Bill Freeman wrote:

Paul,

You and Vance wanted the prop data - I already sent it
to you - in the spreadsheet.  You guys are really missing out
on an incredibly powerful tool by rejecting spreadsheets.

In any case,  here is the data for the particular props that
I was simulating.

R       Beta     Chord
9        64.9      3.96
12      58.3      4.59
15      52.4      4.92
18      47.1      4.97
21      42.4      4.77
24      38.4      4.36
27      35.1      3.76
30      32.4      3.01
33      30.3      2.15
35      30.6      1.19

The point of the exercise that led to the plots was to
examine the effect of chord scaling (all chord values scaled
by a common factor) on performance for a CS prop.
I was initially looking just at cruise speed, 250 mph.
For each speed, the blade was rotated (no change in blade
pitch distribution) until the HP required was 250.  At
250 mph, the chord scale factor made amazingly little
difference, changing the thrust from 299 to 302 lbs over
chord factors from .75 to 1.5.  This seemed weird, so I
decided to see what the effect of chord factor would be
over a range of speeds. This showed the effect of proper
chord sizing on performance.  A too-narrow prop can
work fine at top end, but gives up a huge amount at lower
speeds - remember this is a CS prop.

 Again, my point is that when  the chord is too small, the
blade has to be rotated to exceed stall on the inner portion
(in some cases a majority of the blade) to get it to absorb
250 hp @ 2500 RPM.   So for the too-narrow chords, much
of the blade is producing a very poor (post stall) L/D
at lower fwd speeds, yet absorbing the 250 hp, but producing
reduced thrust.  As the chord is increased, the blade angle
to absorb the 250 hp is decreased, so the low speed
inefficieny decreases, while the high speed performance
tracks the "normal" performance, shown by all the lines
overlapping once they reached a speed where they could
work properly.  Seems sensible to me.  Keep widening the
chord to get the prop to work as well as possible over a wide
range of fwd speeds at a constant 250 hp @ 2500 RPM.

I'd like to hear what Vance's prop sim program will predict for
this particular chord and pitch distribution.  This beta is for
the true geometric zero angle on the airfoil, not the flat
bottom or the zero lift line.  I'm not pushing this chord &
pitch distribution, they are just what I am currently looking
at.  If you have better suggestions, I'll be pleased to try them
out and see what my spreadsheet thinks they'll do.  This is
my whole point in writing this thing.

I need to plug in the data for my two props that I have test
data for, unfortunately they are fixed pitch.

Bill
Long EZ builder & pilot
mechanical engineer

When you can program Bill you don't need spred sheets :-)

Paul Lamar
 
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