Spar sizing calculations.

[Simon Wright]

I am trying to size spars for a project and wass considering using a carbon composite. I have done some research on the internet and located various design tensile stresses including Spruce 5000 psi, Carbon- pultruded 100,000 psi and Oak 8000 psi.

Have read some calculations by Professor Mark Drela (MIT) which seem to work for carbon but give huge numbers for dimensions of spruce spars.

Where can I find suitable formulae or empirical data to calculate the size of spar for bending and shear loads? A calculation to develop torsional strength would be useful too.

thamks for any assistance.

Simon Wright

[Robin Woodhead]

If you do a search for CYPARIS on the LMA web site, click on the result shown as [Cyparis%20data.doc], this will take you to a Excel spreadsheet giving details of various materials.

Robin

[Simon Wright]

Thanks for the link.

I have various figures for materials but need to find worked formulae to use them on.

Any links to a sizing spreadsheet?

[Stuart Solomon]

Simon, will be at Gaydon, let me know if you want a stress comparison sheet between Cyparis,Spruce,Hemlock and Douglas Fir. Stuart-Solutions.

[Rob Buckley]

Simon,

Have a look at CS-VLA, the certification requirements for very light aircraft (which is what large models pretty much are) here...

http://www.easa.europa.eu/ws_prod/g/rg_ ... php#CS-VLA

This should at least give some loads to apply to the structure!

As for the actual calculations, I'd pick the closest looking sections out of Machinery's Handbook and make some conservative assumptions & calcs from there.

I must admit, structures aren't my speciality. I did once have spar shear flow explained to me, and it seemed to make sense at the time. It's gone now though!