An MDO investigation of the impact of practical constraints on an HSCT configuration

Abstract

This paper presents results from an MDO (multidisciplinary design optimization) design procedure illustrating the effects of numerous trim, control, and performance requirements for a high speed civil transport. We optimize the design for minimum take off gross weight, including both aerodynamics and structures to find the wing planform and thickness distribution, fuselage shape, engine placement and thrust, using 29 design variables and 70 constraints to insure realistic results. The constraints include the engine-out and crosswind landing requirements, as well as engine nacelle ground strike, rotation to lift-off attitude, balanced field length, and approach trim constraints. We found that the engine-out condition and the engine nacelle ground strike avoidance were critical conditions. The addition of a horizontal tail to allow take-off rotation resulted in a significant weight penalty. We also examined the effect of engine technology and sizing based on cruise and balanced field length constraints. The field length has a large influence on weight. We included a subsonic leg in our mission analysis, which also resulted in a large weight penalty. The cumulative effect of these considerations leads to very large increases in vehicle weight. We conclude with sensitivity studies performed to understand the effect of some of the constraints and the accuracy of the drag prediction on the optimized results. (Author)