Click
Here to see a QuickTime movie (File size 270kb) of a whistle rocket
launch with a large report at the end. (This video was shot at the 2000 WPA Western Winter
Blast. Free Quicktime player available here.)

This page deals with general info, mixing
the comp - emphasizing the 'wet' method, the construction
of a whistle rocket using your rocket tool set, as well as 'sticking'
and fusing the rocket.

This web site  is prepared for purposes of education only.
If you want to read these pages for an understanding how rocket propellant
systems are physically made and how they fly, then this should suffice. We
assume no responsibility for the use of this material by any person. If
you attempt to use any of these materials in order to make devices, you
should be in compliance with all laws and regulations and observe the
maximum possible safety precautions.

Why a Whistle
Rocket?

A well made whistle rocket is very exciting to watch

Has tremendous lift generating capabilities

Tends to be everybody's favorite

It can be quite spectacular!

Considerations for Whistle:

Whistle rocket comp is *very* energetic. The rocket leaves the 'pad'
at a very high rate of speed

Max altitudes tend to be high. (Not all the time!)

Whistle comp burns very quickly, and hence should bring with it a
much higher awareness for what it is and what it can do.

How a Whistle Rocket works:

The tool set is comprised of a spindle mounted on a base, and two
drifts (rammers). The spindle is quite short when compared to black
powder rockets, and the tube is usually about half the length of a
similar diameter black powder rocket. The rocket is lit as if it is an
end burning rocket. The comp around the core is burned off in a very
short period of time - about a half a second. (This means over half your
comp is gone very quickly!) The rocket then changes characteristics, and
the material starts to oscillates it's burning very quickly - generating
the characteristic whistling sound. This phase still provides lift, so
it will typically travel further than a similarly weighted black powder
rocket. No nozzle material is used.

Tubes and Sticks:

Whistle tubes traditionally are 1/2 the size of BP rocket tubes.
Stick lengths are still comparable in size. Tube size ration:

Tube ID = 1

Tube OD = 1.25 to 1.50 ID

Tube Length = 5 ID

Note all ratios deal with the ID

The following table should help you decide what kind of sized
tooling you will need.

Rocket Size

ID

OD

Length

Min Stick Length*

8 oz.

5/8" (.60")

1"

3 1/8" (3.125")

30"

1 lb.

3/4" (.75")

1 1/4" (1.25")

3 3/4" (3.75")

36"

3 lb.

1"

1 1/2" (1.50")

5"

48"

*Stick lengths and payloads are general recommendations. Longer
sticks will cause the rocket to be more stable, but detract from the
payload weight. Sticks are around 1/4? to 3/8? wide ? stout enough so
they don?t snap when you hold the rocket (with payload attached) up by
the end of the stick. Cut sticks shortly before using them to avoid
warpage.

No weight guidelines are listed, due to the wide varieties capable
of different mixes. It will generally lift greater weights than a BP
rocket.

Tubes can be ordered from many sources. Check out our friends at Skylighter.com for an up-to-date list. You can order
tubes at pre-cut lengths, or in longer lengths so you can cut them
down. (Recommend using a small kerf blade - band saw is
ideal.)

MIXING THE
COMP

CAUTION:
Whistle comp is energetic, and sensitive to static and shock. DO
NOT use a hammer - you must use a press. Make sure you use
anti-static materials (HDPE, paper, or stainless steel [providing
you are not in direct sunlight!]), and that your work surface has
been sprayed with a laundry anti-static spray. (That's right, just
stand back and spray your whole work area. Don't forget yourself!)

Treat completed whistle mix with great
respect.

Whistle comp has a some different variants. The two major formulas
involve Potassium Perchlorate as the oxidizer, and either Sodium
Salycilate, Sodium (or Potassium) Benzoate at the fuel. A catalyst
(typically iron oxide) is added, as well as petroleum jelly to stabilize
the burn rate. It is generally agreed that the salicylate formula is the
faster burning comp and will provide the most thrust, but is also prone
to a higher failure rate and is hygroscopic.

Recommended Whistle Mixes

Salycilate

Benzoate

Potassium Perchlorate

75

70

Sodium Salycilate

25

Sodium Benzoate

30

Iron Oxide

1

1

Petroleum Jelly

4

4

(Other formulas can be found on the PFP web site.)

You will need to melt the portion of petroleum jelly required for the
mix. Do this over a hot plate (or an old iron turned upside down). AFTER
you remove from heat (and any flame source nearby) AND move into a very
well ventilated area, Add to this about 5 portions of toluene or lacquer
thinner. (For a 500g batch, melt 20g of petroleum jelly, mix with 80
milliliters of toluene. Please observe the written warnings that come
with toluene.) Make sure the petroleum jelly is still warm, or it
won't dissolve very well.

The Potassium Perchlorate needs to be milled very fine. Order it
milled, or mill it yourself. Pass it through a 100 mesh screen.
After it is screened, add in the catalyst and screen again until the
color is uniform. (If you're using Iron Oxide, it will result in a light
pink color.) The Benzoate is sticky and will not pass through a fine
screen, so it needs to be screened with a 20 mesh screen (do not force
it!) or you can use the diaper
method to mix. Keep these chemicals separate until read to mix.

Wet Method: Put in the Potassium Perchlorate/oxidizer mix. Add the
petroleum jelly/toluene mix. Add at additional measure of toluene -
enough to turn it into a thin pancake batter. (For a 500g batch, start
with about 150 milliliters of toluene.) Add the Sodium Salycilate or
Sodium Benzoate. Stir this mix together. Add enough toluene to keep the
consistency of thick pancake batter. Keep stirring until it is uniform.
Spread this out on a non-static, non-pourous area (piece of HDPE
plastic, or cookie cutter sheet). Allow to dry. You can test for dryness
by taking a couple of milligrams *well away* from the area, and light
with a butane torch. If it is wet, the toluene will burn off with a lazy
yellow flame, then the mix will ignite and burn like a star. If it is
dry, as soon as the flame touches it, it should go off all at once.
Store the resulting mix in an HDPE
bowl and seal the lid.

Dry Method: (listed here as reference. For safety reasons, we
encourage you to use the wet method.) Screen the Potassium Perchlorate
and catalyst and put into an HDPE bowl. Add in the benzoate or
salycilate and carefully combine all of the dry ingredients together
with a fork. Add the petroleum jelly/toluene, mix, and allow to dry the
same way as the wet method. This method does result in a damp mix
that still needs to be dried. (The wet mix adds in an additional amount
of toluene *before* the benzoate or salycilate is added. The result is a
much safer mixing operation.)

CONSTRUCTION

Whistle rockets MUST be pressed. This is one safety item that cannot
be overstressed. Whistle mix will react to static and shock, so great
care must be taken when handling the fuel. It is highly advisable to use
some kind of adequate blast shield on your press. (Lexan is ideal. You
can use Plexiglas, but it must be thick - over 3/4". Wood is also a good
product to use - again thick - say 1" oak - but you won't be able to see
your work.)

Because of the pressure of the press, a retaining sleeve must be
used. (Refer to the Pressing
vs. Ramming page for more info.)

Whistle rockets do not use a nozzle. After the product is removed
from the spindle, it will appear that there is a nozzle. This is
actually the fuel that has been pressed against the spindle.

Put the reinforced tube on the whistle spindle. Add about one I.D. of
comp. (It is usually a good idea to make a scoop ahead of time to
measure out this amount.) Using the drift with a hole, press the mix.
Repeat this process until the drift has cleared the spindle, then switch
to the solid drift. Continue the process until the comp is about 1- to
1-1/2 i.d. above the top of the spindle. (Experimentation will tell you
how much extra comp to use.)
Remove the reinforcing sleeve, then
carefully remove the spindle. (A strap wrench may be required for larger
diameter spindles.)

The nozzle end of the rocket should look as though it has been made
of clay (when using the iron oxide catalyst). If you observe cracks or
flakes,  then use this rocket with caution.

STICKING AND FUSING THE
ROCKET

Sticking the rocket

Put the stick about 1/2 to 3/4 up the side of the rocket, and secure
using (a minimum of) two strips of strapping tape.

AFTER you have applied the payload, trim the stick until it balances
on your finger just below the nozzle. If the stick is longer, it will be
more stable but be heavier. Shorter, and it will be lighter
(faster/higher), but may be unpredictable. Use strapping tape to adhere
the stick to the rocket in two places.

This balancing technique is a generally accepted rule, and works very
well. You may hear terms like 'center of pressure' or 'center of
thrust', but that is not covered here. Just know that if you balance
your rocket as described above, it has an excellent chance of flying in
a general upward direction.

Fusing the rocket

It is important NOT to stick the fuse up inside of the cavity. (Doing
so will convert your whistle rocket to a large ground salute.) If you
are using Visco, tape the fuse so that a section circles around
the nozzle end at the base of the tube. Leave the cavity clear. (If you
use quick match, make sure the end is secured to the nozzle around the
base of the tube.) Allow enough Visco outside of the tube to give you
time to retreat to a safe distance.

Because of the energy of whistle fuel, it is advisable to be at a
fairly respectable distance when the rocket lifts. If it fails, it usually
fails quite spectacularly. Trust me on this one - this is best viewed from
a distance.