Local Buckling of thin shell NACA airfoils

[israelkk]

Can anyone point me to empirical or analytical local buckling of unstiffened and stiffened thin shell NACA airfoils under bending and/or torsion and other types of loading.

 

[Sparweb]

I've got a book by Niles and Newell, Airplane Structures, which gives section properties and crippling stress curves for streamline tubing. The curves apply up to a T/t=100. That is, thickness of airfoil section one hundred times greater than thickness of skin. Would this be applicable to your case?

I would also need to know the material your wing/strut/? is made of.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[israelkk]

SparWeb

Thanks, I am talking of extruded one piece thin-walled (unstiffened) hollow NACA shaped profile. I am looking for local bucking design criteria for the minimum thickness of the skin thickness with respect to profile section geometry.

I have found data for elliptical, D shaped, tubes etc. but not for actual NACA profiles. I could use elliptical section for approximation the data I have found was for bending with respect to the minor radius of the elliptical section, while I am looking for bending with respect to the major radius of the elliptical section which is the weakest.

 

[joekm]

Check out Roark and Young Table 10.1. There is a formula for an arbitrary thin tube (item 14), that may be of help. One important thing is that, if the thickness is small, the shear stress is nearly uniform.

Also, check out Bruhn, Chapter C4, assuming we are talking about a strut, I would specifically send you to section C4.15.

If all else fails, there's the Needham and Gerard methods (Bruhn Chapter C7), etc.

Good Luck,

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[israelkk]

joekm

Edition of Roark?
Edition of Bruhn (printing year)?

 

[israelkk]

joekm

Did you mean table 10.1 for torsion? If so this is not dealing with local buckling (elastic instability). I looking for elastic instability in bending (mainly) and in torsion.

 

[joekm]

Yea, Table 10.1 for torsion, just trying to give you a well-rounded cross section of references. As for Bruhn, my copy is the June 1973 edition. This is a pretty common reference. If you don't have it at your place of work, you should be able to find it at a nearby university library. Failing that, here is the publisher:

Jacobs Publishing, Inc.
10585 North Meridian St. Suite 220
Indianapolis, IN 46290

Ph: (317) 844-9400

Oh yea, and 7th edition of Roark & Young.

Hope this is of help,

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[israelkk]

joekm

Thanks.