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Date: Mon, 11 Oct 2010 10:39:40 -0400
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Solidity of Prop Disc
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Ed Anderson wrote:

> While increasing the blade chord is the easier option, it is less 
> efficient because the aspect ratio of the blades is decreased resulting 
> in some loss of aerodynamic efficiency.
> 

One reason the thick chord is less efficient is that it creates a much larger tip vortex.  It takes a lot of energy to 
make those tiny tornadoes at the end of a wing.  Paul Lipp's propeller minimizes this by putting all the chord at the 
center and then thinning out to nearly nothing at the tip.  Wittman did the same by putting triangular sections on the 
ends of his main wings.

So, I'll modify the earlier rule.  The best prop would be the longest one that would leave some ground clearance, and 
then absorbs any remaining Hp by increasing the chord, with the chord increase starting near the hub and thinning as it 
moves out to the tip.