I've read the answers provided but I'm still confused that if an aerofoil is designed so that air flows faster over the upper surface for the purpose of providing lower pressure and hence lift why in inverted flight with the shortest airflow uppermost does the aerofoil not provide negative lift?

  • $\begingroup$ can you link to the other answers you've read? $\endgroup$
    – pentane
    Jan 26, 2019 at 16:01
  • 1
    $\begingroup$ Related: physics.stackexchange.com/q/15981 $\endgroup$ Jan 26, 2019 at 16:01
  • $\begingroup$ You are not alone in suffering from the "equal time fallacy", believing that two molecules of air separated at the leading edge must rejoin at the trailing edge, so the upper and lower surface distances matter. They don't. Air flowing along the top surface reaches the trailing edge long before air flowing along the bottom surface. $\endgroup$ Jan 29, 2019 at 13:23