Mullets, stealth and which other Second World War Fighters Achieved This Holy Grail?

The P-51 Mustang has been described as the most decisive combat aircraft in history. Its ability to escort bombers deep into Germany conferred air superiority on the Allies ahead of D-Day. Two factors contributed to the Mustang’s success: it was relatively easy to manufacture and had an exceptionally clean aerodynamic design, famously including a highly efficient ‘laminar flow’ wing. But did the P-51 or any other combat aircraft truly find the holy grail of laminar flow, and did it even matter? And what does the story tell us about the unique nature of American warplanes to this day?

Laminar flow is elusive, difficult to achieve in practice, and often misunderstood, yet the concept is simple. Imagine water flowing over a smooth rock in a stream. If the water glides quietly in neat layers, that is laminar flow—calm, ordered, and efficient. Strike a jagged edge, and the water breaks into turbulent, swirling eddies. Air behaves similarly over a wing. Laminar flow is a state of calm.

Laminar flow reduces drag—the invisible resistance slowing an aircraft—resulting in higher speed, greater range, and lower fuel consumption. From the earliest days of aviation, engineers understood the concept. In practice, achieving laminar flow over a significant portion of a wing was extraordinarily difficult.

In aerodynamic terms, the goal was to keep smooth flow over a substantial portion of the wing’s chord. The wing chord is the distance from the leading edge or front of the wing to the trailing edge (the back of the wing). If you can keep forty per cent or more of the chord remaining laminar before transition to turbulence, you get pretty magical effects. In wind-tunnel experiments, laminar wings promised dramatic reductions in drag. By the late 1930s, laminar flow had become one of the most alluring ideas in aerodynamics, especially as aircraft speeds approached the limits of conventional design.

Business at the front, party at the back

The front of this man’s hairstyle is smooth and orderly, like laminar flow air; the back is turbulent. A laminar flow wing is akin to a classic mullet in which the orderly section goes as far back as possible.

Aircraft generate lift because air moves faster over the upper surface than beneath it, creating a pressure difference (some contrarians will argue with this, but let’s leave that debate for another day). Early-20th-century wings had maximum thickness near the leading edge, producing strong pressure gradients that quickly tripped the boundary layer into turbulence (as in the Curly Mullet above). While turbulence aids predictable handling and prevents flow separation, it increases skin-friction drag.

Laminar-flow airfoils managed this by moving maximum thickness further aft—sometimes forty or fifty per cent of the chord. This allowed smoother pressure recovery (i.e., air pressure rises more gradually along the wing, thereby keeping the airflow smooth rather than breaking into turbulence) and extended laminar flow.

Wind-tunnel experiments confirmed the benefits under ideal conditions: smooth surfaces, precise shapes, and undisturbed airflow. However, many wondered whether real operational aircraft could support such a clean, smooth wing . Military flying exposed wings to exhaust residue, dirt, rain, and maintenance imperfections, never mind guns.

Research establishments in Britain, Germany, the United States, and Japan studied laminar flow. In Britain, the National Physical Laboratory and Royal Aircraft Establishment at Farnborough tested airfoil sections, boundary-layer behaviour, and pressure distributions. Germany experimented with laminar-flow flying wings, such as the Horten H.VIII. The United States developed the NACA 6-series airfoils, which would underpin the P-51 Mustang. Japan pursued laminar-inspired designs through Nakajima and Kawanishi, producing some of the most aerodynamically sophisticated piston aircraft of the war.

The United Flow States

Among operational fighters, the P-51 Mustang exemplified laminar-flow wing theory. Its wings used NACA 6-series airfoils with maximum thickness around 40–45% of chord. This delayed boundary-layer transition, reducing drag at high speed.

The Bell P-63 Kingcobra also employed laminar-inspired airfoils. The jet-powered P-59’s laminar wing, however, remained mostly theoretical; surface imperfections, intake interference, and early jet installation issues caused laminar flow to break down quickly. Despite these limitations, the Mustang realised significant aerodynamic benefits, particularly at high altitude and cruise, directly contributing to its long-range escort capabilities.

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Flight tests on a P-63A in 1945 highlighted the fragility of laminar flow. Boundary-layer transition occurred near the leading edge, limiting laminar extent. Reducing surface roughness—careful sanding, priming, and painting—extended laminar flow to 60% of chord in controlled conditions, illustrating the extreme precision required to achieve operational laminar wings.

Other American aircraft, like the B-24 Liberator with its Davis wing, showed laminar-like characteristics in wind tunnels, but real operational benefits were minimal. True laminar-flow performance remained rare outside of purpose-built designs like the Mustang.

The P-51’s success was the result of holistic thinking. Its entire airframe—thin, lightly loaded wing, flush riveting, smooth surface finish, and efficient fuselage—was optimised to support laminar flow. Brilliant drop tanks further increased range, enabling the Mustang to dominate long-range escort missions.

Britain, the Tempest and the Spiteful

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