Wood glue in HPR - how much motor is too much?

....probably seen too many Red Green shows

The earlier comment about the performance envelope is key. I've flown an H powered rocket built from foamboard, cardstock and Elmers. An I powered rocket with foamboard fins attached with wood glue. There was no attempt to push the envelope.

Another point, which may have been made earlier also, is often the landing is often harder on rocket components that the boost, and this is more true the bigger you get.

Thought I'd chime in with a question.

I have a number of old rockets (some > 30 yrs) that were built with white glue, and some recent ones with wood glue. I've noticed on some (not all) of the older rockets, the glue really has not held up very well. My suspicion is that with age/humidity/etc the glue has simply let go. Is this just a problem unique to white glue (didn't have Titebond II back then)? Perhaps if not well sealed & painted from humidity? I'm not saying my technique was perfect at 10 years old mind you. Anybody got epoxy built rockets that old to compare?

That being said, I can't imagine building Estes style rockets with my Son with anything but wood glue for lots of reasons. For my own HPR building however, I mostly use epoxy because I like the way it handles better, as some have alluded to in previous posts, as well as using materials wood glue is not so great for.

AndyC2 said:

Thought I'd chime in with a question.

I have a number of old rockets (some > 30 yrs) that were built with white glue, and some recent ones with wood glue. I've noticed on some (not all) of the older rockets, the glue really has not held up very well. My suspicion is that with age/humidity/etc the glue has simply let go. Is this just a problem unique to white glue (didn't have Titebond II back then)? Perhaps if not well sealed & painted from humidity? I'm not saying my technique was perfect at 10 years old mind you. Anybody got epoxy built rockets that old to compare?

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White glue is not moisture proof - the wood glues are very very resistant.

I dont know the limits of the glues or epoxe myself. I have built rockets using nothing but JB to hold the MMT and fins in and also have some that use wood glue and have sent them up on a J. I gess it would depend on the design of the rocket and parts for the differnt glues. I like WG and the gell glues rock for no run but the shrink back is bad.
I use white, wood and JB and lately just super glue on my Rose-A-Roc and egg lofter and neither have not flowen yet, darn KS winds.

The bond of Titebond II wood glue is 3,750 psi if kept at room temperature. Left at 150 degrees overnight, the bond strength is 1,750 psi.

https://titebond.com/ProductLineTB.asp?prodline=2&prodcat=1

The bottom line is that the adhesive needs to be able to bond to the parts it is holding, stronger than the parts it is holding, and hold up to the temperatures it is enduring. I have no idea how much heat is coming through the motor tube during firing, but I imagine that most of the heat from a motor is shielded by the liner, then casing and then motor tube. And whatever heat the fin/motor tube is exposed to is for a short period of time. Because it still yields a strength of 1,750 psi after prolonged exposure, there is really no reason *not* to use wood glue for most high power builds, unless it isn't compatible with the materials.

So as it turns out, Titebond II wood glue might actually be the better choice for most high powered rockets. It's cheaper, just as strong or stronger than most hobby epoxies and will hold up to most temperatures.

I think the big reason most people use epoxies (myself included) for smaller rockets is that you can get an epoxy that dries really hard in 5 minutes, whereas wood glue automatically takes an hour or longer. So builds are much faster, and you can have a high power capable rocket ready to fly in an hour or less.

You probably should add phenolic tubes to the list of materials that are better suited to epoxy, right?

A question I have is how important the proximity of the parts are in wood glue apps vs epoxy. Wood glue seems to like being clamped tightly and I wonder if the strength of the bonds remain nearly as strong if they are not. I know I don't clamp my parts. Many of my parts, being made with hand tools, are not as pristine as professionally cut ones. The root edges seem to be at 90 degrees from the plane of the fin but in actuality I bet many are not. Many of my CRs have a funky spot or two on them. Another way of stating this is your real world bond as strong an what the manufacturer gets in the lab?

My general sense is that despite all the facts and figures, I think newbies should start with epoxy for high power. You'll eventually need it and IMHO it is more forgiving. Once you've gotten a few under your belt, you can move on to other methods.

Still, most of my problem with both wood glue and epoxy has been with the surrounding materials. Heck, I've even had white glue rockets rip chunks of the tube off before the bond breaks.

rstaff3 said:

You probably should add phenolic tubes to the list of materials that are better suited to epoxy, right?

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You know, I have no idea how compatible phenolic tubes are with wood glue. I generally avoid phenolic in favor of paper as phenolic gets really brittle over time. But I'm thinking that you're right- phenolic tubes are basically a resin-injected paper, IIRC, so I doubt that wood glue would be the best thing to use there. Perhaps a little testing could be done to see what happens.

A question I have is how important the proximity of the parts are in wood glue apps vs epoxy. Wood glue seems to like being clamped tightly and I wonder if the strength of the bonds remain nearly as strong if they are not. I know I don't clamp my parts. Many of my parts, being made with hand tools, are not as pristine as professionally cut ones. The root edges seem to be at 90 degrees from the plane of the fin but in actuality I bet many are not. Many of my CRs have a funky spot or two on them.

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That's true. Wood glue is not ideal for gap filling or fillets as it shrinks. If your parts tend to have gaps in them, then epoxy is certainly better here. However, your typical kit will have some pretty good parts, so wood glue would work very well.

rstaff3 said:

The earlier comment about the performance envelope is key. I've flown an H powered rocket built from foamboard, cardstock and Elmers. An I powered rocket with foamboard fins attached with wood glue. There was no attempt to push the envelope.

Another point, which may have been made earlier also, is often the landing is often harder on rocket components that the boost, and this is more true the bigger you get.

Click to expand...

Ditto for myself as well, except my 'rockets' constructed with these materials flown on HPR motors used to be gliders, and they held up fine.

Biggest thing is to pick your motors correctly for the intended glider, er, rocket. For example, a rocket that boosts fine on a J90 may indeed shred on an I357 even though the latter motor has half the total impulse. Also, fin design/span come into play.

An even stronger way to utilize foamboard or its subtypes in a large rocket is to make the fins as boxes, this is basically the 'flat equivalent' of a tube finned rocket on a round body. This is advantageous in two ways, one is that you are bonding a flat 'fin' to a flat body surface, dramatically increasing the bonding area thereof. The other big deal is that if you FOLD foamboard into a square 'tube' it gains A LOT of linear strength.

I can take a standard sheet of foamboard, fold it into a square tube, and tape or glue the seam, and prop myself against it. Yea, at my weight that isnt really pushing it but still......

SpartaChris said:

You know, I have no idea how compatible phenolic tubes are with wood glue. I generally avoid phenolic in favor of paper as phenolic gets really brittle over time. But I'm thinking that you're right- phenolic tubes are basically a resin-injected paper, IIRC, so I doubt that wood glue would be the best thing to use there. Perhaps a little testing could be done to see what happens.



That's true. Wood glue is not ideal for gap filling or fillets as it shrinks. If your parts tend to have gaps in them, then epoxy is certainly better here. However, your typical kit will have some pretty good parts, so wood glue would work very well.

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I was too wishy-washy in my previous post...wood glue is not good for phenolic. I guess most HPR will have TTW fins which will help. Still, is it important to, say, keep pressure on a fin when it's setting? Some people add an internal wooden support inside the tube when using wood glue. I read the numbers but part of me is skeptical.

AstronMike said:

Ditto for myself as well, except my 'rockets' constructed with these materials flown on HPR motors used to be gliders, and they held up fine.

Biggest thing is to pick your motors correctly for the intended glider, er, rocket. For example, a rocket that boosts fine on a J90 may indeed shred on an I357 even though the latter motor has half the total impulse. Also, fin design/span come into play.

An even stronger way to utilize foamboard or its subtypes in a large rocket is to make the fins as boxes, this is basically the 'flat equivalent' of a tube finned rocket on a round body. This is advantageous in two ways, one is that you are bonding a flat 'fin' to a flat body surface, dramatically increasing the bonding area thereof. The other big deal is that if you FOLD foamboard into a square 'tube' it gains A LOT of linear strength.

I can take a standard sheet of foamboard, fold it into a square tube, and tape or glue the seam, and prop myself against it. Yea, at my weight that isnt really pushing it but still......

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Yup, '3d' structures are stronger than 2d. On my big 8" dia paper rocket, the flat fins are all bent. Mark Hamilton refined my design and built the fins up from a skeleton and it seemed to work out much better

AndyC2 said:

I have a number of old rockets (some > 30 yrs) that were built with white glue, and some recent ones with wood glue. I've noticed on some (not all) of the older rockets, the glue really has not held up very well. My suspicion is that with age/humidity/etc the glue has simply let go. Is this just a problem unique to white glue (didn't have Titebond II back then)? Perhaps if not well sealed & painted from humidity? I'm not saying my technique was perfect at 10 years old mind you. Anybody got epoxy built rockets that old to compare?
...

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The Loc Heavy Duty Beauty (LOC IV with clustered 24mm outboards) I built in 1988 with epoxy I've had the fins pop out and off due to tired epoxy glue. I glued them back in after some scraping surfaces and kept on flying her.

I flew her on an I69 core with D12 outbaords air started the old fashioned way with thermalite wick at NYpower 11.

The LOC I-Roc I built in 1991 with only CA thick glue on the inside fin tabs with dowels, I've flown on a J420 in 2006.

rstaff3 said:

Still, is it important to, say, keep pressure on a fin when it's setting? Some people add an internal wooden support inside the tube when using wood glue. I read the numbers but part of me is skeptical.

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In general woodworking and carpentry, it is extremely important to not only have close fitting joints but to also clamp them for about 1/2 hour when using aliphatic (yellow) woodworking glue. If done correctly, and with joints where the fiber orientation does not include end grain, the bond will always be stronger than the base materials (wood), and tests will show big chunks of wood busted out instead of the bond failing. It is possible to over-clamp, though, in which case you get what is called a "glue starved" joint. I think what happens there is that too much glue gets squeezed out of the joint before it has time to penetrate the wood pores.

In rocketry, the thing I always have trouble with, psychologically, is that fact that we are usually making an end-grain joint between a fin and a body tube, which is not nearly as strong as a long-grain joint. (End-grain joints are pretty much a no-no in woodworking.) We do that to be able to orient the grain to maximize the strength of the fin, not the joint. But, it turns out that it (the joint) is not usually the weak link anyway, that being the paper of the tube, so, with fillets, it is good enough.

I'm curious to know how Titebond arrives at the strength data on its glues. There is probably an ASTM standard test protocol, but it seems like you would need materials stronger than the glue so that you know that you are measuring the glue strength and not the material strength. I don't know what those would be and still be representative of a wood-to-wood joint. A really strong wood?

Thanks, that what I was remembering. So, the effective strength may not be as the manufacturer specifies. It may not even be as strong as shows up on the rocketmaterials site in that the bonds being tested may be better than the average rocketeer will obtain.

That's still not saying the bond isn't stronger than a cardboard substrate. I'm mostly playing devils advocate since I believe it is good for cardboard/plywood rockets.

Well, your typical epoxy from the hardware store (Devcon or something like that) yields a strength of 1500 psi. Now, I'm merely speculating here, but even if the wood glue bond isn't quite up to the 3,750 psi, chances are it's still going to be stronger than your basic hardware store epoxy. Again, I'm speculating, or hypothesizing, or whatever you wanna call it.

I have no idea what the strength rating for your hobby shop epoxies are, but I doubt they are much stronger (if at all) than the stuff you buy at the hardware store.

In any event, the adhesive simply needs to be stronger than the two parts it's holding together. You're free to use what you want, but wood glue is more than adequate for most high power applications.

The question is academic for me since I don't build HPR anymore. But I have and will continue to use a variety of glues. Sometimes for good reason and sometimes on a whim.

I think the most important thing is the design and fit of the joints , I'm sure a high power rocket could be built with interlocking parts and no glue at all.

DynaSoar said:

My best example of proper design and construction is the Hiroc and Atlas boosters. The airframe was the tank. Tank pressure made them airworthy despite a skin so thin that a dropped wrench could (and did) puncture it. That took some serious engineering thinking. Putting wrist straps on tools to be used around them was just a neat hack.

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I did try that with an airframe made out of a long balloon. It snaked a bit and started a small stubble fire on landing. I couldn't really recommend it, but it was a safe rocket.

spacecadet said:

I did try that with an airframe made out of a long balloon. It snaked a bit and started a small stubble fire on landing. I couldn't really recommend it, but it was a safe rocket.

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:banghead:

Trying to drive the idea that a rocket that was "safe" was the cause of a small fire into my head. Nope... still not going in there. I will keep trying.

:banghead:

You can butt your head a few times for me also :surprised:

I was googling around the forum and ran into this thread.

Just going to bump it for new folks like me who have more questions than sense.

Here's an interesting article I found a couple of years ago. Not an exact relation to our uses, but is still worth reading.

View attachment HowStrongisYourGlue_FWW.pdf