frustum (nosecone) calculations

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Well-Known Member
Jan 18, 2009
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ok, I am working on the little joe project and have come into a snag. the nosecone/capsule is a frustum with the following measurements

d1 = 5.25 d2 = 13.5 l = 10.125

so I crank up a handy spreadsheet for getting a skin template and i get the following

r1 = 6.957 r2 = 17.89 a = 135

I go to lay it out (i did 2 pieces at 117 degrees) and cut it up and then i see it doesnt look right. base is nearly 20+ and the apex is about ten. height looks right

(aha! i screwed up radius vs diameter, right?)

I go online and plug the numbers thru nearly every online transistion calculator google can find and the numbers are right. so what is wrong?