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Wing and Flap Fairings

I fit and drilled my wing fairings while I had the wings on for their initial fit.  I had a little trouble figuring out what the plans meant by fitting everything "flush" to the tanks, and had to work through a few other small issues, but I'll show you here how I figured them all out.  I waited until the wings were on for the final time and the flaps had been rigged before doing the flaps.  I worked a bit on getting the seam to disappear into the curve of the fuselage, and I also had a few problems with edge distance and holes drilled earlier.  This all required some considered improvisation, but everything worked out and I'm very pleased with the results.

Wing fairing

Wing Fairings

Fairing with rulerI spent a lot of time bending the F-872A forward wing root fairing.  I used a piece of PVC that had approximately a 1-½” diameter to get the initial bend, then a lot of hand bending and twisting until it fit snug to the wing and was parallel.  When I first read the “make sure the fairings fit flush to the tanks ” part of the plans, I was confused.  Then I finally figured out what they were getting at.  They wanted me to make it Forward tank bracketsit flat on the wing and continue inboard without pitching up or down.  Make sure you check this all the way around the leading edge, top and bottom.

I found that the tank bracket got in the way of the top of the F-872A fairing, and needed to be trimmed down.

Using a compass to mark the gap
To mark the 3/16” gap along the fuselage, I used an old carpenter's trick.  I set a compass so the distance between the pencil and the point was 3/16”, then ran it along the fuselage with the point touching the fuselage and the pencil marking a line on the fairings.

Flap Fairings

Flap fairing

Flap fairing endI fit the fairing with the flap in the full up position.  I started by making the top lip sit flush on the flap and bending the fairing until the lower leading edge was parallel to the aft edge of the flap.  Then I worked the aft end of the fairing until it fit snug against the fuselage.  I didn’t want the seam in the fairing to continue until the end.  I wanted it to disappear into the curve of the fuselage.  So I spent some time working the very aft end of the fairing to remove the seam and match the curve of the fuselage.  I started by using a large hammer to remove the seam, making the end of the fairing flat.   Then I bent the gradual curve of the fuselage into the fairing.

Flap fairing rivetsWhen I went to back drill the holes for the top of the fairing through the F823 skin and F-815B floor rib, some of the holes would not work.  So I had to make new ones.  The old ones would not have given me edge distance everywhere.  If you look real hard, you can see that the line of rivets isn’t completely evenly spaced.  This was what I had to do to get the new holes with edge distance and out of the way of the old holes.  The new matched drilled fuselage may take care of this issue, but I would still check for edge distance before you drill through the fairing.

How Did That Happen?

How did I mess up the flap fairings?I don’t know how it happened, but I messed up the flap fairings.  I had measured their location with the wings on, and the flaps installed.  Then I removed everything and riveted the fairings in place.  When I went back to finally install the flaps, the fairings didn’t match up.  First, I needed to figure out where I went wrong.

The worst case would be that I had messed up drilling the wings.  I rechecked their angle of attack to ensure they were right on.  The next worse case would be that I had mis-rigged the ailerons.  This would be a simple fix, except for the wig tips.  But they were rigged correctly.  The only thing left is that I installed the flap fairings at the wrong place.  So the answer was to move the fairings.

Unfortunately, if I just lowered the fairings to match the top of the wing, then old holes would show.  This was unacceptable, so I decided to make new fairings that were just a little larger than the originals.  The lower skin of the flaps doesn’t quite lay flat on the bottom of the fuselage, they miss by a little less than ½ inch.  So I decided that while I was at it, I would make the fairings match up to the bottom of the flaps.

Top of new fairingMy new fairings are kind of “U” shaped.  They look a lot like the originals on the top and back side; they are just a little larger to ensure they cover the holes.  It is on the bottom of the fuselage that they differ greatly.  My new fairings are about 3 inches wide on the bottom, giving me room to rivet them to the belly on the inside, while the outside sits under the bottom flap skin.

Bottom view of new fairingI made the pattern by starting with the old fairings.  I added poster board strips to the top and back until I got the size I needed to be able to use the holes across the top and cover the old holes in the back.  Then I added poster board to the bottom to get the size to match to the belly and flap.  Once my cardboard creation fit the top and bottom of the flap, and covered the holes, I flattened out the old fairing.  This gave me a flat template to cut a new piece of aluminum.  I cut and bent the new aluminum to fit the top and back just like the old fairing, and drilled it in place.  Then I spent a lot of time hand bending the bottom until I got a good fit to the belly and flap.  I drilled the holes and then trimmed it to final size.

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