Effects of nonuniform elastic fuselage modeling on flight dynamics of hypersonic vehicles

A framework for modeling of the flexible air-breathing hypersonic vehicles (HSVs) with nonuniform fuselage section is developed and the effects of nonuniformities on flight dynamics are investigated. The flexible fuselage is modeled as a free-free beam with mass density and stiffness varying along its length. The assumed mode method, whose computation cost is demonstrated to acceptable relative to the finite element method, is utilized to conduct mode analysis of the fuselage.A longitudinal coupled dynamic model is obtained by combining the equations of rigid-body motion, elastic fuselage model, wing/pivot system models and actuator dynamics. A baseline control law developed from rigid vehicle assumption is used to stabilize the rigid-body motion and provide the capacity to consider inflight dynamic behavior. The impact of nonuniform mass density and stiffness distribution on static trim properties and dynamic stability are studied with nonuniformities parameterized. Numerical results indicate that the model with uniform section properties may underestimate the effects of fuselage flexibility on rigid-body flight dynamic characteristics if the section properties of the real vehicle fuselage vary apparently; to alleviate the impact of nonuniformity during the structure design of the vehicle, stiffness enhancement is more effective compared to mass layout adjustment.