deployment Bag Help

ckjohnson said:

Chris:

You have the same deployment bag setup as I do.

The long strap sticking out of the opening of the bag connects to the apex of your main chute. The lines of the chute are reefed through the white straps to slow the deployment and keep the lines organized. The small loop at the bottom of your bag connects to your pilot chute.

Here's my setup:

Here you can see the pilot chute is open. The lines of the main chute are extended out, and getting ready to pull the bag from the chute.

Here you can see that the pilot chute has pulled the bag off of the main chute, and the main is just starting to open:

Here the main has opened. You can see the deployment bag between the pilot chute and the main chute. My drogue snagged my nosecone, so it looks like a mess, but it was good.

The recovery harness from the rocket connects to the ends of the main chute lines, as well as a shock cord going to the nosecone.

Click to expand...

You didn't consider the fact that all of the parts and cords below the main tangled an issue? The pilot was below everything else when it opened, it could have been tangle too.

I don't want to seem like I'm trashing how you did your deployment, but I've seen a lot of "successful" deployments that were what I considered near misses. I really believe that just because the main opened doesn't mean the deployment was as safe as it could be. I've had my share of failed deployments but looking at your pictures, I think you got lucky the pilot didn't get fouled and the whole thing crash on this flight. I wasn't there and a couple pics don't really tell the story so please take my opinions for just that, opinion based on a quick peek at what seem to have happened. Maybe I provided a different view of how it worked and some food for thought, or maybe I'm just full of it. Your choice.

ckjohnson said:

My nose cone isn't terribly heavy (572 g / 20.2 oz). How big is your pilot chute? You may want to try a slightly smaller pilot so that it doesn't pull the bag off as quick.

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It's sort of hard to describe this stuff well without pictures, but I think with your setup, if there is enough momentum/weight to the cone, and the bag is between the cone and the pilot, then the chute can get pulled out of the bag before you want it to. I think many of the methods discussed previously have the pilot attached directly to the cone so that the cone does not pull on the bag. Conceptually, I think that is a better approach. It sure would be nice to see some diagrams of the methods that have been discussed though.

Early on, I posted a diagram of the setup I'm using. It's attached again. However, there is one aspect of it that I should clarify. I have separate harnesses for the nose cone and the bag/pilot. That's intentional, because I don't want the nose cone motion to pull the chute out of the bag early. However, as we all know, it is often the case that the weight of the nose cone is required to pull the chute and/or bag out of the airframe. My setup doesn't do that. The missing piece of this is that I use a piston, and with a piston, the weight of the cone isn't required to pull out the chute - the piston does it. I suppose one might argue that as long as the pilot can fall out of the airframe, or if the D bag is sized to nicely fit the diameter of the airframe, then the chute/bag will be ejected. However, I don't think I can recommend my setup unless it is used in conjunction with a piston.

Jim

I have but two comments when using a bag with a conventional dual deploy (ie. all attached together as opposed to the nosecone/pilot yanking off the main bag and coming down on its own smaller chute)

1. Too large a drogue chute.

2. Too small a pilot on the bag.

I've had the experience where I went from a 48" pilot to a 36" pilot and the whole mess just streamered in with no main deploy. Pick the bag up and the chute "falls" out of the bag!

Too large a drogue the rocket is falling at a lower velocity. When the pilot pops it, you want it to "grab" hard so the falling rocket body adds to the pulling extraction of the chute. Slower descent under drogue = less energy My one success was with a drogue-less flight which popped the main at 1000' and I don't think it opened till it hit 500-700 feet. YMMV. Kurt

Handeman said:

You didn't consider the fact that all of the parts and cords below the main tangled an issue? The pilot was below everything else when it opened, it could have been tangle too.

I don't want to seem like I'm trashing how you did your deployment, but I've seen a lot of "successful" deployments that were what I considered near misses. I really believe that just because the main opened doesn't mean the deployment was as safe as it could be. I've had my share of failed deployments but looking at your pictures, I think you got lucky the pilot didn't get fouled and the whole thing crash on this flight. I wasn't there and a couple pics don't really tell the story so please take my opinions for just that, opinion based on a quick peek at what seem to have happened. Maybe I provided a different view of how it worked and some food for thought, or maybe I'm just full of it. Your choice.

Click to expand...

If you look close at the first photo, you'll see that the pilot was considerably in front of the rest of the rocket when it deployed. The body tube that is still smoking just blew that nose cone out toward the camera's point of view. The main was already out of the deployment bag and above the whole setup before the rear shock cord passed over the nose cone. Subsequent flights deployed with absolutely no issues.

ckjohnson said:

If you look close at the first photo, you'll see that the pilot was considerably in front of the rest of the rocket when it deployed. The body tube that is still smoking just blew that nose cone out toward the camera's point of view. The main was already out of the deployment bag and above the whole setup before the rear shock cord passed over the nose cone. Subsequent flights deployed with absolutely no issues.

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Seeing 3D in a 2D pic is kind of tough. I figured I was missing a lot.

Did you do something to the set up on the subsequent flights to prevent an occurrence of the tangles of the first flight? Is there something to ensure the pilot deploys out from under the rest of the rocket or is it possible it could deploy under them? I keep trying to find ways to ensure my deployments always work, but anything you can suggest can only help. I still think it's a matter of chance sometimes even when I get a series of good deployments.

Honestly, I haven't worried about it much. It hasn't been a problem for me. I can see what you're saying, and there is the possibility of it tangling. If you figure out something, share with me also.

I rather prefer an all out the top tether deployment which does not suffer from any of these issues. But that doesn't fit with a conventional break-in-the-middle rocket.

Gerald

Here's how I did mine. The chute is a Skyangle Cert 3 XXL in an XXL free bag. The chute is folded and slipped in the bag. I then fold the lines and lightly tape them with 1/4" masking tape. I then put the lines in the bag for max protection. An additional chute protector is put below the bag. Also note that the bag connection point should be positioned in such a manner that the bag is pulled out, vs the bag pulled off the main while in the tube.

patelldp said:

View attachment 267201

Here's how I did mine. The chute is a Skyangle Cert 3 XXL in an XXL free bag. The chute is folded and slipped in the bag. I then fold the lines and lightly tape them with 1/4" masking tape. I then put the lines in the bag for max protection. An additional chute protector is put below the bag. Also note that the bag connection point should be positioned in such a manner that the bag is pulled out, vs the bag pulled off the main while in the tube.

Click to expand...

I forgot to mention that I do the same thing as you do Dan. I lay my shock cords flat and scissor fold them. I put a couple of small rubber bands on it for every 6 folds. That keeps the shock cords wrapped nicely and also slows the deployment of the shock cord. My deployment bag goes into the body tube with the opening to the top so that the bag is pushed out of the body tube and it can't just pull the bag off of the parachute inside the body tube.

G_T said:

I rather prefer an all out the top tether deployment which does not suffer from any of these issues. But that doesn't fit with a conventional break-in-the-middle rocket.

Gerald

Click to expand...

The only issue I can see for the all out the top is a high speed deployment. Wouldn't that make a mess of things?

Jim

I free bag. Get a 5-6ft shock chord, just enough to exit the airframe. Attach the main chute to this chord and the chord to the airframe. I spike the chute and lay the shroud lines on it so they are in the chute from bottom to top and back to bottom. Grab the top of the chute and stuff it in the bag. Hook the bag only to the nosecone. Attach a chute sized for the nosecone only to the nosecone.

When the main charge fires, the nose pulls the bag out of the airframe, and has nothing to stop it so the chute gets pulled from the bag. Since the chute is fully deployed, there isn't a huge shock. The rocket just swings under the chute.

JimJarvis50 said:

The only issue I can see for the all out the top is a high speed deployment. Wouldn't that make a mess of things?

Jim

Click to expand...

I used drogue descent rates up to 127fps. For a real high speed deployment it would have been fine. My drogue was rated for > mach 1, and the harness etc was fairly stout.

Pictures from different flights...

I just had to throw an apogee shot in there.

The second picture shows the early part of main deployment. This is essentially looking upwards from the rocket. You see the main chute harness in orange tubular nylon. The black object is the deployment bag containing the main chute. Since the main harness has now been stretched out, breaking all its little pieces of masking tape holding it in zig-zag, the bag is about to open. The harness forms a lock on the flap of the bag via rubber band so that the bag does not come open before the harness has been stretched out.

Above the bag you see the line (yellow Kevlar) stretching to the nosecone (white) and the drogue chute which acts as pilot for the dbag (orange). The drogue is pulling the bag up away from the rocket, as the rocket has been essentially dropped out below via release of the tether. The nosecone and drogue/pilot starts out above the rocket and stays there through main deployment, eliminating a lot of tangle possibilities.

The little tube floating in the air is literally a little tube. It is used to duct ejection gasses past the dbag. Usually it stays in the rocket. That was the only flight where it parted company.

The third picture shows the nosecone off to the side with the drogue and deployment bag pulled off the main. The nosecone's main chute is starting to open.

The fourth picture shows the nosecone coming down under its main off to the side of the rest of the rocket which is under its own bigger main. The drogue on the nosecone is now no longer inflated.

I always dropped it in hot at over 100fps to minimize drift. I deployed at 700ft, and main was open and rocket slowed to landing speed by 400ft. It was very consistent.

This setup is a little more complex than I would recommend on average, due to the use of a separate main for the nosecone instead of just the drogue. The nosecone was 9 pounds if it didn't have a payload in its separate bay. The drogue itself was sized small for fast descent. So, to slow it down in the end, a second larger chute was required. Both mains were deployed from the same dbag which requires careful rigging. Without that added complexity, all this is fairly simple. It requires one dbag, one deployment charge (and a backup if you want), a main, and a drogue which is also the pilot. Oh, and a tether to release the main.

It's just different and I think quite superior to the usual break in the middle arrangement.

No load is transferred from the drogue to the dbag until the tether is released. So high speed deployment is not particularly prone to causing a recovery sequence error. Some sort of structural failure would be required to mess up the sequence. With the small drogue used, that would have required near supersonic deployment, +/-.

There are no shear pin pre-release failure modes unlike the break in the middle situation with high speed deployment.

Gerald

Here's a look at the deployment on my L3, set up like Jim's picture. I don't use a piston, but I do have a large nomex protector at the bottom, I use a Fruity Chutes sized bag (5.5" bag/5.5" diameter rocket), and the pilot is right at the end of the payload on a short tether. Slides in and out very easily, but occupies most of the tube. Five ground tests and two flights and no issues having the bag come out cleanly. I z-fold and rubber band the main SC and the NC SC, both go below the bag. The pilot is a Fruity 18" elliptical, the main is a Fruity 84" toroidal. D-bag flap is held over the shroud lines (which are tucked in the elastic of the bag, sorry, no photo) with a rubber band. Rocket is set up to fall nose cone below the fincan, 30" drogue (probably a little big, could have it fall faster). The fincan and payload descend in an inverted-V, so when the main fires it shoots the recovery bundle away from the fincan. In photo 1 you can see the angle, the pilot has pulled the gear above everything else, the main SC is extended, the bag is off, and the main is opening. You can see the NC is well away from the recovery gear. In photo 2 the rocket is descending under the main. I think the bag came off a bit sooner than preferred as the booster still has a way to fall (resulting in an acceleration spike higher than I'd like to see), but a combination of smaller drogue and slightly stronger rubber band around the d-bag flap should improve that.

Thanks to Chris Hobbs for the photos.

David