On the use of control surface excitation in flutter testing

Flutter testing is used to demonstrate that the aircraft flight envelope is flutter free.
Response measurements from deliberate excitation of the structure are used to identify and
track frequency and damping values against velocity. In this paper, the common approach of
using a flight control surface to provide the excitation is examined us ing a mathematical
model of a wing and control surface whose rotation is restrained by a simple actuator. In
particular, it is shown that it is essential to use the demand signal to the actuator as a reference
signal for data processing. Use of the actuator force (or strain) or control angle (or actuator
displacement) as a reference signal is bad practice because these signals contain response
information. It may also be dangerous in that the onset of flutter may not be seen in the test
results. Control sur face flutter is of particular concern.