Friday, April 15, 2011

April 12 -- Elevator Trim Tab

Posts have been sparse lately, thanks to work. Silence cloaked what activity did occur, and perhaps that is just as well.

Picked up a spare elevator trim tab skin while at Vans to get the wings. At the time it looked to be wasted money; however statistically an extra skin is a good investment.

Sure enough, the first attempt was a fiasco when I bent the tabs at the end. Issue was that I pranged the aluminum in every conceivable way while bending. Some (OK a LOT of) research online turned up that (a) the block recommended for forming the bend should be harder than pine, and (b) there is no such thing as "tight enough" when clamping the block down.

Fortunately(?) the mess known as our garage has some hard maple stock in it. Karin's childhood bed frame, to be precise. A piece of that maple made a great forming block, with more maple affixed to the sides of the wood to keep everything aligned. Then three screws in the bottom of the block served to clamp the assembly, and a humongous C Clamp worked on the other end. The genesis of this approach came from this page -- about halfway down.

That's a 10 degree angle in the maple, and I used a jointer to make certain all was super smooth. (The jointer is another bit of clutter in the garage.) The pieces tacked on the side don't quite touch the bottom of the block, in order to ensure that there was not any tilt induced by alignment issues. This setup took me 4+ hours to build, including time spent on some bad tries.

Some thoughts for others who may be reading this blog post as they consider their own construction project.

  • Make certain that you clamp tightly and precisely. Bend the bottom tab first, then the top tab over the bottom. It's easy to miss in the instructions; however the bend line should intersect the middle of those "u" notches on the aluminum. Consider that the top bend will be over the bottom one, so make certain that the first one is spot on.
  • Vans says to use a rivet gun to finish off the bend. I found that was a way to scar the aluminum. Besides, a block of maple and a hammer are all that are required.
  • My bending brake (per Vans instructions) was made with wood from Home Depot. It was wet, green, and warped. Stuck it thru a planer to true it up, then left it on top of the table saw for a week. Result was a rusted table saw top, and wood that warped again. You can draw your own conclusion...
  • That same brake will be used later for (longer) ailerons. Word is that I should have purchased wood long enough for a six-foot brake. I didn't, which is either good or bad, depending on your thoughts about the previous point.

Total Time: 10 hours (includes the bad trim tab not shown here)

Click on photos for a close-up view.

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