Single Airframe Break DD With a Deployment Bag

[watheyak]

Gents,
I'd like a little help with an unconventional setup. I'd like to accomplish dual-deploy with a single airframe break utilizing a deployment bag. I'd also like to avoid the "free bag" setup, my flying field might make that problematic. I've searched on this subject here quite a bit, and while there's some really good info out there, none of the threads quite apply. So I figured I'd throw this out there.

Here's some pf the particulars-

I had Mike from MAC Performance make a custom 4" kit for me. It's am amazing piece of work, I'll post pics in a separate thread. He's quite the craftsman. I had him set it up a little differently to allow dual-deploy from a single airframe break. It still has a mid-mounted coupler av-bay, but it's permanently attached to the booster section. The forward airframe that contains the parachutes attaches to the coupler av-bay with screws. Nosecone separates like normal for deployment. Confused? Here's a quick hotel room sketch that may or may not help. I'll also attach the .ork file.



To help make make this happen I have some options. I currently own a few well used Archetype cable cutters. I also have an unused Rattworks ARRD. I'm also not opposed to purchasing a Tender Descender if that works better for a particular setup.

For electronics I own a Telemetrum and a Raven. I have also entertained a Marsa54 with a MarsaNet remote pyro gadget, possibly with the remote pyro in the nosecone.

Some things I'm unclear about are whether the main stays in the airframe after apogee deployment, or should it leave the airframe, staying contained in it's bag. Also unclear is the layout of the recovery harness, including where the loops go and what attaches where.

And and all help and insight is appreciated, even if you've never done anything like this before.

Thanks for taking time to read through this.

View attachment Singularity.ork

 

[watheyak]

Oops, meant to post this in the recovery section. Can I get a little help moving it from a moderator?

Thanks!

 

[rocketsam2016]

I've got something kindof similar that I used to cert L1 and L2. 4" fiberglass little john with a single break (at the nose cone)


Unlike your rocket, I designed a donut avbay that I slide down into the booster. It has a piece of 1/16" G10 attached to the top of it that divides the area above the electronics and below the nose cone into two parts: a larger part that holds a bagged main parachute and a smaller part for a tender descender.

This next picture shows me sliding it into the rocket. You can see the tender descender on one side and the bagged parachute on the other side



Finally, the drogue sits on top of all this (actually inset into the nose cone coupler). In the below pictures the drogue is already burritoed in nomex:




The sequence of items all strung out is:

Nose Cone -> Drogue -> shock cord ->Tender Descender top link -> short cord -> DeploymentBag -> Top of Main Parachute -> shock cord -> Rocket Body

The connection between the drogue, tender descender top link and the deployment bag is actually a 3 point harness such that the drogue can't pull out the deployment bag until the TD releases.

The Tender Descender lower link and body are also attached to the rocket body (obviously ).

So, at apogee, the nose cone is blown off (I use a pratt ejection canister with motor ejection charge backup), releasing the drogue which is attached to the main rocket body by the tender descender. The tender descender and the main parachute are all 6" down in the rocket while the rocket descends under drogue. When I want the main to fire, the TD releases. The G10 divider means that the top link has nothing to get snagged on so it is pulled out of the rocket by the drogue, and then the line to the deployment bag goes tight and it is pulled out as well. The entire thing descends all tied together.

That make any sense?

 

[watheyak]

That make any sense?

Yeah that makes sense! Thanks for the in-depth reply and pics.

One question I have is when the TD releases, does it pull on the top of the deployment bag, pulling it off the parachute, or does it pull on the parachute harness, pulling it out of the bag?

 

[OverTheTop]

A similar question was recently posted on the TRA forum, so here is my method, mostly verbatim:

I use a single-ended dual deploy in my Velociraptor. My method only uses ejection charges, and no cable cutters or release mechanisms.

A apogee harness goes from the main avionics bay to NC. An altimeter (TeleMega) in the NC blows the NC at apogee (drogueless descent).

The main harness also attaches to the main avionics bay. A deployment bag attaches to the main harness about five feet up. The harness continues to a typical length the main chute on the end.

The chute is stuffed into the bag and the drogue (attached to where the harness and the main join) sits just inside the flap of the deployment bag. The drogue is kept wrapped up under the flap closing the deployment bag. The bag stays in the airframe until the altimeters shove it out. It is not likely to catch any breeze in there. Everything is slightly snug inside the airframe, so the flap containing the drogue won't come open until the bag is blown into the airstream.

So apogee NC ejection leaves the deployment bag in the airframe. Main altimeters fire at the appropriate height and blow the deployment bag out of the airframe and into the airstream. Drogue catches the air and inflates, then drags main into the airstream and completes deployment.

That's what I do. Seems to work Six from six good deployments so far (could be seven from seven?). I will keep an eye on it but no indications of aberrant behaviour have been seen.

 

[watheyak]

When I want the main to fire, the TD releases. The G10 divider means that the top link has nothing to get snagged on so it is pulled out of the rocket by the drogue, and then the line to the deployment bag goes tight and it is pulled out as well. The entire thing descends all tied together.

At this point, with everything deployed, where in the stack is the nosecone attached? Seems like it's attached to the bag which is attached to the crown of the chute?

 

[GrouchoDuke]

Have you looked at the Aeropac 100k Carmack Prize report? They popped off only the nosecone for dual deploy using a Y harness.

I couldn't find it on Aeropac's page, but there's a copy of the report here:
https://forum.nasaspaceflight.com/index.php?topic=25965.60

Look in the Recovery section that starts on page 32. There are diagrams on pages 38 & 39 that roughly show what they did. (It'd be great to see more detail though.)

Fun video too:
[video=youtube;krNFHr2YZBY]https://www.youtube.com/watch?v=krNFHr2YZBY[/video]

 

[rocketsam2016]

Yeah that makes sense! Thanks for the in-depth reply and pics.

One question I have is when the TD releases, does it pull on the top of the deployment bag, pulling it off the parachute, or does it pull on the parachute harness, pulling it out of the bag?

It pulls on the top of the deployment bag, pulling the bag and parachute out of the rocket (so it is important that the drogue parachute pull is strong enough and the bag+chute isn't wedged in too tightly). Then when the main chute shock cord goes taught, the bag is pulled off of the main parachute. The nice thing about this is everything is all lined up and taught at that point. Here's a video from a camera on the side of the rocket pointed up. I added slo-mo of the two deployment events at the end.

[video=youtube;k9F_6r8MC4A]https://www.youtube.com/watch?v=k9F_6r8MC4A[/video]

 

[watheyak]

A similar question was recently posted on the TRA forum, so here is my method, mostly verbatim:

I use a single-ended dual deploy in my Velociraptor. My method only uses ejection charges, and no cable cutters or release mechanisms.

A apogee harness goes from the main avionics bay to NC. An altimeter (TeleMega) in the NC blows the NC at apogee (drogueless descent).

The main harness also attaches to the main avionics bay. A deployment bag attaches to the main harness about five feet up. The harness continues to a typical length the main chute on the end.

The chute is stuffed into the bag and the drogue (attached to where the harness and the main join) sits just inside the flap of the deployment bag. The drogue is kept wrapped up under the flap closing the deployment bag. The bag stays in the airframe until the altimeters shove it out. It is not likely to catch any breeze in there. Everything is slightly snug inside the airframe, so the flap containing the drogue won't come open until the bag is blown into the airstream.

So apogee NC ejection leaves the deployment bag in the airframe. Main altimeters fire at the appropriate height and blow the deployment bag out of the airframe and into the airstream. Drogue catches the air and inflates, then drags main into the airstream and completes deployment.

That's what I do. Seems to work Six from six good deployments so far (could be seven from seven?). I will keep an eye on it but no indications of aberrant behaviour have been seen.

Good visualization, thanks. I had entirely forgotten that there was a TRA forum, I'll have to go find that thread.

 

[watheyak]

Have you looked at the Aeropac 100k Carmack Prize report? They popped off only the nosecone for dual deploy using a Y harness.

I couldn't find it on Aeropac's page, but there's a copy of the report here:
https://forum.nasaspaceflight.com/index.php?topic=25965.60

Look in the Recovery section that starts on page 32. There are diagrams on pages 38 & 39 that roughly show what they did. (It'd be great to see more detail though.)

Thanks for the link. I'd read that write up a while back. I agree more detail in the diagrams would be nice, but a still better than my hotel room sketch!

 

[watheyak]

It pulls on the top of the deployment bag, pulling the bag and parachute out of the rocket (so it is important that the drogue parachute pull is strong enough and the bag+chute isn't wedged in too tightly). Then when the main chute shock cord goes taught, the bag is pulled off of the main parachute. The nice thing about this is everything is all lined up and taught at that point. Here's a video from a camera on the side of the rocket pointed up. I added slo-mo of the two deployment events at the end.

[video=youtube;k9F_6r8MC4A]https://www.youtube.com/watch?v=k9F_6r8MC4A[/video]

That's an outstanding video! It made me realize that I had a few false assumptions about the situation. I didn't realize that the nosecone would be held above the main canopy by the drogue. It's also obvious to me now that the main will stay in the deployment bag until everything is taught.

Good stuff!

 

[rocketsam2016]

That's an outstanding video! It made me realize that I had a few false assumptions about the situation. I didn't realize that the nosecone would be held above the main canopy by the drogue. It's also obvious to me now that the main will stay in the deployment bag until everything is taught.

Good stuff!

Thanks! And yeah one of the critical things about a tethered bag setup like this is that the drogue has to be sized so that the nose cone under the drogue descends at the same speed as or slower than the booster under the main chute so that the tether going up from the main parachute to the drogue + nose cone stays above or at least to the side of the main parachute until touchdown.

In this case because I needed nose weight and had a tracker in the nose cone, this meant having a 24" fruity chutes elliptical drogue even though the rocket without a motor (but otherwise loaded) is 7.5lbs and the nose cone still descends a little faster than the main, but not fast enough to pass it before hitting the ground. This means that it descends rather slowly under drogue: 40fps, which is too slow for the fields I fly on the east coast. As such, on higher flights or windy days, I actually use a Chute Release on the drogue (making it triple deploy I guess!) such as on this flight:

[video=youtube;6nqY6KWqeCE]https://www.youtube.com/watch?v=6nqY6KWqeCE[/video]

You might reasonably ask why bother with all this instead of just using a single Chute Released main The Chute Release is quite awesome and I love having it. I'll confess that if I lost this rocket I probably wouldn't build another the same way, but I planned all this and built it before there was widespread comfort with using the Chute Release on high power rockets, and I'm rather proud of the design and enjoy watching it work. Also, it's possible for the main to deploy at apogee with the chute release if the parachute escapes the bundle, which would lose the rocket on the fields I fly. With the Tender Descender however, the only way to have the main deploy before I want it to is electronics malfunction or forgetting to close the tender descender which is very unlikely....

 

[rocketsam2016]

Oops sorry uploaded wrong video for anyone who already watched. Should be fixed now. And yeah the wind in that video was pretty intense! As you can see it dragged the rocket after landing along the field into very end of the line of parked cars, though fortunately (as planned) it was never remotely close to being over anyone or any cars while in the air.

 

[Kanishka Deepak]

View attachment 308847

You can see the tender descender on one side and the bagged parachute on the other side

View attachment 308843View attachment 308844

Finally, the drogue sits on top of all this (actually inset into the nose cone coupler). In the below pictures the drogue is already burritoed in nomex:


View attachment 308845View attachment 308846

The sequence of items all strung out is:

Nose Cone -> Drogue -> shock cord ->Tender Descender top link -> short cord -> DeploymentBag -> Top of Main Parachute -> shock cord -> Rocket Body

The connection between the drogue, tender descender top link and the deployment bag is actually a 3 point harness such that the drogue can't pull out the deployment bag until the TD releases.

The Tender Descender lower link and body are also attached to the rocket body (obviously ).

This is amazing!
Can you please tell the advantages of attaching the tender descender to the rocket body when compared to this deployment design, where the entire system is out of recovery compartment?

It's a very rough design

The drogue chute(green) is already deployed.
The main parachute is in the deployment bag(brown).
The deployment bag is connected to the decoupling link of the tender descender(orange) and the chord of the main parachute that is enclosed in the deployment bag is attached to the body of the rocket(Red).

Question: Can you please tell the advantages of attaching the tender descender to the rocket body when compared to this deployment design, where the entire system is out of recovery compartment?

 

[OverTheTop]

I used an AARD (similar idea to the TD) for my 1/2 scale Nike Smoke. It kept the entire main chute and bag inside the airframe after drogue deployment. When main fired the drogue pulled the main out of the bag and into the airstream. Keeping it in the airframe means, for me, that the somewhat fragile wires to the deployment mechanism are not flapping around in the breeze, leading to a potential point of failure.

There are large forces on harnesses, and I think it is easy to get wiring on the harness into a situation where it won't work. IMHO main not coming out is a major problem, to be avoided if possible. Design for sub-optimal deployment where possible .