Patent ID: 7225061

Claim:
In an aircraft having: at least one tilting control that controls said aircraft about at least one of its axes of maneuver; and a means operated by a pilot for generating an electric command δ, representative of the amplitude of the tilting of said at least one tilting control, said electric command δ being able to adopt a maximum value δo, a method for detecting pilot induced oscillations in said electric command δ comprising: sampling said electric command δ at a sampling interval Δt to obtain a plurality of N successive samples X k with k=0, 1, 2, . . . , N−1 ; choosing the number of samples N and the sampling interval Δt so that the inverse of their product N.Δt is at least approximately equal to 0.3 Hz; breaking down said sampled command into a Fourier series in such a way that each sample x k adopts the form: x k = ∑ r = 0 N - 1 ⁢ ⁢ 1 N ⁢ A r ⁢ ⅇ 2 ⁢ ⁢ π ⁢ ⁢ j ⁢ ⁢ k ⁢ ⁢ r N in which expression j is the symbol assigned to the imaginary part of a complex number, r is the number of harmonic components in the Fourier series and A r are the Fourier coefficients, each of the latter being equal to: A r = ∑ k = 0 N - 1 ⁢ ⁢ x k ⁢ ⅇ - 2 ⁢ ⁢ π ⁢ ⁢ j ⁢ ⁢ k ⁢ ⁢ r N determining the moduli |A1| and |A2| of the first two Fourier coefficients Al and A 2 , respectively corresponding to r=1 and r=2; calculating the sum |A1|+|A2| of said moduli, said sum being representative of the energy of said signal samples X k for frequencies lying between 0.3 Hz and 0.6 Hz and corresponding to the pilot induced oscillations; calculating an index I that is equal to the quotient of the sum |A1|+|A2| of said moduli divided by the number N of samples; comparing said index I with a fraction q.δo of said maximum value δo of said electric command δ, said coefficient q of said fraction q.δo being determined from a pre-established database grouping together a number of earlier flight scenarios in which such pilot induced oscillations occurred; and generating a signal that is: equal to zero when said index I is lower than q.δo, because then there is no pilot induced oscillation; and equal to a value lying between 0 and 1, when said index I is equal to or greater than q.δo, because then there is some pilot induced oscillation, said value being representative of the amplitude of said pilot induced oscillations.