THE PRODUCTION OF THRUST

A BRIEF HISTORY OF THE PISTON ENGINE

The evolution of today’s airplane has depended significantly on the development of power plant technology. As pointed out by Torell (Ref. 6.1),

“Each successive generation of transport aircraft has been paced by the development of engines with greater power and improved efficiency, and more power for each pound of weight.”

From 1903 until the early 1940s, the piston engine-propeller combination was the only type of power plant used to any extent for airplane propulsion. The earliest piston engine designs were water-cooled, in-line designs requiring bulky, high-drag radiators. The Wright Brothers’ first engine was of this type. This engine had four upright cylinders, weighed 890 N, (2001b), and developed approximately 8.95 kW (12 hp). The liquid-cooled airplane piston engine remained in extensive use through World War II and evolved into powerful, efficient configurations typified by the Rolls-Royce Merlin. This ethylene glycol-cooled V-12 design, weighing 6360 N (14301b), delivered 843 kW (1130hp) at 3000 rpm.

Air-cooled airplane piston engines trace their lineage from the French Gnome rotary-radial design built in 1908. For this configuration, the propeller was attached to the cylinders which, displaced radially, rotated around the engine centerline. The first engines of this type delivered approximately 52 to 60 kW (70 to 80 hp) for a weight of approximately 1023 N (230 lb). The power-to-weight ratio of the rotary-radial engine was an improvement over the contemporary water-cooled designs; however, the fuel and oil con­sumption was high for the rotary-radial designs. Also, gyroscopic effects resulting from their high angular momentum were severe under maneuvering conditions.

The rotary-radial engine was superseded by the static, or stationary, radial configuration. In the 1920s, a competitive series of static-radial piston

engines were produced by the Wright Co. and the Pratt & Whitney Co. The first of these was the Wright Whirlwind. It was a Wright J-5C Whirlwind, nine-cylinder radial engine weighing approximately 2224 N (500 lb) and developing 164 kW (220 hp); that powered the Ryan monoplane “Spirit of St. Louis” in which Colonel Charles Lindbergh made his epic crossing of the Atlantic in May 1927. It was also the Wright Whirlwind, three of them each rated at 224 kW (300 hp), that took Admiral Richard Byrd to Antarctica in a Ford Tri-motor in 1929.

Pratt & Whitney’s first radial engine, developed shortly after the Whirl­wind, was designated the Wasp. This engine, weighing 2891N (6501b), developed 298 kW (400 hp) at 1900 rpm. The Wasp was followed by the more powerful Hornet and then by the Twin-Wasp, a radial engine with two rows of radially displaced cylinders. The Wright Cyclone was a similar design that first powered one of the most famous air transports of all time, the Douglas DC-3. Succeeding versions of the DC-3, were also powered with the Twin – Wasp designated the R-1830. The 1830 refers to the engine displacement in cubic inches. More than 10,000 of the Wasp-powered DC-3’s were built, and many are still flying today.

Horizontally opposed, air-cooled piston engines for light aircraft ap­peared around 1932. These designs are still produced in large quantities today by Continental Motors and Avco Lycoming. Production of the larger radial engines ceased in the late 1950s with the development of the turboprop and turbojet engines.