exit area of the rocket, ft drag coefficient drag coefficient at zero lift drag, lb zero-lift drag, lb aircraft efficiency factor acceleration of gravity, ft sec 2 altitude, ft h + V/2g = energy height, ft lift, lb instantaneous mass of the aircraft, lb ft"" sec mass of propellant consumed per unit time, lb f t 1 sec Mach number atmospheric pressure, lb ft ~ static pressure in the exit section of the nozzle, lb f t 2 local static pressure at a point of the external walls of the aircraft, lb ft ~ air constant, ft sec"" °R~ Reynolds' number wing surface, ft time, sec thrust, lb absolute velocity of the aircraft, ft sec 1 weight of the aircraft, lb average value of the axial component of the relative velocity of the gases in the exit section of the rocket; i.e., velocity referred to a reference frame rigidly connected to the solid part of the aircraft, ft s ec 1 weight of fuel consumed per unit time for an aircraft equipped with air-breathing engines, lb s ec 1 derivative of the air temperature with respect to altitude, ^ f l r 1 ratio of specific heat at constant pressure to specific heat at constant volume = 1.4 for air specific energy, ft sec ~ inclination of the flight path with respect to a horizontal plane (positive for climbing flight) aspect ratio air density, lb sec f t 4