How to get a really big chute out of a really big rocket??

[David Schwantz]

12" DIA rocket, 140" long. What are some deployment ideas and what have you used to get the NC off and the chute out? Thought of cannon, but that would be a really big hole in the side. Thought of a stuffer tube to blow the cone off and pull chute out. Am going to seal chute compartment off from motor as there will be no charge in the motor. So that should lower the volume by quite a bit. So less BP will be needed. What other ideas do you guys have?

 

[SpaceX76]

how big is the chute?

 

[David Schwantz]

Don't really know for sure yet but a good guess would be about 10' or 12' . Still building rocket and do not have an all up weight. Will have lots of room for chute, so that is not a problem. I am looking at how to get the NC off right now so that I can build what ever I need to into the rocket. Like if I use a stuffer tube, can that give enough force to blow that big of a NC out of the airframe? If I go with a cannon, do I blow it out the side, and then do not need to blow NC off. Then I will have to design cannon mounts and build them into the rocket. I have seen cannons blow the chute out the top, but then you still need to get the NC out of the airframe.

 

[lakeroadster]

Piston?

 

[SpaceX76]

Piston?

ye a piston is about your only option

 

[David Schwantz]

Piston might work in a cannon, but not to blow off the NC. Bulkheads, button mounts all would be in the way of a piston. And still that would present the same problem of pressurizing a huge volume to move the piston.

 

[SpaceX76]

Piston might work in a cannon, but not to blow off the NC. Bulkheads, button mounts all would be in the way of a piston. And still that would present the same problem of pressurizing a huge volume to move the piston.

it would push out the NC if you put the parachute in a deployment bag,
but there is no other option with out pressurizing a large space

 

[jbr]

you need a pilot chute
for my 14 foot chute I use a 3 foot chute that is connected to the nosecone, it gets pulled out first and then pulls out the 14 foot

you need to test and make sure you can pop off the cone with enough charge

 

[David Schwantz]

No, you could use a stuffer tube to pressurize a much smaller space, I just do not know if that would be enough force to blow this large of a NC out. A piston in the airframe would not work as there will be no room for it to slide. But a piston in a stuffer tube would, but again it is a question if that will provide enough force.

 

[David Schwantz]

Yes a pilot chute will pull out the main. But the question is getting the NC out. The NC will be large enough to pull out the main. I just need to figure out how to blow the NC out of the airframe.

 

[Wayco]

What is the rocket made of?
You could use Wildman's formula for black powder, 1 gram per inch. With fiberglass, no problem, not so much if you are using sonotube....
Never seen a N/C that 12 grams of BP wouldn't move...
Blow it out or blow it up, either way, no ballistic return.

 

[David Schwantz]

It is sonotube. Foam NC. You can see it here.
https://www.rocketryforum.com/threads/12-foam-nc.162415/

 

[MClark]

I have used one gram per 200 cubic inches.
A local guy had a 16” diameter rocket with a 48” parachute bay. 50 grams got it out.

M

 

[David Schwantz]

I can adjust the height of the bulkhead easy so that I can make the bay just about any size that I need to. Right now I just got the center PVC pipe out and am thinking about putting a 6" tube in the NC and a mating coupler in the airframe and then pressurize the 6" tube with BP. Only thing is now there is a tube sticking out for the shock cord to tangle up on.

 

[David Schwantz]

Do you know what he contained that much BP in?

 

[MClark]

Do you know what he contained that much BP in?

plastic 35mm film can

 

[David Schwantz]

I gotta get me some.

 

[Wayco]

PVC end caps work well too. These are only 3/4 " on a 4" rocket, but they come in lots of sizes. You can add a length of pipe to hold more BP.

 

[David Schwantz]

I like your terminal blocks. Where did you get them?

 

[Ez2cDave]

Here is an option . . .

Use a deployment bag that employs a "drogue chute" to extract it from the airframe.

Dave F.

 

[Bat-mite]

Tom Cohen, MDRA's master of huge, scratch-built Sonotube rockets uses 30g of BP to blow out the NC. He uses three #6 or #8 shear pins. He uses three alts, with charges timed 1 second apart each, 30g in each.

Go to you tube and search for "MDRA tom cohen" to see examples of his flights. I can get you guys in touch, if you want.

 

[PSLimo]

Hi David,

I'm currently making an 11.4" diameter build and will be using a piston for single and another configuration for dual deploy interchangeable in the same rocket. One thing to consider if you're only looking for single deploy you need less powder to get things moving because you only need to pressurize the area from behind the piston to the centering ring which would be minimal compared to pressurizing the whole tube without a piston to get things moving. I'm using a 6" tall piston so the area to pressurize behind it to get things moving is only 11" x 6".

Hope this helps your build,

Phil

 

[Ez2cDave]

He uses three alts, with charges timed 1 second apart each, 30g in each.

Three 30 gram charges . . . I do love "Fireworks" . . . Ka-BOOM !

Dave F.

 

[David Schwantz]

Thanks Dave, but really hope I don't do that to my rocket after all the work I am putting you guys through.

 

[David Schwantz]

Hey John, thanks. I watched the ones on the link, and noticed that all of his rockets use 2 mains. One on the NC, one on the body. That might be the best idea for what I am doing also.

 

[David Schwantz]

Phil, when you say "to the CR" does the piston always stay in the tube?

 

[PSLimo]

Hi Dave,

Here's a piston main ejection in a 7.5" diameter dual deploy build. The piston is part of the shock cord assembly for the main and will guarantee the chute comes out.



In the 11.4" build I'm currently working on for single deploy the piston is the inner diameter of the bodytube. Very simple and very effective with minimal black powder. I'll take a couple of pics of the 11.4" and post for clarity. Been using this method for years without incident.

Phil

 

[David Schwantz]

HI Phil, nice. I have done it the way your pic shows, only I blew it out the side of the rocket.

https://www.rocketryforum.com/threads/how-to-figure-base-drag.156237/
I am not sure yet if I am going to build an internal frame work. But I have ordered LOC's 7.5" tube and coupler. I am going to use the airframe in the NC to both attach the shoulder, a mounting spot for the hard point for the shock cord, and as a stuffer tube for the ejection of the NC. It will all sit around the coupler which will be mounted at the end of the main body tube. I watched the vids John linked and am going to use a chute for both NC and body. Not sure how to position them in the stuffer tube yet. Don't want the to get tangled up with each other. But a piston would work very well in the stuffer tube. But if I may ask, does the piston in your pic also blow out the NC?

 

[David Schwantz]

Tom Cohen, MDRA's master of huge, scratch-built Sonotube rockets uses 30g of BP to blow out the NC. He uses three #6 or #8 shear pins. He uses three alts, with charges timed 1 second apart each, 30g in each.

Go to you tube and search for "MDRA tom cohen" to see examples of his flights. I can get you guys in touch, if you want.

Thanks John, always like to get tips from one that has been there and done that. Dave.

 

[jbr]

1/3 scale V2
The rocket ended up 14 feet long and 22 inches in diameter. It weighed 115 pounds including the 15 pound main parachute. The motors weighed in at 32 pounds, so the total liftoff weight was 147 pounds.

we used 1 ounce of BP for the main 28 foot chute (both for main and backup charge), it had a 6 foot pilot chute to pull the main out of the chute bag