Flight Flutter Testing of a Transport Aircraft with Wing Mounted Store Suspension – Lessons Learned

Altan Kayran, Department of Aerospace Engineering, Middle East Technical University, Ankara, Turkey

Abstract

The methodology backed by relevant analysis results, ground vibration testing, flight flutter test results, and their interpretation was presented for the flight flutter testing of a transport aircraft with wing mounted external store suspension. Before the flight tests, extensive flutter analyses were performed by MSC/Nastran for different weight and CG configurations to reduce the number of costly flutter flight tests based on the results of flutter analysis, and decide on the aircraft test configurations. Flutter analysis phase was supported by the relevant ground vibration testing to update the beam-like half aircraft dynamic model of the modified aircraft.

Finally, six sortie of flight test was performed with an instrumented aircraft for flutter testing of the modified aircraft for two different weight and CG configurations, and envelope expansion was achieved up to the dive speed of the basic aircraft. Analysis results and test results indicate that although the flutter speeds of the modified aircraft were lowered compared to the basic aircraft, the overall damping of the wing vibration modes stayed above the values required by the flutter regulation MIL-A-8870C for the wing structure modes up to about 10 Hz which is a typical frequency range that can be excited by control surface kicks.

Lessons learned from the flight test program, specifically related to the practical difficulty of executing flutter test with the particular transport aircraft type, reliable data gathering and data analysis methods were elaborated.