Not every moment of a test pilot's day is serious business. In a moment of levity, NASA pilots Bill Dana (left) and John A. Manke try to drag Air Force test pilot Peter Hoag away from the HL-10 lifting body while Air Force Major Jerauld R. Gentry helps from the cockpit. These four men were the principal pilots for the HL-10 program. This was not the only prank involving the HL-10 and its pilots. Once ''Captain Midnight'' (Gentry) and the ''Midnight skulkers'' sneaked into the NASA hangar and put ''U.S. Air Force'' on the aircraft using stick-on letters. Later, while Gentry was making a lifting-body flight, his 1954 Ford was ''borrowed'' from the parking lot, painted with yellow-green zinc-chromate primer, and decorated with large stick-on flowers about one foot in diameter. After Gentry returned from the flight, he was surprised to see what had happened to his car.