Flap hinge countersink question

JohnR · Post by **JohnR** » Thu Sep 14, 2006 8:16 pm

On the junction of the bottom wing skin, flap brace, and the flap hinge, which piece should be countersunk? I have been through the plans and must be missing it somewhere. I looked on Dan C's site and he countersunk the hinge. To me it would make more sense to countersink the flap brace. Any suggestions?

Thanks,

jim_geo · Post by **jim_geo** » Thu Sep 14, 2006 8:32 pm

That would be the hinge. Keep your empanage in mind as you build the rest of your plane and esp. keep your emp portion of the manual handy as it has more detail of method than any later section has. As the build continues you can fall back on those two things as reminders. Or you can ask here

.

captain_john · Post by **captain_john** » Thu Sep 14, 2006 8:50 pm

John, nawwww..

You c-sink the hinge. The f-brace isn't thick enough.

It needs to be 0.040 or thicker to accomodate a -3 c-sink without interfering with the underlying material.

Does this help?

CJ

JohnR · Post by **JohnR** » Thu Sep 14, 2006 9:07 pm

Thanks guys, I'm not trying to be argumentive but CJ's comment is the reason I was thinking of countersinking the flap brace, it is .040 which should be thick enough. Wouldn't the hinge be stronger if it wasn't countersunk?

I did a search with Google and found that people have done it both ways.

jim_geo · Post by **jim_geo** » Thu Sep 14, 2006 10:35 pm

The choice by preferance is this. Do nothing, dimple and last is countersink. It is about strength and material integrity. The hinge and it's sinks are in the middle of a sandwich of material one side is a dimple and the other side is a nothing your hinge is held securly that way. That's not to say that all counter sinks should only be in a sandwich but in this case it's prefered. In the case of the flap brace it should be preferable to not do anything but drill and rivet given what it does for a living.

JohnR · Post by **JohnR** » Thu Sep 14, 2006 11:13 pm

Jim, great point to check the empannage instructions as a reference. I did that and was just coming back to post what I had found when I saw your last post. I really appreciate the answers I get here so quickly but my empenage instructions say to:

"Machine contersink the top flange of E-606PP (spar) to accept the dimples of E-701 (skin)" The hinge then goes on the bottom of the sandwich.

By following this it would appear to me to be preferable to countersink the brace instead of the hinge. Doesn't the flap hinge go on just like the trim tab did?

Sorry to keep beating on this but I just want to make sure I understand and that anyone referring to this in the future can understand it also.

I am just a little confused by what appears to be conflicting information.

Maybe I'll call it a night and sleep on it.

Thanks for the quick responses!

jim_geo · Post by **jim_geo** » Fri Sep 15, 2006 2:47 am

So I've gone back to look at pictures I've taken of my work. Yup you're right it looks like the hinge is on the outside of everything and I believe I must have counter sunk the hinge and dimpled the flap brace. I'm not even going to look at the emp. So how's this? If the flap brace is thick enough you counter sink it. If it isn't you counter sink the hinge.

captain_john · Post by **captain_john** » Fri Sep 15, 2006 4:07 am

John, Let's back up a bit.

Why to you does it make more sense to you to countersink the flap brace? Can you explain why?

I feel that the thicker flap hinge which has a hinge pin and an interlocking second component is stronger than the flap brace and would be the wiser choice to countersink.

CJ

Brantel · Post by **Brantel** » Fri Sep 15, 2006 7:32 am

On the emp, the directions say to countersink the spar and dimple the skin and let the shop head form on the thicker material of the hinge. I just watched this on the Orndorf video last night for the 6 and he also countersinks the brace.

I have been taught that anytime you have three layers of material, you dimple the first layer and countersink the middle layer if the third layer is thicker. This combination gives complete support to the shank of the rivet and gives you a nice thick area for the shop head to form.

Brantel
RV7A Wings on Order

Post by **Spike** » Fri Sep 15, 2006 8:11 am

Im not building a 7 and the 9 has fowler flaps so I can only give an opinion. If possible I would counter sink the middle of the sandwich. The reason being the tail is done that way

Actually, I feel that way because whenever you remove metal I would think you weaken the part more than if you dimple it. Therefore Id want the weakened part braced on either side by full strength structures.

The questions I would ask is if you are weakening the brace to the point that it doesnt give you much strength. Tough call I guess. Its Friday, call Vans.

Wicked Stick · Post by **Wicked Stick** » Fri Sep 15, 2006 8:27 am

Brantel wrote:On the emp, the directions say to countersink the spar and dimple the skin and let the shop head form on the thicker material of the hinge. I just watched this on the Orndorf video last night for the 6 and he also countersinks the brace.

I have been taught that anytime you have three layers of material, you dimple the first layer and countersink the middle layer if the third layer is thicker. This combination gives complete support to the shank of the rivet and gives you a nice thick area for the shop head to form.

Brantel
RV7A Wings on Order

Brantel is correct, the flap brace on the RV-7's and 8' are .040 so countersinking the brace is the way to go and it is exactly the same procedure as with the trim hinge on the left elevator.

When countersinking the flap brace, be sure to cleco on the hinge so the countersink bit has something to help keep it from wandering. Or you can get a piece of hardboard and drill and cleco the brace to that and use the holes in the hardboard to do the same thing.

cjensen · Post by **cjensen** » Fri Sep 15, 2006 9:43 am

I can't offer an opinion, only what I've already done...I thought about c-sinking the brace, but the hinge is the thicker material. The brace is thick enough to countersink, but if there is another piece of the puzzle with thicker material, I dimple the thinner stuff, and -sink the thicker...hope that makes sense...

jim_geo · Post by **jim_geo** » Fri Sep 15, 2006 1:37 pm

This morning I drove to the shop for the sole purpose of looking at what was done on the flap brace, hinge area on my wing. Turns out the flap brace is counter sunk. Seems to me you want to bury counter sunk parts whenever possible.

JohnR · Post by **JohnR** » Fri Sep 15, 2006 6:09 pm

Okay, word from the mother ship on this one. I called and talked to Gus. He said the preferable method was to dimple the skin, countersink the flap brace, and leave the hinge alone. This method will provide the strongest joint.

As Brantel and Jim mentioned it is preferable to keep the countersink in between two parts if feasible.

Thanks to all for their input!

PS Welcome to Rivetbangers Brantel!

cjensen · Post by **cjensen** » Fri Sep 15, 2006 9:22 pm

Okay, since this sounds the like the way is should be done, and I have already dimpled my flap brace...if I can somehow get a yoke in there, should I flatten the dimples out, and countersink 'em? I know dimples can be flattened without any trouble, but what about 'sinkin' 'em afterwards?

jim_geo · Post by **jim_geo** » Fri Sep 15, 2006 9:43 pm

Chad I wouldn't bother. If there is a problem you can get to that area just as easily later on as you can now. I would definetly put that item on my 50 hour check list though. By the way you can flaten dimples and counter sink em, not the best thing to do but you can. Even if you could flatten them your flap brace would most likely have to be removed to do the counter sinking.

cjensen · Post by **cjensen** » Fri Sep 15, 2006 10:27 pm

jim_geo wrote:Even if you could flatten them your flap brace would most likely have to be removed to do the counter sinking.

I thought about that just before I got back online this time...the skin would most likely be in the way to get good 'sinks.

cjensen · Post by **cjensen** » Fri Sep 15, 2006 11:02 pm

I just checked Dan C's, as referenced by John. He did what I did, and called Vans about it. They said not to worry about it, won't affect anything, but for his own piece of mind, he put in a .020 reinforcement strip.

Not a bad

, so I think I'll do the same.

JohnR · Post by **JohnR** » Fri Sep 15, 2006 11:04 pm

Chad, from what I gathered from Gus you could countersink the hinge it was just the preferred method was to countersink the brace.

Brantel · Post by **Brantel** » Sat Sep 16, 2006 7:23 am

Since this is already dimpled, I would leave as is and if it really bothers you, put a backer in there like was mentioned before. I did this on my rear spar of my left elevator on the inboard side top because I was having a bad day and countersunk the entire top of the spar not thinking that the hinge does not reach the last 4 inboard holes. Instead of a new spar, I just added a backing strip in there to create the same situation as the holes with the hinge.

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