Why?
Captain Sacto said:
I will be doing something a little similar on my 7-A emp kit.
I tentatively plan to use West System epoxy between some rivets, including where the carrythroughs (Van calls them "stiffeners") mate to the the forward horiz stab spar. (To my untrained eye, this looks like a stress concentration point that could use some extra strength.)
What I will need to test, however, is whether I need to polish the primer off the surfaces before I apply the epoxy. (Simultaneous with setting the rivets).
I know that the West epoxy is used for wood and fiberglass, so my testing will seek to confirm that it bonds aluminum with suitable strength, as well.
If anyone has comments or suggestions, I would love to hear them.
Regards all - - Tom in Sacramento
There are very special adhesives to bond aluminum to aluminum. I recommend you don't bond the stiffeners on. Get some second and third opinions. The beauty of Pro Seal is it has anti corrosion properties and is some what pliable. Pro seal does get credit for increasing the "load transfer" in a long joint. When I say a long joint I mean something that is longer than a few rivets, a bracket or short stiffener. However its not structural but it does bond.
West Epoxy may be brittle and crack with flexing? If that happens it could be a great place for mosture to get into and stay. Boeing learned this the hard way with the early B-737.
Remember the Hawaii Airliner that ripped the top off the fuselage off in flight many years ago. Boeing use both rivets and bonding to attach the lap joint and doubler's. The adhesive was fine, but not so great in the long term. It allowed mosture to live in the joint and promoted corrosion. The early 737's also has thinner aluminum. Well the case in point was a combo of moist tropic air, many cycles with the short haul operations between islands and a brittle adhesive promoting corrosion. It was too many strikes. Would that happen to you. Unlikely but WHY?
I just would not do it with West Epoxy.
There are better products. I am sorry I don't know what to recommend off the top of my head, but its expensive (like $80 for a small amount). However when you get into the wing box / cary through you have to watch stack up dimensions. It all has to fit and you have to slide thru the side of body wing slot.
If we are talking about Clad sheet to Clad sheet I am not sure the adhesive will work to spec? This really gets into material engineering and design. If you are talking thick bare materiel than adhesive is more appropriate. On the other hand its just a Belt to Suspenders approach, a chicken BOND, it really does not matter; you don't need it.
When you do anything like this its engineering, You should talk to Van. My guess they will say its designed for +150% of the max load with just the fasteners. My guess is you could put Elmer's glue in there and not cause too much problem, but again I ask why? Are really doing anything?
I think the Pro Seal discussion was more for sealing the belly area than strength. Other I have read bonded their RV together, with rivets as well of course. I know the BD10 is bonded together with pro seal and some pop rivets. The Bede / Grumman's had al-al bonded parts, but they also are having issue with dis-bonds as they get older.
Pro seal is pretty begin, although not a structural adhesive it does help on long joints in shear so the load in more evenly distributed, verses ganging up on just a few fasteners. In essence it increase the friction of the joint. If you must use something consider the pro seal (thinned down as one suggested). It has the anti corrosion properties and really can't hurt.