DESIGN OF A BODY FREEDOM FLUTTER FLIGHT MODEL WITH CONVENTIONAL CONFIGURATION

When the short-period modal frequency of an aircraft is close to the elastic modal frequency of a flexible wing structure, it is prone to cause rigid-elastic coupling, leading to a special kind of flutter - body freedom flutter. Body freedom flutter is commonly found in large aspect ratio tailless or forward-swept wing configuration, and this paper investigates the design of a body freedom flutter flight model for conventional configuration with short fuselage. For the designed configuration, the influences of the wing swept angle and inertia parameters (with varied mass and position of the payload) on its flutter characteristics (flutter speed and flutter frequency) are analyzed. The calculation results show that the sweptback wing layout is more prone to body freedom flutter than the straight wing configuration, and the flutter speed and flutter frequency decrease with the increase of the wing swept angle. When the swept angle is large enough, the flight model will exhibit body freedom flutter. The flutter speed is decreasing as the mass of payload increasing. Interestingly, the futter speed first decreases and then increases as the mass center of the payload moving forwardly, and the flutter frequency monotonically keeps increasing when the gravity center of the whole model is forward. Correspondingly, the coupling between the pitch mode and the bending mode gets stronger. However, the flutter phenomenon disappears when the mass of payload is moved forward to a certain position. A prototype vehicle has been built and the theoretical model is validated against the modal test results. This study provides a new perspective in understanding the body freedom flutter phenomenon for air vehicles of conventional configuration.