Taper Ratio

What is Taper Ratio?

The taper ratio is a key parameter in wing design, defined as the ratio of the tip chord to the root chord:

Taper Ratio = Tip Chord / Root Chord

A rectangular wing has a taper ratio of 1, while most modern wings have a taper ratio less than 1, meaning the tip is narrower than the root.

Taper Ratio Calculation

To calculate taper ratio:

• Measure the chord at the root (closest to the fuselage).
• Measure the chord at the tip (furthest from the fuselage).
• Divide the tip chord by the root chord.

For example, if the root chord is 1.5 m and the tip chord is 1 m, the taper ratio is 1/1.5 = 0.67.

Taper Ratio and Wing Performance

The taper ratio affects several aerodynamic characteristics:

• Lift Distribution: A moderate taper ratio helps achieve a more elliptical lift distribution, reducing induced drag.
• Stall Behavior: Wings with a low taper ratio (highly tapered) may stall first at the tip, which can be dangerous. Designers often select a moderate taper ratio to ensure the root stalls first, maintaining aileron control.
• Structural Efficiency: Tapered wings can be lighter and structurally more efficient, as less material is needed at the tip where bending moments are lower.

Taper Ratio and Stall

A key operational concern is that excessive taper (very low taper ratio) can cause the wing tip to stall before the root. This is undesirable because it can lead to loss of roll control. To counteract this, designers may use washout (twist) or choose a moderate taper ratio.

Taper Ratio in Aviation Practice

Most transport aircraft use a taper ratio between 0.3 and 0.5. This balances aerodynamic efficiency, structural considerations, and safe stall characteristics.

Related Parameters

• Aspect Ratio: Not to be confused with taper ratio, aspect ratio is the span divided by mean chord, or span squared divided by wing area.
• Thickness-to-Chord Ratio: Another important parameter, but unrelated to taper ratio, describing the aerofoil's cross-sectional shape.