MGS wood epoxy

[ajfriz]

I'm finally getting around to working on my spar blanks and I can't make up my mind on what glue to use. I know most "old school" guys use resorcinol. I like the idea of using epoxy because it's easier to use, clamping force isn't as critical, better at filling gaps, and heat changes don't affect curing as much as it does to resorcinol. I haven't found anything suggesting that MGS weakens as the temperature increases, like T-88 does. MGS is approved to use on certified aircraft, but I haven't found much info about using it on spars. Anyone have experience with MGS?

[Pearson]

Re: MGS wood epoxy

I would consult with my IA before using anything other than what the aircraft was certified with.

[N96337]

Re: MGS wood epoxy

I would consult with my IA before using anything other than what the aircraft was certified with.

AND the local FSDO!

[skip]

Re: MGS wood epoxy

I'm finally getting around to working on my spar blanks and I can't make up my mind on what glue to use. I know most "old school" guys use resorcinol. I like the idea of using epoxy because it's easier to use, clamping force isn't as critical, better at filling gaps, and heat changes don't affect curing as much as it does to resorcinol. I haven't found anything suggesting that MGS weakens as the temperature increases, like T-88 does. MGS is approved to use on certified aircraft, but I haven't found much info about using it on spars. Anyone have experience with MGS?

I just finished four spars for my BC12-D. I used Resorcinol. It turns out that the folklore about the super machining of the wood and the criticality of the clamping preasures are overatted. If you read the specs, the wood finish from using a router and jig to plane off the root spar plywood spaces was well within the published specs and the clamping preasure specs are really quite wide as well. The one thing that I did do with precision was to use a cheap electronic scale to get the 5:1 resin to hardner ratio. I played a little with changing the ratio by a few percent to see how it affected final strength and a few percent didn't seem to make a difference, but I didn't do a real scientific study on breaking strength and such. It was too easy to put a plastic cup on the scale, zero the tare weight, pour in some resin... let's see. this one is 215.7 grams. Divide by 5, add, and then dump in the hardner up to the final weight.

Researching the reasons why Epoxy is not certified, I found two main areas in the mil spec that is the basis for the FAA's certification. The first is the glass transition temperature of the epoxy where the epoxy looses stength. This is different for each epoxy, but is generally in the few hunderd degreee range. Even in a hot summer sun, I don't think the spar interior gets up to that temperature, but even so, the spec requires a wide temperature range. The big part that keeps the epoxy out of the certification is the boils test where the joint is boiled and then tested. This is exactly what folks do to plywood to get curved leading edges and such. Epoxy fails this test on two counts. First, the class transition temperature and the weakening of the epoxy at the elevated temperature. But second, and more important, the epoxy lets small pathways for water to develop that weakens the joint. Now, I don't expect to boil my wings, but Resorcinol turns out to be easy enough to use that I am sticking to it for spar work.

My 2 cents... and corrections are welcome.

Skip
BC12-D sn7700 N34237

[Mark Julicher]

Re: MGS wood epoxy

If you are not going to take your certificate into Experimental territory, please stay with approved glue. When you fill out the 337 Major Repair and Alteration form, you have to show approved methods and data for the repair method. The IA that signs the 337 is putting his license on the line.

[skip]

Re: MGS wood epoxy

I'm finally getting around to working on my spar blanks and I can't make up my mind on what glue to use. I know most "old school" guys use resorcinol. I like the idea of using epoxy because it's easier to use, clamping force isn't as critical, better at filling gaps, and heat changes don't affect curing as much as it does to resorcinol. I haven't found anything suggesting that MGS weakens as the temperature increases, like T-88 does. MGS is approved to use on certified aircraft, but I haven't found much info about using it on spars. Anyone have experience with MGS?

OK, I got curious and dug into the MGS system a bit. After an initial look at the specs, I have some questions and maybe a few comments. This was a brief look. Anyone who has better information is requested to respond.

1: MGS is approved for use on certified aircraft.

It seems that the basis for this is that the system is approved in Germany for use in laminating arimid and fiberglass fibers.
See http://www.mgs-online.com/en/techinfo/ti_frame.htm
Heat treatment (at about 120 degrees F) is required for the approval. This looks like the approval is for use laminating composite structures. I can't find much about its use as an adhesive for wood such as spar work.

Is the "certified aircraft" use anything other than the US and Germany honering each other's paperwork? Is there any US FAA certified aircraft approval?

Can anyone find information about MGS's use as an adhesive for spruce rather than its use as a composite laminating resin? These are two quite different jobs.

2: I haven't found anything suggesting that MGS weakens as the temperature increases...

Aircraft Spruce sells the 335 and 285 resin systems. These (and the other MGS resins available) all have operating temperatures in the mid 100 degree F range. I couldn't find the specs on the glass transition temperature or othe relevant numbers, but it looks like the resins have similar heat properties to other epoxy systems. They do have one high-temperature system (their L 305 resin) that goes to over 400 degrees F, but this requires heat treating during the cure period. Again, this is a laminating resin and not specifically an adhesive.

Realizing that this is a very brief research and I might be missing something, I would avoid MSG as an adhesive for spruce spar work until I had more appropved data. I would also make sure I had US FAA documentation relevant to the use of the MSG epoxy as an adhesive for wood on a US certified aircraft.

I'm not anti epoxy; I have most of my acrosport-II's wings stuck together with West Systems 105. It is just that for aircraft work on a certified aircraft, Resorcinol still looks like an attractive choice.

Skip
BC12D sn7700 N34237

[ajfriz]

Re: MGS wood epoxy

Thanks Skip! I know people have used it with aircraft wood, but I couldn't find anything on spars specifically. It seems to be quite popular with boat builders as well. What I didn't know was that it had to be heat treated.

A friend of mine told me about MGS being certified and how it doesn't break down with heat like other epoxies do, which was one of the reasons it was appealing. There are quite a few tests comparing MGS, T-88, West, etc. and MGS tested quite well. I don't know if those test were performed on wood though....

I think I'll just order resorcinol and be done with it. I was hoping for something a little more forgiving, but I guess I'll just be careful when I apply it.

[Ragwing nut]

Re: MGS wood epoxy

Thanks Skip! I know people have used it with aircraft wood, but I couldn't find anything on spars specifically. It seems to be quite popular with boat builders as well. What I didn't know was that it had to be heat treated.

A friend of mine told me about MGS being certified and how it doesn't break down with heat like other epoxies do, which was one of the reasons it was appealing. There are quite a few tests comparing MGS, T-88, West, etc. and MGS tested quite well. I don't know if those test were performed on wood though....

I think I'll just order resorcinol and be done with it. I was hoping for something a little more forgiving, but I guess I'll just be careful when I apply it.

T-88 is junk. I have seen what happens to it 10-15 years later, you can easily remove the parts glued together. I have also seen a Tailwind box spar failure from T-88. I will only use West Systems in non structural uses and Waco Classic actually got it approved to use it years ago, but never researched what they used it on. Smart to just use resorcinal and play it safe.