On May 6, 1968, NASA astronaut and future first moonwalker Neil Armstrong hovered about 200 feet above the sun-scorched pavement at Ellington Air Force Base in Houston, Texas. Alone in his single-seat craft, peering down toward the ground, Armstrong was simulating a descent to the moon’s surface in a very unusual bird: the Lunar Landing Research Vehicle (LLRV). At 2:38 p.m., the control thrusters abruptly failed and the LLRV suddenly became about as aerodynamic as a brick. Reacting instantly, Armstrong ejected less than a second before the LLRV crashed in a fireball. He parachuted to the ground, miraculously unharmed. Of the craft that almost killed him, he later said, “It was a contrary machine and a risky machine, but a very useful one.”
As early as 1961, NASA planners recognized that in addition to practicing vertical landings in helicopters and ground-based simulators, astronauts would gain hands-on experience in a free-flying lunar landing simulator. Engineers at Bell and NASA knew that there would be enormous challenges in building a craft that flew in the earth’s atmosphere at 1 G while nonetheless approximating conditions in a vacuum at the moon’s 1/6th G. For the vehicle to have any meaningful value to astronauts, it had to “feel” as close as possible to the actual lunar module (LM) in terms of flight characteristics and responsiveness.
For a propulsion system, rockets and jets were considered before the CF700—the turbofan version of the General Electric J85 jet engine—was selected because of its small size, powerful thrust and availability. To allow finer adjustments in the craft’s attitude, hydrogen peroxide rockets (similar to those used on the storied North American X-15) were installed. Early proposals put the pilot directly above the downward-facing engine (as would be the case in the actual lunar module), but this interfered with the engine intake, so the pilot’s position was shifted to the periphery of the craft, also increasing visibility. The engine was gimbaled to face the ground but had the ability to tilt, depending on the flight mode selected. The pilot only had the minimal instrumentation needed to fly the craft as well as a “zero-zero” ejection seat (which functioned at zero altitude and zero velocity). Dubbed the “flying bedstead” by engineers, the LLRV was an awkward contraption with four legs, copious metal tubing, exposed innards, and an electronics bay and open cockpit that were cantilevered on opposite sides of the vehicle.
Bell built two LLRVs for NASA. They could function in a variety of modes, the most notable of which was the lunar simulation mode. This essentially neutralized aerodynamic forces on the craft as much as possible and maintained engine thrust at 5/6th the vehicle’s weight. The complex electronics required to perform this delicate balancing act were very much state of the art for the early 1960s.
X-15 pilot Joe Walker made the LLRV’s first flight on October 30, 1964. That initial flight lasted only 56 seconds, but the results were encouraging enough for Walker to make two more brief flights that day. Walker, his backup pilot Don Mallick and other pilots made a total of 204 flights in the LLRVs, providing valuable feedback for modifications to the vehicle. The test flights also allowed engineers to develop lunar landing flight profiles in detail before the LLRV was used for general astronaut training. Data obtained from the flights also helped engineers develop and build the LLRV’s successor, the Lunar Landing Training Vehicle (LLTV). The LLRV was used as a trainer while the LLTV was being developed. Sadly, Walker didn’t live to see the moon landings; he perished in 1966 when his F-104 Starfighter collided in midair with an XB-70 Valkyrie bomber.
The LLTV, introduced in late 1967, was in many ways an improved version of the LLRV. It enclosed the pilot on three sides and included a cockpit roof to better simulate the environment and view that astronauts would experience inside the lunar module. The roof was later removed after it was discovered that the enclosed cockpit affected the ability of the LLTV to compensate for excessive yaw. That defect had caused the crash of LLTV no. 1, in which pilot Joe Algranti ejected at almost zero altitude but survived. Still, even flying the improved LLTV was a challenge. Apollo 17 commander Gene Cernan said, “The LLTV was inherently less stable than the LM itself; and we also had to contend with gusts of wind that could cause problems.”
All told, 15 Apollo astronauts flew either the LLRV, the LLTV or both. Most of the astronauts who piloted the training vehicles were mission commanders and their backups. Virtually all of the astronauts who completed lunar landings spoke positively about the benefits of training with the vehicles. During his post-flight debriefing, the usually laconic Armstrong put it this way, “For the type of trajectory that was required for us to fly (with a long manual flight at the end), the LLTV was a most valuable training experience.” Apollo 12 Commander Pete Conrad simply noted that the LLTV was “very essential to a successful landing.” John Young said his landing on the moon during Apollo 16 was “just like flying the LLTV.”
Today only one example of each of these vehicles survives. LLRV no. 2 is on display at the Armstrong Flight Research Center at Edwards Air Force Base in California. LLTV no. 3 is displayed at the Johnson Space Center in Houston, Texas, where it hangs in Building 2.
Both ungainly and unglamorous, these flying machines are remembered today for the engineering prowess it took to create them, the piloting skill it took to fly them and the much-needed lessons they taught U.S. astronauts about landing on the moon.
This article originally appeared in the July 2019 issue of Aviation History.