Vance Jaqua wrote:

--- Paul <rotaryeng@earthlink.net> wrote:

Perry Mick wrote:

Paul:

Peter Cowan has kindly donated $100 towards

materials for the

CS prop blades.  Other donations would be welcome.

 I will donate

my time.  I can't see the cost of materials

exceeding $300 so any

excess donations I would forward to your race

fund.

I've been playing around with a 68 inch diameter

prop twisted for

75 inch pitch at "0" degrees of rotation.

Assuming a constant 150

HP, here are some results:

        speed, knots
blade   for 150HP       actual HP       Thrust

     Prop Efficiency

angle   @2800 RPM
-5      10              150.2862        594.8937

     0.121473

-4      80              148.6547        469.0335

     0.774597

-3      100             150.166         414.1032

     0.846248

-2      120             144.8881        352.9075

     0.896954

-1      130             149.4755        340.9437

     0.909948

0       140             153.7152        328.9666

     0.919441

1       150             157.6523        317.5427

     0.927158

2       170             138.9872        250.9947

     0.942105

3       180             141.0632        241.4703

     0.945547

4       190             143.3405        233.0989

     0.948169

5       200             145.9712        225.9701

     0.950111

6       210             149.115         220.1647

     0.951494

7       220             152.9388        215.7559

     0.95242

8       230             157.6159        212.8104

     0.952975

9       240             163.3254        211.3881

     0.953232

and here is data assuming the same prop with pitch

fixed at the

0 degree location:

assumes constant 150HP (which means performance is

actually worse

at the low speed end and better at the high speed

end.

speed,
knots   rpm     thrust
0       2350    425
60      2500    475
80      2520    460
100     2580    420
120     2660    370
140     2780    325
160     2930    280
180     3120    220

The plot tells the story better than the numbers.

I'm getting this

effect at high rotation angles of the blades, +4

to +9 degrees, where

the things seems to want to keep going, i.e., I

keep increasing the

blade angle and keep getting more thrust at higher

speed, thrust is

not going to 0. The thrust curve is flattening

out.  Is this real?

Vance????

There was no blade width given - so for comparison I
sized a prop for an IO 320 160BHP curve I have in my
program for a 68 dia 75 pitch which suggested 3.6
width at .9R 4.6 at .7, 5.8 at .5 and 7 inch at .3. I
set helical pitch for the 75 inch and ran it as a
fixed pitch versus the power curve, and turned the
whole blade for various speeds per the table, My
program appears to be more conservative - predicting
less thrust, even with the 10 more HP and the shape of
the curves does not suggest an arch for the fixed
pitch, nor a significant upturn at the end for the
constant speed. The redrawn curves show what was
predicted for whatever it might be worth - I feel the
efficiencis suggested by the other data are
suspiciously high - Vance

 
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