Additional instructions for Soft Drink Can Launcher
This on Additional instructions for Soft Drink Can Launcher is intended to accompany the image, which graphically details the device described herein.
This is a very short “mortar” constructed for the express purpose of launching soft drink cans straight up into the air. It is crude, prone to rupture during use, and consumes rather inordinate amounts of Pyrodex. But it sure is fun, and it makes an incredible amount of noise when it goes off!
- Large coffee can, empty, no lid
- Concrete mix, admixture, water, etc. (driveway repair mix okay)
- Steel reinforcing wire
- Full soft drink can (non-carbonated, if possible)
- Paper or thin flexible plastic sheeting
- Drill and drill bit to fit fuze wire
Tape either paper or plastic around the soft drink can, enclosing the bottom of it as smoothly and consistently as possible. Try to avoid any kinds of seams, and make a fairly tight fit with whatever size can you intend to launch the most. This wrapped-up can will be used to form the inside of the barrel (I refer to this as the barrel mandrel), so its diameter is important. Some cans are slightly different diameters, so make sure you choose one that is similar to the types of cans you intend to launch. When wrapping the can, you may leave the top part open, but the bottom must be sealed up smoothly.
When you have smoothly wrapped the full soft drink can in paper or plastic, coat the sides of it with a smooth, thin layer of vaseline. This will ensure easy removal after the concrete has set.
Construct a basket out of the steel wire. This basket will sit inside the coffee can and be encased in the concrete, providing tensile reinforcement. Concrete is strong for compressive uses, but this is a tensile use, and the addition of a reinforcing basket will greatly extend the life and maximum loads of this mortar.
If you are unsure how close to space the wires of this basket, then experiment, or ask someone who has experience with reinforcing concrete. As a rule of thumb, the more reinforcing wire you have, the stronger it will be, but only to a point. I would recommend a mesh of no closer than 1/2″, and optimally I would recommend spacing the wires 1″ (one inch) apart from each other.
The inner portion of the basket must be large enough to handle the displacement of the soft drink can barrel. Test this by putting the reinforcing basket into the coffee can, then holding the barrel mandrel approximately where it will go. Adjust the shape of the reinforcing basket to accommodate the barrel mandrel.
When you are sure of the shape of your reinforcing basket, then tape it in place inside the coffee can. This is only to hold it in place while the concrete is poured.
Mix the concrete as directed. The stronger concrete you have the better, but it’s still probably going to end up blowing up after some amount of use. 🙂 It is better to err on the side of a little extra moisture in the concrete mixture, to aid in the removal of air bubbles.
Pour the concrete into the coffee can, allowing it to flow smoothly around the reinforcing basket. Do not fill the coffee can yet! When it is close to full, press the barrel mandrel into the wet concrete right in the center. Seat the mandrel to the required depth for your barrel length. Add any more concrete mix you might need to fill the coffee can completely.
Once everything is poured and the mandrel is straight and true (vertical), shake the can, even banging it on a hard surface (this is where a non- carbonated soda can comes in handy!) or rapping on the side of it with your hands to try and settle the concrete and remove any air bubbles that might weaken the structure.
After the concrete has completely set (anywhere up to a week or so), carefully pull the barrel mandrel out and inspect your work. It may help to rotate the mandrel as you withdraw it from the concrete. You should have a perfectly-shaped shallow mortar made out of reinforced concrete.
If you wish, you may wipe the vaseline out of the barrel. It is not necessary to remove the vaseline, as it will burn off within a few launches. Before using this mortar, it is important to allow the concrete to fully set. Depending on the brand of concrete, this could require up to a full month! Don’t jump the gun (pun intended), because incompletely set concrete is far weaker, and will easily explode during launch.
When the concrete has fully set, use the drill bit to drill a flash hole. Measure your barrel “depth” carefully and drill straight in from the side, right into the very bottom part of the combustion chamber. Choose a drill bit that is approximately the diameter of the fuzewire you intend to use, and drill carefully to make sure it goes in straight. A drill press or drill jig may be helpful to drill accurately.
- Green hobby fuze
- Soft drink can
- Some type of load/filler for can
- Match or lighter
Carefully review the safety notes contained at the bottom of this document before you attempt a launch.
Choose an area of soft grass or dirt to place the mortar. It is best not to place it on a hard surface, since there is nothing to absorb the launch shock, and this will greatly reduce the useful life of the mortar. If you must place it on a hard surface, then place it on a stack of old newspapers or a telephone book to help cushion the launch shock.
A keen feature of this device is that you will be launching the contents of a soda can. When starting out, you may want to just launch an empty aluminum can, as this is very lightweight and will be a good first test of your mortar-building skills. Later you may want to add some water or sand to the can to increase its weight, and therefore its ultimate range.
When you have selected and filled up your projectile, slip it into the barrel to ensure a good fit. Slightly loose is fine (less than 1/10th of an inch diameter), but make sure it does NOT bind or stick firmly on the way down to seat against the bottom of the barrel. When you are satisfied with the smooth operation of the projectile within the barrel, remove the projectile from the barrel.
Insert a length of fuze into the fuze hole, pushing out any remains of burned fuze from a previous launch. Make sure some significant length of the fuze reaches into the combustion chamber to ensure positive ignition. For fire safety, put a small piece of tape over the fuze right where it enters the side of the can.
Add a small amount of Pyrodex RS powder into the launch tube. When I say “start small,” a good amount is a teaspoon or less. You can always work up to more if the mortar is holding together well. The powder should pile up at the bottom of the barrel, and be touching the fuze wire enough to ensure positive ignition.
WITHOUT placing the projectile into the barrel yet, position your mortar at the launching site. I recommend keeping it nearly vertical, or at least tipped no more than about 20 degrees from vertical. If the mortar falls to one side after launch, it can damage itself. If the mortar falls over during fuze burn, there is NO TELLING where that projectile is going to go sideways!
When you are ready to launch, slip the projectile into the barrel, again testing to make sure it doesn’t bind or scrape too badly on the way in. Light the fuze and go and run really, really far away and hide behind a LARGE SOLID OBJECT! Boulders are great places to hide behind, but make sure the projectile doesn’t come down on your head afterwards. 🙂
To reuse this mortar, remove any unburnt or partially burnt fuze and/or gunpowder. Make sure no embers remain. It is usually not necessary to clean the mortar between launches, unless enough grease builds up that it becomes difficult to insert the fuze or load the powder.
BEFORE re-use, carefully inspect the mortar, looking particularly at the concrete for signs of structural failures, cracks, chips, bulges, etc. If the mortar becomes cracked, THROW IT AWAY! DO NOT CONTINUE USING A CRACKED MORTAR. THE NEXT TIME IT WILL MOST LIKELY EXPLODE!
Theory of Operation:
The ignition of the gunpowder will generate gas pressure inside the combustion chamber, and hopefully the weak link will be the soft drink can, which should go skyrocketing out of the mortar. If you load too much powder or weight into the can, you may rupture the mortar. This brings me to Load Notes.
The more powder you put in the mortar, the more total expanded gas might be generated during ignition. I say “might” because if you choose a very light projectile (an empty soda can), then it will leave the barrel long before the powder has burned fully, thereby relieving pressure on the mortar.
Conversely, if you choose too heavy a projectile, it will not have left by the time the powder fully burns, and depending on the amount of powder and gasses generated, it could exceed the structural strength of the mortar.
Remember that every time you make the projectile heavier, that means when the powder burns it has to press a bit harder against the projectile to get it to move. It also means that the projectile will tend to stay in the barrel longer, allowing more of the powder to burn under pressure, generating higher and higher chamber pressures. As all handloaders and black powder enthusiasts know, a TINY increase in projectile weight or powder load can result in a DRASTIC increase in chamber pressure, and rapidly lead to structural failure.
IF YOU MAKE TOO MUCH PRESSURE INSIDE THIS MORTAR, IT WILL STRUCTURALLY FAIL AND THEN EXPLODE LIKE A GRENADE!!!!
Lighter loads will extend the useful life of your mortar. Heavy loads will stress the concrete more and cause it to crack earlier. But they sure are fun!
This device can KILL! Do not attempt any of this without careful supervision from someone who has experience with constructing explosive devices. Do not attempt this without proper eye, hearing and hand protection, in case of accidental detonation or mortar rupture. Do NOT smoke while operating this device, as accidental detonation may occur.
When the projectile leaves the barrel mouth, there will be a fairly impressive blast wave emanating from the device, so be sure to wear hearing protection.
The coffee can around the concrete MAY aid in the capture and retention of concrete shrapnel should the mortar fail, but don’t count on it. Big pieces of high-speed concrete can quickly ruin your day. 🙂