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Old Sep 21, 2012, 11:09 AM
Choppa Nutta's Avatar
UK
Joined Jan 2002
1,030 Posts
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How do I calculate strength of an airframe ??

Hi all,

I'm hoping to pick the brains of some structural engineers on the specific maths required to design large airframes, specifically calculating probable loads twist, shear, cantilever etc.
and how to work through material selections.

for instance, if I have a plane of a 100 kilo's with a 6 metre wingspan and I want it to take 12 G's before it breaks for a 6 G nominal load, how much Carbon Fibre/ Spruce/ Steel etc. do I need ?
assuming a rectangular cross section etc.

Calculating the weight of an airframe is a comparatively simple problem, volume x density of materials = mass, that bit I can do but its the rest I want to learn about, at least to a stage I can present a design to an aero engineer to tell me what I've got right & wrong so that I can do most of the leg work etc etc etc

anyhow, if anyone can help point me in the right direction, books to read, web sites to visit & so on I would be most grateful,
many thanks.
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Old Sep 21, 2012, 12:06 PM
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richard hanson's Avatar
United States, UT, Salt Lake City
Joined Oct 2007
7,367 Posts
No calculations but
based on the size model, you may contact various builder /plans suppliers of ultra lite aircraft-which have construction materials you would likely utilize

Many of these designs were under 500 pounds-some even much lighter .
The present generation of RPV craft are foam and glass- messy and expensive
Sitka spruce - , and plywoods may proove to be desired materials tho some builders utilize very thin aluminium ,sheared bent and rolled - -
You really need a concept of desired results -first.
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Old Sep 21, 2012, 03:43 PM
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peterangus's Avatar
Blackpool, Great Britain (UK)
Joined Dec 2003
1,342 Posts
Choppa

I presume you are aware of the UK Large model association

http://www.largemodelassociation.com/index.html

http://www.largemodelassociation.com/Register.htm
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Last edited by peterangus; Sep 23, 2012 at 04:36 PM.
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Old Sep 21, 2012, 04:34 PM
greg
ciurpita's Avatar
somerset, nj
Joined Feb 2005
372 Posts
Quote:
Originally Posted by Choppa Nutta View Post
for instance, if I have a plane of a 100 kilo's with a 6 metre wingspan and I want it to take 12 G's before it breaks for a 6 G nominal load, how much Carbon Fibre/ Spruce/ Steel etc. do I need ?
assuming a rectangular cross section etc.
these type of questions use to be so common on this forum

the problem is usually how much force can the wings take before they bend and break

these notes may help http://ciurpita.tripod.com/rc/notes/compositeSpar.html

greg
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Old Sep 21, 2012, 06:53 PM
agnotology
kcaldwel's Avatar
Joined Jan 2007
3,678 Posts
"Analysis and Design of Flight Vehicle Structures", Bruhn, is the bible for aerospace structural design:

http://www.amazon.com/Analysis-Desig.../dp/0961523409

Kevin
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Old Sep 22, 2012, 07:58 PM
Choppa Nutta's Avatar
UK
Joined Jan 2002
1,030 Posts
Thank you guys,
I have various projects in mind, at some point I know I'm gonna want make something I can sit in but that dream is far away as yet
but what I'm after here is the understanding and knowledge of the structural design process and the maths behind it, I will try the links
Cheers
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Old Sep 23, 2012, 02:27 AM
Registered User
Estonia, Harju, Tallinn
Joined May 2012
167 Posts
This spreadsheet might help you --> http://www.rcgroups.com/forums/showthread.php?t=1213427
I've used it to dimension my wings.
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