Aligning and Mounting the Flaps   February 2nd, 2010

After ordering a wider piano hinge from Aircraft Spruce, I was able to ‘pull out’ the flap enough to make it match the aileron trailing edge.

At this point the wing is upside down in a wooden cradle, so there is no good way to hold the flap while the hinge is drilled. I used the following method:
  • First, cut two scraps pieces of hinge, long enough to cover about 9-10 rivet holes on each end of the flap. Cleco the bottom skin to the wing and to the flap brace. Put a cleco in every skin-to-flap brace hole, except for the few holes on each end where the scrap piano hinge will sit.
  • Attach the pieces to the flap and mount on the wing using cleco clamps.
  • To check the alignment with the aileron trailing edge, first make sure the aileron is set to its neutral position, and then lightly clamp the flap and aileron together.
  • Before drilling, use a long straightedge (like the red level in the picture below) to make sure the flap and aileron’s trailing edges are aligned. I went one step further and used a digital level to make sure the angle of the aileron trailing edge was the same as the flap trailing edge (don’t expect this angle to be 0 degrees, as the wing will probably not be level with the ground while in the cradle.
  • After I was 100% positive the two trailing edges matched, I very carefully drilled each hole of the two scrap hinges, putting a cleco in every hole as I went.
  • Remove the flap, separate the scrap hinge pieces, and use a dremel tool cutoff disk to remove the loops on the scrap hinge.

  • Now lay the scrap on top of the full-length hinge to be drilled. Match drill the holes from the scrap to the full-length hinge. I used the loop tabs to line up the two pieces, and then clamped them together before drilling.

  • After both ends of the hinge are match-drilled, simply cleco the full-length hinge back on the wing and match-drill the rest of the holes.
The other flap was mounted with the same method, and I was very happy with the resulting alignment on both flaps.
And by the way, I didn’t come up with this method of mounting the flaps — I read it at 🙂
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After mounting the ailerons, I tried to test-fit the flaps to see how well they lined up with the aileron trailing edges.
Well, they did not line up too good 🙁
The two trailing edges are supposed to be even, and as you can see, if I make the flap hinge flush with the flap brace, there is about 0.2″ mismatch between them. I could ‘push out’ the flap some more, but then the holes in the hinge that holds the flap to the wing would be very, very close to the edge.

After doing some research, I found out this is quite common. Fortunately, there is another variant of the flap hinge that is slightly wider, and would allow me to make the flap even with the aileron while maintaining an acceptable edge distance on the hinge.
So, here’s $10+shipping to Aircraft Spruce for a wider flap hinge….
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Riveting Flaps   August 26th, 2009

I started riveting the flaps by attaching the ribs to the bottom skin. Some of these I could do with a squeezer, and some with the rivet gun.

Then I put on the top skin and used the fuel tank cradle to somewhat hold things in place. There is just enough room for a small bucking bar in there, but things turned out pretty good.
The last things to do were to assemble the inboard rib. This rib holds a bracket where the flap actuator is connected. Finally, I riveted the spar to ‘close the flap’
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Flap Hinge   May 28th, 2009

One of the last steps in drilling the flaps was the flap hinge. This is a piano hinge that holds the flap to the wing, so it goes along the length of the entire flap. The hinge is not very wide, and it is not pre-drilled. This leaves very little margin for where the holes are drilled. If the are pretty much not right dead center of the hinge, the rivets will be too close to the edges.

So, how to draw a line that goes exactly through the center of the flap hinge, along the entire length of the flap? I could use a very long straightedge, which I don’t have, or try to rig up a piece of string, etc, etc. Well, instead I found this $14 edge marker block at Avery Tools. I’ll be the first to admit that paying $14 for two pieces of plastic and a screw is very very unlike Mr. Cheapass here, and even now it seems like quite a bit for what it is. However, when you think this is probably hand-made (or very nearly so), and it saves a lot of grief, it probably is worth the fourteen bucks. Anyway, Here is a picture of said tool. You stick a marker in the hole, set the distance for exactly half the length of the hinge, and just draw a nice, long line, as straight as the edge of the flap itself. The only trick is to keep the arm resting on the edge of the hinge at all times.
After drawing this line, I just clamped the hinge to the bottom of the rear spar. I used little wood blocks with a round cutout so my clamps wouldn’t squeeze the loops in the hinge. Finally, I just made sure the line showed exactly through the middle of all the holes int he flap, and started drilling away, putting a cleco in every hole.
Now it’s time to take everything apart and prime. Back to working on the fuel tanks!
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Making the flap brackets   May 26th, 2009

So the flap rear spar and the inboard rib are not at 90 degrees to each other. In fact, they are at something like 96.5 degrees. This means the flat bracket you get as part of the kit has to have a 6.5 degree bend. How do you do this you ask? Well you whack the heck out of it with a hammer!
I’m not kidding either. I put it in the vice between two blocks of wood, and then went at it with the hammer. This is 1/8″ aluminum, and there is not a lot of leverage, so I had to hit it pretty hard for it to move.
How do you know when to stop hitting it? You take it off the vice, test-fit it on the spar with the other bracket, and then go hit it some more. When the two brackets, the spar, and the rib all fit really nicely, you quit hitting it!
This is what a 6.3 degree bend looks like:
This is the other bracket. This one does not come pre-cut. You have to make it from a piece of aluminum angle, and drill it according to the plan dimensions.

The piece on the top is what the bottom one looked like before cutting, drilling and sanding.
The next two pictures show the brackets in place next to the spar and rib. Note that the first picture shows the square bracket before drilling. Because three of the holes will go through the bracket, the spar, and the rib, this one has to get matched drilled to the spar and the rib.
So, I first clamped everything in place, and then used a long 12″ drill to drill from the rib side through the pre-punched holes in the spar and into the bracket. Not hard as long as you have this handy 12″ drill bit.
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Flap skeletons and brackets   May 25th, 2009

Decided to take a quick break from the tanks and work on the flaps. I started by clamping together the flap skeletons, and then the bottom flap skins.
The skin itself is used as the ‘rear spar’, and the ribs don’t always get close enough to the skin. So, I had to make tiny shims out of 0.025″ aluminum to insert between the rib and the skin-formed rear spar. Also, because these rivets will be completely enclosed by the flap skins, they are AN470, 1/8 inch. It is very tempting to just drill them #40 (which is what I did initially), but closer inspection of the plans will set you straight.
Here is the flap with the top skin on.
The most inboard rib will have a bracket rivet to it. This bracket eventually connects to the rod that makes the flaps go up and down. Also, it is important to make sure the rib is oriented correctly. You can tell because the tooling hole on the left (closest to the front spar) is closer to the bottom of the flap.
Next time, I’ll work on making this bracket. Apparently it uses a very non-conventional fabrication method…
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These are the brackets that hold the ailerons to the wings. They come pre-shaped, so I just had to match drill and deburr them.
The next little thing was cutting off a piece of the flap brace. The flap brace is a long thin piece that goes between the wing rear spar and the bottom skin. It gives the skin a little more strength, since the flap is hinged on the skin only (well, and the brace). In order to clear some of the rear spar reinforcement plates, you have to take off a piece of the brace as shown by the blue line below. Just a matter of taking the snips to it and cleaning it up a little afterwards.
After that, it was just a matter of fitting each brace on the wings and match-drilling, then on to get primed.
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