471. Parametric Approach to Aircraft Sizing and Trade-Off Studies

Paper

Abstract

A parametric approach to aircraft sizing and trade-off studies has been developed to aid the design effort. It is particularly valuable for use in the design of V/STOL aircraft, where the choice of propulsion systems is wide and it is necessary to arrive at an early selection of an optimum propulsion system/airframe configuration and airplane size. This paper outlines an engine selection and airplane preliminary sizing procedure and its application to comprehensive weight trade-off studies, The unique weight estimation procedure used to predict the fuel available data, which is a key step, is discussed in detail. The fuel weight available is defined as the difference between the airplane take-off gross weight and the weight empty plus useful load. The procedure permits the estimation of the airplane weight empty in a parametric fashion over a wide range of variables without requiring the definition of the variables by drawing board layout. The weight estimation procedures have been programmed for accomplishment on digital computer facilities, thereby permitting rapid investigation of a large number of cases. The ability of this computerized approach to reflect the influence on airplane weight of the many parameters affecting airplane design is illustrated, including the determination of fuselage size based on a packaging concept. The use of this parametric approach makes it possible to evaluate a large number of propulsion system and airframe configurations rapidly and comprehensively prior to the design stage. This facilitates the design effort, since, at the beginning of the design stage, the area of choice has been narrowed and the weights engineer, as well as the other members of the design team, is provided with a vast amount of weight growth, weight penalty, and trade-off data pertinent to the design and performance of the aircraft.