Motor Ejection and Dual Deployment

Hi, Maybe this is a super simple question but I havent been able to find a direct answer yet. I'm building my first dual deployment kit and have understood the basics, but the one thing I havent been able to figure out is with the ejection charge that comes with the motors. I assume with a drogue charge and the main charge set up that you're just removing it from the motor set up?

Not finding a direct answer is understandable. There's not really One Way to go about it

You can remove it if you want and use it for the drogue charge. (folks that retain their motors through the forward closure will do this) (And if the motor's delay isn't long enough to reach apogee, definitely take it out)

Many folks will just leave it in with the full length delay and use it as a kind of backup if their apogee charge fails.

Many use altimeter based dual deployment because of better accuracy and control of deployment . Specifically,you can set drogue deployment at apogee or a few seconds later. Also, if you use 2 BP drogue charges, one can be set to fire before the other to more ensure deployment via this redundancy. In addition, depending upon conditions (e.g. high winds or not) you can set the main deployment at a lower altitude to prevent too much wind based drift.
When relying on motor ejection only (single deployment), unless you have experience with drilling the ejection charge, the ejection charge is approximate and if too early can cause shredding of parachutes and if too late, a hard possibly damaging landing. Some commercial motors have long delays that even with drilling are too delayed to sustain a safe recovery.
Some also do altimeter based deployment and also utilize the motor ejection as a back up to the altimeter based drogue deployment.
I hope this helps.

Fred, L2
ICBM,S.C.
KG4YGP

Nytrunner said:

Not finding a direct answer is understandable. There's not really One Way to go about it

You can remove it if you want and use it for the drogue charge. (folks that retain their motors through the forward closure will do this) (And if the motor's delay isn't long enough to reach apogee, definitely take it out)

Many folks will just leave it in with the full length delay and use it as a kind of backup if their apogee charge fails.

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that's what I do, use the full length motor delay as a backup. That means it's the drogue in the bottom with the main on top which seems counterintuitive but it's fine. If the drogue deploys at apogee you'll see a puff of smoke from the motor sometime later depending on the delay.

if the altimeter fails to deploy the drogue at least you have a fighting chance getting your rocket back in salvageable state.

I always use the motor as backup if possible. (Later than apogee, usually full delay.) I use more BP in the backup motor charge than I use in the apogee charge to make sure it separates if nothing else.

I never use the motor as back up. I just leave the powder out when flying DD.

Handeman said:

I never use the motor as back up. I just leave the powder out when flying DD.

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I agree. Too many inaccuracies in terms of ejecting at apogee +/-. I am going with a fully redundant Altimeter setup, but my Level 2 rocket is 4” diameter so I have quite a bit of room to deal with.

If you decide to skip the motor charge you still put the delay element in the motor; just skip pouring in the powder. Without the delay element you have an open path at the top of your motor and very bad things will happen. I always use the motor charge as a backup.

Zeus-cat said:

If you decide to skip the motor charge you still put the delay element in the motor; just skip pouring in the powder. Without the delay element you have an open path at the top of your motor and very bad things will happen. I always use the motor charge as a backup.

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Agreed on the delay grain! I’m using a plugged forward closure. Otherwise there’s a hole between the motor casing and the parachute area of your booster, no?

Ben89 said:

Hi, Maybe this is a super simple question but I havent been able to find a direct answer yet. I'm building my first dual deployment kit and have understood the basics, but the one thing I havent been able to figure out is with the ejection charge that comes with the motors. I assume with a drogue charge and the main charge set up that you're just removing it from the motor set up?

Click to expand...

As long as the motor’s ejection charge goes off near the apogee or after, there’s nothing to worry about.

i fly motor back up and as others have said, typically have it "set" to go off well after apogee as to not risk two simultaneous charges.

a motor back up saved my Caliber ISP a few weeks ago. failure to re-arm the altimeter after taking the rocket off the pad was 100% my fault. resulted in a small zipper as the event was WELL after apogee, but it surely saved the rocket.

g.pitts said:

Agreed on the delay grain! I’m using a plugged forward closure. Otherwise there’s a hole between the motor casing and the parachute area of your booster, no?

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I was going to recommend the plugged forward closure and as advised from this forum I would install the delay element so there is no gap in your forward closure to cause some type of CATO

Mrgbus said:

I was going to recommend the plugged forward closure and as advised from this forum I would install the delay element so there is no gap in your forward closure to cause some type of CATO

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That’s correct. Build the motor as recommended by AT or CTI including the delay grain, just omit using the black powder ejection charge (there’s no place for it anyway with a plugged forward enclosure).

The plugged forward closure ensures that no gasses can escape into the booster of your rocket since the delay grain is a pyrotechnic, which could damage your parachute.

And sometimes the rockets especially min diameter designs out fly the delay element time delay and must use electronic dual deployment only without the motor ejection.

g.pitts said:

That’s correct. Build the motor as recommended by AT or CTI including the delay grain, just omit using the black powder ejection charge (there’s no place for it anyway with a plugged forward enclosure).

The plugged forward closure ensures that no gasses can escape into the booster of your rocket since the delay grain is a pyrotechnic, which could damage your parachute.

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Fill the powder well with grease & tape closed.. Use the delay element, but seal it up. That's what I've been told. Done it once earlier this year with no adverse effects..

east coast, which means nowhere to fly MD to it's fullest potential.
I just leave em in and go long....pops long after apogee, but hey...if your altimeter doesn't you still have a chance...

dr wogz said:

Fill the powder well with grease & tape closed.. Use the delay element, but seal it up. That's what I've been told. Done it once earlier this year with no adverse effects..

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I may be in the minority with my opinion, and I’m certainly not saying that anyone is wrong. In my opinion this gets into risk mitigation. It’s betting against enough thermal energy getting to and liquefying the grease, and then penetrating the booster section. Will this idea work? Most of the time perhaps.

For me, I’m betting on my sealed forward closure.

Don’t even need grease. Fill it with dog barf and seal with tape.

Don't even need dog barf, just leave the powder out and fly.

I remove the BP from CTI reloads and don't use it in Aerotech reloads. Fully redundant electronics (2 altimeters) is the best way to go.