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Thread: Airspeed indicator

  1. #1
    Flyjeep's Avatar
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    Default Airspeed indicator

    After looking around here a bit, I think my airspeed indicator may be off. We thought it was reading a little fast but we haven't compared it to GPS yet. But when sitting in the hangar it reads 40 mph. The numbers start at 40 and I thought the needle just rested there but pictures on this site show the needle should face strait up.. I guess the only option is the have it removed and send it in for calibration?

  2. #2
    Pacerfgoe's Avatar
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    Default Re: Airspeed indicator

    I was questioning my airspeed indicator as well at one time...so we borrowed a tester from work. Found out mine was out about 10 mph at 60 indicated, and was even at 120 indicated.
    No wonder the damn thing was sinking like a stone, and I always had t carry power to round out......

    If you have any concerns about your A/S indicator I’d send it in for overhaul.
    Forrest Miller

  3. #3
    Gilbert Pierce's Avatar
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    Default Re: Airspeed indicator


  4. #4
    McDaver63's Avatar
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    Default Re: Airspeed indicator

    I had all my instrument done by these guys a few years back and they were great & fast turn around. http://www.flyaqi.com/ I have heard a lot of good stuff about Rudy’s as well.

    I doubt this is the problem but you might do a check of your pitot/ static lines for blockage. See if the ASI needle moves when you disconnect the lines to it.


    Sent from my iPad using ShortWingPipers.Org
    Both optimists and pessimists contribute to society. The optimist invents the aeroplane, the pessimist the parachute

  5. #5
    Flyjeep's Avatar
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    Default Re: Airspeed indicator

    Thanks for the input. Something didn't seem right but it's a 60 year old new to me plane. Just seemed like it needed a little more speed to take off, and not sink as much on landing.

  6. #6
    Glen Geller's Avatar
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    Default Re: Airspeed indicator

    Hi Folks, I have noticed my ASI is indicating about 8~10 mph faster than reality (vs GPS ground speed, in calm wind, in multiple direction.)
    So on those 70 mph indicated flares, I am really making solid ground contact!
    I also notice my VSI indicated rate of climb can exceed 1500 fpm in a normal ~75 mph climb, though I have not checked VSI on the GPS to compare (1955 PA22-150 O-320 no dash with ~2000 hours.)
    My question is, where do I start digging first: static piping/connections, pitot probe/piping/connections, the instruments themselves.
    I'm guessing all three in the order listed above, but any hints or known gremlins would be helpful.

    Thanks and Happy Holidays,

    GG
    Glen Geller
    1955 PA22-150 "One For Papa!"

  7. #7
    Gilbert Pierce's Avatar
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    Default Re: Airspeed indicator

    The VSI should not be seeing any pitot pressure. Your symptoms mimic what I was seeing when the Clipper had no static port. It was open to the cabin. Fly and open and close the window. If the VSI&ASI react to that they are seeing cabin pressure.

    Incidently the cabin pressure will be lower than static port and the pressure will decrease with speed.
    Last edited by Gilbert Pierce; 12-20-2018 at 06:32 PM.

  8. #8
    Glen Geller's Avatar
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    Default Re: Airspeed indicator

    Quote Originally Posted by Gilbert Pierce View Post
    The VSI should not be seeing any pitot pressure. Your symptoms mimic what I was seeing when the Clipper had no static port. It was open to the cabin. Fly and open and close the window. If the VSI&ASI react to that they are seeing cabin pressure.

    Incidently the cabin pressure will be lower than static port and the pressure will decrease with speed.
    That's a good point Gilbert, thank you.
    GG

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    Glen Geller
    1955 PA22-150 "One For Papa!"

  9. #9
    tnowak's Avatar
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    Default Re: Airspeed indicator

    My Vagabond flies 5 MPH faster when I open the side window!
    No static on a Vag.
    TonyN

  10. #10
    ClippedWing's Avatar
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    Default Re: Airspeed indicator

    I had mine tested this week when the xpndr was certified. 5 mph slow at the low end but right on at 120 mph. Explains the ridiculously slow indicated speeds for slow flight but also I can comfortably fly a bit slower on approach.

    Not sure why it’s not consistent across the range, maybe something to do with angle of pitot at higher AOAs?

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