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Date: Sun, 27 Aug 2006 19:30:11 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: prop speed
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Bob Darrah wrote:

> Well, guys, I think you should look at this a little differently.  The 
> rotational tip speed pf the prop is at right angles to the forward 
> speed and should be added  vectorially.  As a result, it adds very 
> little.  For example, a 72 inch prop turning 2400 RPM going 180 MPH 
> results in a rotational speed of 6' times pi or 18.85 feet per REV.   
> Now, the forward speed  in that length of time (1/30 of a second at 
> 2400 RPM) is only 8.8 feet.  Add those vectorially (the two sides of a 
> right triangle) and the result is 20.8 feet per rev,  almost within 
> 10% of using RPM only.
>
The original post said that the program was calculating the tip speeds 
at .88 to .92 of mach, if I remember correctly.  Add that 10% and you're 
making lots of noise without getting a lot done.

-- 
         ,|"|"|,              Ernest Christley       |
----===<{{(oQo)}}>===----    Dyke Delta Builder      |
        o|  d  |o        http://ernest.isa-geek.org  |