Inverted piston deployment for large hybrid rocket

[yohiyoyo]

Hi Everyone,

I am a student part of my Universities Rocketry Team. We are building an SRAD hybrid for IREC 2019 this june, targetting 30k.

So far our recovery system is very underdeveloped, we are just coming to designing and building the main deployment system.

My question is regarding using pyrocutters and gravity to deploy the main vs using a piston to push the main out. Our industry advisor has recommended not relying on the nose cone to fall away when the line that keeps the main secured is cut. He recommended an inverted piston using CO2 or a charge to push the main out.

I am wondering if anyone has other thoughts about using one method over the other, and does anyone have any examples of an inverted piston design used on a larger rocket.

I have seen this webpage: https://www.deltavrocketry.com/piston.htm referenced a lot throughout old posts, but it seems to be down now. Does anyone know where I can find the information that lived here?

Thank you very much.

 

[blackjack2564]

this what your looking for?

 

[cbrarick]

how about a picture of what you have.

So far, at first blush, you have described two recovery systems I don't use - how about using something conventional?

IMHO most of the unconventional college recovery systems haven't worked. I know, it's cool to do something hard, but when your goal is 30k everything else should be routine. Nothing more. Everything else is diverting attention from your goal and vastly increasing your chances of failure without any benefit.

 

[Wallace]

https://web.archive.org/web/*/https://deltavrocketry.com/htm/* Nothing in the archives at all for delta v...

 

[yohiyoyo]

how about a picture of what you have.

So far, at first blush, you have described two recovery systems I don't use - how about using something conventional?

IMHO most of the unconventional college recovery systems haven't worked. I know, it's cool to do something hard, but when your goal is 30k everything else should be routine. Nothing more. Everything else is diverting attention from your goal and vastly increasing your chances of failure without any benefit.

Thanks for your advice. What are some conventional systems that you have used?

 

[yohiyoyo]

this what your looking for?

This is it! Thanks a lot.

 

[cbrarick]

look at modern high powered rocketry for a good discussion of recovery systems.

 

[Handeman]

Hi Everyone,

I am a student part of my Universities Rocketry Team. We are building an SRAD hybrid for IREC 2019 this june, targetting 30k.

So far our recovery system is very underdeveloped, we are just coming to designing and building the main deployment system.

My question is regarding using pyrocutters and gravity to deploy the main vs using a piston to push the main out. Our industry advisor has recommended not relying on the nose cone to fall away when the line that keeps the main secured is cut. He recommended an inverted piston using CO2 or a charge to push the main out.

I am wondering if anyone has other thoughts about using one method over the other, and does anyone have any examples of an inverted piston design used on a larger rocket.

I have seen this webpage: https://www.deltavrocketry.com/piston.htm referenced a lot throughout old posts, but it seems to be down now. Does anyone know where I can find the information that lived here?

Thank you very much.

Absolutely do NOT rely on gravity to do anything during recovery deployment. You have to remember, gravity is working on all parts equally! It will not pull anything out of a tube like it does when you are on the ground and holding the tube. Also do not depend on air flow unless you are controlling the amount of air flow by using drogue chutes, etc. Only plan for or use forces for deployment that you generate or positively control. Depending on anything else like gravity is a recipe for disaster.

As an example, I watch a G-Force rocket pop it's nose cone and fall flat all the way to the ground without ever pulling the chute from the tube. After it landed the owner picked up the BT with the opening tilted slightly down and the chute literally fell out of the BT. It was that loose in the BT the whole way down but never came out because there were no forces working on the falling rocket that could force the nose cone away from the rest of the rocket while it fell.

Don't use your ground reference for how things work with a falling object that has zero ground reference.

 

[G_T]

I'm not sure what "large" is in this context. Can you give a diameter and recovery weight? 10pounds? 100pounds, 1000pounds?

Options:
1) break it apart to release main.
2) break it apart to release pilot chute to pull main out of deployment bag.
3) everything out top end - have pilot/drogue chute pulling on dbag (deployment bag) that pulls out and releases main in an orderly manner when a line restraining the dbag is released. Optionally nosecone and rest of rocket recover separately after main deployment, or separately from apogee.
4) everything out top end - have pilot/drogue chute pull bundled chute taco out and use linecutter to deploy main

etc.

You will find for larger rockets, deployment bags are far more reliable as you have much more control over the deployment and opening sequence. That's assuming you know what you are doing! #3 above is one of the better systems for larger rockets in cases where you don't want a slipjoint in the middle of the rocket or some other separation method.

Gerald

PS - As for CO2, have you computed the expansion available from a CO2 cartridge at 30kft? You need to look at temperature and atmospheric pressure. You don't want a dry ice maker, for instance, and you don't want to freeze the joints into mechanical friction lock. So examine carefully and plan accordingly when you start getting a little altitude.

 

[AlphaHybrids]

Since I stumbled on Delta V's inverted piston many, many years ago I've only used that concept. Always worked like a charm.

Edward