The 1960s and 1970s were decades of military aviation filled with a plethora of experimentation centering on Vertical/Short Take-Off and Landing (V/STOL) aircraft. Not until the British Harrier in the late 1960s was the dream officially realized in the military sphere. The United States, for its part during the period, undertook its own practical testing of such aircraft and attempted to apply it to more tactically-minded systems than just fighter / strike platforms. The LTV XC-142 was a product of such an initiative and these prototype aircraft represented a V/STOL-capable transport for possible military service.
An initiative born in the late 1950s spurred the major American military services to develop a joint-service V/STOL platform to support existing helicopter-type operations and feature heavily in transporting goods and troops near the fighting lines. Range was of particular concern but speed was also required to move elements from Point A to Point B in short order. The United States Navy was chief lead of the program which became known under the name of "Tri-Service Assault Transport Program".
The original specifications were, of course, revised several times to satisfy each service branch need and Vought's design submission was ultimately accepted for development. A contract covering five total, flyable prototypes was delivered in early-1962 with a targeted first-flight sometime in 1964. The developmental aircraft series was designated XC-142 and the Vought brand label soon switched to LTV ("Ling-Temco-Vought") as Vought was absorbed into a new corporation (1961).
A total of five flyable XC-142A aircraft were built for the program which ultimately involved all of the major service branches as well as NASA. A first-flight was recorded on September 29th, 1964 and this outing saw the aircraft obtain conventional flight. A first Vertical Take-Off and Landing (VTOL) action followed in January of 1965. The aircraft were pushed through basic flight envelopes as well as more mission-minded actions to better simulate operational service.
Externally, the aircraft was given a short, deep slab-sided fuselage with a heavily glazed frontal section for optimal viewing out-of-the-cockpit. The wings were fitted high on the fuselage sides to better clear the large four-bladed propeller systems. Two engines were set along each wing and the whole wing system was given a "tilting" feature in which the engines could face completely vertically for the needed VTOL and conventional forward flight actions. The tail unit consisted of a single vertical fin and mid-mounted horizontal planes. The undercarriage, wholly retractable, was of a tricycle arrangement with double-wheeled main legs and a nose leg. The legs are of short length which gave the aircraft a very low ground profile. A crew of two piloted the vehicle while a third member, the loadmaster, would have made up the final crewman in operational service. Internally, the aircraft was set to carry up to 32 combat-ready infantrymen or up to 8,000lb of cargo. In the MEDEVAC role it would have been outfitted to serve 24 patient litters and staff.
As built, the XC-142A was powered by 4 x General Electric T64-GE-1 turboprop engines developing 2,850 to 3,080 horsepower each. In conventional flight, this propelled the aircraft to speeds of 400 - 430 miles per hour (cruising was closer to 235 - 288 mph). Combat range was 470 miles (3,800 miles ferry range) and the aircraft's service ceiling reached 25,000 feet. Operating weight was 44,500lb and rate-of-climb peaked at 6,800 feet-per-minute.
During testing, issues centering on the wing elements and drive shaft components surfaced which created a host of issues for pilots. Hard landings were not uncommon occurrences and controlling the aircraft proved difficult. At least three were killed in a crash of one of the prototypes. This sort of setback worked against the promising venture and things were made worse when the USN eventually bowed out of the program. The USAF championed a production-quality "C-142B" form but this was never realized. After the tri-services initiative officially failed to produce a viable product, the vehicle was passed on to NASA for additional testing. A civilian-market model was also entertained at one point and this was to carry the name of "Downtowner" while seating up to 50 passengers.
In the end, the XC-142 served as an important technology stepping stone to more modern, advanced systems which finally did go on to see operational service - the Boeing V-22 "Osprey" being a child of decades of work and this program itself not immune to fatalities and mechanical difficulties. Of the five XC-142 airframes completed, just one survived the years that followed and ended as a museum showpiece as the National Museum of the United States Air Force in Dayton, Ohio.