Has anybody built a pitot tube?

[ElectroLawndart]

Has anbody built a pitot tube based on the MPX pressure sensors. I remember reading somewhere that if another pitot tube were mounted back to back it could also be used as a angle of attack sensor.
This would be great! Two sensors in almost the same space as one.

Thnks All
Dart

[danstrider]

I haven't heard the AOA sensor rumor, but I can comment on the pitot probe. You can make one from carbon tubing. Have the tubing connected somehow to one side of the tube and leave the other end open. Mount the probe in a prime location to stay out of the aerodynamic effects of the airframe (try 4" ahead of a wing LE or a few good inches off the fuselage, away from any wing-fuse or wing-tail joints). You want the tube lined up with the aircraft's aero direction which may not be level with the bottom of the wing or level when sitting on landing gear. You also don't want to bevel the inside edge of your probe to look like a cone. The idea of a pitot probe is that the air is stagnant directly at the tip of the probe. There is a theoretical single streamline that does not go around the probe, rather hits the still air inside the probe and provides the pitot pressure to the transducer.

Hope this answers your question, feel free to tell me I wasn't clear. Had I pictures, I would post them. However, I've always used a pitot-static probe. It has both a pitot probe up front and then static ports 7 diameters down the probe that provide measurements for altitude (and to make the airspeed measurement more precise, but that's another discussion).

Dan

[radiohound]

Air speed pitot with mpx pressure sensor can be found here with some code. SteveOnWeb UAV (http://www.steveonweb.com/index.php?id=29,0,0,1,0,0)

Walter

[ElectroLawndart]

Thank Radiohound,
That was what I was looking for.

Danstrider,
I have a .dwg that might help explain but can't upload it.

How do I post a AutoCAD file?

Dart

[chrisgood]

This page details pitot tube mathematics.

http://www.chrisgood.com/uav/avionics/airspeed_slide0024.htm

If you want to get alpha (angle of attack) or beta (side-slip), you have to use a bit more complicated pitot system. A straight tube is fine for dynamic pressure, but you need differential inputs for alpha and beta. The straight ahead tube is surrounded by another tube with four holes pointing out, 90 degrees away from each other. This picture shows it better. The two alpha ports lead to one differential pressure sensor, and the two beta ports lead to another. The resulting differential between the two ports allow for angle of attack to be determined from the two alpha ports and side-slip to be determined from the two beta ports.

[william541]

How do I post a AutoCAD file?

There are two ways I use to get a gif or jpg file for uploading from AutoCAD. I find the gif is more compact and generally does a better job with vector drawings.

The easiest is to go into LAYOUT and frame the drawing view so it looks good on screen. Then hit your print screen key. Next go to the paintbrush program and select paste. Then save as a gif.

The next method gives much better resolution and can be used to insert images into documents for better printing quality. Once again go to LAYOUT (paper space in AutoCAD). Set up your view window and zoom the model space until the image fits the window nicely. While in layout, double click inside the view window so that you are in model space for that view. Then in the command line, type in wmfout <enter>. This will bring up a dialog for saving a windows meta file image. After selecting a place to store the image, the command line will say select objects. Select all the objects and hit enter. Then you can take this file and use any image editing software to convert it to a gif or what ever. You can also use the .wmf as-is to paste into documents.

-Bill-