[flickroll]

I have an RV-8 with the Grove gear, although this question is applicable to any RV-8 (not RV-8A).

The area where the upper gear leg fairing contacts the fuselage has a lap joint of aluminum skins: the upper, vertical, skin overlaps onto the lower, horizontal skin. The lower skin rolls up the side and fits under the upper skin. This lap joint creates a bump. I originally thought I'd cover the skins with packing tape and put some epoxy/micro or epoxy/cabosil (which is better for this application?) on the fairing and let it set up in the joggle area. Then it occurred to me that this would create a visible joggle on the fairing.

Now I'm thinking I may scuff sand the aluminum in the joggle area, and try to 'fair' the joggle area (get rid of the bump) BEFORE I put the epoxy mix on the fairing. This would create a smooth looking joint which would not be noticeable if the fairing is not tightly contacting the fuselage skin.

Has anyone done it this way? Or is this a bad idea? And if it is a good idea, what was used for the filler? Micro, cabosil, or flox?

Thanks

 

[DanH]

Jim, I'd tape the fuselage and apply a small bead of epoxy/cabo to the underside of the fairing edge. Fasten in place, let the edge squeeze out, wipe it flush with your finger, come back 8 hours and do a bit of rounding with 400 grit.

 

[Rick6a]

One way....

......The area where the upper gear leg fairing contacts the fuselage has a lap joint of aluminum skins..

Jim,

I'm sure there are any number of ways to do what you want. In my case, not wanting to spend a whole lot of time fooling with it, I fitted pre-made intersection fairings from Fairings-Etc. They fit the Grove airfoil gear pretty well right out of the box. For a really tight fit to account for the laps you mention and to "snug" the fairings against the structure, I slathered them with a slurry of West System fairing filler and epoxy using nothing more than clear packing tape as a parting agent. I was looking for a generous squeeze-out of excess filler material from around the fairing. Once the epoxy sets up, you break the fairings away and sand as required. You might have to do this once or twice but it really is a simple and effective method to make the fairings fit better. BTW, one of the two screws that hold each fairing into place is through a nutplate attached to the removable landing gear inspection cover. The other fastener I used is a self tapping sheet metal screw.

 

[flickroll]

Dan/Rick

Thanks for the tips. I have an additional question:

What is the main purpose of epoxy/micro? Minor smoothing of surface imperfections? Sounds like epoxy/cabo is a better choice at a wear point since it is harder than micro. Seems to me that epoxy/micro is similar to the lightweight epoxy putties you can buy....but it's brittle so should not be used when structural strength is need or flexing may occur. Right? Thanks

 

[DanH]

Cabosil to make epoxy thixotropic, micro to add lightweight bulk, flox to add structural toughness.

Epoxy/cabo is indeed a better choice at a wear point. Consider; on the microscopic scale, epoxy/cabo is a solid and epoxy/micro is a sponge of glued hollow glass spheres. Epoxy/flox would be even tougher, but it doesn't wipe and filet smoothly so it's not as nice for fine detail work.

 

[Rick6a]

.....What is the main purpose of epoxy/micro? Minor smoothing of surface imperfections?.....

Fairing filler is not a structural material but then neither is the application we are asking it to be used in. Several years ago, I essentially used the same technique with West 410 filler (it is NOT microballoons and according to one source by comparison is 30% lighter by volume than microballoons) on my RV-6A empennage fairing as outlined in my first post. You can see the 410's lighter look around the edges of this fairing before it was painted. I really don't think wear much of a concern and fairing filler is certainly easy to sand...almost like balsa wood. On the other hand if you elect to use much tougher and structural cotton flox in the epoxy instead of fairing filler, you may as well be sanding on concrete....I'm exaggerating of course, but not by much.

Bottom line: Use whatever material you feel most comfortable with, I did.

 

[DanH]

<<Bottom line: Use whatever material you feel most comfortable with>>

True enough. Mostly I stick with base materials (micro, cabo, flox) because they are cheap, and because you can mix them in the same batch in proportion to desired physical property.

A pound of microballoons (a big bag) is $10 or less. West 410 (fr example) is just under $30 for 5 ounces. Either way most of it winds up on the floor <g>

 

[flickroll]

Dan/Rick - next question -

Say I THINK I have everything faired properly, and then shoot it with a primer like K36. However, once the K36 is on and there's better contrast, I see that I need more work with some sort of epoxy slurry. Can I apply the slurry over the K36 (properly scuff sanded), or must I sand it off before applying the slurry? thanks

 

[decathlon737]

Body filler or epoxy mixture can be applied directly to properly scuff sanded K36 primer with no problems.