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Best two-stage separation method? (excluding drag)

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Cameron Anderson

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The "up" portion of my two-stage flight this weekend went exceedingly well. 3" airframe, AT K400 DMS booster to AT 38/600 i435 RMS in the sustainer to 8,184 feet. The "down" portion was marred by booster buring in ballistically. On-board sustainer video shows clean desperation in just two frames (bad luck on camera angle) initiated by 1gram of BP. After that, the coupler charge was initiated (evidence of charring in new nomex chute shield and recovered e-match) but the coupler never separated from the airframe which meant the booster chute at apogee (with chute release set for 500') never deployed.

Mating was achieved by extending the sustainer airframe below the motor and using a coupler from the booster to slide into the sustainer airframe. Coupler was secured to booster airframe with 2 2-56 nylon shear pins. Twisting was prevented by three 3" aluminium 1/4" posts on the coupler that slid into holes drilled in the sustainer thrust plate. Fit was repeatedly tested and sustainer and booster separated easily if held vertically and two separate ground tests.

What methods are out there to assure clean seperation and coupler separation? I have a feeling loads under boost tweaked the coupler and locked it in.
 

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timbucktoo

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I design my flights so that they will separate in the following manner:
Drag separation as primary and should that fail I will have a separation charge as backup. MissileWorks PET2 timer is used to fire the separation charge and since it is a 2 event timer, I use the 2nd event as an apogee event for recovery..
 

Cameron Anderson

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I design my flights so that they will separate in the following manner:
Drag separation as primary and should that fail I will have a separation charge as backup. MissileWorks PET2 timer is used to fire the separation charge and since it is a 2 event timer, I use the 2nd event as an apogee event for recovery..
I used a PET2 as well. I mounted it in the sustainer - first event was seperation @ MECO +0.5, second event was sustainer motor ignition @ MECO +1.0 (dipped an e-match in LOTS of pyrogen and I coated the inside of the top motor grain in even more pyrogen...great method). I had a perfectflite minialt W/D in the booster for apogee chute main deployment with a Jolly Logic chute release.

For your sep charge, so you use a charge well (like a PVC cap) or a cardboard tube with BP? I use caps for my sustainer with coupler pistons, but due to space limitations I used a 1/4" cardboard tube for my sep charge.
 

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I use my RRC3 as primary recovery in boosters interstage coupler. The aux channel ignites a BP charge to seperate the booster and the sustainer. I rely on drag seperation but if that does not work It will seperate after the BP goes off.
 

timbucktoo

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I put my PET2 in the Interstage coupler & run an ematch to forward section. I use 0.5 grams BP wrapped in masking tape in a low, almost flat profile for separation charge. The BP & ematch are in the blue tape.
IMG_4761.JPG
 

Cameron Anderson

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I use my RRC3 as primary recovery in boosters interstage coupler. The aux channel ignites a BP charge to seperate the booster and the sustainer. I rely on drag seperation but if that does not work It will seperate after the BP goes off.
How do you set up your interstage with the sep charge? I wish I took more photos of mine. The sustainer thrust ring was recessed about 2" up from the rear of the airframe. The booster coupler slid in about 1.5" the sustainer airframe so loads we're transferred via the top of the booster airframe and the sustainer airframe, no loads were carried by the coupler. The coupler bulkplate was recessed 2" from the top of the coupler to allow room for the sustainer motor.
 

timbucktoo

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Questions came at a good time. Preparing for launch this weekend. Motor is almost flush with aft end. I’m using a Slim Line retainer. I have about 1/8” clearance between vent band & bulk head.
IMG_4765.jpg

IMG_4766.jpg
 

Cameron Anderson

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Questions came at a good time. Preparing for launch this weekend. Motor is almost flush with aft end. I’m using a Slim Line retainer. I have about 1/8” clearance between vent band & bulk head.
View attachment 364742
View attachment 364743
Quite fortunate for me! 3" with a 54mm?

How much space is there between the bottom of the motor and the charge?
 

JimJarvis50

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I have a feeling loads under boost tweaked the coupler and locked it in.
From your description, it doesn't sound like the coupler was sitting on a ring inside the booster tube. If there is no ring, then maybe the weight of the coupler, aluminum rods and bulkplate cause the coupler to go down further into the booster tube. Then, the shear pins might have just bent instead of shearing, and pinned to coupler into the booster tube.

Typically, the coupler tube would have a switch band on it so that it such that it can't sink into the booster tube.

Jim
 

timbucktoo

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Quite fortunate for me! 3" with a 54mm?

How much space is there between the bottom of the motor and the charge?
Probably 1/16" to 1/8" from motor to separation charge (which is pretty flat against bulkhead.
Forgot to say, I have noticed no issues of sustainer twisting or rotating. It is a really loose fit and i coat it with baby powder before I stack it.
 

Cameron Anderson

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From your description, it doesn't sound like the coupler was sitting on a ring inside the booster tube. If there is no ring, then maybe the weight of the coupler, aluminum rods and bulkplate cause the coupler to go down further into the booster tube. Then, the shear pins might have just bent instead of shearing, and pinned to coupler into the booster tube.

Typically, the coupler tube would have a switch band on it so that it such that it can't sink into the booster tube.

Jim
I was hoping you'd reply Jim, love your videos! Virtually the entire booster was lined with couplers - I use them to reinforce my motor mount bulkplates. The interstage coupler was sitting on a load-bearing coupler in the booster that was resting on the top motor mount plate. I was very worried about acceleration loads so the interstate coupler wasn't under any loads from the sustainer - the coupler just kept it upright. Loads were intended to be distributed airframe to airframe. Although I still think you are right, something shifted and prevented separation. Too bad there wasn't much to examine post-crash. I am fairly confident the booster impact with the interstate coupler still attached since I recovered 2 of the 3 aluminium studs on the coupler and they were bent 45 degrees.
 

Cameron Anderson

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Probably 1/16" to 1/8" from motor to separation charge (which is pretty flat against bulkhead.
Forgot to say, I have noticed no issues of sustainer twisting or rotating. It is a really loose fit and i coat it with baby powder before I stack it.
Wow, right tolerance. I was assuming 1" separation minimum. Baby powder is a good idea too.

Are you finding the charge is unnecessary and drag separates your booster?
 

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Wow, right tolerance. I was assuming 1" separation minimum. Baby powder is a good idea too.

Are you finding the charge is unnecessary and drag separates your booster?
My very first 2 stage, ended up with separation by motor ignition. Not sure what happened. Posted here & many good recommendations. Increased charge from 0.2 grams to 0.5 grams BP & made sure fit was loose. Really hard to say if charge is needed & really hard to tell in that 1/2 second after booster burnout if its the charge or just drag doing it's thing.
 

Cameron Anderson

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My very first 2 stage, ended up with separation by motor ignition. Not sure what happened. Posted here & many good recommendations. Increased charge from 0.2 grams to 0.5 grams BP & made sure fit was loose. Really hard to say if charge is needed & really hard to tell in that 1/2 second after booster burnout if its the charge or just drag doing it's thing.
I had an 808 camera on my sustainer and it is clear that the separation charge and not drag is what separated the booster and sustainer (that's all the camera was good for because it was a sunny day and the playa had a white crust that washed out everything else, including sustainer ignition and burn).
 

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I just looked at video in slow mo. Naturally Mr. Jarvis suggested putting a camera on booster looking up. You can see 2 things. 1) there is no twist/spin & 2) if I am seeing things correctly, you can see the charge go off at 11 seconds right at separation.
 

Cameron Anderson

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I just looked at video in slow mo. Naturally Mr. Jarvis suggested putting a camera on booster looking up. You can see 2 things. 1) there is no twist/spin & 2) if I am seeing things correctly, you can see the charge go off at 11 seconds right at separation.
Great footage. I need a second camera so I don't have to decide between booster up or sustainer down view.
 

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I was hoping you'd reply Jim, love your videos! Virtually the entire booster was lined with couplers - I use them to reinforce my motor mount bulkplates. The interstage coupler was sitting on a load-bearing coupler in the booster that was resting on the top motor mount plate. I was very worried about acceleration loads so the interstate coupler wasn't under any loads from the sustainer - the coupler just kept it upright. Loads were intended to be distributed airframe to airframe. Although I still think you are right, something shifted and prevented separation. Too bad there wasn't much to examine post-crash. I am fairly confident the booster impact with the interstate coupler still attached since I recovered 2 of the 3 aluminium studs on the coupler and they were bent 45 degrees.
OK, that wasn't the problem. So, I guess the problem was that the "nose cone" coupler simply didn't deploy?

FYI, I generally "key" the stages together in some manner so that they can't turn against each other. The pic shows an example. For your design, you might drill a hole bisecting the air frames (two of them, 180 degrees apart), and then put the epoxy dab on the coupler tube. These work quite well, and also make it very easy to put in the shear pins.

Jim
 

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Cameron Anderson

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OK, that wasn't the problem. So, I guess the problem was that the "nose cone" coupler simply didn't deploy?

FYI, I generally "key" the stages together in some manner so that they can't turn against each other. The pic shows an example. For your design, you might drill a hole bisecting the air frames (two of them, 180 degrees apart), and then put the epoxy dab on the coupler tube. These work quite well, and also make it very easy to put in the shear pins.

Jim
Correct, the "nose cone" which was the uppermost removable component of my booster, which was also my interstate coupler, failed to separate. I can confirm that the charge to separate the coupler from the airframe did in fact fire (burned e-match and charring on nomex blanket).

I love your key method, it's far simpler than mine. I used 3 1/4" aluminium rods on the interstage coupler that slid into holes on the sustainer thrust plate. They were snug enough to prevent twisting and loose enough the booster slid out if the stack was vertical.
 

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Correct, the "nose cone" which was the uppermost removable component of my booster, which was also my interstate coupler, failed to separate. I can confirm that the charge to separate the coupler from the airframe did in fact fire (burned e-match and charring on nomex blanket).

I love your key method, it's far simpler than mine. I used 3 1/4" aluminium rods on the interstage coupler that slid into holes on the sustainer thrust plate. They were snug enough to prevent twisting and loose enough the booster slid out if the stack was vertical.
I have a similar booster design, but it's motor deploy and uses a piston. Never had any problems getting the "cone" off. I have considered going to electronic deployment of this with the electronics in the staging coupler, and then using a chute release, but I haven't done it yet. I have wondered about how things would change with the charge above the chute. It would require more BP (since there would be no piston) and it would require that the coupler pull the chute out (requiring perhaps the addition of some weight to the coupler for inertia). The last time I flew the rocket, I was told the booster deployment was pretty late. Hmm.

The key method is quite nice and not difficult. My three stager had seven sets of keys.

Jim
 

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I have a similar booster design, but it's motor deploy and uses a piston. Never had any problems getting the "cone" off. I have considered going to electronic deployment of this with the electronics in the staging coupler, and then using a chute release, but I haven't done it yet. I have wondered about how things would change with the charge above the chute. It would require more BP (since there would be no piston) and it would require that the coupler pull the chute out (requiring perhaps the addition of some weight to the coupler for inertia). The last time I flew the rocket, I was told the booster deployment was pretty late. Hmm.

The key method is quite nice and not difficult. My three stager had seven sets of keys.

Jim
I prefer piston deployment when possible. I was using an altimeter for apogee deployment of my booster chute then a jolly logic release (first flight of the jolly logic, it was reduced to expensive confetti). The interstage was fairly light and I tested it successfully twice and each time it managed to pull the chute out (since the charge was above the chute). I'm toying with the idea of my electronics above the piston in the interstage and running an e-match charge down past the chute into the piston so I still get the piston to "push" (which I'm far more comfortable with).
 

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FYI, I generally "key" the stages together in some manner so that they can't turn against each other. The pic shows an example. For your design, you might drill a hole bisecting the air frames (two of them, 180 degrees apart), and then put the epoxy dab on the coupler tube. These work quite well, and also make it very easy to put in the shear pins.
Jim
It is amazing how much easier keying each section makes re-assembly. I use either a short piece of steel dowel pin, or lately I have been gluing in a piece of CF rod purchased from a hobby store.
 

Cameron Anderson

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It is amazing how much easier keying each section makes re-assembly. I use either a short piece of steel dowel pin, or lately I have been gluing in a piece of CF rod purchased from a hobby store.
I thinking of using a rail button post, it's thin and strong and has a base I can epoxy over.
 

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I thinking of using a rail button post, it's thin and strong and has a base I can epoxy over.
The way I do the epoxy is just to paint the matching air frame cutouts with some teflon release. Then I pour the epoxy, containing enough fumed silica to keep it from running, and I'm literally done.

Jim
 

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And then there's paper tubes where you can just cut a wedge of airframe with a fine blade, glue it to the coupler, and it Becomes the key! (I'll go back to my non-extreme flight corner now ;))
 

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OK, that wasn't the problem. So, I guess the problem was that the "nose cone" coupler simply didn't deploy?

FYI, I generally "key" the stages together in some manner so that they can't turn against each other. The pic shows an example. For your design, you might drill a hole bisecting the air frames (two of them, 180 degrees apart), and then put the epoxy dab on the coupler tube. These work quite well, and also make it very easy to put in the shear pins.

Jim
It is amazing how much easier keying each section makes re-assembly. I use either a short piece of steel dowel pin, or lately I have been gluing in a piece of CF rod purchased from a hobby store.
The way I do the epoxy is just to paint the matching air frame cutouts with some teflon release. Then I pour the epoxy, containing enough fumed silica to keep it from running, and I'm literally done.

Jim
And then there's paper tubes where you can just cut a wedge of airframe with a fine blade, glue it to the coupler, and it Becomes the key! (I'll go back to my non-extreme flight corner now ;))
 
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