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RST Engineering - JIm wrote:
If somebody can tell me how to convert angle of attack to an electrical signal, the rest is rather trivial. Jim "Mike" wrote in message ... Has anyone built an electronic angle of attack meter kit. It seems to be something that would be easy to design but beyond my feeble electronics background. I have seen the products that are out there and they are simple differential pressure gauges and are expensive. I don't like the round differential pressure gauges that many of the companies offer for this kind of system. I was wondering if there would be a way to put something together that would light up different color LED's for the different levels of lift that we could build at home without having to pay out hundreds of dollars for a prebuilt one. We used a reed switch array and a magnet to determine control rod position on my submarine's reactor. You could do the same with an AOA using a magnet on a vane. You'd only need a few reed switches, one for each angle you were interested in: just before stall, best angle of climb and best rate of climb corresponding to red, yellow and green LED's. What else do you care about? -- John Kimmel I think it will be quiet around here now. So long. |
#2
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Heck, my first thought was to take the gas gage & sendin unit out of my
'56 chevy , mount the sendin unit inside with some gears outa of my old alarm clock-(spring busted) sos you get full travel outa the sender with only ten or 20 degrees motion hang a n aluminium vane on the end of it & a fishin sinker forward of it to balance it-You could keep the sinker inside for essthetic reasons. ut then---this was jest my 1st thot--Jerry RST Engineering - JIm wrote: If somebody can tell me how to convert angle of attack to an electrical signal, the rest is rather trivial. Jim "Mike" wrote in message ... Has anyone built an electronic angle of attack meter kit. It seems to be something that would be easy to design but beyond my feeble electronics background. I have seen the products that are out there and they are simple differential pressure gauges and are expensive. I don't like the round differential pressure gauges that many of the companies offer for this kind of system. I was wondering if there would be a way to put something together that would light up different color LED's for the different levels of lift that we could build at home without having to pay out hundreds of dollars for a prebuilt one. We used a reed switch array and a magnet to determine control rod position on my submarine's reactor. You could do the same with an AOA using a magnet on a vane. You'd only need a few reed switches, one for each angle you were interested in: just before stall, best angle of climb and best rate of climb corresponding to red, yellow and green LED's. What else do you care about? |
#3
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Jerry Wass wrote:
Heck, my first thought was to take the gas gage & sendin unit out of my '56 chevy , mount the sendin unit inside with some gears outa of my old alarm clock-(spring busted) sos you get full travel outa the sender with only ten or 20 degrees motion hang a n aluminium vane on the end of it & a fishin sinker forward of it to balance it-You could keep the sinker inside for essthetic reasons. ut then---this was jest my 1st thot--Jerry That's essentially how a vane type works. Dan, U.S. Air Force, retired |
#4
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Hmmmm...for something you could sink your teeth in, Jim, how about a
chip that could be hard mounted inside - with no access to the airflow, that would keep indicating AoA even with a 1/2 inch of ice over the entire airframe? $20 gets you a 3-axis accelerometer, which uses about a couple milliwatts from a 3 volt supply, and provides 300 mV per g. [ADXL330) I have it in mind that the arctan [g(vertical) / g(longitudinal)] gives a useful proxy for AofA, if you process through an op amp ($3), an a/d on a microcontroller ($25). That way, you could have it play Dixie at the appropriate angle if you wanted? :-) That's if a mouth organ reed in a tube from a wing LE aperture is too low tech? Brian W RST Engineering - JIm wrote: If somebody can tell me how to convert angle of attack to an electrical signal, the rest is rather trivial. Jim "Mike" wrote in message ... Has anyone built an electronic angle of attack meter kit. It seems to be something that would be easy to design but beyond my feeble electronics background. I have seen the products that are out there and they are simple differential pressure gauges and are expensive. I don't like the round differential pressure gauges that many of the companies offer for this kind of system. I was wondering if there would be a way to put something together that would light up different color LED's for the different levels of lift that we could build at home without having to pay out hundreds of dollars for a prebuilt one. |
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On Sat, 09 May 2009 19:58:21 -0500, Brian Whatcott
wrote: Hmmmm...for something you could sink your teeth in, Jim, how about a chip that could be hard mounted inside - with no access to the airflow, that would keep indicating AoA even with a 1/2 inch of ice over the entire airframe? $20 gets you a 3-axis accelerometer, which uses about a couple milliwatts from a 3 volt supply, and provides 300 mV per g. [ADXL330) I have it in mind that the arctan [g(vertical) / g(longitudinal)] gives a useful proxy for AofA, if you process through an op amp ($3), an a/d on a microcontroller ($25). That way, you could have it play Dixie at the appropriate angle if you wanted? :-) That's if a mouth organ reed in a tube from a wing LE aperture is too low tech? Brian W RST Engineering - JIm wrote: If somebody can tell me how to convert angle of attack to an electrical signal, the rest is rather trivial. Jim "Mike" wrote in message ... Has anyone built an electronic angle of attack meter kit. It seems to be something that would be easy to design but beyond my feeble electronics background. I have seen the products that are out there and they are simple differential pressure gauges and are expensive. I don't like the round differential pressure gauges that many of the companies offer for this kind of system. I was wondering if there would be a way to put something together that would light up different color LED's for the different levels of lift that we could build at home without having to pay out hundreds of dollars for a prebuilt one. Won't indicate RELATIVE AIR FLOW, only absolute attitude - useless as AOA or lift reserve (iminent stall) indicator. |
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#7
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On Sat, 9 May 2009 09:50:56 -0700, "RST Engineering - JIm"
wrote: If somebody can tell me how to convert angle of attack to an electrical signal, the rest is rather trivial. Jim "Mike" wrote in message ... Has anyone built an electronic angle of attack meter kit. It seems to be something that would be easy to design but beyond my feeble electronics background. I have seen the products that are out there and they are simple differential pressure gauges and are expensive. I don't like the round differential pressure gauges that many of the companies offer for this kind of system. I was wondering if there would be a way to put something together that would light up different color LED's for the different levels of lift that we could build at home without having to pay out hundreds of dollars for a prebuilt one. Generally "lift reserve" is more accurate than angle of attack as a description. |
#8
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I would start with two small ports in the leading edge of the wing,
with capillary tubes running to a MEMS differential pressure sensor. Since the purpose of the device is to tell the pilot how close the AOA is to the stall value these ports should be placed straddling the stall stagnation point. (maybe plus-minus 1/2 inch?) Then the pressure difference is zero at stall, at any airspeed. The differential pressure IC can feed an LED bar graph. This should give very good stall prediction accuracy. Isn't there a voltage-to-LED-bar-graph IC? I seem to remember such a thing. That would make the circuit simple. When approaching an accelerated stall (at higher airspeed than while landing) the unit would tend to overestimate angle. Actually, it measures something more like "lift reserve" than angle of attack. But isn't that the better quantity to report to the pilot? Anyway. the feel of the controls is very different in these two cases, so I think most pilots would learn to adjust their interpretation of the reading, as long as the yellow light comes on, then red, then the plane stalls. -Jeff |
#9
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On May 9, 8:35*pm, wrote:
I would start with two small ports in the leading edge of the wing, with capillary tubes running to a MEMS differential pressure sensor. Since the purpose of the device is to tell the pilot how close the AOA is to the stall value these ports should be placed straddling the stall stagnation point. (maybe plus-minus 1/2 inch?) Then the pressure difference is zero at stall, at any airspeed. The differential pressure IC can feed an LED bar graph. This should give very good stall prediction accuracy. Isn't there a voltage-to-LED-bar-graph IC? *I seem to remember such a thing. *That would make the circuit simple. When approaching an accelerated stall (at higher airspeed than while landing) the unit would tend to overestimate angle. *Actually, it measures something more like "lift reserve" than angle of attack. But isn't that the better quantity to report to the pilot? Anyway. the feel of the controls is very different in these two cases, so I think most pilots would learn to adjust their interpretation of the reading, as long as the yellow light comes on, then red, then the plane stalls. -Jeff The LED bar graph chip used to be call LM3916, now replaced by NTE1549 |
#10
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Yes. It was made by National Semiconductor and you could get it linear or
logarithmic. It was obsoleted by National about fifteen years ago, but there are still a few of them in the pipeline at a pretty hefty price. Jim wrote in message ... Isn't there a voltage-to-LED-bar-graph IC? I seem to remember such a thing. That would make the circuit simple. |
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