2-Stage MPR class 1?

[Saint_Tiki]

Hello. Thinking about making a 2-stager for the fun and challenge of it. Would be keeping it low, visual recovery regime. Just trying to figure out if I can do this and still be a class 1 rocket at a mid-power launch? I'll be below the weight and propellant weight limits. Should be good then?

Here are my current thoughts on the project. Let me know if I'm missing something.

LOC 2.6" air frame, keep the weight low.
Booster, no electronics, motor deploy, chute release as required based on altitude
Sustainer will probably have a raven altimeter since it can do everything I want in one package
Pyro charge for staging because it's fun
Sustainer motor probably CTI for better ignition reliability
Probably a G to F launch
Upper stage dual deploy

How do people normally run wiring the length of the fin-can from the AV bay? My thought was to have maybe an aluminum tube or something that runs the length through the motor rings with some terminals on the end. I also need to figure out how to disconnect the wiring from the AV bay and the fin can during separation, or else have 8 feet of wiring along the length of the shock cord. I could use banana connectors or something and just wear them in a bit so they don't fit too snug? Any other usual solutions?

 

[waltr]

I have a 2-stage that meets the Class 1 weight limits (<1.5kg).
This was built from 2 BMS 3" school rocket kits. The short one for the booster and simple motor eject.
The long kit for the sustainer with an Eggtimer Proton for Separation charge, sustainer ignition (CTI motor), drogue deploy and cable cutter for main.

Biggest issues I had was obtaining plenty of velocity from the booster for the rocket to keep going up and not tilting over waiting for the sustainer motor to come up to pressure.
Tried an F67W but not enough velocity. Then G74 which is just enough if sustainer motor does not take too long to light. Started with AT D15T in sustainer but moved to CTI F & E motors. Had one D15 take 4 seconds to light with bad results (rocket had arced over). The CTI have been lighting in about 1 second.

Do LOTS of simulations with various delays on sustainer ignition times.
Ensure there is plenty of velocity at booster burn out. I have been going for a minimum of 100ft/s at 1-2second after burnout.

Go to Eggtimer's web site and download his Proton user manual. near the end is a great discussion on staging/airstarts that apply regardless of the controller.

Have you done any Dual Deploy?
If not I recommend learning to relaibly have DD working. That is much to go wrong in DD and much more with airstarts. If you have DD working well then do go for airstart. It is challenging but great when it all works.

 

[Saint_Tiki]

I have a 2-stage that meets the Class 1 weight limits (<1.5kg).
This was built from 2 BMS 3" school rocket kits. The short one for the booster and simple motor eject.
The long kit for the sustainer with an Eggtimer Proton for Separation charge, sustainer ignition (CTI motor), drogue deploy and cable cutter for main.

Biggest issues I had was obtaining plenty of velocity from the booster for the rocket to keep going up and not tilting over waiting for the sustainer motor to come up to pressure.
Tried an F67W but not enough velocity. Then G74 which is just enough if sustainer motor does not take too long to light. Started with AT D15T in sustainer but moved to CTI F & E motors. Had one D15 take 4 seconds to light with bad results (rocket had arced over). The CTI have been lighting in about 1 second.

Do LOTS of simulations with various delays on sustainer ignition times.
Ensure there is plenty of velocity at booster burn out. I have been going for a minimum of 100ft/s at 1-2second after burnout.

Go to Eggtimer's web site and download his Proton user manual. near the end is a great discussion on staging/airstarts that apply regardless of the controller.

Have you done any Dual Deploy?
If not I recommend learning to relaibly have DD working. That is much to go wrong in DD and much more with airstarts. If you have DD working well then do go for airstart. It is challenging but great when it all works.

Thanks waltr.

I did my L1 about 2 years ago and converted that to dual deploy. It's a 3" scratch built MAC rocket. I got the dual deploy sorted out with that so I'm confident in the electronics side of things. Several successful launches on it. Haven't launched in a while so it'll be a little bit before I get this project off the ground as I get back into things. Leaning towards a Blue Raven altimeter, 4 channels, tilt lockout, etc. Probably launch it single stage with DD first.

I've since moved from the mid-west where the recovery area was vast and the waivers are near limitless... to the east coast where it's harder to find a good site nearby. Closest HPR site is 4k' ceiling. That's fine, I like a good challenge.

My sim assumptions are motor ignition at burnout + 1 second but the reality is I'll likely program the air-start for 0.25s delay. I've got a hobbyline 40-120 and the G76 reload for that thing absolutely KICKS off the pad. If I'm not mistaken, it's got the most initial kick of any mid power motor at nearly 150N then dropping steadily. It's a very favorable thrust curve in my opinion. The sim currently has me with an off the rail velocity of 55fps, peak of about 310fps on the first stage, and min of about 200fps when the 2nd motor lights at +1 second. Also been messing with various wind and launch angle parameters to see how that affects the verticality of the sustainer at ignition. My G to F initial plan has it under 2k peak altitude.

 

[Titan II]

I typically use aluminum tube through the fin can. No terminals anywhere. For the break wires read this:

https://www.rocketryforum.com/threads/how-to-break-wires.177885/#post-2389940

 

[Saint_Tiki]

I typically use aluminum tube through the fin can. No terminals anywhere. For the break wires read this:

https://www.rocketryforum.com/threads/how-to-break-wires.177885/#post-2389940

Awesome. Simpler is usually better. Makes it easy to replace wires if they get corroded or damaged. Thanks for this.

 

[waltr]

Ok, you've done DD so go for a 2-stage airstart.
I also like the G76 for quick off the rail.

I used 1/4" cardboard launch lug tubing through CR to get igniter wire to the sustainer motor. This or aluminum, whichever is lighter will work.