Hill Climb- page 2 | History | Air & Space Magazine
Moss was hardly deskbound, posing with the pilot who held the Army's altitude record, J.A. Macready (left). (NASM)

Hill Climb

Why General Electric put an airplane engine on a truck and drove it to the top of Pikes Peak.

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In 1901, he began studies and research at Cornell Uni-

versity, and after working for a year, persuaded a spherical combustion chamber to deliver a continuous source of flaming hot energy. Gas-

es from the chamber were directed against a five-inch-diameter turbine wheel; Moss wrote that it was probably the first time a turbine had ever been driven by combustion gases in the United States—or perhaps anywhere.

Moss’ 1903 doctoral thesis, “The Gas Turbine, an Internal Combustion Prime Mover,” caught the eye of General Electric executives. Formed in 1892 as the amalgamation of the leading AC and DC power companies, GE was responding to mounting consumer demand by constructing ever larger electricity generating and distribution systems. Moss came to GE at the very time when reciprocating engines for power generation were being replaced by more efficient steam turbines.

He worked for four years at GE on gas-turbine reliability, but he couldn’t crack the efficiency nut. His best turbine consumed four gallons of kerosene per hour for every horsepower produced, versus only one gallon per horsepower-hour for the day’s best reciprocating engines. The materials available in 1907 could not withstand the high temperatures needed to achieve better efficiency in a turbine, so GE shelved its research. But back in Europe, the war was heating things up nicely.

The advent of the Great War focused intense interest on packing more air into engines to gain altitude performance. In Germany, Mercedes, Maybach, and BMW took a brute-force approach, building bigger engines that also squeezed the air-fuel mixture to a greater degree during the piston’s compression stroke. Power had to be limited at sea level or the engines would fail structurally, so BMW’s 19.1-liter engine, with a compression ratio of 6.4 to one (4 or 5 to one was more typical), had three throttle levers. If all three were opened at sea level, the engine would destroy itself, so the throttles were opened progressively as the airplane climbed. The first-stage throttle delivered 185 horsepower for take-off at a modest 1,400 rpm. The other two throttles were opened in succession above 6,500 feet, permitting higher engine speeds without the usual loss of power because the engine’s high-compression design squeezed more energy out of the thinner air. Rumpler C.IVs equipped with 260-horsepower “over-dimensioned” Mercedes engines and oxygen for their crews flew reconnaissance missions above 20,000 feet, well beyond anyone’s reach. The Germans were slower than the British and French at sea level, but at altitude they ruled.

The British government’s Royal Aircraft Establishment experimented with reciprocating-piston air compressors and Roots blowers, which have intermeshing vanes, but the trials bore no fruit. So the RAE concentrated instead on high-speed centrifugal blowers. A BE2C biplane powered by a 537-cubic-inch air-cooled eight-cylinder engine took 35 minutes to climb to 8,500 feet. With an experimental gear-driven supercharger, it climbed 3,000 feet higher. But engine maestro Sam Heron at the Royal Aircraft Factory had doubts, which he expressed in muted terms: “The observer sat forward with his feet under the fuel tank and over the supercharger’s gear drive. The gears were quite inadequate and the pinion failed in flight, producing showers of sparks and a feeling of distinct concern.”

August Rateau, an enterprising inventor, engineer, and industrialist in France, dusted off a 1909 idea of Alfred Buchi’s for a turbocharger and fitted it to SPAD, Breguet, and ALD types with some success. One turbocharged Renault engine improved the rate of climb at 14,000 feet by 15 percent and boosted top speed from 104 to 120 mph. The British evaluated Rateau’s equipment, noting a 23 percent improvement in the rate of climb, but suspended research after a catastrophic turbine failure at 13,500 feet.

Rateau’s turbocharger caught the eye of the U.S. Army Air Service’s technical experts stationed in Paris, and soon investigations were under way at McCook Field in Dayton, Ohio, with an experimental unit running on a Liberty engine. Excessive heat caused persistent failures. A parallel effort initiated in November 1917 by William Durand, chairman of the National Advisory Committee for Aeronautics, was more fruitful. Earlier, Durand had been at Cornell, where he first learned of Moss and his research. He was also well aware of GE’s prominence in steam turbines and centrifugal compressors. Durand promptly petitioned GE’s president for Moss’ assistance.

Engineering drawings of the Rateau device were available, but Moss’ GE team had its own ideas. By June 1918, GE’s Lynn Steam Turbine Department in East Lynn, Massachusetts, had shipped a prototype to the War Department’s Airplane Engineering Division at McCook Field for adaptation to a Liberty 12 aircraft engine. It was a teenage marriage: an untried turbocharger wed to an engine that one year earlier had been just a glimmer in the War Production Board’s eye.

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