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Top five engine myths: the science of piston aircraft engine operation has been overhauled in recent years, putting to rest many myths. How many of these five do you still believe?

Article Excerpt
It seems that since Leonardo de Vinci first placed his mental concept of a flying machine on paper we aviators have had a hard time separating fact from fiction. Aviation, not unlike most other human endeavors, has its share of commonly stated "truths" the scientific data doesn't support. Let's call them aviation myths. Why then, do they continue? One reality is that we are all busy in our daily lives and digging through reams of material to verify what someone else says is just too time consuming--not to mention boring. Another issue is that we have learned that those who have gone before us are generally a reliable source of information on how not to get one's name included in an NTSB report--much less looking stupid in that report. It's an understandable shortcoming.

Let's take a look at a few of the commonly held aviation concepts related to engine operation for which there is no supporting data, contradicting data or, at the very least, data calling them into question.

HIGH RPM INCREASE WEAR

This one looks like it should be true. In a way it is, but let's look more closely. A thin film of oil must separate metal parts inside an engine or they won't be running for very long. In literally seconds, metal-to-metal contact will result in catastrophic failure. So, where does this increased wear really come from and is it something we should be concerned about? Does oil wear metal? Sure, maybe over a thousand years! How else did David get that smooth, slick river rock to sling at Goliath? But, does it matter to my 1700-hour TBO engine?

In the grand scheme of operational concerns, there are many other things to worry about before questioning whether high rpm causes abnormally high engine wear. This is at least a third-order effect and there seems to be no reason to reduce rpm for that concern.

That said, other reasons to use lower rpm are supported by data. For example, lower rpm increase propeller efficiency and improve the process of horsepower getting turned into thrust. That's like getting free horsepower.

Lower rpm are quieter. Lower rpm result in reduced frictional losses. Lower rpm produce less noise and in an aviation-unfriendly environment can help our cause.

A corollary to this myth is that reducing rpm shortly after takeoff is always a good idea. The short answer is "no." I use maximum rpm for takeoff...