75mm/98mm case retention

[ClayD]

Pfffft. put a couple of wraps of fiberglass around the end of the motor tube. Cut 4 slots paralleling the lenght of the body tube. Wrap enough tape around the end of the motor. Insert motor until you can see the motor tube segments bow out a tiny bit. Use a stainless steel band clamp around the MT, tighten. Yah, a radiator hose clamp.

Yah, it's cheap and dirty but I know it holds, I used a Kosdon M2240 with 500 pounds of thrust with no outside snap ring and the motor never moved, well, except for it's trip up a mile

Then again, I can see being ignored. The AeroPac retainer is a solution but not the only one and I'm one for NOT doing things to add expense to a device who's ultimate doom is a hole in the ground

I have aeropac retainers on my small stuff that i dont feel like messing with...
But, its cheaper- by 40 or 50 bucks to make something yourself on the bigger birds.

I like the idea of the tailcone for aerodynamic purposes, and using it as retention at the same time...

For certification flights, what you are suggesting, probably wont fly with "most taps"...
I had a short motor tube, and was going to round my motor with ductape, and put a clamp on it like you describe, (reverse thrust ring) for retention...
(they woulnd sign off on it..)

 

[JDcluster]

I had it happen once.
It was about 5 years ago the rocket was under chute & about 300 ft from the ground when it let go. The booster was trashed all I was able to save from it was the fin can.


JD

Never had it happen. Never heard of that either. Heard of eye bolt opening up but not unscrewing themselves.
You would need a lot of torque to unwind a properly tightened eye bolt. A drop or two of Loctite(red or blue) on the threads and there's no way in hell that it'll come off unless in a vise.

 

[bobkrech]

Pfffft. put a couple of wraps of fiberglass around the end of the motor tube. Cut 4 slots paralleling the lenght of the body tube. Wrap enough tape around the end of the motor. Insert motor until you can see the motor tube segments bow out a tiny bit. Use a stainless steel band clamp around the MT, tighten. Yah, a radiator hose clamp.

Yah, it's cheap and dirty but I know it holds, I used a Kosdon M2240 with 500 pounds of thrust with no outside snap ring and the motor never moved, well, except for it's trip up a mile

Then again, I can see being ignored. The AeroPac retainer is a solution but not the only one and I'm one for NOT doing things to add expense to a device who's ultimate doom is a hole in the ground

Dave

You get it. It may not be pretty but it works for me as well.

You don't need to overbuild, nor do you need to spend a lot of money to retain a L2/L3 motor casing in a rocket. A TAP or L3CC who doesn't understand how it works, or how to check that it's strong enough probably shouldn't be approving L3 certification attempts.

Bob

 

[ClayD]

Dave

You get it. It may not be pretty but it works for me as well.

You don't need to overbuild, nor do you need to spend a lot of money to retain a L2/L3 motor casing in a rocket. A TAP or L3CC who doesn't understand how it works, or how to check that it's strong enough probably shouldn't be approving L3 certification attempts.

Bob

I dont think requireing "positive" motor retention is a diservice to a certifier.
Nor, do I think it's (bad for them to say they wont sign of on a friction fit - certification flight) that doesnt mean they dont understand it. escpecially when the design is such that allows positive retention.


I spent 4.60 cents on my retention....it was a bulkhead between my forward closure and the eyebolt that shouldered the motor mount... the aluminum(i had aluminum on hand - birch would have cost a buck or 3) was free and 4.60 cents for a box of 8-32 stainless machine screws.

 

[degreaser]

Then again, I can see being ignored. The AeroPac retainer is a solution but not the only one and I'm one for NOT doing things to add expense to a device who's ultimate doom is a hole in the ground

It should be on the opposite end of the thing sticking in the ground so you can unbolt it from the carcass and take it with you

 

[Mike Di Venti]

Actually, it does happen, I have seen it a few times myself, and read articles on Rocketryplanet where people had it happen to them.
(and they claimed to have employed the exact thing you just suggested.)
Since all your doing is compressing the threads, all it takes is enough torgue to overcome the friction of that compresion. once that happens, all it has to do is continue rotating in the right direction...

It happens...

I guess I have a horse shoe lingering around me then or I haven't flown enough motors!
All of my rockets that fly 54mm and up get the shock cord attached to the eye bolt in the forward closure. I use Loctite and the eyebolt, no split-lock washer.


I like the idea about the pipe clamp also. I used two of them to hold a 54/2550 motor on a Douglas Fir this past Jan. It held on while a K1000sk did it's thing.

 

[AHansom]

where are you getting forged stainless?

Lots of forged stainless hardware avalible at boating stores.

https://bosunsupplies.com/products2.cfm?product=S0314