XC-142A at the National Museum of the U.S. Air Force
The basic design was fairly typical for a cargo aircraft, consisting of a large boxy fuselage with a tilted rear area featuring a loading ramp. It had a wingspan of 67 ft (20 m) and was 58 ft (18 m) long overall. The fuselage housed a 30 ft (9.1 m) long, 7.5 ft (2.3 m) wide 7 ft (2.1 m) high cargo area with a somewhat boxy cockpit on the front for the crew of two pilots and a loadmaster. The wing was high-mounted and the tail surfaces were a "semi-T-tail" to keep the rear area clear during loading. Tricycle landing gear were used, with the main legs retracting into blisters on the fuselage sides. In normal parked configuration it would appear to be a conventional cargo plane.
For S/VTOL operations, the aircraft "converted" by tilting its wing to the vertical. Roll control during hover was provided by differential clutching of the propellers, while yaw used the ailerons, which were in the airflow. For pitch control the aircraft featured a separate tail rotor, oriented horizontally to lift the tail, as opposed to the more conventional anti-torque rotors on helicopters that are mounted vertically. When on the ground, the tail rotor folded against the tail to avoid being damaged during loading. The wing could be rotated to 100 degrees, past vertical, in order to hover in a tailwind.
The C-142 was powered by four General Electric T64 turboshaft engines cross-linked on a common drive-shaft to drive four 15.5-foot (4.7 m) Hamilton Standard fiberglass propellers which eliminated engine-out asymmetric thrust problems during VTOL operations. Compared to conventional designs it was overpowered it had 0.27 hp/lb compared to 0.12 hp/lb for the contemporary Lockheed C-130D Hercules. This extra power was required for safe VTOL operations, and gave the aircraft excellent all-around performance which included a maximum speed of over 400 mph (640 km/h), making it one of the fastest VTOL transport aircraft of the era.
General characteristics
Crew: 2
Capacity: 32 fully equipped troops or 24 litter patients and four attendants
Payload: 8,000 lb (3,336 kg)
Length: 58 ft 1 in (17.71 m)
Wingspan: 67 ft 6 in (20.60 m)
Height: 26 ft 1 in (7.95 m)
Wing area: 534.5 sq ft (49.67 m²)
Empty weight: 22,595 lb (10,270 kg)
Max. takeoff weight: 44,500 lb (20,227 kg) (STOL)
Powerplant: 4 × General Electric T64-GE-1 turboprop, 2,850 hp (2,126 kW) each
Performance
Maximum speed: 431 mph (375 knots, 694 km/h) at 20,000 ft (6,100 m)
Cruise speed: 288 mph (250 knots, 463 km/h) at sea level
Combat radius: 470 mi (409 nmi, 757 km)
Ferry range: 3,800 mi (3,300 nmi, 6,100 km)
Service ceiling: 25,000 ft (7,620 m)
Rate of climb: 6,800 ft/min (34.5 m/s)