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?
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.
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.