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skin seam sealant

rjcthree

Well Known Member
I thought I would find something in the archives on this one, but no joy in my searches(4).

Did anyone seal the fuselage skin seams - other than the firewall? I'm not looking for a proseal nightmare, but that would work . . .

???

Rick 90432
 
I thought I would find something in the archives on this one, but no joy in my searches(4).

Did anyone seal the fuselage skin seams - other than the firewall? I'm not looking for a proseal nightmare, but that would work . . .

???

Rick 90432

Maybe off the subject but I am wondering why you would want to do this.
 
Reason

Neatness. Maybe avoid the risk of paint-suck into the seam.

If nobody has done it or sees the need . . . I'm not looking for another titchy task, lol.

Rick 90432
 
Top idea

Hi Rick,

It's a good idea to seal your skin lap joints, helps keen the joints clean and tight especially later in the airframe life when rivets start to work and smoke and fine dust gets into the lap joint.

Any faying surface sealant would work fine in this application (PR 870 is perfect http://www.bergdahl.com/SealantTable.htm[/url]) as long as it's not a low adhesion sealant. Choose a working life for the job your doing.

My RV-6 has the belly skins sealed, 10yrs later there is no working rivets and still looks as good as the day she was built.

Good luck..
 
Take a look at these two links.

http://www.aviationproductsinc.com/files/tds/flamemaster/cs2415.pdf
http://www.skygeek.com/flamemaster-cs-2415-exterior-sealant.html

An A&P buddy of mine ordered some for his RV-10 and apparently he decided to order a tube for me too. I just got off the phone with him a few minutes ago and he said I should be seeing a package soon. I wasn't really looking for it, but since it's here I might try it out on a scrap piece and decide if it's something I want to put on my airplane.

I also want to send a sample up to Grady and see how well it takes primer and paint. The documentation says it should take paint without any issue at all, but I'd like to know for sure.

It's the real stuff though. MIL-S-38228

Phil
 
Polysulfide on fuselage joints...

...is commonly used to seal pressurized aircraft. The BEDE 5 kit aircraft are assembled with polysulfide and pop rivets. I did not do my -4 this way, but will consider for my next plane.... When I built a new rudder for my -4 (using 0.020" skin), I used polysulfide on the faying surfaces of the stiffeners, spar, ribs, fairings, etc. It worked great and seems to have taken paint well (~3 years so far..)

Good luck

Dean Pichon
Bolton, MA
 
Sealing Skins

For better or worse, I prosealed a thin bead on all fuselage top skin joints down to the longerons. Thought it might stiffen-up the fuselage, reduce resonance, and make it more waterproof.

Jim Diehl
RV-7A
99% complete
 
Sealing the seams with CS 2415

Hi guys (Sealing the Seams)
cs2415%20picture.jpg

I haven’t made many posts in the last three years but I guess I’m the A&P friend Phil was talking about.
I have a substantial amount of information on the subject of sealing fretting surfaces and seams on my web site if you’re interested. In my opinion you should seal at least the bottom of the aircraft seams if not all of them.
Note: I'm suggesting CS 2415 for external seam sealing and I'm planning on using...
ES 6228 Aeropoxy, (thin viscosity epoxy adhesive) for Faying surfaces. (lap joints)

http://www.txrv10.com/pages/CS2415.html

Dave Murphy
RV10
 
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For better or worse, I prosealed a thin bead on all fuselage top skin joints down to the longerons. Thought it might stiffen-up the fuselage, reduce resonance, and make it more waterproof.

If you do apply sealant you should roll it on, very thin layer (there is a spec but I don't recall the thickness off hand)

Fay surface sealing is standard practice in the jet production world, but keep in mind these are all pressurized aircraft and they generally fly more in a year than an RV will fly in 10 lifetimes. Airframe hours of 60, 000+ are not unusual in the airline world :eek:

So do "need" to fay surface seal, well it definately won't hurt anything but not sure it's really necessary.

I worked for a while building Sikorsky black hawk helicopter airframes (the workhorse of the military), no sealant is used even in the Navy model.
 
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Seam sealing with Sikaflex 227

Hi All,

My question is around seam sealing after priming. It is common after priming of a car to add seam sealant (like polyurethane Sikaflex 227) along edges to bridge the gap for top coating and prevent moisture egress. These can be used over any primer, and can be topcoated with PU. I fay sealed/wet riveted the lower skins of my fuselage, however not my wings or top skins of the fuselage. I am thinking that I would run a small seam along the edge of an overlapping skin, or where there is a butt joint, such as along the main spar where corrosion is common on certain types of certified aircraft. I have noticed on certified aircraft that there can be a significant gap between the overlapping skins (especially where 1/8" rivets are used), leaving the joint susceptible moisture entry. Has anyone done this (where they haven't fully fay sealed in a traditional sense), and are there any downsides (apart from time)?
Cheers,
Tom.
 
I used the flap as a test case yesterday. It had been primed with Wattyl Super Etch the day before. I called Sikaflex tech support and they confirmed that 227 should be fine directly over the etch primer, and in turn the PU can be applied directly over the Sikaflex. I filled some MK319-BS rivets with it, then ran a very fine bead along the bottom skin seam. Because the skin is so thin, this seam is extremely fine and I suspect that the topcoat will bridge this quite adequately without the seam sealer, and that the seam sealer will be more appropriate along the top of the main spar and some of the thicker fuselage skins but I wanted to test it on this smaller surface before I went full speed on the fuselage. I have left things to cure for a full day before top coating, as the full cure speed is approximately 2mm per day at current temperatures, although in the spec sheet it says that top coating can be performed as soon as skinning has occurred.
Tom.
 
The mechanics at the float operation I used to fly for would mask off a thin strip along each skin seam, then apply a thin bead of proseal along it to seal the edge. Not the most streamlined, but I plan on doing that to my fuselage as my RV will probably be staying outside for the foreseeable future.

Alex
 
Sealing

lap joints is a good thing. I have been thinking about the structures that have previously been built and think I have a decent suggestion.

There are some products that are very low viscosity that can be applied to the lap joint that will wick into that joint interface. They are pretty good at sealing things up, as they use this in the tank areas on helicopters.

I will try to get the information on this product, as I cannot dredge up the name of the stuff right now.
 
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