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Rocket development update, and a quation


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Question* (doh!)

Some of you showed slight interest in my work, and since not much is happening, I decided to post last test and some pics of these short motors I researched.
Stuff I changed and modified since the last time:
1. Use De Laval nozzle
2. Put a cross of BM on each end of the grain, to ensure ignition(Now thrust graph looks like it should), and seal it in tape, to prevent epoxy sticking to it, and it getting moist.
3. Instead of gluing plugs in the tube, then drilling holes into them through tube, and putting epoxy-concrete powder mix into them, to lock them in, using screwdriver I make lots of tiny holes inside the tube (Figure 3), and make grooves in the plugs, so when I glue them in, epoxy-concrete mix gets into these spaces, locking them in, eliminating need for making these retainer pins, reducing cost, and manufacturing time. Point of mixing epoxy with concrete powder is diluting epoxy (it's damn expensive), making it harder, and more heat resistant.

Motor performance:
It = 28.6 N/s
Isp 71.5 s
Burn time = 1,17 s

I pretty much perfected the technology behind this motor, and there is no point in making these motors, as they have poor mass ratio, and pretty low power, so I retired these motors, and I want to move onto making rockets of this kind, just with multiple grains, I used in this rocket. First i'm gonna do 2 grains. The tube, top plug, and grains are going to be the same, only thing which will be designed specifically for the new motor is nozzle, now the question is, How should I shape it? I'm going to use 45 and 15 degrees (from the axis of symmetry) convergent-divergent nozzle, but how long should I make it? The ID is 30 mm, and length of nozzle I used in this video is 20mm, so how long should I make my nozzle? 25, 30 mm? is making it longer increase the efficiency, to outweigh extra mass?

Edited by Oinikis
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