Possible uses of polyurethane (Gorilla) glue in rocket construction.

[Senior Space Cadet]

A couple days ago, I was trying to join two sections of body tube with a coupler. I spread yellow wood glue around the inside of one section of body tube and tried to insert the coupler. The fit was really tight and I was having trouble getting it started. By the time I did, the glue had already started to set. I got the coupler in about half an inch and the glue grabbed. It absolutely would not go in any farther and would not come back out. I've had a couple engine mount failures that I feel are a direct result of the glue drying too quickly and my fear of glue grab.
This is why I decided to try polyurethane glue. There are pros and cons.
Polyurethane glue needs moisture in the air or components to work. Colorado is semi-arid, but yesterday was more humid than normal and I had no problem with the polyurethane glue curing.
If I had used polyurethane glue to glue in the coupler, I could have inserted it, taken it back out and inserted it again. It is slippery and has a long working time. I used it to make a motor mount last night and it went together easily and is now completely cured. God couldn't get it apart.
Polyurethane glue foams as it cures. Seems like this would make it bad for fillets. It also means you might have to do minor sanding before a motor mount, glued with polyurethane, would slip into a body tube.
It probably works best in humid climates but you probably have less problems with yellow glue in humid climates, so there's that. I wouldn't use it for fins or lugs. I would use it for motor mounts, couplers, and baffles.
It can be messy to work with. Parts can slide around so you need to be aware of how you position things for curing. Interestingly, it has a long work time, but it's total cure time is fairly fast. Once cured, it is more waterproof than wood glue but less so than epoxy. It is stronger than wood glue, but less than epoxy. It will glue things other than paper and wood.
A bottle has a short shelf life. Buy small bottles.

 

[KennB]

Some years back, there was a fellow who sold kits that used polyurethane glue as a structural member in the motor mount. Instead of centering rings, the kits had a 3x5 index card with two centering rings drawn on it. You were to cut these out, position them on the motor mount tube, spritz them with water, apply the PU glue and insert the assembly into the body tube. With time, the glue would foam up and secure the whole thing.

I've got a couple of the kits on my build pile but haven't done anything with them. I'll definitely work with a mock-up before I try the real thing. To date, I've not heard of one of these coming through the line at our club launches.

 

[kuririn]

Use white glue instead of yellow for couplers and motor mounts.
Longer working time, no instant grab.
Strength of white vs, yellow glue is a non issue, since both are stronger than the materials they bond.
Personally, I still use yellow(wood) glue for motor mounts but I dry fit first. If the fit is too snug I sand the rings/coupler until I get a smooth (but not loose) fit. Then I position the glue bead just behind the final ring position so that the sliding motor mount will not hit any glue until just before it's final position.
I only use foaming PU (Gorilla) glue to lock in nose weight for LPR rockets. Got tired of throwing away 3/4 full foam spray cans due to clogs inside the can after just a few uses. Due to the expansion of the foam inside the nose cavity it will still lock the weight even if the adherence of the glue to the plastic should fail. Just be sure to fill the whole cavity.
I put a few drops of water in with the glue so ambient humidity is not an issue with the curing.
The big boy HPR pros use a two part foaming glue for nose weight and fin can integrity.
Laters.

 

[jqavins]

It's also super sticky while liquid and a PITA to clean up; for that reason I don't like using it for anything, rocketwise or otherwise. There are times and places that it's a necessary evil.

The swelling of the foam means it will always take a good deal of sanding anywhere that shows; for that reason, I'd never use it for anything on the outside of a rocket.

In case you hadn't figure it out, I don't like the stuff.

I did use it once to secure lead shot inside a Big Daddy nose cone with the base cut out, and it was just the thing for that. The sloppy stickiness made it one of the few things I could count on the adhere to the plastic, the foaming ensured that it would encapsulate the lead, and the bumpy, lumpy surface would never be seen. And I still managed to get a little on my fingers which needed acetone to remove. Still, it worked well for that one job and I might use it again for the same job in the future.

White glue for couplers and motor mounts. Unless I absent mindedly reach for the wood glue bottle I have to hand, which is most of the time. I had a coupler grab on me once, and never had a problem with a motor mount. The more contact area you've got, it seems, the more likely it is to grab, which makes couplers much more grab prone than thin centering rings.

 

[MClark]

For large upscales we had a member who used Gorilla Glue to bond plywood skins to aluminum honeycomb. It foams Up a bit around the aluminum edges and creates a very strong bond.

M

 

[ThirstyBarbarian]

I’ve used it on couplers to avoid having them grab. I don’t moisten the joint with water. It air cures overnight. And I’ve used it to secure nose weight in a nose cone. In that case I put in a few drops of water.

 

[H_Rocket]

've got a couple of the kits on my build pile but haven't done anything with them. I'll definitely work with a mock-up before I try the real thing. To date, I've not heard of one of these coming through the line at our club launches.

I built one of those. Damn thing was light as a feather and damn near indestructible.

 

[LW Bercini]

I used Gorilla Glue to secure nose weight in a polyethelyne nose cone from a Rocketarium kit.

 

[samb]

I'll add my testimonial to those who have successfully used polyurethane glue for motor mounts, couplers, and securing nose weight. It just works. Have you ever secured a motor mount to the airframe with white or wood glue and come back the next day to find a ring or puckering in the body tube where the centering ring contacts the airframe ? That's the white/wood glue shrinking as it cures. You don't get that with polyurethane.

 

[jqavins]

Have you ever secured a motor mount to the airframe with white or wood glue and come back the next day to find a ring or puckering in the body tube where the centering ring contacts the airframe ?

No. I've heard of it, but I've never experienced it.

 

[Chad]

i use gorilla glue a lot on wood and cardboard fins and airframes, it's pretty much my goto when i'm not using an epoxy. The Gorilla Glue Clear version doesn't foam.

https://www.gorillatough.com/product/clear-gorilla-glue/

 

[jrap330]

A couple days ago, I was trying to join two sections of body tube with a coupler. I spread yellow wood glue around the inside of one section of body tube and tried to insert the coupler. The fit was really tight and I was having trouble getting it started. By the time I did, the glue had already started to set. I got the coupler in about half an inch and the glue grabbed. It absolutely would not go in any farther and would not come back out. I've had a couple engine mount failures that I feel are a direct result of the glue drying too quickly and my fear of glue grab.
This is why I decided to try polyurethane glue. There are pros and cons.
Polyurethane glue needs moisture in the air or components to work. Colorado is semi-arid, but yesterday was more humid than normal and I had no problem with the polyurethane glue curing.
If I had used polyurethane glue to glue in the coupler, I could have inserted it, taken it back out and inserted it again. It is slippery and has a long working time. I used it to make a motor mount last night and it went together easily and is now completely cured. God couldn't get it apart.
Polyurethane glue foams as it cures. Seems like this would make it bad for fillets. It also means you might have to do minor sanding before a motor mount, glued with polyurethane, would slip into a body tube.
It probably works best in humid climates but you probably have less problems with yellow glue in humid climates, so there's that. I wouldn't use it for fins or lugs. I would use it for motor mounts, couplers, and baffles.
It can be messy to work with. Parts can slide around so you need to be aware of how you position things for curing. Interestingly, it has a long work time, but it's total cure time is fairly fast. Once cured, it is more waterproof than wood glue but less so than epoxy. It is stronger than wood glue, but less than epoxy. It will glue things other than paper and wood.
A bottle has a short shelf life. Buy small bottles.

Next time..do a test fit..........

 

[jrap330]

No. I've heard of it, but I've never experienced it.

Same here..excerpt maybe on fin fillets......

 

[ghostfather]

Because I sometimes include 3D printed things using PET filament (nose cones, fins, canopies, bulkplates), PolyUrethane glue is my go-to glue to get PET plastic to stick to anything, as epoxy doesn't stick to PET very well.

 

[kuririn]

Have you ever secured a motor mount to the airframe with white or wood glue and come back the next day to find a ring or puckering in the body tube where the centering ring contacts the airframe ?

No. I've heard of it, but I've never experienced it.

Not a motor mount, but you can see in this pic where there's a ring in the tube at the top of the transition shoulder due to glue shrinkage.