First Church of Combustion
Never operate your airplane engine lean of peak exhaust gas temperature. These guys aren't buyin' it.
- By George C. Larson
- Air & Space magazine, July 2004
(Page 3 of 5)
By 1993, Braly had teamed up with an Ada-based parts manufacturer, Tim Roehl, to form General Aviation Modifications, Inc. He and Roehl began to experiment with injector nozzles calibrated to deliver fuel at a rate precisely matched to the needs of each cylinder. They had help from new microprocessor-based systems that displayed in monkey-simple graphics all the important engine data: exhaust gas temperature-not just for the engine, but for each cylinder-cylinder head temperatures, and, for turbocharged engines, turbine inlet temperature.
Braly started looking for an expert to help with the process of getting a Supplementary Type Certificate from the FAA for GAMI's new injector. Someone recommended a Texan named Carl Goulet. "I had no idea at that time that he was the former head of engineering at Teledyne Continental Motors," Braly recounts. "We had a very short and very remarkable conversation. I was considerably his junior, and he said, 'Now young man, tell me what you plan to do.' I told him, and these were his exact words: 'Hot damn! Somebody's finally gonna fix this problem!' "
GAMI applied for an STC in 1996, and the FAA approved it in the same year. At Goulet's suggestion, Braly submitted a proposal to Teledyne Continental Motors offering to supply fuel injectors and provide customer support. Hearing nothing, GAMI began to market the modification to pilots. Deakin and Atkinson were among the first to install the new injectors in their engines.
Atkinson remembers that after getting the injectors installed and heading home in his airplane, he leaned the mixture by ear, the way he'd been used to. Ignoring the EGT gauge, he liked to pull the leanerator until the engine ran rough, telling him he was just lean of peak, then adjust the mixture from there. "Except this time it wouldn't run rough," he recalls. "I kept pulling it back and it just kept running smoothly."
George Braly had been reading Internet postings by veteran airline pilots from the propeller days saying that they used to run their big radial piston engines on the lean side of peak EGT. Deakin had loads of Pratt & Whitney R-2800 time and could affirm to Braly that the names of instruments and methods may have differed, but leaning was leaning, and airline crews had been ordered by their companies to run their engines lean in order to reduce fuel consumption. But in the bargain they got cleaner spark plugs, valves, and cylinders, and perhaps the most important bonus of all-cooler operating temperatures-all as pure gravy. Braly couldn't understand why what worked in one piston engine wouldn't work in any piston engine. Born with enough tenacity for two people, he kept talking, asking questions, and reading.
That fall, a veteran pilot on the AVSIG forum told Braly that he had an old American Airlines book on how to operate the Wright R-3350. You might find it interesting, said the old vet. Perhaps the most complex powerplant ever to propel an airliner, the mighty -3350 squeezed every ounce of energy from the combustion process, in one version even using the exiting exhaust gas, already stripped of most of its energy by the turbo-supercharger, to turn a set of turbines that were geared back to the propeller shaft in order to capture the last twistlet of torque.
As soon as Braly got the old operating manual and read about the American pilots' lean-of-peak technique, he grabbed the factory graphs and charts for his Continental engine and calculated where his engine would be on the power curve if it were running under the same settings the -3350s were run at. The point corresponded to a power and fuel flow setting at exactly 50 degrees Fahrenheit lean of peak EGT. "It was the eureka moment," he recalls. By the summer of 1997, Braly, Deakin, and Atkinson were routinely flying with their engines running on the lean side of peak EGT and were ready to tell the world.
For a couple of years they hosted flying clubs at GAMI's hangar at Ada on Saturday mornings. In 2001, Atkinson put together a slide show to make the whole thing clearer.