prop formula - another thought

[Kenneth Blackwell]

I've been watching the discussion about prop formula.....i.e equivalency
between 2-3-4 blades etc.

So far the discussion and calculations have just covered diameter, pitch and
number of blades. However, there has been no mention of blade planform. As
you know APC makes blades with all sorts of planforms wide, narrow,
standard. In addition as you progress from one style prop (sport, pattern,
etc.) the planform distribution differes wildly. A prop is just a rotating
wing with a particular planform. Some are wide giving more planform area for
the same diameter while some are narrower. Obviously the two will provide a
different load on the engine. So, the only way that you could correlate the
load expectation between 2-3-4 bladed props would be with those of similar
planforms.

You may use a formula to get you in the ball park or maybe the parking lot,
but in the end you will just have to spend some bucks and try a size or two
to see what works for you and your engine.

Cheers,

Ken Blackwell

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