Process for aiding the takeoff of an aircraft
View Patent ↗An aircraft takeoff process may include applying a pitch command deflecting an adjustable horizontal tailplane of the aircraft by a predetermined angle. Thereafter, the pitch command is corrected in accordance with the deviation between a takeoff rotation speed and a stall reference speed VRref of the aircraft.
1. A process for aiding the takeoff of an aircraft comprising trailing edge flaps, leading edge slats, and an adjustable horirontal tailplane to which are hinged elevators, said process comprising:
before takeoff, when the aircraft rests on a runway preparing for the takeoff:
a) predetermining a value VR of speed of the aircraft at which the takeoff rotation must begin,
b) determining a reference speed VRref which is equal to the product K×VS 1 g , in which K is a coefficient greater than 1 and VS 1 g is the speed at which said aircraft stalls when it is flying horizontally with a configuration of the leading edge slats and of the trailing edge flaps which is similar to that used for takeoff,
c) for this reference speed VRref, determining a fixed value iH 1 of the angle of deflection of said adjustable horizontal tailplane solely as a function of the longitudinal position of the center of gravity of said aircraft on takeoff,
d) deflecting said adjustable horizontal tailplane by an angle whose value is equal to said fixed value iH 1 ,
e) determining the difference VR−VRref between said rotation speed VR and said reference speed VRref, and
f) determining a fixed pitch correction angle ΔiH for said adjustable horizontal tailplane or a fixed pitch correction angle δq 2 for said elevators as a function of said difference VR−VRref; and
before or during the takeoff rotation:
g) applying: (1) said fixed pitch correction angle ΔiH to said adjustable horizontal tailplane, (2) said fixed pitch correction angle δq 2 to said elevators, or (3) part of said fixed pitch correction angle ΔiH to said adjustable horizontal tailplane and part of said fixed pitch correction angle δq 2 to said elevators.
2. The process as claimed in claim 1 , wherein said fixed pitch correction angle ΔiH is applied to said adjustable horizontal tailplane.
3. The process as claimed in claim 2 , wherein part of said fixed pitch correction angle ΔiH is applied to said adjustable horizontal tailplane and,
part of said fixed pitch correction angle δq 2 is applied to said elevators.
4. The process as claimed in claim 2 , wherein the value ΔiH is of the type
Δ iH=K 1×( VR−K×VS 1 g )
in which expression K 1 is a coefficient dependent on the reference speed VRref, the longitudinal position of the center of gravity and the configuration of the trailing edge flaps and of the leading edge slats.
5. The process as claimed in claim 4 , wherein the mean value of K 1 is of the order of 0.16°/kt.
6. The process as claimed in claim 4 , applied to an aircraft in which said adjustable horizontal tailplane is n times more effective, as regards the fixed pitch correction angles ΔiH and δ 2 , than said elevators, wherein K 2 =n×K 1 .
7. The process as claimed in claim 1 , wherein said fixed pitch correction angle δq 2 is applied to said elevators.
8. The process as claimed in claim 7 , wherein said angle δq 2 is of the type
δq 2 =K 2×( VR−K×VS 1 g )
in which expression K 2 is a coefficient dependent on the reference speed VRref, the longitudinal position of the center of gravity and the configuration of the trailing edge flaps and of the leading edge slats.
9. The process as claimed in claim 8 , in which the characteristic tied to the airplane and giving the deflection of the elevators as a function of the order of deflection of said elevators comprises a nose-down part and a nose-up part that are linked together at a neutral point, wherein said characteristic is modified by supplementing it with said additional angle δq 2 .
10. The process as claimed in claim 9 , wherein said additional angle δq 2 is added at at least one point of said nose-up part.
11. The process as claimed in claim 1 , wherein said speed difference between said values VR and VRref is estimated by the ratio between them.
12. The process as claimed in claim 1 , wherein said speed difference between said values VR and VRref is estimated by the difference between them.
13. The process as claimed in claim 1 , wherein the coefficient K depends on the ratio of the thrust of the aircraft at takeoff to the weight of said aircraft.
14. The process as claimed in claim 13 , wherein the coefficient K exhibits a mean value of around 1.11.