There are several tasks which must be finished off before closing the wing with the bottom skins. The Pito mast connects the Pito tube to the underside of the wing.
What is a Pito tube? Glad you asked. The Pito tube in its simplest form is just a small pipe stuck out into the wind. The air that is forced into the end of the pipe forms a pressure that is proportional to the wind speed. Or in our frame of reference, the speed of the airplane though the air. The Pito tube was invented by Henri Pito about two hundred years ago. Unfortunately for old Henri, his invention had to sit on the shelf for nearly a century before the powered airplane was invented.
The Pito mast (blue) is attached to the main spar and to the bottom skin at one end, and of course, the Pito tube (silver) on the other. To get the mast through the skin, we simply cut away all the aluminum that would prevent us from doing so. Easy. I start with four 1/4" holes that I can further enlarge with a uni-bit so that the holes just touch the line. Then file and sand to smooth the edge.
And check the fit with the mast.
Good. Now this Pito tube also happens to be a heated Pito tube. The purpose of the heat is to discourage ice formation that could block the tube. The heater has a controller to regulate the temperature and this controller must be mounted near the Pito tube.
And so it is. Out of the way, yet close to the Pito tube's attachment location and to the bell crank inspection plate. The last thing to do is to prepare the plumbing that is coming out of the Pito tube.
The keen observer notes that there are two tubes emerging from the Pito mast. One is for the Pito function and the other is a second Pito tube whose end meets the air stream at an angle relative to the first. A computer in the cockpit can measure the difference in pressure between the two tubes and calculate the Angle of Attack of the aircraft.
Those not familiar with aircraft terminology will be relieved to know that the AOA meter in the cockpit does not suggest the angle at which we should meet the enemy. Instead, the AOA meter indicates the angle of the wing relative to the air stream impinging on it. All wings will stall at a given angle which is unique to that wing. Therefore, knowing the angle at which the wing is flying, gives us pilots a leg up on preventing a stall which, surprisingly, many passengers will find objectionable.
To connect to the plumbing which eventually makes its way though the wing and into the cockpit, the the tubes coming out of the Pito need AN fittings. The AN fittings in this case are just anodized aluminum couplers that fit the aircraft standard of 37 degree flared ends. So I put the flares on the two ends of the Pito and presto, we're ready to install.
Well not quite ready. The actual installation will have to wait until the bottom skin is being riveted on as the three rivets along the forward edge of the base plate also go through the skin and spar.
Next, I will battle the aileron bellcranks and the autopilot roll servo installation.
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