Re: prop size?


Leon - C <leon@...>
 

David;

With the offset thrust line (I assume a belt reduction with the 2/1 ratio rather than planetary) is is possable that whirl mode resonance might also be a problem and contribute to prop flutter even if properly "clocked"? I have seen visable resonance of this type with some ultralight aircraft.
============
Leon

The spreadsheet Leon tried to send you is located here:
http://david.gall.com/files/Airplane/Prop-100.xls.
It is based on NACA Technical Memorandum 212. It should be sufficient to get
you "into the ballpark" for your propeller selection. It can recommend pitch
and diameter for either a two- or a three-bladed prop.

Your reported propeller failures sound like resonance problems. With a 2:1
reduction, the propeller is in lock-step with the vibration of the engine
from the power pulses. <<

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