Buckling limit of spruce longerons for homebuilt aircraft 1

[craddojc]

Hi Eng-Tippers,

When designing a homebuilt aircraft fuselage with 1/2" square spruce (wood) longerons that can see compressive loading, what criteria should be used for buckling limit? I'm working on designing my own aircraft, and I have searched Bruhn's 'Analysis and Design of Flight Vehicle Structures' with no luck...

Thanks in advance
Jeff

 

[MiketheEngineer]

You can alwyas use Eulers - or test a couple of them

 

[rb1957]

solid sections, or laminated ?

i'm guessing you don't have an E (for euler).

try some old texts, maybe NACA, for properties of wood.

sigh ... a quick google "strength of spruce" yielded some interesting hits, like

http://www.sportair.org/articles/aircraft wood - part one.html

and MIL-SPEC 6073 and

http://www.woodbin.com/ref/wood/strength_table.htm.

a quote from the sportair site "The primary source of information for the builder may be obtained from FAA Advisory Circular 43-13, government bulletin ANC-19, and from a copy of Mil-Spec-6073."

sorry, but i expect people should do the basic stuff before asking us.

 

[rb1957]

from homebuiltairplanes.com, from a google for mil spec 6073 ...

"Mil Spec 6073
Hello Everyone,

I'm new to this forum and thought I'd offer a copy of Mil Spec 6073 (dated 1950) to anyone that wants it. It details Spruce selection for aircraft use. It is a very boring read and is probably well summarized in AC 43.13

I searched this forum to make sure it wasn't already posted somewhere but I may have missed it.

I have it as a Word document and it also includes an Excel spread sheet I think. I don't think this is a copyright infringement or anything since I copied it from a government document. Someone let me know if I'm wrong about this.

If anyone wants it drop me an email at rblassett(at)alltel.net

Russ"

the google also found the mil spec under the eaa site ...

 

[btrueblood]

Dodissp still works (see link below), and you can search for all MIL documents there, even cancelled ones. This one has a reinstatement notice (for replacement purposes) listed there, dated 2009. Now I'm wondering what aircraft is being rebuilt by the military using spruce wood (latest stealth fighter = Sopwith Camel?).

http://quicksearch.dla.mil

 

[KENAT]

btrue, I believe the Canberra used some limited wooden construction and a couple are still flying with 'NASA' for some testing etc. Plus who knows what some of the UAV's and 'special missions' aircraft might use.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[craddojc]

Guys,

thanks for the help but I already have properties for spruce.

To clarify, what I was hoping to find is what criteria to use to determine buckling stress for wooden columns- is Eulers useful for a non-isotropic material like wood, or do I need to use something else? In commercial building frames, Ive heard the Merchant–Rankine–Wood method applies...

Does the aerospace industry use one of these for wood structure?

Thanks in advance
Jeff

 

[verymadmac]

Have you checked ANC-18 - Design of Wood Aircraft Structures

 

[WKTaylor]

A copy of ANC-18 is available on the homebuiltairplanes.com forum, thru the atttached link..

Forum - Technical Discussion Areas - Wood Construction - ANC-18 - Design of Wood Aircraft Structures.

http://www.homebuiltairplanes.com/f...8-anc-18-design-wood-aircraft-structures.html

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[craddojc]

Wil,
Thankks very much! ANC-18 was exactly what I needed.
Jeff