One of the more unusual vertical/short-takeoff-and-landing (V/STOL) aircraft flown by the U.S. military services was the Ling-Temco-Vought XC-142. The four-engine aircraft ably demonstrated its capabilities, including operations from an aircraft carrier. Despite successful trials, however, the service sponsors—Army, Navy, Marine Corps, and Air Force—each eventually pulled out of the program for lack of interest.
The military services began the project in 1959, seeking an aircraft with V/STOL capabilities to provide greater range and speed than existing cargo-carrying helicopters. On 27 January 1961, they agreed to undertake the Tri-Service Assault Transport Program, to be managed by the Navy’s Bureau of Naval Weapons (BuWeps).
Early planning envisioned the aircraft as a replacement for the Sikorsky HR2S Mojave helicopter (later designated CH-37), with a payload on the order of 10,000 pounds. Preliminary specifications called for an operational radius out to 250 miles and a maximum speed of 345 to 460 miles per hour. For the Marine Corps version, however, the fuel load could be reduced to keep the maximum gross weight under 35,000 pounds.
BuWeps released a request for proposals in 1961, and a combined proposal from Vought, primarily with fixed-wing aircraft experience, and Ryan and Hiller, both with extensive helicopter experience, won the design contest. A contract for five prototype aircraft was signed in early 1962. The design initially was known as the Vought-Ryan-Hiller XC-142, but that naming was dropped when Vought became part of LTV (Ling-Temco-Vought).
The XC-142 shipboard trials were conducted on board the USS Bennington (CVS-20) and amphibious transport dock Ogden (LPD-5) in 1966–67. But during prototype development the Navy left the program over concern that the propeller downwash could make the aircraft difficult to operate on board carriers.
The initial prototype XC-142A made its first conventional flight on 29 September 1964, its first hover flight on 29 December 1964, and its first complete in-flight transition (vertical takeoff, changing to forward flight, and landing vertically) on 11 January 1965. The Air Force took delivery of that aircraft in July 1965. Five XC-142 prototypes were produced, flying a total of 420 hours in 488 flights.
The XC-142 design was typical for a cargo aircraft: a large box-like fuselage that featured a tilted rear area with a loading ramp. Its four turboshaft engines had 15½-foot fiberglass propellers and were cross-linked on a common driveshaft to eliminate asymmetric thrust problems during V/STOL operations.
To convert to V/STOL operations, the aircraft tilted its wing to the vertical. Roll control during hover was provided by differential clutching of the propellers; yaw control was provided by the ailerons, which were in the slipstream. For pitch control the aircraft had a separate tail rotor, oriented horizontally to lift the tail (more conventional antitorque rotors on helicopters are mounted vertically). When on the ground, the tail rotor folded against the tail structure to protect against accidental damage during cargo loading.
During flight tests the aircraft’s cross-linked driveshaft resulted in excessive vibration and noise, causing a very high pilot workload. In addition, the aircraft proved susceptible to wing flexing. The shaft problems coupled with operator errors resulted in a number of “hard landings.” One aircraft crashed as a result of a failure of the driveshaft to the tail rotor; there were three fatalities.
In 1966, while tests still were underway, the Air Force requested an industry proposal for a production variant: the C-142B. Because the Navy already had left the program, the carrier-compatibility requirement could be eliminated, which greatly reduced the aircraft’s weight constraints. Other changes proposed for the production variant included a streamlined cockpit, larger fuselage, upgraded engines, and simplified engine maintenance.
After reviewing the C-142B proposal, the triservice management team could not develop an actual requirement for a V/STOL transport aircraft. Thus military XC-142A testing ended; the single remaining flying aircraft was turned over to the National Aeronautics and Space Administration for research tests, which were carried out from May 1966 to May 1970.
In service, the production C-142B variant was to carry 32 equipped troops or 8,000 pounds of cargo. It would have had a maximum gross weight of 41,000 pounds for vertical takeoff and 45,000 pounds for short-run takeoff. A civilian version—labeled the Downtowner—also was proposed. That aircraft would have carried 40 to 50 passengers at a cruise speed of 290 mph using only two of its engines. That project was not pursued.
Thus ended a most interesting and innovative V/STOL aircraft concept.