Single Alt/Timer Fired BP charge..DUAL Deploy??

Just wondering...for my first DD rocket, I was thinking that I'd use regular motor delay/ejection charge for the drogue and then have the alt or timer(still thinking that one over) to fire the main.

Is that common...or do most people use plugged motors & dual-event altimeters & two e-matches? That sounds more expensive and a bit 'riskier'.

Am I missing something?

i would test you altimeter by doing single deply with motor backup just to get the hang of it. Then you can use the BP fromthe motor and fill the well with vaseline or used aplugges closure.

thanx, Ben

I actually did it the other way around the first time. I planned to have the charge in the motor eject the main and the altimeter deploy the drogue at apogee. I used a longer delay than I would ordinarily use for the motor / rocket combination so that the main would deploy sometime after apogee. Unfortunately the delay was quite a bit shorter than it was supposed to be so both the drogue and main were deployed near apogee.

Agreed.

You do it the other way around. Use a long delay that provides a "past apogee" backup deployment charge. Use the altimeter as the main deployment at apogee.

-Tim

HUH??

I don't get this....there's no way you can get a motor delay long enough (or accurate enough) to eject your main chute @ 300-500'.

What I'm imagining is that the motor/delay fires at apogee...pop goes the drogue....then either the altimiter fires the main chute when it hits the right altitude or a timer does that after "x" seconds.

Originally posted by JJI
I actually did it the other way around the first time. I planned to have the charge in the motor eject the main and the altimeter deploy the drogue at apogee. I used a longer delay than I would ordinarily use for the motor / rocket combination so that the main would deploy sometime after apogee. Unfortunately the delay was quite a bit shorter than it was supposed to be so both the drogue and main were deployed near apogee.

Click to expand...

Sorry for the confusion...

The motor delay will only work as a back up to your drouge deployment. It is possible that you do not use the altimeter or timer as the apogee deployment main event, but usually this comes for "free" (unless you have a single event timer).

If you only have a single event timer then yes, motor delay deployment for drouge followed by timer delay for main will work fine (although no back up in either case).

If you don't have a single event timer and you are still contemplating an electronics purchase, I would just get a dual event altimeter. It is much more consistent and reliable than getting the motor delay to work right at apogee and getting your timer to fire the main at just the right altitude.

-Tim

Originally posted by Deandome
HUH??

I don't get this....there's no way you can get a motor delay long enough (or accurate enough) to eject your main chute @ 300-500'.

What I'm imagining is that the motor/delay fires at apogee...pop goes the drogue....then either the altimiter fires the main chute when it hits the right altitude or a timer does that after "x" seconds.

Click to expand...

Remember - there are no wrong ways to do this..... or right ways. But there are different ways and each different way has worked for different people.
The way you describe it is how I got my L2.
A stock PML Tethys with 2 grain CTI for L1.
Then for L2, I added a PML 18" payload bay. I built a Transolve P6K for the altimeter into a module in the payload bay. It only handles the main deploy. The motor still did apogee deploy.

For testing, you put the main where the drogue would normally go for DD config and let the motor ejection blow out the main at apogee. You fly low enough that it will not drift off with the main at apogee (I used an AT I200W). And then you see if the altimeter does its job right by blowing the nosecone out that has its own separate chute at the specified altitude (NC NOT attached to the rest of the rocket or payload bay) This is where the main would normally go in true DD config.
If the altimeter doesn't work, so what!! The NC stays in the payload bay and comes down under the main that was deployed by the motor eject. If you did everything right and the altimeter blow out the NC at the specified altitude, it just returns separately, but at a low altitude.
Once proven, I used a CTI 5 grain for my L2.
Good Luck.

More Tethys mods/info here:
https://www.rocketryforum.com/showthread.php?s=&threadid=10636&perpage=20&pagenumber=3

I believe (based on nothing <grin>) that you should go for full dual deployment on the first electronics flight, using motor backup for the drogue. You use a long delay in the motor, and expect the altimeter to deploy your drogue at apogee and your main at a lower altitude.

I certainly would not fly it with just the main connected to the altimeter, using motor deployment alone for the drogue. If you have an altimeter in there anyway, why not use it for both? It will give you a more accurate and reliable apogee deployment than the motor delay will.

The main advantage that an altimeter has over either a motor delay or a timer for deployment is that it detects apogee - you're not just guessing at where apogee will be. The altimeters we're using are reliable.

I suppose if you're really nervous about it, you can use motor ejection for the main on a low flight, as others suggest, but I trust the altimeter at least as much as I do motor ejection.