Saturday, May 1, 2004
An Advanced Course In Engine Management
When you have to pay for fuel, repairs and overhauls, you’ll want to treat your powerplant to the values of science, not hearsay
Our engines are expected to endure such harsh conditions, safeguard our lives and then abruptly start the whole cycle over again. We demand that our engines run smoothly, efficiently and reliably for 2,000 hours, regardless of whether it takes 10 or even 20 years to reach TBO. Aluminum and steel must perform at 100% in a moment’s notice, with a thin film of oil as a lubricant, from zero to furious in minutes.
No other internal combustion engine is asked to do as much as the modern piston aviation engine. Perhaps racecar or marine engines come close, but the duty cycles and assumed failure risk don’t even approach the environment faced by engines we fly behind every day. The basic design of the aviation piston engine hasn’t changed drastically in decades. This is the 21st century, surely we can run our engines better now because we know more about them.
The answer is yes and no. In fact, the engineers who designed our engines and the big radials of the past knew what they were doing. Without modern technology and test equipment, they came pretty close to the answers that pilots ask every day.
The trouble is that we’ve forgotten those answers. How many hangar bull sessions discussed leaning techniques? How many times has your instructor talked about running rich of peak or lean of peak, and why? How does lead cushion valves, and extra fuel cool a cylinder head? All this corporate knowledge must be based on fact, right?
Those old-time engineers built and tested engines, producing power charts that we all use. They defined how exhaust gas temperature (EGT), cylinder head temperatures (CHTs) and horsepower relate to fuel consumption. During World War II, engineers plotted their test results from full rich to lean, and the Army classified the chart as top secret. Charles Lindbergh taught fighter pilots in the Pacific how to run lean of peak EGT, a technique that helped him across the Atlantic in 1927. Max Conrad used lean of peak to set distance records in his Comanche in the 1960s when he flew over 7,600 miles nonstop.
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