Need help with tshirt cannon

[jcgill]

I plan on building a t-shirt cannon with a 3" barrel and would like to achieve distances of around 150 yards if thats possible. I plan on making it out of aluminum but wasn't sure if steel would be necessary, I was using aluminum to keep the weight down. Are there better options than aluminum or steel as far as materials go? what type of valve should I use? about how much psi would be required to shoot a tshirt that far?

[Technician1002]

That distance is difficult to reach with a rolled up t shirt. You will be doing good to reach 100 yards. Why so far?

Pressure is only part of the solution. Flight dynamics of the shirt will need to be considered. They tend to tumble and turn sideways and quickly lose velocity. A fast high flow valve will be required for a 3 inch barrel. PVC or ABS works well for t shirt launcher barrels. A piston valve at least 2 inches porting is recommended.
The best distance was with a 3 inch port piston valve feeding a 4 inch barrel. The shirt was rolled into a ball and secured with duct tape. Launching round duct tape balls gives the best distance.

5 inch piston with a 3 inch port. Broken pistons was a problem for this team.


Several schools had a competition. The launchers and results are on the official contest wiki. No combustion cannons were allowed. A maximum of 100 PSI was permitted.
http://inteltrailblazerschallenge.wikispaces.com/

[kjjohn]

Welcome to Spudfiles!

First off, a 3" barrel is probably too big for optimal performance shooting T-Shirts. A 1.5-2" barrel should be very sufficient.

150 yards? I wouldn't expect to get distance like that for a T-Shirt cannon, but anything's possible. If I may ask, why do you need to launch T-Shirts 150 yards?

In terms of pressure, I see you've posted this in the pneumatic section, so the "pressures you're dealing with" will obviously depend on how much you pump up the gun. A standard air compressor or bike pump will reach 120psi, which is safe to use in PVC pipe, although I like to stay below 110 for PVC. If you are planning on going higher, especially once you get above 200PSI, aluminum would be a good material.

What kind of valve are you planning on using?

[jcgill]

Well I made a PVC cannon recently and it gets around 50 yards with 115 psi and a 3" barrel. So I wanted to go bigger 150 yards isn't necessary 100 is what I'd prefer. I know that commercial cannons can exceed 400 feet so I thought I might be able to match that or at least come close. I was planning on using around 300psi, would a large helium tank be able to supply that? Not sure what type of valve I will use any recommendations?

[Lockednloaded]

you will not be able to fit a t-shirt in 2" ^ more like 2.5 for a tight fit

aluminum would be best because it is much lighter than your other options, and I assume a T-shirt launcher needs to be pretty mobile

[jcgill]

Yes preferably shoulder mounted but it might be too heavy for that(air supply can be separate)

[Technician1002]

In our testing for the competition, the 3 inch barrel is better than the 2.5 inch. The shirt is folded in 1/4ers and then rolled to fit. This makes the shirt shorter than if it was folded in thirds and rolled. The shorter more compact roll flies further than a long skinny sausage roll.

We managed to toss a rolled up t shirt through a piece of carpet.

[kjjohn]

Really? 3" a better fit? I always thought it would be more in the range of 2". Thanks for correcting me anyway.

300psi of regulated helium would work, and aluminum would definitely work for that.

[Technician1002]

Unless you have money to burn, I would not use Helium. At the speed of typical shirt launches, there is no advantage. More Helium will leak through the shirt on the launch. Reserve Helium for stuff in the transonic and supersonic ranges that are limited by speed of sound of the gas.

The light gas gives little if any advantages in a t shirt launcher. All small leaks become huge when using light gas.

[jcgill]

I planned on using a 12"x3" tube for my pressure chamber? Is this too big? or too small? What could i use to pressurize it to 300psi if not helium?

[Technician1002]

That is OK to toss shirts, but not for 150 yards.

[jcgill]

How big should the chamber be?

[Technician1002]

I have not reached 150 yards with a t shirt using a 3 gallon tank and a 2 inch valve.

There is a great tool called Gas Gun Design Tool. You can model various configurations and find your expected muzzle velocity.

Using the ballistics tool in the program you can see if you are reaching your goal distance.
http://thehalls-in-bfe.com/GGDT/

I've only managed 100 yards with a t shirt.