Douglas transport gliders

The Douglas Aircraft Company based in Santa Monica, California (later Long Beach) is famous in the annals of US aviation history for producing a plethora of civil and military transports, including the DC-1, DC-2 (military designations: C-32, C-33, C-34, C-38, C-39, C-41, C-42, R2D), DC-3 (military designations: C-41A, C-47 Skytrain, C-48, C-49, C-50, C-51, C-52, C-53 Skytrooper, C-68, C-84, C-117, C-129, R4D, CC-129), DC-4 (military designations: C-54 Skymaster, C-114, C-116, C-117, R5D), DC-5 (military designations: C-110, R3D), DC-6 (military designations: C-112, C-118 Lifmaster, R6D), DC-7, DC-8, DC-9, C-74 Globemaster I, C-124 Globemaster II, and C-133 Cargomaster. However, one aspect of the Douglas company's design and development of transport planes that is largely overlooked by most military aviation historians is the fact that in the 1940s, Douglas itself tinkered with cargo gliders for the US Army Air Force (later US Air Force). During a visit to the Planes of Fame Museum in Chino, California in April 2019, I happened to notice a subscale plastic model of the Douglas XCG-17 prototype transport glider in the Foreign Hangar building of the museum, and it may quite surprise some historians that Douglas developed transport glider designs of its own because the vast majority of American transport gliders built in World War II were made by the Waco Aircraft Company. Therefore, I thought it would prudent to discuss the Douglas company's design and development of transport gliders.

Left: Desktop model of the Douglas XCG-17 transport glider at the Planes of Fame Museum.

Right: Douglas XCG-17 transport glider being towed during flight testing, 1944.

Following the introduction of the Douglas C-54 Skymaster military transport version of the DC-4 airliner, the US Army Air Force, facing the challenge of hauling troops and war material over the Himalayas from India to China, realized that its existing transport gliders would be unsuitable for towing over the "Hump" because of altitude, turbulence and additional payload. Therefore, it felt that a larger transport glider based on an existing powered transport plane was better suited to be towed by a C-54 over the Himalayas at higher speeds because it had much higher wing loading, and therefore withstand mountain turbulence. At the behest of Lieutenant Colonel Chet Decker, the USAAF suggested converting a C-47 Skytrain to glider configuration (Norton 2012, p. 176). One C-47 (serial number 41-18496; originally built as a Northwest Airlines DC-3 with the civil registration N69030) was earmarked by Douglas for modification to a transport glider in April 1944 and given the designation XCG-17. Conversion of the aircraft, completed on June 12, involved removing the engines and covering the engine nacelles with hemispherical domes, but also removing the radio operator and navigator spaces as well as bulkheads and wiring. The XCG-17 had a towing speed of 290 mph, a glide speed of 190 mph, with a capacity of 42 troops or 15,000 pounds (three jeeps and a 4x4 truck), carrying 3.75 times the payload capacity of the Waco CG-4. The first flight of the XCG-17 took place on June 14, 1944, and flight testing continued through the remainder of 1944. Despite satisfactory results of the flight test program, the XCG-17 was not ordered into production because the aircraft did not meet the USAAF requirement that it prove its ability to land on unimproved airfields. In any case, the war situation in Asia reached the point that the need for a large transport glider like the XCG-17 was obviated. The sole XCG-17 was sent to the boneyard at Davis-Monthan Air Force Base in August 1946, and it was eventually modified back to DC-3 configuration and sold to Mexico, where it remained in service until 1980.

Douglas C-47 "Nez Perce" (serial number 43-16229) after being converted to a transport glider, January 1946

The XCG-17 was not the only conversion of a C-47 airframe to transport glider configuration, however. In January 1946, a C-47 with the serial number 43-16229 was ferried to Nichols Field in Manila, the Philippines, for conversion to a glider transport; as with the XCG-17, the engines were removed and fairings mounted on the nacelles, but the nacelle fairings were octagonally shaped rather than hemispherical. An auxiliary power unit was taken from a B-24 Liberator to enable the operation of a radio and other electrical equipment. The converted C-47, christened "Nez Perce", flew on June 17, 1946, towed by a C-54 transport. Flight tests of the "Nez Perce" proved stellar, and later in June, the aircraft was towed by C-54 from Luzon to Tachikawa Airfield, Tokyo, with an overflight stay in Okinawa Airfield. The flight, which covered a distance of 1,800 miles, suggested that the "aerial freight train" concept of using large gliders for regular transport might be viable, but that concept never really caught on. In August, the "Nez Perce" had its piston engines reinstalled and converted back to C-47 configuration.   

Three-view drawing of the Douglas XCG-19 transport glider (after Mrazek 1977)

Douglas Aircraft's next foray into transport glider design when the USAAF's Air Service Technical Command on January 31, 1946 announced a requirement for two new assault gliders, a light glider able to carry an 8,000 pound payload and a heavy glider with a payload capacity of 16,000 pounds. The proposed gliders were to be of steel tube and monocoque construction, with provisions for loading men and military equipment into the aircraft via a ramp at the rear of the fuselage, as well as cargo space 35 feet long, 8 feet 8 inches wide, and 7 feet 11 inches high (10.67x2.64x2.41 meters) (Cox and Kaston 2019, p. 67). Douglas responded to this requirement with two designs, the Model 1028 light glider and Model 1029 heavy glider. Both proposals were similar in having a shoulder-mounted wing and an upswept rear fuselage rectangular in cross-section. The Model 1028's rear fuselage was hinged to swing sideways, while the Model 1029 had clamshell doors, each with triangular folding panels for ground clearance together with an integral ramp. Besides being intended to carry an 8,000 pound payload, the Model 1028 would be 61 feet long, with an 85 foot wingspan and gross weight of 14,200 pounds; the Model 1029, on the other hand, not only would carry a 16,000 pound payload but also have a length of 76 feet and five inches, a wingspan of 107 feet 3 inches, and a gross weight of 28,500 pounds (Cox and Kaston 2019, p. 69). The Douglas Model 1029 lost the heavy glider contract to Chase's MS-3 (designated XCG-20, later XG-20), but the Model 1028 and Chase's MS-7 won the light glider competition, receiving the designations XCG-19 and XCG-18 respectively. A mockup of the XCG-19 was inspected by USAAF officials in March 1947, but budget restrictions imposed later that year forced the USAAF to cancel the XCG-19 in favor of Chase's XCG-18, since the Chase XCG-18 prototypes were nearing completion (Mrazek 1977, p. 143).*    

Although somewhat outside the scope of this post, it should be noted that two other aircraft manufacturers in southern California issued their own proposals in response to the ASTC requirement. Hughes submitted its Model 31 and Model 32 designs, the former with an upward-swinging rear fuselage and the latter having a full-width loading ramp that formed the lower surface of the rear fuselage. North American, for its part, proposed the RD-1413 heavy glider which was unusual for having a detachable fuselage 'egg' for accommodating troops and cargo hanging from a rack under the glider (Cox and Kaston 2019, pp. 72-73). Of course, like the Douglas designs, the Hughes and North American glider proposals remained paper projects only. 

The Douglas transport glider designs represent a seldom-noticed footnote in the history of the Douglas Aircraft Company, but they also were a reminder that in the post-World War II era, the notion of large gliders designed to haul men and war materials to the battlefield was becoming a thing of the past due to the advent of helicopters and powered tactical transports.

*Although the XCG-19 and Model 1029 never reached the hardware stage and large transport gliders were rendered obsolete by powered tactical airlifters and helicopters, Douglas proposed powered derivatives of the XCG-19 and Model 1029 as the Model 1044 and Model 1072 respectively, both of them powered by Ranger XV-770 inline piston engines (Cox and Kaston 2019, p. 74). Like the XCG-19 and Model 1029, however, the Model 1044 and Model 1072 never left the drawing board.

References:

Cox, G., and Kaston, C., 2019. American Secret Projects 2: U.S. Airlifters 1941 to 1961. Manchester, UK: Crécy Publishing.

Mrazek, J., 1977. Fighting Gliders of World War II. London, UK: St. Martin's Press.

Norton, W. J., 2012. American Military Gliders of World War II: Development, Training, Experimentation, and Tactics of All Aircraft Types. Atglen, PA: Schiffer Publishing.