This is the second part of our 2-part series on making homemade
model rocket engines. Costing almost $2 each, cosys can go up quickly.
These engines cost around 25 cents each.
| WARNING: If you decide to follow
this tutorial and make your own engines, I will not be held
responsible for your actions. If you get injured or injure someone
else, it is not my fault. The materials required to make the
engines are very dangerous, and should only be handled by adults.
Please wear a face covering helmet |
Packing the Propellant
Because this propellant is slower burning than others, we can't
just pack it into the casing and light it. There has to be a core.
When the core ignites, it causes more of the propellant to burn
than if we just lit the end.
Since the whole core has to be ignited almost instantly, you need
to use gunpowder. How do you get such a thin core of gunpowder in
there? Well you need to pack the propellant around something so
that there is a hollow core in the engine so we can pour the gunpowder
in. To do this, you will need to make a coring mandrel and packing
tamp.
You can make a single coring mandrel, or several of them. I made
6 of them on one board so I could pack the propellant faster. I
used an old 2x4 and I drilled holes partway into the board using
a 3/32" or 5/74" drill bit. Then I cut up pieces of metal hangers
(you can use piano wire, nails, or anything that has a diameter
of 3/32") and pounded them into the holes. Then I cut the tops off
at 1.5" above the wood. Make sure you drill the holes straight and
make sure the wires are straight.
Now get another 1/2" wooden dowel (do not use the wrapping/putty
one) and drill a hole into it about 3/4" or 1" deep with a 7/64"
drill bit. This will allow you to pack the propellant as you pour
it in.
Put the engine on the coring mandrel, with the nozzle at the bottom.
Funnel the propellant into the engine, in small amounts (about a
teaspoon at a time).
Put the tamp in and pound it with a hammer a couple of times. Check
the propellant level. If you can still see the coring mandrel wire,
add more powder. When you can no longer see the wire, you are done
packing the propellant.
Rip off a small piece of kleenex or paper towel and pound that on
top of the propellant.
Now you need to close off the end of the engine so the only way
the gases can escape is through the nozzle. You can use epoxy for
this, and put 1/8" to 1/4" in the end, but epoxy is pretty expensive.
I just use the putty I used for the nozzle. But put at least 1/2"
of it in there and make sure it is packed down against the kleenex
(don't pound on it with the tamp though). 
I usually wait for the end plug to dry before I take the engine
off the coring mandrel, but you can probably take it off right away.
Just remember to keep it upright so the putty or epoxy doesn't get
lopsided. Also go slowly when taking it off, because you don't want
the propellant to fill in the hollow core.
Ignition
Since we packed the propellant around the coring mandrel, there
will now be a hollow core in the engine. This core needs to get
ingited all at once, so a fast burning powder must be used. Gunpowder
(or blackpowder, whatever you want to call it) works great. Go to
your sporting goods store and find the finest grained powder you
can find.
Pour the gunpowder into the hollow core until it is full. Then make
a little pile of it on the nozzle. If you want, you can add a tiny
bit of water to it so it will dry in a hard cake, but I just leave
it as powder because you have to put tape over it anyways.
Get a fuse that's a few inches long (get it from a fireworks store,
or wait until I write the tutorial for making fuses) and lay it
on top of the little pile of gunpowder. Get some masking tape and
secure the fuse. If you didn't get your gunpowder wet, you should
completely seal the nozzle with tape so the powder won't fall out.
That's all there is to it! Put the engine in your rocket and see
if it works! Remember that these engines don't have anything to
pop your parachute out, so you will want to use an old rocket probably.
Also watch out when it comes down, because it will be falling very
fast (only launch in a deserted area).
As you can see, I have used this rocket many times (no fins and
electrical tape holding the launch tube on)
<< Part
1
I use homemade gunpowder for my rocket fuel. Dump some of this gunpowder on a piece of paper, then crease the paper a little so that the gunpowder piles up into a ridge several inches long. Next, get some string, dip your index finger in a tiny dip of white glue, pinch the string between the index finger and thumb and smear the glue down the string 3 or 4 inches being sure to wet all sides of the string lightly with glue. Then immediately lay the string in the ridge of gunpowder and fold the paper over so that it dumps powder all around the string. Then press on the string to help embed the powder. For more fuses, skip an inch and repeat the above. Hang up for a few hours to dry.
I\'d guess my fuses burn at about 3/4 inch per second (3 inches = 4 seconds). You need to handle this fuse carefully because if you knock off too much powder it may work sporadically.
I use a string with a diameter near the size of the nozzle so that you can just cram it in so that it plugs the hole and helps hold the powder in place.
Dennis