Chute recovery on gap-staged booster

Murdnunoc said:

Say again? Not following.

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1 ea 24-18-13 should fit, I think.

dhbarr said:

1 ea 24-18-13 should fit, I think.View attachment 390209

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Any engine, besides a MicroMaxx, in the tube with the 24mm will push the 24mm engine to the very edge of the body.
That offsets the thrust line by 8mm or 40% body radius from center. Not sure how big a deal that is. The rocket is 23" tall. But it's enough to make my eye recoil a little.

Murdnunoc said:

All while maintaining that sweet, sweet symmetry!

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https://www.rocketryforum.com/threads/double-mach-diamond.149662/

BABAR said:

https://www.rocketryforum.com/threads/double-mach-diamond.149662/

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Think offset thrust line would do as well as offset fins?
I guess the fins move the vertical CP off axis, so the net result would be the same as that caused by and off-center motor...

Sure would make "off-centering rings" easier, as the 3x 18mm cluster I have is about to fall apart into four pieces, since the body tubes touch.

I may have to enlist a friend with a laser cutter.

The coupler/ chute bay so far.
The delayed ejection charge from the main booster will travel up the body chamber and through the openings at the bottom of the chute bay. Then push the chute out.
I hope...

For low power (up to D) I have used foam board (available at any Walmart and probably Walgreens) for centering rings without any problems, largest was going from BT20 to. BT80 (also BT50 to 80.)

The holes I cut with a hole drill, I use an 18 mm hole cutter for BT-20 holes and 22 mm hole cutter for BT50. Yes, both are 2 mm off, but with VERY minimal sanding gives a good snug fit. I make the outer cut, say BT80, by creating a template first with the holes properly centered (or ec-centered) and cut out, the outer diameter is the BT80, place it over the precut holes in the foam board to trace the outer diameter. That is cut out with an Exacto knife. Yes, a little big, but sands down to fit snug.

Knock wood, yet to have the foam board centering ring be a point of failure.

"Centering" and "ring" are two liberally used words here.

I use a forster bit to drill the initial hole. They also come out undersized, and then I use a few tapered drill sanding attachments to ream out for final fit.
For the outside of the disk, I glue it to a mandrel of some sort and spin it in the drill while holding a spinning sander up to it. Kind of a back alley lathe.
This is the first one I've had to glue to a backer board before turning down because there was literally nothing holding it together.
For centered rings, I fit the inner, then leave it on the drill to sand down the outside.

Used 1/8" Baltic birch on these because I needed the rigidity for the shaping operation, and there's really not that much wood in there.

Last good look at things before they start disappearing inside the body.

Some of the thrust line issues look to be working out with the nature of construction.
The main motor tube angles inward toward the center of the rocket as it moves forward to meet the sustainer motor, directing the thrust to the outside of the rocket. This should counter some of the off-center thrust from the main booster motor being on the side of the tube.

I like it!

I had never considered “containing” my deployment pod INSIDE the booster body tube . I always just glued the pot on the outside. Gave it its own nose cone.

one thing to consider you may want to put a sheet or two of wadding forward of your booster parachute as well as aft, just to keep it from being singed by the sustainer motor as it lights.

BABAR said:

I like it!

one thing to consider you may want to put a sheet or two of wadding forward of your booster parachute as well as aft, just to keep it from being singed by the sustainer motor as it lights.

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That's what I've just been testing!
I'm stuffing a sheet of wadding at the bottom to act as a plug/piston to keep the bay sealed as the charge pressurize it. Then stuffing the chute in with a blanket of wadding over the top to protect it from the sustainer's plume.

Just been blowing through the tube, and it's all going to come down to chute packing. Folding the plastic Estes chute creates hard corners that like to snag coming out. For the static ejection testing, I'll make sure it has a softer nylon chute in there.

Also just drilled my vent holes through the CRs!
The booster forward burn gas will vent out the sides of the motor tube just before the sustainer motor, and then be free to travel down the CRs out the tail.

BABAR said:

I like it!

I had never considered “containing” my deployment pod INSIDE the booster body tube . I always just glued the pot on the outside. Gave it its own nose cone.

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I'll tell ya it would have been a lot simpler to give the recovery its own little "rocket"
But the Starship just wouldn't be right if it had something else hanging off the side.

Looks like with a D12 on the booster, the booster coasts for around 2 seconds before its apogee. The simulation graph doesn't seem to include any push-back on the booster as the sustainer pushes it back, so it's still an unknown how long it will truly coast. Definitely don't want to assume over 2 seconds, though. With A10-3T as the ejection engines, that will mean the D burns 0.8 seconds longer than the mini engines, and the minis will eject 2.2 seconds after booster burnout. Close as it gets for armchair play-calling!

The booster and sustainer bodies are all built up, with motor mounts, parachute bay, and shock cords installed.
I'll use a generic nose cone and build up a removable fin can until it's flight proven before putting in the work to dress it up smooth and shiny for a true Starship look.

BFR!!
The fins are temporarily attached. If I can get it to sim stable with booster fins that are identical to the sustainer, I'll do that. I've seen some drawings like that. But if it needs bigger on the booster, I'll put some clear fins on.
Couple buttoning-up things like motor blocks, parachute and launch lug, and it'll be ready for a test flight!
Think I'll do one static fire on the booster main to ensure sustainer ignition, and another fire of just the ejection motors to make sure the chute gets out of its bay.

Looking good. I recommend an A8-3 or A8-5 on the sustainer.

BABAR said:

Looking good. I recommend an A8-3 or A8-5 on the sustainer.

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That WOULD keep it more retrievable.
And save some weight in the nose and overall rocket.

Got a test launch today.
The gap staging worked perfectly.
The off-center thrust line coupled with the canted motor tube seemed to just about equal out. Just a tiny bit of snakiness to the ascent trail.
The booster chute came out of its internal pocket with time for about a minute descent. This was a stressor for me, as one bench test only halfway ejected the chute. And several "blow tests" got about a 50% successful ejection rate. It all comes down to packing tight enough to maintain the seal in the chamber all the way out with the chute, and loose enough to allow movement. Nailed it this time, at least.
I was hoping to have slow motion video capturing the staging and ejection, but it happened too quick and high to catch the events.
I think this thing could go on a C11-0 in the booster to keep things lower.
I'm seriously excited now to get this thing dressed up like a true Starship/Super Heavy!

Congrats.

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Starship Superheavy looks cool, going to be rough to get stable, especially with those canards up front and those micro fins on the booster.

Can't get the video small enough to post, so here's a few screen grabs.

The ignitor leads held on until they were yanked out, so I'm thinking it took that long for at least one of the two A10-3 engines to ignite. They were both spent on retrieval, though.

The rocket, at least with the temporary fins, had a gentle roll that kept it on track by dampening out any pitching caused by the off center thrust line.

Third picture shows the successful staging, and the booster just starting to fall away.

Much smaller exhaust trail from the sustainer's burn on the A8-5.

The nose cone and chute did leave the sustainer behind. The ejection charge somehow burned through the Kevlar shock cord. But all the parts were recovered and the sustainer received no damage even with a lawn dart recovery.

Now with the demonstrator proven, it's on to the dress-up phase! I'll replace the temporary fins with slick and sealed ones and nice fillets.
The booster will either get clear fins with fillets shaped like the full scale's stubby fins, or solid fins that match the size and shape of the sustainer. Haven't decided yet.
Then I have to find the shiniest silver paint possible!

BABAR said:

Congrats.

Starship Superheavy looks cool, going to be rough to get stable, especially with those canards up front and those micro fins on the booster.

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I did a single stage Starship without the booster a little while ago. Flew it without the canards first, then added them. It flew just as straight with the canards. I was also between 1.5-2 caliber stability according to Open Rocket so there seems to have been enough margin to still be stable even with the additional surfaces up front.

Still, I'll make them 20-30% smaller than actual scale to reduce their influence but keep the visual.

Also not flying with the stubby fins on the booster. Thinking it'll wind up with some good size Lexan fins painted a little ways up the root to look like the stub fins.

Murdnunoc, that is some awesome work! I've got a gap staged Big Bertha I've been working on, but I took a completely different approach for booster recovery. At first I was trying to squeeze a thin rubber tube into the gap between the 24mm core and the BT60 body to act as a spring to push the chute out, but that has proven to be too tight of a fit, so I am going to have a long kevlar cord taped to the bottom of the sustainer drag the parachute out. Hopefully, the little bit of grab from the tape isn't enough to throw off the course of the sustainer. For the next one, I am going to try reducing the diameter of the core tube partway up from 24mm to 18mm so the flame is focused more toward the center for the sustainer, and also to give me more room for the recovery system. Here are some shots of my setup:

ebruce1361 said:

Murdnunoc, that is some awesome work! I've got a gap staged Big Bertha I've been working on, but I took a completely different approach for booster recovery. At first I was trying to squeeze a thin rubber tube into the gap between the 24mm core and the BT60 body to act as a spring to push the chute out, but that has proven to be too tight of a fit, so I am going to have a long kevlar cord taped to the bottom of the sustainer drag the parachute out. Hopefully, the little bit of grab from the tape isn't enough to throw off the course of the sustainer. For the next one, I am going to try reducing the diameter of the core tube partway up from 24mm to 18mm so the flame is focused more toward the center for the sustainer, and also to give me more room for the recovery system. Here are some shots of my setup:

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I think there is a good chance your system will deploy as designed.....BUT

If it does, at the time of separation your rocket “stack” (combined sustainer and booster) are probably at their COMBINED Max velocity (sustainer May accelerate AFTER separation once its own engine ignites, but since there is no delay on the booster, the combined rocket is going as fast as it is gonna go.). After separation, the booster still has all that inertia. Think of it as putting a booster zero delay motor in a SINGLE stage rocket. At booster burn through, it ejects the chute at MaxV. This is really rough on the parachute (I know. I tried something like your set up with a two stage. Chute was in a side pod off the sustainer. It did exactly what I asked it to do, deployed the chute at separation. Ripped every shroud line right off the chute.)

May want to consider a streamer instead of a chute.

Did you consider putting an internal nosecone on your parachute bay? The nosecone would protect your parachute from the exhaust plume of the sustainer, and the mass of the nosecone would help pull the chute out without having to rely on having a precise parachute roll that is tight enough, but no too tight.

BABAR: I have thought about that, and in addition to the high speed deployment, I still have limited space available to pack the parachute, so I might go with a long streamer. I'll sim the whole thing further after I'm done painting so I can get the weight exact and see what the deployment velocities look like. On a later project where I have sufficient room, I might try a nomex drogue with kevlar shroud lines to both take the sudden deceleration force and be able to stand up to the sustainer exhaust.

Mr. Rocket: unfortunately I have too little room inside to have a nose cone or other type of plug. What I'm going to do is layer a few pieces of regular paper wadding on top of the booster parachute (or streamer) to take the sustainer exhaust. The kevlar cord is 16 inches long before it pulls out the parachute/streamer, so by the time it comes out, it should be far enough back to not be burned. Hopefully.

Mr Rocket said:

Did you consider putting an internal nosecone on your parachute bay? The nosecone would protect your parachute from the exhaust plume of the sustainer, and the mass of the nosecone would help pull the chute out without having to rely on having a precise parachute roll that is tight enough, but no too tight.

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I do like that idea. It wouldn't be shaped anything like a nose cone due to the fat C-shape of my booster parachute bay. But I could make something of a C-shaped plug that's a snug fit that would help drag the chute out.

Then I could pack the chute so it's an easy slip fit into the bay and rely on the plug to pull the chute out.

EBruce,
Thanks for the positive feedback!
It's been a design challenge for sure, but so fulfilling when it worked in flight.
I was really surprised to see my searches turn up pretty empty when searching for a tried and true method to do this, so I'm glad to have others at least interested and trying different methods to figure it out.

With a streamer on a booster, it might help to have an external shock cord attached at the cg of the booster with spent engine. The body falls a little slower when suspended horizontally by the streamer.

GlenP said:

With a streamer on a booster, it might help to have an external shock cord attached at the cg of the booster with spent engine. The body falls a little slower when suspended horizontally by the streamer.

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Good point! I'll see how much room I have to work with, but it's looking more and more like a streamer on my setup is the way to go. I have a bunch of .5mm nylon string, so I'll see if I have enough room underneath to attach the end to the inside of the body next to the booster motor.

ebruce1361 said:

BABAR: I have thought about that, and in addition to the high speed deployment, I still have limited space available to pack the parachute, so I might go with a long streamer. I'll sim the whole thing further after I'm done painting so I can get the weight exact and see what the deployment velocities look like. On a later project where I have sufficient room, I might try a nomex drogue with kevlar shroud lines to both take the sudden deceleration force and be able to stand up to the sustainer exhaust.

Mr. Rocket: unfortunately I have too little room inside to have a nose cone or other type of plug. What I'm going to do is layer a few pieces of regular paper wadding on top of the booster parachute (or streamer) to take the sustainer exhaust. The kevlar cord is 16 inches long before it pulls out the parachute/streamer, so by the time it comes out, it should be far enough back to not be burned. Hopefully.

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If you use standard forward attachment point for your chute or streamer, the booster will most likely come down tail first. For your rocket and most aft-swept fin rockets, this means the fins hit terra firma (often all too much firma) first, and may break, particularly if you use a streamer instead of a chute. Still IMO better than tumble recovery.

My most common solution to this if you use a streamer or small chute is to design the rocket with FORWARD swept fins, so that when the booster descends tail first the MOTOR casing takes the first hit. This would be easily do-able with your two stage Bertha. You may want to OpenRocket this, the fins in the forward swept orientation are a little less effective than stock position.

Other options (which I have NOT tried, so take this with a grain of salt) would be an external shock cord attachment on the SIDE of the booster (something like streamer duration competition models), so the booster comes down sideways. As @GlenP stated. Still will hit fin first, BUT gives you the extra aerodynamic drag of the fins and body tube to slow rocket down. Could also have external attachment at the aft end of the booster, so it comes down forward end first, but this may crimp your body tube (which will impact first), which may or may not be better than breaking a fin.

Hope you get two straight trails and a safe recovery!