Friday is here again and it is time to talk about airplanes/aviation history. The Curtiss C-46, Commando, is an airplane that was overshadowed by the the DC-3 and has been largely forgotten; however, I have not forgotten and this week I want to reintroduce you to an airplane that made a lot of history and is still making money for commercial operators around the world.
The Curtiss Commando began life as a design for a 36-seat commercial airliner with a pressurized cabin, designated the “CW-20”, with development initiated by Curtiss in 1936. The CW-20 was intended to provide a larger, more capable competitor to the Douglas DC-3, which was then entering service. The CW-20 featured a roomy “Double Bubble” fuselage, with a cross-section in the form of two circle segments mated together, top and bottom. This configuration provided large internal volume and the structural strength to support pressurization. The junction between the small segment and the larger top segment was faired over to improve aerodynamics. The CW-20 also featured a low wing with twin radial engines, twin tailfins, and fully retractable tailwheel landing gear — the single-wheel main gear retracting into the engine nacelles. The cockpit windscreen was flush with the fuselage contour, giving the aircraft a whale-like appearance.
Flight tests quickly showed that the twin-fin tail left much to be desired, and it was replaced by a conventional tail arrangement with a single tailfin. The modified aircraft, now known as the “CW-20A”, was demonstrated to airlines, and there were some interest in the type. However, in September 1940 the US Army Air Corps (USAAC), implementing an increasingly frantic program to prepare for war, ordered 200 modified “CW-20Bs” with the military designation of “C-46”. Production began at the Curtiss plant in Buffalo, New York, with the first “Commando” delivered to the US Army Air Forces (which had superseded the Air Corps in the meantime) on 12 July 1942. With a war on, Curtiss focused on military production, and commercial production was out of the question for the duration.
Adapting the CW-20 to military service as the C-46 Commando needed few changes. The first 25 aircraft, designated C-46, were built essentially to the original specifications. The Pratt & Whitney R-2800 engines were replaced by Wright Double Cyclones and plans to provide pressurization were abandoned, as well as a number of minor changes were incorporated.
The Commando initially went into service on the South Atlantic ferry route, and would also participate as a glider tug in the Rhine crossings in March 1945. However, due to its long range, it was primarily used in the Pacific and China-Burma-India (CBI) theaters, becoming the primary cargo lifter for ferrying supplies from India to China over “the Hump”, the Himalaya Mountains, after the Japanese shut down the Burma Road in 1943. Commandos of Colonel Edward H. Alexander’s “India-China Wing” of the USAAF Air Transport Command flew from primitive airstrips in the Indian state of Assam, climbing with overload cargoes to clear ridges from 3.7 to 4.3 kilometers (12,000 to 14,000 feet) high, to land at Chunking and drop off their loads for USAAF General Claire Chennault’s 14th Air Force and Nationalist Chinese forces.
The loss rate of the C-46 was high and it had a mixed reputation with aircrews. Partly the problem was the fact that environment was very harsh, operating conditions were difficult, and Japanese fighters were an occasional threat. However, stories still circulate that the C-46 also suffered from a large number of engineering and manufacturing faults, in particular a leaky hydraulic system. Crews were said to take a barrel of hydraulic fluid along on flights to make sure that the hydraulic systems were topped off before they were used. There was also apparently a fuel leak problem that took a long time to work out, with aircraft being lost in midair explosions at a steady rate until it was.
It doesn’t appear that the C-46 was an inherently bad aircraft, it was just rushed into service without the level of qualification that it would have been run through in peacetime, and it took a lot of work to get the bugs fixed. The aircraft’s detractors called it the “Curtiss Calamity” and the “Leaky Tiki”, though it was also more affectionately named “Dumbo”, after the flying baby elephant in Walt Disney’s 1941 animated movie.
The airlift from India to China, “Flying the Hump,” was the real hour of glory for the Curtiss C-46 Commando. The following is from an article that I found on the web:
In Feb. 1942 President Roosevelt ordered General Arnold to open a supply line across the Himalayas in support of General Chiang Kai-Shek (and his air adviser Claire L. Chennault) at a time when the Japanese offensive was at its peak. Rangoon fell in March 1942 and this cut off the supply via the Burma Road. The initial 26 aircraft for this project were 10 ex-airline DC-3s and some C-53s. The flights were started in late 1942 by the China National Aviation Corporation (CNAC) and the USAAF. By December of that year some 62 DC-3s of various types were involved, but already 15 had been destroyed. Conditions were poor at the airfields serving the China airlift, in September 1942, e.g. fuel was still being pumped by hand from drums.
Chennault, a retired USAAC Colonel who had become special adviser to the Chinese Air Force in 1937, formed the American Volunteer Group (AVG) with 100 US-financed P-40Bs and began operations against the Japanese from bases at Kunming, the first successes recorded on 20 December 1941. In fact, this was the only air defense China had to offer at that time. The AVG ceased to exist on 30 June, 1942. The aircraft were taken over by the 23rd Fighter Group, developing into the China Air Task Force under Chennault who had been recalled to active service as a General. Because the Japanese controlled the Chinese coast and the fall of Burma closed off the last remaining supply routes over the ground, all supplies (including aviation fuel!) had to be airlifted in. Existing numbers of aircraft had to be increased to be at all effective.
In early 1943 General Arnold ordered to build up strength to 112 C-47s and 12 C-87s (converted B-24s). Enlarging the effort, they encountered problems of pilot inexperience, weather personnel problems, problems in communications, engineering and maintenance, lack of radio aids and direction finders…. The airfields were not complete and monsoon rains (beginning in June and lasting over 5 months!) played havoc with the facilities. Colonel Alexander, CO of the India-China Wing declared the C-47 unsuitable and requested C-46s. By 15 April 1943, 30 C-46s were delivered, replacing an equal amount of C-47s. More were to follow.
The direct distance between the Assam bases and Kunming was only some 500 miles, but the route is the most rugged imaginable. Chabua, on the banks of the Bhramaputra River, is only 90 ft above sea level but the Valley Walls climb to 10.000 ft. in the Patkai range. A series of ridges rise to a height of 14.000 ft and over, while Kunming itself sits at 6.200 ft. elevation. The icing level is at about 12.000 ft. and the flying was mostly done on instruments in foul weather: constant cloud cover, frequent violent thunderstorms, and tricky wind currents over the mountains…. Men and machines were put through extremes here, pushing the limits!
The service ceiling of the C-46 stood at 16.000 ft., above which it is not completely stable. The Hump was flown at 20.000 or 22.000 ft. eastbound and 21.000 ft. westbound…! As the C-46 cannot climb at 500 ft. per minute, it was necessary to climb near the base to gain sufficient altitude for the crossing.
During the dry season (winter) there was the danger of attacks by the Japanese fighters, but the biggest enemy was the weather. Carburetor icing was encountered, but this was a relatively well understood phenomenon. But there was more… The engines were susceptible to vapor lock at altitude, but as long as fuel was fed from one tank, there was no problem. On attempting to change tanks at altitude, the low atmospheric pressure and the suction of the engine driven pump caused vaporization of the fuel in the line, leading to the engine stopping… The engine could usually be restarted at lower altitude, but over the mountains there was no room to maneuver. The solution proved to be an electrically driven fuel pump inside each tank.
The early C-46s (as flown by Eastern Airlines) were fitted with 3-bladed Hamilton propellers. Fairly early in production these were replaced by the 4-bladed Curtiss electrically operated props. An electric motor was used to alter the angle of the blades. With a little corrosion, the electric contact could be lost, resulting in the prop moving into fine pitch and the engine overspeeding. This was particularly serious on takeoff from high altitude fields. Like Kunming. With gross weights above those initially intended by the designers….! The cumulative effect of the problems encountered was such that by November 1943, some 721 modifications had been ordered. The flow of new C-46s was stopped for a time while a modification program was put into effect. In 1942, when the airlift was first planned, a target of 7.500 tons per month was set, but this proved to be overoptimistic. This goal was not reached till October 1943. A typical payload for a flight consisted of 23 55-gallon steel drums of aviation fuel and 1 1/2 tons of bomb fuses. Other items carried included earth moving equipment aircraft engines and other spares. Little was carried out of China. From 8 February 1944, 25 C-46s were diverted from their original tasks and were seconded to supplement Troop Carrier Command aircraft for a few days of supply droppings in the Arakan region to help British troops to stem a northward Japanese advance; the 22.000 troops were down to two days supplies. Assignments like these happened quite often. Sometimes the C-46s played their part in evacuations. While the Hump operation progressed, statistics showed impressive figures: in July 1944 19.050 tons was carried, in December 31.935 tons, by 250 aircraft (daily average availability) in 7.612 trips…. Kunming could not handle all this and Luliang (60 miles East) became an India-China Division terminal in August 1944.
The total number of aircraft assigned to the Hump continued to rise to a maximum of 332 in July 1945, during which 71.042 tons were carried. At present day this would take 536 sorties by C-5 Galaxies…! Personnel involved peaked at 22.359.
By 1945 the tide of war changed and other routes became available; thus the C-54 could now could be put to use (it lacked the ceiling of the C-46, but on the routes now available it could carry 1.7 times the payload of the C-46).
The Hump was officially closed on 30 November 1945.
Have a good weekend, keep family and friends close, and remember that tomorrow when we wake up our lives are one day shorter.
October 30, 2015