Replies to This Discussion

Permalink Reply by Gagarien on January 18, 2010 at 4:52am

A rotary position sensor and a vane would be the simplest er cheapest? I recon

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Permalink Reply by Roger Gerrard on January 18, 2010 at 5:56am

I agree the rotary position sensor is the simpler way to go, until you start trying to find a place to put it that has a consistent airflow relative to the wing chord. I have a hall effect sensor and vane and have been moving it around the aircraft. I think I shall have to write a paper about the interaction of the airfoil and the vane from induced flutter to errors as AoA changes. I am now working on a 3-axis probe that can extend well ahead of the airframe to give me relative wind and a better measure to compare sensors to as I place them at different locations on the airframe. I am assuming the probe mounted sensors will elliminate the interaction problem, but from experience anticipate a whole new set of problems.

There is a very good reason early measuring devices like smoke or wool tufts were used. I might drop back to a camera and wool tufts again until I figure out the calibration system.

Roger

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Permalink Reply by Gagarien on January 18, 2010 at 8:25am

Roger what is your ultimate goal with an AOA sensor? Because it sounds like you want to measure more than AOA with a 3-axis probe.

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Permalink Reply by Garry Qualls on January 18, 2010 at 9:45am

I think you definitely want to go with a rotary vane of some kind. Here is a small pic of an alpha-beta probe that I googled:

You could probably snag a low friction potentiometer/encoder from one of these home weather station wind vanes:

Garry

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Permalink Reply by Stephen Carlson on January 18, 2010 at 10:33am

If the Hall Effect or ultra-low-friction potentiometers options are workable, I agree that they are far superior to my P-effect rotor idea. None-the-less, I have continued work on my prototype: The attached image shows my progress. I'll try testing this using my car in the near future.

Roger: How are you using Hall effect sensors to measure the angular deflection? (Did you make the rotatory position Hall effect sensors, or purchase them?)

-Steve

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Permalink Reply by Simon Wood on January 18, 2010 at 12:16pm

Would the behaviour of a 'vane' type arrangement be altered by the gravity/centrapedal forces on the aircraft, or would this be too little to worry about.

I was thinking that you could use the drag force on a small horizontal post, measured in 2D with strain gauges. The more the post is turned/pushed by the flowing air more more speed can be inferred. By mounting 2 posts at 90 degrees (ie. pointing up and left) you could determine forward, climb and cross wind speeds.

Calibration would still be an issue, but I think that this could be worked out by flying in still air and 'running' the numbers.

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Permalink Reply by Mikko Saarisalo on January 18, 2010 at 3:22pm

IMO Garry's vanes are good. The gravity and acceleration forces are cleanly handled by a balancing weight - also seen in bot of his pictures. The calibration need arises from up wash that takes place in front of the wing and easily spans way forward from the tip of the fuselage.

-mikko

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Permalink Reply by Glenn Langton on July 18, 2010 at 3:34pm

I've been working on a wind direction finder for small boats and I've found a magnetic shaft encoder with low friction ball bearings that would also likely work for an angle of attack probe. http://www.usdigital.com/products/ma3/ It's not as cheap as a simple potentiometer but it has 360 degrees of free rotation and is reasonably small. As long as the attached vane is balanced properly, flight maneuvers (pitch, roll, yaw) should not alter the vane's angle of attack indication.

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Permalink Reply by Gábor Zoltán on August 12, 2012 at 2:49pm

Hi Roger,

I think no additional sensor is needed.  

Need to write a little function that measure it from pitch, ground, speed, clib rate (vario), and might be airspeed (this sensor we already have).

I might do it for MinimOSD. Will see if i have enough time.

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