September 14, 1967: NASA X-24A Lifting Body

  • Published
  • Air Force Flight Test Center

A C-130 brought the Martin X-24A lifting body research vehicle to the Center. The wingless aircraft was delivered to the National Aeronautics Space Administration Flight Research Center on October 5 to be mated to its B-52 launch aircraft. The X-24A program’s objective was to evaluate and develop the subsonic, transonic and supersonic handling qualities and performance of typical reentry configurations.

Subsonic indicated any speed lower than the speed of sound within a sound-propagating medium.  Subsonic aircraft, a flying machine that flies at air speeds lower than the speed of sound.  Subsonic ammunition, a type of bullet designed to avoid creating a loud shockwave when fired.  Subsonic flight, an aircraft flight at air speeds lower than the speed of sound in air.  Subsonic and transonic wind tunnels.

Transonic flight is flying at or near the speed of sound relative to the air through which the vehicle is traveling. A typical convention used in aeronautics is to define transonic flight as speeds in the range of Mach 0.72 to 1.0 (600–767 mph) at sea level.  This condition depends not only on the travel speed of the craft, but also on the temperature of the airflow in the vehicle's local environment. It is formally defined as the range of speeds between the critical Mach number, when some parts of the airflow over an air vehicle or airfoil are supersonic, and a higher speed, typically near Mach 1.2, when most of the airflow is supersonic. Between these speeds some of the airflow is supersonic, but a significant fraction is not.

Supersonic travel is a rate of travel of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343.2 m/s (1,126 ft/s; 768 mph; 667.1 kn; 1,236 km/h). Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic. Flights during which only some parts of the air surrounding an object, such as the ends of rotor blades, reach supersonic speeds are called transonic. This occurs typically somewhere between Mach 0.8 and Mach 1.2.

Supersonic sounds are traveling vibrations in the form of pressure waves in an elastic medium. In gases, sound travels longitudinally at different speeds, mostly depending on the molecular mass and temperature of the gas, and pressure has little effect. Since air temperature and composition varies significantly with altitude, Mach numbers for aircraft may change despite a constant travel speed. In water at room temperature supersonic speed can be considered as any speed greater than 4,724 feet per second. In solids, sound waves can be polarized longitudinally or transversely and have even higher velocities.  Supersonic fracture is crack motion faster than the speed of sound in a brittle material.

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