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Wing root fairing attachment nutplate holes

SabreFlyr

Well Known Member
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The plans have me thoroughly confused about dimpling/countersinking the wing skins for the fairing attachment screws. I'm currently verifying the steps already completed in my QB wings. There are many steps that were missed.

On page 41-05, it seems to be indicated that all of the wing-side attach screws are AN507C-832R8 flush screws, including those on the fuel tank attach brackets. Yet, on page 16-02, it's stated very specifically that, on the top inboard wing skin, only the aft-most screw hole is dimpled. I would presume that the others would be countersunk but there is no mention of that. The nutplates are riveted in place on the next page thus making it difficult, even impossible, to countersink them later.

I have the same issue/question regarding all of the other attach holes on the bottom wing skins and fuel tank skins. I can dimple the holes in the fuel tank skins except that I have to get some Proseal out of the way. I can also countersink the holes on the bottom wing skins without any problem.

The fuel tank attach brackets are another matter. On page 18-04, the two forward #19 holes on the shim on the top of the attach brackets are dimpled yet the other five holes on the top and bottom of the brackets are not. The proximity of the attach bracket makes it impossible for me to dimple the hole for the one-leg nutplate. I did talk to the factory about that one and we decided that I should just drill out the hole to clear the dimple in the fairing.

All of the five nutplates on the top and bottom of each attach bracket were installed. Therefore, if I'm going to countersink these holes, I've got to drill out the rivets in all of these nutplates, except maybe the one-leg where, if I'm careful, I could still drill out the screw hole.

Interestingly, also on page 16-02, it is specifically states NOT to dimple the rib top flanges under the wing walk doublers. However, I would expect them to be and indeed they were on my QB wings.

I can see what I need to do in all of these cases to accommodate the flush screws. However, because of the way the plans are specific about the holes to be dimpled (page 16-02 and 18-04) makes me wonder if I'm missing something.

Can anyone help me clear up these mysteries?
 
I had similar questions that I asked on facebook.

Here is a link to it. https://www.facebook.com/photo?fbid=10219095614083628&set=gm.985270831948881

As far as the countersink holes Van's support said the following.

Countersinking is intentionally left until after the nut plates are installed to keep the cutter piloted due to how deep the countersink will be once finished. We use this same technique on the nut plates attached to the spar. In this case you will select a countersink with a smaller pilot that will fit inside the threads of the nut plate, #30 pilot for -8 nut plates and #40 for -6. No modifications should be needed”
 
Countersinking is intentionally left until after the nut plates are installed to keep the cutter piloted due to how deep the countersink will be once finished. We use this same technique on the nut plates attached to the spar. In this case you will select a countersink with a smaller pilot that will fit inside the threads of the nut plate, #30 pilot for -8 nut plates and #40 for -6. No modifications should be needed”

Duh! That's it! Never occurred to me that I would use a smaller cutter. Didn't understand how I could do that without damaging the nutplate threads.

Thanks!

(Still curious why the plans specified not dimpling the top rib flanges under the wing walk doublers. They were obviously dimpled in my QB wings.)
 
Duh! That's it! Never occurred to me that I would use a smaller cutter. Didn't understand how I could do that without damaging the nutplate threads.

Thanks!

(Still curious why the plans specified not dimpling the top rib flanges under the wing walk doublers. They were obviously dimpled in my QB wings.)

Don't feel bad. I actually took my #8 cutter and ground down the pilot. I did this before hearing back from Van's support.
 
Pictures?

Hi, I'm looking at these holes on my QB kit and trying to visualize how to countersink these holes. I'm imagining this will lead to knife-edging on the skins, is that right?

Does anyone have pictures or a blog post that they can point me to?

Thanks!
 
I deviate from the plans for the R-10 (or 14) wing root fairing. I dimple the holes, rib, backing plate and skin. I also dimple the ribs, backing plate and skin for the entire backing plate.

For the wing root, I then go back and slightly countersink the dimples so the fairing dimples fit flush.

Carl
 
Hi, I'm looking at these holes on my QB kit and trying to visualize how to countersink these holes. I'm imagining this will lead to knife-edging on the skins, is that right?

Does anyone have pictures or a blog post that they can point me to?

Thanks!

The very end of This Post shows the holes in the tank attach brackets / shims and how I countersunk them.

I chose to dimple the wing walk doublers and ribs instead of countersinking all the holes on the skins - didn’t like the idea of that. I was able to install the nutplates by dimpling the holes in the nutplates instead and amending the rivet lengths. So the only one I countersunk on the wing skin side was the single hole where the tank attach bracket is located. You can see it here in this post

Yes - the top sheet of the stack will be knife edged.

I would be careful in selecting your cutter - depending on the thickness of the stack, a #30 pilot cutter would not have the pilot in the threads at the start of the cut (due to the thickness of the stack / type of nutplate etc). It will chatter and wreck your work. I always checked that the cutter pilot was the right size and used what ever cutter fit the screw hole size first - then once the pilot of this started to hit the nutplate threads, swapped to a -# cutter whose pilot then fit inside the threads to finish the cut off. I hope this makes sense? It’s harder to explain than to do.
 
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