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Alternatives to Fuel tank sealant on non fuel tank components during the build?

R

RNB

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I'm working on RV10 elevators, there are numerous spots to use Fuel tank sealant in area that are not for sealing fuel. Are there acceptable alternatives? Any two part glues I can squeeze out and mix as I go or even RTV?

I saw someone online advocate using TotalBoat Thixoflex for the inserts.

My sense of things is that there ought be alternatives but I am not enough into material science to know what would work.

Trailing edges?
PVC inserts?
Elevator service bulletin?
 
I'd personally suggest sticking with the plans. ProSeal/Flame Master (polysulfide family of sealants) stays flexible (pliable?) for decades. This has been proven in thousands of applications here and beyond EAB. No real material compatibility issues. It is paintable, etc.

Example = the pain involved with potentially doing major surgery/matching paint/repainting a flight control surface a few years from now isn't worth the risk. You'll probably get the usual "xxx hours with yyy product. No issues!" comments here. Doesn't mean d!ck compared to the very long & good track record of the designers suggested material application.
 
If you want alternatives recomend downloading a copy of MIL-STD-7179A and looking at the allowable materials for Faying surface sealant this is what the USAF uses
 
CaptPausert said:
If you want alternatives recomend downloading a copy of MIL-STD-7179A and looking at the allowable materials for Faying surface sealant this is what the USAF uses
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Thank you.

My brief search says the stock fuel tank sealant does not meet this standard
 
The minimum specification is 200 psi tensile and 200% elongation. The manufacturers usually claim theirs as good to 300 psi, still a tiny fraction of any structural adhesive. UTS aside, at 200% elongation, there is almost no effective load sharing between the "adhesive" and the rivets.

It's a good faying surface sealant, but it's not an adhesive.

BTW, using proseal in your firewall seams is a very bad idea.
 
As I understand it, the use of proseal in the elevator is to dampen vibration, not to provide any structural benefit. At least that was true on the earlier RV's.
 
DanH said:
The minimum specification is 200 psi tensile and 200% elongation. The manufacturers usually claim theirs as good to 300 psi, still a tiny fraction of any structural adhesive. UTS aside, at 200% elongation, there is almost no effective load sharing between the "adhesive" and the rivets.

It's a good faying surface sealant, but it's not an adhesive.

BTW, using proseal in your firewall seams is a very bad idea.
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Respectfully I'm going to counter, Sir.

First and foremost, it is a sealant and a very good one. Of course there are stronger adhesives but they also tend to be much stiffer. This would not be good for most of the non-tank sealant apps where the designer calls for PS. One would guess the kit supplier has attempted to limit the number of materials required for the build. That said, a stiff bond is usually not desirable for materials with a high alpha like Al.

Yes, it is over applied in the cult of Vans and the FW seam example is not "made up." That said, I'll reiterate the OP should stick with the plans here.

Cheers boys and happy Friday
 
For a lot of the RV called out applications, like riveted trailing edges, my take is:
1. You need a flexible adhesive that is just good enough to act as a cleco until the part is riveted and is not intended to be the final means of joining the parts together
2. Vans tends to take a jack of all trades approach towards materials in that if something can be used to meet multiple requirements, even if it's not the best solution for that particular application but good enough, then so be it
 
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Freemasm said:
That said, a stiff bond is usually not desirable for materials with a high alpha like Al.
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Exactly

Consider for a moment what the coefficient of expansion difference is between the foam rib and skin in an elevator?

It is true that tank sealant isn’t nearly as strong of an adhesive as a lot of other alternatives, but that doesn’t matter. It only needs to be as strong as is needed in the application it is being used for.
A good RV relevant example being the comparison of an LP4-3 blind rivet and an AN470AD4 rivet. The strength ratings are hugely different, yet each one is used in structural applications on RV’s when the proper engineering and testing was done for a particular application.
Anyone that has removed a fuel tank access cover can confirm that though it might not be the strongest adhesive available, it is way better than Elmers glue.

To the OP, of course there are alternatives to tank sealant. The challenge is determining which is appropriate.
The benefit of using what is recommended is that actual static load testing was done on test articles that were built using the recommended adhesive and process. In addition, there is now 27 years of impeccable service history on foam ribs in RV control surfaces.
It would be difficult for most builders to do any testing to prove that an alternative could stand up to these two benchmarks. Which in my opinion makes just using what is recommended, the best choice.
 
So just an FYI if proper industry standard is used in design. Adhesive is not considered as adding any additional load capability. The 8802 sealant is primairly designed as a fuel tank sealant due to its fuel resistance. Other faying surface sealants are primairly designed for water resistance and corrosion protection (most have corrosion inhibitors) make sure you wear gloves if using ones that have hexchrome.
 
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