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Why does the twin otter have wing fences? Planes like the Cessna 172 don't have them, so why does the twin otter have them? (I know that it is used for STOL purposes, but how would wing fences help in that way?)

My guess is that they're for helping with stalls, but how would wing fences help with a stall? (This picture is of an RC twin otter, couldn't find a good real-life one) enter image description here

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    $\begingroup$ Why there's shouldn't be any spanwise flow on a unswept wing? You have even asked about it in another question of yours!?! $\endgroup$
    – sophit
    Dec 27, 2023 at 3:49
  • $\begingroup$ @sophit the spanwise flow I was talking about there is a pretty minor effect, read the second comment on this answer to see what I mean. Since that effect is pretty minor, I didn’t see a purpose in wing fences. I’m still going to edit this question, because you’re right about me contradicting myself. $\endgroup$
    – Wyatt
    Dec 27, 2023 at 4:19
  • $\begingroup$ Here is a real-life photo, although a poor one, plus an unauthoritative answer. Briefly: spanwise flow does happen on the Otter; the fences avoid stall where the ailerons are, esp. when ailerons droop along with flaps. That preserves roll authority on approach and flare. $\endgroup$ Dec 27, 2023 at 16:20
  • $\begingroup$ @Wyatt spanwise flow is minor at full speed and minimal angle of attack, in "normal" airflow. When a part of a wing ceases generating underpressure (stall) while the other part continues, it becomes major enough. Also, during normal operation overwing spanwise flow is towards center, and when the center stalls, it reverses. $\endgroup$
    – Agent_L
    Jan 1 at 11:13

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