Lunar Landing Research Vehicle Was One Of The World's First Fly-By-Wire Aircraft

President John F. Kennedy's 1961 challenge to put a man on the moon and return him safely to Earth by decade's end electrified much of the country, but it floored most NASA engineers.

Not that going into space was a new idea to engineers at NASA, or its predecessor, the National Advisory Committee for Aeronautics. NACA engineers had been discussing putting humans into space since the early 1950s. But contemplating orbital flight is not the same thing as planning for an excursion to the moon's surface.

Interestingly, two organizations were simultaneously thinking about the same thing: regardless of what vehicle NASA settled on to get to the moon, astronauts would need something to simulate, here on Earth, the descent to and landing on the moon. The two organizations were NASA's Flight Research Center at Edwards, Calif., and the Bell Aircraft Corp. in Niagara Falls, NY.

Among the challenges was simulating the moon's gravity, which is only a sixth of Earth's. How, in the early 1960s, are you going to do this with a wingless aircraft? What method will you use to negate five-sixths of the Earth's gravitational pull in flight? How will you compensate for the fuel you burn off while in flight? (Keep in mind the state of computing in 1962, and especially, of portable computers.)

And how are you going to reproduce the moon's lack of atmosphere right here on Earth? Flying in a vacuum is quite different from flying in an atmosphere, more different that you would expect, as the astronauts later attested. Even small wind gusts will affect a simulation like the one in question.

What NASA and Bell came up with was the Lunar Landing Research Vehicle, or LLRV. The LLRV – quickly dubbed the Flying Bedstead – was powered by a General Electric CF-700, the fan-jet version of the J-85 engine, mounted inside two gimbaled rings. The dual gimbals enabled the engine to provide true vertical thrust-perpendicular to the Earth's surface-while allowing the rest of the vehicle to rotate freely in pitch and roll. Eight thrusters were fixed to the frame as lift rockets, capable of producing 500 pounds of thrust each. These were used for lift when flying a lunar landing simulation.

For maneuvering, the engineers chose 16 smaller thrusters, four at each corner of the vehicle. These were fired in pairs, one up and one down at opposite corners of the vehicle. Half of the 16 thrusters were adjustable on the ground to vary their output from 18 to 90 pounds thrust so engineers could experiment to find which setting was best suited for training. The craft carried two fuels: JP-4 for the jet engine and hydrogen peroxide for the thrusters. The hydrogen peroxide was a 90 percent pure solution, and was pressurized with helium to ensure a constant flow to the thrusters.

Bell delivered the first LLRV to the Flight Research Center in the spring of 1964. The second vehicle followed not long after. Ground tests began once the first vehicle was uncrated and assembled, and in October of that year Joe Walker, the center's chief pilot, took the LLRV up for its first flight. The CF-700 engine could produce 4,200 pounds of thrust under ideal conditions, barely enough for a thrust-to-weight ratio of 1.05 to 1.

Perhaps more remarkable than anything else about it, the LLRV was a fly-by-wire aircraft - one of the very first - controlled by three analog computers. There was no mechanical backup control system of any kind, primarily because of weight considerations.

In preparation for the first flight the vehicle was towed to South Base at Edwards and covered with two tarpaulins. That night it snowed and when the crew arrived the next day there were eight inches of snow on the vehicle.

The flight tests at the Flight Research Center convinced NASA that the LLRV was a viable training tool, and the agency contracted with Bell for three additional vehicles. Built according to modifications made at the Flight Research Center to the two LLRVs, the three new vehicles were dubbed Lunar Landing Training Vehicles, or LLTVs.

Although the Apollo astronauts used other Lunar Lander simulators, to a man they all said later that the LLTV was the most realistic trainer. Neil Armstrong went so far as to say on his return that the LLTV was so good at simulating the lunar landing that he was entirely comfortable with what he was doing when he made his actual descent to the moon that memorable day in July 1969.

The second LLRV still resides at the Flight Research Center, now known as the NASA Dryden Flight Research Center. Meant to go to Houston to train Apollo astronauts as had the first LLRV and the three improved LLTVs, it never left the center. Instead, it was cannibalized for parts to support the training program at the Manned Spacecraft Center, now NASA's Johnson Space Center.

The second LLRV underwent a partial restoration in the late 1990s for use in filming of the television mini-series "From the Earth to the Moon" about the Apollo program, and it is now an historical highlight during tours of NASA Dryden.

(Image provided by NASA.)

FMI: www.nasa.gov/centers/dryden