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Static RPM seems to be widely misunderstood. Some folks don't know what it is, some think it is something they need to "obey", much like the red line, and some think it is a specification, like horsepower. It is none of these. It is a certification limit, much like control surface travel or oil pressure. It is a condition that your plane must meet in order to be considered airworthy. Each combination of airframe, engine and prop has a specified static RPM range. This range defines 2 things. First, assuming a correctly performing engine, it defines the range of pitche the prop may have and still meet certification requirements. A "maximum" cruise prop will give a static RPM at the bottom of the range. An extreme climb prop will give a static RPM at the top of the range. Props that give readings outside the range are not suitable for that engine/airframe combination. Second, given that you have a airframe/engine/prop combination that can meet the above, your static RPM at a given moment is a measure of the soundness of your powerplant. If you cannot make the minimum static rpm limit then you cannot expect "normal" performance. Static RPM is fairly insensitive to field elevation, density altitude, temperature, etc. While your engine will not make as much power at higher altitudes, the air is less dense and the prop easier to turn, so they pretty much cancel each other out. In fact, at sea level on a really cold day your static RPM will be lower than standard, even though the engine is producing more power. Your static RPM should be checked at a minimum at each annual inspection. You may want to check it more often, like every time you take off on a runway less than 5000' long or higher than 500' MSL or after a 3 month layup or after june bug season... Well, you get the idea. Get an idea of what you can expect under a range of conditions and take notice when you get a reading you don't expect. Most of all, don't launch into the trees if the reading's below the minimum. The TCDS is the governing document, unless you're operating under an STC, in which that modifies the TCDS. John ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers/
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