Mode Tracking During Flutter Testing Using the Modal Assurance Criterion

Abstract

Tracking the aeroelastic modes of an aircraft through changing flight conditions is an essential element of flight flutter testing, which is made difficult by corrupted data and high modal density. The modal assurance criterion (MAC), a method of evaluating the consistency of two modal vectors, is shown to simplify the mode tracking procedure by putting a numerical value on the correlation between pairs of modes identified at consecutive flight conditions. Representation of the resulting MAC values as a colour map gives a clear visual indication of modal consistency. An automated approach to mode tracking is introduced and shown to work on aircraft-type systems, over significant changes in flight condition up to and beyond the flutter speed. Some potential problems of a practical implementation are discussed.