Dimensional formulas: How do you skin a cone?

Tenderizer · Post by **Tenderizer** » Fri Oct 28, 2005 10:03 am

Ok, new guy on the block, so please be patient.
I know how to calculate the volume and surface area of a cylinder. That's a breeze. But what I'm trying to figure out how to do is to calculate the surface area of a cone-- and then how to draw it on a flat sheet of [whatever] so I can cut it out to put a "skin" on a conical framework. Sounds easy, right? WRONG. Sadly, my math skills are a little rusty, so if anybody has a formula, I'd be happy to hear it.

What do you mean, "what do you mean"? It's like this-- take a paper cup [or plastic-- I don't care] and cut the bottom off of it. Now cut a line straight down the side and flatten out the plastic. I want to know how to calculate and draw THAT shape so I can successfully put a skin on a cone of varying size. And no, I don't have the phone number of the JPL, or else I'd ask them.
Needless to say, this has been driving me a little crazy. I figure if I have the radius of the top end of the cone and the bottom end of the cone and the distance between the two, SOMEBODY has to know a formula for "skinning" the cone.

Help?

Tenderizer · Post by **Tenderizer** » Fri Oct 28, 2005 10:05 am

The cup from which you cut the bottom is a tapered cup-- like a Starbucks cup or something-- thus, conical.

Matt2893 · Post by **Matt2893** » Fri Oct 28, 2005 10:20 am

Sounds like you should talk to some Designers of Paper / Card Models.
There is a forum here for paper models http://www.starshipmodeler.net/cgi-bin/ ... m.php?f=42
There are several "webhomes" for them as well, http://www.smartgroups.com/groups/papermodels is a good place to start.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Fri Oct 28, 2005 11:29 am

Welcome to Starship Modeler. You aren't next door to Woozle are you?

I don't recall who first posted this, but
I thought EVERYONE had this bookmarked already...

http://www.realmcommunications.com/rbla ... udcalc.htm

8) 8) 8) 8) 8)

macfrank · Post by **macfrank** » Fri Oct 28, 2005 12:12 pm

The math isn't hard, but you don't have to figure it out - it's been done for you. Try Shroudcalc. You can use it for cones as well.

naoto · Post by **naoto** » Fri Oct 28, 2005 2:17 pm

Yep, that "shroudcalc" applet is pretty handy. Comes in handy in those situations where you need to make a transition section on a model rocket. Funny thing is that whenever I came across this very situation I usually found myself sitting down with a pencil and piece of paper to derive out the formula (doesn't take more than a minute or two and doesn't require anything beyond high school trigonometry).

It's been a long time since I took that course in drafting, but I vaguely recall some aspects of how to derive the layout of other shapes like transition sections between non-cylindrical sections (e.g. the tapered section on a Nike-Hercules, or the aeroshroud on a DC-X), as well as what you can call "tilted cones" (e.g. the nosecones on the strap-on boosters you see on a Buran/Energia stack). If you look hard enough, you should be able to find software in which not only does it compute the dimensions (as with shroudcalc), but it also gives an option to print out the template (I know they exist, as I've seen them before -- I just never bothered to bookmark them).

Tenderizer · Post by **Tenderizer** » Sat Oct 29, 2005 8:40 am

Thanks to all who suggested the "shroudcalc" link (http://www.realmcommunications.com/rbla ... udcalc.htm). It was just what I needed. As I said, I'm not the greatest math whiz in the world and high-school trig/calc-- heck, COLLEGE level trig/calc was quite a few years ago, and I've more or less NEVER NEEDED ANY OF IT until this little dillemma of mine popped up.
So thanks again, everybody!

The Tenderizer 8)

Kekker · Post by **Kekker** » Mon Oct 31, 2005 5:19 pm

You can also use a vector-based drawing program to do the shapes. I used CorelDraw to do this. You can set the angles and the dimensions really easily, and then just print out a paper pattern.

Count Kekkula

dekesdragon · Post by **dekesdragon** » Mon Oct 31, 2005 6:57 pm

if one is in the manual mode, the NAR (National Association of Rocketry)
handbook has a single page of explanation of how to do 'transitions' by hand
based upon the small dia, large dia, and altitude.
Of course as with any method like this, the material thickness is
assumed to be zero and has to be accounted for
but I like the applet, something that my Autodesk Inventor software makes into an interesting affair to handle

rocketrider · Post by **rocketrider** » Mon Oct 31, 2005 8:26 pm

Ive been looking for months for something that does this.

thanks
Glen

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Dimensional formulas: How do you skin a cone?

Dimensional formulas: How do you skin a cone?

How do you skin a cone: The answer to my prayers!