M2-F1 NASA Manned Experimental Airplane. The NASA M2-F1 was a lightweight, unpowered prototype aircraft, developed to flight-test the wingless lifting body concept. Its unusual appearance earned it the nickname "flying bathtub" and was designated the M2-F1, the M referring to "manned", and F referring to "flight" version. In 1962, NASA Dryden management approved a program to build a lightweight, unpowered lifting-body prototype. It featured a plywood shell placed over a tubular steel frame crafted at Dryden. Construction was completed in 1963.