Curtiss C-46 "Commando"Manufacturer: Curtiss-Wright Corporation
Production period & total: 1941 through 1944.
Total purchased 3140
Basic design for the airliner Curtiss Wright CW-20, began in 1936. This was later to become the C-46. At that time the Boeing 247 was the most prominent airliner, powered by 2 600 hp Pratt & Whitney engines and seating 10 passengers. American Airways had put its faith into the Curtiss Condor (2 Wright Cyclone GR-1820 engines and seating 15 passengers). TWA operated the DC-2, which came about in 1934 (2 Wright Cyclone 875 hp engines, 14 seats) and its excellence was accepted allround. Douglas improved this with the DC-3, powered by 2 1.200 hp Cyclone R-1820s or Pratt & Whitney Twin Wasps also good for 1.200 hp. American had experimented with the Condor in socalled sleeper configurations and configured the DC-3 with 21 seats while in day use and 14 sleepers for flights during the night.The DC-3 had entered service in 1936.
In 1935 Pan American World Airways had started its trans-Pacific routes with the Martin 130 flying boat (four 830 hp Twin Wasps, 14-32 passengers).
The Curtiss Wright CW-20 had to do better.
The prototype was powered by two 1.700 hp Wright Cyclones and was aimed at the 24 to 34 seat market (while also able to reconfigure into 20 sleepers). The width of the fuselage was presumably such as would permit the berths fitted across its width and still leave room for a corridor ! In order to be able to pressurize the cabin, the designers had to strengthen the fuselage and this led to a circular cross-section for the fuselage. To have used one complete circle for the fuselage would have led to immense dimensions and too much drag. This was solved by the "double bubble" design and led to the typical shape of the C-46.
By the middle of 1940, the war situation in Europe had deteriorated and the US military foresaw the involvement of the USA in what was to become World War 2. An unprecedented large amount of transport aircraft were ordered: 200 C-46s and 545 C-47s. Other types ordered in large numbers included A-20, B-24, B-26, P-38, P-40 and AT-6.
The airlift from India to China, the socalled "Flying the Hump" operation, was the real hour of glory for the Curtiss C-46 Commando. 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 advisor 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 defence 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, 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, 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/min, 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. Carburettor icing was encountered, but this was a relatively well understood phenomenon. But there was more... The engines were susceptible to vapour 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 manoeuvre. 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 propellors. 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. Wiht a little corrosion, the electric contact could be lost, resulting in the prop moving into fine pitch and the engine overspeeding. This was perticularly serious on take off 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 were 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 mls E) 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.
It was quite natural that the Chinese Air Force was to receive some C-46s and some 20 were left behind under Lend-Lease agreement. In fact, some C-46Es awaiting delivery in Tennessee, were picked up by Slick Airways and operated with the blue and white rudder striped with the Chinese Air Force markings.
The C-47 benefitted from its excellent reputation during the war, but also from the DC-3 pre-war days with the airlines. The surplus C-46s were picked up by entrepeneurs who sought to make money flying cargo on a non-scheduled basis. Capitol, Flying Tigers and World Airways were among them.
The CIA was an avid user of the C-46. It played a role in many operations. Cuba and the "Bay of Pigs" fiasco was one. The CIA's "Liberation Air Force" for Cuba was stationed (clandestine) at "Happy Valley" in Nicaragua, consisting of five C-46s, as well as other types (C-54, B-26).
The structural life of the C-46 was determined for some 50.000 hrs, but many did not get that far due to corrosion problems (particularly in the tail unit). The Hamilton engine replacements and overhauls have become expensive and time-consuming (the typical 1.450 hrs between overhaul on the R-2800 compare poorly with the 8.000 hrs and up on jet engines). The Hamilton 3-bladed props, installed to overcome the problems with the 4-bladed electrical Curtiss props, have become a rare commodity.
The C-46 Curtis Commando
Some links to look elsewhere, for some nice information about the Curtiss C-46 in general and s/n 22595 in particular:
To the Smithsonian and its C-46