Liquid apogee engine

Transcription

In a previous project I went to the hobby store and picked up some F-class rocket motors, to try launching a rocket, made out of pool noodles. Now these motors are amazing, but the catch is they’re $17 each. So in this project let’s see if we can use powdered sugar and kitty litter, to make a homemade version, that will rocket up over 2,000 feet high, and cost less than $0.50 make. To start this project we’ll need powdered sugar, potassium nitrate, and a cheap bag of kitty litter. We’re also going to need 3/4” PVC tubing and a 3/4” oak dowel. This is schedule 40 PVC, and you can see I’ve cut the tube into sections 5” long, exactly. The dowel is twice as long as that, and you can see if we push it inside the tube, it’s actually a pretty good fit. This will be a ramming rod, and a template as well. And the markings you see on the stick are designed to make the simplest form of an “E45 equivalent” rocket motor. The markings are actually in reverse order to how we’re going to build it, but you’ll see why it needs to be that way in just a minute. Alright, let’s get ready to make the rocket fuel, and to start off we’re going to need a small blender that we’re not afraid to damage. I found this one at a local thrift shop for $5, and the first thing we have to do is measure out 65 grams of potassium nitrate. I typically get mine as a special brand of stump remover, and it’s a pretty fine grain to begin with, but you can see that after blending it up for about 20 seconds, it becomes a fluffy white powder, that looks a lot like powdered sugar. Now speaking of powdered sugar, we’re going to need some of that next. So let’s zero out our scale, and add exactly 35 grams of sugar to the mix. At this point the powder is a pyrotechnic composition that could ignite with too much heat, so instead of mixing this up with the blender, we’re going to have to shake it by hand for about 3 minutes. This should give it enough time to blend completely, and that’s important because we need this white mix to be as intimate as possible. Alright, our rocket fuel is finished, so let’s transfer it to another container to free up the blender, because now it’s time to bring out the kitty litter. This 7 lb bag was only $0.98, and surprisingly, the cheap kind is the best kind, because it doesn’t have any fragrances or dyes added to it. It’s just a big bag full of bentonite clay, which is probably why the stuff is as cheap as dirt. Alright let’s throw a handful of clay into the blender for 10-20 seconds so it grinds into a power. Holding the blender at a bit of an angle helps mix it better, and reduces the load, on the motor as well. Now when it’s time to remove the lid, it’s important to wear a mask, or do it outside. Because you can see the powder is so fine it escapes like a gas, and its not really good to breathe this stuff in. Ok, we’ve got everything we need, so let’s get to work putting it all together. Place one of the PVC casings on a slab of concrete, and drop in a third of a tablespoon of kitty litter. Now let’s make sure we keep the tube firmly on the concrete so the clay doesn’t spill out the bottom, then slide the oak ramming rod inside, and smack the top firmly with a rubber mallet. It’s going to need about 5-10 good whacks, to compact it as tight as we need it. And you can see it will make a nice little clay plug, at the bottom of the tube. Let’s repeat this process 2 more times until the plug is 3/4” thick, which you can see is conveniently indicated by the marking on the stick. If too much clay gets packed in, no worries. You can just twist the dowel around a few times to loosen the top layer, then pour out the extra clay until it lines up perfectly. At this point, we’re ready to add the white mix. This stuff is extremely light and fluffy, so it’s important to push the ram rod down, very slowly. Once it’s compacted by hand though, we can ram it with the mallet, just like we did the clay, until the rammed “white mix” lines up perfectly with the next marking. The last step for this simple motor is a kitty litter end cap. This will be 3/4” thick as well, the same as the one we made before. But here you can see there’s still a little room left in the tube, and you’ll see what that’s for in another project video. Ok our rocket motor is just about finished. The only thing left to do is make the nozzle. For these motors I use a 7/32” drill bit, which happens to be the exact length and width we need to turn this rammed powder tube, into a core burning rocket. Now to gauge the depth on how far in to drill, we can use the markings on the ram rod to measure exactly where the white mix ends, then mark the drill bit at the point where it lines up with the clay. Now it’s really important to drill this out very slowly and carefully because, remember, this is a rocket motor, and you don’t want to set it off by accident. I’m drilling mine out by hand, so it’s easy to control any heat generated, from the friction. When the marking on the bit lines up with the bottom of the casing, the rocket motor is finished and should look something like this. Now to test the power of these motors I went way out into the dessert, miles and miles away from any people, property or anything flammable. When this one lit off I was blown away by what it could do. The motor, just shot up 2,300 feet high. And of course if we’ve got rockets going that high, we’re going to need a way to deploy, some kind of a recovery system. So the next step, is to give our rocket motors a built in time delay, and a parachute ejection charge. The 100 gram batch in this video is enough to make two “E45 equivalent” motors, with about 20 grams of propellent left over. Which is what I mix with baking soda, to slow the burn, and create a 5 second delay. So watch for those modifications in another video. Well now you know how to repurpose some simple household items, into powerful hobby rocket motors, for less than $0.50 each. Just make sure you have the right permits, location, and common sense before you try launching them. Well that’s it for now. If you liked this project, perhaps you’ll like some of my others. Check them out at www.thekingofrandom.com If you are even considering the thought of trying to build one of these, please promise me you’ll do one thing first. Get on google and do a search for local rocket clubs. They don’t cost much, and they’ll have the best idea of how to keep you out of trouble with the FAA, and make sure nobody gets hurt. Having said all that, I hope you felt the same excitement for this project that I did. I’ve spent 4 years playing with different variations of sugar motors to get to this point, so I’m super excited to finally be able to present this to you. Now going forward, you can expect to see a few more rocket related videos, and then we’re getting into metal melting projects, so please make sure you’re subscribed to my channel because I’d really like to see you around for those project videos. I’ll talk to you then.