10 - Configuration Development and Flying Qualities

Summary

Our treatment of aerodynamic performance (i.e. the mapping from shape to lift and drag for clean wings) idealized the plane as a mass point with lift and drag forces. The variation of the aerodynamic forces on the aircraft along the flight path determines its stability and the need for control with sustained authority. Addressing this issue requires an airplane model responding to gravity, thrust, and realistic aerodynamic forces and moments. A six-degree-of-freedom Newtonian rigid body model is compiled from the mass and balance properties of the airframe. Computational fluid dynamics (CFD) is used to predict the aerodynamic forces and moments, expressed in look-up tables of coefficients, and a major part of the text explains how such tables can be populated efficiently. The stability properties describe how well the aircraft recovers from external disturbances and how it reacts to commanded changes in flight attitude. The response in steady flight to small disturbances can be represented as a superposition of a small number of natural flight modes, the quantitative properties of which provide the quantified flight-handling qualities. A number of examples are given, from redesign of the Transonic Cruiser configuration for better pitch stability to CFD investigation of vortex interference on control surfaces on an unmanned aerial vehicle.​