On the optimum cruise speed of a hypersonic aircraft

Some preliminary results that have been obtained in the frame of the SANGER system studies are presented. SANGER is a West German study project and technology reference system for a future advanced space transportation system. The first stage of this vehicle is a hypersonic aircraft from which a passenger version could be derived. The analyses indicate that a speed of Mach 4.4 will lead to maximum seat mileage per day as well as to minimum propellant consumption. The speed-related cruise altitude of 24500 m or 80000 ft is above the most sensitive ozone layer and high enough to produce only one-third of the noise ground pressure which is considered as the acceptable limit (1 lb/ft²) over populated areas. The aircraft surface temperatures at these conditions can still be managed by a conventional titanium alloy structure with special provisions only at the leading edge and the engine inlets. The potential route structure and economics of such an aircraft are discussed