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Aspect ratio is mentioned in chapter 1 of AFM .. why do pilots need to know this and its specific value; what should a pilot derive from that value?

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    $\begingroup$ I’d bet few pilots even know what it is let alone know what the AR is of the plane they fly. $\endgroup$
    – Jim
    Oct 23 '21 at 2:28
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    $\begingroup$ @Jim: Well, I do know what it is, but not from anything to do with flying :-) $\endgroup$
    – jamesqf
    Oct 23 '21 at 3:51
  • $\begingroup$ @jamesqf - Yes. I’m sure there are a good few who do. But percentage-wise not so many. $\endgroup$
    – Jim
    Oct 23 '21 at 3:53
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    $\begingroup$ Why do you assume that pilots "need" to know everything that appears in some book by the FAA? Pilots don't "need" to know anything about aerodynamics or flight dynamics. For example, many falsely believe that lift is greater in a climb than in level flight- yet somehow they manage to fly ok. Asking what pilots "need" to know iin order to fly well can only lead to highly opinionated, subjective answers. Better to rework the question to ask "How might a pilot benefit from understanding what aspect ratio is and how it affects an aircraft's performance and handling", or something like that. $\endgroup$ Oct 23 '21 at 12:25
  • $\begingroup$ Plus if you only are going to ever fly one model of plane, you surely don't "need" to know anything about how a different model of plane would fly differently, and why-- $\endgroup$ Oct 23 '21 at 12:28
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In power planes high aspect ratios usually mean better climb performance for the available power, and similarly, a flatter glide. Also better efficiency overall at altitude.

It's nice to know because it lets the pilot anticipate certain flying behaviours (like a flatter glide). By way of direct comparison, if someone puts you into a plane with a low aspect ratio, like a Piper Cherokee, you can expect a steeper glide and more of a tendency to drop out of the sky on landing than its higher aspect ratio Warrior sibling, and having the same engine and at the same all-up weight, you can expect the Warrior to have a somewhat better rate of climb.

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  • $\begingroup$ Thanks for explaining the practical impact; I never really got it until now! $\endgroup$
    – StephenS
    Oct 24 '21 at 23:21
  • $\begingroup$ Yeah it's why the Luscombe 8A performs so well on only 65 hp. Nice long wings. Meanwhile, the "short wing" fabric covered pipers, like the Tri Pacer, are well known as flying bricks. On the other hand, the low aspect airplanes will have generally snappier roll control. $\endgroup$
    – John K
    Oct 24 '21 at 23:40
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Where in handling will a large aspect ratio make itself noticed:

  • Roll damping. The airplane is sluggish in roll, with high lateral stick forces in case of manual control.
  • Adverse yaw: The airplane will need a large vertical and ample rudder to keep the ball centered when rolling at low speed.
  • Low maximum load factor: Span means wing mass, and large root bending moments. A plane with a high aspect ratio will fly straight well but be poor for maneuvering.
  • All optimum speeds will be shifted to higher lift coefficients when compared to a lower aspect ratio airplane, meaning they will be nearer to the airplane's stall speed.
  • Low power-to-weight ratio: The lower drag will reduce the need for installed thrust. Conversely, if the power-to-weight ratio is the same as that for a low aspect ratio plane, the one with the high aspect ratio will climb much faster and steeper.
  • Long approach and noticeable ground effect from the low drag at low speed.
  • Special landing technique in crosswind: Definitely crab during the approach and kick the rudder on touchdown to align the fuselage with the airstrip. Do not attempt to land with one wing low.
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  • $\begingroup$ I'd argue the short wing (of the same area) has more "noticeable" ground effect. High AR makes the airplane glide well, and especially well over the runway, sometimes making landing harder; yet the change is greater for low AR: it approaches like a brick but over the runway it suddently flies. $\endgroup$
    – Zeus
    Dec 8 '21 at 0:09
  • $\begingroup$ @Zeus: Right, the difference in L/D between approach and flare will be greater with a longer chord, but the absolute distance until speed bleeds off enough from equal starting positions will make the high aspect ratio airplane glide much further, so its absolute landing distance will be longer due to ground effect. $\endgroup$ Dec 8 '21 at 7:14

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