Tuesday March 13, 2007
Stored HS, Drilled Pitot/AOA Line Holes
(Horizontal Stabilizer, 0.5 Hours Wings)
0.5 Hours Total

The horizontal stabilizer is about eight feet long and two feet wide, so it was taking up a lot of space in my tiny shop/garage. My dad has free space at his house, though, so he offered to let me store some of my airplane junk there. We loaded my HS into his car and took it over to his house. It is now hanging from the ceiling of his basement and my shop has a whole lot more space.

Later, after I got back home, I drilled out the tooling holes in the inboard 10 ribs on the left wing to provision for Pitot and AOA port lines running from my future pitot tube. I've mostly decided to go with the Dynon EFIS system in my plane and I'll use their combination AOA/Pitot tube. Unlike a normal pitot tube, this one has two holes, one for normal pitot air and one for the AOA functionality. That means you have to run two tubes from the pitot to your avionics. I'm going to use the SafeAir1 plumbing kits and pitot tube mast, which are designed for the Dynon tube. The plumbing kit uses 3/8" bushings, so I drilled the tooling holes on my ribs out to 3/8". The hole in the middle is 7/16" and was there already.

What, you may ask, is "AOA"? AOA stands for "Angle of Attack", the angle of the chord line of the wing of your airplane to the wind passing by. In general, the higher your angle of attack, the more lift you are generating, until you reach the critical angle of attack where the wind simply can't flow smoothly over the wing anymore. That critical angle of attack is where the wing stalls. By measuring the AOA with an instrument, the pilot is aware, during flight, of his proximity to stalling the airplane. This is particularly useful during landing, where the object is to land as slowly as possible without prematurely stalling the aircraft. Apparently, the AOA instrument was developed for military pilots landing on the decks of aircraft carriers.

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