Flutter speed prediction based on frequency-domain identification of a time-varying system

This article introduces as new approach for flight envelope clearance of aircraft. This can now be performed as one continuous test, resulting in a major time saving. Both analysis of the current behaviour of the structure, and prediction towards higher velocities are important for flight flutter testing, and are dealt with in this article. The time-varying weighted non-linear least-squares estimator is used to obtain the frozen system poles of a cantilever wing under test in a low speed wind tunnel. The obtained smooth variation of the transfer function coefficients is used as basis for predicting the damping ratio towards higher velocities. Comparison with time-invariant measurements have shown that only one tenth of the measurement time is needed to obtain equal uncertainties on the estimates when performing a flight flutter test as one continuous test.