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How does induced drag change of an aerofoil with configuration(flaps)?

Asked by: 3279 views , ,

The reason I am asking this is because in the ATPL books and also other documentations that I tried, effect of flaps on drag mostly considered in an aspect of total or parasite drag. I could not find information about the effect on induced drag.

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2 Answers

  1. Bill Trussell on Jun 04, 2013

    First, see the following site for a decomposition of the formula for Drag:


    Second, recall there is a direct relationship between lift and induced drag. The more lift, the more induced drag. The reason you can not find the complete answer is that typical flap configurations produce varying degrees of each type of drag depending on flap type and deployment amount. Typical fowler flap deployment includes a increase in surface area first, then a larger increase in form drag with increased deployment. As you see with the surface area impact on the drag equation, any increase will increase total drag.

    Wing form also causes variations in the division of drag among the various types of drag.

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  2. oktay karahan on Jun 04, 2013

    let me put the question in a different way… Think of a level flight so L=W then you set say flaps 10; after compensating for the balooning effect it will be level flight again thus the lift will not change… So if we stick to the formula induced drag should not change. Reasoning that we are just decreasing AoA and CL is going to be the same also S will be same…

    nonetheless after doing some research on the web, I found out flaps will change the elliptical distribution of lift which in turn will increase induced drag…


    In return, I just want to understand what really happens to induced drag… does it differ from assumption to assumption?

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