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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
Ed A
----- Original Message -----
Sent: Wednesday, December 21, 2005 7:08
PM
Subject: [FlyRotary] Re: Props
Don't ask me George. I'm not an engineer or good with
mathematics. Ed A will know better.
Buly
On Dec 21, 2005, at 6:20 PM, george lendich wrote:
Thanks Buly,
So, Pitch" = MPH
x12 x 5280
RPM x 60
I figure 12 (inches in a foot)
and 5280 ( feet in a mile) and 60 ( minute in an
hour).
So the top line is converted
into inches per minute and the bottom line RPM.
So, Pitch " = inches
per minute
RPM
Does that look right to you
?
George ( down
under)
Thanks George. my mistake was that i did not convert it to MPH.
I was also given the formula for cruise speed:
Pitch" x RPM x
60 = MPH
12 x 5280
Buly
On Dec 21, 2005, at 4:39 PM, george lendich wrote:
Buly,
Looking at the
formula given by members on this list, 2 out of 3 were spot
on with Hoverhawk and
the third was close.
Examples:
1. Prop Dia x 3.1416x
RPM/ 720 - Correct!
2. Prop RPM x Dia x
.00436 - Correct ( 3.14/ 720 =.00436)
3. 3.14 x 64 {given
prop dia} ( 5500/2.17 {given RPM})= 508346/707 -
slightly incorrect (
as compared to the other 3 examples, which include
Hoverhawk)
i.e 3.14/ 707 =
.004809 whereas all the others are 3.14/ 720 = .00436.
Now that I have that
sorted - can someone tell me how to calculate pitch,
easily!!
George ( down
under)
Thanks Perry. This
makes me feel much better. Looks like the formulas
given to me were
not good.
Buly
On Dec 19, 2005, at
2:00 PM, Perry Casson wrote:
I think your math
is off a bit - Here's a online calculator http://
www.hoverhawk.com/propspd.html
I think 6900 puts
a 72" prop close to
mach 0.9 but I've never ran
mine above
6500
Perry
Casson
--
Buly
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