The prop program by Dokus and Dubner shows a 2.2% loss of efficeincy
between a 76.4" prop (at 2700 RPM) and a 64" prop (at 3225 RPM).
This would indicate that there is not much difference between the 2.17
ratio and the 2.85 ratio.  These numbers are for a tip speed of 900 ft
per second.  900 ft per second is 80% of Mach at sea level on a

'normal'

day (1114.4 fps).  This also explains why the canard guys go so fast
with small diameter props.

Ken Powell

I'll let Bill explain the chord factor because I  don't understand it

yet.

I think this is for a 16 series.

The second chart is lift to drag ratios at Mach .78 for different

airfoil

sections.

Paul Lamar

Yes, Bill, Please explain the Chord Factor.  What ever it is, clearly 1.5
looks better than 0.75.  If it implies some width to length ratio, I am
interested as I have a narrow chord prop - am I losing efficiency due to
this??

Ed Anderson

Sorry to jump in the middle of this, but one of the reasons to turn the prop
higher is more HP.  How does this figure into the mix?  I am assuming that
these numbers are based on the same HP, just a different RPM.  Does the more
HP make up for and surpass the efficiency?

Todd Carrico

Yes.

Paul Lamar
 
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