Curtiss C-46 Commando - Design and Development

Design and Development

The prototype for what would become the C-46, the Curtiss CW-20, was designed in 1937 by George A. Page Jr., the chief aircraft designer at Curtiss-Wright. The CW-20 was intended as a private venture intended to introduce a new standard in pressurized airliners. The CW-20 had a patented fuselage conventionally referred to as a "figure-eight" (or "double-bubble") which enabled it to better withstand the pressure differential at high altitudes. This was done by having the sides of the fuselage creased at the level of the floor that not only separated the two portions but shared in the stress of each, rather than just supporting itself. The main spar of the wing could pass through the bottom section which was mainly intended for cargo without intruding on the passenger upper compartment. A decision to utilize a twin-engine design instead of a four-engine configuration was considered viable if sufficiently powerful engines were available, allowing for lower operating costs and a less complex structure.

Engineering work involved a three-year commitment from the company and incorporated an extensive amount of wind tunnel testing at the California Institute of Technology (Caltech). The resultant design was a large but aerodynamically "sleek" airliner, incorporating the cockpit in a streamlined glazed "dome". .= The engines featured a unique nacelle "tunnel cowl" where air was ducted in and expelled through the bottom of the cowl, reducing turbulent airflow and induced drag across the upper wing surface. After a mock-up was constructed in 1938, Curtiss-Wright exhibited the innovative project as a display in the 1939 New York World's Fair.

Although the company had approached many airlines in order to obtain their requirements for an advanced airliner, no firm orders resulted, although 25 letters of intent were received, sufficient to undertake production. The design of a 24-34 passenger airliner proceeded to prototype stage as the CW-20 at the St. Louis, Missouri facility with the initial configuration featuring twin vertical tail surfaces. Powered by two 1,600 hp R-2600-C14-BA2 Wright Twin Cyclones, NX-19436 flew for the first time on 26 March 1940 with famed test pilot Edmund T. "Eddie" Allen at the controls. After testing, modifications were instituted, including the fitting of a large single tail to improve stability at low speeds.

The first prototype was purchased by the United States Army Air Forces (USAAF) to serve as a master for the series and was designated "C-55", but after military evaluation, the sole example was returned to Curtiss-Wright and subsequently re-sold to the British Overseas Airways Corporation (BOAC). During testing, General Henry H. "Hap" Arnold became interested in the potential of the airliner as a military cargo transport, and on 13 September 1940, ordered 46 modified CW-20As as the C-46-CU Commando; the last 21 aircraft in this order were delivered as Model CW-20Bs, designated C-46A-1-CU. None of the first C-46s purchased by the U.S. military were pressurized. The design was then modified to the C-46A configuration, receiving enlarged cargo doors, a strengthened load floor, and a convertible cabin that speeded changes in carrying freight and troops. The C-46 was introduced to the public at a ceremony in May 1942, attended by its designer, George A. Page Jr.

A total of 200 C-46As in two initial batches were ordered. At this time, one other important change was made; more powerful 2,000 hp Pratt & Whitney R-2800 Double Wasp engines replaced the two Wright Twin Cyclones. A number of minor modifications, such as fuel system changes and fewer cabin windows were also adopted. Subsequent military contracts for the C-46A extended the production run to 1,454 examples, 40 of which were destined for the U.S. Marine Corps, to be designated R5C-1. The military model was fitted with double cargo doors, a strengthened floor and hydraulically operated cargo handling winch; 40 folding seats were the sole passenger accommodation for what was essentially a cargo hauler. Tests indicated that the production C-46 was capable of carrying a substantial payload, and could fly well on one engine. When empty, the aircraft could even climb on one engine at 200–300 ft per minute.

The final large production run C-46D arrived in 1944–45, and featured single doors to facilitate paratroop drops; production totaled 1,430 aircraft. Although a one-off XC-46B experimented with a stepped windscreen and uprated powerplants, a small run of 17 C-46Es had many of the same features as the XC-46B along with three-bladed Hamilton-Standard propellers replacing the standard Curtiss-Electric four-bladed units. A last contract for 234 C-46Fs reverted to the earlier cockpit shape but introduced square wingtips. A sole C-46G had the stepped windscreen and square wingtips but the end of the war resulted in the cancellation of any additional orders for the type.