Got it. Friction fit.

Well, friction fit would work but internal clamping or an eyebolt in the forward closure attached to shock cord and/or bulk heads helps keep the worries down.

After I posted the question, I thought worst case, so the casing pops out the back. Everything is still attached, and the main would come out later on. At least, the rocket would be apart and less likely to lawn dart.

What about a slimline retainer. Since most likely you would be doing tip-to-tip FG on the fins, you could merge the transition from the retainer to the airframe with FG.

Just a thought...

Ken, that might work. Good suggestion.

How much room do you have? How about combining a threaded forward closure, an eyebolt, and a bulk plate epoxied in place at the forward end of the motor casing?

Basically the retention is on the forward end of the motor. The bulk plate keeps the motor from sliding out the back, and the eye bolt is a pretty secure way of tying the case to the rest of the bird.

This would work if you can reach far enough into the 4" tube to screw the eyebolt into the forward closure of the loaded motor casing.

One drawback is that this would only work for the case it's designed for.

Ed, that's a great idea. The rocket would be 3"/76mm, and I will be attaching the harness to the casing at the forward closure. Putting a bulkplate between the eyebolt and the closure would definitely hold that puppy in enough. I plan to use my 75/6400 casing, so I could fit the bulkplate to that length. Fortunately my hands are small enough to probably get in far enough to secure it. Or, I can build a tool to do it. That will work.

What Ed said...

Warren

You guys have the answers.

Actually similar to what Ed was explaining But a little different.

Epoxy a Centering ring in place just down a little from top of the booster. Then using a piece of all thread cut to length for the specific motor size/length you would screw it into the motor forward closure and I even recommend using a double nut or lock nut to hold it tight to the closure so it wont back out. Slide the all thread and motor into place into the booster section. You would now have a couple inches or so of all thread sticking out above the centering ring with the motor tight at the bottom on its thrust ring.(you will need to cut the all thread to length) Then you would have a Bulk plate with a hole in the center for whatever size all thread that would be sticking up. I would also recommend putting larger diameter flat washers on this and then nut them into place with the bulkplate on top of the Centering ring. Now the bulkplate is tight and the motor is held in place via forward retention. All you need now is a forged eye nut and a locknut to hold it in place. You now can tie your harness directly to the top at the eyenut. If you want to run a different size motor just change the all thread length. Hope that made sense.. If not give me a shout and I would be glad to show you.

Doing it this way makes it easy to do without having to stick your hands down inside the tube as well as it will fit several different motors including as long as will fit in the booster.

Bruce, and others, Here is a description of what I am doing..

I have 2 min diameter projects I am working on. First is the 98mm project. It will use a form of friction fit. The actual motor case will protrude up out of the booster section and will act like a coupler for the upper airframe to booster(this part is also slightly modular in design to accommodate a few different case sizes from 24" to 48" long motors). My apogee deployment will be drougless and held in the lower section of the upper airframe. Upper airframe will be no more then 24" long and this also includes where the ebay will rest. Which will be Housing 2 altimeters the batteries and a GPS downlink and tracking module. From there the upper airframe portion thats still part of the 24" and then to the nose cone. A Von Karmen nose. It will house the chute and the main harness as well as the standard tracking device. Launch will be via Tower. No rail buttons. It will be shear pinned on both ends. The case will have a special closure built that holds an assembly for the shear pins to push into. But thats it in a nut shell. Both the same ways for 75mm and 98mm. As JW always says "Come on in the waters is fine" Well time for the sharks to hit the water.

So far I should be a max length of 8ft. Or I should be under. With a weight of less then 10lbs (no motor) probably close to 8lbs-9lbs max. All glass construction with a 2 layer 1/2 & T2T laminate on the fin section with Carbon Fiber. should be interesting. On the pad with the 17500 motor should be around 28 to 30 lbs max weight. That will be riding close to 85% full N power. Should be a boost.

Conway, Like this but bigger?
Tony

The knowledge this club has is incredible! Conway, I know what you're saying, and thanks, that'll do it. Tony2, that rocket looks perfect!

That rocket of Tony's is incredible. I've seen it. Weighs less than 5# empty. And yes, folks - that is an M casing in that rocket. Post flight (in other words, it WORKED!).

Note that there are no upper restraining bulkheads, rings, etc. There is also no aft retainer. That is friction fit motor retention.

Tony, will see you in August on the playa. My rocket will look vaguely familiar to you 😉

JW