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Thread: Static System Calibration

  1. #11
    Senior Member turbopilot's Avatar
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    Default Re: Static System Calibration

    Quote Originally Posted by Andy View Post
    What is the redundancy problem? A single static system has no redundancy whether it is fuselage mounted or combined with a pitot probe.
    Two ports just incase one port gets clogged frozen moisture, insects ect.
    Bob Anderson, CC11-00435, N94RA

  2. #12
    Senior Member Andy's Avatar
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    Default Re: Static System Calibration

    Quote Originally Posted by turbopilot View Post
    Two ports just incase one port gets clogged frozen moisture, insects ect.
    If one fuselage port is clogged the other gives misleading information. The reason there are two ports is to average the pressure on each side of the aircraft not to provide redundancy. Redundancy is provided by adding static port pairs. Most transport aircraft have two or three independent static port pairs.

    A Prandtl static tube has four static sensing holes so, if your argument is valid, it has twice the redundancy of fuselage mounted static ports, and it can be heated.

    My G5 and G3X are on the same pitot and static and agree well on IAS. If I experiment with a Prandtl tube I'd first connect it only to the G5. That should give a very quick indication of the static source difference.

  3. #13
    Senior Member Andy's Avatar
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    Default Re: Static System Calibration

    Quote Originally Posted by turbopilot View Post


    Your static ports are not painted. My FX-3 static ports were not masked when the fuselage was painted and the entire port button, including the hole, was painted.

    Static ports are normally not painted. I'd like to hear if other FX-3 were delivered with painted static ports.

  4. #14
    Senior Member turbopilot's Avatar
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    Default Re: Static System Calibration

    Quote Originally Posted by Andy View Post
    Your static ports are not painted. My FX-3 static ports were not masked when the fuselage was painted and the entire port button, including the hole, was painted.

    Static ports are normally not painted. I'd like to hear if other FX-3 were delivered with painted static ports.
    Actually, this is a picture of my 2014 SS which had the static port service bulletin applied. My new 2020 SS has painted ports. No significant difference between the two CAS to TAS.

    I looked through both the SS and FX-3 AFM. It appears they have nearly identical CAS to TAS errors, except the SS graph only goes out to 110 mph since it is an LSA. Each airplane indicates 10 mph fast at 75% power and around 5 mph fast around 44% power. I see the last update of the SS AFM was 2016. If I recall the SB came out for static ports late 2014. Mine was one of the last to be built using the cabin as a static source.

    The Garmin G3X was introduced late 2014 in the SS so most likely they made the change to "normal" static ports with the introduction of the G3X.

    I don't recall much of a difference in CAS to TAS error when sensing from the cabin but the pressure would change depending on overhead vent settings in the cabin.
    Bob Anderson, CC11-00435, N94RA

  5. #15
    Senior Member turbopilot's Avatar
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    Default Re: Static System Calibration

    I applied a .025" aluminum disc just aft of the static port hole on both sides.

    Without the discs my new SS TAS indicated +5.1 mph faster than GPS calibrated "TAS" @ 75% power and + 1.3 mph faster than GPS calibrated "TAS" @ 44% power.

    Just made a flight with the .025 discs held in place with a small drop of RTV. Now at 75% power indicated TAS is -3.4 mph compared to GPS calibrated TAS @ 75% power and -4.5 mph under actual @ 44% power. For this test winds aloft were very low out of the Northwest below 5 mph at 1,000' agl.

    So it is clear very small changes in airflow near the static ports can have a big impact on TAS indicated. I will split the difference for the next test at .012 to .015 thickness. May have to use layers of tape to get that thin.

    Bob Anderson, CC11-00435, N94RA

  6. #16
    Senior Member turbopilot's Avatar
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    Default Re: Static System Calibration

    Just made a new test flight. This time with a .015 aluminum disc just aft of the static ports.

    At 44% power on this flight TAS on the G3X was 90 mph and GPS calculated TAS was 91 mph

    At 75% power on this flight TAS on the G3X was 114 mph and GPS calculated TAS was 112 mph

    Winds aloft were around 342 degrees @ 11 mph for this test. GPS calculated winds aloft were very close to G3X calculated winds. There were higher winds aloft on this test compared to previous tests which introduced some light turbulence. So I will repeat the test again with L&V winds aloft and no turbulence.

    For now it would appear the .015" aluminum disc aft of the static port just about corrects the static port error over the nominal speed range of the cub.

    Bob Anderson, CC11-00435, N94RA

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