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Airflow around the fuselage is not free, even near the aircraft nose. I assume some correction is applied to the measured angle to get the corresponding freeflow angle.

How is the reponse curve for this correction obtained (for narrow/wide-body airliners)? There must be some other sensor to compare with. This cannot be GPS, since that would give pitch, not AoA.

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During development testing the airplane has a "test boom" which in additional to pitot and static inputs has traditionally used mechanical vanes driving pots or resolvers to measure pitch and yaw in the free stream. Nowadays they are using "smart booms" that do the same thing by measuring pressure distribution at the tip of the boom and working it out with software, but it's still just a way to measure the free stream out where it's minimally affected by the fuselage body.

From that data and from the AOA vane itself, the variations between AOA vane and true are plotted and calibration tables are loaded into the Stall Protection Computer software so the SPC can correct the AOA data internally before it is used for the various functions that need AOA information.

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