Modeling and simulation of flexible flight vehicles

The effects of flexibility on the flight dynamics of large aircraft have been shown to be quite significant, especial ly as the frequencies of the elastic modes become lower and approach those of the rigid-body modes. The handling characteristics of such vehicles are altered significantly from those of a rigid vehicle, and the design of the flight-control system may become drastically more complex. Consequently the need to model accurately the dynamics of such vehicles, and to develop valid simulations, is becoming particularly acute, The theoretical development of a generic flexible-aircraft model is reviewed. This modeling technique allows far the flexible degrees of freedom to be added to an existing simulation model of the vehicle's rigid-body dynamics. The data necessary for modeling a specific vehicle include aerodynamic stability derivatives, aerodynamic influence coefficients, elastic mode shapes, modal frequencies and damping, and generalized masses, Two case studies are presented, both involving the development of motion-based simulations in NASA Langley Research Center's simulation facility, The first example investigates an aircraft similar in geometry to the B-1, whereas the second investigates a large highspeed commercial transport, The dynamic responses (time and frequency domain) for these vehicles are presented, along with the evaluations of the effects of dynamic aeroelasticity on their handling characteristics. The vehicle responses are critical to evaluating hardware and software requirements for simulation fidelity, far example, visual and motion cues. Finally. a brief assessment of the effects of limitations of the simulation facility is presented, Limitations considered include digital time delay, motion hardware bandwidth, and motion washout logic.