Centering Ring -- What Am I Missing?

[COSTransplant]

Ok. I have a 3" 2nd stage connected to an AC-74 Airframe Coupler connected to a 3" 1st Stage. The ID of the coupler is 2.851 inches. Obviously, the 2nd Stage (with fairing and parachute and Jolly Logic Chute Release and altimeter) has to separate from the 1st Stage so that the 2nd Stage engine can kick off, but does anyone sell a 29mm centering ring that will go inside this coupler? Do I have to sand down the standard 29mm centering ring to fit inside the coupler -- which will just float there when the two stages separate? It seems like I am trying to do a pretty standard thing here, so what am I missing?

 

[David Schwantz]

You want the CR in 1st stage or 2nd stage? And what do you mean by float?

 

[COSTransplant]

You want the CR in 1st stage or 2nd stage? And what do you mean by float?

I had been thinking that the CR would be in the 2nd stage, as that will be going farther / higher, but that was just a guess on my part. I am new to this, so I am open to suggestions! As far as floating is concerned, the coupler is attached to the 1st stage, so when the two stages separate, the 1st stage will take the coupler leaving the upper stage engine retainer and centering rings loose at the bottom (towards the engine) and tight at the top. The 2nd stage engine retainer will have a standard 29mm/3" centering ring at the top -- closest to the fairing where there is no coupler and the BT has a 2.923 ID. But the centering ring closest to the engine, where you have the BT and the coupler to compensate for, will be less than the ID of the coupler -- so less than 2.851 inches and can't really be glued in place so that the 1st stage can separate. I am sure that I am making this more complicated than I have to.

 

[David Schwantz]

Just install the CR far enough up into 2nd stage so the couple has room to slide into 2nd stage BT. I did one that has slots cut out in the coupler that the TTW fins go into. This keeps 1st stage from rotating out of alignment.

 

[COSTransplant]

Just install the CR far enough up into 2nd stage so the couple has room to slide into 2nd stage BT. I did one that has slots cut out in the coupler that the TTW fins go into. This keeps 1st stage from rotating out of alignment.

Can do -- and will do! The possible problem is that the 2nd stage motor is not secured on both sides -- just at the back end with two centering rings about 1 inch apart. Does anyone see a problem with that?

 

[David Schwantz]

Why can't you put a CR at the top of the mmt?