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Thread: Engine RPM
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Old 25th January 2004 | 08:47
  #6 (permalink)  
smarthawke
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Joined: Jun 2002
Posts: 630
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From: UK
Hold on there, don't scrap the aircraft just yet!

Most Lycomings driving a fixed pitch prop with a max rpm of 2700 will only pull 2200-2300 static.

Engines turning variable pitch props (a la Aztec) should reach red line when static.

Whilst a poorly engine may well result in a lower static rpm achieved, a knackered prop may also cause a discrepancy between two similar aircraft. An old prop with the tips clipped to the minimum allowable diameter normally revs higher (on the ground and in the air) than a new thick and long one.

Remember that with mechanically driven tacho, at 2300 rpm, a 10% error (often seen on car speedos) will mean a 230 rpm mis-read!

On the CofA flight test the static rpm is carried out (and should be recorded by any decent engineer on a ground run after any servicing). This is normally carried out crosswind to prevent the wind effecting the results.

As for checking it, pre-flight, why not check it as you begin the take off run and still have time to abort.

At 2500ft you are unlikely to see max rpm unless the prop is a low drag one - clipped and thin through age normally. The POH should tell you what power setting/altitude will give what rpm.

Hope that helps.
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