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what is induced drag and when is it at its highest?

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Aerodynamics, Aircraft Systems, Private Pilot, Student Pilot

when students are asked to explain induced drag, they often say it is a byproduct of lift. but this answer does not explain what induced drag really is. can someone explain the concept to me?

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1 Answers

  1. Aaron on Dec 12, 2014

    Induced drag occurs with the tilting of the lift vector due to differential pressures above and below the wing. High-pressure air below the wing wants to equalize with low-pressure air above the wing. The only place It can really do this is at the wing tip. Thus at the wing tip the low-pressure air from below the wing spirals up and over and inward to the low pressure area above the wing. This is the cause of those pesky vortexes we know to avoid. The air flowing off the back of the wing (down wash) continues flowing back off the wing and is balanced by air at the front of the wing. However the upwards-trending air at the tip tends to occur just outside of the tip, where the downward-trending air tends to remain closer on the tip of the wing. This creates a net-downward moment which tilts the lift vector of the wings back a little bit, creating two sub-vectorial components, a horizontal and vertical component (in much the same way banking the plane does, but in different axis). The horizontal component of the moment produced by the wing’s production of lift is induced drag, and is highest when the plane is producing the most lift (or when the pressure differential and vortices are at their greatest) I.e. Slow, clean, and heavy. This is why those nifty winglets not only look neat and help reduce wingtip vortices, but also save fuel by reducing induced drag. After all, wingtip vortexes are a direct cause of induced drag.

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