The Wright Cyclone was a straightforward development of that engine — nine large cylinders around the propeller shaft, like the spokes of a wheel. As a piston moved toward the hub, the cylinder filled with 201 cubic inches of air mixed with gasoline, to be fired by two sparkplugs; the heat was carried away by cooling fins like those on a lawnmower. The Cyclone was designated R- 1820, for radial engine, displacing 1820 ci. The early models developed 575 horsepower at takeoff, less at higher altitudes.
The Cyclone powered most U.S. Army bombers of the 1930s, including the immortal B-17 Flying Fortress. Donald Douglas picked it for a new passenger plane that the airlines thought would be a trimotor. Douglas gave it two, and when the prototype took off and crossed the Continental Divide on only one engine, the airlines never again questioned the reliability of the Cyclone or the plane that became the DC-3, arguably the greatest aircraft of all time.
Other Cyclone-powered planes included the Douglas SBD dive bomber and the Lockheed Hudson light bomber — but not one important fighter. The engine wasn't suited to the high-g stress of fighter combat, probably because of the way lubricating oil reached the cylinders in the early models. Oil leaks and oil starvation are a constant of the Brewster Buffalo story, even in the B-239 that did so well in Finnish service.
There was one exception to the general rule. When the Navy wanted a fast-climbing fighter for convoy duty, it chose a Wildcat variant built by General Motors and powered by an R-1820- 56 Cyclone. The valves, cylinder heads, transmission gears, lubricating system, and supercharger had all been improved by this time. Even so, the FM-2 couldn't match the high-altitude performance of its Grumman cousins with their Pratt & Whitney engines — but that scarcely mattered, because it was intended for low-level work, finding and strafing submarines.
In the end, the Wright Cyclone had a production run of 25 years, and it flew more miles than any other piston-driven aircraft engine ever built. - Dan Ford
Wright worked constantly at changing the cyclinder head and fin design of the Cyclone. I recall metallurgic changes and a 'W' fin design to improve heat flow. All internal combustion engines depend on the oil system to carry away a large part of the heat.... Bad oil cooling either due to design or operating conditions (climb, high altitude, high ambient temps) will raise the cyclinder temps and lead to increased engine wear.
The Buff's problems where in the the way the engine's oil system was sealed. The Cyclone had valves and rocker arms at the top of the cylinder head. Yup it was a pushrod engine with the cam mounted concentric to the crank. The rocker reversed the pushrod motion to operate the valves. All this stuff needs oil and the rocker/valve stem clearance needs regular adjustments. On the Cyclone there is a stamped metal cover, one to each side of the cyclinder seated on a gasket to allow access to the rocker and valve stem. [Some of] the RAF buffs in Burma had rebuilt engines off DC-3s, and I doubt Brewster paid for top of the line rebuilds. Once this stuff got good and warm and the wind got to blowing the covers leaked and the slipstream carried the oil mist out the cowl flap openings to the windscreen. It doesn't take much junk on the windscreen to make your eyes want to focus on it and not the outside world. [Also see what Vic Bargh said on this subject.]
Good maintenance, clean oil, lower ambient temps and correctly rebuilt engines would have probably prevented this problem and may explain why the Finish Buffs didn't have the oil leaks. I will hasten to point out I am NOT an airframe and powerplant mechanic.
[As for the structural difference between the Wright Cyclone on the Buffalo and the Pratt & Whitney Twin Wasp on the F4F Wildcat, Ben adds:]
The significant difference between those two engines is not the 10 cubic inches, but the bore and stroke of the cylinders. The Twin Wasp had 14 cylinders to the Cyclone's 9 and almost the same displacement. Less displacement per cylinder in the R-1830 means a smaller bore and stroke. Short stroke engines tend to rev higher and develop peak power at higher rpm vs long stroke engines which tend to develop max tourque at lower rpm. Back before Detroit put the same blocks in everything truck engines were all long strokers and sports cars had high reving short strokers. The anology may not be completely accurate in aircraft, but a look at the spec for the R-1830 show peak power at 2,100 rpm and for the R-1820 peak power at 1,500 rpm.
The G-5 model used by the Finns was rated at 1000 h.p. for take off, 850 h.p. at 6000 ft, and 750 h.p. at 15.200 ft. (2100 rpm).
The G-105A used by the 339 export models was rated at 1100 for take-off, (2.350 r.p.m.) 900 at 6700 ft. (2300), and 800 h.p. at 2350 rpm at 17,200 ft.
the G-205 used by the F2A2 and A3 and the 439 was rated at 1200 h.p. at 2,500 rpm at take off, 1000 h.p. at 2300 rpm at 6700 ft.; and 1000 hp at 2500 rpm at 14,200 ft.
The increase in power at altitude is small for the 339, compared to weight increases, but the US examples seem to have a better power loading, and even the fully loaded A3 compares well with other allied fighters.
I have no figure for the normal loading of the Buffalo I, but guessing at a figure of 6400 lbs. the wing loading is approximately the same as the Hurricane Mk IIB trop, (30) and the power loading would be 8 at 17,200 ft, compared to 6.76. At a normal loaded weight of 6350 lbs, the A3 would have had a power loading of 6.35.
The F4F4 had the parameters, w.l. 28.5, and p.l. of 7.4 at 19,000 ft.
The P-40E had a w.l. of 35 and p.l. of 7.36 at 15.000 ft.
Spitfire Vb trop; w.l. 27.5, p.l. 5.6 at 16.000 ft.
At 5800 lbs, the 239 would have had a w.l. of 27.75, and a p.l. of 7.73 at 14.200 ft. At 5200 lbs, the parameters would have been 24.8 and 6.9. Which figure is accarute for Finnish Brewsters, I do not know, (the higher is from Eric Brown).
The fall off in power of large bore american and british radials at altitude is notable. The Sakae 21 had a take off rating of 950 hp at 2600 rpm, 1020 at 6,400 ft, and 885 at 15,700 ft. The Zero had a wing loading of 22 and power loading at altitude of 6.
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Posted February 2016. Websites © 1997-2016 Daniel Ford; all rights reserved.