How to calculate the extra lift gained by the intake lip of a duct? Aside from improving efficiency by preventing tip vortices, if a duct has a bell-shaped intake, this lip around the edge creates extra lift because the incoming air sticks to and curves around it which lowers it's pressure. This pressure difference between the duct lip surface and the surrounding air is what causes the extra lift.

The concept was used on the US military's Hillier Flying Platform with some success however, I cannot find any information on how to calculate the exact amount of lift generated by the duct lip for a given flow characteristic through the duct.

I made my own model but I have no idea if it's accurate, hence the need for experimental data to check it against.

  • $\begingroup$ The concept of getting lift from an engine inlet seems highly dubious. The typical velocity of the air entering the engine is about Mach 0.3 to 0.4. Which means at aircraft speeds higher that that, the air in the intake is slower than the air underneath (or outside) the intake. Slower air has a higher static pressure. So, it won’t be generating lift. But if you have a link for an intake generating lift, please add it. $\endgroup$
    – Penguin
    Oct 6, 2018 at 11:05
  • $\begingroup$ @Penguin This is for a craft in hover. $\endgroup$
    – Aviator S
    Oct 6, 2018 at 15:34
  • 1
    $\begingroup$ OK, but Bernoulli’s law applies to that as well. And, the “lift” force will act around the entire circumference of the duct, so, even if it does exist, would be expected to be canceled out. Maybe you need an illustration in your question that can explain why / how these factors won’t exist? $\endgroup$
    – Penguin
    Oct 8, 2018 at 9:49
  • $\begingroup$ That may help, even if for UAV: Effects of Duct Lip Shaping and Various Control Devices on the Hover and Forward Flight Performance of Ducted Fan UAVs $\endgroup$
    – mins
    Feb 15, 2019 at 17:05


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