Fiberglass Coupler Alternatives for Level 2 Certification Attempt

[SeaSiren33]

Hello!

I am someone who has completed their level one certification with a cardboard tube on an H-motor. For my next rocket, I am using fiberglass tubes for the first time. I want to connect 3 4-inch fiberglass tubes, but I don't want to spend money on pre-bought fiberglass couplers. Are there any cheaper alternatives that will work for high-power rockets? I have access to a 3D printer and have thought of 3D printing couplers with PLA. Would this be strong enough to survive the high stress on a level 2 or even 3 certification?

 

[rharshberger]

Hello!

I am someone who has completed their level one certification with a cardboard tube on an H-motor. For my next rocket, I am using fiberglass tubes for the first time. I want to connect 3 4-inch fiberglass tubes, but I don't want to spend money on pre-bought fiberglass couplers. Are there any cheaper alternatives that will work for high-power rockets? I have access to a 3D printer and have thought of 3D printing couplers with PLA. Would this be strong enough to survive the high stress on a level 2 or even 3 certification?

Spend the money, buy the right product, fiberglass tube needs fiberglass couplers or you are just asking for a failure at the coupler. 3D printed parts will not survive as couplers without significant reinforcement.

 

[Hobie1dog]

aren't 3d printed parts not allowed on L3 rockets? I know you are going for a L2, but I thought someone will answer your question that can answer mine too.

 

[Handeman]

@rharshberger is absolutely correct. The shear strength of 3D printed parts is weakest in the direction a coupler would be bending. I would never trust it.

Buy the correct parts. If you can't afford the correct parts, you might want to reconsider building that size rocket and doing certs to those levels. The motors are going to eat up a lot more $$$ than what the rocket costs. 2 L3 flights and 4 large L2 flights a year can easily cost over $2,000 just in reloads.

 

[Raythain]

@rharshberger is absolutely correct. The shear strength of 3D printed parts is weakest in the direction a coupler would be bending. I would never trust it.

That’s only if you print the coupler vertically. You could print the coupler horizontally for a better bending strength.

But the larger point still stands. Don’t shave cost at the couplers, especially when you’re talking about motors that cost as much or more the the whole rest of the rocket.

 

[rharshberger]

That’s only if you print the coupler vertically. You could print the coupler horizontally for a better bending strength.

But the larger point still stands. Don’t shave cost at the couplers, especially when you’re talking about motors that cost as much or more the the whole rest of the rocket.

Even printed horizontally the the coupler will still not be strong enough without some form of reinforcement on a 3" or larger airframe, it will be stronger against bending but won't be near as good as FG, with its multi-axis filament winding.

 

[Brent]

You do not need a fiberglass rocket to cert 1, 2 or 3. You can easily build a rocket out of LOC parts do do this.

 

[cbrarick]

If you're sweating the price of a fiberglass coupler ($2.54 each) you should stay with L1 motors.
compromising on materials generally result in failures - so you spend a lot of money for nothing

 

[bobbyg23]

Cardboard rockets are plenty strong for L2. Hell, they are strong enough to get your L3.

 

[Steve Shannon]

The coupler is frequently the part of the rocket subject to the most stress. If you want to save money use LOC cardboard tubes for the body tubes and reinforce the couplers with stiffy tubes.

 

[SeaSiren33]

Spend the money, buy the right product, fiberglass tube needs fiberglass couplers or you are just asking for a failure at the coupler. 3D printed parts will not survive as couplers without significant reinforcement.

That makes sense, I'll probably just pay for the fiberglass tubes. Thank you!

 

[SeaSiren33]

If you're sweating the price of a fiberglass coupler ($2.54 each) you should stay with L1 motors.
compromising on materials generally result in failures - so you spend a lot of money for nothing

Last time I checked, they were $2.54 per inch. If you can find them for $2.54 each for a 4-inch body tube, I would greatly appreciate it!

 

[David Schwantz]

If a coupler fails at launch, you are putting people at risk.

 

[thzero]

Hello!

I am someone who has completed their level one certification with a cardboard tube on an H-motor. For my next rocket, I am using fiberglass tubes for the first time. I want to connect 3 4-inch fiberglass tubes, but I don't want to spend money on pre-bought fiberglass couplers. Are there any cheaper alternatives that will work for high-power rockets? I have access to a 3D printer and have thought of 3D printing couplers with PLA. Would this be strong enough to survive the high stress on a level 2 or even 3 certification?

No

 

[TheTank]

Last time I checked, they were $2.54 per inch. If you can find them for $2.54 each for a 4-inch body tube, I would greatly appreciate it!

Even at 2.54/inch... if you ran a 12" av bay which is fair longer than it would ever need to be, you'd be at 31$. Not at all expensive in the world of HP rocketry, especially at L2 and the cost of J, K, and L motors these days.

 

[Banzai88]

Two other points:
-PLA will deform in a hot car on a sunny day. 100% a 'no go' choice of material for a critical structural element of a level rocket.

-Knowing that it's PLA, I think that any RSO familiar with 3D printing would have grave reservations about allowing it in such a critical stress area regardless of printing orientation and shell/infill. Any RSO not familiar with 3D printing should be all stop and asking folks who are familiar.

Bottom line, use the proper materials.

 

[Rocketclar]

My Stinky Sewer Pipe rocket has flown successfully 12 times on mostly K's. It's a HDPE clad rocket. I bought 10' of HDPE tubing at a home improvement store for $9 several years ago. It's the white, black lined plastic pipe (much lighter than PVC). It's just very slightly larger than LOC tube so I just put it over the LOC tubing. I wrote an article about it for Sport Rocketry a few years ago. Turned out to be a very rugged rocket. I left it natural with the bar codes still showing. So for a few LOC parts, fins, and a NC, you can greatly strengthen it with HDPE clad. Oh,...I do use LOC's Stiffys for my ebays at the switch band/couplers.