Patent ID: 8442703

Claim:
A method of estimating the attitude angles (θ, φ) of an aircraft, the estimating being a computed data processing operated by a computed attitude unit onboard the aircraft, wherein: the computed attitude unit generating said estimate of the attitude angles (θ, φ) and an estimate of a heading angle (Ψ) and an estimate of a linear speed vector ({right arrow over (ν)}) expressed relative to navigation axes (N, E, D) by algorithmic integration of measurements from an inertial measurement unit with strapdown components, said inertial measurements being indicative of an angular velocity ({right arrow over (ω)})and of a linear acceleration ({right arrow over (γ)}) of said aircraft; characterized in that at least one of the strapdown components in the inertial measurement unit is a vibrating structure gyro that provides at least some of the inertial measurements for the algorithmic integration, and said algorithmic integration also having inputs for correcting said inertial measurements, the inputs being expressed relative to navigation axes (N, E, D) by two horizontal components and by one vertical component and serving to correct: angular acceleration ({right arrow over (ρ)}); angular velocity ({right arrow over (ω)}); and linear acceleration ({right arrow over (γ)}); the computed attitude unit forming a linear speed difference expressed relative to navigation axes (N, E, D) by subtracting the estimated linear speed vector ({right arrow over (ν)}) expressed relative to navigation axes (N, E, D), generated by said algorithmic integration, from a measurement of the linear speed of the aircraft coming from a linear speed sensor and expressed relative to navigation axes (N, E, D); the computed attitude unit forming an estimate of the rate of turn of the aircraft by estimation from the measured angular velocity about a vertical navigation axis using a projection operator that is a function of said attitude angles (θ, φ); each of the two horizontal components of said angular acceleration ({right arrow over (ρ)}), angular velocity ({right arrow over (ω)}), and linear acceleration ({right arrow over (γ)}) corrections is a linear combination of the two horizontal components of said linear speed difference, wherein the two horizontal components are the horizontal component which is parallel to the corrections and the other horizontal component which is not colinear with said corrections; whereby cross coefficients are obtained between said horizontal axes; and each of the coefficients of said linear combination is a continuous function of time and depends on said estimated rate of turn such that an attitude filtering is independent from a heading filtering and a vertical filtering allowing the estimated attitude angles to be stable, including while the aircraft is turning.