Motor Retention Advice for a 75 mm motor in a 5.5 inch fiberglass body tube

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SeaSiren33

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Hey Everyone! I am planning to build a fiberglass rocket using the M1350W motor. However, I am unsure on the best way to attach the motor to my rocket. I have heard of many people using fin cans and many other people using a fiberglass motor mount and attaching directly to the booster with fiberglass centering rings. I am not sure which one to use please let me know what you guys think!
 
Hey Everyone! I am planning to build a fiberglass rocket using the M1350W motor. However, I am unsure on the best way to attach the motor to my rocket. I have heard of many people using fin cans and many other people using a fiberglass motor mount and attaching directly to the booster with fiberglass centering rings. I am not sure which one to use please let me know what you guys think!
Everything you need to know about motor mounts and motor retainers should be learned by building smaller rockets first, then just scale them up.
 
Hey Everyone! I am planning to build a fiberglass rocket using the M1350W motor. However, I am unsure on the best way to attach the motor to my rocket. I have heard of many people using fin cans and many other people using a fiberglass motor mount and attaching directly to the booster with fiberglass centering rings. I am not sure which one to use please let me know what you guys think!

Meh, details!

Order all the rocket parts and motors you will need ASAP. You want to make sure you get the orders in before all the holiday sales. You don't want to miss out, support our vendors!
 
This sounds like a typical college rocketry program starting up. They want to build L3 rockets for Spaceport or similar competitions and have no clue how to actually build and fly rockets. Usually a group of L0 students with resources and drive, but no experience. That is why they are asking basic questions a L1 rocketeer should know, while trying to build a L3 rocket.

My advice in these cases is to find a L3 Tripoli mentor, not the professor or school advisor since they seldom have any experience either. That's especially important if they aren't entering the COTS competitions and want to build their own motors like the OPs previous posts about using custom CF motor casings seems to suggest.

Find a mentor!
 
I think your wording is what is making people think that you don't know what you're doing... you don't retain the motor to the "fin can" directly (unless you're doing a minimum-diameter rocket, but if you were then you probably wouldn't be asking this question.) The first response you got was probably the correct answer... Aeropack 75mm retainer epoxied to the motor mount.
 
Lol I got my L2 Don't gotta post about everything. Learned my lesson w/ chute release and moved on. Ur rly helping other ppl get into the hobby here. Real hero
Riiiiiiiiiiiiiiiiight. Thanks for the laugh. If that were the case, you wouldn't be asking such a basic common-sense question that anyone with an L2 would know the answer to. Nice approach. Real Einstein.
 
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Lol I got my L2 Don't gotta post about everything. Learned my lesson w/ chute release and moved on. Ur rly helping other ppl get into the hobby here. Real hero
Riiiiiiiiiiiiiiiiight. Thanks for the laugh. If that were the case, you wouldn't be asking such a basic common-sense question that anyone with an L2 would know the answer to. Nice approach. Real Einstein.

From these responses, I believe this is a typical college rocket program start up. We've had several like this. They have several students with L1 certs because the college bought a bunch of kits and motors so they could have certified fliers for their programs. They all went out and did a cert flight on the same day with the same kits and the same motors. For most or all of them, it was their first and only rocket flight. The L2 cert students flew a J, maybe on with the same rocket. They usually only flew 2 flights, unless they missed on one of the cert flights, then they might have 3 flights under there belts.

I've seen this same process play out with several college rocketry programs. They may have a L1 or L2 cert, but they really have no experience at all and the college is still pushing them to fly large L3 projects, make their own motors, etc. because at the college, students or faculty, don't know what they don't know.

This can be a huge learning experience for everyone involved on the college team, even if they are relearning well known subjects by trial and error. It can be a huge headache for the local clubs running the launches where the college groups are doing their test flights and/or test motor burns.

The one thing that mitigates the problems for both the colleges and clubs, is a good, experienced, L3 mentor for the team.
 
Lol I got my L2 Don't gotta post about everything. Learned my lesson w/ chute release and moved on. Ur rly helping other ppl get into the hobby here. Real hero
So then - how did you retain the motor on your L2 flight? Take what you learned from your L1/L2 and other HPR experience, and apply it to what you're doing now...
 
My preference is to use the Aeropack-style minimum diameter mounts, as other upthread have said, and keep the rear thrust ring off the back of the motor mount tube. Let the motor mount at the front take the thrust to the airframe. That way you keep the back half of the rocket in tension.
 
If it’s a single use college project just slather a bunch of JB Weld in the motor mount tube and glue the motor in place 😧
 
Lead bricks. large ones. That way I don't have to duck when they press the button.
 
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