Glueing couplers

[dave carver]

also keeps the chute etc. from moving the cg aft and thus reducing the need for nose weight. not to mention providing an anchor point for the shock cord .
Rex

When I've done it that way I still run the shock cord lead on the outside of the ring between the body and ring. The rings aren't all that strong without the hole being glued to something else, like another tube.

I'm just checking to see if that's what others do, too.

 

[Rex R]

have not tried it on anything larger than a 3" mid power bird. I would imagine a short piece of the appropriately sized coupler just forward of the shelf should do the trick.
Rex

 

[gna]

DO NOT use yellow wood glue (carpenters wood glue)... it locks up NOTORIOUSLY fast, ESPECIALLY when smeared into an extremely thin layer, as it is when snug to tight-fitting couplers are inserted into tubes... The wood fibers (paper) inside the tubing and the coupler both wick moisture out of the glue, causing it to "lock up" extremely quickly.

Now you tell me

 

[TopRamen]

also keeps the chute etc. from moving the cg aft and thus reducing the need for nose weight. not to mention providing an anchor point for the shock cord .
Rex

This is what I use them for precisely. I use two Centering Rings, joined with either Balsa or a smaller than BT Diameter Tube, so that the Assembly slides into position properly level. I like to use an eye bolt in the upper CR of the Shelf to attach my Shock Cord to, as it keeps my CG forward as possible as opposed to using an eye bolt through say the upper CR of the MMT Assembly.
Also, it keeps the Kevlar shock cord out of the hottest area of the ejection gasses at deployment, since they say that Kevlar wears out eventually from exposure to such things.

 

[lakeroadster]

Saw this video today and wanted to share it on the forum

When gluing couplers, Tim Van Milligan suggests using wood glue, and a lot of it. "When gluing in a coupler… use a lot of Wood Glue, then the glue acts as a lubricant."

Go to 1:40 here

 

[Back_at_it]

Saw this video today and wanted to share it on the forum

When gluing couplers, Tim Van Milligan suggests using wood glue, and a lot of it. "When gluing in a coupler… use a lot of Wood Glue, then the glue acts as a lubricant."

Go to 1:40 here

I've never understood the issue with using wood glue on couplers. When I do it I use the same method as Tim. Glue on the inside of the tube and glue on the outside of the coupler. Slide together in one motion and wipe away the excess. The only time I use epoxy is when I have a batch made up for another project.

The only time I've ever had one catch was when using TBIII. Not sure it was the glues fault. Just think I didn't use enough.

 

[rharshberger]

I've never understood the issue with using wood glue on couplers. When I do it I use the same method as Tim. Glue on the inside of the tube and glue on the outside of the coupler. Slide together in one motion and wipe away the excess. The only time I use epoxy is when I have a batch made up for another project.

The only time I've ever had one catch was when using TBIII. Not sure it was the glues fault. Just think I didn't use enough.

One of the tricks to using wood glue is as you stated, glue needs to be inside the airframe and on the coupler, the extra glue does two things 1)pre-soaks the paper, 2) acts as a lube. The coupler also needs to go in in one smooth motion. The quick lock-up of a coupler is usually caused by the glue thinning as the coupler is pushed in and soaking into the paper.

 

[Hobie1dog]

more lube is always a great thing.

 

[David Schwantz]

Hey, this is a family forum, D@mn it!!!!

 

[BABAR]

For paper tubes and couplers, I have never understood why you would use wood glue or epoxy unless you simply don’t HAVE white glue, unless you are in a hurry to fly the rocket (in next hour) in which case epoxy is the best choice.

Couplers stay temporarily in place with NO glue, so you don’t need or want a fast tack.

White glue is cheaper and lighter than epoxy, doesn’t stink, and doesn’t require gloves.

White glue has a far slower tack for everything, so while you should always test fit BEFORE apply glue and practice smooth coupler insertion and mark and recheck the depth coupler needs to go, it is less likely to lock up early although if you dilly dally it can . Yellow glue is far more likely to lock prematurely.

Polyurethane glue also unlikely to lock, it is heavier and requires a bit more care as drips are more difficult to clean up.

Regarding strength, paper to paper white glue bond is generally stronger than the tube and coupler. This means that while we can debate strength of glues, for couplers assuming you use a decent amount of white glue, the tube or coupler will fail before the joint fails.

Same goes double for engine block placement, white glue holds just fine and is less likely than yellow glue to lock the spacer or expended casing you use to shove the block in.

Again, epoxy WORKS fine, just heavier, smellier, and you need gloves.

YMMV

 

[bjphoenix]

I've used epoxy with no problems, and I've used Titebond II with no problems. These days for LPR I use Titebond II because it is more convenient. I measure the coupler and put a pencil mark at the midpoint. Then I slide the coupler into the tube to that point and put a couple of wraps of masking tape even with the front of the tube. Then I take the coupler out, put a liberal layer of glue inside the tube using my finger, then quickly push the coupler back in until the tape buts the end of the tube. I think the problem with couplers is if you are slowly pushing it in so you don't go too far, and it locks up because you are going too slow or stopping. Since I put tape on the coupler to stop it in the right position I don't have to go slow.

 

[lakeroadster]

I've used epoxy with no problems, and I've used Titebond II with no problems. These days for LPR I use Titebond II because it is more convenient. I measure the coupler and put a pencil mark at the midpoint. Then I slide the coupler into the tube to that point and put a couple of wraps of masking tape even with the front of the tube. Then I take the coupler out, put a liberal layer of glue inside the tube using my finger, then quickly push the coupler back in until the tape buts the end of the tube. I think the problem with couplers is if you are slowly pushing it in so you don't go too far, and it locks up because you are going too slow or stopping. Since I put tape on the coupler to stop it in the right position I don't have to go slow.

And the masking tape doesn't pull off a layer of the coupler tube when you remove the tape?

 

[ep29030]

If you must use TBII for this don;t use a thin layer. Add a bit more than you need and wipe away excess once the part is in place. I usually use a thin coat of 5 min epoxy for couplers because it does not cease.

This is the trick. Then you put on a generous layer of glue you can move the part around. Another point about glue for couplers and centering rings: yellow (aliphatic) glues shrink as they dry. Especially with centering rings, you will have an area outside the airframe that gets pulled in as the glue dries-you have to fill it to have smooth airframe. To avoid it, use white glue, epoxy or gorilla glue - they don't shrink while drying.

 

[bjphoenix]

And the masking tape doesn't pull off a layer of the coupler tube when you remove the tape?

I haven't had a big problem with that. I use blue tape and it is less sticky. A person could test their tape with their coupler and if there was a problem they could put a thin coating of glue on the outside of the coupler where the tape would go and let that dry before putting on the tape.