Better epoxy for secondary bonding?

[Steve Innova]

Most of the epoxies we use are primarily intended for laminating (I use MGS 285/287). They generally have low viscocity and high sheer strength.

 

For secondary bonding (e.g. bonding bulkheads to the fuselage, etc...) our plans have us mix the laminating epoxy with flocked cotton to make a thick paste.

 

While it seems to work fine, it's heavy, has non-uniform consistency, and and indeterminate (at least to me) bond strenght. I'm not sure it's the optimum use of laminating epoxy.

 

I've heard that various Hysol epoxies are specifically intended for secondary bonding. Does anyone have any recommendations, pros/cons?

[Big Steve]

Burt Rutan the designer of these little airplanes we build and fly says it is fine. So I am satisfied with what is presently used. STeve build on

[Steve Innova]

Burt Rutan the designer of these little airplanes we build and fly says it is fine. So I am satisfied with what is presently used. STeve build on

He said MGS was fine? Unlikely.

[TMann]

Kids! ......... pay no attention to that little man behind the curtain over there.

Use only approved epoxy.

[gullikson]

You may note that in the Rutan Long-EZ roll over plans it states:

"I used Hysol 9317 structural adhesive to bond my roll over into the canopy frame. It is expensive but it is incredibly strong, (and messy!). Since there is no way to back up a flox or micro bond with fasteners, we believe that this important a structural bond needs the strength of a structural adhesive such as Hysol 9317."

[ZUCZZ]

FWIW, some of my alum epoxied parts came adrift by accident, this made me decide that all my alum parts were put in place using a structural epoxy ... especially the nosewheel assembly to the strut - Now, I don't think that little screw does anything but conform to the plans :-)

 

Believer in structural epoxy for alum parts.

 

cvh

[airnico]

european DynAero uses (or at least used 5 years ago) an epoxy glue called AXON adekit A170/400.

[brainfart]

Have you been to Darois? Nice builder support program they have going on there. Had a look at the MCR01 two years ago. Nice plane!

 

> epoxy glue called AXON

 

Yep, they still use that stuff.

 

While flox is widely used for gluing airplane stuff, specialised adhesives often have better adhesion due to some of the ingredients used. Rock hard bond lines aren't necessarily the best way to glue things together, in many cases a little flexibility will produce a better bond which can absorb more energy.

[WolfManSpecial]

i would need more information about structural epoxi,who sell,where buy,internet adress..etc...etc.

see you

[airnico]

I agree with wolf: there's a lack of information about structural glues.

although flox works good, I do not believe that we have to close our eyes and say that if it was Burt's best choice in 1980 it must be today's best choice

[Marc Zeitlin]

I agree with wolf: there's a lack of information about structural glues.

although flox works good, I do not believe that we have to close our eyes and say that if it was Burt's best choice in 1980 it must be today's best choice

How many failures of flox joints have there been in the ~3000 flying Rutan derivative canard composite aircraft?

[Steve Innova]

How many failures of flox joints have there been in the ~3000 flying Rutan derivative canard composite aircraft?

Before or after they hit the ground? Joking.

 

I'm doing a few things differently on my aircraft. One specific change has been seat backs with integral safety harnesses, and I need a way attach these to the fuselage.

 

I could use flox, but I suspect this will heavier than neccessary.

 

Also, I'm conducting destructive testing on one seatback & fuselage cross-section. Flox might not have the most consistent characteristics, batch to batch. I don't have the time or money to conduct multiple tests, so I'd prefer to use an alternative commercial adhesive intended for secondary bonding, and with consistent, known qualities.

[Steve Innova]

If I recall, Velocity uses a separate "structural adhesive" for secondary bonding. Anyone know what they use?

[Steve Innova]

How many failures of flox joints have there been in the ~3000 flying Rutan derivative canard composite aircraft?

Didn't Yar Gil's flox joint from his nose strut to the nose wheel assembly fail?

[Marc Zeitlin]

Didn't Yar Gil's flox joint from his nose strut to the nose wheel assembly fail?

That failure could hardly be attributed to the flox.

 

Besides which, that whole nose gear attach design is less than optimal, to be kind. There's no "mechanical" lock - it's totally dependent upon a wrong way taper joint.

[CBarber]

IIRC Velocity only uses two epoxies in larger quantities, EZPoxy and Velocipoxy (which is just a bulk purchase of AlphaPoxy relabled for copyright reasons or some such issue). Velocipoxy/AlphaPoxy is NOT structural. They also use a five minute epoxy in small quantities and AeroPoxy in certain structual situations, such as bonding the bulkheads to the fuselage.

 

All the best,

 

Chris

[Steve Innova]

Let's take this back a step. I'm trying to decide if I should use flox for secondary bonding or use something like Hysol 9430.

 

(Again, this is for a modified design -- flox has been demonstrated to work "just fine" for the plans applications)

 

To make that decision, I would need to know what are the properties of an MGS-285 based flox slurry?

 

The only estimate of flox strength I could find turns out to be from none other than Marc Zeitlin, posted to the Cozy Builders email list 21 SEPT 2008, message titled "Re: COZY: Re: fuel vents":

"Good question. Most of the laminating epoxies that we use, while

having pretty good strength in bending, etc. are pretty crappy bonding

adhesives. I always have a hard time finding info on the bond

strength of the laminating adhesives. But lets say that it's on the

order of 1000 psi - could be a factor of three in either direction,

I'd think."

Anyone else have suggestions on how to compare Hysol 9340 w/ and MGS 285 flox mix?

[TMann]

If I were you, I would build a segment from both and break it.

 

If I were me, I'd spend my time making the finished part using flox and move on.

[Lynn Erickson]

Let's take this back a step. I'm trying to decide if I should use flox for secondary bonding or use something like Hysol 9430.

 

(Again, this is for a modified design -- flox has been demonstrated to work "just fine" for the plans applications)

 

To make that decision, I would need to know what are the properties of an MGS-285 based flox slurry?

 

The only estimate of flox strength I could find turns out to be from none other than Marc Zeitlin, posted to the Cozy Builders email list 21 SEPT 2008, message titled "Re: COZY: Re: fuel vents":

"Good question. Most of the laminating epoxies that we use, while

having pretty good strength in bending, etc. are pretty crappy bonding

adhesives. I always have a hard time finding info on the bond

strength of the laminating adhesives. But lets say that it's on the

order of 1000 psi - could be a factor of three in either direction,

I'd think."

Anyone else have suggestions on how to compare Hysol 9340 w/ and MGS 285 flox mix?

I would like to see you break the flox off of a glass structure without destroying the structure. how much stronger do you need it? never seen the flox come loose, it always stays stuck and takes glass with it. use what you know works or be a test pilot for a new product. thats a no brainer

[Steve Innova]

If I were you, I would build a paegment from both and break it.

 

If I wer me, I'd spend my time making the finished part using flox and move on.

Not sure what a "paegment" is, but whatever it is, breaking won't help me, as I don't have access to the equipment necessary to measure the peel, compression, or tensile strength differences between an flox and Hysol bond.

[Steve Innova]

I would like to see you break the flox off of a glass structure without destroying the structure. how much stronger do you need it? never seen the flox come loose, it always stays stuck and takes glass with it. use what you know works or be a test pilot for a new product. thats a no brainer

Under normal flight circumstances, no flox bond should ever be stressed enough that the flox bond could break.

 

But this is intended to bond a seat frame to the fuselage. The only time I need it to work (that is, stay bonded to the fuselage) is during a crash, when it will be subjected to not-normal loads.

 

I think that flox is probably strong enough, in large enough quantities. But I really don't want to use 5 lbs of flox to bond the seat frame to the seat-back, fuselage floor, and side walls.

 

If flox was the best way to do this kind of thing, it would be the only thing that aviation companies use for secondary bonding. But that doesn't seem to be the case.

[gullikson]

Under normal flight circumstances, no flox bond should ever be stressed enough that the flox bond could break.

 

But this is intended to bond a seat frame to the fuselage. The only time I need it to work (that is, stay bonded to the fuselage) is during a crash, when it will be subjected to not-normal loads.

 

I think that flox is probably strong enough, in large enough quantities. But I really don't want to use 5 lbs of flox to bond the seat frame to the seat-back, fuselage floor, and side walls.

 

If flox was the best way to do this kind of thing, it would be the only thing that aviation companies use for secondary bonding. But that doesn't seem to be the case.

We use Hysol EA 9396, EA 9321, and other, depending on application, for secondary bonding on two fighter programs I work on. I would go to the Henkel website and check out the various spec sheets for the different types.

I am going to be using some Hysol in place of flox in a couple of applications on my Long-EZ project. I will be talking to two M&P engineers Monday regarding this topic.

PM me Monday afternoon and I'll share my info.

[Marc Zeitlin]

Let's take this back a step. I'm trying to decide if I should use flox for secondary bonding or use something like Hysol 9430.... Anyone else have suggestions on how to compare Hysol 9340 w/ and MGS 285 flox mix?

I don't think that there's any question that the Hysol bonding epoxy will have a better (but not necessarily more adequate) secondary bond than just about any laminating epoxy, mostly due to the improved peel strength, if peel is an issue.

 

That said, the secondary bond properties of West 105/205/206 are actually pretty dang good for a laminating epoxy, especially with flox.

 

Since it's hard to go wrong with either MGS285/flox, West/flox, or any other laminating epoxy/flox, you'd certainly be OK with the more expensive Hysol as well. But if you don't have the equipment to do testing, you probably want to use very conservative #'s for tensile strength, shear strength, and peel - for the Hysol, you'd probably want to use something along the lines of 1500 psi for tensile, 1000 psi for shear, and 20 pli for peel. Give yourself at least a safety factor of three.

 

Although the published #'s for neat 285 for tensile strength (no #'s for shear or peel) are substantially better than for the 9430, I'd probably use the same #'s for the laminating epoxies for tensile and shear, just to be safe. Peel - I don't know - the basic goal for ALL Scaled/Rutan designs is to ELIMINATE peel as a factor - you NEVER design parts to be in peel, so then you don't care about peel strength. I can't find any info on peel strength of the laminating epoxies, but it's hard to imagine that they'd be as good as the Hysol.

 

Anyway, if you're designing so that peel isn't an issue, then the laminating epoxies should be fine. If you can't design out peel, then you probably want to use something like the 9430.

[Steve Innova]

Thanks Marc, Gullikson!

 

We'll know how well I've designed out peel in about 4 weeks, when I do the destructive test of a fuselage cross-section & seatback combo. Should be lots of fun!

 

-- If I have enough material left over, I'll build a standard plans MkIV shoulder brace & seat harness attach and test that too.

 

Here's a sneak peak of the seat-back, in it's early phases. (Working with Carbon Fiber BID 282 is just the greatest thing ever. That little bit of stiffness makes it so much more controllable than the fiberglass BID!)

[Kent Ashton]

Steve, Ain't it wonderful that we can build what we want? I love to see folks innovating (I do not understand that seatback picture, though).

 

I think your concerns about laminating epoxy are unnecessary. Just go by the plans. Standard flox + epoxy is plenty strong enough.