The Douglas R4D-8 emerged from an unsuccessful attempt by Douglas to extend the commercial lifespan of the aging DC-3. At the end of the Second World War a vast number of DC-3s, C-47s, C-53s and Dakotas flooded onto the commercial market, but by the end of the 1940s many of these aircraft were threatened by increasingly strict Civil Air Regulations in the United States, and the looming expiry of their airworthiness certificates in 1952.
Douglas responded by developing a modified version of the DC-3, the DC-3S or Super DC-3, which could be produced by upgrading existing aircraft. The new aircraft had a stronger longer fuselage, with room for 30 passengers. The passenger door was moved forward, and the door itself could be used as the boarding stairs. Both the vertical and horizontal tail surfaces were enlarged, and given square tips, improving the single-engine performance of the aircraft. The engine nacelles were modified so that they could carry either 1,475hp Wright Cyclone engines or 1,450hp Pratt & Whitney R-200-D7 radial engines, and to allow the wheels to be fully enclosed. Finally the outer panels of the wing were shortened, and 4 degrees of sweepback was added to the trailing edges.
The first modified aircraft made its maiden flight on 23 June 1949, and was a technical success. Payload increased, while top speed went up by 40mph and cruising speed by 44mph. Unfortunately the aircraft was a commercial failure. Despite its improved performance, the Super DC-3 still trailed behind newer aircraft (most notably the Convair Liner series), which appealed to the larger airlines, while smaller airlines were eventually able to get their DC-3s recertified. Only four commercial aircraft were sold.
An attempt to interest the USAF was no more successful. The first prototype was evaluated as the YC-47F (after a short spell as the YC-129), but was rejected in favour of the Convair C-131, based on the Liner. The aircraft was then passed on to the Navy, and finally found a customer.
After evaluating the aircraft during 1951, the US Navy awarded Douglas with a contract to convert 100 of their existing R4D-5s, -6s and 7s to the new standard, with the designation R4D-8. They retained this designation until 1962, when under the combined Department of Defence system they became the C-117D.
Three special versions of the R4D-8 were developed – the R4D-8T (TC-177D) trainer, the R4D-8Z (VC-117D) staff transport and the R4D-8L (LC-117D) cold weather aircraft.
The Navy’s R4D-8s saw combat in Korea, where they were used for night drops and as flareships, to illuminate areas under attack at night. In Vietnam most were used as conventional transport aircraft, but some were used as electronic monitoring aircraft.
Engines: Wright R-1820-80 x2
Power: 1,475hp each
Crew: Three plus 33 passengers
Wing span: 90ft
Length: 67ft 9in
Height: 18ft 3in
Empty weight: 19,537lb
Maximum weight: 31,000lb
Maximum speed: 270mph at 5,900ft
Cruising speed: 251mph
Maximum range: 2,500 miles