Full-Span Flying Wing Wind Tunnel Test: A Body Freedom Flutter Study

Abstract

Aiming at the experimental test of the body freedom flutter for modern high aspect ratio flexible flying wing, this paper conducts a body freedom flutter wind tunnel test on a full-span flying wing flutter model. The research content is summarized as follows: (1) The full-span finite element model and aeroelastic model of an unmanned aerial vehicle for body freedom flutter wind tunnel test are established, and the structural dynamics and flutter characteristics of this vehicle are obtained through theoretical analysis. (2) Based on the preliminary theoretical analysis results, the design and manufacturing of this vehicle are completed, and the structural dynamic characteristics of the vehicle are identified through ground vibration test. Finally, the theoretical analysis model is updated and the corresponding flutter characteristics are obtained. (3) A novel quasi-free flying suspension system capable of releasing pitch, plunge and yaw degrees of freedom is designed and implemented in the wind tunnel flutter test. The influence of the nose mass balance on the flutter results is explored. The study shows that: (1) The test vehicle can exhibit body freedom flutter at low airspeeds, and the obtained flutter speed and damping characteristics are favorable for conducting the body freedom flutter wind tunnel test. (2) The designed suspension system can effectively release the degrees of freedom of pitch, plunge, and yaw. The flutter speed measured in the wind tunnel test is 9.72 m/s, and the flutter frequency is 2.18 Hz, which agree well with the theoretical results (with flutter speed of 9.49 m/s and flutter frequency of 2.03 Hz). (3) With the increasing of the mass balance at the nose, critical speed of body freedom flutter rises up and the flutter frequency gradually decreases, which also agree well with corresponding theoretical results.

Numerical Investigations of Subscale Flexible High Aspect Ratio Aircraft on a Dynamic Wind Tunnel Rig

“…A wire suspended full-span aircraft model has been used to study body freedom flutter by Shi et al in Ref. [14] which showed good agreement with theoretical predictions and found a decrease in body freedom flutter speed as a result of wing flexibility when compared with a cantilever wing model.…”

Experimental and Computational Investigation of a Highly Flexible Airframe Taxiing Over an Uneven Runway for Aircraft Vibration Testing

“…Enhanced aircraft efciency and reduction in emissions necessitate a reduction in structural weight and utilizing lightweight composite materials. A drawback of this approach is the increase in aircraft fexibility, which results in larger deformations under external loads and a decrease in the frequencies of the fexible structural modes [12][13][14]. The latter gives rise to aeroelastic instabilities (futter) and the fexible modes interacting with the aircraft's rigid body modes and the pilot biodynamics, resulting in degraded performance or catastrophic loss of the airframe.…”

“…Similar observation can be made about the second mode (1 st symmetric bending) in Figure4.12 for the V T = 0.3 and V T = 0.4 speeds when compared to the one in Figure4.2. Although the third, the fourth and the ffth mode shapes of the three taxiing speeds, shown in Figures 4 13…”