M2-F1 lifting body is being towed. The wingless, lifting
body aircraft design was
initially conceived as a way to land an aircraft horizontally after
The absence of wings would make the extreme heat of re-entry less damaging
to the vehicle.
For some missions, particularly human
spaceflight missions, designers wanted a pilot to be able to control the
craft so it would land it at a specific spot. Beginning with the Mercury
and Gemini spacecraft programs in the late 1950s through the mid-1960s,
U.S. aerospace engineers investigated the possibility of providing space
capsules with some amount of lift during re-entry so their landing could be
controlled to some extent. Of course, the most logical method for
generating lift is through wings. But wings create a problem for a
re-entering craft because they have to be very strong to handle the extreme
stresses of the wind pushing against them from below at hypersonic speeds
(at least five times the speed of sound) during re-entry.
The concept of
lifting body aircraft is all about generating lift from it's body itself
without the aid of wings. Such aeroplanes use wings only for their
stabilising and steering effects. There are other concepts which fly using
wings with the body contributing a smaller but significant amount of lift.
In 1962, NASA engineer Dale Reed began
urging research on wingless aircraft that could re-enter from space and yet
still be flown to a landing. He called these wingless airplanes "lifting
bodies" because they generated their lift from the body of the aircraft,
rather than from wings like in a conventional aircraft. He advocated a
design that was essentially a cone cut in half. Many of the people he
spoke to were sceptical, so he constructed a model out of balsa wood and
threw it off the roof of a building. It proved stable in flight (in other
words, it did not tumble uncontrollably but glided through the air) and
soon he was towing the model into the air behind a gas-powered model where
it was released to glide to a landing. He filmed his experiments and
showed them to colleagues at the NASA Flight Research Centre (now NASA's
Dryden Flight Research Centre) at Edwards Air Force Base in California.
Soon he headed a small development team that had approval to build a
lightweight, full-scale manned aircraft designated the M2-F1, "M"
signifying a manned vehicle and "F" designating a flight vehicle. Others
soon began calling it the "Flying Bathtub."
Like its tiny model predecessor, the
M2-F1 was built of wood. Officially it was only a full-scale wind tunnel
model, but Reed and his team members planned to tow it behind a Pontiac
Catalina that was souped-up by a hot-rod shop in Long Beach, California,
so that it could drive faster than normal. They did this for some initial
tests of the aircraft in March 1963, towing it along the desert floor
behind the car and then flying it a few feet off the ground. It proved
stable and earned them further support.
On August 16, 1963, the
M2-F1 was towed into the air behind an R4D (C-47) "Gooney Bird" transport
plane. Over the next two years, Reed and his NASA team conducted a number
of tests using the aircraft to determine its flying characteristics. These
tests showed that the aircraft could indeed fly. Interest in the aircraft
grew both in NASA and the U.S. Air Force and NASA approved the development
of a heavier aircraft to explore higher speeds. This was designated the
M2-F2 and it was equipped with a rocket engine and dropped from a B-52
airplane, like many of the X-plane experimental
M2-F2 lifting body aircraft crashes when landing on May 10, 1967.
Engineers at NASA's Langley Research
Centre in Virginia developed another lifting body design. It was
designated the HL-10. The HL-10 design offered a great amount of internal
volume for its size, meaning that an operational version would be able to
carry a lot of people or cargo inside. It differed somewhat from the M2-F2
by having the rear edges of the fuselage extended outward into angled
vertical fins. The M2-F2 and HL-10 would be dropped from the B-52, ignite
their rockets to achieve high speeds, and then glide to un-powered,
"dead-stick" landings on the dry lakebed at Edwards Air Force Base.
The M2-F2 made its first glide flight on
July 12, 1966. The HL-10 made its first glide flight in the same manner on
December 22, 1966. But the HL-10 did not fly again for 15 months because
those running the program became concerned about its safety. This was
prompted in part by a number of near crashes and temporary losses of
control with the other lifting bodies such as the M2-F2.
One of the big problems the lifting
bodies had was with what is called "flow separation." The airflow over the
fuselage became turbulent and did not flow smoothly. The HL-10 designers
fixed this by extending the leading edges of the fins (the edge that heads
into the airflow) and cambering, or curving, them.
On May 10 1967, the M2-F2 crashed when
its pilot, Bruce Peterson, lowered the landing gear half a second too
late. It rolled down the dry lakebed and tumbled, severely injuring its
pilot. (Footage of this crash was later used in the opening credits of the
1970s TV show The Six-Million Dollar Man.) The M2-F2 was damaged
but later rebuilt as the M2-F3, with an additional vertical fin.
M2-F3 lifting body is being launched from NASA-s B-52 mother ship.
The HL-10 was eventually flown to a
speed of Mach 1.86. Several powered landings were also conducted with this
aircraft, using rocket engines to provide power as the aircraft set down
on its landing gear, but these demonstrated that powered landings were
little better than un-powered ones. Another aircraft, the X-24A, was also
built and tested. In 1972 it was modified into the dart-shaped X-24B,
which was used to explore higher speeds. It eventually reached a speed of
Mach 1.75. NASA also experimented with the unmanned Hyper III lifting
body. Long, thin, and angular, it could not land without help, so a
one-piece pivoting wing was developed that deployed just before landing,
generating more lift at lower speeds.
X-24B is seen on the lakebed at NASA's Dryden Flight Research Centre in
This was the last aircraft to fly in Dryden's Lifting Body program.
The final flight took place on September 2, 1975.
People usually think of technology
development in terms of producing items that they can use. But often
developing technologies can demonstrate limitations and the need for
either new technological approaches or the need to accept existing,
less-than-ideal solutions. The lifting bodies developed by NASA during the
1960s demonstrated the limitations of aircraft without wings. Their
primary limitation was their high landing speeds, which made controlling
them difficult and dangerous. As a result of this experience, NASA
engineers chose to develop a Space Shuttle that had wings. Although the
Space Shuttle still has a high landing speed, it is slower and more
manoeuvrable than a large lifting body design would be. However, another
value of the lifting body research was that it proved that un-powered
landings could be safe. The space shuttle benefited greatly from this
In the early 1990s, Langley Research
Centre proposed an upgraded HL-10 known as the HL-20 Personnel Launching
Vehicle to serve as a "space taxi" to the International Space Station.
Although a mock-up was built, the program was not approved and no flight
tests took place.
Later, in the 1990s, NASA engineers
began evaluating a lifting body again as a Crew Return Vehicle (CRV) for
the International Space Station. The CRV would serve as a lifeboat,
attached to the Space Station and capable of returning the crew to Earth
in event of an emergency or injury. It had to be able to decelerate
through the atmosphere at a relatively low rate so not to put too much
strain on an injured crewmember. It also had to be able to glide a great
distance so that the crewmembers could detach from the space station
anywhere in their orbit—even over the oceans—and still return to a safe
area. A craft that could generate lift during its re-entry into the
atmosphere was ideal for this because it could detach from the space
station far from its landing site and glide for thousands of miles before
X-38 is seen under the wing of NASA's B-52 mother ship before launch of the
lifting-body research vehicle.
The photo was taken from the observation window of the B-52 bomber.
Designers chose to develop a lifting
body and initiated a testing program using a new vehicle, designated the
X-38. The X-38 uses the same exterior configuration as the X-24A,
including the rounded bump on the upper fuselage where the X-24A had a
cockpit even though the X-38 has none. This was done to be able to use the
X-24A's testing data to maximum extent. The one key difference is that the
X-38 does not land conventionally on wheels on a runway. Instead, the X-38
deploys a rectangular parachute as it nears the ground and floats to a
landing. This method was chosen because NASA learned during its earlier
lifting body research that lifting bodies have unsafe landing