An Investigation of the Attainable Efficiency of Flight at Mach One or Just Beyond

The Breguet range equation indicates that to the first order of approximation range will be maximized by maximizing ML/D, where M is the Mach number and L/D is the lift/drag ratio. Since the drag coefficient increases very rapidly as the Mach number approaches one, this leads to the design of a long range aircraft which fly at high subsonic speeds, typically in the range Mach 0.8 to 0.85, just before the onset of drag rise. The results of the present investigation indicate that a wing swept back at an angle of 50 to 55 degrees and a carefully shaped fuselage it may be possible to delay the onset of drag rise, to Mach one or even to a Mach number slightly greater than one. This would enable the design of a long range aircraft which cruises at a speed just above Mach one, but low enough that there would be no supersonic boom.