2.6" Rocket with 54mm MMT -- where/how to attach shock cord?

I am open to suggestions. Not true minimum diameter, and I don't plan to buy plugged motors with eyebolts on the forward closure.

What do people do?

I would be happy to glue the cord to the MMT, but then I would have to completely cut a piece out of the top CR. Doesn't seem wise.

I could just epoxy it to the booster above the motor, like an Estes but without the little paper thingie. Thoughts?

Better ideas?

That means your centering rings are 1/4 inch thick on each side. What shock cord are you using? You should be able to file a small notch in the centering ring and shove it under your shock cord.

I did it with a 1/8" kevlar cord in a 2" rocket with 38mm hole.

Like he said. File a notch in the forward centering ring. Slide the cord through that notch, epoxy the cord to the motor mount. Done and done.

cut two notches in the centering ring and epoxy a loop to the mmt. make sure they aren't in the way of the fins. make the loop longer than the booster tube so you can easily tie a knot in it and attach to it. there isn't room for a knot or joint between a 54mm motor and the body tube. I would use the 5/16 kevlar rocketry warehouse sells. even if you have to cut all the way through the centering ring it will be fine.

I like the fixed piston design.
Cut a 1 caliber length piece of coupler, then glue a bulkplate into it with your favorite Eye bolt, U-bolt setup.
You can either attach it with glue or just screws.

JD

I would be happy to glue the cord to the MMT, but then I would have to completely cut a piece out of the top CR. Doesn't seem wise.

But it is wise. It's just a centering ring. It only needs to make three points of contact with the mount and three more with the tube. In some designs it may not be glued to one or the other.

Igotnothing said:

I would be happy to glue the cord to the MMT, but then I would have to completely cut a piece out of the top CR. Doesn't seem wise.

But it is wise. It's just a centering ring. It only needs to make three points of contact with the mount and three more with the tube. In some designs it may not be glued to one or the other.

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Looks like that is what I'll have to do. The CR is 1/8" deep and 4.33 mm between the inner and outer edges.

You can drill some holes in a bulkhead, then put an eyebolt on it and epoxy into the tube.

rocketjet787 said:

You can drill some holes in a bulkhead, then put an eyebolt on it and epoxy into the tube.

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Yeah. I use a non-redundant AV system and kind of like to have motor back-up as an option.

If you drill holes in it then the ejection gasses can still flow through it.

rocketjet787 said:

If you drill holes in it then the ejection gasses can still flow through it.

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Hmmm, true. Might be worth a shot. Thanks.

NEW RELATED QUESTION. If I go this route, and use a bulkhead, which bulkhead do I buy? A coupler bulkhead or an airframe bulkhead?

Does this mean it fits inside or outside the specified tube?

Airframe bulkheads fit inside the airframe, coupler bulkheads fit inside a coupler. A airframe bulkhead is the same O.D. as a coupler, so it will not go inside the coupler which is nice if you want the coupler to act as reinforcment for the bulkhead.

I typically use an airframe bulkhead because my coupler is the avebay.

And does it matter if the tube is thin wall or standard FG? RW doesn't seem to make a distinction, so I assume internal diameter is the same either way?

No as long as the bulkhead fits snug enough for you to be able to secure it it should be fine.

Bat-mite said:

And does it matter if the tube is thin wall or standard FG? RW doesn't seem to make a distinction, so I assume internal diameter is the same either way?

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On the Rocketry Warehouse thin wall tubing, it looks as though the outer dia of the airframe is smaller, and the inner diameter of the coupler is smaller. I can measure for sure when I get home. I had ordered some plywood airframe bulkheads and inner coupler bulkheads from Giant Leap to go in my Fire Flyer. The airframe bulkheads fit like a champ, but the inner coupler bulkheads were so loose, they never touched the walls of the coupler.

A bulkhead with a short (~1") piece of coupler above the bulkhead provides a solid SC mount that won't pull out. As previously mentioned, drill a few holes for motor back-up.