Aspect ratio (AR) is the ratio of a wing’s span to its mean chord (average width), or equivalently, the square of the span divided by the wing planform area. A long, narrow wing (sailplane, AR 15–30) has high aspect ratio; a short, wide wing (delta fighter, AR 1.5–3) has low aspect ratio.
High aspect ratio reduces induced drag — the drag penalty caused by generating lift with a finite-span wing. This improves cruise efficiency and range. But high-aspect-ratio wings are structurally demanding: the long spar must resist large bending moments, requiring stronger (heavier, more expensive) materials and more precise manufacturing.
The UAV spectrum spans nearly the entire practical range of aspect ratios:
| Platform | AR | Rationale |
|---|---|---|
| Expendable delta (Shahed, LUCAS) | 1.5–2.5 | Structural simplicity, manufacturing tolerance |
| FPV racing quad (arm span / body) | N/A | Rotary-wing; disc loading replaces AR |
| Small fixed-wing (Raven, hand-launch) | 5–8 | Balance of portability and efficiency |
| Tactical (ScanEagle) | 8–12 | Loiter endurance priority |
| MALE (MQ-9 Reaper, TB2) | 12–20 | Long-endurance cruise efficiency |
| HALE (RQ-4 Global Hawk) | 25–30 | Maximum aerodynamic efficiency at altitude |
A delta wing with AR 2.0 has roughly four times the induced drag of a conventional wing with AR 8.0 at the same lift coefficient — but the delta’s spar weighs less, costs less, and can be manufactured by unskilled labor or 3D printing with wide tolerances. The choice of aspect ratio is always a compromise between aerodynamic efficiency and structural/manufacturing cost — see Wing Planform Selection for UAVs.
Related terms
- Wing Loading — the complementary parameter that, together with aspect ratio, defines the flight envelope
- Induced Drag — the drag component directly governed by aspect ratio
- Span — the dimension that aspect ratio relates to chord