Upper fuse skin

I?m pretty much complete with all the metal work on my -10. Over the entire build thus far, the only place where I?m not happy with my metal work is the upper fuse. I have no dings or marks on the entire airframe, something I?m proud of as a first-time builder, except? where the upper fuse skin wraps around the sub panel/panel frame flanges. It?s very difficult to see in the pics, but there are a few outies where circled:


I decided to live with it, but truth be known, it was grating on my OCD every time I glanced at it. While working on this piece I ran into another problem once I riveted the skin to the substructure and tried installing it back onto the fuse. While the center rib flange lined up with the holes in the firewall, the two outer rib flanges weren?t even close. Right rib flange:


Left rib flange:


A call and some emailed pics to Van?s was met with some head scratching ? said they went into the warehouse and noticed the same misalignment? Their answer was to send some angle and have me attach new flanges to re-drill in the proper locations off of the firewall:




OCD getting the better of me, I decided to also start over and replace this:


with this:


I?m at a loss because I can?t seem to get around getting the outies ? I can see them just clecoing the new skin to the new substructure ? let alone what?s going to happen when I hit it with the gun. I?ve hit the corners ? marked with red sharpie in the pic ? with the Scotchbrite wheel as much as I can:


The metal at the corners of the flanges is already thinner than I?d like. Not really sure how to get around this. I?d hate to do all this rework only to get the same stinkin? outies in the same spots?

You will never see those spots once the glare shield material and the window is installed. The significant epoxy and body work you will be performing to blend the window to the upper fuse will cover anything you may be seeing now. Use your original piece and build on......

Also, don't final install this piece until you have your avionics sorted out and installed......

Bill.Peyton said:

You will never see those spots once the glare shield material and the window is installed. The significant epoxy and body work you will be performing to blend the window to the upper fuse will cover anything you may be seeing now. Use your original piece and build on......

Also, don't final install this piece until you have your avionics sorted out and installed......

Click to expand...

Thanks, Bill. Absolutely the spots on the right hand side of the first pic will be covered, but I'm not sure about the left hand rivet row. I've looked at pics on the web, but don't have a good idea about how far forward the windshield fairing glass blend will be.

Aesthetics aside, I'd like to hear how to work around this issue - just to improve my knowledge and skills as a builder. Again the corners in the last pic are the culprits. I hit them as much as I'm comfortable with on the wheel. The metal is already pretty thin from trying to knock down the points. Any thinner and I'm sure it would be a prime spot for an eventual fatigue crack - if not already that thin.

I would not sand the skin at all. Here is a pic of my windshield after most of the body work was completed. Your painter will know how to take care of any dimples and dents.

Oh wow - thanks for the pics. That definitely makes up my mind to roll with the original piece. You just saved me a nice chunk of work. Now back to the doors

Jon,

Are you sure those spots (in the 1st post) are really 'outies'? If you wrap a flexible straightedge around that curve, what do the areas around the adjacent rivets look like, relative to the normal curve?

I'm not building a -10, but that look isn't uncommon in highly curved areas over bulkheads. Often, the rivet is pulling the skin down to the inadequately curved flange of the underlying structure. That will make a corner ('outie') over the adjacent corner of the bulkhead flange 'finger'.

You can shim the flanges to maintain the normal curve. Or, after the fact...

There's a technique someone taught me years ago to move the riveted 'innie' back out to the normal curve. Too lengthy a description to type (but relatively quick/easy to do), but if you're interested, you can PM me your # & a good time to call so I can describe it.

Charlie

rv7charlie said:

Jon,

Are you sure those spots (in the 1st post) are really 'outies'? If you wrap a flexible straightedge around that curve, what do the areas around the adjacent rivets look like, relative to the normal curve?

I'm not building a -10, but that look isn't uncommon in highly curved areas over bulkheads. Often, the rivet is pulling the skin down to the inadequately curved flange of the underlying structure. That will make a corner ('outie') over the adjacent corner of the bulkhead flange 'finger'.

You can shim the flanges to maintain the normal curve. Or, after the fact...

There's a technique someone taught me years ago to move the riveted 'innie' back out to the normal curve. Too lengthy a description to type (but relatively quick/easy to do), but if you're interested, you can PM me your # & a good time to call so I can describe it.

Charlie

Click to expand...

Thanks a lot, Charlie. I think I know what you're talking about. Shimming was the only way that I could think to prevent it - after the fact, which obviously doesn't remove my "outies". I'm not sure if they are truly outies or they could be removed. I believe I've read about the technique you're referring to - tapping the shop head of the rivet to push the skin back out...? I'll have to play around with it a bit. Thanks!

Avoid hitting the shop head. Make a wood (hardwood, not pine/fir) or plastic tool that can 'nest' the shop head in a ~1/2" round end to move the aluminum flange/skin; not the rivet. Never ever hit it without some sort of dolly on the outside. Otherwise, you'll have a real outie around the rivet that will be unrecoverable.

You just might lose the outies if you restore proper curvature at the rivet.

Good luck,

Charlie

Thanks again for the info, Charlie. I was out messing around with it today and took the pic below with a steel rule clipped to the sub panel flange. As you stated in an earlier post, they aren't true outies, just the corners protruding due to the extreme curve.

So, obviously, I do need to shim the 2 or 3 flanges in the curve. I'm assuming I should shim each flange segment individually. Seems like it would defeat the purpose of shimming if I used one piece across several flange segments...

Glad it helped find the problem. You can do some massaging of the flanges to improve the fit to the curve, or just shim with squares, as you mentioned. Be sure to round the corners if you use square shims, or you might get 4 outies instead of one.

Charlie

Thanks a lot for the advice, Charlie. I did a combo of massaging and shimming the flanges. Looks way better than before. Granted, it's not riveted yet, but all the flanges are flat to the skin - I think it will be ok once riveted. Before I could see the flange corners protruding into the skin while clecoed together

Looks great!

Jon - I didn't understand the problem when you initially posted. Is this similar to the vertical stab and the tight bend around the forward ribs?

I'm near the same point as I've got my upper FWD section assembled and drilled - but not riveted. I'd love to see a picture of the shims you used if you have one.

Has anybody done any bending/shaping of the top skin before assembly. I'm thinking similar to the curve we had to do on the fuselage side skins. I'm just too chicken to try without a better plan than just "bend it up". It seems like a forehead slap waiting to happen.

TFeeney said:

Jon - I didn't understand the problem when you initially posted. Is this similar to the vertical stab and the tight bend around the forward ribs?

I'm near the same point as I've got my upper FWD section assembled and drilled - but not riveted. I'd love to see a picture of the shims you used if you have one.

Has anybody done any bending/shaping of the top skin before assembly. I'm thinking similar to the curve we had to do on the fuselage side skins. I'm just too chicken to try without a better plan than just "bend it up". It seems like a forehead slap waiting to happen.

Click to expand...

Hi Tim - similar to the vertical ribs pushing out on the leading edge skin, only here it is the corner of the flanges. I did make a few shims - they are literally individual .032 pieces the same size as the flanges. I can try to snap a pic tomorrow. As I messed around with it, I think the overriding issue was that a few of the flanges weren't 90 degrees to the web, which allowed increased contact with the corners because the top skin was pulled in too far when riveted. As I mentioned in a previous post, you could see the deformation when the skin was clecoed together.

Tim,

If you cleco one of the cone sectioned skins (tailcone or forward top skins) onto the underlying structure, then remove most of the clecos, leaving the ones at the edges, you should be able to look at the bulkhead-skin interface & see some flange 'ears' that touch the skin, and others that don't. The mission is to determine which ears are 'high', and which are 'low', relative to the skin. The flexible stainless steel ruler trick is effective in seeing which are high or low, by looking at the overall curve.

The ears can be drifted higher or lower (in or out) to some degree with hardwood blocks, both square and wedge shaped, and a mallet. I guess it's kinda like doing body work.

A little tweak to the 90* flange idea; the angle should match the bulkhead to skin angle. Some are >90*; others are <90*, depending on which way the flange faces, relative to the cone shape.

Charlie

rv7charlie said:

A little tweak to the 90* flange idea; the angle should match the bulkhead to skin angle. Some are >90*; others are <90*, depending on which way the flange faces, relative to the cone shape.

Charlie

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Very good point - indeed, I had to bend some of the flanges >90. This alone probably did more to smooth out the curve than anything else.

I think you guys just clarified something back in Sect 29. Page 29-12, Step 4. Without knowing what I was looking for, the firewall flanges at that time seemed perfect! ;-)

I'm guessing that since the firewall is more malleable that it didn't affect as much.

Thanks for talking it through.