Flaperon Trailing Edge Riveting Question

[N213RV]

I'm builiding a SS7. It discusses using flush rivets for riveting the trailing edge of the flaperons. I have the quickbuild wing and the flaperons are already assembled, less trailing edge rivets. The skin is too thin to countersink, and the trailing edge is filled with hysol so I don't believe it can be dimpled.

How could you possibly use flush rivets? What am I missing? The optimum design would be to dimple the top and bottom skin prior to assembly, and then double flush set the rivets. Basically that is how it's done on the RV-10 rudder and elevator trailing edges.....

Thoughts?
Thanks

[Dave S]

Hi Mike,

I thought about this too when building our S7. Our KF is an older model which came with pop rivets and maybe the current kits have gone to the flush rivets - can't argue against them looking better. I don't have any RV build time so can't speak to the comparisons. I did visit with a couple A & Ps in our club at the time - these guys had more aluminum experience than I will ever have as they worked on Boeings. In both cases, both indicated the pop rivets were fine on the KF flaperons. Because of the thin skin on the flaperons - alternatively they suggested solid non-flush rivets and indicated they would have no advantage over the pop rivets in this application. These guys suggested staying away from the flush rivets because of the thin skin on the flaperons; although I think I have heard of people using the flush rivets with great care - these are experimentals and we do experiment - maybe that is what is done on the newer kits.

I decided to stick with the pop rivets and was also advised that a KF will not see any measureable drag reduction by getting away from the pop rivets.

One option I can think of setting flush rivets is to do a very careful and very shallow countersink - but I haven't experimented with this at all and I am not sure there is enough material thickness.

Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

[WISDAN]

I used standard solid rivets on my flaperon trailing edges. If I remember right my manual said to use the solid rivet for a better look compared to pulled rivets. It does look very good.

[HighWing]

I think the reasoning for the rivets might help with the decision. The trailing edges of the flaperons on the early Kitfoxes were glued with structural adhesive only. After some time, some of the seams began to open because the adhesive failed. Whether the failure of the adhesive was due to improper preparation before gluing has always been my suspicion, but it is just speculation on my part.

The rivets are simply like suspenders for those who already wear a belt. In my opinion at least, they are not structural, but only serve to absorb some of the forces that work on the glue joint. both of my Model IVs have flush rivets over carefully countersunk top holes. The first IV flew almost ten years with no trailing edge separation and I did the same with my new one.

I understand the thoughts from a person with aluminum construction experience. It seems contrary to everything riveted to countersink two thicknesses of .015 aluminum, but it seems to me that to dimple and then rivet, the end result will be not quite as clean as using conventional rivets. Stronger, yes, but great strength is not the purpose here. One further thought - it might not be a bad idea to dip the rivet in a bit of Hysol so that there will be no possibility of the rivet working loose.

One thing I did to clean up the contour a bit was to use the flat set for the flush top.

6614

I used a rounded head set in the squeezer to give a rounded effect to the rivet extension on the bottom.

6615

[JoeRuscito]

Lowell did you use a hand squeezer for those rivets? like this one? https://www.aircraftspruce.com/catalog/topages/tatco12-03674-87.php?clickkey=4583

[HighWing]

Yes, I used that squeezer.

[efwd]

I would say that those are a pretty pricey proposition for just those few rivets. If that is what your were thinking also, rest assured that they can be used in a couple other spots as well. Sometimes allowing you to do a bit cleaner job than whats called out in the manual. Flush rivets are pretty nice. You can get dimple dies to go with the squeezer as well. Just more money. Fortunately I had my stuff from a previous project.

[JoeRuscito]

Agreed it’s pricey. What is the other option? I haven’t been able to find any good pictures of the stock pull rivets and what they end up looking like with paint, but it does seem most people use solid rivets. I’d prefer to not spend the money and use vice grips or just the pull rivets but I don’t think you can get the same nice rounded shop end with vice grips. Please correct me if I’m wrong!

[Shadowrider]

Do you know any local aircraft mechanics? Do you have any local maintenance facilities? I found that most are very helpful. We got our flaperons all ready, and then borrowed a rivet squeezer for a couple hours. Most are very helpful if you tell them what you are doing.

[HighWing]

Truth be told. I did modify a Vice Grip to fit into some tight spaces desiring the rounded look to the back side of the solid rivet. First sanded and polished smooth both sides, then a shallow drilled hole as a centering point, then a rounded Dremel burr for final shaping. About $5 from Harbor Freight and a half hours work and save a hundred bucks - or more. I do have both though.

[JoeRuscito]

Oh I love it! Work well? I think this is the method I will use on the trailing edge. If Im using round head rivets Im guessing I need to dimple both sides...

Thanks!

[HighWing]

It works fine. The leverage from vice grip geometry makes the difference in squeeze power. One challenge, though with rounded dimples on both jaws would be the centering top and bottom. A solution might be to use a very small drill - #60 for a drill through one jaw, then slightly into the other jaw then enlarge and shape.

[jiott]

I used vice grips with flat on both jaws. Slightly countersunk the top rivet hole. Ended up looking quite nice on both sides, maybe not quite as elegant as Lowell's, but nice anyway.

[TJay]

I kinda did the same thing that Lowell did but I bought a dimple die set from Aircraft Spruce and welded them to the end of some vice Grips worked great I think they only cost around 6 bucks each.