Glue

[Adair]

So if not T88 what glue to use from aluminum to aluminum--spar on flap to
hinge which fits on the spar?

[Richard Lamb]

Adair, are you building from plans or making it up as you go?

The reason I ask is that I doubt that ANY plans show al to al bonding
for primary flight critical structure.

It's not something you can reliably and repeatedly do in a garage shop
enviornment.

Not that I'd be want to hang my life on anyway.


So what is it, specifically, that you are trying to do?

Richard


Adair wrote:
>
> So if not T88 what glue to use from aluminum to aluminum--spar on flap to
> hinge which fits on the spar?

[Bob Kuykendall]

Earlier, "Adair" > wrote:

> So if not T88 what glue to use from aluminum to aluminum--spar on flap to
> hinge which fits on the spar?

I'm not an engineer, but I've done some aluminum bonding in the home
workshop environment, specifically on parts of my HP-18 kit sailplane.
The most important things about such joints seem to be to make sure
that the stresses are spread out over a substantial bond area, and to
make sure that there are mechanical attachments that prevent the joint
from seeing any appreciable peel stress.

On the basis of working on HP parts, I'd suggest that you use whatever
glue is specified by the original designer. If you're doing your own
design, I'd suggest that for a concentrated load such as a hinge you
use mechanical fasteners such as rivets or screws. On the bonded HPs,
all of the flap, aileron, and ruddervator hinges are secured primarily
with rivets. Also, the wing skins are riveted around their entire
perimeters, so that the torsional envelope of the wing is closed with
mechanical fasteners. That's especially important in large and limber
(and therefore potentially flutter-prone) structures.

And, by the way, the usual glue for the HPs is Hysol EA9430. It's been
around in various forms for about 30 years, and is currently a
Locktite product. It has about the best peel strength of any epoxy
(about 60 lbs per linear inch under lab conditions), but even that
peel strength is pretty wimpy in comparison with mechanical fastening.

And like many if not most epoxies, all its strength values go down
pretty quickly with increasing temperature. So whereever you use it,
you want to make sure that it and any surrounding structure is painted
white or at least a very light color. Anything that could get so hot
you can't hold it in your hand is not a good candidate. And airplane
parts painted dark colors will easily soak up enough sunlight to get
so hot you can't even touch them. That's too hot. According to the
following table, the shear strength goes from 4500 psi at 77 degrees f
down to 750 psi at 180 degrees f:

http://www.gluguru.com/HysolEpoxyTable.htm

There are high-temperature epoxies that you can use, but they often
don't have very good peel strength, or lack other characteristics that
you want. And there are some other high-temperature bonding operations
that you can use, but only if you have autoclaves or other specialized
equipment at your disposal.

In general, I tend to agree with Richard Lamb's subsequent post; that
for critical stuff you stick with mechanical fasteners. That is,
unless you know what you're doing and have validated it with test
articles.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

[Blueskies]

good stuff:

http://www.adhesive-sealant.com/categories/react.htm



--
Dan D.



..
"Bob Kuykendall" > wrote in message m...
> Earlier, "Adair" > wrote:
>
> > So if not T88 what glue to use from aluminum to aluminum--spar on flap to
> > hinge which fits on the spar?
>
> I'm not an engineer, but I've done some aluminum bonding in the home
> workshop environment, specifically on parts of my HP-18 kit sailplane.
> The most important things about such joints seem to be to make sure
> that the stresses are spread out over a substantial bond area, and to
> make sure that there are mechanical attachments that prevent the joint
> from seeing any appreciable peel stress.
>
> On the basis of working on HP parts, I'd suggest that you use whatever
> glue is specified by the original designer. If you're doing your own
> design, I'd suggest that for a concentrated load such as a hinge you
> use mechanical fasteners such as rivets or screws. On the bonded HPs,
> all of the flap, aileron, and ruddervator hinges are secured primarily
> with rivets. Also, the wing skins are riveted around their entire
> perimeters, so that the torsional envelope of the wing is closed with
> mechanical fasteners. That's especially important in large and limber
> (and therefore potentially flutter-prone) structures.
>
> And, by the way, the usual glue for the HPs is Hysol EA9430. It's been
> around in various forms for about 30 years, and is currently a
> Locktite product. It has about the best peel strength of any epoxy
> (about 60 lbs per linear inch under lab conditions), but even that
> peel strength is pretty wimpy in comparison with mechanical fastening.
>
> And like many if not most epoxies, all its strength values go down
> pretty quickly with increasing temperature. So whereever you use it,
> you want to make sure that it and any surrounding structure is painted
> white or at least a very light color. Anything that could get so hot
> you can't hold it in your hand is not a good candidate. And airplane
> parts painted dark colors will easily soak up enough sunlight to get
> so hot you can't even touch them. That's too hot. According to the
> following table, the shear strength goes from 4500 psi at 77 degrees f
> down to 750 psi at 180 degrees f:
>
> http://www.gluguru.com/HysolEpoxyTable.htm
>
> There are high-temperature epoxies that you can use, but they often
> don't have very good peel strength, or lack other characteristics that
> you want. And there are some other high-temperature bonding operations
> that you can use, but only if you have autoclaves or other specialized
> equipment at your disposal.
>
> In general, I tend to agree with Richard Lamb's subsequent post; that
> for critical stuff you stick with mechanical fasteners. That is,
> unless you know what you're doing and have validated it with test
> articles.
>
> Thanks, and best regards to all
>
> Bob K.
> http://www.hpaircraft.com