High Power Staging question

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Sooner Boomer

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How are the booster and upper stages fit together in a high power stack? Are they just friction fit like a low power Estes rocket? I've seen several videos on YouTube where it looks like the upper stage drag separates and continues for a second or two before igniting the motor (the booster continues to ascend as well before reaching apogee and deploying recovery).
 

roytyson

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That's how mine is. The first/second stage just slides into one another. I have a separation charge to separate the rocket if drag separation does not work.
 

David Schwantz

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Mine also. Just friction, but I do cut a slot in the booster coupler where the rail button screw goes. This is used to index the 2 together.
 

JimJarvis50

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On rockets that are minimum diameter, it is possible to use the motor as the coupler. The motor extends out of the bottom of the air frame by a caliber or so and fits into the top of the booster. On my rockets, I put a bulkhead down into the booster for the sustainer to sit on. The bulkhead protects the booster chute from the separation charge and from the wind after separation. It's shear pinned to the booster.

On rockets that aren't minimum diameter, the most common approach is to use a coupler tube that goes up into the sustainer and down into the booster. This interstage coupler has a switchband on it. So, this coupler is essentially an "open" nose cone on the booster. There is a bulkhead inside of the coupler tube for connecting recovery harness and for isolation the separation charge from the booster chute. It is possible to put electronics for the booster and/or the separation charge in the lower part of the coupler below the bulkhead. I'm doing that on a rocket now. The coupler is shear pinned to the booster but not to the sustainer.

Jim
 

kswing

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On my high power two-stage I use a coupler between the upper and lower stages to join them. I designed it to try to get it to drag separate, but, so far out of three flights that hasn't happened. I sanded the booster/sustainer coupler so that it was a very loose fit and I didn't round off the edges of the booster fins so they would have more drag, but, so far they have still stayed together until the upper motor lights. Part of my problem is that both the booster and the sustainer are 4" in diameter, so, there's no drag from a transition to help.

I knew that drag separation might not happen, so, I lined the inside of the coupler with thinned JB weld, so, it is protected from the exhaust of the upper motor. I'm considering adding a small separation charge that will be triggered by the altimeter that ignites the sustainer about 3/4 second before the sustainer fires. That way it is easier on the coupler and I can get the cool effect of the two parts flying together before the sustainer lights.

Here is a link to my build thread: https://www.rocketryforum.com/threads/blue-stage-high-power-two-stage.143899/
 

JimJarvis50

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On my high power two-stage I use a coupler between the upper and lower stages to join them. I designed it to try to get it to drag separate, but, so far out of three flights that hasn't happened. I sanded the booster/sustainer coupler so that it was a very loose fit and I didn't round off the edges of the booster fins so they would have more drag, but, so far they have still stayed together until the upper motor lights. Part of my problem is that both the booster and the sustainer are 4" in diameter, so, there's no drag from a transition to help.

I knew that drag separation might not happen, so, I lined the inside of the coupler with thinned JB weld, so, it is protected from the exhaust of the upper motor. I'm considering adding a small separation charge that will be triggered by the altimeter that ignites the sustainer about 3/4 second before the sustainer fires. That way it is easier on the coupler and I can get the cool effect of the two parts flying together before the sustainer lights.

Here is a link to my build thread: https://www.rocketryforum.com/threads/blue-stage-high-power-two-stage.143899/
One factor that can prevent drag separation is torque in the air frame causing friction at the point of separation. I've had this happen. Don't assume that a size reduction from the booster to the sustainer increases the likelihood of drag separation. A larger booster is also relatively heavier, which works against drag separation. Having said the above, it appears that your rocket should drag separate.

Jim
 

StreuB1

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On my high power two-stage I use a coupler between the upper and lower stages to join them. I designed it to try to get it to drag separate, but, so far out of three flights that hasn't happened. I sanded the booster/sustainer coupler so that it was a very loose fit and I didn't round off the edges of the booster fins so they would have more drag, but, so far they have still stayed together until the upper motor lights. Part of my problem is that both the booster and the sustainer are 4" in diameter, so, there's no drag from a transition to help.

I knew that drag separation might not happen, so, I lined the inside of the coupler with thinned JB weld, so, it is protected from the exhaust of the upper motor. I'm considering adding a small separation charge that will be triggered by the altimeter that ignites the sustainer about 3/4 second before the sustainer fires. That way it is easier on the coupler and I can get the cool effect of the two parts flying together before the sustainer lights.

Here is a link to my build thread: https://www.rocketryforum.com/threads/blue-stage-high-power-two-stage.143899/

Epoxy 3 or 4 drag paddles to the OD of your booster. Just simple basswood or fiberglass plinth blocks that protrude into the air stream about 3/8" with a 45° angle facing towards the direction of flight.

These would mimic the deployable drag paddles on the Talos-Taurus interstage. Except they would be permanent and be installed on the airframe.

Quick sketch below....


1641389694873.png
 

wrad

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I used a coupler on top of the booster that slotted into the second stage by about the same distance as 1 tube diameter. the fit was loose, however I used a small separation charge set to burnout +0.5 seconds to separate the 2 pieces. I have also used 3 carbon rods sticking up from the top of the booster, that slot into 3 matching tubes mounted into the second stages motor mount. This method is more complex to build and get the fit right, however has the advantage of not needing to recess the bottom centring ring of the second stage to far into the body.
both of these methods can be seen in my 2 skylark builds.
 
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