Go-Getters
From PyroGuide
Go-getters are best described as self-propelled stars. They are used in an aerial shell as inserts or the head of a rocket. Each Go-getter is capable flying through the air like a rocket without a stick. The flight of a Go-Getter may be a slow lazy curve, a straight line up to several hundred feet, a zig zag or they may spin wildly in place, overall they travel in wild unpredictable paths.
The thrust of a Go-Getter is produced by a fierce burning composition, without a nozzle or a core which is necessary in most rocket motors.
[edit] Construction
Go-getter construction uses unchoked paper tube 9/16" to 5/8" diameter by 1-1/2" in length, usually described as M-80 tubes. One tube end is taped or a paper plug is inserted, the finely powdered composition is made into a slurry with plenty of solvent until it has the consistency of pancake batter. Then poured into tubes filling them about 80%, a piece of black match or thermalite is inserted in the slurry. These inserts are left to dry for many days, and the one end is dipped in a fire-proof material, like waterglass, to prevent the Go-Getter from taking fire in both ends.
Original Formula :
Ammonium Perchlorate_____50%
Copper Oxychloride________15%
Aluminium ( Fine atomized ) 7%
Hexamine __________________3%
Rosin or Vinsol _____________5%
Parlon_____________________20%
BLUE & ORANGE ALUMINUM GO GETTERS FORMULA :
In Percent---------------------------------BLUE-------------------------------------------------------ORANGE
Ammonium Perchlorate .............->50............................................................->50
Copper Carbonate .....................->15................................................................./
Calcium Carbonate ....................../................................................................->14
Aluminum (325 m, 30 mic.)........->10.............................................................->10
Saran Resin................................->5.............................................................. ->5
Cryolite ........................................./................................................................->1
Parlon........................................->20.............................................................->20
All chemicals are run through a mixing screen a few times and, with the aid of a funnel, are poured into an acetone proof plastic (I use an empty mustard squeeze-type bottle made of LDPE (low density polyethylene)). If you do not have access to LDPE containers, you must experiment to find a flexible plastic material that is not affected by acetone. I find that, except for occasionally plugging up, the squeeze-type container works very well and gives more control over the flow of material than pouring from a plastic drink cup. Dave Johnson's book covers the construction of Go Getters in great detail, so I will only point out the highlights and differences.
The Tube
I use a standard 9/16" ID. x 1 1/2" long spiral-wound, machine-made tube with a 1/16" wall thickness and standard 9/16" end plug. The end plug does not need to be glued in as the parlon, once it sets up, is quite hard and will not blow the plug until the Go Getter is almost done burning, if at all. The tubes are then bundled into a convenient size package (I use bundles of nineteen) with rubber bands and set on plastic film (Saran Wrap), ready for filling. While Go Getters made with these tubes go quite nicely, the tubes are still relatively heavy. If you have the inclination, you might want to try hand-rolling some tubes from Kraft paper with a thinner wall to see if they fly better. Go Getters are end burners, so you should not have to worry about blowing out the tube.
The Solvent
A 90:10 mixture of dry acetone:xylene is used as the solvent. Both acetone and xylene are hygroscopic (absorb water) so it is important to use dry material. Fresh solvent is best, but if you have any doubts about the dryness, the mix may be dried in the following manner. First, the desired quantity of solvent mix is prepared. Then a small quantity (an ounce or so) of drying agent (I use calcium chloride or "Damp RidTM" in Florida) is placed in an acetone proof plastic container (plastic two liter soda bottle), the solvent is added, the container is capped and shaken to allow the drying agent to absorb the water. CAUTION: be sure to release the pressure in the container by loosening the cap/lid from time to time. Only a brief time is needed to absorb the water and then the mix is allowed to settle for a few minutes. Lastly, the mix is filtered to remove any solids by pouring it through a double layer of coffee filters and stored in an air/moisture proof plastic container and the drying agent is discarded (it's cheap). It is a good idea to dry only as much acetone as is needed for the batch of Go Getters you are making.
CAUTION: acetone evaporates very quickly, the vapors are heavier than air and extremely flammable. Good ventilation and no sparks are a must.
The acetone/xylene solvent mix is added to the composition in the squeeze bottle at the rate of 35-45% by weight. Some experimentation may be necessary to get the proper viscosity of the mix with your chemicals. The correct consistency is somewhere around a slightly thickened pancake batter (depends on your recipe). After placing the top on the squeeze bottle, squeeze out about 25% of the air (to allow for expansion of the acetone vapor), hold your gloved finger over the spout and shake vigorously for two to three minutes or until everything is thoroughly blended. Depending on the size of the batch you are pouring, you might want to give the bottle a good shaking every once in a while just to keep everything in suspension (don't forget to squeeze some air out first). The tubes are then filled to the brim, ready for insertion of the fuse. It is a good idea to keep a toothpick handy to unplug the nozzle and some paper towels to wipe the nozzle and your hands.
The Fuse (The Secret)
Black match or any other potassium nitrate containing fuse probably should not be able to be used with aluminum Go Getters like it can with the magnesium varieties. This is because of the ammonium perchlorate and potassium nitrate reacting to form the very hygroscopic ammonium nitrate, which may result in a wet interface between the fuse and composition. The trick is to use Thermolite. The Thermolite will not react with the composition and provides a nice hot flame to light the Go Getters. Cut (carefully) the Thermolite in about 1 ΒΌ inch pieces, remove as much of the fabric-wound outer layer as you can, bend the fuse into a narrow "U" shape and insert it into the Go Getters, "U" end first, about half way, and lay them over against the side of the tube. Make sure you prepare enough fuses to complete the job before you mix the slurry. Once you pour the Go Getters, the stuff sets up rather quickly. After the fuse is inserted, set them aside to dry on a piece of plastic wrap until no odor of acetone is detected (about 3-4 days). As the Go Getters dry, they will shrink back into the tube a little because 1/3 of the slurry, by weight, evaporates.
By having two ends of the fuse exposed to the expanding flame front within the shell, ignition of the Go Getters is improved and more initial thrust is generated due to the two points of ignition.
Construction of a Six-Inch Round Go Getter Shell
A round Go Getter shell is constructed much like any other ball shell of comparable size with a few minor differences. The time fuse is cut to allow a delay of about 4 seconds between cross matching. A fuse extender made from three turns of 30 Lb. Kraft paper is rolled on a suitable former and only pasted on the last 1/4" or so of the trailing edge, just enough to keep the tube from un-rolling. The tube is then slipped over the cross-matched end of the time fuse and securely taped in place (remember, at this time you only cross-match the end of the fuse that goes inside the shell). The fuse is glued into the hemisphere and the fuse extender is cut off so that it just reaches the center of the shell. Two or three pieces of thin black match are inserted into the extender tube to quickly transfer fire from the cross match to the center of the shell (just like building a regular chrysanthemum shell).
The Burst
There are two theories behind the burst charge for Go Getter shells. The first is to use a relatively hard burst to scatter the stars and let them swim back toward each other. Since the stars are placed randomly in the shell, and they are not smart enough to know which way to go, the result is a big boom and Go Getters scattered all over the sky, with the distinct possibility that some of them will be driven toward the ground hard enough that they will not burn out before impacting the earth. My preference is to use a soft break, only strong enough to open the shell and light all of the stars. Meal powder on rice hulls works well for this purpose. A 3:1 or 3.5:1 ratio of meal to hulls works very well. Remember, they are self-propelled stars and don't need to be blown all over the place with your favorite "atomic" flash burst.
Putting It All Together
Two pieces of tissue paper are cut of sufficient size to line the shell hemispheres with enough left over to fold across the top of each shell half to hold the contents in the halves while assembling the shell. A hole is pierced in the center of one piece of tissue and the tissue is inserted over the time fuse and smoothed out against the inner wall of the hemisphere. The second piece of tissue is placed in the other half in a similar manner except for the hole for the time fuse. The Go Getters are then placed against the inner wall of the shell about half way up the wall. Care must be exercised not to obscure any of the fuses. Burst is now poured in to fill all of the crevices between the Go Getters. At this point, just enough burst is used to fill the crevices and leave a thin layer over the already placed stars. Stars and burst are added in alternating layers until the hemisphere is full. Remember to keep forcing burst into the crevices between the Go Getters as this is the only way to ensure shell integrity. The extra tissue that has been hanging over the edge of the shell and getting in the way is now folded toward the center of the shell, secured with a couple of pieces of masking tape. The other shell half is finished in the same manner and the two halves are joined using your favorite shell glue.
As was discussed earlier, you do not need a hard break for Go Getter shells. Consequently, you do not need to paste endless layers of paper on the shells. Four to six layers of 60 lb. Kraft paper will suffice. After pasting, the shell is finished in the normal manner with the final cross match, lift and leader. Good luck and SAFE SHOOTING!
MORE ON COLORED GO GETTERS
Subsequent to writing the original article, I have done some additional experimentation as explained below.
Colors and Catalysts
I didn't realize when I first started making the blue Go Getters that copper acted as a catalyst to increase the burning speed of the composition to make a more lively star. It is therefore quite easy to shift the color toward either purple or lavender by substituting the proper amount of strontium carbonate for some of the copper carbonate to achieve the desired color.
Other colors require a different approach since copper compounds are out of the question due to the blue tint imparted by them. The answer to this quandary may be found with the High Power Rocketry people. More specifically, an article in the Journal of Pyrotechnics # 3 entitled "Ammonium Perchlorate Composite Basics" which discusses, among other things, burn rate modifiers which may be used to control the burning speed of ammonium perchlorate propellants (remember, these Go Getters are baby rockets). Due to time constraints, little research has been done by this author on the suitability of these catalysts, but red iron oxide seems like a likely candidate.
Fuse Alternatives
While Thermolite makes an excellent fuse for Go Getters, its limited availability and high cost discourage its use in any but the smallest of projects. The most promising solution is to use an alternate form of fuse. My first thought was to use an H-3 based fuse (potassium chlorate and air float charcoal), but this is not a viable alternative due to the double decomposition reaction between ammonium perchlorate and potassium chlorate resulting in the formation of the rather sensitive ammonium chlorate (Lin Collins, private communication, September 1995). The next logical choice would then be match based on KP burst (75% potassium perchlorate, 15% air float charcoal and 10% sulfur with 5% additional dextrin). Because the perchlorate isn't particularly soluble in water, you end up with a slurry which must be stirred from time to time while the match is being made. Five strands of single ply cotton string works well for this purpose (you want a fairly small diameter match, like the black match used for cross matching). The slurry must be thoroughly worked into the string before it is drawn through the sizing orifice. When the KP match is dry, cut it into lengths of approximately 1 1/4" or so and insert them about halfway into the filled tubes as you would with Thermolite.
[edit] References
David S. Johnson's "Go Getters" July 1989 Attributes his work with go getters to an article by Troy Fish "Green and Other Colored Flame Metal Fuel Compositions Using Parlon" published in Pyrotechnica VII (the green issue) May 1981
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