Method and device for determining the dynamic stability margin of an aircraft
View Patent ↗A method of determining a dynamic stability margin M SD of an aircraft includes calculating the longitudinal position X MP of a maneuver point MP to find the distance between the maneuver point and the position X CG of the aircraft center of gravity CG, as a function of the angular velocity ω O of an incidence oscillation of the aircraft. A device for determining the dynamic stability margin M SD or a position X MP of the maneuver point MP includes means or acquisition of data and or calculating a dynamic stability margin. The means receive data for generating, the aircraft mass m and pitch inertia Iyy; the flight speed V; the angular velocity ω O of the incidence oscillation at a flight point; a coefficient C* α representing Cz α of a “quasi-static” model of the aircraft. The aircraft flight control laws may be adapted according to the stability margin and to X MP .
1. A method for determining the dynamic stability margin M SD of an aircraft in flight in which a position X MP along a longitudinal X axis of the aircraft of a maneuver point MP is calculated in order to find the distance between said maneuver point and a position X CG along the longitudinal X axis of a center of gravity CG of the aircraft, wherein the position X MP along the longitudinal X axis of said maneuver point MP is determined as a function of an angular velocity ω O of an incidence oscillation of the aircraft, said angular velocity ω O being measured during the flight of the aircraft.
2. A method according to claim 1 , wherein the position X MP is determined by the equation:
(
X
M
p
L
ref
)
-
(
X
c
g
L
ref
)
-
(
I
y
y
m
V
L
ref
)
(
ω
0
2
C
α
*
)
in which equation:
L ref is a reference length of the aircraft, the terms X MP /L ref and X CG /L ref representing reduced values of X MP and of X CG respectively;
I yy is an inertia of the aircraft about an axis of rotation in pitch parallel with an axis Y of the aircraft reference system perpendicular to a vertical plane of symmetry of the aircraft;
m is a mass of the aircraft;
V is a speed representing the true aerodynamic speed of the aircraft at the point of flight in question for the measurement of the angular velocity ω O ;
C* α is a coefficient of the status matrix [A] of a “quasi-static” model of the aircraft.
3. A device able to determine a dynamic stability margin MSD of an aircraft and/or a position XMP along a longitudinal axis of the aircraft, called the X axis, of a maneuver point MP, wherein said device comprises first means of acquisition of data and of calculating the dynamic stability margin MSD, said first means receiving data corresponding to or sufficient for generating:
a current mass m of the aircraft;
a current inertia Iyy of the aircraft about an axis of rotation in pitch, parallel with an axis Y of the aircraft reference system perpendicular to a vertical plane of symmetry of the aircraft;
a current true aerodynamic speed V of the aircraft at the flight point in question;
an angular velocity ω O of an incidence oscillation of the aircraft at the flight point in question;
a coefficient C* α of a status matrix [A] of a “quasi-static” model of the aircraft.
4. A device according to claim 3 , wherein the first means determine the dynamic stability margin M SD , in a reduced form divided by a term Lref, where Lref represents a reference length of the aircraft, by application of:
M
S
D
=
(
I
y
y
m
V
L
ref
)
(
ω
0
2
C
α
*
)
.
5. A device according to claim 3 comprising second means of data acquisition and of calculating the position X MP , of the maneuver point MP, said second means receiving data corresponding to or sufficient for generating a position X CG along the X axis of a center of gravity CG of the aircraft and determining the position X MP of the maneuver point MP as a result value, in a reduced form X MP /L ref , where L ref is a reference length of the aircraft, by application of:
(
X
M
P
L
ref
)
=
(
X
c
g
L
ref
)
-
{
Reduced
dynamic
stability
margin
established
by
the
first
means
(
of
acquisition
of
data
)
.
6. A device according to claim 5 , wherein the second means of data acquisition and of calculating the position XMP generate data depending on the difference between the value of the dynamic stability margin M SD and one or more predetermined threshold values.
7. An aircraft comprising a flight control device able to receive the data generated by the device according to claim 3 and to modify piloting laws of said flight control device according to received data.