Besides the obvious pair of Allison T40-A-14 turboprops, each mounting a pair of Curtiss-Wright turbo-electric three-bladed propellers and putting out a total of just over 11000 horsepower, there was also a 1530-kg-thrust Westinghouse J-34 turbojet located in the aft fuselage that provided the greatly-needed pitch control. The propulsion system, although it wasn't immediately evident when viewing the plane, carried three engines. Looking at the mechanicals of the X-18, it quickly comes to light that this was an extremely complicated machine and certainly was pushing the state-of-the-art for the time period. Shortly thereafter, the X-18 - like a number of the other X planes - would be disassembled and cut up for scrap. During this phase, the plane would serve to generate a data base for the four-engine XC-142 Tilt-Wing transport that would follow.ĭuring its final days, the X-18 would be damaged when a ground test stand upon which it was mounted failed. The fact that the engines were not cross-shafted together contributed to worries with the program.īut after the flight testing was over, there was still another important mission to be performed by the X-18. When a problem occurred with one propeller's pitch control system, it served as the main reason for the termination of the program. It was that final flight of the program that actually spelled disaster. There would be twenty flights in the program, with the program ending in July 1961. The first actual flight test took place on November 24, 1959. The first, and only, prototype was completed in 1958, and quickly became involved in an extensive ground test program.
The task was aided greatly during its early phases by a series of wind tunnel tests at NACA Langley, Virginia. The model was to also be constructed using as much conventional fabrication techniques as possible.
In addition to its vertical take-off and landing capabilities, the X-18 was also required to have a significant forward speed capability of about 640km/h.Īnother consideration of the flexibility of the plane was that where landing strips were available, the X-18 could be used in a conventional take-off mode, resulting in an increased payload capability.
The contract called for a twin-engine, Tilt-Wing convertiplane. It would also be the largest VTOL aircraft built to date at the time. Even though the plane was built from scratch as a research-gaining testbed, the X-18 definitely carried the look of an era transport. Three years later, the Air Force pushed for the construction of a prototype and a flight test program, and awarded the company a $4 million contract to accomplish the awesome task. The company's potential also attracted the interest of the Air Force in 1954. It generated enough interest from the Navy, with its expertise receiving a contract in 1957 for a four-ton payload, tilt-wing transport. Its investigations pointed to the advantages to be derived from the Tilt-Wing concept. Hiller Aircraft was one of the pioneers in VTOL flight and investigated the possibilities of the phenomena following World War II. Hiller X-18 helicopter - development history, photos, technical data