Stability and Control Assessment of a Blended-Wing-Body Airliner Configuration

Abstract

Blended-wing-body type airliner configurations offer significant benefits over conventional designs. However, there are several problems to be overcome, one of which concerns flying qualities, stability and control. The European Union 'VELA' (Very Efficient Large Aircraft) project was set up to investigate tools for design of novel configurations of this type, including those associated with the flight mechanics challenges. In this paper, the static and dynamic characteristics of a novel airliner for a specific flight phase are shown and some preliminary flying qualities criteria have been applied. Bifurcation diagrams are used for the investigation of its nonlinear behaviour, and the problems of jump phenomena and mode coupling are identified. Time histories are plotted to verify the results of the bifurcation analysis more fully. For the more realistic investigation over its dynamic characteristics, some constraints are made in the model, and then the daisy chain control allocation technique is introduced using the pseudo-inverse method. This system is also programmed in the continuation and bifurcation analysis framework such that the gains for a pole placement stability augmentation system are computed simultaneously with the aircraft steady states and the control surface deflections over a wide operating range. Results are shown for an example for which the airframe is unstable in pitch and for which the stability and control augmentation system is then designed to satisfy Level 1 handling qualities criteria throughout the operating region.