If I remember my equations for buckling of long columns, they do NOT include any factors for the STRENGTH of the material. What does matter is unsupported length, thickness (or diameter), and material MODULUS (stiffness). Carbon fiber is stiffer than fiberglass and so would be better. However this material stiffness is a linear term. Thickness is a cube term, so MUCH more important to avoid buckling. If you remember Joe Wurts' lay-up spreadsheet for computing stressed skin wings (vacuum bagged wings with no real spar), it dealt with ultimate wing strength in an interesting way. If you examine his formulas, the 'strength' difference between carbon and glass (of the same weight cloth) was TOTALLY due to the difference in thickness due to carbons lower weight. Joe developed this spreadsheet empirically by building and breaking many samples. Since this spreadsheet doesn't include any factor for carbons much higher strength, (and even ignores it's greater stiffness), it can be concluded that most stressed skin wing structures fail by buckling. Field failures also bear this out. Also note on this spreadsheet, that wing strength improves when all additional thickness is added to the TOP skin (to avoid buckling). In fact this highlights a small problem with interpreting the spreadsheet too literally. Any none zero amount of material on the bottom and all the rest on the top produces the strongest wing for the weight. Obviously a little reason is in order here ;) John from Denver Please note my new e-mail address is [EMAIL PROTECTED] Get more from the Web. FREE MSN Explorer download : http://explorer.msn.com |
- RE: [RCSE] composite strengths and buckling Ted Garman
- John Kappus
