Composite/Fiberglass End Pieces

[permagray]

I am working on the rudder assembly and am concerned about riveting the composite rudder tip (part of it is countersunk) There is not a lot of material to begin with, and once it has been countersunk, it seems really thin. Are folks doing anything such as maybe reinforcing the back with rivet washers?

[PhilipRueker]

So the parts that are to be countersunk should have at least 0.04 inches thick and there should already be some reinforcement there.
In my case, it was a bit too short, so I had to extend the reinforcement a bit further.


After adding reinforcement to cover those extra 3 holes that need it for countersinking:


So if you need to add some fiberglass with epoxy, I've detailed what I did here:
https://slingtsi.rueker.com/2019/09/20/ ... forcement/

After that, I just riveted them and it seems to be holding up just fine.

[permagray]

THANKS! Glad I asked.

[permagray]

So, what do you recommend if I have a tip skin fit that is like this:

https://photos.app.goo.gl/YGpr4soz8Swdpm668

[PhilipRueker]

That looks like you should re-drill the holes in the fiberglass tip, starting from the second from the front and working backwards towards the tail to flatten out that buckling of the metal.

You might have to fill in the holes if the re-drilling would enlarge the existing holes. To fill them you'd need some epoxy and a filler like cotton flock (can get both from Aircraft Spruce) and probably a strip of fiberglass to reinforce.

[permagray]

The tail is flush with the skin. To accommodate any extra distance from tail to front, would make the front of the tip ride up high enough as to make the holes too close to the edge of the fiberglass. Also, the rudder fiberglass tip comes with the back end canted outward, whereas the actual rudder skin is canted inward (I ground it down to make it fit.)

Maybe I will pull the front two clecos and do some fiberglass fill or something. Arggh. I've got to get the rudder off of my worktable.

[permagray]

Also, is there some recommended sealant that one should use to prevent water incursion at the rudder tip?

[PhilipRueker]

I had to trim (just filing it away) a little bit off the tail edge in order to fit it in.

If you have any gaps you want to fill you can use Micro Filler mixed with Epoxy.

Other than that, once it will be painted, the paint will seal over the fiberglass and metal.

For general sealant recommendation, you could use the GE 5050 metal silicone sealant, which was the recommendation from the factory to use for a part of the Horizontal Stabilizer (the instructions were changed since then I think.
But do note that that one is not paintable.

[permagray]

I finally figured out in your previous post that your tip came (at least partially) reinforced from the factory (the black part) Mine did not, and I assumed that you had put the black reinforcement on yourself. I guess I now have the further conundrum of first doing a whole reinforcement layer. I epoxied sheet metal screw nut plate clips on the back side as reinforcements. Of course if I have to move the holes, these are pretty moot. Thanks for your help. Going back at it today.

[PhilipRueker]

Yes correct, the factory had the black reinforcement already applied, but for some reason it was too short in part based on which holes needed to be countersunk, so hence I had to extend that reinforcement with some fiberglass strips (which mine were white) to bring up the total depth to > 0.04 inches (which is the minimum you need for countersinking, since you can't dimple fiberglass for obvious reasons).