The C-46 Curtiss Commando

Background Information

Curtiss C-46 "Commando"

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.

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 US Army Air Corps was renamed US Army Air Force (USAAF) on 20 June 1941.
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 (like less cabin windows). Deliveries after the initial 25 were more adapted to the military role, like fitted with double cargo doors, a strengthened floor and hydraulically operated cargo handling winch. Forty folding seats took care of the seating in the C-46A.
The US entered the war on December 7th, 1941.
The C-46s and the C-47s were used on short and medium routes. The war effort required more orders and thus an order for 150 C-46As was placed for the USAAF and 120 C-46As for the US Navy in June 1942. Followed in October by another order for 200 more. Some examples were modified on the production line to C-46D standard. The next order was for a 1.000 aircraft and these were followed by a further 2.250 C-46s in late 1943 and 1944. But after V-E Day (May 7th, 1945) cancellations were put in effect.

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.
One C-46 was delivered to the Russian Air Force. No production C-46s were supplied to the RAF, but the original CW-20 prototype was purchased by the USAAF and supplied to Britain in 1942; BOAC used it for 18 months or so, mainly for flights to Lisbon, but it was broken up in late 1943.
Records showed an abnormal number of explosions (31 between May 1943 and May 1945) in C-46s and this was attributed to the payload (gasoline drums, unpressurized cabin, high altitudes.. a leaky drum and a spark from the electrical system: a deadly combination). But after the war it was discovered that the unvented wing structure of the C-46 was the problem. Fuel leaking in the wing had nowhere to drain. A spark or static discharge led to the inevitable explosion. All C-46s certificated after the war were required to have a wing vent modification incorporated.
After the war, Curtiss proposed civilian developments of the C-46 and Eastern Air Lines ordered a number of CW-20Es late in 1945. The order was however cancelled and further C-46 developments were ceased by Curtiss.

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.
In many South American countries, surface transport is hindered by the nature of the terrain: Amazone jungle, the Andes, extensive swamplands. The C-46 became a common sight in countries like Bolivia, Peru, Brazil, Argentina and Chile. A workhorse like the C-46 could be put to good use there, mostly carrying cargo of all sorts.

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).
In the process, Southern Air Transport was bought (consisting of only 1 C-46 at that time) in the early 1960s. The CIA had much use for aircraft in various roles and ended up owning its own airline: Civil Air Transport (CAT). A respectable airline opened many doors and provided a good cover. It was renamed Air America in 1959. And it even made money !
The holding company named Pacific Corporation, owned by the CIA, was stationed in Delaware. Many people involved did not know they worked, in a way, for the CIA, as it also operated as a normal commercial airline.
By comparision, during the 1960s when Flying Tigers (at that time the largest US transport company) operated 28 planes and had 2.000 employees, and Air America had more than 150 planes and 8.000 employees ! Southern Air Transport played a similar role for the CIA and there were more. War surplus aircraft provided a good start, required little funding and the specifications fitted the covert operations like a glove. Quite a few pilots operating missions for the CIA, had their hands on the controls of a C-46 over the Himalayas. Air America used the C-46 in Vietnam, on routes between Saigon and Da Nang, but also during the last months of the Vietnam War with markings of the ICCS ("I Can't Control Shit") for the International Control Commission, to control the peace agreement. Quite a few C-46s disappeared without a trace while in use with the CIA.

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.

Serial numbers:
41-5159 through 41-5204, 41-12280 through 41-12433, 41-24640 through 41-24775.
42-3564 through 42-3683, 42-60942 through 42-61091, 42-96529 through 42-96707 and many nonsequentially assigned serial numbers in the 42-96700 series, 42-96800 series, 42-101000 series, 42-101100 series, 42-101200 series, 42-107200 series, 42-107300 series.
43-43339 through 43-43340 (43-43341 through 43-43838 was cancelled), 43-46953 and 43-46954 through 43-47304, 43-47305 through 43-47314, 43-47315 through 43-47402.
44-77295 through 44-78544.

Variants:
CW-20T*: Prototype of the airliner, equipped with 2 Wright R-2600 Cyclone engines and 2 tailfins
C-55*: Adapted CW-20T prototype with a single tailfin, engines changed to 2 P&W R-2800 radials (

also designated XC-46)
C-46A: Wright R-2800-51 (2000 horsepower), single cargodoors, strengthened floor, cargo door on port side, folding seats for 50 troops
TC-46A: At least 3 C-46As were converted to crew trainers (42-96605, 42-96756, 42-107320)
EC-46A: Given to Japanese Air Self Defense Force. C-46A modified for airways calibration.
XC-46A: C-46A 43-46956 was temporarily used for development tests. It was reverted back to C-46 status after completion of the tests.
XC-46B: C-46A 43-46953 was outfitted with a stepped windscreen and 2.100 horsepower R-2800-34W engines; see photo right.
XC-46C: Two C-46As fitted with Rocket Assisted Take Off (RATO) gear.
C-46D: Specialized troop carrier version of C-46 with a modified door (for paratroop dropping). More than 1.400 of this model Commando were purchased.
TC-46D: 15 C-46Ds were converted to crew trainers.
C-46E: 17 C-46Ds were modified with single cargo door, 3-bladed propellors, stepped windscreen and R-2800-75, 2.000 horsepower engines
C-46F: Same as C-46D, but powered with R-2800-75 engines (234 were bought)
C-46G: Same as C-46F, but with single cargo door and 2.100 horsepower R-2800-34 engines. Only 44-78945 was built in this configuration and it was eventually converted to XC-113, to test the Curtiss-Wright TG-100 (later T31-GE-3) gas turbine engine.
C-46H: More powerful version of C-46F, with twin tail wheels. 300 were ordered and later cancelled. One C-46A (42-107294) was modified to this standard after the war.
C-46J: Designation given to a planned, but never ordered, update to C-46E.
XC-46K: Projected as a conversion of C-46F, powered by R-3350-BD, 2.500 horsepower engines.
XC-46L: Reportedly 3 C-46As were modified with the 2.500 horsepower, R-3350-BD engines and used as flying testbeds.
ZC-46E: Created by redesignating the C-46E in 1946.
C-46R*: conversion for Riddle Airlines, equpped with 2 P&W R-2800, 2.100 hp, engines - able to lift an extra 1.000kgs and speed increased by 64km/h (a.k.a. Smith Super 46C).

Statistics:
Crew:4
Cruising Speed: 236 mph (378 km/h)
Engines: 2 Pratt & Whitney R2800-34 Double Wasp radials Service Ceiling: 24.500 ft
Range: 3.150 miles (5.040 kms)

Physical characteristics:
Wingspan: 108 ft (32,93 m)
Length: 76 ft, 4 in (23,26 m)
Height: 21 ft, 9 in (6,62 m)
Empty weight: 30.000 pounds (13.608 kgs)
Gross weight: 45.000 pounds (20.412 kgs)
Max. payload: 15.000 pounds (6.804 kgs) or 50 passengers

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Credit:

for the above information goes to:
Curtiss C-46 Commando , by John M.Davis, Harold G. Martin, John A. Whittle (published by Air-Britain)
Wings of the CIA , by Frederic Lert
The 'C'-Planes, US Cargo Aircraft 1925- to the Present , by Bill Holder & Scott Vadnais
*) added designations from Dutch magazine Vleugels, extensive artincle on 'Curtiss C-46 Commando' by Loet Kuipers (2024 #3)

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