HOME BUILT ROCKET ENGINES
This is that information on home constructed rocket engines I
mentioned I would put together. I hope I've covered everything you
could possibly need to put something together, but if anyone has any
additions they might want to suggest, please mail them to me (or post
them). If you have any flames, mail then too. But make sure anything
you say is worth reading...
I'll warn you now that this is not the safest method (there are no
safe methods to make anything using potentially explosive stuff), but
this version is, I hope, safer than others. This is the product of
about three years of experimentation with home-built engines. Out of
the various methods we've tried, this causes the fewest explosions, is
the simplest to make, and flies the straightest. Just remember one
thing. Before you really start playing with these things, TEST them.
TEST THEM MANYMANYMANYMANY TIMES. Know how they work, how to get the
best performance. Make one so that it explodes on the ground, just to
see how close you don't want to be. Learn how to run quickly. Learn
how to take cover quickly. Then you can start using them.
Before you actually decide to build something, I'd like you to
consider this. When rockets were first built, they were not used by
the military because they were dangerous and unreliable. And when the
military calls something dangerous, it's agood idea to take the hint.
Thanks to Greg Deer for his large part in this information. Not to
mention for dragging me to emergency when one of MY brilliant ideas
blew up on me.
My apologies for any spelling/grammar that might
offend any English students out there. My apologies for any diagrams
which might offend any Artsies/Engineers out there. And my apologies
for any factual errors which may offend any Chemists out there.
Requests for any other apologies may be mailed my way. I'll
apologise if they're valid.
-------------------------------------------+-------------------------------+
Chris Beauregard |Any ideas and/or opinions |
cpbeaure@descartes.waterloo.edu |expressed here are solely mine.|
"If you can't beat 'em, take 'em with ya!" +-------------------------------+
--- Chop Here
Okay, first a little history of our experimentation with rocket
engines.
The first method we ever tried was the good old fashioned paper tube
with clay nozzles and packed gunpowder. We found, for several
reasons, that this simply did not work. Explosions were _very_ common,
and when they did fly, they flew all over the place. We created
various forms of them, but the one form that we did stick with was a
type with a hollow core. This has been used throughout all our various
types.
After a while, and a lot of research, we discovered out number one
problem. Gunpowder. We managed to come up with a formula for some
very nice rocket fuel, and this cut down on misfires tremendously.
Unfortunately, we had a tough time finding tubes for the engines, and
making them was too much trouble.
About then we were experimenting with pipe bombs. We were using
copper pipe with the ends brazed closed. We decided to try this as
an engine tube, and it worked. Somewhat. We could put an engine
together rather quickly, but they still exploded a lot. With the force
of a typical pipe bomb. A little more experimentation later, we
discovered that brazing the pipe weakened it considerably. A
non-brazed method was them used rather well for a while.
Then we discovered PVC pipe. And our most successful form was born.
Now, on to the good stuff.
One of the most important points about making these rockets is the
powder used. The thing about gunpowder is that when it's burned
under pressure, it burns at a tremendous speed. Rocket fuel, on the
other hand, burns very quickly, but at a more or less constant rate,
regardless of how much pressure it's under.
Here are the formulas for gunpowder and rocket fuel, using either
sodium or potassium nitrate.
nitrate carbon sulphur
KNO3 gunpowder 75% 15% 10%
NaNO3gunpowder 71% 18% 11%
KNO3 rocket fuel 72% 24% 4%
NaNO3 rocket fuel 69% 27% 4%
These percentages are by weight.
The first thing you'll note is that the rocket fuel mixtures use much
more carbon than their gunpowder counterparts. The second thing
you'll note is that they use much less sulphur. I'm not completely
sure why it works, but after a lot of experimentation and analysis of
the components of Estes rocket fuel, those are the numbers we've come
up with.
If you try to make the powder yourself, refer to some kind of manual
on how it's done. For optimum performance, the powder should be
milled. If you don't have a mill, just mix it to the best of your
ability. (by the way, you should mix this stuff with about 10% of its
mass in water. It's much safer).
You could also modify store bought powder by adding more carbon.
Rocket fuel will work with up to about 12% sulphur. You should use
carbon from softwood. Hardwood works, but it burns much slower.
Willow, pine or spruce will work (from my experience). Spruce is the
easiest and cheapest to get. Just burn a couple two-by-fours. I'll
leave it as an execise for the reader to figure out how much to add.
The Engine
Materials needed
Powder (rocket fuel recommended)
1/2" PVC pipe
1/2" dowel
Tools Needed
Drill and 1/8" bit and one to match nails (below)
Some nails. The smaller, the better
Hammer
Saw
A bar that fits into the PVC pipe.
Plastic is best, but you can get away with metal or wood.
Sandpaper, or a something else that you can use to shape wood
A hot plate, or stove
A metal plate. Sheet metal, aluminum,
something like that.
Procedure
1. Put the metal plate on the burner of the hot plate, and turn it
up to max. This should be done in a well ventilated area, because
you're going to be melting plastic on it.
2. Cut a length of PVC. the specific length depends on how long you
want the engine to burn, but 5" is a good start.
3. Cut two 1/2" lengths of the dowel. The dowel should not be able
to slide easily into the PVC. It should be larger that the inside
diameter of the PVC. Take each dowel, and sand one end end the edges
somewhat, until it looks sort of like this:
+-------+
| |
| |
\-------/
4. Take one piece of the dowel, and pound it into the piece of PVC.
You should sink it in about 1/8", so you get this:
-------------------------------------
| |
| <------- Dowel
| |
-------------------------------------
^
|
PVC
5. By now the hot plate should be warm enough. Take the pipe, and
place it so that the end with the dowel in it is on the piece of
metal. Press slightly. The PVC at the bottom should melt. If it
doesn't, the plate isn't hot enough. What you want to do is melt down
the end of the pipe so that the dowel CANNOT slide out. The excess
melted plastic on the ouside of the tube can be removed, by sanding,
cutting, or whatever.
make sure that when you melt the end, that you don't press really
hard. One of the properies of the plastic being melted under these
circumstances is it slide on the metal plate really easily. If you're
preesing down really hard and the pipe slides away, you hand usually
moves downwards very quickly.
A sort of diagram of what heppens is:
|| ||
||-----||
PVC ==>|| ||
|| <======dowel
|| ||
||-----||
@||@ @||@
Where the '@' stands for melted plastic. WARNING: Platics are, as a
general rule, not healthy or pleasant to breath.
6. Take the powder, and add about 10% of its mass of water. Mix
well.
7. Take this powder, and fill the PVC with it. Now take the rod and
hammer, and pound the powder down. Do this very hard. What we're
trying to do is turn the powder into a single grain. What you have is
this.
| |
| |<===== Rod
| |
| |
|| ||
|| ||
|----|
| |
| <===== powder
PVC ==>| |
|----|
| <==== dowel
|----|
Keep adding and pressing the powder until there's about 3/4" of free
space in the top of the PVC.
WARNING: IF YOU'RE USING FRICTION SENSITIVE ROCKET FUEL, DON'T TRY
THIS.
8. Take the remaining pience of dowel, and pound it into the top.
9. Take the drill and the very small bit, and drill two holes
through the PVC and top dowel. The holes should be perpendicular to
each other, and should not meet in the wood. A top view looks like
this:
---
/ | \
/ | \
|---+---|
\ | /
\ | /
---
10. Take one of the nails, and put it through one of the holes. The
nail should go through the hole and have extra left over.
Preferably, the nail should ablso be a bit bigger than the hole, so you
have to use the hammer. Bend the ends of the nail over, or cut them
off.
11. Repeat with the other hole.
12. Now, take the enngine, and clamp it to something.
13. Take the drill with the 1/8" bit, and drill through the melted
end into the middle of the engine. It should look like this:
|----|
| <==== top wood plug
|----|
| |
PVC ==>| |
| <=== powder
| | |
| |<=== hole
|--|-|
bottom plug =====> | |
|--|-|
The hole should be as close to the center as possible. Only drill
about 2" into the rocket. You'll have to build a few rockets and
experiment with different depths because of the variation in powder,
but 2" ia`s a good start. If the hole is too deep, the engine will
probably explode. If it's too shallow, well, it'll sit there and make
a nice shower of sparks.
Don't try to drill the entire hole at once. Drill about a 1/4" to
1/2", then romove the drill and clean the powder off it. Powder
tends to build up on the bit, and this cuts down on the efficiency of
the drilling. It also builds up some heat. If the powder is wet, this
shouldn't be a worry. Make sure you have plenty of room around you
though, in case the powder is set off. DON'T TRY THIS IF YOU USE
FRICTION SENSITIVE ROCKET FUEL!!!!! YOU WILL IN ALL PROBABILITY SET IT
OFF.
14. Okay, now you have an engine, but the powder is wet. The safest
way to dry the engine is to leave it in the sun for a number of
hours. Applying a constant, gentle heat from a variety of sources will
also do. For example, you might set up a hair dryer, set on low or
medium, to heat the engines for a few hours. Make sure the heat source
isn't too hot, or the plastic will melt and possibly, the powder will
ignite.
Alternative Building Methods
I'll outline a few other methods that CAN be used. They really
shouldn't be, though, because they are not, by any means, safe. Try
the basic engine before you attempt any of these.
The first is that the rocket fuel does not have to be moistened. It
can be pounded in and drilled while it's completely dry. As you can
imagine, this is considerably faster, but a little bit
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