Bill Freeman wrote:

Paul,

I've been spending some time reviewing the old NACA papers
on prop design, and there is one thing that seems to be a very
good fit - both for your constant speed prop and for Perry's
fan.

NACA developed a special family of airfoils intended for props
which will delay the onset of compressability problems (shocks)
and give good performance (low drag).  The family member
airfoil for your application is selected by choosing a design
lift coeff (~0.1 to  0.5) and a percent thickness.  If you can
select the lift coef, percent thickness and chord at a few stations
I can provide full sized printouts of the airfoil sections to make
carving templates.  I would think that about 0.1 to 0.2 lift coeff
and a 6% or 8% thickness at the tip (~6-8"), going to about 10-12% in
the middle sections and thicker near the root would work well.
For a 6% tip you'll want all carbon fiber to get enough stiffness
to avoid flutter.

Perry may see some substantial advantages, esp if he is using a
Clark Y and 12% or more thickness, which are std wood prop
practice.  A 12% Clark Y is truly bad at high tip Mach.  Some of
these airfoils avoid a shock until surprisingly high Mach.

This series is the NACA 16 series, with examples like 16-106 being
a 0.1 design lift coeff and 6% thickness, 16-210 being 0.2 lift coeff
and 10% thickness, specifically intended for high Mach applications
like props.

Bill

Great info Bill. Thanks. We are certainly making progress here
as John Moran is machining the prototype. All we need now is someone
to make the blades.

Paul Lamar
 
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