This is my first Kn/Sorbitol motor. It uses 1 1/8" OD Aluminum tubing with .058" wall. The nozzle is steel with an aluminum closure. Nozzle and closure are sealed with silicone O Rings.
Above is the motor after firing. No throat erosion was evident. The motor burned for .75 seconds. No test data is available. Motor was very "hot" after burn. A liner may be required.
This work is a search for an inexpensive "sport propellant" with low burn temperature to allow for use with re-usable steel nozzles as in the motor shown above.
These were bored with .25" bore on a lathe. Formulation was as follows:
Kn 70%, Epoxy and hardner 20%, Magnesium 600 Mesh 8%, DOA 1%, Red Iron Oxide 1%. Formulation was very "dry" but compressed well. Resulting propellant was reasonably elastic, not hard or brittle.
Motor was made of 29mm phenolic tubing with phenolic nozzle (RCS). Each grain segment was separated by an "O Ring". End closure was with a 1/8" phenolic disk and .75" of epoxy. Motor built with five (5) 1 1/2" segments. Throat diameter is .180" Kn will range from 450 to 560 during burn. Past results with epoxy/Kn (No Magnesium) required Kn of 900-1000. Magnesium should increase burn rate. This motor is expected to perform at low pressure and be a basis for future, higher pressure motors. Test stand results to follow.
Phenolic nozzle epoxied into motor tube
Nozzle, O-ring Separators and Phenolic Disk End Closure
The Motor was assembled with an O-Ring separator between each grain. The top grain was separated from the Phenolic disk by an O-Ring. Epoxy was then poured over the Phenolic disk to a depth of .75".
Epoxy End Closure
After all the segments were placed inside the motor tube the Phenolic disk was placed at the end of the last segement, separated with an O-Ring. Epoxy was then poured over the Phenolic disk.
Epoxy Motor Test Results - Test Motor TM001EP
Motor was fired on test stand on 1/19/03
Outside Temperature was 34 degrees F - Motor was ignited with homemade Kn/Magnesium/epoxy ignitor - Motor lits quickly and began a series of 50 high speed chuffs - Chuffs were on average about 1/2 seconds duration building from 8 pounds thrust to a high of 25 pounds thrust, and then fading progressively lower to zero. Burn lasted over 30 seconds and badly overheated the phenolic casing. The phenolic nozzle has surprisingly little erosion. The casing was badly burned due to the long burn time. Kn was as expected, too low. I have the burn results available on a dataq file if anyone may be interested.
Conclusion
Kn was purposely set low for this motor to avoid a destructive CATO (my test stand took too long to get going to take a chance). I plan to test again with a reloadable motor and steel nozzle much like the one used with the Sorbitol motor shown above. Results will follow.
Motor TEST001EP During Burn