- Dec 30, 2003
- Reaction score
Heh. I bet!Originally posted by Joe Burger
It is called the J825 and is on engineering hold. This motor has big bugs to work out.
Without divulging company secrets, can you tell me if I'm on the right track:
Erosive burning. This is a huge one. The motor is very long, so the gasses are moving pretty quick at the nozzle end, shearing off propellant from the aft few grains. To combat this, you could either put a "slow redline" propellant in the load, as you do "slow WL" with the J570 (possibly needing another TMT testing becasue of a different formula!). Another way to combat erosive burning would be to make the aft 2-3 grains have a larger core, letting the gasses expand, thus slow down at the aft end, reducing erosive burning. There could be problems with the larger cores, however. If the cores were not exaimened, the directions read improperly, or people simply did not realize that the 2 or 3 grains with the larger cores need to be at the bottom, KABOOM! There would be no way to prove they installed the propellant improperly, so you would have to reimburse them.....
Also, with the longer motor length, the aft grains get a considerable compression force acting on them. This could lead to the grains cracking, increasing surface area and, again, KABOOM! This is espically important for AP based propellants, as they are "spongey" (a la Spongebob propellant by Ellis Mountain), and have less of a compressive loading ability before they crack as opposed to brittle propellants (candy).
Plus the fact that redline is a fast propellant by nature, so there would be a greater buildup of pressure in the case, and you may not be able to make the nozzle throat wide enough to make up for the insane pressure. If you were able to make the throat wide enough (which I imaine you could), you would have a less than ideal expansion ratio, limited by the 38mm OD of the nozzle, making the propellant inefficient. A way to lower the pressure would be to decrease the Kn of the motor. This would entail longer grains, and I assume all AT 38mm grains are the same length, so a different machine may be needed if you were to make the grains longer. This would also lead to a progressive burn, a thing not all too common in AT motors.
That's just my brainstorming, though......