To give the astronauts practice piloting the LM on its descent, NASA commissioned Bell Aircraft to build two Lunar Landing Research Vehicles (LLRV), later augmented with three Lunar Landing Training Vehicles (LLTV). Nicknamed the "Flying Bedsteads", they simulated the Moon's one-sixth gravity using a turbofan engine to support five-sixths of the craft's weight. On May 6, 1968, above the ground, Armstrong's controls started to degrade and the LLRV began rolling. He ejected safely before the vehicle struck the ground and burst into flames. Later analysis suggested that if he had ejected half a second later, his parachute would not have opened in time. His only injury was from biting his tongue. The LLRV was completely destroyed. Even though he was nearly killed, Armstrong maintained that without the LLRV and LLTV, the lunar landings would not have been successful, as they gave commanders essential experience in piloting the lunar landing craft.