deployment bags???

Is there any good sites that show the complete setup? I don't like the idea of a drag chute removing the deployment bag, does anyone hook the bag to the rocket so that the cone will pull it out of the bag?

Final question, do you recommend deployment bags on a Level 3 rocket?

My 6" bird had a PML fiberglass nose cone weighing in at 24 oz.

If the 24 oz cone had been able to pull out the 3.5 lb parachute i may have just allowed it to but the fact is those heavier chutes aren't that easy to pull out and the cone by itself wouldn't budge the parachute.

The D bag doesn't allow the chute to "relax" in the tube, and maintains the fit. Without a D bag the chute is able to relax and then fill the tube until it's too tight as well as slam down to the bottom and mushroom the bottom out there if it's a high thrust motor.

If you have a chute in a Dbag and it is not overly tight in the tube, all you have to worry about then is getting the pilot chute to deploy, small pilot chutes in large airframes are very easy to pop out.. If that pilot chute comes out and deploys your main will deploy.....the system works very well.

I was very wary myself of getting into Dbags as they were knew to me with my L3 project, but now having used them on two flights I won't do it any other way with the larger chutes...plus it's darn pretty to watch..

Your final question, yes i do....

Look at Dbags available from Rocketman, skyangle and Quickburst..

My wife made one for me for my project and though it looks similar to the rocketman and skyangle bags it works like the quickburst in that i pack the chute and lines into the bag instead of through the loops on the outside of the bag..

Originally posted by Flash
Is there any good sites that show the complete setup? I don't like the idea of a drag chute removing the deployment bag, does anyone hook the bag to the rocket so that the cone will pull it out of the bag?

Final question, do you recommend deployment bags on a Level 3 rocket?

Click to expand...

See:
https://www.quickburst.net/images/dbag_step7.jpg

This shows the whole set up.

The pilot does not pull the bag out. The ejection charge blows the nose cone off and the bag out at the same time. When the bag comes out, the pilot inflates stretches the shroud lines out, then pulls the bag off. It works very well.

"The pilot does not pull the bag out. The ejection charge blows the nose cone off and the bag out at the same time. "

It can work that way but it depends on the setup, 4 grams of FFFF will send my nosecone across the 70' of the back yard, yet 6 grams when it's hooked to the d bag will not deploy the bag, and the sound difference is incredibly different so I know i'm pushing things..

If I pack the chute "tighter" then the charge just goes around the chute, i pack it "looser" and it hits the bag, does not move it out, and then takes the nosecone off with less authority.

You can pack the dbag to fit very tight and then cannon it out but you're really picking up the pressures inside the tube depending on the weight of the bag you're trying to move..

I use 4.5 grams for flight and it works just fine.. sometimes it moves the bag out a little sometimes it doesn't much move it at all...

So your main charge may very well move the bag out, or it may not but either way the pilot will get the job done as long as it's properly sized...

Originally posted by firemanup
plus it's darn pretty to watch..

Click to expand...

Yes it is. The stress of deployment is greatly relieved.

Jason is pretty right here... for the setup to work properly the charge has to eject the nosecone and the pilot and if the dbag isn't a tight fit inside the airframe the pilot will extract it and safely deploy the main.

Ground testing showed that clearly in my case as well: nc few feet away (I was using shear pins), dbag halfway out of the tube (but very loose inside it) and pilot out: in flight extraction was a breeze as you can try on the ground by pulling the pilot and feeling how little resistance it offers at being completely extracted.

Again, David reccomends it and it is indeed fine, use baby powder as a neat and effective dry lubrificant between dbag and airframe.

Get dbags a try, you won't be disappointed and... they will make your recovery setup look pretty professional !

If you want a nice inexpensive way to try it, do what I am doing. My fixed up thor is going to be using a larger chute, needs about a 60". For $12 aerocon systems sells a military 66" chute, with fiberglass shrouds (fire proof) and a deployment bag. Not sure if it uses a pilot but it looks like it, I plan on using this chute/bag with the thor when flown single deploy.

Flash, the right setup depends upon how your rocket is designed to recover. There are multiple possibilities.

The best way to get the bag/parachute and pilot chute out of the rocket is to use a piston. Placing a BP charge under a chute is not a reliable method. I learned that lesson years ago. Too many times the gas will blow through and around a parachute, leaving the chute in the rocket. A piston ensures that everything will get pushed out rather than hoping the nose cone pulls the chute out when it gets blown off. Plus hot gas and a nylon chute don't mix well. A piston keeps the flame, heat and chute separated.

When I started using a deployment bag I studied the available literature. I figured there was a good reason that every skydiving pilot chute used mesh rather than suspension lines. The mesh prevents inversion and tangling. Most of the time if a pilot chute with mesh rolls over something it will roll off unlike a chute with lines. If you have jumped out of an airplane you don't want a pilot chute snagging on your foot.

"One size fits all" is not a phrase that applies to pilot chutes any more than it applies to main chutes. The right size depends upon the deployment bag's design and the descent rate before the main is deployed. The pilot has to produce enough drag to separate the bag and chute.

My largest rocket has a 10' main and the bag uses a 36" pilot. The pilot uses nylon mesh rather than separate suspension lines.

You should use a bag and pilot if you want a better probability of success. However, you also have to know how to use them, which is no different than learning how to correctly assemble a motor. I recommend that you become familiar with them before using one on your L3 cert flight, though. Do a few K/L flights with a setup first.

The recovery system's organization for my rockets depends on the rocket's size and the nose cone's weight. Smaller and lighter rockets (4" diam, plastic cone) recover with everything staying connected to each other. For larger rockets I recover the nose cone on a separate chute, which solves two problems. First is that I don't have to worry about the ejection charge being too large since the cone won't be attached and won't come to a snap at the end of the line. Blow an attached cone off with too much force and something will break. The second problem that is solved by recovering the cone separately is that the cone is nowhere near the chute or lines.

Spherachutes makes my pilot chutes with mesh. Spherachute also made a special drogue chute for me that has worked perfectly for me. Many times an altimeter would not detect apogee at apogee but a while after apogee. The result was a stripped drogue when a heavy rocket finally deployed the drogue. I asked Spherachutes to make a ballute type of drogue for me, which is a parachute design that requires speed to open. This drogue does not snap open and apart. I've had famous name chutes shred. The special drogue has taken everything, including a high speed deployment when a motor failed 0.9 seconds into flight, and never failed.

Dean

Well, welcome Dean (Roth?)!!! Nice to have you on board!!!

I know you love pistons... but I haven't tried them yet... and never had any deployment failure in deployment bag setups.

The key (at least for what I saw from my flights) is that the bag isn't working as a piston... even if the gasses work their way around it (which is exactly what happens), it will be pulled out by the pilot (not by the nosecone) as soon as the bag is fitted loose inside the airframe (which is a must).

So, pack the bag loose, get the pilot out and the system will work just fine.

Nice feature your mesh drogue! I saw one at Aerocon but I think yours is better... are they standard or custom made?

Again, welcome aboard TRF and thanks for sharing your recovery experience with us!

I would recommend a sabot, but a piston is a simpler solution that works well to protect a chute from heat and flame and shove it out of the rocket.

Have you seen this? https://www.landspeed.com/hispdchutes.asp

Dean

Originally posted by Flash
Is there any good sites that show the complete setup? I don't like the idea of a drag chute removing the deployment bag, does anyone hook the bag to the rocket so that the cone will pull it out of the bag?

Final question, do you recommend deployment bags on a Level 3 rocket?

Click to expand...

Hi Flash, here is yet another way it has been used on my Booster Bruiser and my friend's LOC Big Nuke M.

We put the bag at the bottom of the parachute tube and anchor it to the U bolt. we tie the Pilot chutes harness to the "ring" at the top of the main chute.

The charge blows the nose and pilot chute out and the pilot chute pulls the main chute out of the bag, while the bag stays inside the payload tube/parachute cannon.

now, here is the advantage to that.

if using drogeless dual deploy, the nose cone stays with the rocket. this was used by Mike Schneider's Nuke M.

In my BoosterBruiser, I use a Defy Gravity Tether.

the apogee charge blows the nose and pilot chute out. the pilot pulls on it's harness till it's all drawn out, but the tether keeps the mains chute ring "fastened" to the ubolt.

The big bruiser comes down rather fast and straight under the pilot, and at about 1200 feet we release the tether.

the pilot pulls the main out of the bag and the cert-3 xl fills with air at about ~ 750 feet.

Everything is all straight up and out the top.

No large forces are at play and the recovery is gentle.

Deployment bags are -a must- if dual deploying from a single compartment using devices such as the ARRD and/or the DG Tether in the config you described.

When do you need to consider using a deployment bag?
Or is it a matter that with some rockets, unders some circumstances you can use it instead of dual deployment or other more exotic methods of recovery?

I'm guessing here that it can be used with a "regular" motor ejection charge.

For example I'm going to build a LOC IV and L1 (maybe L2?) - would this be a good idea or can I just depend on standard blow the NC off, deploy the parachute type of recovery?

Sounds kind of neat really.

Any vendors for mesh bottom pilot chutes?

Thanks for all the answers.

A deployment bag is part of the recovery system design to ensure successful parachute deployment. The use of a bag does not ensure successful recovery if the rest of the system is not designed and packed correctly. It is only one part of a system. A brief summary of what a bag should help do:

1. Orderly deployement. Get events to happen in the right order.

2. Get the parachute into clean air, away from turbulance that might cause a failure to open.

3. Get the parachute away from stuff (airframe, fins, nose cone, etc.) that might tangle it.



Using a bag is only one part of a successful recovery plan. There are other factors to consider, such as:

1. Protecting the recovery hardware (tubular nylon, parachute, etc.) from the BP charge.

2. Length of the riser ("shock cord").

3. Where the nose cone attaches to the system, if it is attached at all.


A deployment bag can be used with single deployment (pop the main at apogee) or dual deployment.

If a bag is used, how do you get the parachute out of the bag? Some bags are supposed to "fall open" and release the parachute. I've used bags that were supposed to do that. Sometimes they did. Sometimes they didn't. Everyone else (aerospace, skydivers, BASE jumpers, etc.) uses a pilot chute to pull the bag off the chute. The pilot chute has to produce enough drag to overcome whatever is holding the chute in the bag.

A rocket using dual deployment is usually falling fairly slowly, such as 50 - 75 feet per second. A skydiving falls at about 175 feet per second (120 mph). The slower an object falls and the less it weighs the larger the pilot to produce enough drag to separate chute and bag. I usually use a 36" pilot chute. If your rocket uses a 48" main chute there's little value in using a bag with a 36" pilot chute.

In short, in my opinion, consider a bag when the rocket weights around 10 pounds or more. Otherwise the pilot chute can get as big as the main chute.

To ensure that a pilot chute works right (does not invert or tangle) it is often made using nylon mesh rather than suspension lines. Lots of companies make parachutes designed to be used as a pilot chute, but not for rocketry. The typical pilot chute for skydiving costs $100 or more. Spherachutes has made the pilot chutes for rocketry, with nylon mesh, for me, and they have cost far less than $100. I don't recall the exact price. The price for a 36" pilot has been around Spherachute's usual price for a 36" chute.

Why not make the main chute with nylon mesh? Because it gets too heavy and can fail to open. The weight of mesh on a small (36") chute isn't significant. The weight on a large chute becomes significant.

A deployment bag, if made of the right material, such as Nomex, can provide some protection from the ejection charge, but not a lot. A piston or sabot will protect a nylon chute from the heat and flame of the ejection charge.

A deployment bag will not ensure that a parachute exits a rocket. The most commonly used method to extract the parachute from the rocket is to blast the cone off and use it to pull the chute out. Sometimes that works. Sometimes it doesn't work. I prefer to use a piston to shove the chute out, and protect the chute. (You don't want to melt many 10'+ chutes. It gets expensive.) My piston design is not the same as PML's piston design. Piston design is a separate topic.

Summary: In my opinion, for most rockets that weigh less than 10 pounds, use Nomex/Kevlar heat shields between the parachute and ejection charge. You might want to use two.

Dean

Dean - Thank You very much for that info.
Very informative. Very well written. Very logical.

I would appreciate it if you could also post your piston design info when you have a chance.

Thanks again.

Excellent post Dean.

That really helped me out a lot. In planning to shoot some HPR and possibly try for L1 & L2 there is a lot of stuff to wade through and a lot of opinions!

Like always, it seems that simplier is probably better!!

I'll probably just get a parachute protector and go with that. My chute is only 36" (LOC IV). I was also planning on putting in a third CR and u-bolt, adding a length of tubular nylon with a protector to attach to the LOC supplied shock cord.
It is good to use a swivel on the chute, yes?

I would also be interested in your piston design. That's another thing I've heard a lot about but was wondering how well it "really" worked and whether it was worth the effort.

I will try to post info about the piston design soon.

Dean

Originally posted by snowman2
I will try to post info about the piston design soon.

Dean

Click to expand...

Thanks

There should be an attached image. It is a piston for a 4" diameter rocket. The piston is about 2" tall.


Materials:

Two-part foam
Phenolic (or flex phenolic) coupler
Wax paper
Epoxy
Something (electric drill) to cut a slot in the cured foam


How to make it:

-Put wax paper on the floor.
-Put coupler on the wax paper.
-Mix foam and add. Hold the coupler to the wax paper to prevent leakage. Don't try to fill the whole coupler at once. Mix and add small amounts to prevent overflowing and getting foam on everything.
- After the foam cures cut coupler to desired height. A single coupler can produce multiple pistons.
- Cut a slot in the middle for the tubular nylon
- Put a layer of epoxy on the two faces and the surfaces of the slot. This prevents the charge and TN from eroding the foam.

The finished piston should slide easily down the airframe. Release the piston and it should slide through the tube. It should not stick. Sand or remove a layer if it is too tight.

The slot should be wide enough for the TN to easily slide through. The piston will probably slide along the TN when ejected.

I cover the TN that is between the piston and ejection charge with a Nomex cover, and put enough TN under the piston to allow the piston to exit the airframe before it would have to start sliding on the TN.

This piston is a solid device. The walls cannot deform and possibly cause the piston to jam.

Dean

That piston idea is neat.
So, it never sticks?
How often have you used it?
Do you have to use foam? Can you just make it out of a regular coupler and solid bulkheads?

I've used this piston design for years and many, many flights. Some of my rockets have a piston for apogee separation and for main parachute deployment. I use phenolic ("flexible phenolic") tube. Plain cardboard absorbs crud and can be hard to clean. Phenolic and fiberglass tube can be cleaned with a hose and water.


This type of piston is solid. The wall cannot bend or deform. A non-solid piston can deform and jam. The only place the force from the increased air pressure can act is on the bottom of the piston.

Let's look at what can happen with a hollow piston made from a length of coupler with a cap on the top. There will be an increase in air pressure when the black powder charge burns. The force will press on the cap and rocket, pushing the piston and rocket apart, which is what causes the nose cone to pop off and the parachute to get pushed out. However, the force will also press on the piston's wall, pushing the piston against the airframe. If the piston's walls flex enough, the piston can jam. You won't see the jam when the rocket is recovered because the rocket was either destroyed or by the time you get to it the pressure from the BP charge has bled away and the piston has unjammed.

Assume you make a piston from a length of coupler and put a plywood bulkhead on each end. You cut a slot in the bulkheads for the TN to slide through. The piston's wall can still bend or collapse and jam. Plus, I can tell you from experience that TN does not easily slide through a slot in two plywood bulkheads. The epoxied slot in foam works better. (Don't epoxy the TN into the slot! Just cover the foam with epoxy to prevent the TN from eroding the foam.)

A piston needs to be loose enough to freely slide down an airframe. Tubes are never perfectly round, and roundness varies from end-to-end. During flight tubes deform. A deformed airframe can also cause a piston to jam. Therefore you don't want a piston to fit snugly in the rocket.

Dean

My CR15 (covert recovery) chute is pretty big, not sure exactly but I am sure it is a good sized chute to take my #25 rocket down at 13FPS. It comes with a D-bag but I am not sure how the D-bag is set up. I want my nose to stay attached, how is this reliably done? I have alway's wanted to try a D-bag. What size pilot would be good, are the spherachute meshed drogues spherical (higher drag)? Anybody have some pictures of the order everything goes into the rocket?

You want your nose (cone?) to stay attached to what?

It is difficult to provide a pilot chute size without more information, such as knowing how a "covert recovery" deployment bag functions.

I consider our rocket recovery to be similar to BASE jumping. The rocket falls relatively slowly from apogee until the main deploys. BASE jumpers often use a larger pilot than a skydiver because they are moving slower when the parachute is deployed, and you want the pilot to extract the main now, not 60 seconds from now.

Consider using at least a 36" pilot. Larger (42") if the bag is complex, using suspension line stow loops, or if the chute fits tightly in the bag.

You might find this info interesting.

https://www.vertical-visions.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=PCBR

Dean

Here is how a covert bag work's, for the drogue chute there is a small cylinder bag with no flap, the bag is attached to the harness just above the body tube, the drogue is attached toward's the upper part of the harness, when the harness is pulled tight it will pulled the drogue out. The main bag has loop's for shroud's and has a flap. The orignall design for the main worked the same way as with the drogue, the new design with a pilot chute work's like this, a 2' section of TN is attached to the apex and then attached to the pilot. When the main is rolled the 2' of TN get rolled up with it. Then the main is inserted into the bag with the pilot folded outside (on top of) the bag. My 3rd idea was attaching the pilot to the nose and still having the basic setup. What do you think?