Which statement best describes the influence of wing aspect ratio on lift-to-drag ratio and overall efficiency?

Which statement best describes the influence of wing aspect ratio on lift-to-drag ratio and overall efficiency?

• A. Lower AR always yields the best lift-to-drag ratio.
• B. AR has no effect on wing efficiency.
• C. Higher AR reduces induced drag and improves L/D up to structural limits; beyond practical limits, weight and bending stiffness constrain benefits.
• D. High aspect ratio wings increase parasitic drag at all speeds.

Answer: (C)

Increasing the wing’s aspect ratio means a longer, narrower wing. This reduces induced drag because the wing saves on the energy lost to wingtip vortices that arise when a wing generates lift. Since induced drag drops with higher AR, the lift-to-drag ratio and overall efficiency improve for a given lift load, especially at cruise where induced drag is a large portion of total drag. But the benefits aren’t unlimited. A very high aspect ratio wingspan requires more structural weight and stiffness to resist bending moments, which adds weight and aeroelastic concerns. Beyond a practical limit, that extra structural demand offsets the gains from reduced induced drag, so the improvement in efficiency tapers off. Lowering aspect ratio increases induced drag and reduces L/D, so the statement that lower AR always gives the best L/D isn’t correct. Aspect ratio clearly affects efficiency, so saying it has no effect isn’t true. While higher AR can raise some parasitic drag components, the net effect is not that parasitic drag increases at all speeds; the induced-drag reduction usually dominates within typical flight regimes.

Increasing the wing’s aspect ratio means a longer, narrower wing. This reduces induced drag because the wing saves on the energy lost to wingtip vortices that arise when a wing generates lift. Since induced drag drops with higher AR, the lift-to-drag ratio and overall efficiency improve for a given lift load, especially at cruise where induced drag is a large portion of total drag.

But the benefits aren’t unlimited. A very high aspect ratio wingspan requires more structural weight and stiffness to resist bending moments, which adds weight and aeroelastic concerns. Beyond a practical limit, that extra structural demand offsets the gains from reduced induced drag, so the improvement in efficiency tapers off.

Lowering aspect ratio increases induced drag and reduces L/D, so the statement that lower AR always gives the best L/D isn’t correct. Aspect ratio clearly affects efficiency, so saying it has no effect isn’t true. While higher AR can raise some parasitic drag components, the net effect is not that parasitic drag increases at all speeds; the induced-drag reduction usually dominates within typical flight regimes.