A Brief History of Radial Engines
As early as 1904, Charles Manly used a type of radial engine to power Dr. Samuel Langley's Aerodrome. This machine was unsuccessfully launched from a houseboat in the Potomac River. While Langley's Aerodrome was not successful, the engine pointed the way to high horsepower, low weight aircraft engines.
During W.W.I, LeRhone, Gnome and Bentley rotary engines provided the necessary power, while avoiding the difficulties of liquid cooling, in the harsh airborne environment.
The rotary is characterized by a crank fixed to the fuselage and a spinning row of cylinders. This provided the necessary cooling for high power engines, before high strength materials were available. While these engines had the necessary high power-to-weight ratio for flight, the gyroscope effect limited the ability of the aircraft to maneuver properly. After a brief debut on the world stage during W.W.I, the rotary engine was gone.
In the 1920s, the development of the radial engine continued along two very different paths.
Sleeve Valve Radial
The approach taken by Sir Roy Fedden and L.F Butler at England's Bristol engine works was the development of a series of sleeve valve radial engines. These were characterized by a conventional main crank and piston arrangement. Surrounding the piston was a hollow sleeve between the piston and cylinder. Each sleeve was driven by a smaller crank running at half the crankshaft speed.
The porting was accomplished by moving the sleeve in an elliptical path. The ports aligned to allow the introduction of the fuel and air mixture and the exhaust of the combustion gasses.
The advantages of this arrangement were improved volumetric efficiency because the large ports allowed improved gas flow into and out of the cylinder, a higher compression ratio and smaller engine frontal area because the overhead poppet valves were eliminated.
Alas, while a great number of sleeve valve engines were produced and powered Britain through W.W.II, the problems of high oil consumption and high manufacturing cost outweighed the advantages.
U.S. Radial Engines
A second approach was taken in 1925 by Rentschler, Willgoos and Mead at a newly formed American company -- Pratt & Whitney. These radial engines were equipped with conventional poppet valves. With refinements such as improved superchargers and sodium-filled exhaust valves, these engines provided much of the aircraft power for America in W.W.II.
Double Row Engines
Soon it was apparent to both the English and American companies that the bore of the cylinder was limited by the distance the flame could travel in the limited time available.
Future increases in horsepower could be made only with the introduction of a second bank of cylinders. The double row engine with either 14 or 18 cylinders was developed.
Pratt & Whitney's double row 18 cylinder engine, the R-2800, developed one horsepower per cubic inch of displacement and one horsepower per pound of engine weight.
By the end of the piston engine era, P&W had even developed the famous R-4360 engine. Nicknamed the "Corn Cob,'' it had 28 cylinders arranged as 4 rows of 7 cylinders each.
The Pratt & Whitney motto " Dependable Engines " is recognized around the world. The following helps explain the pride that Pratt & Whitney has in its work.
At an engine show, Alfred Meyer of West Simsbury, Connecticut, shared with us his memory of the speech given to newly hired engineers in 1961 by Phil Newsom, assistant to the chief of design for Pratt & Whitney. It speaks of the pride and purpose of those venerable times.
" Gentleman, I want you to know, you work for
the company that builds the finest aircraft engines in the world.
There must never be a job left undone.
You must always give the best you have.
Remember, men will bet their lives on the work you do. "
The quest for airplanes that could fly higher and faster ended the development of the radial engine, as the jet engine provided the power needed. But the old timers will tell you :
Nothing Sounds Like a Radial !