Sep 21, 2012, 10:09 AM UK Joined Jan 2002 1,030 Posts Discussion 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.
 Sep 21, 2012, 11:06 AM Registered User United States, UT, Salt Lake City Joined Oct 2007 6,889 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.
 Sep 21, 2012, 02:43 PM Registered User 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 Last edited by peterangus; Sep 23, 2012 at 03:36 PM.
Sep 21, 2012, 03:34 PM
greg
somerset, nj
Joined Feb 2005
371 Posts
Quote:
 Originally Posted by Choppa Nutta 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
 Sep 21, 2012, 05:53 PM "...certainty is absurd." Joined Jan 2007 3,603 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
 Sep 22, 2012, 06:58 PM 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
 Sep 23, 2012, 01:27 AM Registered User Estonia, Harju, Tallinn Joined May 2012 159 Posts This spreadsheet might help you --> http://www.rcgroups.com/forums/showthread.php?t=1213427 I've used it to dimension my wings.