Why do birds have so much rough surface (overlapping feathers) compared to aircraft? Isn’t that cause additional skin friction drag?

Could planes maybe benefit from this?

link: https://www.researchgate.net/publication/263394314_Gliding_Swifts_Attain_Laminar_Flow_over_Rough_Wings

enter image description here


It may seem counterintuitive, but by introducing a small amount of turbulence, this interrupts the slower boundary layer which is directly in contact with the wing, thereby delaying local airflow separation and aerodynamic stall. Essentially, at the expense of a small amount of parasitic drag, the stall performance and control effectiveness of the wing can be improved.

Aircraft add small fins called Vortex Generators to achieve this effect on otherwise smooth wings, flaps, ailerons, rudders, and elevators.

enter image description here

Here is a link to check out: https://en.m.wikipedia.org/wiki/Vortex_generator

  • 6
    $\begingroup$ Also, the Reynolds number of birds and airplanes are very different. What works for birds may not be necessary or even helpful at other Reynolds regimes. What works for insects also doesn't work quite as well for birds. $\endgroup$
    – JZYL
    Jul 8 '20 at 16:59
  • $\begingroup$ @JZYL you mean because speed of airplane is so much faster then birds? $\endgroup$ Jul 8 '20 at 17:07
  • 2
    $\begingroup$ Please google Reynolds number. $\endgroup$
    – Jpe61
    Jul 8 '20 at 17:11
  • 2
    $\begingroup$ Another factor is that bird wings (and to some extent the feathers) have a highly variable geometry that's under very precise control. The bird can thus position the wings to minimize drag (or whatever) as its speed changes. $\endgroup$
    – jamesqf
    Jul 8 '20 at 17:58
  • 2
    $\begingroup$ @AeronauticFreek reynolds number just tells us how (un)important the viscosity of the air is relative to the plane. And yes, it increases with both chord and speed. For larger, faster planes, the viscosity of the air is less important (though it still is very important). $\endgroup$
    – Abdullah
    Jul 9 '20 at 4:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.