Bill Freeman wrote:

Perry and Paul,

The only changes that I would suggest should not cause
Perry any additional work at this stage.  First, with
the fwd speed and the circumferential speed combined,
the prop shouldn't go over 72 inch diameter to stay below
Mach 0.8 at the tips.  Also, from a pretty detailed
reading of a major NACA paper with about 80 (literally)
charts of actual wind tunnel testing of 16-series airfoils
with 5 inch chords, I want to slightly change the design
lift coefficient of some of these airfoils.  In some cases
this will make manufacture easier by going to an essentially
flat bottomed airfoil (not the reason to change, just a nice
fallout) and in all cases it should work better.  OTOH,
if you have progressed to where this will cause a lot more
work, don't worry about it.

So, i am attaching an XL spreadsheet with
 the improved version . . . . .  (I think)    :-)

If you don't want to change to the 370XX (nearest to
Clark Y in shape at 12% that I could find in my software),
just stick with the 16-7XX foils.

I think we should have a fairly square tip with slightly
rounded leading and trailing edges, perhaps a 1/2"radius
in planform.

The Hartzells that I found at S&F was about 3% thick with
a wide (4") swept tip.  The sweep was about 3" at the tip,
if the TE was extended "normally" in the radial direction
(unswept) the tip would have been about 1" chord.

They were on a Baron 58 registered to "AIR
VENTURES INC" of WILMINGTON, DE and
it was registered experimental on 26-Aug-1999. Isn't
that just after Reno?

I am also attaching a plot from my aerodynamics text that I
used in college.  It is the thrust coefficient (Ct) and torque coeff
(Cq) plotted vs blade radial position.  By integrating the Ct
curve you can find out the contributions of the various parts
of the blade.  For this example (apparently a typical curve)
I did a graphical integration and came up with this info.

Inner third of the blade =   7.5% of total thrust
middle third of blade    =  35%  of total thrust
outer third of blade     =  57.5% of total thrust

The take-home is that the effort on the inner third should
be mostly to make sure it is structurally adequate and
not too draggy, but this is not important.  The middle third
is important, but about half as important as the outer
third.

Bill

Long EZ builder & pilot
mechanical engineer

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