465 lines
20 KiB
Plaintext
465 lines
20 KiB
Plaintext
Path: uuwest!spies!apple!news.bbn.com!uwm.edu!cs.utexas.edu!utgpu!watserv1!watmath!descartes!cpbeaure
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From: cpbeaure@descartes.waterloo.edu (Chris Beauregard)
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Newsgroups: rec.pyrotechnics
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Subject: Home built rocket engines - long
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Keywords: Rocket
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Message-ID: <1991Oct21.212228.26484@descartes.waterloo.edu>
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Date: 21 Oct 91 21:22:28 GMT
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Organization: University of Waterloo
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Lines: 454
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This is that information on home constructed rocket engines I
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mentioned I would put together. I hope I've covered everything you
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could possibly need to put something together, but if anyone has any
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additions they might want to suggest, please mail them to me (or post
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them). If you have any flames, mail then too. But make sure anything
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you say is worth reading...
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I'll warn you now that this is not the safest method (there are no
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safe methods to make anything using potentially explosive stuff), but
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this version is, I hope, safer than others. This is the product of
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about three years of experimentation with home-built engines. Out of
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the various methods we've tried, this causes the fewest explosions, is
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the simplest to make, and flies the straightest. Just remember one
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thing. Before you really start playing with these things, TEST them.
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TEST THEM MANYMANYMANYMANY TIMES. Know how they work, how to get the
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best performance. Make one so that it explodes on the ground, just to
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see how close you don't want to be. Learn how to run quickly. Learn
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how to take cover quickly. Then you can start using them.
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Before you actually decide to build something, I'd like you to
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consider this. When rockets were first built, they were not used by
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the military because they were dangerous and unreliable. And when the
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military calls something dangerous, it's agood idea to take the hint.
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Thanks to Greg Deer for his large part in this information. Not to
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mention for dragging me to emergency when one of MY brilliant ideas
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blew up on me.
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My apologies for any spelling/grammar that might
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offend any English students out there. My apologies for any diagrams
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which might offend any Artsies/Engineers out there. And my apologies
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for any factual errors which may offend any Chemists out there.
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Requests for any other apologies may be mailed my way. I'll
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apologise if they're valid.
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-------------------------------------------+-------------------------------+
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Chris Beauregard |Any ideas and/or opinions |
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cpbeaure@descartes.waterloo.edu |expressed here are solely mine.|
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"If you can't beat 'em, take 'em with ya!" +-------------------------------+
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--- Chop Here
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Okay, first a little history of our experimentation with rocket
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engines.
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The first method we ever tried was the good old fashioned paper tube
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with clay nozzles and packed gunpowder. We found, for several
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reasons, that this simply did not work. Explosions were _very_ common,
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and when they did fly, they flew all over the place. We created
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various forms of them, but the one form that we did stick with was a
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type with a hollow core. This has been used throughout all our various
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types.
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After a while, and a lot of research, we discovered out number one
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problem. Gunpowder. We managed to come up with a formula for some
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very nice rocket fuel, and this cut down on misfires tremendously.
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Unfortunately, we had a tough time finding tubes for the engines, and
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making them was too much trouble.
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About then we were experimenting with pipe bombs. We were using
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copper pipe with the ends brazed closed. We decided to try this as
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an engine tube, and it worked. Somewhat. We could put an engine
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together rather quickly, but they still exploded a lot. With the force
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of a typical pipe bomb. A little more experimentation later, we
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discovered that brazing the pipe weakened it considerably. A
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non-brazed method was them used rather well for a while.
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Then we discovered PVC pipe. And our most successful form was born.
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Now, on to the good stuff.
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One of the most important points about making these rockets is the
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powder used. The thing about gunpowder is that when it's burned
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under pressure, it burns at a tremendous speed. Rocket fuel, on the
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other hand, burns very quickly, but at a more or less constant rate,
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regardless of how much pressure it's under.
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Here are the formulas for gunpowder and rocket fuel, using either
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sodium or potassium nitrate.
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nitrate carbon sulphur
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KNO3 gunpowder 75% 15% 10%
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NaNO3gunpowder 71% 18% 11%
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KNO3 rocket fuel 72% 24% 4%
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NaNO3 rocket fuel 69% 27% 4%
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These percentages are by weight.
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The first thing you'll note is that the rocket fuel mixtures use much
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more carbon than their gunpowder counterparts. The second thing
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you'll note is that they use much less sulphur. I'm not completely
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sure why it works, but after a lot of experimentation and analysis of
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the components of Estes rocket fuel, those are the numbers we've come
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up with.
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If you try to make the powder yourself, refer to some kind of manual
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on how it's done. For optimum performance, the powder should be
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milled. If you don't have a mill, just mix it to the best of your
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ability. (by the way, you should mix this stuff with about 10% of its
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mass in water. It's much safer).
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You could also modify store bought powder by adding more carbon.
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Rocket fuel will work with up to about 12% sulphur. You should use
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carbon from softwood. Hardwood works, but it burns much slower.
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Willow, pine or spruce will work (from my experience). Spruce is the
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easiest and cheapest to get. Just burn a couple two-by-fours. I'll
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leave it as an execise for the reader to figure out how much to add.
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The Engine
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Materials needed
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Powder (rocket fuel recommended)
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1/2" PVC pipe
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1/2" dowel
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Tools Needed
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Drill and 1/8" bit and one to match nails (below)
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Some nails. The smaller, the better
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Hammer
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Saw
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A bar that fits into the PVC pipe.
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Plastic is best, but you can get away with metal or wood.
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Sandpaper, or a something else that you can use to shape wood
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A hot plate, or stove
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A metal plate. Sheet metal, aluminum,
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something like that.
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Procedure
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1. Put the metal plate on the burner of the hot plate, and turn it
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up to max. This should be done in a well ventilated area, because
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you're going to be melting plastic on it.
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2. Cut a length of PVC. the specific length depends on how long you
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want the engine to burn, but 5" is a good start.
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3. Cut two 1/2" lengths of the dowel. The dowel should not be able
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to slide easily into the PVC. It should be larger that the inside
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diameter of the PVC. Take each dowel, and sand one end end the edges
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somewhat, until it looks sort of like this:
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+-------+
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\-------/
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4. Take one piece of the dowel, and pound it into the piece of PVC.
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You should sink it in about 1/8", so you get this:
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-------------------------------------
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| <------- Dowel
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-------------------------------------
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^
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PVC
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5. By now the hot plate should be warm enough. Take the pipe, and
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place it so that the end with the dowel in it is on the piece of
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metal. Press slightly. The PVC at the bottom should melt. If it
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doesn't, the plate isn't hot enough. What you want to do is melt down
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the end of the pipe so that the dowel CANNOT slide out. The excess
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melted plastic on the ouside of the tube can be removed, by sanding,
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cutting, or whatever.
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make sure that when you melt the end, that you don't press really
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hard. One of the properies of the plastic being melted under these
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circumstances is it slide on the metal plate really easily. If you're
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preesing down really hard and the pipe slides away, you hand usually
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moves downwards very quickly.
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A sort of diagram of what heppens is:
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||-----||
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PVC ==>|| ||
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|| <======dowel
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|| ||
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||-----||
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@||@ @||@
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Where the '@' stands for melted plastic. WARNING: Platics are, as a
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general rule, not healthy or pleasant to breath.
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6. Take the powder, and add about 10% of its mass of water. Mix
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well.
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7. Take this powder, and fill the PVC with it. Now take the rod and
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hammer, and pound the powder down. Do this very hard. What we're
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trying to do is turn the powder into a single grain. What you have is
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this.
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| |<===== Rod
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|----|
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| <===== powder
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PVC ==>| |
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|----|
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| <==== dowel
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|----|
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Keep adding and pressing the powder until there's about 3/4" of free
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space in the top of the PVC.
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WARNING: IF YOU'RE USING FRICTION SENSITIVE ROCKET FUEL, DON'T TRY
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THIS.
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8. Take the remaining pience of dowel, and pound it into the top.
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9. Take the drill and the very small bit, and drill two holes
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through the PVC and top dowel. The holes should be perpendicular to
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each other, and should not meet in the wood. A top view looks like
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this:
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---
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/ | \
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/ | \
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|---+---|
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\ | /
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\ | /
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---
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10. Take one of the nails, and put it through one of the holes. The
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nail should go through the hole and have extra left over.
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Preferably, the nail should ablso be a bit bigger than the hole, so you
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have to use the hammer. Bend the ends of the nail over, or cut them
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off.
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11. Repeat with the other hole.
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12. Now, take the enngine, and clamp it to something.
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13. Take the drill with the 1/8" bit, and drill through the melted
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end into the middle of the engine. It should look like this:
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|----|
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| <==== top wood plug
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|----|
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PVC ==>| |
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| <=== powder
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| |<=== hole
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|--|-|
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bottom plug =====> | |
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|--|-|
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The hole should be as close to the center as possible. Only drill
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about 2" into the rocket. You'll have to build a few rockets and
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experiment with different depths because of the variation in powder,
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but 2" ia`s a good start. If the hole is too deep, the engine will
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probably explode. If it's too shallow, well, it'll sit there and make
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a nice shower of sparks.
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Don't try to drill the entire hole at once. Drill about a 1/4" to
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1/2", then romove the drill and clean the powder off it. Powder
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tends to build up on the bit, and this cuts down on the efficiency of
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the drilling. It also builds up some heat. If the powder is wet, this
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shouldn't be a worry. Make sure you have plenty of room around you
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though, in case the powder is set off. DON'T TRY THIS IF YOU USE
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FRICTION SENSITIVE ROCKET FUEL!!!!! YOU WILL IN ALL PROBABILITY SET IT
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OFF.
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14. Okay, now you have an engine, but the powder is wet. The safest
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way to dry the engine is to leave it in the sun for a number of
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hours. Applying a constant, gentle heat from a variety of sources will
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also do. For example, you might set up a hair dryer, set on low or
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medium, to heat the engines for a few hours. Make sure the heat source
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isn't too hot, or the plastic will melt and possibly, the powder will
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ignite.
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Alternative Building Methods
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I'll outline a few other methods that CAN be used. They really
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shouldn't be, though, because they are not, by any means, safe. Try
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the basic engine before you attempt any of these.
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The first is that the rocket fuel does not have to be moistened. It
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can be pounded in and drilled while it's completely dry. As you can
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imagine, this is considerably faster, but a little bit <insert
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sarcasm here> more dangerous. Black powder is not considered
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friction or shock sensitive, but impure chemicals can alter this
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tremendously. As well, while friction isn't normally a problem, the
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heat generated by drilling into this stuff can be. If you're going
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to try this, make sure you have plenty of room, and a friend
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nearby...but not too close. He's there to take you to the
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hospital/bury you in case of accident.
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The engine can be set up to ignite something on the end of them.
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This can be easily accomplished by drilling a hole through the top
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plug. Make sure you don't drill through the nails, though, because
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they're there to keep the thing together. If they're weakened, the
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top of the rocket has a nasty tendency to leave without the rest. It
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generally looks like...
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==============
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------------------------ |
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| | | | whatever |
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==== engine ==== you want |
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| | | | to blow |
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------------------------ |
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==============
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A delay can be added by sticking a slow burning powder into the hole
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(like a lot of sulphur with a little BP). It should be packed in
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fairly tightly. If you want it to go right away, it's not really
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necessary to put anything in. We like to add a little loose powder
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though, just in case.
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It's very easy to modify one of these things for explosions. The
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easiest method is to simply add a little extra tube somewhat larger
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than the engine, and fill it with whatever you want. However,
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there's a much cleaner way. It makes a very powerful explosion,
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however, so make sure it's going to go where you want it to go.
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Meaning, if you can't get a rocket to fly straight, don't try this.
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What you do is add about two inches to the engine. When you put the
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top plug on, put it about 2" into the tube. Drill a hole in it as
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outlined above, and fill the resulting cavity with whatever you want
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to use. Then add a second plug in a manner similar to the first.
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The result looks like
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==============================================
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| | regular portion | | explosive| <=== extra plug
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| ^ | | ^ | | |
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===|=========================|================
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first plug second plug
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It you want more of a shower than shattering explosion, leave the
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nails out of the top plug. This will cause it simply to pop out.
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Note that your powder in the top has to be able to blow that top part.
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This method would also be nifty for a parachute flare, assuming that
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the parachute was insulated.
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IF YOU'RE USING FRICTION SENSITIVE POWDER FOR THE EFFECTS, BE EXTRA
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CAREFUL PUTTING THAT TOP PLUG IN. Preferably, the powder should be
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put into some kind of paper cartridge, so that none of it gets on the
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wall where the plug is inserted.
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Launch Techniques
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The first thing you should do, after making your first engine, is
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test it. Now, you probably don't want to go through the trouble of
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putting together a nice rocket, complete with fins and nose cone, so
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this is one simple way of getting it up there. It's quite possibly
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the oldest method ever used. Take a stick, about 1/4" diameter and
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2' long. TGhe specific dimensions don't matter that much, nor does
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the exact shape. Round or square does it well. It MUST be a
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straight as possible. Some gardening stores sell some very nice
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bamboo sticks used for holding up plants. These work very well.
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Anyway, take the rocket engine, and tape it on near the top, with the
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nozzle facing down the length on the stick. Tape it very securely.
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Good. Now, to launch it, put the stick into the ground, and make
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sure it stays pointing up. Make sure it also slides out of the
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ground easily. Now fire the rocket. The stick will keep the rocket
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more or less straight as it flies (assuming it's a decent engine).
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It's arcs somewhat though, depending on which side of the stick the
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engine is one before launch. It will arc away from that side.
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Remember this. It's easy to get into the habit of "Oh, we're safe
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behind the rocket, it'll go that way." when some day you forget and
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put it backwards. And these things can move very fast.
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Conventional methods for launching are outlined in various model rocketry
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books. Check your local library.
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One neat way of launching rockets that we've been experimenting with
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is a cylindrical stabilizer. Take a light cylinder with open ends
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and attach it to the end of the engine in such a way that air passes
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it. This method is very nice for tube launched rockets. It looks
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roughly like
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--------------
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^ \
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===================
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cylinder | Engine |
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| ===================
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| /
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v /
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--------------
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We've successfully used popsicle sticks and hot glue to hold a piece
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of pop can onto the engine. It can be fired from a tube. We've also
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managed to fire it by simply sitting it on the ground. It's also
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used in commercial parachute flares to get the flare up there. One
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model we examined used a large aluminum cartridge for both the
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engine, flare, and guide. About 3" of space was left at the bottom
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end, and large holes punched out.
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Ignition Techniques
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The simplest way of igniting a rocket is to insert a piece of fuse
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into the hole, light it, and run. You should have a minimum of 15sec
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running time. More is preferred if you acutally want to turn around,
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catch your breath, and watch the rocket launch. And you can see it
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coming should it decide to go your way. However, 15 seconds will
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normally get you far enough. 50' is about the minimum distance. I
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get farther myself though. Another method is to use the good old
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fashioned Estes Solar Igniters and a battery. There are a variety of
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other lectrical fire methods, but this is our favorite. First of
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all, find a unused and un-needed camera flash. Open it up, and look
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at the capacitor (there should be a big cylider somewhere in there.
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It's probably the capacitor). You want one with a rating of over
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300v. Less can be used, but it doesn't give the same oomph as a
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bigger one. Now disconnect the flash bulb, and wire it up somehow to
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your ingition wires. You should also have a safety switch of some
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kind in there. Now take the fart that plug into the camera, and
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rewire it into a push button. This method will allow you to put that
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300+ volts through your ignition wire. As an alternative, other type
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of light flashers can be used (sirens, strobe lights, etc). Make
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sure you know what you're doing though, because 300+ volts can really
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hurt.
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The actual fuse varies. A small wire attached between two
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larger wires and put into the end of the engine does a nice job.
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Even better, however, is a small resistor. Take a 1/8 watt resistor
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(I think the higher the resistance, the better, but with 300+VDC, it
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doesn;t really matter). Attach this between two wires and solder it
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on. Now, you're probably asking yourself "Why?". This allows you to
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get MULTIPLE FIRES from that little resistor. I'm not sure how
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many. We tried it with one, and we got about 200 nice big sparks
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from it before our push button welded itself.
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General Safety Stuff
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One of these things exploding tends to be a rather awesome effect.
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It can also be a tad dangerous. When they explode, they have the
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distinct advantage of breaking into fairly large pieces (unlike
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glass, which is really nasty about little pieces). Two of the pieces
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are generally the top half and the bottom half. As you can guess,
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the top half goes more or less up and the bottom down. However, the
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pieces in between are smaller, fly outward more or less horizontally,
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and because they are smaller, they are faster. They normally fly
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about a max of forty or fifty feet. A rocket with a random flight
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path is dangerous as well. The sheer speed that these things fly can
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easily kill you. If it doesn't, it will hurt you. There is of
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course the little flame at the end to consider as well.
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That little flame is also very capable of setting fire to many things.
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Namely houses and trees. Fire it in a desert or over a lake if you
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can help it.
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Whatever you do, make sure there are no people nearby
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(within a mile of its supposed flight path is a good mumber to go by)
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aside from yourself.
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That about covers it. Enjoy.
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