As usual, click any photo to bring up a larger version.
...but it sure is fun!
I subscribe to Make Magazine; They always have all kinds of fun stuff in their issues. One of their classic articles is an air rocket system, from issue #15. This involves rockets made from paper and a launch system from PVC pipe bits and a sprinkler valve. My project here is 95% based on that article.
Here is a link to the makershed website, where you can buy a rocket kit like this. It's not that I want you to buy the kit, I didn't buy it myself, mostly since it was out of stock. But they have a nice video there that walks you through building one, and launching it.
This is a great parent/child project. Depending on the age and ability of your child, they can do a lot or a little of the construction alongside you. My son was actually the driving force behind us building this. I didn't realize how much fun it would be until we got it built!
Here is what the core of the completed launch system looks like. There is a pressurized air chamber at the bottom, made out of a section of 2"PVC. Above it coming from a T-connection is an electric sprinkler valve, for releasing the air, and then a launch tube where the rocket is mounted.
Here are two rockets. They're just paper and tape. You can find a download PDF template on the Make Air Rocket article page on the Make website that prints on legal sized paper. It took me about 45 minutes of cutting and rolling and taping to make each one. I made one using duct tape, and one with just green masking tape. Both were about equally easy. I'm sure as I get more practised I'll knock that time down. There is no parachute, it just falls back to earth after a launch. They're light enough, though the nose cone might get banged up a bit hitting the ground. (You can see that in this photo - those rockets have each been launched a handful of times, landing in some soft spring ground.)
BE SAFE! These are light, and just paper, but I still would strongly recommend that you DO NOT stand directly under one as it falls.
At the one end of the air chamber are some brass reducers which hook up the chamber to a length of hose. (I need to get some small hose clamps, as the zip ties are NOT strong enough. The hose currently pops off when we hit 50lbs pressure.)
At the other end of the hose you need a bicycle pump. Pick one with a gauge on it, as you need to know how much you have pressurized the system. A tire valve from a scrap tube is fitted into the end of the hose, secured in place with a hose clamp.
The sprinkler valve is the key to making this work. You need a way to quickly dump out the pressurized air, in order to launch the rocket. This is probably the most expensive piece of the launch system to buy. I found that they were priced at around $25-$27 here in Canada at the big box home stores. In contrast, I found them for $12-14 in Lowes over the border in Michigan. Look around and hopefully you can find one cheap for your kit.
You also need a battery and switch in order to open the electric valve. You can make that yourself with a pair of 9v batteries wired in series with a momentary switch of some kind. I macgyvered this setup instead.
I had a flashlight that came with my 12v Hitachi drill/driver kit. The flashlight died ages ago, so I ripped off the top and wired it up with some lamp cord to the valve. That gave me a quick, safe, and easy way to hook up a 12v battery (since I can just pop it in and out of the bottom) and a switch all in one. One issue is that this is an on/off switch, and not a momentary switch. So we have to remember to hit the switch twice each time, so that it also turns off and releases the valve. (As a matter of extra safety we are always pulling the battery out of the handle any time we stop using the launch system. I don't want any power in the system when it is not being used.)
Here it is, ready to launch. I tried, but found it impossible to catch it mid-way through a launch with my camera. I might try again another time.
Here it is, way up top in the photo, falling fast. It is about 1/3 of the way down at this point.
REMEMBER: there is no parachute, don't stand directly under it!
This shot was taken after a modest 30lb pressure shot, and it still cleared 100ft with ease. With 50lb of pressure I would estimate it reaches over 200ft in height. Once I get some hose clamps on the system I'll try it at 70 or 80 lbs pressure!
Thanks for reading!