Aircraft Design - Flight, Wings, Engines

The selection of aircraft must be various critical requirements.  The initial aircraft sizing for the aircraft takeoff gross weight (TOGW) must be estimated. The Takeoff wing loading (W/S)to for landing and takeoff with consideration of the operational or intercept altitude and speed. The airfoil section that takes into consideration of the section, t/c, camber, nose shape, and planform shape which is the aspect ratio, taper, sweep, fixed versus variable geometry. The fuselage sizing and shape must be considered for the volume requirements of crew, payload, engines, fuel, and avionics. The fuselage fineness ratio l/d (ratio of length of maximum diameter) are requirements for estimate of whether the aircraft will be used for subsonic, supersonic, or mixed velocities.

The estimation of tail size must defined as to if it is an aft tail, canard, or tailless configuration. An important consideration of all the above factors is the aircraft zero-life drag C_D0, lift curve slope C_La, and drag-due-to-lift factor K Mach number.

The sizing of the engines must be considered to evaluate the engine thrust-to-weight  ratio (T/W)_TO is an important factor that considers such factors as efficient cruise or loiter, take off, air combat, minimum time to intercept, and service ceiling. Design consideration of the inlet sizing to match engine requirements for issues of pressure recovery, thrust data correction, bypass drag, and spillage drag. (Nicolai 1975). The sizing of the tail and control surface are important to determine the trim drags. A cost estimate must be made of all the design components for prototype and production of the aircraft. An estimate must be made of the operations and maintenance cost to give an indication of the life cycle cost (LLC) for the aircraft. There are specifications of most of the world’s aircraft in “Janes All the Worlds Aircraft 2004-2005” which gives great deals to flight specifications for aircraft. (Jackson 2004-2005)

The Lockheed SR-71 Blackbird was a high speed swept wing jet, with an aspect ratio of 1.7 that can cruise at Mach 3.2 or more than 2200 mph, at altitudes of up to 100,000 ft. and range of 3000 miles. The A-12 and YF-12 were reconnaissance planes developed at the Lockheed “Skunk Works” in the 1950’s. The cost of operating the Blackbird SR-71 is over $50,000 per hour. 

The engines were two Pratt & Whitney J58 jet engine each producing 35,500 lb of thrust.  The compressor is a 9-stage, axial flow, single spool with a two-stage axial flow turbine. The J58 fuel flow rate was 8,000 gallons per hour, and exhaust-gas temperature of 3,400° F. A special AG330 engine start cart was used to spool the engines up to the proper rotational speed of 3,200 RPM for starting. The SR-71 had a fuel capacity of 80,000 lbs. fuel it usually only was filled in the range of 45,000-65,000 lbs. of JP-7 aviation fuel.

The airframes were built almost entirely out of titanium and exotic alloys capable of withstanding 600° F. During high speed flight the balance of total thrust was produced by a unique engine inlet and moveable conical spike at the front of each engine nacelle. The air inlets allowed the air to bypass the engines and go directly into the afterburners and ejector nozzles, acting as ramjets at high altitude. The vertical tails are canted slight to deflect large radar returns they would produce. Tires are filled with nitrogen and impregnated with powdered aluminum to withstand heat.