Technical analysis of the Spitfire’s wing design: modified ellipse, controlled asymmetry, reduced drag, and improved maneuverability.

The Spitfire is distinguished by its elliptical wings, often considered perfectly symmetrical. However, there is asymmetry in the wing planform: each wing is not an exact ellipse. This choice of shape is the result of a careful compromise between minimal aerodynamic drag and the integration of weapons, fuel tanks, and structure. The engineers, notably Beverley Shenstone and Reginald Mitchell, designed a modified ellipse from the outset to align the center of pressure with the main spar, ensuring rigidity and stable behavior at high speeds. The wing also features geometric washout, a twist that tends to reduce the angle of attack at the tip, ensuring a gradual stall from the root to the tip. The maximum deviation from a theoretical ellipse is approximately 5 cm towards the tip, over a wingspan of approximately 11.23 m, representing less than 1% of the wing area. Despite its subtle nature, this asymmetry significantly optimizes overall performance.

The modified elliptical wing of the Spitfire: design and objectives

As early as 1934, Mitchell and Shenstone adopted a semi-elliptical shape for the wing to minimize induced drag, while accommodating the landing gear, armament, and fuel in a thin profile with a thickness relative to the chord at the root of 13%, decreasing to 9.4% towards the tip. The main objective was a quasi-elliptical lift-chord profile, as a perfect ellipse is not viable because it causes simultaneous stalling across the entire wingspan. The final wing planform was therefore curved slightly forward of the major axis of the theoretical ellipse so that the quarter-chord line was straight, aligned with the main spar, thus ensuring torsional rigidity and effective control of the wing tips. This slight adjustment induces asymmetry in accordance with aerodynamic specifications. The actual area is 22.50 m², compared to 22.54 m² for the perfect ellipse, a difference of only 0.04 m² (≈ 0.18%), which is imperceptible to the eye but relevant for aerodynamic efficiency.

Why each wing is not a perfect ellipse

In practice, manufacturing an exact elliptical wing is complex and expensive: molding curved skins, non-uniform ribs, and low structural tolerance. The production team simplified the shape by recomposing the ellipse into adjusted circular arcs, while maintaining the aerodynamic benefits. The inclusion of washout, i.e., a gradual decrease in the angle of attack from +2° at the root to -0.5° at the tip, results in a less elliptical but controlled lift distribution. This washout is necessary for the inner wing to stall first, providing haptic feedback to the pilot and preventing sudden tip stalls. The result is an optimized lift/drag profile, but each wing is asymmetrical relative to the theoretical ellipse.

Measured impact of asymmetry on drag and handling

Studies indicate that the maximum deviation between the actual shape and the ideal ellipse is 50 mm at the tip (≈ 2 inches). This small offset is insufficient to significantly alter the induced drag under normal flight conditions, but it is technically sufficient to align the center of pressure with the wing chord, improving twist resistance and robustness in tight turns. The washout contributes to sound stall behavior: the stall begins at the root, generating a progressive vibration in the fuselage, warning the crew. This mechanism improves high-speed handling, as the ailerons at the tips remain in lift longer. In this respect, the Spitfire was among the best of its time, with a critical speed of Mach ≈ 0.89, which was remarkable for a propeller-driven aircraft.

Comparative analysis

Compared to other aircraft of the time (e.g., Dewoitine D.520 or Messerschmitt Bf 109), the Spitfire offers a unique compromise: reduced induced drag thanks to the modified ellipse, and the ability to integrate weapons and fuel into a thin wing. This asymmetry, although minimal, allowed for a synthesis of optimal aerodynamics, lightweight structure, and increased maneuverability. Unlike other aircraft manufacturers, who abandoned the elliptical wing in favor of trapezoidal wings that were easier to manufacture, Supermarine maintained a sophisticated and high-performance design. However, production experience showed that this complex shape was more difficult to manufacture, requiring a large number of parts and precise adjustment, which explains why it was not widely reproduced after the war.

Get in touch to live a unique fighter jet experience – we fly in France AND YOU CAN TAKE THE CONTROLS!!!