July 5-6, 2008

Drilling flap brackets; countersinking the spar - 5.0 hrs.

After working some scattered hours at various times yesterday and today, I made a lot of progress on these flaps. I managed to drill the flap brackets, FL-706B's, to each flap, then dismantled everything for deburring, scuffing, cleaning and priming. I also countersunk the flap spars for flush rivets. The dimples from the flap skins will sit down in these countersunk holes. You can't dimple the spar in this case because the flap hinge gets riveted on the bottom surface of the flap flange, so it needs to remain flat. You'll see how it all works out.

Here's the FL-706B bracket clamped for drilling to the spar and the end rib on the flap. You can now see why the end of this bracket had to be bent 6.3 degrees. Notice how the other ribs are all perpendicular to the flap spar, or at 90 degrees. But the end rib angles toward you in the picture above by, you guessed it, 6.3 degrees. In other words, the angle of the rib to the spar is 96.3 degrees. So the end of the bracket is bent so it lies flat on the spars' end flange and can be riveted tightly together.

Making sure this bracket is firmly clamped in its precise position is very important before drilling. This bracket connects to the flap actuator that moves the flap up and down. You can imagine the forces that will act on this flap with the airplane traveling 100 mph as it is lowered into the wind, slowing the entire airplane down and giving it more lift for landings and so on. All of that leverage is focused on this corner of the flap. No wonder it has to be so beefy and riveted so solidly. Once again, I am very impressed with the engineering that went into this kit. Above, I've drilled and clecoed the end of the bracket to the flap spar. Below, the rest of the holes are drilled and clecoed to the flaps' end rib.

Here's the inside of the end rib, showing how it gets drilled to the spar. There's a rectangular stiffener plate on the other side of the spar (the ends of the clecoes are sticking through it) to make the corner of the flap even stronger.

Finally, this hole is reamed open to 1/4". This is where the flap actuator rod will attach, that moves the flap up and down. This whole process was repeated for the other flap.

Now everything is disassembled except for the ribs, and I'm countersinking the spar for flush rivets. The dimples from the skin will sit down in these countersunk holes.

A closeup of the countersinking process.

Finally today, I started the final deburring, scuffing, and cleaning work before these parts get primed. Hopefully, in the next day or two.

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