Air-Cooled Cylinders 2

Air-Cooled Aircraft Engine Cylinders
An Evolutionary Odyssey

Part 2 - Developments in the U.S.
by George Genevro

The Lawrance-Wright Era



Sam. Heron played a key role in cylinder development.

Sam Heron, ever on the move, had emigrated to the U.S. in 1921 after a disagreement with his employer, J.D. Siddeley of the Siddeley Deasy Company, over Siddeley's efforts to alter one of Heron's cylinder designs. It has been said that Heron did not suffer those he considered fools gladly-or at all- and apparently he did not make exceptions for employers or company owners. After his arrival in the U.S. he went to work for the U.S. Army Air Service at McCook Field (now Wright-Patterson AFB) in Dayton, Ohio as a development engineer. In 1926, he joined the Wright Company, of which Lawrance was now vice-president, and his work in cylinder development was largely responsible for the success of the Wright J-5 engine. The Lawrance cylinder design had evolved from an all-aluminum cylinder with a steel liner that suffered from breakage of the aluminum mounting flange to the J-5 type that had a finned steel cylinder barrel with a screwed-on head and much more fin area, especially around the exhaust valve port. A major step had been taken in improving the radial air-cooled engine but much remained to be done.

Pratt & Whitney set a new standard for cylinder design with its first engine, the Wasp

A New Player in the Horsepower Race

Pratt & Whitney set a new standard for cylinder design when their first engine, the Wasp (which we now know as the R- 1340 in its military designation) was introduced in 1926. It incorporated the best features of Heron's latest cylinders and improvements such as integral rocker arm housings and additional fin area. That some of the best features of the Heron cylinder design should appear in this new engine is not surprising since Pratt & Whitney was formed by F. B. Rentschler, who had resigned as president of Wright in 1925. George Mead, Wright's former Chief Engineer, and Andrew Willgoos, Assistant Chief Engineer for Design, left Wright to assume similar positions at Pratt & Whitney. The Wasp was an immediate success and the Navy, by now heavily committed to building a carrier force, ordered 200 engines, an especially large order for that era. Almost immediately, the Navy expressed a need for a larger engine and the 1,690 cubic inch Hornet was designed and built, passing its Navy type test in 1927. The horsepower race had started in earnest.

Wright responded to this challenge with an even larger engine, the 1,790 cubic inch single row direct-drive nine cylinder Cyclone. Its displacement was soon increased by 30 cubic inches and as the R-1820, it powered a number of military and civilian aircraft. Its rated power output rose from about 500 horsepower in 1927 in its original direct-drive form to as much as 1,525 horsepower in the versions produced after World War II. The author clearly remembers an instance in the early 1980s during forest fire season when a heavily loaded (very probably overloaded) ex-Navy Grumman S2F "borate bomber" took off from the Ramona Airport in southern California on a fairly hot day. The rate of climb was minimal but the sound of the two very hard-working Wright R-1820s echo off the surrounding hills was memorable.



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