APCP Burning Characteristics in REHAB
Sirs,
I watched your REHAB test today with extreme interest. As per some of the other comments regarding the pressure inside the REHAB chamber I question the ability to maintain a high vacuum after the igniter fired. Both the Aerotech and Cessaroni motors use Ammonium Perchlorate Composite Propellant (APCP) which has a positive coefficient of burning with respect to pressure. In other words the higher the pressure inside the motor the faster the propellant burns.
This would explain both the failure of the Aerotech motor to remain lit and the long delay between igniter activation and the full power burn of the Cessaroni reload. The Aerotech apparently burned, but not fast enough to bring the pressure inside the casing up to normal operating pressure before the heat leached away into the motor's casing. The Cessaroni motor on the other hand uses a thick plastic, instead of a cardboard, liner so the heat was retained until the pressure in the chamber increased enough for the motor to start operating at normal internal pressure.
I'd suggest adding a large pressure tank between REHAB and the vacuum pump to maintain the low pressure inside the chamber once the pump is isolated. In addition I would look into adding a burst diaphram to the motors. A simple disk of copper or aluminum made from 0.002" shim stock, with a hole just large enough for the igniter, could be added to the Aerotech motor between the nozzle and the propellant grain for example. You could also experiment with a smaller nozzle on the Aerotech motor. I would contact Aerotech and ask Gary Rosenfield if you could obtain a number of un-drilled nozzels for the 32/60 reload casing. I'd start by reducing the nozzel's exit area by about 50% and then proceed based upon tests in REHAB.
Respectfully,
Kenneth G. Holloway