EVALUATION AND EXTENSION OF THE FLUTTER-MARGIN METHOD FOR FLIGHT FLUTTER PREDICTION

For a binary flutter the so-called flutter-margin method is a good way of extrapolating from subcritical flight test data to estimate the flutter speed; the best estimates are obtained with a linear extrapolation. Good estimates of the flutter speed can be obtained from data at speeds as low as 50% of the flutter speed. The flutter-margin is shown to be relatively insensitive to errors in the damping measurements, but is very sensitive to errors in frequency measurements. It does not give good predictions of the flutter speed when the instability is dominated by a single degree-of-freedom mechanism. A new form of flutter-margin has been developed for a trinary flutter, which also varies in a sensibly linear manner with dynamic pressure; it is also relatively insensitive to errors in damping, but is very sensitive to errors in frequency.