How to Make a Fireworks Strobe Rocket

What is a Strobe Rocket?

If I had to make the choice of being able to construct only one type of rocket, it would be a difficult decision. I truly love the low-level simplicity and effect of the Spectacular Glitter-Tailed Rocket with Willow-Diadem-Horsetail Finish.

But for pure, high-powered, awe-inspiring and crowd-pleasing rocketry display, the strobe rocket is sure hard to beat.

The following video is a six-pound strobe rocket. I constructed this 1.5-inch ID model in a seminar I taught at a local pyro club event.

Note: The “one-pound” and “six-pound” rocket motor designations have nothing to do with what the rocket actually weighs. They are fireworking terms, which refer to the rocket engine tube’s inside diameter (ID), and have their roots in antique rocket-making terminology.

That baby was really up there by the end of its flight. You can tell that from the delay between the video and audio of the report heading. These large strobe rocket engines really do sound like helicopters in flight, too. For such a relatively simple fireworks device, they sure are satisfying and attention grabbing when they work well.

Even when they don’t “work well,” and CATO (blow up) on the launch pad, these rockets are impressive! There is a lot of power packed into that engine tube, so it pays to put a long piece of Visco fuse on them, and have everyone plenty far away from the launch area just in case.

This is the third in a series of whistle-related articles. The first installment dealt with making whistle fuel and simple fireworks whistles. That same fuel will be used in these strobe rockets. The second article described the construction of basic whistle rockets. Many of those same techniques will be used now to make strobe rockets. So, it’s a good idea for you to familiarize yourself with those basic methods before forging ahead with this project.

Note: I will not be repeating all the basic construction details from the whistle rocket tutorial. You really will need to be familiar with those techniques if you are going to tackle this strobe rocket project.

A strobe rocket utilizes whistle fuel for power, along with strobe fuel to create the popping sound and flashing light that is unique to them.

Pressing Rockets

Note: Once again, as in the whistle projects, hand ramming with a mallet is never employed with these fuels and devices. Only a press equipped with a safety shield should be used to press these items. Fireworks Tips #121 detailed the construction of such a hydraulic rocket press. For small rockets, some folks use a manual arbor press to consolidate (press) the fuels.

Strobe Rocket Fuel

In addition to the whistle fuel I referred to above, one other fuel is necessary for these strobing rockets–strobe fuel. This fuel is very similar to the composition that was used to make strobe pots. Please study the methods and precautions that were spelled out in that essay.

This strobe fuel is what gives these rockets their distinctive popping sound and flashing light as they fly. But, strobe fuel alone is not powerful enough to make a rocket fly.

Back in the ’80’s, Doc Barr started playing with a basic strobe rocket, using a black powder fuel to boost the strobe fuel’s power. His results are chronicled on Page 58 of The Best of AFN II.

A funny and educational quote from Doc’s article is, “All rockets have the potential of exploding on takeoff, but these do it with an annoying frequency. About 1 out of 10 act more like an open-ended salute than a rocket. So ‘light fuse and retire quickly’ is my Eleventh Commandment.”

In the late 80’s and early 90’s, folks like Doc and Steve LaDuke started working with whistle fuels in rockets, resulting in the high-powered fireworks whistle rockets like I described in the whistle rocket article mentioned above.

Somewhere along the line, these rocketry pioneers had the bright idea to combine the powerful whistle booster fuel with the impressive strobing fuel, and the modern strobe rocket was born.

Traditionally, nitrocellulose (NC) lacquer is added to the standard white strobe composition specified in my strobe pot article. In his BAFN article, Doc Barr said he pressed his strobe fuel slightly dampened with NC lacquer. Many modern builders dampen their fuel with NC lacquer, granulate the dampened fuel through a 12-mesh screen, and dry the granules before pressing the fuel in the rocket motor.

Years ago I made a slight change in this method. Rather than using NC lacquer, I now dampen my strobe fuel with an additional 2% mineral oil dispersed in Coleman Fuel, as I described in the whistle-fuel procedure.

Chemical	Percentage	16 Ounces	450 Grams
Ammonium Perchlorate	0.57	9.15	257.1
Magnalium, 200 mesh	0.24	3.8	107.1
Barium Sulfate	0.14	2.3	64.3
Potassium Dichromate	0.05	.75	21.5
Mineral Oil	+0.02	0.3	9

Note: The ammonium perchlorate, barium sulfate, and potassium dichromate are each milled individually in a blade-type coffee mill until they are fine enough to pass through a 100-mesh screen.

Warning: Potassium dichromate is toxic and a known carcinogen. A good respirator and rubber gloves are required when working with this chemical, and when using it in pyrotechnic compositions. Don’t breathe this stuff or get it on your skin. Wear your protective gear even when you are pressing the finished fuel in the rocket motor.

I’ll be making 3/4-inch ID (one-pound) size, strobe rocket motors. Each motor will use about 39 grams of whistle fuel and 25 grams of the strobe fuel. So, the 450-gram batch of strobe fuel shown in the formula above will be enough for approximately 18 motors.

All the dry chemicals are weighed out individually, then mixed thoroughly by gently passing them through a 20-mesh screen or kitchen colander. I put this mixed powder into a small plastic bucket.

I weigh out the mineral oil into a clean quart jar, such as a spaghetti sauce jar, and then I add 1/2 cup of the Coleman Fuel to the oil. After tightly screwing the jar’s lid on, I shake the liquid to completely mix the two ingredients.

This mixed liquid is then added to the dry powder, and it is completely blended in with gloved hands. The damp composition is then dried over a pot of hot water, as described in the tutorial on making whistle fuel. Once again, the fuel is never brought anywhere in the vicinity of any open flame or source of sparks.

After a couple of hours of drying over the pot of warm water, the fuel will be dry, will stop smelling of Coleman fuel, and will resemble grayish-green sand. I use my gloved hands to break up fuel clumps as it is drying.

The Rocket Tooling

To make the 3/4-inch ID strobe rockets for this project, I’ll be using my tooling, which is very similar to the Skylighter TL1361 tool set. Strobe rocket tooling is almost the same as whistle rocket tooling. The main difference is the spindle is about twice as long. The number of rammers (”drifts”) can vary from tooling to tooling.

Just as I did in the whistle rocket project, I polish the drifts and spindle using very fine sandpaper and metal polish to facilitate removal of the drifts during the pressing.

Strobe Rocket Motor Tubes

Once again, because of the high pressures used to make these engines, and the high thrust they develop, I use the extra-strong TU1066 3/4-inch ID paper tubes. For these motors I cut the tubes 6 inches long.

The Tube Support

A 6-inch long, PVC plumbing pipe and band clamp tube support is used to reinforce the paper tube during construction.

Drilling the Fuse Hole

Just as I did with the whistle rocket motors, I drill a 1/8-inch hole through the side of the paper engine tube, right where the bottom of the fuel grain will be.

Marking the Tooling Drifts for Safety

At least 1/8-inch clearance is allowed between the spindle and the point where the drifts would contact it. I mark my tool drifts with masking tape to be absolutely sure they never pinch fuel between the drift and the spindle while the fuel is being pressed. Pinched fuel can explode upon pressing. That 1/8-inch clearance is enough to prevent this.

My particular tooling set only has one hollow rammer and one solid rammer. Some tooling comes with two or three hollow drifts, and each one must be marked with tape accordingly for safety.

Pressing a Strobe-Rocket Motor

The first thing I do in this pressing process is scoop out a paper cup full of whistle fuel, and a paper cup full of strobe fuel, set them aside and put the large tubs of my fuels away in safe storage. As I’ve mentioned before, this is perhaps the most important safety precaution: limiting the amount of exposed flammable composition when working with it.

For my strobe rocket, I press the whistle fuel in the tube in the same way and with the same pressures I did when making the whistle rocket motors. Pressing three 7-gram increments, and one 4-gram increment of the whistle fuel brings that fuel halfway up the spindle. These increments are pressed with the hollow rammer.

I use black rubber o-rings on my rammers to keep dust down to a minimum during the pressing. These o-rings, as seen at the top of the solid drift in the photo of the tooling above, also serve another purpose.

Each time the rammer is about to be reinserted into the tube, I slide/roll the o-ring down toward the end of the rammer. Then, as I insert and press the drift down into the tube, the o-ring seals against the top of the tube and prevents much dust from blowing out. When the drift is removed after that increment, the o-ring’s position marks where the top of the tube was, and just how far into the tube the drift went while pressing that increment.

When the drift is removed from the motor after an increment is pressed, the o-ring stays put on the drift exactly where the top of the motor tube was before the drift was removed.

Critical: I keep a full-scale sketch of the motor on my workbench as I’m pressing the motor. I’ll put the drift, with the o-ring marking where the top of the motor tube was, down on the sketch, and keep track of how high the pressed fuel is coming in the motor. In this way I can precisely determine when the whistle fuel is pressed up to the desired level, and switch to the strobe fuel increments.

I keep the hollow rammer cleaned out as I press the fuels, because I never want to be pressing fuel up inside the rammer, between it and the spindle.

Then I press three 7-gram increments of the strobe fuel with the hollow rammer, and one 4-gram increment of that fuel with the solid rammer, being very careful to not press past the safety-tape line on that rammer.

This brings my strobe fuel up to about 3/16-inch to 1/4-inch above the end of the spindle, as checked once again by comparing the drift and o-ring with my sketch. The final strobe fuel increment is adjusted so that it reaches that level.

This strobe-fuel distance above the spindle is critical. Too little strobe fuel will cause the motor to start its whistling delay burn too soon. Too much strobe fuel above the spindle will cause the motor to burn too long, turn back toward earth, and perhaps even return all the way to the ground before the heading bursts.

Note: Ask me sometime how I know about the effect created when too much strobe fuel is pressed above the spindle. The story deals with a six-pound strobe rocket coming back to earth, going through the roof of a meeting tent as there was a “parting of the seas” in the crowd, bouncing off a swimming pool diving board, and the heading explosion nearly scaring Doc Barr to death, or at least into regaining the memory of most of his previous sex life. Oh, I can laugh about it now, but it was damn embarrassing at the time.

After the strobe fuel has been pressed to that critical distance above the spindle, another two 7-gram increments of the whistle fuel are pressed above the strobe fuel, as shown in the sketch above. This whistle fuel section creates the whistling “delay” portion of the rocket’s flight before the ignition of the header.

As I mentioned in the whistle-rocket article, other “delay” effects can be produced. Colored fuels can be used instead of the whistle delay fuel, or titanium can be added to the whistle delay fuel. The amount of delay fuel has to be dialed in to produce the desired effect and length of flight.

The motor is then capped off with a 7-gram increment of bulkhead clay, with a passfire hole hand-twist-drilled into it. I never drill into whistle fuel with titanium in it, as I warned in the whistle-rocket article.

If I do use whistle fuel containing titanium in the delay section, I cap it off with 1/8-inch of fuel with no metal in it. Then I carefully hand-twist-drill the passfire hole.

Troubleshooting: The various amounts of fuel, and the distance up the spindle between the two fuels, have been dialed in for my own fuels and tooling. If your pressed rocket motor blows up on the launch pad, then less whistle fuel and more strobe fuel should be used. On the other hand, if your rocket doesn’t have enough power at launch, more whistle fuel and less strobe fuel should be used.

So, there we have it, a finished strobe-rocket motor. One final thing I’ll do is carefully re-enlarge the fuse hole with my awl since the hole can become a bit closed down and filled with fuel during the motor’s pressing.

Creating a Rocket Header

These rockets can fly so high that I really like to only use report headers on them. The effect of a star-shell header could get lost up at that altitude. As I showed with the whistle rockets, the hollow end of the motor tube can be filled with loose whistle fuel, perhaps containing some titanium, and then capped off to create a small report heading.

Loose strobe fuel, which is also a powerful explosive, can be used in this way, too. If more hollow space is desired, the motor tube can be extended with an extra piece of the same motor tube, glued and taped onto the motor tube to extend it.

For a larger, more impressive report heading, Skylighter’s PL1020 or PL1022 plastic #5 can shell casings can be used. These plastic cans measure slightly less than 2 inches in diameter, and work well on these one-pound rockets.

I fill the recess in the can’s cap with hot glue, drill a quarter-inch hole in the can’s bottom, and hot-glue a piece of quickmatch or fast fuse into that hole. When gluing the fuse into the can, I make sure all the gaps around the fuse are filled with glue to prevent any composition from leaking out of the can after it is filled.

The fuse will transfer fire from the top of the rocket motor to the heading.

Then I fill the can with my report composition of choice. The traditional filling would be flash powder, but making flash has become a bit problematic for some in the current legal climate.

If one has legal access to the necessary chemicals, I’ll describe a safe way to make a flash report with one of these cans. But first, I’ll detail three alternatives for making a report without flash powder.

A simple report can be made by filling the can with black-powder-coated rice hulls, with the addition of some coarse titanium if silver sparks are desired. One of the cans can hold 45 grams of the BP-coated hulls, and 14 grams of the titanium.

Two other alternatives would be to fill the can with loose whistle fuel or loose strobe fuel. A can will hold 57 grams of my whistle fuel, or 67 grams of my strobe fuel. For silver sparks, 14 grams of titanium can be added to either of these fuels by putting the fuel and the titanium into a small paper cup and gently swirling the two together to mix them before pouring them into the can.

Note: I mention this flash report composition option out of a sense of responsibility. Folks will make flash reports. There is a long tradition of it in all kinds of fireworks. But, flash powder is the most powerful composition that fireworkers work with, and many really serious pyro accidents involve it.

No matter which report composition I used, I then glued the caps onto the plastic casing cans with PVC plumbing cement from Home Depot. I did this outdoors because of the fumes, wiping the excess glue off with a paper towel.

I then strengthened the casings with some 1/2-inch wide fiberglass-reinforced strapping tape. Since my tape roll was 1-inch wide, I split the end of the tape in half. This allowed only one half of the width to tear off as I used it.

Note: During this taping process, the normal handling of the binary-mixed flash report is enough to sufficiently mix the ingredients. No rough shaking is necessary. Once the can is closed, handling this report is no more dangerous than the normal handling of a commercial fireworks salute.

I then finished the headings off with a layer of aluminum foil duct tape.

Here is a video of each of the four different report compositions, made as described above.

Attaching a Heading, Fuse, and Stick to a Strobe-Rocket

I first trim the header fuse so that it is long enough to go all the way through to the bottom of the passfire hole, and is pressed against the rocket’s fuel grain. I bare the last 3/4 inch of the fuse.

Then I put a bead of hot glue around the top of the motor tube and quickly install the header, carefully making sure the fuse goes all the way down into the passfire hole as I do so. I reinforce the joint between the header and the motor tube with an additional fillet of hot glue.

I’ve found that the slick side of a piece of the paper backing from the aluminum foil duct tape comes in handy for smoothing fillets of hot glue without burning my fingers.

The joint is then reinforced with some vertical, 3-inch strips of strapping tape, finished off with horizontal bands of the tape around the heading and the motor tube. This really strengthens the connection.

A 45-inch long, 5/16-inch-square, poplar rocket stick, with a beveled end, is then hot-glued and strapping-taped to the motor. If the rocket is to be flown immediately, then a 6-inch piece of Visco fuse is inserted into the motor’s fuse hole.

If I am going to store the motor for a while before launching it, I won’t install the Visco fuse now, but will instead seal the end of the motor and the fuse hole with aluminum foil tape to prevent the whistle fuel from absorbing moisture.

Well, it’s been a bit of a journey, but in the last 3 projects we’ve made whistle fuel, whistles, whistle rockets, strobe fuel, strobe rockets, and impressive report headings. While these powerful fuels and devices are not exactly beginner’s projects, if they are approached one step at a time, with good safe work habits, they can indeed be some of the most impressive and satisfying fireworking devices around, both for the builder and for the audience.

Stay Green and Have Fun,
Ned

How to Make Fireworks Whistle Rockets

What Is a Whistle Rocket?

I think a really impressive fireworks device speaks for itself, so here’s a video of one of these whistling firework rockets in action.

A whistle rocket does just that: whistles and screeches as it leaps skyward. The motor uses the same whistle fuel that was used in the “How to make a whistle” article. Whistling rockets are “hot.” They leap off the launch pad and can really reach a seriously high altitude if they’re made well.

I’ve made whistle rockets in sizes from 1/4-inch ID super-bottle-rockets up to 1.5-inch-ID “six-pounders.”

I’ve lifted some big ball shells (called “headings” when they’re carried by rockets) with the larger whistle rockets. But, often they fly so high that the effect of such a heading is lost. For that reason I prefer to simply put a large report heading on them with some coarse titanium in it for impressive silver sparks when the header explodes.

Other variations in construction can include various “delay” effects during the coasting portion of the flight following the initial powerful thrust portion–from simply allowing the rocket to continue whistling across the sky, to having the whistle change to a brilliant red flare or a color changing one, before the heading finishes the rocket’s flight.

Be aware, though, that whistle rockets are not your “father’s black-powder rockets.” The rocket fuel used in these babies is powerful. If the rocket engines are not dialed in carefully and fused properly, very impressive CATO’s (”bombs on a stick”) can result.

Warning: Do not EVER hand-ram whistle rockets using a mallet. The fuel is sensitive and could be set off in that process. Whistle rockets must be pressed using a manual arbor press for small rockets or a hydraulic press for larger motors, which require more pressure. It is wise to use a safety shield on a press just in case something goes wrong and the motor ignites during construction.

Whistle Rocket Fuel

I’ll be using the same fuel that I specified in the article on making whistles. The alternative fuels I mentioned in that essay can be used to make whistle rocket motors. But there will be the requisite “dialing in” in order to maximize performance and consistency with those variations.

So, study that article and make some of that whistle fuel, observing all the pertinent safety precautions.

Whistle Rocket Tooling

I will be making one-pound, 3/4-inch ID, whistle rocket motors for this project. Skylighter carries TL1311 tooling used to make these engines.

This tooling set comes with a base, a spindle, a hollow rammer for pressing the fuel increments around that spindle, and a solid rammer with which to press the increments of fuel above the spindle.

Note: You may notice the tooling I’m using in this project, which I’ve had for years, is different than the Skylighter tooling. But, my spindle is about the same size and the motor construction and performance are very similar.

Whistle Rocket Motor Tubes

Because of the high pressure at which the fuel is pressed in these motors, and the thrust they develop during flight, high-strength paper tubes must be used in their construction.

Skylighter TU1066 3/4-inch ID, 1/8-inch wall, extra-strong tubes are an excellent choice for these whistle rocket motors. I cut the 30-inch long tubes into 4.75-inch long tubes for these engines.

The Tube Support

Because of the high pressure used to press these motors, the tubes would bend, split, and collapse if they were made using no tube support. A good support is absolutely essential when making these motors.

A 4.75-inch piece of 1-inch ID, PVC plumbing pipe serves well as a tube support. It is sliced lengthwise with a hacksaw to ensure that it will go around the paper tube and fit snugly when the slice is closed. The support is held tight with metal band-clamps, installed side-by side, and tightened with their screw-adjusters alternated around the circumference of the support.

Polishing the Tooling

Unlike the fuels for charcoal tailed rockets, whistle rocket fuel tends to be “sticky.” The high pressures used to press the fuel around the spindle cause the fuel to adhere to it. This makes the motor hard to remove from the spindle once the engine is pressed. And the sodium salicylate fuel I prefer is reportedly stickier than fuels made with potassium benzoate or sodium benzoate.

Here is a solution, though, regularly touted by master-rocketeer Steve LaDuke. Polish your tooling, especially the spindle, using very fine, 600-grit sandpaper and a good metal polish. I got an excellent polish, Mothers Billet Metal Polish, at my local auto-parts store.

First, if I have any scratches or small imperfections on the spindle, I remove them using a small piece of the sandpaper to smooth the tooling. Sanding in a lengthwise direction on the spindle ensures any remaining scratches run in that direction, rather than in a circumferential pattern, which would make the motor-removal more difficult.

Then, using a small section of soft rag, the tooling, including the rammers, is polished until it all has a mirror-smooth finish. This really enhances the ease of use of the rammers, and the finished rocket motor’s ability to be removed from the spindle.

I even do the best I can to polish up inside the hole inside the hollow drift (”drift” is another word for “rammer”). This will help release any fuel which gets between that hollow part and the spindle during pressing.

Polishing the tooling this way is time well spent. It will help avoid a lot of aggravation in the next steps of pressing the motor and removing it from the spindle when it’s done.

Pressing a Whistle-Rocket Motor

Besides being pressed in a longer tube, and on a longer spindle, a whistle-rocket motor is not much different than a regular whistle. But I do fuse whistle rocket motors differently than I fuse standard whistles.

Drilling the Fuse Hole

You’ll note that the fusing technique shown in the diagram is different than most rocket fusing. There is a method to my madness.

The first thing you might notice is there is no clay nozzle in whistle rocket motors. A whistle rocket needs to have the bottom of its motor tube wide open. So the fuel has to be ignited right at its bottom edge, or else there’s a good chance the motor will blow up due to over-pressurization after ignition.

It can be a challenge to install a fuse from the bottom of the motor, only touching the edge of the fuel-grain, with no nosing to hold it in place.

Some folks hot-glue the fuse to the inside surface of the paper tube. Others use masking tape to attach the fuse to the rocket stick. I’ve tried both of those methods. With some care they can work fine, but at other times I’ve had the fuse fall off as it was burning, before igniting the motor.

So, I came up with the solution of installing the fuse as shown above. Before pressing any fuel, I drill a 1/8-inch hole through the motor casing, right at the outside edge of where the fuel grain will begin. I use a piece of wooden dowel to back up the inside of the paper tube during the drilling operation.

Marking the Tooling Drifts for Safety

Next, I mark the tooling drifts with masking tape to ensure they never come into contact with the spindle when I’m pressing a motor. I allow about 1/8-inch margin of safety between the drift and the spindle when I’m applying the tape.

Pressing Rocket Fuel into the Tube

The hollow drift is used to press the increments of fuel, until the fuel is above the spindle. All the increments are pressed to 7500-psi (pounds per square inch) on the composition.

In the article on making whistles, I illustrated the method for determining how much hydraulic press force to use with a solid drift. Applying 2200-psi of pressure according to my press’s gauge results in an actual 7500-psi on the composition with the solid drift.

But, since the hollow drift has the hole in it, less force will have to be applied to it to achieve this same pressure on the fuel.

With some math, I’ve determined that the surface area of the end of this hollow drift is about 80% of the surface area of a solid-end drift. For this reason, when using the hollow drift I’ll only apply about 80% of the force with my press that I’d apply when using the solid drift.

So, for the increments that are pressed around the spindle with the hollow drift, I’ll press up to a gauge reading of 1750-psi on my hydraulic press.

The first thing I do when pressing a motor is remove a small paper cup of the fuel from the tub of fuel. Then I close the tub tightly and set it aside away from where I am working. That way, only the small cup of fuel is exposed in case something goes wrong.

With the support securely fastened around the paper tube, and with the fuse-hole-drilled end of the tube mounted on the spindle, I introduce 7 grams (1/4-ounce) of the whistle fuel, using a funnel.

I then consolidate that fuel increment with the press in two steps, by first pressing up to only 1000-psi on the gauge.

I remove the drift and use the smooth, round end of my awl to clean any fuel that is wedged in there out of its hole. Then, I insert the drift back into the tube and press the rest of the way up to 1750-psi on the gauge.

If I press all the way up to the full pressure on the hollow drift in one step, fuel will work its way up between the drift and the tube, and between the spindle and the drift, in its hole. This can bind the drift in the motor, which makes it difficult to remove after the increment is pressed. Pressing the increment in two stages, and cleaning the drift between those two pressings usually eliminates stuck-drift syndrome.

When I’m pressing a really large motor, such as a 1.5-inch ID model, I’ll actually press each increment in 3 or 4 stages to reach the full pressure in order to keep the drifts from getting stuck.

Four, 7-gram increments of the fuel, pressed in this manner with the hollow drift, bring the fuel to just above the spindle, using my fuel and tooling. This can vary a little from batch to batch of the fuel, or with different tooling.

After the fuel is above the spindle, I switch to the solid drift. Now I press the same 7-gram size increments in one pass up to the full 2200-psi reading on my gauge.

For the rocket shown in the initial video in this article, I press fuel to one inch above the spindle. That requires three 7-gram increments with the solid drift, for a total of 49 grams of fuel in this motor.

I cap the motor off with a 7-gram increment of bulkhead clay mix.

Adjusting the Total Flight Time of the Whistle Rocket

The portion of the rocket’s flight after the initial high-thrust phase, and before the heading bursts, is called the delay section of the flight.

The fuel around the circumference of the spindle, and above it for that same distance, about 1/4-inch, burns very rapidly in the highly pressurized thrust period of the rocket motor’s burn.

Then, the solid portion of the fuel above that thrust fuel burns more slowly in a less pressurized environment. That’s why the whistle sound changes so drastically after the initial thrust burn.

So, in this rocket motor I had 1/4-inch of thrust fuel above the spindle, and then about 3/4-inch of delay fuel above that. If I shorten that delay fuel, the delay portion of the flight would be shorter. If I lengthen the delay fuel column in the motor, that delay portion of the flight would be longer.

Looking at the video at the beginning of this article, the one-inch of total fuel above the spindle produced that particular flight and delay before the heading exploded. I was pretty happy with that rocket’s flight. I might have lengthened the delay fuel column another 1/4-inch to see if that produced a more pleasing flight in the next rocket.

Other interesting modifications can be made to the delay fuel grain. Once the fuel has been pressed to above the spindle, spherical titanium can be added to the fuel increments that get pressed with the solid drift. The delay fuel is weighed into a paper cup. I add 10% of that fuel’s weight in titanium. Then the cup is swirled to mix the components.

The titanium fuel mix is pressed one increment at a time, the same as described above. The metal will produce a silver spark trail as the delay-fuel burns. If the hard metal is added to all the fuel (below the top of the spindle), it will tear the spindle up pretty quickly. Since it also might pose a sparking threat, I only add it to the delay fuel.

If I plan to have a passfire hole, I usually drill the hole down through the center of the clay bulkhead into the fuel. But, I don’t want to drill into any fuel containing titanium; so I’ll cap any titanium-fuel off with 1/8-inch of plain fuel (no titanium in it). Hand-twist-drilling into that is safer.

The effects you can create using the delay fuel are limited only by your imagination. For instance, in his article “How to Make Fireworks Rockets with Green and Red Tails,” Dave Stoddard describes delay fuels used to change the rocket tail’s color to a green or red flare as it flies upward.

Removing the Tube-Support from the Tube, and the Motor from the Spindle

After the fuel and clay have been pressed in the tube, it’s time to remove the motor from the spindle. This is easier if the support is removed from the engine first, which loosens the motor on the spindle just a tad.

First, I loosen and remove the metal band-clamps from the support, and then slide the PVC support off of the motor.

Then the motor is twisted off the spindle. Putting the spindle base in a vise or holding it rigidly in the rocket press can facilitate this. Using both hands to twist it, the motor is carefully removed from the tooling. Do not use clamps or pliers on the motor itself, or you will risk cracking the fuel grain, which will cause the rocket to explode instead of fly.

Drilling Passfire Hole into Clay Bulkhead

If I am going to put a heading on the rocket, then I’ll need a passfire hole in the clay bulkhead to transfer fire from the last of the rocket fuel to the heading.

I create this passfire hole by carefully hand-twisting a drill bit into the center of the bulkhead just through the clay into the pink fuel. (Remember that the last 1/8-inch of fuel that was pressed should contain no titanium, even if titanium was added to the rest of the delay fuel.)

Warning: Never use a power drill to create the passfire hole. The friction and heat caused by such fast drilling could ignite the motor. Only use hand twisting on the drill bit to create the hole.

I’ve found that starting the hole with a sharp 1/8-inch drill bit, hand twisted through the clay until it just barely penetrates the fuel, works well. Then I’ll expand the hole with a 1/4-inch diameter bit to widen and create the final passfire hole.

Simple Rocket Headers

Several types of simple headers can now be employed on this whistle rocket.

There is a 1-inch long empty space in the motor tube above the drilled clay bulkhead. First of all I like to insert a couple of pieces of black match, from either quickmatch or fast-fuse, into the drilled bulkhead passfire hole. I cut these pieces of match about 1.5-inches long so they reach the bottom of the passfire hole, and extend just to the end of the motor-tube.

These strands of blackmatch ensure positive fire transfer from the last of the rocket-fuel to the header.

For a spray of stars at the end of the rocket’s flight, a small amount of black powder can be put into the tube’s recess, followed by some of the stars.

For a falling glitter comet, some of the black powder followed by a single 3/4-inch comet can be used to fill the end of the motor.

For a small report at the end of the rocket’s flight, the end of the tube can be filled with either loose black powder or loose whistle fuel. A pinch of coarse titanium can be added to either of these powders to produce silver sparks when the header fires.

With any of these types of headings, the motor is then capped with a 1-inch end disk, glued on.

If a report heading has been made, I like to reinforce the report tube-section and end cap with some strapping tape, finished off with some peel-and-stick aluminum-foil duct tape. This reinforcement really helps a report heading to “pop.”

For a star or comet heading, simply gluing a paper disk on is sufficient to finish the end of the motor.

Installing Rocket Stick

The last step to finishing this rocket is to install the stick. I’m using a square poplar stick that I ripped on my table saw. It measures 5/16-inch square by 36-inches long. I bevel the end of the stick, hot-glue it straight on the motor, and finish the attachment with two bands of strapping tape. I make sure the stick does not cover the fuse-hole.

A 6-inch piece of Visco fuse can now be inserted into the fuse hole, and the rocket is ready to be placed in a launch tube and flown.

Sealing the Rocket Motor for Storage

If I’m going to store the finished rocket for a while, I like to seal the bottom of the motor and the fuse-hole with some aluminum-foil duct tape. This prevents the hygroscopic rocket fuel from absorbing atmospheric moisture during storage, and protects the motor from flame or sparks until flight-time.

Prior to flight, the tape is completely removed from the motor’s bottom, and the Visco fuse is installed through the fuse hole.

Motors without sticks can be stored in sealed plastic baggies along with a bag of desiccant to ensure they do not absorb moisture.

Conclusion

Well, there you have it–one of the most interesting and powerful rockets you can make.

Next time I’ll show you a nice variation on this basic motor, the strobe rocket, and some different ways to create a rocket heading.

See ya then,
Ned