The use of a Reflectometer as a Monostatic Radar for Measuring Aircraft Structural Flutter

As the drive for increased aviation efficiency continues to push airframe designs toward lighter, more flexible configurations, the technology limits for modelling and monitoring airframe and control surface flutter events continue to be a challenge. Presented is a new flutter sensing technique that configures a commercial microwave reflectometer as a monostatic radar to measure low frequency vibrations typical of subsonic aircraft structural flutter. The stepped frequency continuous wave (SFCW) system with bandwidths of 90 MHz and 7.5 GHz was used to measure vibration frequencies from 1Hz to 125 Hz in a carbon fiber-reinforced polymer (CFRP) composite panel. In addition to the SFCW mode, a single frequency mode has been used to determine the velocity of vibration from 1Hz to 75 Hz. The data presented demonstrates that commercial reflectometers can be used to measure flutter-induced aircraft vibrations.