M2-F-1 in flight over lakebed on tow line.
The lifting body concept evolved in the late 1950s as researchers considered alternatives to ballistic reentries of piloted space capsules. The designs for hypersonic, wingless vehicles were on the boards at NASA Ames and NASA Langley facilities, while the US Air Force was gearing up for its Dyna-Soar program, which defined the need for a spacecraft that would land like an airplane.
Despite favorable research on lifting bodies, there was little support for a flight program. Dryden engineer R. Dale Reed was intrigued with the lifting body concept, and reasoned that some sort of flight demonstration was needed before wingless aircraft could be taken seriously.
In February 1962, he built a model lifting body based upon the Ames M2 design, and air-launched it from a radio controlled "mothership." Home movies of these flights, plus the support of research pilot Milt Thompson, helped pursuade the facilities director, Paul Bickle, to give the go-ahead for the construction of a full-scale version, to be used as a wind tunnel model and possibly flown as a glider. Comparing lifting bodies to space capsules, an unofficial motto of the project was, "Don't be Rescued from Outer Space - Fly Back in Style."
The construction of the M2-F1 was a joint effort by Dryden and a local glider manufacturer, the Briegleb Glider Company. The budget was $30,000. NASA craftsmen and engineers built the tubular steel interior frame. Its mahogany plywood shell was hand-made by Gus Briegleb and company. Ernie Lowder, a NASA craftsman who had worked on the Howard Hughes "Spruce Goose," was assigned to help Briegleb.
The prototype of a 21st Century spacecraft required the fabrication of hundreds of small wooden parts meticulously nailed and glued together. It was a product of craftsmanship that was nearly obsolete in the 1940s.
Final assembly of the remaining components (including aluminum tail surfaces, push rod controls, and landing gear from a Cessna 150) was done back at the NASA facility.
In the meantime, other NASA engineers devised a special M2-F1 flight simulator, and a hot rod shop in Los Angeles souped-up a Pontiac Catalina convertible to be used as the lifting body ground-tow vehicle.
The M2-F1 did not have ailerons. Instead, it had elevons which were attached to each of the two rudders. A large flap on the trailing edge of the body acted as an elevator. This unconventional arrangement prompted the engineers to rethink the flight control system as well. They eventually devised two schemes. One system was fairly traditional. It used rudder pedal inputs to move the rudders for yaw control, and stick inputs to provide differential deflections of the elevons for roll. The other system used stick inputs to control the rudders for yaw, while rudder pedal deflections moved the elevons for roll.
Milt Thompson tried both systems in the simulator, and surprised the design team when he said he preferred system number two. He reasoned that although side slip delayed roll (which was a result of dihedral effect), the roll rate was twice as high using the rudders instead of the elevons. He said he would rather have the higher roll rates available to him if needed, while the slip could be overcome with proper piloting technique.
This was the system that Thompson practiced on the simulator, and he used it during the initial auto tows. Auto tows were done using a 1000 foot rope fastened to the NASA Pontiac. Rogers Dry Lake provided miles of unobstructed motoring.
On April 5, 1963 Thompson lifted the M2-F1's nose off of the ground for the first time on-tow. Speed was 86 miles per hour. The little craft seemed to bounce uncontrollably back and forth on the main landing gear, and stopped when he lowered the nose to the ground. He tried again, but each time with the same results. He felt it was a landing gear problem that could have caused the aircraft to roll on its back if he had lifting the main gear off of the ground.
Looking at movies of the tests, it was decided that the bouncing was probably caused by unwanted rudder movements. Flight control system number two was replaced in favor of number one, and it never bounced again.
Speeds on tow inched up to 110 miles per hour, which allowed Thompson to climb to about 20 feet, then glide for about 20 seconds after releasing the line. That was the most that could be expected during an auto tow.
In the spring of 1963 the M2-F1 was shipped to Ames Research Center, where it was mounted on twenty-foot poles inside the 40 foot by 80 foot wind tunnel. For two weeks, Thompson and engineers Dale Reed and Ed Brown took turns "flying" it as air blasted by at a 135 miles per hour. They learned more about its flying qualities, and accumulated important data for the upcoming aero tows.
A NASA C-47 was used for all of the aero tows. The first was on August 16, 1963. The M2-F1 had recently been equipped with an ejection seat, small rockets in the tail to extend the landing flare for about 5 seconds (if needed), and Thompson prepared for the flight with a few more tows behind the Pontiac.
Forward visibility in the M2-F1 was very limited on tow, requiring Thompson to fly about 20 feet higher than the C-47 so he could see the plane through the nose window. Towing speed was about 100 miles per hour.
Tow release was at 12,000 feet. The lifting body descended at an average rate of about 3600 feet-per-minute. At 1000 feet above the ground, the nose was lowered to increase speed to about 150 mph, flare was at 200 feet from a 20 degree dive. The landing was smooth, and the lifting body program was on its way.
The M2-F1 proved the lifting body concept and lead the way for subsequent, metal "heavyweight" designs. Chuck Yeager, Bruce Peterson and Don Mallick also flew the M2-F1.
More than 400 ground tows and over 100 aircraft tow flights were carried out with the M2-F1. 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, and the X-24 program. The Lifting Body program also heavily influenced the Space Shuttle program.
To learn more about Lifting Bodies check out the following publications:
- Testing the Lifting Bodies at Edwards
- Wingless Flight