Electric flight control system for aircraft elevators
View Patent ↗The invention relates to an electric flight control system for aircraft elevators. According to the invention, the flight control system can be controlled in terms of load factor or rate of pitch. The inventive system comprises built-in protections in relation to load factor, incidence and pitch attitude.
1. An electric flight control system for the control in terms of load factor of the elevators of an aircraft, said elevators being controlled by a control section that compels said elevators to take a deflection position dependent on an electrical signal δ mc representative of a controlled value of the angle of deflection δ m of said elevators, said system comprising:
a first calculation section for calculating, on the basis of an electrical signal nzc representative of a controlled value of said load factor, a first electrical signal {dot over (γ)} c representative of a controlled value of the derivative, with respect to time, of the aerodynamic slope γ of said aircraft;
a first constituent device, which:
is configured to receive at its input said first electrical signal {dot over (γ)} c ;
comprises a first protection section configured to maintain said first electrical signal {dot over (γ)} c between a first minimum value and a first maximum value;
on the basis of said first electrical signal {dot over (γ)} c , determines at least a second electrical signal α c , representative of a corresponding controlled value of the incidence α, and a third electrical signal θ c , representative of a corresponding controlled value of the longitudinal attitude θ;
comprises a second protection section configured to maintain said second electrical signal α c between a second minimum value and a second maximum value; and
delivers at least said third electrical signal θ c to its output; and
a second constituent device, which is configured to receive at its input at least said third electrical signal θ c or a fourth electrical signal θ d similar to said third electrical signal θ c ;
comprises a third protection section configured to maintain said third or fourth electrical signal between a third minimum value and a third maximum value; and
is configured to deliver at its output a fifth electrical signal which constitutes said signal δ mc , representative of the corresponding controlled value of the angle of deflection δ m of said elevators.
2. The system as claimed in claim 1 , further comprising a first switching section configured to take:
either a first position for which the output of said first constituent device is connected to the input of said second constituent device, so that said third electrical signal θ c is then transmitted to said second constituent device;
or a second position for which the input of said second device receives said fourth electrical signal θ d , similar to said third electrical signal θ c and produced on the basis of a sixth electrical signal q d , representative of a desired value for a rate of pitch q.
3. The system as claimed in claim 1 , wherein said first constituent device determines, in addition to said second electrical signal α c and said third electrical signal θ c , a seventh electrical signal q c , representative of a corresponding controlled value of the rate of pitch q, and a first switching section configured to transmit said seventh electrical signal q c to said second constituent device.
4. The system as claimed in claim 3 , wherein said first constituent device delivers, for the seventh electrical signal q c , an approximate value equal to that of said first electrical signal {dot over (γ)} c .
5. The system as claimed in claim 2 , further comprising:
an automatic pilot configured to deliver a first controlled load factor signal nz c ;
a manual piloting member configured to deliver, by switching, either a second controlled load factor signal nz c or said sixth electrical signal q d , representative of a desired value for the rate of pitch q; and
a second switching section for:
transmitting to said first constituent device either the first controlled load factor signal delivered by said automatic pilot, or the second controlled load factor signal delivered by said manual piloting member;
or else transmitting said sixth electrical signal q d to a first integration section configured to form the fourth electrical signal θ d , representative of a desired value for an attitude θ,
said first switching section being configured to transmit to said second constituent device said fourth and sixth electrical signals θ d and q d , instead of said third and seventh electrical signals θ c and q c produced by said first constituent device.
6. The system as claimed in claim 1 , wherein, to determine said second electrical signal α c on the basis of the first signal {dot over (γ)} c , said first constituent device comprises a second calculation section for calculating the expression
α c =({dot over (γ)} c −F 65 )/ G y
in which F γ and G γ are functions of the state of the aircraft with
F
γ
=
g
·
cos
(
γ
)
V
+
1
2
ρ
m
·
V
·
S
·
Cz
a
=
0
and
G
γ
=
1
2
·
ρ
m
·
V
·
S
·
∂
Cz
∂
α
|
α
=
0
+
T
m
·
V
where g is the acceleration due to gravity, γ the aerodynamic slope, V the speed of the aircraft, ρ the density of the air, m the mass of the aircraft, S the reference area of the aircraft, Cz α=0 the coefficient of lift of the aircraft for a zero incidence,
∂
Cz
∂
α
❘
α
=
0
the gradient of the aerodynamic coefficient of lift as a function of the incidence and T the thrust of the aircraft.
7. The system as claimed in claim 3 , wherein said first constituent device comprises a second integrator section configured to integrate said seventh electrical signal qc and a first summator for forming the sum of the integral delivered by said second integrator section and of said second electrical signal α c , so as to form said third electrical signal θc.
8. The system as claimed in claim 5 , wherein said second constituent device, either on the basis of said third electrical signal θ c and of the seventh electrical signal q c , originating from said first constituent device, or on the basis of said fourth signal θ d and of said sixth signal q d originating from said manual piloting member, well as current values q r and θ r of the rate of pitch q and of the longitudinal attitude θ, determines an eighth electrical signal {dot over (q)} c , representative of a corresponding controlled value of the pitch acceleration {dot over (q)}, then, on the basis of this eight electrical signal {dot over (q)} c said second constituent device determines said fifth electrical signal δ mc .
9. The system as claimed in claim 8 , wherein said second constituent device calculates said eight electrical signal {dot over (q)} c , through the relation
{dot over (q)} c =K 1.θ v −K 2.θ r +K 3. q v −K 4. q r
where θ v said third or fourth electrical signal, θ r the current value of the longitudinal attitude θ, q v said sixth or seventh electrical signal, q r the current value of the rate of pitch q, K 1 , K 2 , K 3 and K 4 being constant coefficients.
10. The system as claimed in claim 8 , wherein, to determine said fifth electrical signal δ mc on the basis of said eighth electrical signal {dot over (q)} c , said second constituent device comprises a third calculation section that calculates the expression
δ mc =( {dot over (q)} c −F q )/ G q
in which F q and G q are functions of the state of the aircraft with
F
q
=
1
I
y
·
1
2
·
ρ
·
v
2
·
S
·
l
·
Cm
δ
m
=
0
+
1
I
γ
·
T
·
b
·
cos
(
τ
)
and
G
q
=
1
I
y
·
1
2
·
ρ
·
v
2
·
S
·
l
·
∂
Cm
∂
δ
m
|
δ
m
=
0
where I y is the pitch inertia, ρ the density of the air, V the speed of the aircraft, S the reference area of the aircraft, l the reference length of the aircraft, Cm δm=0 the coefficient of pitch, T the thrust, b the lever arm of the engines, τ the angle of longitudinal trim of the engines and
∂
Cm
∂
δ
m
❘
δ
m
=
0
the effectiveness of the elevators.