Installing pitot tube

Posted Jul 4, 2024 Updated Aug 25, 2024 5:00

By Fan Zhang

5 min read

TLDR

Finished wire harness layout in the left wing
Installed and tested pitot tube

Wire harness

I went through each zip tie hole on the center stringer and tied down the harness.

Zip tied wire

I also installed some teflon wire protector at the wing root area as it seems the wire takes more stress/chafing in that area.

I also cut a buch of edge protectors to install on the stringer itself, so the metal doesn’t cut the wire over time. Edge protector along the entire stringer

Pitot tube installation

This was the difficult part in the wing.

Firstly it’s new. It involves many things I have never done before. Secondly the component is very expensive. I was scared any mistake will break it. So overall I think I took more time than most people, but in the end I think I got the job done.

Pitot Mast

I ran into a problem on the first step - riveting the mast onto the wing.

Because I previously installed the long aileron tube first, the tube blocked access for rivet gun to pull the rivets. So I drilled a large hole on the wing jig root end and pulled out the aileron tube by about 15 inches, then the mast was able to rivet to the spar no problem.

Screw issue on the pitot tube

The pitot tube required 4 6-32 machine screws. But for some reason one of the holes simple does not take the screw. I switched many screws but just could not get the screww to fully go in.

At one point I used too much force, and twisted off the screw head. I was really surprised how little force I needed to do that. So any way, the screw was stuck in the hole, and has about 1 mm protruding, which was too short to use a plier to screw it out, and too long that it blocks the entire pitot tube from sliding out.

I had to undrill a few solid rivets from the mast assmebly, then was able to get the entire pitot tube out and remove the screw carefully using a thin plier.

I have an #6-32 3/16 screw on order. They are supposed to be shorter than the ones I’m usnig now. 3/16 is still within the acceptable range specified by Garmin, And hpefully they will be short enough to fully go in.

This hole does not fit 5/16” length screw

Control box mounting

The next big job was to mount the Garmin GAP26 control box near the pitot tube.

I know some folks just drill 4 holes on the inspection plate and mount it there. I wasn’t thrilled about the idea of having expensive parts and wire attached to an inspection plate. So I decideded to mount it to the rib right next to the pitot tube.

First I cut a scrape piece of aluminum and match drilled 4mm holes using the controller box as a template.

Then I transfered the holes from the aluminum template to the rib. I enlarged the holes to fit 4 M4 rivnuts (with loctite 277).

Finally I mounted the controller to the rib using hex screws.

The controller mounting points

The template

Controller is mounted

Air hoses

The next step is straightforward. I ran 2 air tubes through the wing to reach the pitot tube.

I chose the GREEN tube as pitot, and the RED as AOA.

Running tubes for the pitot assembly

Bending the pitot tubes

The 2 aluminum tubes came with GAP26 was super long, and stright goes up. I needed to both cut them and bend them so they can smoothly connect to the plastic tubes, and they have to be longer than 8 inches.

I tried to bend them with hand while attached to the wing. I was able to do that but all the parts around it were shaking as I moved things around. I decided to just take the part off the wing to bend it, then insert back.

While I was removing/inserting the tubes, I noticed the rivets inside of the mast were rubbing the tubes, so I put some temperary silicon tape for protection. They were removed at the end.

Bending tubes in progress, and note the silicon tape for temperary protection.