Oops- Flattening Dimples? Fuse Repair

Noah · #1 07-01-2007, 10:05 AM

Greetings-

Last month I purchased an RV-7A project from another builder. The fuselage is substantially complete, with top skins to be riveted on and some cabin work. I recently discovered that the fuse side skins, which are completely riveted except at the firewall and the forward top skin, were dimpled but the longeron underneath wasn't countersunk at the intersection of the side skin and fwd top skin. There is no way to get a countersink tool under the skin at this point. (See Photo) The fwd top skin is not yet dimpled.

Because the top skin will cover the top line of rivet holes in question, the dimpled side skins will be hidden. One builder friend recommended not dimpling the longeron, flattening the existing dimples in the side skin, then countersinking the side skin, then dimpling the top skin and riveting. This has the advantage of being quick and easy, but I am concerned about how flat the already dimpled side skin can be made, and the additional cold working of the dimpled, then flattened area, and the potential for cracks.

Another builder recommended removing enough rivets from the side skin around the area in question so that the side skin can be peeled back, allowing the longerons underneath to be countersunk. This will require a lot of rivets to be removed to get a drill and countersink in there, which will take a lot of time and increase the potential for additional damage. There are seven holes (fourteen both sides) which are supposed to take 1/8 rivets, but the existing holes in the side skin and longeron are oversized by .018-.025.
I suppose that either of these repairs will require the use of "oops" rivets due to the oversize holes in the skin and longeron.

Any recommendations? So far, I've (almost) completed Van's toolbox kit so this will be a steep learning curve!

Highest Regards,

Noah Forden
Rhode Island
RV-7A Finishing

morlino · #2 07-01-2007, 10:33 AM

Once you have your tool box together, drill out all of the rivets and re-assemble it. This will give you enough practice to determine if you can drill out enough rivets to peel back the skin and countersink the longeron without messing anything up.

It seems like that is a better option than flattening out the existing dimples. Although the consensus seems to be that you can re-dimple the other way or flatten out a dimple one time without worrying about work hardening the skin too much. There are some threads about figure 8 dimples and dimpling the wrong direction that discuss work hardening.

I would also suggest building the other van's practice kit and maybe drilling out and re-assembling that one too. Try to make as many mistakes as you can on the practice kits before learning new skills on your airplane.

Man, I can't wait until my wings get here.

Mel · #3 07-01-2007, 01:47 PM

Since the side skin will be "sandwiched" between the top skin and the longeron, it is acceptable to countersink the side skin and longeron together. Then dimple the top skin.

bsacks05 · #4 07-01-2007, 02:17 PM

Quote:

Originally Posted by Mel

Since the side skin will be "sandwiched" between the top skin and the longeron, it is acceptable to countersink the side skin and longeron together. Then dimple the top skin.

That's what I would do.

Paul Thomas · #5 07-01-2007, 03:02 PM

Quote:

Originally Posted by Mel

Since the side skin will be "sandwiched" between the top skin and the longeron, it is acceptable to countersink the side skin and longeron together. Then dimple the top skin.

Great idea. That's where having access to an EAA tech counselor come in handy, most of them have seen it before.

Noah · #6 07-01-2007, 04:31 PM

I understand that countersinking a middle skin and longeron behind is standard practice, but the issue here is that that middle skin is already dimpled, and needs to be flattened prior to countersinking. Is this the consensus as the best repair option? What is the best way to flatten the dimples - a hand rivet squeezer? Is there any chance this would result in cracking or any other detrimental effects in the skin? Will the flattened dimples be truly flat so that the repair will be "invisible", or will it only get it "partially" flat?

Thanks to all for the responses.

Highest Regards,

Noah Forden
Rhode Island
RV-7A Finishing

captainron · #7 07-01-2007, 05:11 PM

Quote:

Originally Posted by Noah

I understand that countersinking a middle skin and longeron behind is standard practice, but the issue here is that that middle skin is already dimpled, and needs to be flattened prior to countersinking. Is this the consensus as the best repair option? What is the best way to flatten the dimples - a hand rivet squeezer? Is there any chance this would result in cracking or any other detrimental effects in the skin? Will the flattened dimples be truly flat so that the repair will be "invisible", or will it only get it "partially" flat?

Thanks to all for the responses.

Highest Regards,

Noah Forden
Rhode Island
RV-7A Finishing

As others have advised you to flatten, I would just use a hand squeezer with a thin nose, no-hole yoke. Van's says that you can re-dimple once in the opposite direction-you are only going back to flat. Since you'll be riveting into a longeron, you'll be able to put some effort into your work with the rivet gun. A couple of "taps" with the gun before bucking the rivet will make sure things are flat. I think you'll be fine.

cytoxin · #8 07-01-2007, 05:37 PM

I would remove enough rivets to machine countersink the area. This is the engine mount attach point as well. the crack potential would concern me and you wont be able to see it because it is sandwiched. however you know your skills better than I do. Make sure you totally understand how to properly drill out a rivet.
1 select one size smaller drill bit
2 drill only deep enough to snap off the head.
3 tap remaining rivet shaft out. watch out on the thin subs as they can bend over
if you are not comfortable with rivet removal the methods mentioned earlier would most likely be adequate.

drilling off a sheet is no problem.
what if it does crack?

NOTE: you can carefully drill all the way through with the SMALLER drill bit. this helps immensely in the shaft removal. Drilling out rivets in this area should be a non event because the sub-structure is thicker than sheet stock.

Norman CYYJ · #9 07-01-2007, 06:51 PM

As Mel said countersink the side skin. This is a common practice and will be strong enough for this section. Flattening the side will pose no problem. Use your rivet squeezers with two flat snaps in it. This will not fatigue the AL. The side skin is thick enough to be machine countersunk for the 3/32 rivets. When you countersink the 1/8 rivets only a small amount of the angle AL will be removed.

Mel · #10 07-01-2007, 08:05 PM

Actually this method adds a little strength to the londerons as they will not be countersunk quite as deeply as they would to receive the dimpled side skin.
However you do it is certainly your choice and you are the one that has to be comfortable with the decision. I'm just saying that this is perfectly acceptable and is the way I would do it.