HPR Two Stage Questions

I'm thinking ahead to a 4" OD HPR two stage design. Problem is, I'm not really sure about the changes in construction techniques needed to couple the booster to the sustainer. I doubt that Estes Pop and Go type coupling will work (I know that electronics are necessary for second stage ignition).

Anybody got a link to a HPR two stage kit's instructions (or a link to a build thread for someone's scratchbuild)?

Thanks!
Jim

https://www.publicmissiles.com/PMLStagingFAQ.pdf is a good place to start. The PML stuff is a little old-school but gives you a good idea of how the typical interstage works.

You can also build a very capable two-stage HPR rocket with a simple interstage coupler (sans electronics): https://www.rocketryforum.com/showthread.php?21235-Two-Stager.

The real trick lays in getting separation and recovery regardless of sustainer ignition. Sometimes you are simply going to get a bum ignitor up there, and it will be a little late to change it.

I use a separation charge wired along with the upper stage igniter.
It gets you an extra 250+ ft of altitude.

JD

Think about your interstage. 4" is that transition size between smaller rockets and big ones. There are really two ways to go:

1) coupler interstage, you can use a traditional coupler or the second stage motor if you don't mind it hanging behind the rocket (common in minimum diameter two stagers)

2) Rod interstage, have four rods made of carbon or aluminum, (stainless if you are building something big and heavy).

I've been dabbling in minimum diameter stuff for the last few years so I use the upper stage motor. But 10 yrs ago I built my Nike Corona rocket that was a 7.5" booster to 6" sustainer. The interstage consisted of four stainless steel rods .5" diameter. Heavy, yes. But it was far from a performance rocket. [video=youtube_share;T5Gdt0pxDwQ]https://youtu.be/T5Gdt0pxDwQ[/video]

I agree with others separate actively before lighting the second stage.

I wanted to say thanks for all the replies...

Sorry I was a little slow on doing that. I've been packing to move, and when I'm not loading boxes, I'm pretty beat. Today I kinda got the day off as I had an appointment.