The Barn Find Build

[jrevens]

Jim's right... you want aluminum oxide, if anything. Silicon carbide is bad. Also, FWIW, I'd be cautious of too much sanding. I believe those 0.016" skins are 2024-T3 alclad - a very thin layer of pure aluminum on the surface of the 2024 alloy. I would hazard a guess that you have already removed much of that protective layer. A good protective primer is going to be very important. I'm sure you probably know that already, but figure it doesn't hurt to mention it.

[Eric Page]

Thanks, guys. I'm using 3M aluminum oxide paper. I'll give them a couple of good wipe-downs with acetone and get a mist of primer on them once I'm finished, so they're protected until paint.

[PapuaPilot]

From what I see in the pictures you haven't gone through the Alclad layer. It is usually very obvious if you have sanded though the layer, the alloyed aluminum in the center is not as shiny.

The AMT General Handbook says the outer layers are normally 5.5% of the total thickness per side. This means for 0.016" aluminum the outer layer would only be about .001" thick. That doesn't leave much for sanding.

[Eric Page]

If that's the case, I'd have a hard time believing that I didn't get through the Alclad in a few places. Some of the scratches were sharp enough that I definitely wanted to eliminate them, and deep enough to exceed 0.001".

[PapuaPilot]

I would recommend using the red Scotch Brite to finish up.

[Eric Page]

Do you mean maroon ("very fine")? The charts I've found list maroon pads as 320-grit aluminum oxide, same as the paper I've been using. What's the advantage of using a Scotch-Brite pad of the same grit?

[PapuaPilot]

Yes, maroon. I like how it works because it doesn't lose any of the grit. It does a great job over an around rivet heads and getting in corners. It doesn't sand down rivet heads like sandpaper does.

[bumsteer]

I would totally agree with Phil.

Rick

[Eric Page]

Ah, OK, got it. Just easier to work around various items on the surface with a pad than with paper.

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Started out today by finishing sanding out the flaperon scratches. Once I was happy with that, I wiped them down really well with acetone, then mixed up a few grams of SuperFil and smeared it into all of the dents. Many of them were very small and probably could have been left alone, but I had the cup in my hand, so I went nuts. Those will get another light sanding to take down the SuperFil in a couple of days.

IMG_1366.jpg IMG_1372.jpg

Maybe then I'll see what I'm going to do about shaping the outboard ends. I bought the plastic tips from Kitfox, but I'm not much impressed with how they fit; I think another round of pink foam, Hysol and SuperFil might be faster and easier than fighting with those.

Next I fabricated the second antenna ground plane, for the ADS-B receiver. I used a cut-off wheel on the angle grinder this time, and it went a LOT faster than the hand nibbler. That got it within about 1/8", and about 10 minutes at the disc sander and Scotch-Brite wheel had it dialed in exactly. I got one side shot with primer and I'll get the other side tomorrow.

IMG_1368.jpg

A package arrived from Kitfox a few days ago, containing the fabric reinforcing plates that I'll need for covering, and a new chunk of Delrin for the horizontal stab bearing blocks. I cut that in half, sanded it to fit the holders on the leading edge and installed the stab to set their position.

I dug out the horizontal stab brace rods for the first time since bringing the plane home, cleaned and lubricated the rod end bearings, used ACF-50 and Scotch-Brite on the male threads at the top ends of the rods to remove a little rust, installed the missing jam nuts and set about aligning the stab. That's where I've run into a problem.

I've measured the horizontal stab's position three different ways:

• Using a tape measure from the middle of the vertical stab tip to the middle of the horizontal stab tips
• Using a string from the outer bushing carriers across the top of the vertical stab
• Using a digital level to compare the horizontal stab with the wing rear spar carry-through

In the first two cases the measurements agree exactly and with the digital level it's within 0.2°, which is probably within the accuracy/repeatability of the instrument.

My problem is this: the rod end bearing on the left side has about 1/4" of thread showing between the bearing body and the end of the tube, but on the right side, I've got the rod end threaded on as far as it will go but the assembly is still too long by about 3/32".

IMG_1371.JPG

The only solution I can think of is to grind some length off the body of the rod end to allow more room to wind it further onto the rod. Is that permissible, or can anyone offer another idea? At this point I'm kinda stuck!

[jrevens]

[QUOTE=
My problem is this: the rod end bearing on the left side has about 1/4" of thread showing between the bearing body and the end of the tube, but on the right side, I've got the rod end threaded on as far as it will go but the assembly is still too long by about 3/32".

The only solution I can think of is to grind some length off the body of the rod end to allow more room to wind it further onto the rod. Is that permissible, or can anyone offer another idea? At this point I'm kinda stuck![/QUOTE]


Just curious... have you compared the exact length of the two struts?