Rudder Stiffeners - Proseal or not

[JDBoston]

After seeing postings regarding cracks on the .016 rudder skins on other models some people mention that they proseal the stiffeners. Since there is no mention of it that I can see in the plans what is the general practice here?

If you do choose to do this, is what you are doing similar to the tanks (the mating surface) or a small amount in another location?

My thought was also that you wanted to avoid introducing any additional weight of the rudder at all, even small amounts.

Thanks

[Logan]

Jeff, I think the pro seal globs were for rudders of a different design, where the trailing edge was a bent skin. The -14 has a wedge of aluminum there, which I believe changes things. The trailing edge isn't trying to "unbend" as the wedge keeps the right shape.

I didn't put any pro seal in my rudder for the reason you mentioned: No step in plans to do so!

[F1Boss]

3M makes some very VERY Sticky high bond tape that would be much easier to use if you want to add a bonding agent to your assembly. Wings and wheels.com sells the best quality I have found - it is on their gap seal page. I bought a roll of this stuff maybe 8 years ago, and I stilll use that same roll for any sort of bonding that I feel necessary.

If you want to use a compound as opposed to a tape product, you should look at faying surface compounds as opposed to fuel tank sealants. The fuel tank sealants do not have the adhesive properties that the faying surface compounds do.

Carry on!
Mark

[N804RV]

This is the 2nd time I've seen threads about using Proseal on the trailing edge stiffener tips to prevent cracking on the bent trailing edge design.

I thought the recommendation from Van's was to use RTV because it is a little softer. I thought I'd heard somewhere that Proseal was too heavy and stiff for this application. Am I incorrect?

[JDBoston]

Originally Posted by N804RV

This is the 2nd time I've seen threads about using Proseal on the trailing edge stiffener tips to prevent cracking on the bent trailing edge design.

I thought the recommendation from Van's was to use RTV because it is a little softer. I thought I'd heard somewhere that Proseal was too heavy and stiff for this application. Am I incorrect?

I am spreading this as well like everyone else. Maybe I should generalize. It is not mentioned in the plans at all so I assume not a recommendation. Should we put anything (RTV, Proseal, tape, etc, etc) on the stiffeners?

[andyrv]

I don't have any knowledge on the 14 but the rudder on my 7A cracked at about 150 hours.

This were quite a few stories about this on VAF. The cracks occur on the front end of the lower stiffeners at or near the vertical spar. Proseal on the stiffeners of my second rudder cured the problem so far.

http://www.vansairforce.com/communit...=rudder+cracks

Andy

[rvbuilder2002]

As already mentioned, the RV-14 rudder and elevators internal structure is quite different from the earlier models. The structure ties together already without adding the sealant.

The primary cause of skin cracking at the fwd end of stiffeners on the other models is leading edge rolls that were not completed properly. If there is a lot of strain from the skins being forcibly pulled together for riveting, it all gets concentrated as a bending force right at the first rivet.

[RV7ForMe]

I have been thinking about this for a while and there seem to be endless opinions.

Cracks seem to form on the forward end of the stiffners...

Yet so many people put a blob proseal / RtV on the aft end of the stiffner.

Some also at the forward end.

Some people seem to just proseal of epoxy the whole stiffner before riveting.

So This leaves me as a new builder quite confused. Do I do: non, some or all of the above? I think weight does matter here. The plans dont call for it at all. Hoever it says something about it the section on how to bend TE of the elevators... Nothing about the rudder. I can't tell if the Vans 5.whatever is general info directed to any of their products of specially to the one I am building...

Also RTV.... I searched the archive for a while and cannot definitely say what kind is ok and may or may not cause corrosion... By the way this is the part about building I do not enjoy. Having to waste weeks on what product to use and still being unsure if that is the right choice. considering I wont be able to get in there after the TE is locked.

[PilotjohnS]

I can help you on the rtv front. It is not a good idea to use any rtv on aluminum that cures using acetic acid. This is the kind that smells when it is curing. And this is 90% what is out there. The rtv for electronics is better because it is not acetic acid cured but dont know the exact chemistry so cant recommend it yet. The two part stuff you buy at an industrial supply house could be OK, but it is best to pull the data sheet and look at the chemistry. For right now, all I found is proseal.

[JDBoston]

I chose to follow the manual and not add anything, thanks for all the opinions.

Scott: I will also take care to get the bends correct for the leading edge so there is very little load on the skins themselves which may induce cracking on that first set of rivets in the stiffeners.