Fixing a busted ARF: a RE-build thread.

First, laugh about it. Second, take a picture. Then turn off everything, unplug batteries, check the tank for leaks. If you have parts dangling by covering alone, might as well slice them apart at the field. clean stuff off so it wont dirty her car up.

then get it into the shop and investigate.

here's whats wrong with the katana:

-the fuse broke clean apart at the diagonal joints near the wing's spar.
-the balsa of the fuse is split/cracked in some places, and the balsa making up the wing saddle sort of crumbled out near the LE.
-end of one aileron is broken
-landing gear is twisted, balsa in between the outer ply of the LG is crushed, the wood in between the LG straps is completely detached from fuse.
-wing fairings came off, taking a nice chunk out of the fuse, and one is broken.
-tailwheel is loose. (pre-crash condition, may as well fix now)

here's looking forward into the nose, note the missing balsa at the bottom of the LE of the saddle, and the truss pieces below it that are now unattached to anything. I think the LG mounting block was here, but it was balsa, so way too weak.

hey, I can attach more than one pic in a post?

1-bottom of fuse nose, with pieces from the fuse sides from between the LG block and the diagonal joint with the fuse rear. (the pieces are backwards in the picture.
2-chunk taken out of side of fuse. note that the covering is torn, this is *usually* a good sign that the sheeting underneath is cracked and needs glue.
3- landing gear, balsa still attached, and it's all crushed.

The easiest thing to do is to repair cracks and splits by holding the wood into its original shape and flowing thin CA along the cracks. you can usually tell where the cracks are from either wrinkles or splits in the covering

I like to do the easy things first, so we'll start here.

now the ghetto way to do this is to peel back the covering, glue any cracks, then iron it back on, and packing tape over any cracks. I'm going to do it the "right" way, because (a) I have a boatload of yellow ultracote, and (b) the chinacote thats on there probably wont iron back on once you pull it off, and it leaves a fair amount of its backing on the wood anyhow.

If you don't have matching covering, and are worried about having a patchy plane, you could strip all the covering off a section and recover it all later, but thats more work and money than this really needs. I mean, come on, this wont be the last time I crash this plane!

(picture 1)so cut away the covering around the cracks, you'll patch this up later.

(picture 2) glue stuff back in place and set it aside. note that you'll now have CA on the outside of the plane. this WILL show through any covering patches as high spots, so hit it with a small sanding block or metal file later.

thats it for today, we're looking at about 10 minutes worth of work while I drank beers with my dad.

Hey capncrunch, Great thread!!! I love it when guys take the time to do a repair right... It really isn't' that hard and if you do it right, the weight gain is minimal...

I always look for a way to join the broken pieces so that the structure retains it original geometry. It's a little tougher when you have to rebuild large hunks of missing plane! But if you have just enough to get her tacked together, you can redo some of the sheeting or strengthen some of the broken sticks after you have the geometry set.

When I redo sheeting, I use a straight razor blade and scrape of the old sheeting in the places it want to redo. Then I use little scraps under the old sheeting to serve as a lip to attach the patch. Install the new sheeting with the grain running in the direction that you need the strength. i.e. on the fuse, install the sheeting with the grain direction from front to back, not top to bottom. If you have a small gap between the new and the old sheeting, you can use a little baking soda and thin CA.

If you're really paranoid and want to make sure it's strong enough, use a little fiberglass close and resin.. Just be very sparing with the resin to keep the weight down.

Today I spent about an hour or two on the second stage of repairs.

now that everything's been stripped and assessed, I'm moving ahead with the section that needs the most work - the LG mount/back part of the lower fork of the fuse front.

here is where keeping all the parts is the most important. I'm not going to use these little pieces in the rebuild, but I *do* need them as templates.

first things first, i used a razor saw to clean up the front edge of the break, then trimmed up the wing saddle area. I removed all of the bracing parts left on those two side pieces, and sanded them so they'd sit flat against the block of wood im planning on filling that section with. Since the gear legs were crushing the balsa in between the LG mount, I am going to strengthen things up by cutting a basswood block to go here. I'll use the side bits to get a template for the shape it needs to be, and also for balsa to fill the wing saddle.

pictures: 1) cleaned up front of break at LG mount
2) side piece with stuff left on it
3) both pieces sanded flat, except where one has a piece of the diagonal joiner at the rear, im leaving this in so that I can mark the rear of the basswood block so it will be flush with the joiner (which is mostly intact and glued in the rear of the fuse)
4) one piece taped to the fuse to form a template.

using the taped-on side piece as a template, i measured the rectangular size I'd need for the basswood block. I *could* have made it flush with the wing saddle, probably stronger, but its much easier to work a shape into balsa than basswood, so I'll be putting a balsa piece on top of it for the saddle shape.

I bandsawed out a 12cmx5cmx1cm piece of basswood, then marked and cut the angle to clear the joiner. after a little sanding, I had a block that would fit perfectly in all dimensions.

From a structural standpoint, it doesnt NEED to go back to the joiner, but this is the simplest way i can think of to do this. It should also be a good attachment point for my tuned pipe clamp, so that's another plus to making it fill this whole section.

I went and beveled the ply at the front of the cut, for a lap joint with the new sheeting, which I'll cut using the old pieces as partial templates. I cant glue this all together until last, because the fuse front won't slide over the thickest part of the wing unless there's clearance. so the block is the "keystone" that will lock all the parts together at the end.

next I took the fuse rear that I glued back into shape yesterday and checked it for fit against the wing saddle and also for fit with the wing fairings, as they took some chunks out of the sheeting when they broke off. fit was good, so i decided that I'd leave the broken wood where it is and glue things back into place without, say, resheeting the rear of the fuse. this is a bit of a shortcut, and I may change my mind.

I also took a look at the fairings. one is fine, the other is pretty torn up. both sides will need to be re-covered, but the covering that's there is doing a pretty good job of jigging the parts, so i left one side of it on while I held the whole piece flat and flowed new CA into the joints and cracks in it.

pictures:

1) basswood block came out to 0.6 ounces, I can live with that.
2) rear fuse fits well with the wing, and alignment is maintained.
3) cracked-up fairing
4) fixed fairing

the next step will be to cover all the parts I've stripped, form the bottom front of the fuse saddle, then epoxy everything back together! shouldn't take more than a couple more hours.

-barrett

next up was the cracked aileron tip. in this situation, the existing wood was pretty well crunched and needed to go. I trimmed it out flush with the existing lines with a razor saw, and ran a little sandpaper over the edge to smooth it up. also here's a place where I dont want to recover the whole part (the whole of the aileron) so i just cut the covering over to the nearest solid piece and will patch the whole triangle there. when patching heatshrink with heatshrink, you cant use loose covering as a tacking point.

I sawed up a piece of 3/16" scrap (was part of a laser cut sheet left over from a kit build) to replace the end stringer, and glued it in place. I trimmed it up a little with a razor blade (in the meantime trimming about 1/8th of an inch of the top of a knuckle, fucking thing wouldnt stop bleeding and made me late to work) and then covered over it.

I also got some covering on the sides of the fuse and on the fairing that I stripped. the yellow matches fairly well, it certainly wont look any different at more than 10 feet. the blue is off, i had some the wrong shade, and some the right shade, but metallic, so the luster is weird. you can see the blue patches in the second pic.

last, I epoxied the fuse back to the wing, keeping the alignment carefully straight.

ought to be finished tomorrow!

-barrett

I wound up just using epoxy, and my repairs came out about 1.5 or 2 oz heavier than I remember. It's at 4.70 pounds, including an ounce of "junk in the trunk", and slightly heavier wheels than stock.

I need new landing gear. are crazy legs still being sold somewhere? or does anyone know a source for nice strong profile landing gear?

here's the fixed up landing gear mounting area, and the finished product. not too shabby!

-barrett