Aeroelastic characteristics of a highly flexible aircraft

This paper describes an aeroelastic analysis performed on a human-powered aircraft. The structural characteristics of this aircraft (namely, very flexible wings, high aspect ratio, and low wing loadings) are typical of proposed high-altitude long-endurance aircraft. Because of these unique features, the aircraft exhibits uncommon aeroelastic characteristics. The structural dynamics of the airplane are obtained from a finite element model. In an assumed mode approach, a subset of the natural mode shapes is used to calculate the quasisteady and unsteady generalized modal forces using a two-dimensional strip model, which includes unsteady drag and leading-edge suction forces. The aeroelastic model predicts the airplane to be stable (at both sea level and high altitude), except for a mildly unstable phugoid mode. The results indicate that unsteady aerodynamics are significant for this type of aircraft and that the flexibility of the aircraft must be included to correctly model the dynamics for control purposes. A final conclusion is that the aircraft dynamics are highly dependent on the flight conditions (flight speed and altitude). d,D e J k,K Nomenclature = area of span station i • parasite drag coefficient = slope of lift curve = aerodynamic moment about the aerodynamic center at zero angle of attack = half chord (ct/2) at span station i - damping, damping matrix = Oswald's efficiency factor