The back end view of a L-1049 Super Constellation's R-3350 power plant, complete with an attached Curtiss Electric Propeller~

An evolution of Curtiss-Wright's Cyclone family of radial piston engines, the R-3350 was developed in the 1930's to compete against Pratt and Whitney's newly developed R-2800 Double Wasp. The Duplex-Cyclone was first run in 1937, but was a temperamental engine that was rife with mechanical and reliability issues. Wright was slow to resolve the mechanical issues because of the complexity of the engine, and increased attention on the newly developed R-2600 Twin-Cyclone, which was a smaller, 14-cylinder derivative of the 18-cyinder R-3350. The first Duplex-Cyclones did not fly until 1941, when the Douglas XB-19 was lifted into the air by four R-3350's.

When the Second World War broke out, the R-3350 was suddenly seen as the future of Army aviation. It had the power, and growth potential for the new generation of bombers that were being envisioned. Despite the great urgency and exigencies of the war, Curtiss-Wright was still slow to correct the lingering issues of the Cyclone-18. During the development phase of the Boeing B-29 Superfortress, and Lockheed C-69 Constellation, both aircraft ran into serious issues with the Duplex-Cyclone- mainly in overheating and mechanical breakdowns. With the C-69 program, Lockheed ran into serious complications with the electrical harnesses, carburetors, and cylinder heads unscrewing in flight. Early in the B-29's career, the unmitigated overheating issue lead to numerous crashes and engine fires, especially during maximum weight takeoffs in the Pacific Theater. The choice of magnesium as the crankcase alloy lead to engine fires burning at near 5,000 degrees Fahrenheit, which could melt the wing spars in seconds. Another culprit of engine fires was a poorly designed carburetor intake for the supercharger, which lead to fuel-air mixture complications. Post war, after a number of fires and crashes, the R-3350 was developed into a direct fuel injected engine. This greatly improved reliability, and the Cyclone-18 became popular on large commercial transports after the war, such as the Lockheed Constellation airliner.

In the late 1940's, Curtiss-Wright evolved the design further, with the introduction of the turbocompound system. The piston engine portion of the R-3350 was "compounded" by three exhaust gas blow down "power recovery turbines" (PRT), which scavenged energy from the exhaust stream, and put it back into the engine via a fluid coupling. In this method, the engine gained an extra 500HP and improved fuel economy, but the engines became more temperamental as the increased backpressure and heat lead to valves being swallowed again. Mechanics mockingly called the PRT's "Parts Recovery Turbines". The R-3350 was the only piston engine that adopted the turbocompound system to be put into mass production. Initially these engines were restricted for military use only, until authorized for civilian use in 1953. Significant aircraft that used this variation included the L-1049 Super Constellation, DC-7, CP-107 Argus (Canada), P-2 Neptunes. A significant number of these engines still remain in use to this day, though they're restricted in power because of the use of 100LL avgas vs 115/145 avgas.

In my series, the R-3350 is the important radial engine in operation by Rob Barion (fursona) and his gaggle of aviators. His twin brother Jake Barion builds a licensed derivative of the R-3350, made out of modern metals that increased reliability. Rob and his brother are working to develop a modern R-3350-972TC-18DA-3 that can still run its superchargers on low octane fuel.