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A point of confusion for me has been this: Does the pitot tube measure the airspeed of the plane in the direction of its flight path, or does it measure the speed of the air parallel to the pitot tube itself. For instance, in a Cessna 152 that may be in a decent but the nose is not pointing down as sharply as the decent path, is the pitot tube accurately measuring the downward speed along the flight path, or is it only measuring accurately the speed of the air parallel to the direction the pitot tube is pointing?

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    $\begingroup$ Related $\endgroup$
    – Pondlife
    Commented Aug 2, 2021 at 2:05
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    $\begingroup$ Also, the pitot tube doesn't measure speed at all. It measures pressure. $\endgroup$ Commented Aug 2, 2021 at 15:26
  • $\begingroup$ @CamilleGoudeseune: and the air speed indicator (ASI) doesn't indicate air speed, but pressure difference. $\endgroup$
    – mins
    Commented Aug 2, 2021 at 17:00
  • $\begingroup$ Error increases with AoA. A sustained indicated reading of 35 knots was observed in a 172 at full power in slow flight (at altitude). If anything, the lower IAS readings provide a safety margin to help avoid stalling, but the error is less as AoA decreases. $\endgroup$ Commented Aug 2, 2021 at 21:58
  • $\begingroup$ @CamilleGoudeseune that error is for a “venturi-shrouded pitot probe”, which is something like magenta unicorn. For normal pitot the error becomes significant much earlier. $\endgroup$
    – Jan Hudec
    Commented Aug 4, 2021 at 5:08

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