Notes on Color Cylinder Shell for Small Rockets

WARNING AND DISCLAIMER:  If you are underage, then consult with your parents or guardians before attempting any of this.  You are on your own - I'm not responsible for your actions or harm you may bring to others because of your actions.  Making the items described below  can result in injury or death to you or people in your vicinity. Some things mentioned here may be illegal to make in your city, county, state, or country so check the laws that apply to you before you attempt anything described here. These notes are not complete on purpose. If you are reading them and new to pyrotechnics, then you are making a mistake. Stop now - this page is not for you. Get a beginning book on fireworks (see Skylighter or American Fireworks News (very quick shipping)  for a start) and read up. You can't make any of this work without more information so read up or join a club or ask someone to help you.

Above is a representative shell on a completed motor

 

This is a note on a single break color canister shell meant to fly on a one pound (3/4") motor.  Much of this construction is like the Cap Plug Shell construction so photos will be interchanged as needed.

The following pictures and captions show one way.  You may wish to do it more traditionally.  This is a rocket header so it does not need to be pasted in. Pasting primarily provides fireproofing but we can make the header fireproof enough for a rocket launch without all that extra weight.  

 

Motor Configuration

The total weight of this shell will be about 180 grams - which can be lifted with many 3/4" BP motors.  The BP motor can be nozzled or nozzleless so see the rocket section on how to build one. The one used for this shell was 3/4", 4" spindle with a 3/8" base and a 1% taper. It used a clay nozzle and a clay bulkhead. The fuel was RP equivalent (see composition page). The delay was 3/4" of the same fuel with 20% Ti added. The dimensions of the spindle are similar to the LWS motors produced by Steve La Duke and his tooling set would work fine.  If a 'standard' BP spindle is used, then the fuel will need to be slowed down by adding charcoal - start with about 5%.  I use two sticks on each motor - one is 5/16 x 32 and the other is 1/4 x 18.  For slightly heavier shells (200 grams or so), I increase the 18" stick slightly.  For lighter shells, I decrease it or remove it. For instance, for the five times report shell which is less than 100 grams, I remove the 18" stick entirely.

While BP is probably the most complimentary to this shell, just about any 3/4" motor would lift it.  Whistle, red/green mag, strobe or any of the variants could be used.

We'll make a lightweight shell case first. 


Start by cutting out some end plugs (2 for each shell)
If you use the former shown below, you can use a
2.5" hole cutter to make some 2 3/8" plugs out of
1/8" particle board.



Optionally, you can make some cover pieces for the
ends of the shell. These are cosmetic but are nice

The plastic tube is a 2" conduit. It's outside diameter is
2 3/8". The hole saw (above this) cuts a plug that is
just about right for this combination.  The paper is
50 lb Kraft 5.5" wide and about 15" long - enough for
two wraps around the former.

Wrap the paper around the former and either tape
or glue it.  I like to glue it since it makes a nicer
looking shell.

After pasting the paper, drop one of the end plugs in
 
Snip the paper and form a rose. Open up the rose so
you can see all the petals and add a dab of paste to
each petal and to the end plug
 
Fold together
 
Press on a board or flat surface and you get something
like the above
 
Optionally, you can add a bit more paste and put on
the cover. This makes a nice looking shell case.
 
Put a spare plug on each end of the work and
squeeze it to make sure the glue and paper are in good
contact.  Leave the pressure on for just a few minutes
else you may end up permanently gluing the spare plug
onto the end. ;-}
 
While you are at it, make up a few.

 

Now let's make the inner chipboard liners


Cut some 2.5" strips of chipboard.  You can use
commercial stuff or cereal boxes or other sources.

Mist the cut pieces lightly so they will form more easily

Wrap them around your case former. Just keep
wrapping them until you have made up several.

Once they are wrapped, put a piece of tape on them
to hold them tightly.

Slide them off the former and let them dry.

For a single shell, cut enough to make a 15" length
(two layers inside the shell)

 

Fill the shell casing


Start by putting 1/4"-5/16" stars in a circle at the bottom
of the can. Fill the voids with BP coated rice hulls
and pack tightly. Rice hulls are used to keep the weight
down.  You can save 30 to 60 grams this way. The
stars are parlon stars by Gary Smith.

About half way up (the shell takes about 7 rows of
15 stars) put in a passfire filled with black match. Add
about 2 - 2.5 grams of slow flash or whistle.


After 7 rows of stars, fill to the top of the chipboard liner
with BP coated rice hulls. Press them down firmly .
Add about 2 - 2.5 grams of  slow flash or whistle to
the burst at this time. This will be a total of 4 or 5 grams
of slow flash or whistle and the break will be brisk. 

Snip around the shell paper so you can make another
rose

Glue the rose - similar to the way you did the bottom
of the shell

Fold the glued tabs over and make it look nice

You can add a clean end disk - same as we did on
the bottom - to make it look even nicer.

Cut a hole in an end cap and clamp things together for
a few minutes to get the glue to hold tight

Spike the shell


Get some spiking twine - if you can't get hemp
or flax, then use some good cotton butcher's string that
is 6 ply or better. You want cotton and not an
artificial fiber or waxed string - it needs to shrink after it is
wetted with paste. 24 lb twine is best for this shell.

Wrap about 20 feet of twine between two bolts on
your work bench. I like about four or five feet spread
between the bolts.

Rub some wheat flour glue on the twine

Start wrapping the vertical spikes on the shell. If
you break the string while spiking, just tie the
broken ends together and keep on truckin.

For this shell, I use 16 vertical spikes with 28 lb
string. This is done with something called 'off center'
spiking - you can see how it works in the picture.
You use the fuse as the pivot to change directions
with the string wrap

Once the vertical spikes are done, roll the shell on its
side and do the horizontal wraps.  For this shell, I like
about 3/8" between the horizontal wraps. Don't be
afraid to pull the strings tight!  The shell should be rock
hard when you are done spiking. If it is soft, you need
to re-spike it.

Once wrapped, slather a bit of paste over the strings
and let it dry.

Click on the above image and see our rocket fly.  Not
perfect but heck... it was fun!  This shell had 3.2 grams
of slow flash.  It could have used a bit more..