Mechanical angle of attack indicator?

Discussion in 'Instruments / Avionics / Electrical System' started by cluttonfred, Apr 22, 2017.

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  1. Apr 22, 2017 #1

    cluttonfred

    cluttonfred

    cluttonfred

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    I know about the air pressure-based AOA indicators driving electronic displays or analog differential pressure gauges, and the vane-type gauges driving sensors for electronic displays, and the old Bacon Saver arrow on a stick. But does anyone know of any mechanical AOA indicators that drive a cockpit display with no electronics at all? I can certainly imagine a vane driving a push-pull cable to move a mechanical display, for example, but someone must have done something like this before. Perhaps using model aircraft push-pull cable and ends?
     
  2. Apr 22, 2017 #2

    Highplains

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    A Wheatstone Bridge with a resistive sensor at the vane is the easy traditional method. Then you have an analog meter to watch.
     
  3. Apr 22, 2017 #3

    cluttonfred

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    Ummm, thanks, but how is that mechanical rather than electronic?
     
  4. Apr 22, 2017 #4

    TFF

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    Too much friction or too much monkey motion to be any good.
     
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  5. Apr 22, 2017 #5

    Highplains

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    Do you want something that works, or something from Disney? Besides, no semiconductors will be harmed or even present. Just a few resistors, a pot or two, meter and a small battery. It's so 19th century. On the plus side, you can mount the vane and the meter without regard to their relative positions.

    Initially I considered synchro resolver (mid 20th century), but remembered the old bridge circuit. Frankly, the new designs based on air pressure differentials should be dirt cheap to build. Motorola makes (or did make) a diffential pressure sensor that sold for maybe 5 bucks, and single chip MCUs with analog inputs cost far less than a package of cheap pens.
     
  6. Apr 22, 2017 #6

    Pops

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    Wrong post.
     
  7. Apr 23, 2017 #7

    Hot Wings

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    Maybe not so much. The old VW mechanical fuel gauges were all cable and ha very little friction.

    Did a quick Google for apparent wind indicators for sail boats. If anyone had ever built a mechanical one it would have been a sailor. Didn't find anything mechanical........
     
  8. Apr 23, 2017 #8

    Dana

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    You could always mount a wind vane horizontally on the interplane strut of your biplane... if you have a biplane...

    Or, two pressure taps driving a mechanical +/- pressure gauge or u-tube manometer?

    Or simplest of all, a vane on the fuselage side, a short shaft going through beaing, connected to a pointer on the inside cockpit wall.

    Dana
     
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  9. Apr 23, 2017 #9

    Victor Bravo

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    How about a yaw string that also goes up and down with AoA?
     
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  10. Apr 23, 2017 #10

    cluttonfred

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    Pops mentioned the old VW Beetle mechanical fuel gauges over on the Homemade Gas Gauge thread. Seeing this pic of one with the face off suggests that it would make a great AOA indicator mounted sideways and driven by a mass-balanced vane in clear air. You could easily print out a nicely marked and color coded label for the face with a cutout to view the needle.

    2339-2.jpg vw mechanical fuel gauge for angle of attack indicator.jpg
     
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  11. Apr 23, 2017 #11

    skier

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    Why limit yourself to a mechanical system? I'm sure you could devise something, but there's a good chance it would be more compex, more difficult to use, and more expensive than a simple electrical system.
     
  12. Apr 23, 2017 #12

    cluttonfred

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    I just like the idea of a completely independent system with no need for 12v power or batteries. The analog differential pressure gauge systems provide that, I am just looking at alternatives.
     
  13. Apr 23, 2017 #13

    delta

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  14. Apr 23, 2017 #14

    radfordc

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    Only for a pusher prop configuration.
     
  15. Apr 23, 2017 #15

    radfordc

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  16. Apr 23, 2017 #16

    pictsidhe

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    Friction will be the accuracy killer. The nearer the vane is to the true angle, the less force it will exert. Bowden cables etc don't seem low enough friction to me.
     
  17. Apr 23, 2017 #17

    Hot Wings

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    Maybe if you could find a good used one. Otherwise they are kind of expensive to buy new just to salvage for parts.

    Bulk bicycle brake cable is very similar to the cable used by the VW system and is cheap enough. some even comes with different ends already pre-swaged. Starting from scratch with just the cable means you have the choice to make either a rotary gauge, like the VW, or a linear one. A linear one, preferably vertical with a scale next to the indicator would be quick and intuitive to interpret. Easier to make than a rotary one too...
     
  18. Apr 23, 2017 #18

    ultralajt

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    Who needs AOA indicator... I am just thinking out loud....
     
  19. Apr 24, 2017 #19

    vtul

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    Love the string, VB.
     
  20. Apr 24, 2017 #20

    larr

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    Doesn't this come up every year or two?
    This is the usual answer, O'neill Bacon Saver:
    AOA3.jpg AOA1.jpg download.jpg
    I'm pretty sure O'neill is out of business now, but it seems simple enough to copy.

    History Moment:
    During the open cockpit taildragger era pilots would lean out the port side for visibility. DeHavilland put mechanical airspeed indicators on the port strut because if you were leaning out you couldn't see the cockpit instruments.
     

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