set of computers 14 is, for example, installed in an avionics bay 2 of the aircraft.

[0028] During operation, during the takeoff phase of an aircraft on an airport runway, the aircraft pilot activates a thrust lever for the aircraft's engines, which commands the aircraft's engines to deliver the thrust necessary for takeoff. The aircraft then taxis down the runway while accelerating. This phase of takeoff, during which the aircraft taxis down the runway while accelerating, is also called the takeoff run. The flight control computer 16 is connected to other avionics computers on the aircraft, from which it receives information indicating that the aircraft is in this takeoff run phase. The flight control computer 16 also receives information about the aircraft's airspeed (V) from the set of information sources 13, for example, from an inertial measurement unit (IMU) or a satellite navigation system receiver.When the aircraft is in the takeoff roll phase and, advantageously, its speed exceeds a predetermined speed threshold Vs, the flight control computer 16 implements the steps of the process illustrated in [Fig. 3]. The predetermined speed threshold Vs is, for example, 80 knots, or approximately 148 km / h. In a first step 30, the flight control computer 16 determines a deflection angle of the elevator 5, corresponding to a desired load Fz to be applied to the aircraft's nose landing gear, such that said load Fz is within a predetermined load range [Fzmin; Fzmax]. This load range corresponds, for example, to a mass range [100; 2.5 tonnes] applied to the nose landing gear.Even if the flight control computer 16 controls only one elevator, or only some of the elevators in the elevator assembly, the deflection angle is determined by considering that the elevator(s) not controlled by this flight control computer 16 are also controlled, by other flight control computers, at the same deflection angle. All the elevators in the elevator assembly are controlled at the same deflection angle. Advantageously, the first step 30 comprises the following substeps:

[0029] - a substep 32 for estimating a total moment about a pitching axis of the aircraft;

[0030] - a substep 34 of estimating a moment, around the pitch axis, induced by the elevators; and

[0031] - a substep 36 for calculating the elevator deflection angle 5 as a function of the total moment, the moment induced by the elevators, said load Fz to be applied to the nose landing gear, and a distance between the aircraft's center of gravity and the nose landing gear.

[0032] In one embodiment, in substep 32, the flight control computer 16 calculates an estimate of the total moment MTOTAL about the pitch axis using the following equation:

[0033] TOTAL — MTangage ^Lift ^Thrust MFrenage + GroundSpàlers

[0034]

[0035] in which: ^Pitch ~ Cm . S . 1 . Pdyn

[0036] ^Lift ~ ^MainTrain-*CG • ( “ Cz ■ S . Pdyn )

[0037]

[0038] Mthrust ~ Engine-*CG • Pthrust M Braking — dMainTrain~*CG • POP CGFreinage

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045] M GrmmdSpoilers — ' ^GSP • 5 • / - Pdyn + ■ &GSP • 5 • Pdyn ■ dcGr*Center of thrust with: Cm; aerodynamic pitch coefficient Cz;aerodynamic lift coefficient S; reference surface Z: mean aerodynamic chord Pdyn: dynamic pressure

[0046]

[0047]

[0048]

[0049] m: mass of the aircraft S: gravitational constant nx;acceleration along the longitudinal axis of the aircraft fuselage (Forccp^^f^^)

[0050] Foi CG Braking — 1

[0051] fj(nx) is a first function of nx and in particular of the sign of nx

[0052] fS^x) is a second function of nx and in particular of the sign of nx

[0053] ôGSP: deflection of the airbrakes, also called ground brake flaps (ground spoilers)

[0054] Cm§: aerodynamic efficiency coefficient related to the deflection of the airbrakes (ground brake flaps)

[0055] drrainPrinâpal-HJG: component, along the longitudinal axis of the aircraft fuselage, of the distance between the aircraft's main landing gear and the aircraft's center of gravity

[0056] dMotew~*CG: component, along the longitudinal axis of the aircraft fuselage, of the distance between the aircraft's propulsion engines and the aircraft's center of gravity;

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071] dcG-*Center of thrust: distance between the aircraft's center of gravity and the center of thrust. Among this information, those whose value is variable (dynamic pressure, acceleration, etc.) are for example transmitted to the flight control computer 16 by information sources from the set of information sources 13. Those whose value is constant are for example recorded in a memory or a database of the flight control computer 16 or in a memory or a database of an avionics computer that is part of the set of information sources 13. In one embodiment, at substep 34 the flight control computer 16 calculates an estimate of the moment, around the pitch axis, induced by the elevators 5 using the following equation: Mgouvernes — Ht. Ôq = S. I. Pdyn • ^^ôq with : ôq: elevator deflection Cm^: coefficient of aerodynamic efficiency related to the deflection of the elevators. In one embodiment, at substep 36 the flight control computer 16 calculates the elevator deflection angle 5q as a function of the total moment MTOTAL, the moment MgoUvemes induced by the elevators, said load Fz to be applied to the nose landing gear and the distance between the aircraft's center of gravity and the nose landing gear using the following equation: x MT()t<ü + Fz. dx<.^w Oq — v iw governs with : dX(G-*NW: distance between the aircraft's center of gravity and the front landing gear. Advantageously, the flight control computer 16 calculates two elevator 5 deflection angle values: a minimum 5qmbi deflection angle value and a maximum deflection angle value, corresponding respectively to the minimum Fzmin and maximum Fzmax bounds of the predetermined load range [Fzmin; Fzmax]. These two steering angle values ​​are calculated using, for example, the following equations: s MTotal + F^i„ ■ Oq . — ij * mm m governors "MTotal + F^c ■ Oq — 17 x max i rJ governs

[0072] These two values ​​delimit an interval [(¾ . :Ôq ] of admissible values ​​of LJL ' +maxJ the elevator deflection angle 5 to allow obtaining a load on the nose landing gear within the predetermined load range [Fzmin ; F 1 x zmaxj •

[0073] The method further includes a second step 40 in which the flight control computer 16 commands the elevator actuator 18 5 so as to apply to the elevator the steering angle calculated in step 30. This makes it possible to apply the desired Fz load to the nose landing gear.

[0074] In a particular embodiment, step 30 further includes a substep 38 for limiting the elevator deflection angle, previously calculated in substep 36, between a minimum and a maximum deflection angle. The minimum deflection angle is, for example, -5 degrees (pitch up) and the maximum deflection angle is, for example, 10 degrees (pitch down). This limitation of the deflection angle ensures that the commanded elevator deflection angle 5 remains within a range of values ​​chosen so as to allow elevator deflection commands issued by an aircraft pilot to have an effect on the aircraft.

[0075] As previously stated, the condition for carrying out steps 30 and 40 of the method, whereby the aircraft speed exceeds a predetermined speed threshold Vs, represents an advantageous embodiment, but it is not limiting to the invention. Compliance with this condition makes it possible, in particular, to control the load applied to the nose landing gear only when this is most useful for the aircraft's pitch-up rotation. Furthermore, since the effect of elevator deflection on the load applied to the aircraft's nose landing gear is greater at higher aircraft speeds, implementing steps 30 and 40 of the method at speeds below the predetermined speed threshold Vs could unnecessarily result in large elevator deflections to control the load Fz on the aircraft's nose landing gear.

[0076] Implementing steps 30 and 40 of the method allows control of the Fz load applied to the aircraft's nose landing gear. As a result, the nose-up pitch maneuvers for different aircraft takeoffs are consistent. The Fzmax limit of the interval [Fzmin; Fzmax] within which the Fz load to be applied to the aircraft's nose landing gear is selected is defined such that when the pilot commands a nose-up deflection of the elevators 5, the time required to unload the nose landing gear of the Fz load applied by the aircraft is sufficiently short compared to to the operational constraints of takeoff. Advantageously, the Fzmin limit of the interval [Fzmin ; Fzmax] is defined in such a way that the load Fz to be applied to the nose landing gear of the aircraft is sufficient to avoid an autorotation phenomenon of the aircraft during the takeoff run.

Claims

Demands

1. 1) Flight control system (10) of an aircraft (1) comprising at least one flight control computer (16) of the aircraft intended to control an elevator (5) of the aircraft characterized in that the at least one flight control computer is configured to implement the following steps repeatedly during an acceleration phase of the aircraft during its ground taxiing in preparation for takeoff: - determination (30) of a deflection angle of the elevator (5), corresponding to a load (Fz) to be applied to a nose landing gear of the aircraft such that said load is within a predetermined load range ([Fzmin ; Fzmax]); - control (40) of an actuator (18) of the elevator (5) so as to apply said deflection angle to the elevator.

2. 2) System according to claim 1, characterized in that, the elevator (5) being part of an assembly of elevators of the aircraft, the step (30) of determining the elevator deflection angle comprises the following substeps: - estimation (32) of a total moment about a pitch axis of the aircraft; - estimation (34) of a moment, about the pitch axis, induced by the elevators of the assembly of elevators; and - calculation (36) of the elevator deflection angle as a function of the total moment, the moment induced by the elevators, said load (Fz) to be applied to the nose landing gear and a distance between the center of gravity of the aircraft and the nose landing gear.

3. 3) A system according to any one of the preceding claims, characterized in that at least one flight control computer is further configured to acquire a current airspeed (V) value of the aircraft and to implement the steps of determining (30) the elevator deflection angle and controlling (40) the elevator actuator so as to apply said deflection angle to the elevator control only if the current speed value is at least equal to a predetermined speed threshold (Vs).

4. 4) System according to any one of the preceding claims, characterized in that the step of determining the elevator steering angle includes a substep (38) of limiting said elevator steering angle between a minimum steering angle value and a maximum steering angle value.

5. 5) Method of controlling an elevator (5) of an aircraft (1), the aircraft comprising a flight control system (10) including at least one flight control computer (16) intended to control the elevator, characterized in that it comprises the following steps implemented repeatedly by at least one flight control computer during an acceleration phase of the aircraft during its ground taxiing in preparation for takeoff: - determination (30) of a deflection angle of the elevator (5), corresponding to a load (Fz) to be applied to a nose landing gear of the aircraft such that said load is within a predetermined load range ([Fzmin ; FzmaJ]); - control (40) of an actuator (18) of the elevator (5) so as to apply said deflection angle to the elevator.

6. 6) A method according to claim 5, characterized in that, the elevator (5) being part of an assembly of elevators of the aircraft, the step (30) of determining the elevator deflection angle comprises the following substeps: - estimation (32) of a total moment about a pitch axis of the aircraft; - estimation (34) of a moment, about the pitch axis, induced by the elevators of the assembly of elevators; and - calculation (36) of the elevator deflection angle as a function of the total moment, the moment induced by the elevators, said load (Fz) to be applied to the nose landing gear and a distance between the center of gravity of the aircraft and the nose landing gear.

7. 7) A method according to any one of claims 5 or 6, characterized in that it further comprises a step of acquiring a current speed value (V) of the aircraft and in that the steps of determining (30) the elevator steering angle and of controlling (40) the elevator actuator so as to apply said steering angle to the elevator are only carried out if the current speed value is at least equal to a predetermined speed threshold (Vs).

8. 8) Method according to any one of claims 5 to 7, characterized in that the step of determining the elevator steering angle includes a substep (38) of limiting said elevator steering angle between a minimum steering angle value and a maximum steering angle value.

9. 9) Aircraft (1), characterized in that it comprises a flight control system (10) according to any one of claims 1 to 4.

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