s Preliminary testing occurred at
Moffett Field Naval Air Station, CA. The first flight (hop) was on 11/20/1959 followed by the first real flight on 11/24/1959 with Hiller test pilots George Bright and Bruce Jones. Further test flights were held at
Edwards AFB, ultimately recording 20 flights. A number of problems plagued the X-18 including being susceptible to wind gusts when the wing rotated, acting like a sail. In addition the turboprop engines were not cross-linked, so the failure of one engine meant the airplane would crash. Thrust control was through throttle changes, which were too slow for acceptable height and roll control. On the 20th and final flight in July
1961, the X-18 had a propeller pitch control problem when attempting to convert to a hover at and went into a spin. The crew regained control and landed, but the X-18 never flew again. However ground testing of the tiltwing concepts continued. Eventually a VTOL Test Stand was built on which the X-18's vertical takeoff and landing and hover control was to be tested. One engine run was successfully conducted to the full wheel height on the VTOL Test Stand. The program was canceled on January 18, 1964, before further VTOL Test Stand testing could be conducted, and the X-18 was cut up for scrap. The program proved several things that contributed to further tilt-wing VSTOL technology programs: • cross-shafting between the engines was necessary in order to avoid loss of control in the event of an engine failure. • direct propeller pitch control was necessary for precise height and lateral control during VTOL and hover. This knowledge was employed in the successful development and flight tests of the Tri-Service
XC-142A tilt-wing VSTOL transport. ==Specifications (X-18)==