Before the start of testing, a military test team was assembled at Edwards Air force Base, California. This team consisted of Test Directors and Test Pilots from each of the Tri-Services. In addition, a maintenance team was supplied by the Air Force. The military test team was supported by an onsite contractor group comprising engineering and technical personnel from Vought, Hiller, and Hamilton Standard. The Air Force Test Director was the military Program Director.
The first XC-142A (No. 2) was delivered to the test team in July, 1965. During the period of military testing as many as three XC-142A’s were being supported and flown by the test team at Edwards AFB. Many contractor performance tests were verified by the Air Force while additional flight tests were being conducted by the contractor.
During 1966, the Edwards test team launched an extensive Operational Evaluation program. The first flight with a payload, an Army jeep, was performed on February 17. One plane was flown to the Navy’s Parachute Test Facility at El Centro, California, in May for an air-drop test program. Dummy cargo loads up to 4,000 pounds were dropped from heights of 5 feet up to 5,000 feet and forward speeds of zero to 125 knots.
Some cargo was dropped at low speed without parachutes, being rolled out through the open cargo door onto the runway a few feet below. This verified the XC-142A’s capability to drop supplies where no landing facilities existed. While the airplane was at El Centro, 10 parachutists were dropped at altitude by walking off the cargo bay ramp.
While tests were being conducted at El Centro, another airplane flew out to sea off San Diego and landed aboard the aircraft carrier U.S.S. Bennington. Forty-four V/STOL cycles were performed during operations on the Bennington. Hovering flight was conducted with one wing beyond the edge of the deck to investigate ground re-circulation effects in asymmetric downwash. The carrier operations were conducted to establish the plane’s shipboard capabilities in preparation for additional tests on U.S.S. Yorktown. The XC-142A also performed V/STOL operations on the helicopter carrier U.S.S. Ogden. Additional VTOL operations were conducted on an amphibious dock transport off the California coast.
On a routine delivery flight from Dallas to Edwards AFB the XC-142A set two new world records for the type. Those were: the longest nonstop flight by a VTOL transport (1080 miles), and the fastest time for the flight,3 hours and 43 minutes, cruising at 375 miles per hour.
In other tests, high-altitude operations were performed at Bishop, California (4,100 feet), and in the Lake Tahoe area (6,000 feet); and live simulated rescue tests were performed over land and water.
In 1966, while the airplanes were at Edwards, three of them participated in a raw desert display of cargo- and weapons- carrying capabilities. They made STOL landings and takeoffs from a narrow, dusty strip scraped from the desert. They demonstrated unloading a recoilless rifle, a 105-mm howitzer with its tow truck (total weight 10,500 pounds), and an empty 1500-gallon fuel cell.
During May and June 1967, the XC-142A was transported to Rota, Spain, on the carrier U.S.S. Saratoga to participate in the Paris Air Show.
In 1966, while operational tests were being performed, the Air Force requested Vought to submit a proposal for a production C-142B incorporating changes found necessary from flight tests and ground tests of the XC-142A. A major improvement was proposed to eliminate the Navy carrier compatibility requirement. This allowed the nose to be lengthened to provide space for streamlining the nose to reduce drag and also wind noise in the cockpit. The flight test ejection seats were also to be eliminated, as were wing and tail folding which would reduce cost and weight.
After reviewing the C-142B proposal, the tri-services management team could not develop a requirement for a V/STOL transport. XC-142A testing was terminated and one flying airplane was turned over to the National Aeronautics and Space Administration (NASA) for research testing.