Tuesday, January 28, 2014
Some Thoughts On Engine Reliability
Heed the advice of a master mechanic
The number of ways pilots can contribute to their own downfall is practically legend, and in this case, we're only considering engine failure.
Fortunately, that doesn't have to be the case. Properly maintained and operated aircraft engines are almost unbelievably durable. In many respects, they're more reliable than automotive engines. Most pilots will fly their entire lives without a murmur of complaint from the Lycoming/Continental/Jacobs/Pratt & Whitney out front.
To better appreciate the reliability of general aviation engines, we contacted Victor Sloan of Victor Aviation in Palo Alto, Calif. Sloan's technicians produce about 150 overhauled Lycoming and Continental powerplants each year, all balanced, blueprinted and cryogenically treated to minimize heat and vibration and deliver consistent power. Sloan's XR Black Edition VII engines have become a standard against which many overhaulers and original equipment manufacturers measure their products.
We asked Sloan about piston-engine reliability. He said, "Most people analogize aircraft engines to automotive engines, and aircraft powerplants will nearly always come out ahead in any comparison of reliability, if not technology. A standard Lycoming IO-360-A1A rated for 200 hp, for example, carries a TBO of 2,000 hours, and contrary to what you might imagine, that's not an unrealistic number if the engine is built correctly, flown often and treated properly with periodic servicing." Convert those hours to nm in a Cardinal RG or Mooney 201 at 150 knots, and it works out to roughly 300,000 nm. How many cars do you know that will run that far on their original engine?
Sloan also feels the difference in how automotive and aircraft engines are operated gives aircraft mills the edge. "While it's true most auto engines are rarely called on to deliver full power, they're usually revving up and down on most trips, and that generates stress. An aircraft engine is designed to deliver brief periods of full power, then run at 65% to 75% power all day long, and many of them do that very well on ferry flights across the Atlantic and Pacific."
When I asked him if there was one over-riding mistake that damages engines more than others, he responded, "Heat is the nemesis of all piston engines. Some pilots don't truly appreciate the importance of maintaining cylinder head temps at or below 380 degrees, either by use of cowl flaps, an adequately rich (or lean) mixture or lowering the nose to put more air through the cowling. Aircraft piston engines are constructed with a variety of metals, and each expands and contracts with a different heat coefficient. Even lean-of-peak operation is acceptable on many engine models as long as you maintain power settings and temperatures within limits.
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