Propeller Pitches

Okay, where do propeller pitches come from?

I understand the no friction Number of inches a propeller will move one one revolution but what about the angle it is cut/sanded/twisted/molded at? How is that arrived at?

I tried to measure a couple props with a protractor. I got one measurement for a 4, 5 , and 6 inch pitch prop. There didn't appear to be any noticeable pattern. Like 4inch - 40 degrees, 5inch - 50 degrees, 6inch - 60 degrees.

I thought about creating my own pitch scale, but it would not be correct by a uniform standard.

The formula for helical pitch props is :
tan(theta)=pitch/(2*pi*r)
where:
theta - is the angle at the blade station
pitch - the advance for one revolution
pi - 3.1415926........
r - radius at the blade station

you can invert this to:
theta = inverse tan(pitch/(2*pi*r))

Pat MacKenzie

>
>Okay, where do propeller pitches come from?
>
>I understand the no friction Number of inches a propeller
>will move one one revolution but what about the angle it is
>cut/sanded/twisted/molded at? How is that arrived at?
>
>I tried to measure a couple props with a protractor. I got
>one measurement for a 4, 5 , and 6 inch pitch prop. There
>didn't appear to be any noticeable pattern. Like 4inch - 40
>degrees, 5inch - 50 degrees, 6inch - 60 degrees.

Of course, the angle depends on the distance from the center of rotation, too. Pat has the correct relationship below.

There's also an article in this month's SN.
Brett

I just got the issue and there it is.....

thanks....

Tell me, Jon, is this modern age wonderful, or what? You ask a question on this forum and Bam! the answer comes to you in printed format delivered by the mail man--and in a magazine no less!

Where, but in America?