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From: "Barry Gardner" <barrygardner@gmail.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-1351307@logan.com>
Subject: Re: [FlyRotary] Re: prop speed
Date: Sun, 27 Aug 2006 19:12:13 -0500
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----- Original Message ----- 
From: "Bob Darrah" <RDarrah@austin.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, August 27, 2006 4:19 PM
Subject: [FlyRotary] Re: prop speed


> 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.
>
>
>
> FWIW
>
> Bob Darrah


Thanks, Bob. That's exactly the kind of help I was looking for. It still 
sounds like the hoverhawk.com site recommendations would be biased on the 
high side.

Barry Gardner
Wheaton, IL/