JimJarvis50
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Hi Jim,
Thank you for taking the time to write up such a detailed response. Your efforts did help to explain a lot of issues. I still have a few more questions if you don't mind.
You stated that the interstage is the weak point in a two stage rocket. Others on this forum have complained about their interstage's without stating the problem. Would it be better to replace the interstage tube with a carbon fiber one in the fiberglass rocket? Do you have a better technique to wrap the interior of the fiberglass tube with carbon fiber? I have used carbon fiber socks on the exterior of tubes with great success. The only way I could see wrapping the inside of such a narrow diameter tube would be with multiple strips of material.
Do do you place any gas vent holes in the upper end of the interstage? One of your great photos shows a band of blue painters tape securing the ignition wires to the aft end of the sustainer. Do you do anything to prevent the red motor nozzle cup from sliding off? Do you have any problems with ignition wire sliding down out of position in the sustainer motor?
Do you install a seperate switch above and beyond the altimeter power switch to break the sustainer ignition wire connection?
How much of a time delay do you use between the black powder interstage separation and ignition of the sustainer? Have you ever had the black powder charge damage the ignition wire for the motor?
Would you like to write a book? I loved your high power high altitude launch videos.
Thanks,
Bob
Getting a carbon coupler for the interstage would be just fine as long as it matches with the fiberglass tube. When I line the inside, I just use one wrap at a time, overlapping a bit, but a carbon coupler would be better.
No vents in the interstage. Generally, the little red caps stay on just fine. The picture was taken quite a while back, and I now an more aggressive in protecting the wiring from the separation charge. On the other hand, I've done it the way shown in the pic many times with no problems. I typically use a separation charge of 0.3 g of black powder. On these smaller motors, the igniter doesn't move much, but I use a stick to support it for 75/98 mm.
I use two switches beyond the power switch. The circuit is shown below. I turn on the altimeter first - no continuity. Then I close the switch that opens the path to the altimeter. There is a continuity tone. Then, I open the shunt if everything has powered up correctly. Shunts must be short, use heavier wire, and must be ground tested using the actual lengths of wire for the igniter. It is best to avoid Lipo batteries, as the amount of current they provide can overwhelm the shunt and/or burn it out. Unfortunately, the Easymega only uses Lipo's, so it's best to use a smaller Lipo for the firing battery. Also good to minimize the firing time to as short as possible.
The timing just depends. I often separate the booster a second or so after burnout. Sometimes, I let the rocket coast together and then separate after the velocity drops a little. I have found that waiting until the rocket slows to Mach 1.3 is usually OK for my carbon rockets. I previously laid out criteria for lighting the sustainer, so the coast time would be the time between the two events.
I might also mention that the way the Easymega and/or Raven gets programmed for staging is an art by itself. Ask about that when the time comes.
I've written several articles on carbon fiber construction, but not on staging. However, everything that I have ever done is documented somewhere in this forum.