Part of the Charles A. Lindbergh Lecture at the National Air and Space Museum, Smithsonian Institution by lifting-body pilot Bill Dana.
The other "heavyweight " lifting body contracted for by NASA on the basis of a successful lightweight lifting body program was the Langley-designed HL-10 (slide). It was delivered to the Dryden Flight Research center in 1966, flew first in December of that year, and in the succeeding three years flew 37 flights. Twenty-four of these flights were powered; the HL-10 was flown to an altitude of 90,000 feet and a speed of about twice the speed of sound. Data were obtained on subsonic,
transonic and supersonic stability and control, structural loads, and terminal maneuvering.
At the time the plywood M2 was coming into flight status, Air Force Colonel Chuck Yeager was Commandant of the Air Force Test Pilot School. (Slide.) Chuck was a friend and long-time colleague of the Dryden center Director. The center Director invited Chuck to fly the plywood M2, and Chuck was impressed by the lifting body's capabilities. Chuck recommended through channels that the Air Force become acquainted with lifting bodies, and the Air Force Research and Development Command
contracted with the Martin-Marietta Corporation for the design and manufacture of a third distinct lifting body shape known as the X-24A (slide).The X-24A was developed completely independently of NASA, but when the time came to fly it, it was injected into a joint NASA/Air Force lifting body test force, and it flew alongside the M2 and HL-10 starting in 1969. It flew 28 flight and reached a Mach number of 1.6.
X-24A transformation to X-24B
While the X-24A was still in flight phase, the Air Force became interested in another class of lifting bodies, and because of advances in materials and thermal protection, the gently rounded contours of the lifting bodies were no longer required. To build a flight demonstrator for the new class of vehicle, the Air Force chose as a core the X-24A itself, onto which were grafted a long, pointed nose and horizontal fins outboard of the vertical fins, (slide) giving the new vehicle a
triangular planform (slide). The result was called the X-24B, and it was more of a spaceplane than a lifting body (slide).
X-24B with horizontal fins outside of the vertical side fins
All of the lifting bodies, including the X-24B, were flight demonstrators rather than true spacecraft. All were dropped from the same B-52 that on other days carried the X-15, and all were powered by a small rocket engine that accelerated them to between Mach 1.5 and Mach 2 to allow evaluation at transonic speeds.