Wave Drag Characteristics of a Low-Drag Supersonic Formation Flying Concept

Abstract

I n the past 50 years, although the technology for transonic flight has matured, commercially practical civil supersonic transport has not been realized. The two major problems that have been preventing supersonic commercial transportation are wave drag and sonic boom. Wave drag, which is the dominating component of drag at supersonic speeds, leads to a deterioration of cruise efficiency. And sonic booms have a problem of public acceptance, which imposes strict limitations on overland flights by supersonic transports. This leads to less flexible operation capabilities, reducing the profitability of their operation. Many attempts have beenmade tominimize the wave drag and the sonic boom in the past. Among them, many studies approached this problem by optimizing the shape of the wing-body configuration. However, most studies have shown a strong tradeoff between wave drag and sonic boom, making it impossible to minimize wave drag and sonic boom simultaneously, for a given aircraft overall length. The supersonic formation flying concept in this paper uses the benefits of multibody favorable wave interference to reduce the volume and lift dependent wave drag of the following aircraft. When aircraft fly through the air at supersonic speeds, they leave momentum in the air behind them, as shock waves and expansion fans. This is the cause of wave drag. This pressure gradient can be used to generate lift and thrust, which results in the collection of the momentum left in the air by the leading aircraft. Friedman and Cohen [1] carried out linear analyses on bodies of revolution, imitating a fuselage and stores. As a result, they have shown that wave drag per total cross-sectional area can be reduced when placed in an optimal relative position. Positions of the stores that were favorable for wave drag reductionwere positionswhere the stores were placed inside a shock wave, which is a positive pressure jump. The shock wave that impinges on the stores generate thrust, canceling a part of their drag. In this paper, wave drag characteristics of this concept is investigated using Euler simulations. The dependence of wave drag to the relative position of the aircraft is investigated to evaluate the effectiveness of this concept and gain insight on the wave drag characteristics of supersonic formation flying.