To Whistle or Not to Whistle?

This is the first of three related projects that Ned is creating for you on how to make whistling fireworks. I want to preface them by saying one thing:

If you want to make whistles, this article can save your life!
Look, I think most of us build fireworks because we want to have fun. And whistles, when you see and hear them, are definitely awesome. But this is one area of fireworks making that, if it goes wrong, will definitely take the fun out of fireworks for you, and quite possibly for others in your life as well.

So, to anyone who has ever aspired to making a whistling rocket, or any other sort of fireworks whistle, read this fireworks-making project twice before starting.

Why You Should NOT Try to Make Whistling Fireworks

Whistles are DANGEROUS. Whistle mix is highly explosive, and sensitive to just about everything you could inadvertently do: too much pressure, too much impact, or any friction, sparks or static electricity. Screw up and you’ll have a catastrophic explosion and possibly injure or even kill yourself.

Making whistles means equipment. You need a press and special tooling to start with. This can cost money and takes space. Don’t take this on, unless you’re ready to make the necessary investment in the kinds of good equipment that Ned shows you how to use in this project. Believe me, you cannot cut corners when making whistles: either you invest in the right equipment and learning, or you fail, possibly catastrophically.

Making whistle fireworks is not instant gratification. Whistle fuel takes time to make. And you have to be extraordinarily careful, and you cannot rush it.

Why You Might Want to Learn to Make Whistles

Making a big whistling firework and using it in a fireworks display is a guaranteed crowd pleaser. It is something most of them will never have seen and heard before. This is a firework the big boys make and that audiences just love.

The satisfaction you can get from adding whistles to your aerial shells, or launching your first whistle and strobe rocket, is mind altering. It will pump you up like few other fireworks can.

Within this and the next two projects, you have what I consider to be the best tutorials ever written on making whistles and whistling fireworks (rockets, fountains, etc.). That means, that if you follow Ned’s instructions closely, you can pretty much be guaranteed of successfully making just about any kind of whistling firework you can imagine. It’s an opportunity to learn something that only pyrotechnic experts know how to do. And to do it well.

Harry Gilliam
Chief Cook & Bottle Washer

How to Make a Whistle

What are Fireworks Whistles?

Often when making fireworks we focus on visual effects. But our ears can detect a lot of other effects that are going on. The special sound of a charcoal, core-burning rocket as it quickly “Whooshes” out of the launch tube is quite different than the slow “Shhhhhhhh” as an end-burner launches, and I enjoy the sound of them both.

For the Pyrotechnics Guild International’s convention I have made girandolas containing multitudes of these core-burning motors, and I eagerly look forward to hearing them as they rise skyward. It’s a bit like a jet engine taking off.

For a different sound, I have some girandolas, which have whistle motors on them, and I also have some of these whistlers on my competition Chromatrope wheel. Whistles add one more auditory dimension to fireworks effects, and while Saturn Missiles can wear thin on me after a while, I do enjoy a whistling effect occasionally.

So what, then, is a whistle? For the purposes of this article it is a pyrotechnic device designed to produce a shrill audible effect. But there are whistles and there are whistles. There are two primary types, and you need to know the difference before you make them, so that you can pick the correct tooling.

There are whistles designed to generate powerful thrust in order to fly, and whistles, which have lower thrust. Whistles with high thrust are normally used as whistle rockets. Low-thrust (or simple) whistles are used to add a sound effect to a firework device and/or as drivers to turn wheels. Both types emit showers of sparks.

Note: To make any kind of whistle, you must use a press (either hydraulic or arbor) and tooling that is specially designed to make whistles. The important thing to remember is that you use different types of tools for different kinds of whistles. Simply put, there is whistle rocket tooling, and there is simple whistle tooling. Be sure you have the correct tooling before you start.

Warning: Attempting to make whistles without the proper tooling can be fatal. Whistle composition is highly impact and friction-sensitive, and is a very powerful explosive.

Whistle rockets have a sound all their own, and can be flown with only the whistle engine, or with other pyrotechnic effects, such as strobes, shells, or salutes.

A simple row of stand-alone whistles, mounted like fountains on the ground, will certainly grab an audience’s attention during a fireworks display.

Whistles can also be loaded into an aerial shell, such as a color-whistle-and-report shell. When the whistles have a bit of titanium in them, they make wonderful silver-tailed whistling inserts. If they are used as shell inserts, only the amount of fuel that will burn for 4-5 seconds is pressed in them so that they don’t burn all the way to the ground.

Whistles can also be mounted on the exterior of an aerial fireworks shell, ignited when the shell is launched out of the mortar, and serving as a whistling rising-effect as the shell rises skyward.

Making whistle fuel and pressing simple whistles are two of the first steps to making whistle rockets and strobe rockets, which I’ll be exploring in follow-up articles. That means the skills I’m about to describe are building blocks for further, more advanced projects.

What Makes A Fireworks Whistle Whistle?

Honestly, the precise answer to that is a bit beyond the scope of my expertise. Rather than it being a result of gasses passing through a tube and across an opening, as in a musical instrument or a simple “coach’s whistle,” pyrotechnic whistles produce their sound through a rapid, oscillating burning, which produces the sound.

There, that’s as much as I know about that. But I do know that if I follow the next procedures, I’ll end up with a device that whistles.

How to Make Whistle Mix

Warning: Whistle fuel is powerfully explosive stuff, roughly equivalent in power to that of flash powder. Much care must be exercised when making and using it. You’ll notice that in the method I’m about to describe, the fuel is never mixed in a dry state. Some parts of it are mixed together; then that mixture is dampened with a wet solution. Only then is the remaining dry ingredient added. This greatly reduces the risk of unwanted ignition due to static or friction.

Fireworks Tips #45 contains Dan McMurray’s article,
“Whistle Rocket Fuel in Under 8 Hours.” I have always made my whistle fuel based on the recommendations in that essay, but have slightly modified it for my purposes. I’d recommend that readers familiarize themselves with that method before proceeding.

Especially, please study all the safety recommendations contained in Dan’s article. I’m not going to repeat them all here. I strongly suggest that you familiarize yourself with them before proceeding with the following steps.

Making whistles is very similar to making gerbs, and I’d recommend a familiarization with that process, as well.

I’m about to make whistles using a common formula, which contains sodium salicylate as the fuel and red iron oxide as the catalyst. There are other fuels such as sodium benzoate and potassium benzoate, which can be used to make whistles. The list of alternative catalysts is almost endless.

My friend, Danny Creagan, has done extensive research using these alternative fuels and catalysts, and has tabulated his results, and you can see his whistle mix data here.

I highly recommend a look at this information for anyone interested in achieving different power or sound with their whistles by varying the fuel and/or catalyst in the mixture. I suggest you pay particular attention to the video of the whistle composition explosion there.

The first thing I do when making whistle fuel is get a large stainless steel pot of water boiling. This pot of hot water will be used to dry the whistle mix. I never get whistle mix anywhere near the burner that I use to heat the water.

I use a slightly modified version of Dan’s formula for whistle mix. This formula is slightly less energetic, and mineral oil is used instead of Vaseline. So the formula I use is:

Whistle Mix Fuel

Chemical	%	64 ounce batch	1800 grams
Potassium Perchlorate	0.66	42.25 ounces	1188 grams
Sodium Salicylate	0.29	18.55 ounces	522 grams
Red Iron Oxide	0.01	0.65 ounces	18 grams
Mineral Oil	0.04	2.55 ounces	72 grams
Total	1.00	64 ounces	1800 grams

Note: I use the mineral oil instead of Dan Murray’s Vaseline, because it does not have to be melted before mixing it with the Coleman fuel. I use this slightly “toned-down” formula because I find it to be a little more forgiving, resulting in fewer “CATO’s” (blown up devices).

The potassium perchlorate is a very fine powder, capable of falling easily through a 100-mesh screen. Screening it through a 40-mesh screen breaks up any clumps in it.

The sodium salicylate and iron oxide are mixed together by screening through a 20-mesh, kitchen colander screen. Be sure and use the 20-mesh screen; the sodium salicylate will not pass through a finer mesh screen. These two mixed chemicals are placed in a stainless steel pot, which is a bit smaller than the one that contains the hot water.

The mineral oil is placed in a one-quart jar, like a clean spaghetti sauce jar, and the jar is filled the rest of the way with Coleman Camping Fuel. VM&P Naphtha, which is available in the paint department of Home Depot, may also be used, as described in Dan’s article.

I get my Coleman Fuel in the camping department of my local sporting goods store. The mineral oil can be found in the health-and-beauty section of a grocery store or pharmacy. The oil’s label indicates it can be used as a “lubricant or laxative.”

I shake the fluid mixture a bit after putting the lid on the jar, and then the liquid is added to the sodium-salicylate/iron-oxide mixture. That composition is then stirred with gloved hands until it is a thoroughly dampened, homogenous mixture. I add just enough Coleman fuel so that the mixture is about the consistency of spaghetti sauce.

The screened potassium perchlorate is then added to the dampened mixture and more kneading is done until I have a thoroughly mixed, red composition. More Coleman Fuel may be added as necessary in order to produce a putty-like consistency, similar to soft bread dough.

All of this has been done in the smaller stainless steel pot, and that pot is now placed in the larger pot of hot water, after the burner has been turned off and the pot of hot water has been relocated to an area away from the burner. I absolutely never want to get the whistle fuel anywhere in the vicinity of an open flame.

Every step of this procedure is carried on outdoors, of course.

Every hour or so, as the fuel is drying, I stir the whistle composition with gloved hands to break it up and stir it around so that it dries throughout. Then after a few hours when it is almost completely dry, I screen the mixture through a 12-mesh kitchen colander, carefully pushing it through with my gloved hands.

I put it back in the pot to complete the drying, and then pour it out onto kraft-paper lined trays for additional drying overnight.

Sodium salicylate, like most sodium compounds, is very hygroscopic–it will absorb moisture out of the air. Because of that, I store my dry fuel in a tightly sealed bucket with a bag of desiccant in with it to keep it dry.

The whistle mix shown above is a bit desensitized by the oil in it, but it is still a powerful explosive and those of us who work with it treat it with a large amount of respect.

Pressing a Fireworks Whistle

On my wheels and girandolas I like to use whistles pressed into 3/4-inch ID parallel tubes, 3.75-inches long. These little devices make quite a racket and will burn for up to 15 seconds, depending on how much composition is pressed into the tube.

You’ll notice I said, “pressed.” Whistle mix is never rammed (pounded by hand with a mallet). It is shock sensitive and is liable to explode if rammed. Pressing whistles with a hydraulic press is much safer, but I still employ a safety shield on my homemade press.

Because of the high pressures necessary to consolidate whistle fuel, I use only Skylighter’s
TU1066 extra-strong-wall paper tubes. The inner layers of paper of a standard tube would crush outwards under the force necessary to press whistles. I cut these tubes to length, and use Skylighter’s
TL1270 Whistle Tooling.

Some kind of tube support must be used to reinforce paper tubes during the pressing operation. Otherwise the tube would burst under the pressure while the fuel is being pressed. Several types are shown below.

For instance, I use an aluminum “clamshell” support like this one.

But a piece of 1-inch ID PVC pipe can also be used as a tube support. The pipe is split lengthwise with a hacksaw, and enough of a lengthwise slice of the pipe is removed to allow it to fit snugly on the paper tube. Metal band clamps are installed, side-by-side, on the support and tightened to create a very sturdy tube support.

A friend of mine, Dan T, uses double-walled PVC pipe tube supports. In this case a 1.25-inch ID piece of pipe would be split to fit snugly on the piece of 1-inch ID pipe, and then the clamps installed. This would create an extremely sturdy support.

Next, I carefully lay out my tooling and put a piece of masking tape on my drift so that it never comes into contact with the spindle, which could pinch whistle composition between the two and cause it to ignite.

The white PVC pipe tube-extension shown in the photo above is used to temporarily increase the length of the paper tube, which makes it easier to introduce and press the final fuel increments and the clay bulkhead, as described below.

I only use the solid rammer, which came with my whistle tooling. But, I am extremely careful to avoid any contact between it and the tip of the spindle, as I mentioned above. I can’t overemphasize that point. Notice the 1/8-inch gap between the tip of the spindle and the end of the rammer in the photo above. The location of the tape ensures the rammer never gets any closer to the spindle than that 1/8-inch margin of safety.

Whistles and whistle rockets do not use a clay nozzle, as black powder rockets do. Whistle fuel burns so quickly that a clay nozzle would over-pressurize the tube and cause the device to explode.

The first thing I do prior to pressing any fuel is weigh out abut 2 ounces of the whistle mixture in a paper cup to work out of. I then tightly seal my larger container of whistle fuel and set it in a safe place, away from my immediate work area to minimize exposure of whistle composition during the pressing. This reduces the amount of explosive material near me in the event of an accidental ignition of any kind. This is the best way to avoid a serious accident.

I introduce a heaping tablespoonful (15 grams) of the whistle fuel into the tube through a funnel, and press it to 7500 psi (on the composition–2200 psi on my press’s gauge. To understand the difference, see below). All the while I keep an eye on the masking tape marker to make sure the drift does not press into the tube so far that it would hit the spindle. If necessary I add a bit more fuel to this first increment before pressing it to the full pressure, to ensure that the drift never gets closer than 1/8-inch to the spindle.

Note when pressing this first increment of fuel: It’s a larger quantity than the following ones, so that it can completely cover the spindle. But with this much fuel, the drift can get jammed in the motor, which is caused by too much fuel powder wedging itself between the drift and the tube wall. To prevent this, first press up to about 1000 psi on the gauge on the press. Then, remove the drift, and then reinsert it. Finish this first increment by pressing the rest of the way up to the 2200 press-gauge psi.

Note: Before pressing, you need to know something: the psi showing on the gauge is not the same as the actual psi being applied to the material in the tube. Without boring you with the reason for this seemingly nonsensical fact, here’s what you have to do to convert the gauge reading to the actual 7500-psi (pounds per square inch) I want on my fuel.

The end of my drift is 0.75-inch in diameter, so it has a radius of half the diameter, 0.375-inch. The area of the end of the drift is determined with the formula: Pi (3.1416) x radius², or 3.1416 x 0.375 x 0.375 = 0.44 square inch.

There is a number of pounds of force, X, that I need to apply to that 0.44 square inch of area to achieve 7500 pounds per square inch. X divided by 0.44 square inches = 7500 psi. Multiplying both sides by 0.44 solves for X, and X = 3300 pounds of force. If I put 3300 pounds on 0.44 square inches, I achieve a 7500 pounds-per-square-inch pressure.

As I stated in the article about building my press, the reading on its gauge must be multiplied by 1.5 to determine the actual number of pounds of force it is exerting. Dividing my desired 3300 pounds by 1.5 yields the reading I want on the press’s gauge when pressing these whistles, or 2200 psi on the gauge.

So, I simply press each increment of whistle fuel to this 2200 psi reading on the press’s gauge to achieve the actual 7500-psi pressure on the fuel grain.

Note: All of this ciphering is something that can sound a bit like “Greek to me” until one does it a few times and gets the gut feeling for what is being determined by the calculations. Don’t be put off by it. You’ll get it if you haven’t already.

After the initial fuel increment is pressed, further increments of flat 1/2-tablespoonfuls (6 grams) are pressed until there is about 3/4-inch of empty space left in the tube. This takes a total of about 1.8 ounces (52 grams) of composition. I then press a bulkhead of 1/2 tablespoonful (8 grams) of bulkhead clay to finish the whistle. Except for the first one, each fuel increment and the clay bulkhead end up being about 3/8-inch thick (half a tube ID) after pressing.

Note: Photo taken without safety shield installed, for clarity.

Sometimes I want titanium sparks in the spray from a whistle. If that’s the case, I’ll press the initial 15-gram increment without titanium in it to reduce the chance of sparks or damage to the tooling. I don’t want that hard metal being pressed against my steel spindle.

Then I mix 4 grams of spherical titanium into 35 grams of the whistle fuel, simply swirling the metal and fuel together in a paper cup, and press the remaining increments of fuel.

If I am going to hand-twist-drill through the bulkhead to create a passfire, as when a whistle driver is to pass fire to another driver, I’ll finish the pressing of the whistle mix with some whistle composition which has no titanium in it. I don’t want to hit titanium with the hand-twisted drill bit when drilling the passfire hole.

Even hand-twist-drilling into whistle composition is not something to be taken lightly; it is something that should be done lightly, and slowly with the utmost care.

Whistles take fire very easily, and do not require any priming. Nosing with kraft paper and fusing with Visco-fuse or quickmatch gets the whistle ready to perform its duties.

Results

Here is a video of a whistle which had only plain fuel pressed in it. It burned for almost exactly 15 seconds.

And, here’s a video of a stationary whistle that had fine spherical titanium in all but the first 15 grams of the fuel.

Finally, here’s a video of a 24-inch diameter girandola I flew at the 2007 PGI convention, which uses whistle drivers. Thanks to Steve Majdali for the video.

Next, I’ll be following up on this article with rocket projects, which use this whistle fuel and technique to create very unique and impressive effects.

Stay tuned,
Ned