Recovery system- will this work?

[brentius]

Basically, the idea for my recovery system for my L1 is to have some sort of piston ejection. The piston (green) gets forced forwards, until it runs into the coupler and stops. This pressurizes the top segment, which forces the nosecone out. The parachute is tied to a loop in the shock cord, so it gets tugged out by the NC. WIll this work, or will I have to reconsider the recovery system? Thanks a lot.

 

[lakeroadster]

View attachment 633494

Basically, the idea for my recovery system for my L1 is to have some sort of piston ejection. The piston (green) gets forced forwards, until it runs into the coupler and stops. This pressurizes the top segment, which forces the nosecone out. The parachute is tied to a loop in the shock cord, so it gets tugged out by the NC. WIll this work, or will I have to reconsider the recovery system? Thanks a lot.

You'll need some way to vent the pressure that's trapped behind the coupler, otherwise bad things may happen to the Piston.. or the Body Tube.. or the Motor.​

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None of this is needed. K.I.S.S.​

 

[brentius]

You'll need some way to vent the pressure that's trapped behind the coupler, otherwise bad things may happen to the Piston.. or the Body Tube.. or the Motor.​

​

None of this is needed. K.I.S.S.​

I understand, but I'm a bit worried about the ejection charge itself not being powerful enough to force the NC out.

 

[lakeroadster]

I understand, but I'm a bit worried about the ejection charge itself not being powerful enough to force the NC out.

Then run a stuffer tube from the motor mount up toward the recovery bay. You can always do a static test on the ground to prove the concept.​

 

[Banzai88]

I understand, but I'm a bit worried about the ejection charge itself not being powerful enough to force the NC out.

Ground test

 

[cbrarick]

I bet you're worries are unfounded.
go here https://rocketrycalculator.com/rocketry-calculator/bp-estimator/
or any other calculator.

most H motors have 1.3 grams of black powder in their kits

you could, of course test this. Stick a used motor in the mmt. use one of your spent g's or if you use hardware, just tape the forward end
run a ematch to a glove finger with the calculated amount of be out the vent hole, connect it to a long piece of wire (far enough to be safe) and then hit it with a 9 volt battery.

Your idea is unnecessarily complicated and unlikely to work. Smashing pistons into couplers intentionally will cause damage and also not solve anything. There's a reason why nobody is doing this. However I love your attempt to think outside the box.......

 

[Tractionengines]

Pistons work well in some types of rockets or situations, but they cone with their own challenges:

* They MUST slide easily. (fit changes with temperature, so ALWAYS check right before flight.)

* You MUST clean the residue from the body ID / piston OD every flight. (Looks like yours is captive between Motor mount and coupler. So will not work. Unless the coupler is removable in some way.)

* (as noted earlier) If you don't eject the piston completely from the body. Then you NEED to have a significant vent port uncover near the end of travel to quickly vent the pressure. Also what ever "stops" the piston needs to absorb all the remaining kinetic energy. ( It's easier to just eject the piston.)

* It's still MUCH BETTER to ground test your charges, even with the piston, than just guess, or rely on calculators. (Some places that's not an option, but try to find a way.)

(* Be ready for lots of people to tell you how bad pistons are, and listen to stories of failures, etc. REMEMER they're entitled to their "opinion"...)

[ Edit to add: " WIll this work, or will I have to reconsider the recovery system?" As-shown. NO THIS WILL NOT WORK.]

 

[David Schwantz]

This will not work. The amount of area to be pressurized by the piston will not provide enough compressed air to eject the NC with enough force to pull out chute. if NC does come out, it may just dangle and beat into body tube.

 

[rcktnut]

Definitely asking for trouble with that set up. You need to reconsider!!

 

[cerving]

How about just making a baffle just behind where the parachute would go?

 

[JimByrne]

Get rid of the piston and let the ejection charge do the job. Keep it simple and avoid problems.

 

[Voyager1]

I wouldn't do it this way. If you wish to use a piston, then allow it to exit the booster tube by having it tethered to the motor mount. You need to fully vent the pressure from the motor's ejection charge.

 

[brentius]

I bet you're worries are unfounded.
go here https://rocketrycalculator.com/rocketry-calculator/bp-estimator/
or any other calculator.

most H motors have 1.3 grams of black powder in their kits

you could, of course test this. Stick a used motor in the mmt. use one of your spent g's or if you use hardware, just tape the forward end
run a ematch to a glove finger with the calculated amount of be out the vent hole, connect it to a long piece of wire (far enough to be safe) and then hit it with a 9 volt battery.

Your idea is unnecessarily complicated and unlikely to work. Smashing pistons into couplers intentionally will cause damage and also not solve anything. There's a reason why nobody is doing this. However I love your attempt to think outside the box.......

The problem is, the calculator reads that I need 1.7 grams of BP, while CTI Pro38 reloads come with 1.4g...

Also, I live in the UK, where buying BP is illegal.

 

[cbrarick]

hmm, i'd ask the guys flying the big stuff what they do.
of course, you can always go down this route: https://rousetech.net/product/cd4-kit/

 

[cerving]

The problem is, the calculator reads that I need 1.7 grams of BP, while CTI Pro38 reloads come with 1.4g...

Also, I live in the UK, where buying BP is illegal.

Then use a stuffer tube, and you can incorporate a baffle in it while you're at it.

 

[rocket_troy]

I use a similar method for pretty much all my HPR flights and it's 100% reliable for me, mind you, I use a pyroless cold gas deployment and deploy rearwards, so that could make a difference.

TP

 

[RocketDestroyer]

Don't do it. I see no benefit at all from keeping the piston inside the rocket.

I fly with a piston on my dual deploy fiberglass rockets all the time and have good luck with it. I flew a piston on all three of my certification rockets.

Everything must be VERY CLEAN. I clean everything after the flight and clean it again before assembling it for the next flight. I then check to make sure that the piston will fall freely through the rocket body and not stop anywhere.

I had problem on one flight where the piston hit the bottom of the nosecone. Pieces of the nosecone got trapped between the piston and the rocket body jamming the piston in place rather than coming out the rest of the way. I can see the same thing happening when your piston slams into the coupler.

 

[Voyager1]

Don't do it. I see no benefit at all from keeping the piston inside the rocket.

I fly with a piston on my dual deploy fiberglass rockets all the time and have good luck with it. I flew a piston on all three of my certification rockets.

Everything must be VERY CLEAN. I clean everything after the flight and clean it again before assembling it for the next flight. I then check to make sure that the piston will fall freely through the rocket body and not stop anywhere.

I had problem on one flight where the piston hit the bottom of the nosecone. Pieces of the nosecone got trapped between the piston and the rocket body jamming the piston in place rather than coming out the rest of the way. I can see the same thing happening when your piston slams into the coupler.

Yes! If you can't remove the piston, how are you going to clean out the exhaust residues from the tube and from the piston surface? Is the coupler removable, so you can remove the piston for cleaning?

Additionally, that piston doesn't have far to travel before it hits the coupler; you might just damage the tube, forward centering ring, motor mount, or motor hardware with the excess pressure and trapped hot exhaust.