Wing planform and aspect ratio
Planform: wing shape viewed from directly above. Airfoil = cross-section.
Dimensions:
- Span: max distance wingtip to wingtip.
- Area: total wing surface, control surfaces included.
Planform factors (set the wing's aerodynamic character):
| Factor | Definition | Effects |
|---|---|---|
| Aspect ratio | Span / mean chord (chord: see Airfoil anatomy; TP 1102) | See below |
| Taper | Chord (or thickness) decreases root to tip | Cuts drag (most at high speed), adds lift, saves structural weight |
| Sweepback | Rearward slant of wing | With low aspect ratio: demands very precise flying, especially at slow speed |
Aspect ratio:
- Higher: cuts drag (most at high angle of attack; greater span relative to chord = less induced drag, TP 1102), helps climb, more forgiving of poor technique.
- Very low: high wing loading, high stall speed.
- Trade-off: higher lengthens span, adds structural weight, loses part of drag saving.
Elliptical vs. rectangular (stall progression):
| Elliptical | Rectangular | |
|---|---|---|
| Stall warning | Little | Adequate |
| Ailerons near stall | Poor effectiveness | Stay effective |
| Other | Least induced drag for its aspect ratio; comparatively hard to build | Favoured for low-cost, low-speed aircraft |
- Rectangular stalls first at root, progresses to tips (TP 1102, Symptoms of an Approaching Stall).
- Most straight-wing aircraft designed to stall root first, so ailerons stay effective (PHAK ch.5).
Wing twist (wash out):
- Design feature in some wings. Improves aileron control near stall (high angle of attack on approach) by starting stall at roots (TP 1102, Symptoms of an Approaching Stall).
Trap: elliptical wing is aerodynamically best planform, not safest; gives up the stall warning rectangular keeps.
References
- PHAK ch.5 Aerodynamics of Flight, Effect of Wing Planform
- PHAK glossary: Wing span, Wing area, Chord line, Wing twist
- TP 1102, Symptoms of an Approaching Stall