Patent Application
20140236399
This application claims the benefit of the French patent application No. 1351382 filed on Feb. 19, 2013, the entire disclosures of which are incorporated herein by way of reference.
The present invention relates to a method and a device for automatic estimation of an unwanted pitch moment of an aircraft, in particular a transport aircraft, and also a method and a system for controlling the pitch of an aircraft performing automatic compensation for such an unwanted pitch moment.
It is known that on an aircraft with electrical flight controls, the aircraft is controlled in flight by a pilot, in a manual flight mode, using control members, namely the control stick (in particular a mini-stick), the rudder bar and the thrust control lever. The flight computer(s) interpret(s) the actions of the pilot on these control members and produce corresponding commands which are then sent to control surface actuators (ailerons, spoilers, elevators, etc.) of the aircraft to control the deflection of these control surfaces and thus the aircraft's flight.
With regard to the pitch axis of the aircraft, particularly for a short-term command (of the order of a few seconds, and generally less than ten seconds) made by the pilot of the aircraft, the flight control computers calculate elevator deflection commands, using for that purpose, in general, a standard mathematical law known as C*, detailed below.
However, the pitching movement of the aircraft in flight can be disrupted by (short term) moments that are unwanted, such as:
Within the scope of the present invention, the term “unwanted pitch moments” is used to describe pitch moments of the aircraft as described above, which are produced in the short term (of the order of a few seconds), which have disruptive effects as detailed below, which are not produced by an action by the pilot on the control stick (mini-stick) and which are not wanted.
These unwanted moments can impair the performance of the aircraft, when it is controlled by the C* law alone. They can also have an adverse effect on the comfort of the pilot and the passengers.
The present invention relates to a method for estimating an unwanted pitch moment of an aircraft, which can be used to remedy the disadvantages mentioned above.
To this end, according to the invention, said method for estimating an unwanted pitch moment of an aircraft is distinctive in that it comprises steps to:
Δ{circumflex over (m)}={dot over (q)}−mα*(α−αeq)−mq*q−mδq*δq
where:
Thus, by virtue of the invention, any unwanted pitch moment that may be produced on the aircraft is estimated automatically, accurately and in real time. This estimated unwanted pitch moment is a total moment that illustrates the difference between the actual pitch behavior, observed on the aircraft, and the behavior that ought to occur according to the current situation, taking into account a reference model, as detailed below.
This total pitch moment can correspond to one or more of the following moments, which are produced at the current time on the aircraft:
The determination, in accordance with the present invention, of this total unwanted pitch moment does not require any knowledge of the change, over time, in the different individual unwanted moments that can act on the aircraft, such changes over time being difficult to estimate.
Advantageously, said current values of the angle of attack, pitch rate and angle of deflection of the elevator are measured on the aircraft.
Furthermore, advantageously, said step of determining the current coefficient values comprises:
The unwanted pitch moment, determined in accordance with the invention, can be used by different means (or systems) of the aircraft, known as user means. In a preferred application, this pitch moment is used to calculate compensation commands enabling compensation to be effected automatically.
Therefore, the present invention also relates to a method for controlling the pitch of an aircraft, able to implement automatic, active compensation for disruptive (unwanted) pitch moments.
According to the invention, said method for controlling the pitch of an aircraft, of the type comprising a step of producing a command for controlled deflection of at least one elevator, in accordance with a standard control law, said controlled deflection command being representative of a manual actuation by a pilot, and a step of applying to the aircraft an actual deflection command dependent on said controlled deflection command,
is distinctive in that it comprises, in addition, steps of:
Thus, by virtue of this method, any unwanted moments that disrupt the pitch of the aircraft are automatically and actively compensated in such a way that said pitch remains unaffected by these moments as far as the pilot is concerned. This compensation, which uses the method according to the invention for estimating an unwanted pitch moment, therefore does not require any knowledge of the different individual unwanted moments that can act on the aircraft.
Advantageously, the compensation command δANLqc is calculated using the following expression:
δANLqc=−(Δ{circumflex over (m)}/mδq)
where:
The present invention relates, in addition, to a device for estimating an unwanted pitch moment of an aircraft, which is distinctive in that it has:
Δ{circumflex over (m)}={dot over (q)}−mα*(α−αeq)−mq*q−mδq*δq;
and
Furthermore, in a particular embodiment, said second means for determining the current coefficient values comprises:
The present invention also relates to a system for controlling the pitch of an aircraft, of the type that comprises means for generating a command for controlled deflection of at least one elevator, in accordance with a manual actuation by a pilot taking into account a standard control law, and means for applying to the aircraft an actual angle of deflection dependent on said controlled deflection command. According to the invention, this system for controlling pitch comprises, in addition:
This system for pitch control therefore produces, by virtue of the invention, an automatic and active (real time) compensation for any unwanted pitch moment.
The present invention further relates to an aircraft, in particular a transport aircraft, that is provided with such a device and/or such a system.
The appended drawings will give a better understanding of how the invention can be embodied. In these drawings, identical references designate similar elements.
The system 1 according to the invention and shown very diagrammatically in
Usually, this system 1 which is on board the aircraft AC comprises, in particular, as shown in
In order to do this, said means 2 has, usually:
To this end, said means 5 uses a standard mathematical law known as C*. This law C*, which is intended for the control of the flight of an aircraft on the pitch axis, is widely used in the field of aeronautics. In a general and known manner, it calculates a controlled deflection command δC*qc to control the longitudinal load factor Nz of the aircraft, in accordance with a reference Nzc, being robust relative to external disturbances (using an integrator in the loop). It uses two measurements, namely the load factor Nz and the pitch rate q, as feedback.
Furthermore, said means 7 comprises, usually, means 8 for actuation of the elevators 3 of the aircraft AC. These usual actuating means 8 are formed so as to move said elevators 3, as shown via a link 9 indicated by a dot-and-dash line, into a particular position, representative of an angle of deflection known as actual received δeff.
The present invention applies during a short-term command for a pitch movement (of the order of a few seconds, and generally less than ten seconds) issued by the pilot acting on the control stick, for which said pitch movement by the aircraft AC in flight can be disrupted by unwanted moments, and its object is to compensate for such moments.
In order to do this, said system 1 further comprises, according to the invention:
Said means 11 calculates the compensation command δANLqc using the following expression:
δANLqc=−(Δ{circumflex over (m)}/mδq)
where:
Consequently, the present invention proposes an additional flight control law for compensating for the unwanted pitch movement, which is defined by two functions.
More specifically:
Thus, by virtue, in particular, of the means 10, 11 and 14, the pitch control system 1 produces a correction to the standard control command (in accordance with the C* law) in order to send an actual deflection command δeff which enables compensation to be made for an unwanted pitch moment.
Said system 1 thus compensates automatically and actively (acting on the elevators 3), in real time, for any unwanted moments that disrupt the pitch of the aircraft, so that said pitch remains unaffected by these moments for the pilot. This compensation, which uses the results from the device 10 for estimating an unwanted pitch moment, therefore does not require any knowledge of the different individual unwanted moments able to act on the aircraft AC, as detailed below.
Furthermore, said device 10 has, as shown in
Δ{circumflex over (m)}={dot over (q)}−mα*(α−αeq)−mq*q−mδq*δq
where, in addition:
The device 1 also comprises links 12 and 24 to send to the user means the pitch moment thus calculated, which represents an estimated unwanted pitch moment.
In a particular embodiment, said means 20 comprises:
These predetermined tables, which comprise the values of said coefficients, as a function of values of parameters related to the flight point of the aircraft, have been formed in advance using calculations and tests, and are recorded in a storage means 28. This storage means 28 can be incorporated into specific means of the device 10 and in particular into the means 26.
Thus, the device 10 according to the invention makes it possible to estimate automatically, precisely and in real time any unwanted pitch moment Δ{circumflex over (m)} that is produced on the aircraft AC. This unwanted pitch moment Δ{circumflex over (m)} is an overall moment that illustrates the difference between the actual longitudinal movement, observed on the aircraft, and the longitudinal movement as it ought to be according to the current situation taking into account a reference model, as detailed below.
Determining this overall unwanted pitch moment does not require any knowledge of the change, over time, in the different individual unwanted moments capable of acting on the aircraft AC, such changes over time being difficult to evaluate.
The mathematical formula used to calculate the unwanted pitch moment Δ{circumflex over (m)} will now be detailed.
It is known that the longitudinal movement of the aircraft AC can be described by its equation of pitch motion, around an equilibrium characterised by an equilibrium angle of attack αeq (which is obtained in the standard manner):
{dot over (q)}mα*(α−αeq)+mq*q+mδq*δq+Δ(x)
In this equation Δm represents all the unwanted pitch movements, is expressed in deg/s
Δm is unknown, whereas mα, mq, mδq, are known (they can be determined) and are available in real time in the flight control computers.
The desired longitudinal movement of the aircraft is defined by the following reference model:
{dot over (q)}=mα*(α−αeq)+mq*q+mδq*δq
An estimated Δ{circumflex over (m)} of the unwanted pitch moment can be defined, in theory, by the equation given above:
Δ{circumflex over (m)}={dot over (q)}−mα*(α−αeq)−mq*q−mδq*δq
In practice, the equation Δ{circumflex over (m)}={dot over (q)}−mα*(α−αeq)−mq*q−mδq*δq is calculated by the means 21 using filters which, in the Laplace transform (of variable s), are defined as:
A/
F1(s)=(τ1s/(1+τ1s))
B/
F21(s)=(s/(1+τ2s))
C/
F22(s)=(1/(1+τ2s))
τi is a time constant (for i=1, 2, . . . ).
The estimated Δ{circumflex over (m)} is therefore calculated by the means 21 using the values α, q, δq and the following expression:
Δ{circumflex over (m)}(s)=F21 (s)*F1(s)* q−F22(s)* F1(s)*(mα*α−mq*q−mδq*δq)
Consequently, if the accuracy of the estimated Δ{circumflex over (m)} is sufficient, in other words, if Δ{circumflex over (m)}≈Δm, the equation of longitudinal motion of the aircraft AC, namely {dot over (q)}=mα*(α−αeq)−mq*q−mδq*δq+Δm(x), is not affected by any unwanted pitch moment (when δq=δqeff, which is obtained by the internal dynamics of the elevators 3) and the dynamics of the aircraft AC exactly follow the behavior of the reference model {dot over (q)}=mα*(α−αeq)−mq*q+mδq*δq.
The unwanted pitch moment, determined by the device 10 according to the invention in the manner described above, can be sent by the link 12 to said means 11 of the pitch control system 1, as indicated with reference to
This unwanted pitch moment can also be sent by a link 24 to other means or systems (not shown) of the aircraft AC, which might need such information.
As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1351382 | Feb 2013 | FR | national |
