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 fl utter speed; the best estimates are obtained with a linear extrapolati on. Good estimates of the flutter speed can be obtained from data at s peeds as low as 50% of the flutter speed. The flutter-margin is shown to be relatively insensitive to errors in the damping measurements, bu t is very sensitive to errors in frequency measurements. It does not g ive good predictions of the flutter speed when the instability is domi nated by a single degree-of-freedom mechanism. A new form of flutter-m argin has been developed for a trinary flutter, which also varies in a sensibly linear manner with dynamic pressure; it is also relatively i nsensitive to errors in damping, but is very sensitive to errors in fr equency.