While air pressure and combustion can both be used for launching potatoes, no one (to the best of my knowledge), uses combustion to launch t-shirts. The problem is that the heat from the explosion will singe the shirts. This cannon uses metal screens as heat sinks that take away enough heat from the explosion without losing the pressure along with it. This is an older project of mine and I know longer have the cannon, so please excuse the lack of pictures and specifics. If you'd like, you can think of this more as a modification to an existing idea. To help make up for the lack of pictures, I'm going to put somewhat relevant xkcd comics instead. Because I like xkcd*.

More information on this project can be found on my blog here.

SAFETY DISCLAIMER: You are building a homemade combustive device. This is incredibly dangerous. Do not attempt this unless you completely know what you are doing.

*All images are taken from xkcd.com with permission as per their Creative Commons License..

Step 1: Materials & Tools

The stuff you'll need are pretty similar to a potato cannon. The differences are the use of a BBQ ignitor for the trigger instead of the common taser and, of course, the chicken wire for heat sinks.

Materials:

Normal potato cannon materials - PVC piping, screw-on back, PVC primer/glue - To help, here's a link to an Instructable for a potato cannon. This is where I got the idea of using a BBQ ignitor to begin with.

Chicken wire

Tools:

Hacksaw, or whatever you're using to cut the PVC

PVC primer - He does not include this, but it will help the bond

Step 2: Assembly

Again, you'll mainly be following the instructions from the other Instructable here.

The only additional thing you'll be doing is putting some chicken wire into the barrel. For the amount, I originally guesstimated. Now, after taking heat transfer, I agree with my original method. I recommend rolling enough chicken wire that it makes a spiral with about 3/4" between each wall. Try firing a shirt at a (very sturdy) brick wall and seeing if it's on fire when it leaves. If it's not, you can CAREFULLY check to see if it's hot or singed. This will give you a better idea of whether you have enough wire. More wire means more heat lost to the shirt, but also a slight decrease in pressure. I mention this only so you don't completely fill the barrel. Safety is more important than performance.

Regardless of how much you use, the wire should stop far enough before the mouth of the barrel so you can fit a rolled shirt with about half a foot space left till the top.

The picture shown in the first step and here again is my original design and not what I ended up working with. It might work as well but having the chicken wire there would be difficult to assemble and would block the air a lot more.

Step 3: Technique

This is mainly based on the method given in the other Instructable.

Put the rolled T-shirt into the barrel.
1. How tight you roll the shirt is important and very annoying to get right. Too tight or too loose, and it won't leave or not go far. Experiment. Good luck.
Spray whatever you're using as fuel into the back of the barrel.
1. There's a reason this comes after you load the cannon. Safety first.
Aim away from everything ever and fire.

Note that the wire heats up after each firing. This generally dissipates pretty quickly, but definitely do not touch the metal until you are 100% sure it has cooled. Also, if you fire several shirts in quick succession, the wire might stay hot enough that the shirt will singe. Something to keep in mind.

Another note is that I found hairspray to be terrible fuel. It ignites, but coats the inside of the combustion chamber with goop that prevents firing.