The success of Dryden's M2-F1 program led to NASA's development and construction of two heavyweight lifting bodies based on studies at NASA's Ames and Langley research centers--the M2-F2 and the HL-10, both built by the Northrop Corporation. The "M" refers to "manned" and "F" refers to "flight" version. "HL" comes from "horizontal landing" and 10 is for the tenth lifting body model to be investigated by Langley. The M2-F2 weighed 4,620 pounds, was 22 feet long, and had a width of about 10 feet.
The first flight of the M2-F2 was on July 12, 1966 with Milt Thompson was the pilot. Thompson was dropped from the B-52's wing pylon mount at an altitude of 45,000 feet on that maiden glide flight. The glide flights showed that the M2-F2 was hard to control. Several pilots experienced "pilot induced oscillations," (PIO) in which the vehicle rocked side to side.
On May 10, 1967, during the sixteenth glide flight, NASA pilot, Bruce Peterson experienced a PIO. He was able to bring the M2-F2 under control, but the vehicle was too low for the landing gear to fully extend before it hit the lakebed. Peterson was seriously injured in the landing accident, and the M2-F2 was severely damaged.
NASA pilots and researchers realized the M2-F2 had lateral control problems, and, during the rebuilding effort,it was modified with an additional third vertical fin. This was centered between the tip fins, and much improved the control characteristics. the modified vehicle was renamed the "M2-F3." NASA donated the M2-F3 vehicle to the Smithsonian Institute in December 1973. It is currently hanging in the Air and Space Museum along with the X-15 aircraft number 1.
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