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General Forums => Aircraft and Vehicles => Topic started by: Bradburger on November 20, 2001, 07:46:00 PM

Title: A question for Wells (Or some other Aero Engineer)
Post by: Bradburger on November 20, 2001, 07:46:00 PM

Gotta ask! How does one calculate Oswalds Wing Efficiency Factor?

Cheers

Paul  ;)

Title: A question for Wells (Or some other Aero Engineer)
Post by: funkedup on November 20, 2001, 07:51:00 PM

Going from memory here (textbooks are in storage).

A perfect elliptical wing is 1.0.
I think a rectangular wing is 0.8.
Common range is 0.7 to 0.9.
I think you have to do a surface integral to find it exactly.

Zig? Wells? Help!

[ 11-20-2001: Message edited by: funkedup ]

Title: A question for Wells (Or some other Aero Engineer)
Post by: wells on November 21, 2001, 12:36:00 AM

It depends on a lot of factors, like fuselage interference, lift and twist distribution, planform, taper ratio, induced angle of attack etc...

But, basically, what it comes down to is a proportionality to aspect ratio (AR) to correct for a finite wingspan where there are losses at the wingtips.  For a rectangular wing, you can use

1-1/AR

For an elliptical wing,

1-0.57/AR

So, for an aspect ratio of 6, you'd get a value between 0.83 and 0.90

Title: A question for Wells (Or some other Aero Engineer)
Post by: HoHun on November 21, 2001, 01:43:00 AM

Hi Wells,

do you happen to have the actual definition of the Oswald factor?

I wonder how to apply it - for example, if I got the test data of the performance of a finite rectangular wing in a wind tunnel, with Reynolds number given, do I apply an Oswald correction just to account for the non-rectangular shape, or has the starting point to be a lift-drag curve for an infinite wing?

Regards,

Henning (HoHun)

Title: A question for Wells (Or some other Aero Engineer)
Post by: Zigrat on November 21, 2001, 03:00:00 PM

i recommend theory of wing section by abbott and von doenhoff if you wanna know more. its the best book ive seen on the subject. they have all the info on converting section data to wing data based on planform. the correlations they use work well for the types of wings used on ww2 fighters. the relations used to do the necessary conversions are too complicated to put up here though..

Title: A question for Wells (Or some other Aero Engineer)
Post by: wells on November 21, 2001, 06:10:00 PM

Here's a couple of sites:
 http://www.desktopaero.com/appliedaero/potential3d/induceddrag.html (http://www.desktopaero.com/appliedaero/potential3d/induceddrag.html)
 http://adg.stanford.edu/aa241/drag/induceddrag.html (http://adg.stanford.edu/aa241/drag/induceddrag.html)