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Registered Member #308
Joined: Sun Mar 12 2006, 03:30PM
Location: Denmark
Posts: 7
Hi
I have recently begun working on a project where i have to measure the angle of attack, the angle of attack for an aircraft. The finished system will be implemented on a Glider. Obviously the method would be to use a kind of pivoted vane mounted on a potentiometer and hereby get a readout as the vane would align to the flow and the pot-meter would change resistance, fairly simple. BUT i have been told that this method can cause problems because of the friction in the potentio-meter, since it will be mounted on a glider where the flow will be relatively weak because the system have to work all the time while the glider descends and lands.
I will try and test the potentionmeter solution, but because of the problem mentioned it might not be posseble to use it. Would it be posseble to use an optical detection solution instead perhaps?, still using the pivoted vane?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
You can get very 'loose' pots, wirewound ones come to mind (especially mutiturn ones). if that fails you could use a quadrature encoder out of a mouse, but be warned that has a limited resolution. You could try making a disk that has a varying degree of opacity (I once saw a person who used a 35mm film camera to take a picture of a disk he printed on a full sheet of paper, then used the negative as the encoder since it had a very high resolution at that point) although again the absolute accuracy will be limited by how linear your photodiode is, and how well you can shield the assembly from external light...
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
maybe a circular capacitive strip in which one electrode is the rotating part, and the other is a strip that widens from one point to the other or a few, equally positioned same size electrodes, and measuring the difference (this is the fixed electrode of course)
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
In WW2, pilots found that various rotary instruments (compass repeaters for instance) that worked flawlessly in the air would misbehave on the ground. They realised that the vibration from the engines was shaking the movement and adding a mechanical dither signal which effectively removed the friction-induced deadzone that would otherwise prevent small movements. If you want to use a real rotary potentiometer, some way of shaking it, perhaps with a cell-phone vibrator, would improve the readings.
However, is this a model glider or a 15m span sail-plane? You don't really want the complexity on any glider, but you don't need the extra weight and power requirements of a vibrator on a model, so the mechanical dither solution is not a good one. The optical methods of sensing angle sound good, though digital, via a grey-coded disk, rather than relying on photodiode linearity might be better.
Registered Member #308
Joined: Sun Mar 12 2006, 03:30PM
Location: Denmark
Posts: 7
thanks for the answers
The idea of a contactless Rotary postion sensor seems very interesting, i think i will try that approach and see what kind of results i get, then i will consider the alternatives. It is an educational project so the idea is to implement the system on a model glider.
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Detection system for Measuring the Angle of attack from a weak airflow
