The X-24 was one of a group of lifting bodies flown by the NASA Flight Research Center (now
Armstrong Flight Research Center) in a joint program with the U.S. Air Force at
Edwards Air Force Base in
California from 1963 to 1975. The lifting bodies were used to demonstrate the ability of pilots to maneuver and safely land wingless vehicles designed to fly back to Earth from space and be landed like an airplane at a predetermined site. Lifting bodies’ aerodynamic lift, essential to flight in the atmosphere, was obtained from their shape. The addition of fins and control surfaces allowed the pilots to stabilize and control the vehicles and regulate their flight paths. The X-24 (Model SV-5P) was built by
Martin Marietta and flown from Edwards. The X-24A was the fourth lifting body design to fly; it followed the
NASA M2-F1 in 1964, the
Northrop HL-10 in (1966), the
Northrop M2-F2 in 1966 and preceded the
Northrop M2-F3 (1970). The X-24A was a fat, short teardrop shape with three fins for control—the center fin vertical and the left and right fins canted slightly outward. It made its first, unpowered, glide flight on April 17, 1969 with Air Force Maj.
Jerauld R. Gentry at the controls. Gentry also piloted its first powered flight on March 19, 1970. The craft was taken to around 45,000 feet (13.7 km) by a modified B-52, drop-launched, then either glided down or used its rocket engine to ascend to higher altitudes before gliding down. The X-24A was flown 28 times at speeds up to 1,036 mph (1,667 km/h) and altitudes up to 71,400 feet (21.8 km).
X-24B The X-24B's design evolved from a family of potential reentry shapes, each with higher
lift-to-drag ratios, proposed by the Air Force Flight Dynamics Laboratory. To reduce the costs of constructing a research vehicle, the Air Force returned the X-24A to the Martin Marietta Corporation—as Martin Aircraft Company became after a merger—for modifications that converted its bulbous shape into one resembling a "flying flatiron",
i.e., rounded top, flat bottom, and a double
delta planform that ended in a pointed nose.
John A. Manke was the first to fly the X-24B, a glide flight on 1 August 1973. He was also the pilot on the first powered mission 15 November 1973.
X-24C A variety of "X-24C" proposals were floated between 1972 and 1978. Perhaps the most notable was a Lockheed
Skunk Works design, the
L-301, which was to use
scramjets to reach a top speed of Mach 8.
SV-5J After learning about a remark by
Chuck Yeager that he would like to have some jet-powered lifting bodies for training purposes, Martin designed and built, on its own initiative, two examples of the SV-5J. The SV-5J was a jet-powered version of the rocket-powered X-24A. The SV-5J had identical dimensions to the X-24A, but was powered by a single
Pratt & Whitney J60-PW-1 jet engine of 1360 kgf, in place of the X-24A's Reaction Motors XLR-11-RM-13 rocket engine. Martin also manufactured a full-scale, unflyable, mock-up of the SV-5J. (Confusion over number built may be due to the mock-up being included in the production list.) Martin were unable to convince
Milt Thompson to fly the SV-5J, even after offering a $20,000 bonus. Both examples remained unflown. As the original X-24A was converted to X-24B, one of the SV-5Js eventually was converted to represent the X-24A, for display at the
National Museum of the United States Air Force,
Wright-Patterson AFB,
Ohio, beside the original X-24B. ==Operational history==