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The following is a web page of a document given to me by Eric Hunkins. After some reflection, he said that distributing it would be the proper thing to do. Other than formatting and titles, this document is by Eric and should be credited to him.
Here is the partial text of one of our emails that explains why he went down this design path:
The problem with whistle rockets has always been the thrust curve. They have a very short, powerful one, but after that, there is nothing. The multi core designs are just an effort to extend the thrust curve. Straight or parallel cores make louder whistles and tapered cores a bit less. The idea was to keep as much of the walls of the core as parallel as possible, extend the core, but not make so much surface area available at one time to cause failures. The tri-core was the result of that thinking. I also have a quad core for 1lb but I don't remember if I ever tested it, so I didn't include it.
My guess is that the ultimate lifting whistle rocket would be a tri-core made with no catalyst that had an end burn of a catalyzed mix.
Good luck, have fun.
References to ‘Current New’ and references to ‘your design’ are from the design used to do the whistle catalyst testing (see: http://www.creagan.net/fireworks/rockets/whistletests.html ) Dan Creagan, December, 2006
Whistle Rocket Core Design
Notes on Core designs Eric Hunkins 12/5/06
The “Pusher” design was create by Scott Found around 1982 and was used by him, Don Mueller, me, and Tim Feider until around 1987. I believe Scott is no longer in Fireworks, and I haven’t talked to Tim in several years. This design was used for PGI competition in 1984 and 1985. This design was used in 4oz, 1lb, 4lb, and 6 lb sizes.
The tri and quad cores were developed by me around 1988. These rockets were all made without catalysts or oil and were made using 72.5% KCLO4 and 27.5% Sodium or Potassium Benzoate. Sometimes up to 3% sponge titanium was added. These rockets were pressed on a press. Unfortunately I can’t tell you what the loading pressures were. I sold my original press many years ago and we never recorded the pressures.
From memory I believe the 4oz pusher version lifted 350 gram 3 inch can shells for the payload. The 1lb pushers lifted up to 600 gram shells. For competition the 4lb versions had 6” and 8” ball shells for payloads. The Tri-core #2 1lb version lifted 750 gram shells.
Tubing was commercial available paper rocket tubes. Later we went to phenolic tubing for all rockets.
The purpose of the Tri and quad cores was to elongate the thrust stage. As you probably already know the whistle rockets are very peaky. Once the core burns there is very little lift generated because of the lack of nozzle.
Below I have listed the 4oz and 1lb pusher designs and an extrapolated 5/8 version. Listed is the Tri core #1 and Tri-core #2 and an extrapolated tri-core for 5/8” I also included your current “New” design. You will notice that all of designs contained a 1” space at the bottom of the tube. We found that this was required for whistle resonance and all designs have it including the 4oz.
The tri-core spindle I have has a removable steel pin for the top core. I had several lengths of pins for the different mixes I used. Shorter pins for hotter mixes.
I also included a graph of the expected thrust curves. This is simply based on surface analysis and is only included to give you an idea of what the goal thrust curve for the tri-core should look like and how in compares to what you are using now. The tri-core spindle also has a 45 degree chamfer where the core sections meet. I didn’t put this in the drawing.