I have been beating my head against the wall on this one for awhile. I have two thoughts:A rotary position sensor and a vane. Has anyone built one? Or is there a commercial one out there?More recently I have been looking at a laser doppler anemometer measuring wind velocity a few centimeters ahead of the wing in undisturbed air. I have been playing with a design using fiber optics and a diode laser. Is anyone familiar with this technology and what has been done or what is available?Any other thoughts for an AoA?Thanks, Roger
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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.
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?)
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.
A rotary position sensor and a vane would be the simplest I recon, something like a cannard mounted to the front out in clean air if you have a pusher, pivoted at the centre of pressure or there someware of this cannard(symetrical profile) and a potentiometer to give analog values out. Calibration by data logging straight and level and stalls (as far as I know most airfoils stall at +/- 16 deg.).
I have done some simple test with a vane and a pot. but found the pots. I have even the small one's from a servo had a high internal friction from the cantacts to be sensitive enough for the vane to move at low airflow, so the idea is a larger vane like a symetrical airfoil that would alway be relativly true to airflow or somthing like that.
AOA can be more usefull than airspeed eg. given AOA well calibrated would result in a certian airspeed irrespective of wind direction etc. can be set up for maximum endurance, best climb rate, auto land were you can be assured the lowest airspeed without stalling etc.etc. ---- my 2 cents.
Hey, this thread topic looks familiar. Check out my post in my blog. I figured I could use the P-effect using little pager motors with uni-directional micro props as tiny potential difference generators. I've made some progress since my blog post last month, see pics attached...
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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.
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.
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
You could probably snag a low friction potentiometer/encoder from one of these home weather station wind vanes:
Garry
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
simplester cheapest? I reconI have done some simple test with a vane and a pot. but found the pots. I have even the small one's from a servo had a high internal friction from the cantacts to be sensitive enough for the vane to move at low airflow, so the idea is a larger vane like a symetrical airfoil that would alway be relativly true to airflow or somthing like that.
AOA can be more usefull than airspeed eg. given AOA well calibrated would result in a certian airspeed irrespective of wind direction etc. can be set up for maximum endurance, best climb rate, auto land were you can be assured the lowest airspeed without stalling etc.etc. ---- my 2 cents.
http://diydrones.com/profiles/blogs/alphabeta-sensor-probe-wo
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