Re: Optimum Prop Diameter

From: LeRoy C Cordes <lcordes_at_juno.com>
Date: Tue, 11 Sep 2007 10:44:15 -0500

WOW - just what I need another set of variables - I have enough trouble
as it is <Grin>

LeRoy Cordes
AMA 16974
Chicago, IL
In God We Trust

On Fri, 7 Sep 2007 11:20:07 +0100 "John Barker"
<john.barker783_at_ntlworld.com> writes:
> quote<Why is it that a larger prop will have a higher drag?>endquote
>
> Thank you for the question even though it embarrasses me! I assumed
> the
> larger diameter propeller would have more drag and I still feel that
> that is
> the case but of proof I have not a shred. Looking at the matter
> from the
> point of view of the aspect ratio of the blades does not seem very
> easy.
> The usual way of doing propeller calculations using the vortex
> theory
> approach uses wing section coefficients for infinite aspect ratio
> and blade
> aspect ratio is not used in the calculations. Solidity does not
> appear to
> be a substitute because, say, two wide blades or four narrow blades
> of half
> the width would have the same solidity.
>
> I suppose it would be possible to run through the design procedure
> for two
> propellers of different diameter, giving the same thrust and finding
> if
> there was any difference in the power required - which I think is,
> in
> effect, your ‘torquenal’ drag approach.
>
> However I think once one started looking into this one would realize
> that
> different diameter propellers may work better with different rubber
> cross
> sections at different rotational speeds and … and …and. It may be
> quicker
> to make a few props.
>
> John
>
>
> [Non-text portions of this message have been removed]
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>



LeRoy Cordes
AMA 16974
Chicago, IL
In God We Trust
Received on Tue Sep 11 2007 - 11:47:44 CEST