Resonant frequency on Arrow question for you mechanics

Mattio

Mattio

Well-Known Member
Does anybody know if the RPM range limitation (not to linger 2000-2350 RPMs) is because of resonant frequency or quicker wear to the engine at those RPMs?

Thanks!
 
Resonant frequency of the engine and propeller combination. I have never heard of this condition with a fixed pitch prop, only with variable pitch propellers (such as constant speed props).
 
The majority of the aircraft with this restriction are equipped with a four cylinder Lycoming and Hartzell two blade propellers. PA28 series, certain Pitts models, Christen Eagle.... Sometimes you'll see that in a fixed pitch application as well.

A vibration is created in that RPM range, and it is prone to cause component cracking. Here's a tip, tachometers can be inaccurate. So if the caution range is 2100-2350. Don't ride at 2400, because if there is a tach error you are now in this RPM range. Find a mechanic with a portable digital tach to verify that tach is accurate.
 
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