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Thursday, November 10, 2005

Fabricating a heated pitot tube

Today I started fabricating a heated pitot tube. This is a copy of the work of James Redmon as found at http://www.berkut13.com/berkut41.htm

He documents the components, but not the fabrication. I'm not sure if he made all the components himself or if he was able to purchase them. I did not find a source for them so I began to fabricate my own. Since I have an engine lathe it is a matter of aquiring the materials and performing the cutting operations.

  • 1 foot of .058 3/4" aluminum tube
  • 1 foot of .035 1/4" aluminum tube
  • 2 foot of 3/4" round aluminum bar
  • 1 Cessna 0721105-5 80W Heater (from http://www.broadiesaircraft.com )
  • 1 foot of 3/4 I.D. x 1 1/4 O.D. G-10 (Phenolic like substance)
I purchased the G-10 from a company in Poway, CA called Plastifab. It is used to isolate the heat from the airframe. It does not conduct heat well and can operate at up to 130 celcius. The 3/4" aluminum tube specified on the Berkut13 site specifies .063 wall 3/4" tubing but the heating element I purchased would not fit into the thicker wall tubing. The .058 works fine. In the first photo, I am facing the tube so that I have a straight, clean cut.




In this step, I am polishing the tube. I wanted a nice polished look for the tube.
I used a series of sandpapers to polish the tube, starting with 220 grit and working my way to 2000 grit. The 1000 grit and higher comes from an auto body painting supply store. I used water with the sandpaper starting at 800 grit.


Next I chucked the 1/4" tube into my lathe and locked the spindle. This makes a great holder for threading. I used a 1/4" 28 die to thread the tube.


Here is a fitup of the small tube through the existing hole in the heating element.

Next I chucked up the 3/4" round rod. I faced it, turned it to a .750 O.D., turned a shoulder to fit the I.D. of the tube and drilled a center hole. Next I drilled a #23 hole 2.5" deep and a #3 hole .5" deep. I threaded the #3 hole 1/4" 28 to accept the small tube that was threaded earlier.

I parted the piece off of the bar using the parting tool.

I re-chucked the part and turned the angle until I was happy with it's appearance. I don't have a ball turning tool for my lathe so I will have to be happy with an angled look. I've got plans to build a ball turning tool but I haven't made it yet.

Here are the parts fitted up.

Using the same techniques as the nose, I machined the tail piece and threaded it 1/4 28 to accept the 1/4" tube and 1/8 NPT on the other side to accept the nylaflow tube adapter.

Here is a shot of the nose piece fitted to the 3/4" polished tube.

This shot shows the 3/4" tube fitted up to the G-10. To finish the pitot tube, I need to cut the 3/4" tube and the G-10 to length. I need to drill a hole in the 3/4" tube for the wires to exit and thread the freshly cut 1/4" tube so the whole thing can be assembled. To do this, I need to drill a hole in the front of the plane and measure the length that I need for both the 3/4" tube and the G-10, cut them to length and install in the aircraft.

Next I had to make a stick tube adapter for the Infinity grip. Our LongEZ has the plans 5/8" steel tube for the stick grip to mount on. The infinity grip allows for a 3/4" O.D. tube mount, so an adapter to 5/8" is needed. I used the Mill to cut a slot in some 3/4" .058 tube and drilled a 29/64" hole to match the infinity grip.

Accomplished more today than I did yesterday!

2 comments:

Capt Meatballs said...
This comment has been removed by the author.
Capt Meatballs said...

Awesome job, by the way!