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Bob my email server automatically deletes exe
files, could you zip first please.
Thanks
Greg
Attached is a Prop
Design program, which I found some time ago, that has the following
explanation on its help page. You can play with the numbers to match your prop
and see what speed you will get or you can plug in the variables and see what
size prop you should have. I hope you can receive the attached
file.
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Thursday, December 22, 2005 7:46
AM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
Re: Props
I really do not know,
George. I have known folks with aircraft speeds somewhat faster than the
"screw" calculations would have predicted - perhaps this "lift" factor played
a role. Most figures I have seen puts efficient of prop around 80-85%
mostly around 80.
----- Original Message -----
Sent:
Thursday, December 22, 2005 4:45 AM
Subject:
[FlyRotary] Re: Props
I like to reduce things down to
the simplest formula, provided one doesn't lose track of what's
relevant.
So I guess I should look at this
as 100 % theoretically efficient - whereas we may be looking at only 80 %
efficiency ( in real terms), Do you agree with 80%?
However your saying that the
lift may give more speed ( MPH, in real terms) - So are you
suggesting that these two (variables) may balance
out?
Or should we use a fudge factor,
and that could be what?
I'm not looking for a
finite answer, just close enough to be able to access the experts opinion,
and we all know what an expert is - " A drip under
pressure".
Yes, George. If we
assumed no slip in the prop then theoretically the formula will give you
the pitch of the prop you would need to screw through the air and achieve
your MPH at your RPM input. This is based simply on the screw
principal. I am certainly not a prop expert, but I also believe that
since the prop is a spinning wing (airfoil), that there is a lift
component in the direction of flight which may result in more speed
than the formula could account for.
Your second equation can be
reduced further from (Inches/Minute)/(RPM) =
(Inches/Minute)/(Revs/Minute) = inches/Rev
--
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