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From an aerodynamic aspect, how do partial flaps and full flaps compare for gusty approaches?

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  • $\begingroup$ What does the manual say? $\endgroup$ – fooot Feb 20 '18 at 16:36
  • $\begingroup$ How do you rate what’s best? Best in what sense? $\endgroup$ – Cpt Reynolds Feb 20 '18 at 18:53
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    $\begingroup$ What kind of airplane are you talking about? The answer would likely be different if you were talking about a B757 versus a Cessna 150. $\endgroup$ – 757toga Feb 20 '18 at 22:17
  • $\begingroup$ I fly my archer with 2 notches instead of 3 on gusty days. I yank the last notch in on short final, I find it helps with the yawing a bit. Maybe add 5 knots to my approach speed as well. $\endgroup$ – Dave Feb 21 '18 at 2:33
  • $\begingroup$ My question is mainly in general as the aerodynamic principal will remain the same for all fixed wing aircrafts. $\endgroup$ – Jai Feb 21 '18 at 7:20
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I’m not sure when it comes to large aircraft, but when you select partial flaps or opt for a no-flap approach and landing, it results in a higher speed on approach and landing.

If you then break down the wind components in vectors, the cross-wind component becomes relatively smaller, so it is as if you have less cross-wind and don’t need to have such a large cross-track angle upon landing (less crab) or less cross-control when touching down. Even though the effect is small, it is noticeable.

You can compare it with a small single-engine piston trying to stay on course with 30° of crosswind at 100 kts needing perhaps 15-25° of cross-track angle while a fighter flying at 450 kts only needs 3-5° or so under the same conditions.

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It varies from airframe to airframe, though often times OEMs recommend partial flaps and a gust factor be added to Vref in order to ensure positive control all the way through the approach and roundout - at least for light aircraft.

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