Wind Tunnel Test of Full Span Flutter Models of Small Supersonic Experimental Aircraft

Three wind tunnel tests for flutter have been conducted under the development of the National Experimental Airplane for Supersonic Transport (NEXST-1) of JAXA launched in 2005. Three kinds of flutter were investigated by using three different wind tunnel models at that time. Discussion of this paper is mostly on the one for a main wing model. The planform of the NEXST-1 wing is a cranked arrow having warp in the out of plane direction. For flutter, the model showed the so called transonic dip of which bottom speed was at Mach 1.02. It was also subjected to limit cycle oscillation (LCO) in the transonic regime. The flutter was dominantly the bending of the out board wing. In the design stage of the NEXST-1, a 20% reduction was anticipated for the transonic regime by the flutter analysis with the linear aerodynamic theory. The wind tunnel experiment resulted in 21% lower in the flutter speed that was slightly higher than the assumption. The NEXST-1 aircraft was launched in the piggy back style by the solid rocket booster. Therefore, the flutter was also investigated for this launching configuration. The flutter speed reduction in this case was 27%, which was larger than that for a sole airframe. As a consequence, the design methodology for transonic flutter is thought to be confirmed for supersonic flight vehicles.