New at fiberglassing

OK, I want to make a minimum diameter fiberglass airframe. How do I insure that the the motor casing will fit into this body tube and not be too loose or too tight? Do I use a motor tube as a mandrel and leave it in place? Is this minimum diameter? Also what about couplers?

Thanks in advance-

You use 0.014" Mylar waxed with mold-release wax (at least two coats, but do this after taping). You can overlap and tape the Mylar or butt-seam it.

I'll let others address couplers.

Greg

My technique to do a minimum diameter airframe or motor mount tube has been to wrap parchment paper around a mandrel/motor casing to a diameter a few layers more than needed. Here is a thread from a rocket I built way back when that may illustrate this better than I can describe it now.
https://www.rocketryforum.com/showthread.php?31616-Blackhawk-38-Scratch-build
Making your own coupler tubes is much more difficult but I've successfully done it. May require a little trial and error and calculation to get it but totally do-able.
-Ken

boby tubes using a motor case as the mandrel
[video=youtube;q3wtcNTd9wg]https://www.youtube.com/watch?v=q3wtcNTd9wg[/video]

couplers using a mandrel
[video=youtube;2aumKTUIlZ4]https://www.youtube.com/watch?v=2aumKTUIlZ4[/video]

couplers made from a piece of body tube
[video=youtube;wbyt8r9l7fo]https://www.youtube.com/watch?v=wbyt8r9l7fo[/video]

Tony

Nice videos, very good information, thanks for sharing them.

A technique I use is to first pick a coupler tube to use as a mandrel and then use that same coupler material for your couplers and your ebay. I typically use the PML phenolic coupler tubing as a mandrel. Then, I can take that same coupler material and line it on the inside with fiberglass or carbon for strength. If you use a thin piece of mylar for rolling the tube, then the coupler/ebay will be an exact fit to the tube. This approach takes out all of the guesswork.

Jim

Use hi-temp epoxy, not the car/boat polyester resin - which shrinks. While it makes a nice tight motor mount, it is a bugger to get off the case once it is set. It also is said to not take later adhesives as well as epoxy - which would be important when bonding fins on the outside.