An experimental and analytical study of a lifting-body wind-tunnel model exhibiting body-freedom flutter

Flutter analysis of the proposed National Aerospace Plane indicates that in the subsonic to transonic flight regime, the vehicle may be susceptible to an instability known as body-freedom flutter. Body-freedom flutter is a dynamic instability involving a vehicle rigid-body mode coupling with one or more of the vehicle's elastic modes. In the case of the NASP, the body-freedom flutter predicted by analysis involves the short-period mode of the vehicle coupling with the pivot mode of the all-movable wings. A wind-tunnel test was designed to investigate this phenomenon. Parameter studies included variations in wing-actuator stiffness, wing-pivot shaft location along the root chord, and thickness of the fuselage. The wind-tunnel test was conducted in the NASA Langley Transonic Dynamics Tunnel. Flutter boundaries were measured in the wind tunnel for three configurations and a model divergence point was measured on a fourth configuration. At the last flutter point obtained during the test, body-freedom flutter proved to be rather violent. The analysis used in this study incorporated thin-wing theory aerodynamics and did a fairly good job of predicting the flutter boundaries.