Envelope function - A tool for analyzing flutter data

In this article a new tool for flutter clearance is presented and a preliminary assessment of its capabilities undertaken. It is intended to be complementary to other approaches. The method is based on quantifying the change in the shape of the decay envelope associated with control pulse responses or impulse response functions. An indication of overall stability is obtained without curve fitting by way of a shape parameter which cjuickly shows whether there has been any significant change since the last test point. In addition, the envelope functions can be overlayed from different speeds. The method is illustrated with data from a simulated aeroelastic model of a multiengined transport aircraft, and the effects of turbulence are considered. Finally, the method is successfully applied to real flight test data.