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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
----- Original Message ----- From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, August 26, 2006 11:53 PM
Subject: [FlyRotary] Re: prop speed
Barry Gardner wrote:
That would mean that the rpm they calculate would be too high for an aircraft (except for the first five seconds of takeoff) and the prop length recommended would be longer than an aircraft could use because the longer tip could go supersonic when the forward velocity is added in.
Anyone want to tackle this or straighten me out?
No straightening needed. Your course line is perfectly straight. Your conclusions are solid.
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