Pros and Cons of Pro-Sealing Skins Together

attackpilot · #1 03-04-2007, 12:06 PM

Hello Everyone:

I am almost to the point where I will start riveting the skins onto my tailcone. I am thinking about pro-sealing the skins together where they overlap to prevent any water/exhaust intrusion, help prevent corrosion, and to perhaps increase the strength. I have a technique of getting the pro-seal on very thin, so it wouldn't look stupid, and I am just thinking of only doing it where the bottom skin and side skins meet so if the cosmetics aren't great it will be mostly hidden.

I would like to know if anyone has done this and what are the pros and con or is. Right now I am just thinking and will not do it if it is not a good idea.

Joe Hutchison
RV-10 Tailcone
AH-64D Instructor Pilot

Rick6a · #2 03-04-2007, 12:49 PM

Joe;

Prior to riveting, I prosealed the belly skin into place on my 6A. In addition to rivets, the footsteps, rudder cable fairings and stops, and data plate were all fay sealed to help prevent moisture from gaining a toe-hold. The lower empennage fairing is held in place with proseal alone. My opinion is.....proseal away! I don't know what your technique is to make proseal thin, nor am I in favor of it. Why would you do that? I'd contact a sealer manufacturer before altering the mix with whatever agent and thereby risk its long term viability. Just mask off the local area so you don't make too big a mess. After the proseal sets up, the excess squeeze-out is quite easily removed using a plastic scraper.

ptrotter · #3 03-04-2007, 01:31 PM

Joe,

If you want to go to that trouble, I think it is a great idea. It will ensure that no moisture gets in and it will probably reduce virbration. You might want to look into getting type C Proseal which is designed for this type of application, that is applying to faying surfaces. If you want to thin the standard type B proseal that Van's sells, use toulene. Toluene is the proper thinner for Proseal and will not change its characteristics.

TSwezey · #4 03-04-2007, 05:35 PM

I prosealed everything on my plane! I think the plane will stay together without the rivets. I was taught by people who build Gulfstreams and that's the best way they do it. Lots of salt air and corrosion in Savannah. You should see the corrosion/rust on the clecos just from sitting in the garage.

hgerhardt · #5 03-04-2007, 07:16 PM

I used 3M 2216 Structural Adhesive on all faying surfaces for all the same reasons as above. Also used it on the control surface stiffeners to try to prevent the cracking so many have observed. We'll see how that works out in a few weeks when my -6 flies for the first time.

attackpilot · #6 03-04-2007, 07:23 PM

To All:

When I said I can get the pro-seal thin, I don't mean by thinning its consistency. I mean that I use a wallpaper roller to put on a thin even coat. I did this on the elevators and got great results.

Now for another question: What are faying surfaces? Is it where two parts overlap parallel to each other or something?

Thanks again.

Joe Hutchison
RV-10 Tailcone
AH-64D Instructor Pilot

P.S. I primed all the tailcone bulkheads today using AKZO and I have to say it was a lot more work than I expected. I hope it is going to be worth it.

osxuser · #7 03-04-2007, 09:48 PM

Proseal can be thinned down with MEK.

gmcjetpilot · #8 03-04-2007, 10:15 PM

Pro seal is pretty great stuff and folks above stated the pros. I'll do the con, cost, weight, time, mess and its not really needed. True if you etch, alodine, seal prime, inside and out, the plane will last forever in sea water. I'm planning on not living forever of flying off of salt water. Primer cost money and time and yes weight just like pro seal.

I have "fay surface sealed" some parts my self but just be careful when you do. You will change dimensions and if its too thick, in the lap joint on thin skins, it may pillow between rivets and make a less than attractive appearance, especially on exterior joints. The belly and tail cone area are thicker skin, so that may be a better choice.

The worry of corrosion is over kill in my opinion with our land based aluminum clad planes, but I can't argue it does two good things, makes a stronger joint and can prevent corrosion in the lap.

Captain Sacto · #9 03-04-2007, 10:30 PM

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

gmcjetpilot · #10 03-05-2007, 01:36 AM

Quote:

Originally Posted by Captain Sacto

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.