Old 2nd Jan 2019, 19:56
  #66 (permalink)  
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Join Date: Jun 2009
Location: florida
Age: 76
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according to FCeng

When considering the potential for AOA sensor installation to have played a role in this event, it is important to recognize the difference between AOA vane angle and AOA body angle. The local flow that the vane measures is distorted by the fuselage. As a result, the vane angle changes much more than one degree for each degree change in airplane AOA. Within the AOA signal processing logic is conversion of the vane angle back to the corresponding body angle. This conversion has a gain factor of just about 0.5 to get from vane to body.
Well, FCeng says that the vane deflection requires a "0.5 gain factor" someplace in the sftwe or A2D chip/device, wherever that is.. Is the "gain" two degrees of wing chord to free stream flow? Is it sensed AoA times two or divided by two? Hard to believe the AoA difference between the sensor and the wing chord remains constant when airflow about the nose doesn't seem to be at a constant angle when the plane changes the actual AoA, so a linear "correction" seems too easy. Who does that signal processing? And most important....and according to latest diagram we have of the "system"....

Our diagram shows analog AoA is sent from the SMYD and thence to the stick shaker. But it has been stated that AoA is also used to "correct" airspeed and maybe that value is used for the STS versus raw pitot dynamic pressure. Where do the ADIRU's , cockpit displays and FCC boxes and the MCAS get AoA? From the SMYD? . There must be plenty of room for mischief here. Ya think?

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