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It seems that most of the pitot tubes are "L" shaped. However, there are some pitot tubes that shapes like a straight pipe. I am wondering that, for a straight pitot tube installed on the wing, what is the minimum distance the pitot tube need to extend out from the leading edge so it would receive free air and not the boundary layer air?

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    $\begingroup$ Wouldn't that depend on the shape of the wing? $\endgroup$
    – Ron Beyer
    Nov 15 '21 at 4:01
  • $\begingroup$ Why the downvote? I think its a very good question. $\endgroup$
    – Christo
    Nov 15 '21 at 14:29
  • $\begingroup$ @Christo - The downvote was because the only possible answer to the question is “long enough to get into the free stream” but OP has already indicated that he understands this in the question. The other answer is zero because OP asks for the minimum distance required, and at the appropriate conditions that minimum length is zero. Other than that this question is akin to “How much horsepower does a car need?” $\endgroup$
    – Jim
    Nov 17 '21 at 5:54
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That’s going to vary from airframe to airframe based on windtunnel data. Ideally you’re searching for a place where the tube orifice has good access to free stream air that is undisturbed by airflow around the airframe, the wing etc. Also placement in a spot where interference is minimized by changes in angle of attack, side slip, etc. This minimizes discrepancies between calibrated and indicated airspeed.

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