Re: Prop Efficiency

From: markdrela <drela_at_mit.edu>
Date: Fri, 25 Aug 2006 21:05:58 -0000

--- In Indoor_Construction_at_yahoogroups.com, "John Kagan"
<john_kagan_at_...> wrote:
>
> It looks like Javaprop is telling me that my current prop's Cl is
> 7.68. Does that sound reasonable? If so, I'm looking at almost
> doubling the cord.

I assume you mean 0.68, not 7.68.

Yes, 0.68 is too high -- it means the blade airfoils are right at
stall, or even just beyond stall. But how confident are you of your
assumed velocity? You might vary this up or down a bit to see the
effect on the predicted blade cl. If it's very sensitive, then a
careful measurement of velocity would be a good idea.

Also, make sure the blade cd's are OK, even though this is less
important than the velocity. Anything between 0.03 and 0.06 is
reasonable, and won't affect the predicted cl's very much.
Received on Fri Aug 25 2006 - 14:07:42 CEST