# Glue strength test samples

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#### AncientAviation

##### Well-Known Member
Greetings all...

wondering if there is a best practice for glueing up some samples with the glue after making a rib or some other join?

I have just been cutting some capstrips up or glueing some off cut ply or the ice cream sticks I used to mix the glue. No surface prep or nice clean joint like the ribs/trusses I have been making.

In hindsight I suspect this might no be the best idea and perhaps I should have taken more time on the samples?!!?
Been making about 5 or so per rib.

#### TFF

##### Well-Known Member
Depends on where you live regulatory.
In US, not required anymore but for piece of mind.

I would think each batch of glue mixed, but 5 per rib is a little much. One per rib, 1 per five ribs. Once for every new glue bottle. Major assemblies. I would set a procedure, not just everything as you will have as many tests as you have airplane parts.

Are you just spot checking or are you logging where each batch and sample are on the airframe? Temperature of application? It can get complicated.

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
When I was building with Weldwood plastic resin I made a sample with every glue batch. Numbered the glue batch and the same number on the parts glued. There was a second sample for the FAA inspector.

#### blane.c

##### Well-Known Member
HBA Supporter
When I was building with Weldwood plastic resin I made a sample with every glue batch. Numbered the glue batch and the same number on the parts glued. There was a second sample for the FAA inspector.
How'd you make the samples?

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
This was in the mid 1970's so give me some slack. IF I remember correctly I used scrap 3/4" square spruce 3" long and overlaped about 1 or 2 inches. After drying for a few days, set it up on an end and hit with a hammer or do the same in a vice. The wood should break away from the glue line and not the glue line. I know the FAA inspector ask if I had glue samples but I don't remember if he broke any or not. At that time you couldn't enclose any thing up without an inspection. The KR-2 has a box spar. Build it all except for closing it up with the plywood on one side . Have the inside wood varnished and the plywood of the closing plywood varnished where its not going to be glued. After it was inspected, he signed it off for ready to close.

#### AncientAviation

##### Well-Known Member
Depends on where you live regulatory.
In US, not required anymore but for piece of mind.

I would think each batch of glue mixed, but 5 per rib is a little much. One per rib, 1 per five ribs. Once for every new glue bottle. Major assemblies. I would set a procedure, not just everything as you will have as many tests as you have airplane parts.

Are you just spot checking or are you logging where each batch and sample are on the airframe? Temperature of application? It can get complicated.
UK based but falls outside of the regualtions here so the local association isn't all that interested...
No need to log temparature - its summer in the UK so at least half the time its be cold and rainy

I get the point though about it being complicated - thanks

#### AncientAviation

##### Well-Known Member
When I was building with Weldwood plastic resin I made a sample with every glue batch. Numbered the glue batch and the same number on the parts glued. There was a second sample for the FAA inspector.
Thanks for the input.... more or less doing this so on the right track then which is good

#### AncientAviation

##### Well-Known Member
This was in the mid 1970's so give me some slack. IF I remember correctly I used scrap 3/4" square spruce 3" long and overlaped about 1 or 2 inches. After drying for a few days, set it up on an end and hit with a hammer or do the same in a vice. The wood should break away from the glue line and not the glue line. I know the FAA inspector ask if I had glue samples but I don't remember if he broke any or not. At that time you couldn't enclose any thing up without an inspection. The KR-2 has a box spar. Build it all except for closing it up with the plywood on one side . Have the inside wood varnished and the plywood of the closing plywood varnished where its not going to be glued. After it was inspected, he signed it off for ready to close.
I'm being cheap and only using scraps and off cuts... some of the wood isn't great (not enough grains or grain slopes too much) so think I will find the worst and dedicate that to the sample batch.

I like this hammer test - you're a star!

#### Bill-Higdon

##### Well-Known Member
I had a friend who was killed in a T-40a crash due to glue failure in the main spar. The main spar on the T-40 & T-40A is a lot of 1/4" laminations glued together. The builder was a working engineer who was very detail oriented he did 2 sets of test blocks for each batch of aerolite glue he used. 1 was tested & the other was saved for "historical" reference. He also monitored & logged the temperature & humidity of his work shop area. After the spar failure the FAA looked at the samples & a lot of them showed the same deterioration. Up to that time I'd been a Aerolite Fan boy but after that I wasn't any more.

#### AncientAviation

##### Well-Known Member
found the worst bit of spuce I could grain wise and simple, neat and quicker than pervious method putting together some samples....

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#### AncientAviation

##### Well-Known Member
I had a friend who was killed in a T-40a crash due to glue failure in the main spar. The main spar on the T-40 & T-40A is a lot of 1/4" laminations glued together. The builder was a working engineer who was very detail oriented he did 2 sets of test blocks for each batch of aerolite glue he used. 1 was tested & the other was saved for "historical" reference. He also monitored & logged the temperature & humidity of his work shop area. After the spar failure the FAA looked at the samples & a lot of them showed the same deterioration. Up to that time I'd been a Aerolite Fan boy but after that I wasn't any more.
Interesting... Aerolite is one of two glues recommended here in the UK.
I assume T88 is too expensive to ship so it isn't mentioned much here locally but assume this is now the favourite?

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#### TFF

##### Well-Known Member
T-88 is close to idiot proof, which is why it is a good homebuilt glue. It is not certified but in

Aerolite is for certified repairs and probably is the best glue but for these reason, the glue joints have to be perfect; the clamping pressure has to be perfect; the temperature has to be perfect; the mixing has to be perfect. If all that happens, it will out perform epoxy.

#### TFF

##### Well-Known Member
Epoxy is the easiest to use for the most part no matter the brand. Supposedly there is a slight temperature advantage with T88 which is why most go with it, and it is packaged as simple, not a chemistry set like West’s. The resorcinol glues soften at about 400 deg. More than double of T88 with West’s a little less than that. That is why epoxy is not used in certified repairs without permission and a 337 form.

For the most part saving $20 over the run of a whole project is not worth it to me. Doesn’t keep me from searching out best price, but to just use something non standard because it’s$5 cheaper is not on my list. Im going with tradition until there is a better tradition.

I have thought of the CEPS for varnish more than once. The problem is over one project you might save \$40 over using the proper stuff from Polyfiber. Still if your mission is to build and not use anything standard, it would be on my list.

#### blane.c

##### Well-Known Member
HBA Supporter
It is that some of the epoxy's are supposed to make the wood more resistant to decay, which could be advantageous in an amphib. It certainly isn't about saving such a small amount of money. The T88 is recommended by the designer .

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#### don january

##### Well-Known Member
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Log Member
My view has became that every batch that is stirred up and set and you move on to the next step WILL IT HOLD?I have came back in my mind to the Glue put down towards the beginning of the build. Is it going to do the job ? If your covering flat sides the fear is less because of confidence in the glue such as sheeting the belly . But those more compound curves you need to get around they are really the times that puts on the stress if glue joints are going to hold. I ask myself how many flyers depend on the fabric holding the panels in place ? I bet I'd be surprised.

#### TFF

##### Well-Known Member
T88 has been around a long time. No one is trying to topple it either. I’m sure a better product could be made, but what? No one is putting money into development for a few airplanes a year. It would have to be an accidental discovery.

I’m sure lots of joints are getting some help by some other stuff. Im not one of the master craftsmen out there, but I’m good at looking at someone else’s work and knowing how good they are. The masters can curve something and it will have no stress like it was just sitting there. It takes time to be that good though.

#### BJC

##### Well-Known Member
HBA Supporter
T88 has been around a long time. No one is trying to topple it either.
I've wondered why FPL-16A never really caught on with homebuilders.

BJC

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#### TFF

##### Well-Known Member
I would say it’s got more data behind it, but it’s not as easy to work with. I imagine health now would be partial consideration. I do think it might be certified in Germany. There is a company that builds WW1 airplanes in Germany and they use what they call white glue. It’s an epoxy. They don’t mean Elmers.

#### AncientAviation

##### Well-Known Member
T-88 is close to idiot proof, which is why it is a good homebuilt glue. It is not certified but in

Aerolite is for certified repairs and probably is the best glue but for these reason, the glue joints have to be perfect; the clamping pressure has to be perfect; the temperature has to be perfect; the mixing has to be perfect. If all that happens, it will out perform epoxy.
I played around with Aerolite and ??? (whatever the other local glue is called - it escapes me now) and found I didn't like it.... much for these reasons. I played around with various samples but if there was a gap you were poked. One claimed to have gap filing properties - but I suspect that was the marketing boys being creative!