Hi Mike,
I saw your question at RC groups as well (
http://www.rcgroups.com/forums/showthread.php?t=2023310). Your number for
CL_a is wrong because you use alpha in degrees, not in radians.
For example if you only look at the first linear part of your graph (from 0
to 5 degree) you can see an increase in CL of roughly 0.48. The 5 degree
change in alpha should be converted to radians (devide by 180/PI=57.3),
thus 5/57.3=0.0872.
Now CL_a (actually the change in CL due to a change in alpha) is
0.48/0.0872=5.5.
The rest of the differences are probably due to a slightly different input
in Xfoil/xflr5.
BTW, where can I find the example you used?
Best wishes,
Kevin
2013/10/23 mkirda_at_sbcglobal.net <mkirda_at_sbcglobal.net>
> **
>
>
> Greetings.
>
> I've been looking at this program on and off for a year or so.
>
> Dr. Drela included some example files for F1D props, specifically John
> Kagan's.
>
> Silly me, I like to understand things. So I follow the documentation and
> after computing the polars for a 3% arc file (as generic as it gets for
> prop airfoils), I try comparing to the examples.
>
> And as you might guess, nothing matches. Some things are close, however I
> cannot understand how he got the numbers in the example files using the
> polar at Re5000 as indicated.
>
> Is there anyone on-line that I might work with offline a bit to understand
> this a bit better? I have to assume I am doing something wrong...
>
> Regards.
> Mike Kirda
>
>
>
Received on Mon Oct 28 2013 - 06:55:40 CET