The Spitfire’s wing is usually described as beautiful. That description is not wrong, but it is a description of the result, not the reason. The shape that became an icon was chosen in late 1934 by a small design team at Supermarine, working under R. J. Mitchell, and the reasons they recorded have almost nothing to do with appearance. They have to do with induced drag, wing thickness, gun bays, undercarriage volume, and the placement of a single spar. The beauty is a byproduct. The mechanism is the subject.
The story that will not die
The persistent claim is that Supermarine copied the elliptical planform from the German Heinkel He 70 Blitz, a fast five-seat mailplane first flown in 1932. The claim has legs because the He 70 did have an elliptical wing, and because Mitchell himself wrote to Ernst Heinkel praising the German aircraft. In a letter quoted by Air & Space magazine, Mitchell admitted that Supermarine had been unable to achieve such smooth lines on its Schneider Trophy racers, and reported that a He 70 fitted with a Rolls-Royce Kestrel was “appreciably faster than our fighters.” That is a real compliment from a real designer about a real aircraft. It is also not a statement about wing planform.
Beverley Shenstone, the Canadian-born aerodynamicist who worked on the Spitfire wing, addressed the copying claim directly in a 1977 contribution to a Royal Aeronautical Society publication. His words, reproduced in J. A. D. Ackroyd’s 2013 paper for the Journal of Aeronautical History, are unambiguous: “It has been suggested that we at Supermarine had cribbed the Spitfire’s elliptic wing shape from that of the German Heinkel 70 transport. This was not so. The elliptic wing shape had been used in other aircraft and its advantages were well known. Our wing was much thinner than that of the Heinkel and had a quite different section.”
Shenstone then explained what the He 70 actually contributed. “The Heinkel 70 did have an influence on the Spitfire, but in a rather different way. I had seen the German aircraft at the Paris Aero Show and had been greatly impressed by the smoothness of its skin. There was not a rivet head to be seen.” When detailed design of the F.37/34 began, Shenstone used the He 70 as a benchmark for surface finish, not for planform. The transfer was a standard of workmanship, not a geometry.
This distinction matters because it is the first place where the popular story and the primary record diverge. The visible shared feature — an elliptical wing — masks a different and more consequential transfer. The shape was already in the aerodynamic literature. The finish was the thing Shenstone saw in Paris and wanted his team to match.
What the ellipse was for
The aerodynamic case for an elliptical planform rests on finite-wing theory developed during the First World War by Ludwig Prandtl and his student Max Munk at Göttingen. Munk’s analysis showed that induced drag — the drag that comes from producing lift — is minimized when the lift is distributed elliptically across the span. The simplest way to approximate that loading is to give the wing an elliptical planform. Frederick Lanchester had argued something similar in 1907, and Hermann Glauert’s 1926 textbook The Elements of Aerofoil and Airscrew Theory made the result available to British engineers. Shenstone had studied Glauert. The theory was not obscure.
Shenstone’s own account of the decision, quoted by Ackroyd, is worth reading in full because it shows how the aerodynamic argument was bundled with structural and volumetric ones:
“The elliptical wing was decided upon quite early on. Aerodynamically it was the best for our purpose because the induced drag, that caused in producing lift, was lowest when this shape was used; the ellipse was an ideal shape, theoretically a perfection. There were other advantages, so far as we were concerned. To reduce drag we wanted the lowest possible wing thickness-to-chord ratio, consistent with the necessary strength. But near the root the wing had to be thick enough to accommodate the retracted undercarriage and the guns; so to achieve a good thickness-to-chord ratio we wanted the wing to have a wide chord near the root. A straight-tapered wing starts to reduce in chord from the moment it leaves the root; an elliptic wing, on the other hand, tapers only very slowly at first then progressively more rapidly towards the tip.”
That is the whole argument in one paragraph. The Spitfire needed a thin wing to reduce drag. Thin wings have less room inside. The guns and the retracted undercarriage needed volume near the root. A straight-tapered wing loses chord — and therefore internal depth — immediately outboard of the root. An elliptical wing holds its chord longer before tapering, which gives the designer more room where the equipment sits while still allowing a low thickness-to-chord ratio. The ellipse was not chosen because it was pretty. It was chosen because it was the shape that let a thin wing carry the things the Air Ministry required it to carry.
Mitchell’s own view, as Shenstone recalled it, was blunt: “I don’t give a b….. whether it’s elliptical or not, so long as it covers the guns!” Shenstone added the aesthetic note almost as an afterthought: “The ellipse was simply the shape which allowed us the thinnest possible wing with sufficient room inside to carry the necessary structure and things we wanted to cram in. And it looked nice.”
The Smithsonian account of the same constraint is more specific. The RAF required four .303 machine guns per side. Those guns would not fit within a thin wing of straight taper. The elliptical wing’s taper began far enough outboard that it enveloped them comfortably. The wing was, in a literal sense, a gun bay with an aerodynamic surface wrapped around it.
The shape was not a simple ellipse
Here the popular story goes wrong in a second, less noticed way. The Spitfire’s wing is not a simple ellipse. It is a double ellipse: two semi-ellipses joined at a common major axis, with the forward semi-ellipse having a smaller minor axis than the rearward one. The leading edge curves back gently; the trailing edge curves forward more sharply. The common axis sits at roughly one-third chord. This is the feature that makes the Spitfire wing visually distinctive, and it is the feature that almost never gets discussed in the copying debate.
Ackroyd’s 2013 paper makes a careful and explicitly speculative case that this double-ellipse geometry came from Prandtl. In a 1918 Göttingen report, Prandtl illustrated a wing formed from two semi-ellipses, and in the 1931/1934 Prandtl–Tietjens lecture notes the same shape appears as Figure 166, with a comment that the arrangement puts “the centres of pressure of the individual profiles … all on a straight line.” In modern terms, the aerodynamic centres of the individual wing sections lie along a straight line. For a designer who wants a single main spar running perpendicular to the fuselage centreline, that is a structural gift: the spar can sit close to the line of section aerodynamic centres, which is both strong and light.
Ackroyd notes that the semi-minor axes of Prandtl’s double ellipse are in a 1:2 ratio, and that the span-to-root-chord ratio is 4.1 — both identical to the Spitfire’s planform when fuselage width is excluded. He suggests that Shenstone, who spoke German and had worked in Germany, is the most likely person at Supermarine to have seen either the German or English edition of the Prandtl–Tietjens notes and understood the significance of the figure. He is careful to present this as a possibility, not a proven transmission. The alternative is that someone at Supermarine arrived at the same geometry independently. The evidence does not settle which happened.
What the evidence does support is the structural logic. Ackroyd’s 2016 paper on the aerodynamics of the Spitfire describes how the semi-elliptical planform placed the quarter-chord line perpendicular to the aircraft’s fore-and-aft axis in plan view. In earlier straight-taper layouts, the lift load on the spar acted to the rear of the spar’s fuselage joint, creating a twisting moment that would have required a heavier, strengthened joint. The straight-spar layout eliminated that moment. It also, as Supermarine’s E. J. Davis noted, made the spar-rib arrangement easier to manufacture, because the components met at right angles rather than at an angle that complicated tooling.
So the double ellipse solved several problems at once. It approximated elliptical lift loading, which minimized induced drag. It held chord near the root, which gave volume for guns and undercarriage inside a thin wing. It put the section aerodynamic centres on a straight line, which allowed a single spar near the quarter-chord. And it made the spar perpendicular to the fuselage, which simplified both structure and manufacture. No single one of those constraints dictated the shape. The shape is what remained when all of them were satisfied together.
The thickness that did the real work
There is a further complication in the popular account. The Spitfire’s low drag is often attributed to its elliptical planform, but the retrieved sources suggest that the wing’s thinness mattered at least as much, and possibly more. The Spitfire used NACA 2200-series sections, with thickness-to-chord ratios of 13 percent at the root and 6 percent at the tip. Shenstone described these as “the thinnest we thought we could get away with.” The Hurricane, by comparison, used a Clark YH section with thickness-to-chord ratios of 18 percent at the root and 12 percent at the tip.
Ackroyd’s 2016 paper describes a 1940 investigation by A. R. Collar comparing the drag of the Spitfire and the Hurricane. Collar’s analysis indicated that a significant part of the Spitfire’s lower drag could be attributed to the better boundary-layer behaviour produced by its thinner aerofoil section. That is a claim about thickness, not planform. The elliptical wing made the thin section possible by providing root volume; the thin section then delivered much of the drag benefit. The two are coupled, and separating their contributions is not straightforward.
The Smithsonian account adds a further caution. Real aircraft have fuselages, engine nacelles, control-surface gaps, radiators, intakes, and guns, all of which disturb the lift distribution away from the ideal ellipse. “The battle for perfection was inevitably lost before it began.” The elliptical planform was a theoretical ideal that the actual aircraft could only approximate. That does not make the choice irrational. It makes it a compromise, which is what design is.
What the wing actually teaches
The Spitfire wing is a useful case because it shows how a famous form can be the residue of coupled constraints rather than the expression of a single intention. The aerodynamic theory supplied a target — elliptical lift loading. The structural requirement supplied a second target — a single spar near the quarter-chord, perpendicular to the fuselage. The armament and undercarriage requirements supplied a third — root volume inside a thin wing. The double-ellipse planform was the geometry that hit all three at once. Appearance was noted afterward, by Shenstone, in four words: “And it looked nice.”
This has a practical implication for anyone who designs under constraints. Copying the outline of a successful shape without copying its constraint set reproduces the look but not the mechanism. A modern wing with an elliptical planform but a different spar layout, a different thickness distribution, and a different internal equipment arrangement is not a Spitfire wing. It is an ellipse. The shape is the visible part; the constraints are the part that made it work.
The unresolved question is the provenance of the double ellipse. Ackroyd’s case for Prandtl is careful and circumstantial. The dimensional match is striking. The presence of the figure in a widely translated text is documented. Shenstone’s German and his time at Göttingen-adjacent institutions are documented. But no retrieved source shows a Supermarine drawing annotated with a reference to Prandtl’s Figure 166, and no retrieved source shows Shenstone stating that he used it. The transmission remains a plausible inference, not an established fact. The structural logic stands on its own regardless of where the geometry came from.
What is established is narrower and more useful. The elliptical wing was not chosen for beauty. It was not copied from the He 70. It was a negotiated solution to a set of constraints that included induced drag, wing thickness, gun volume, undercarriage volume, spar placement, and manufacturing simplicity. The beauty is real, but it is a consequence. The wing was never about beauty. It was about covering the guns.
FAQ
Was the Spitfire wing copied from the Heinkel He 70?
No. Beverley Shenstone explicitly refuted the claim, stating that the elliptical shape had been used on other aircraft and that the Spitfire’s wing was much thinner and had a different section. The He 70’s actual influence was on surface finish, which Shenstone used as a benchmark for aerodynamic smoothness.
Why did the Spitfire use an elliptical wing?
For coupled reasons. An elliptical planform approximates the elliptical lift loading that minimizes induced drag. It also holds chord near the root, which provides internal volume for guns and retracted undercarriage inside a thin wing. The double-ellipse variant additionally places the section aerodynamic centres on a straight line, allowing a single spar near the quarter-chord and perpendicular to the fuselage.
Was the Spitfire’s wing a simple ellipse?
No. It was a double ellipse: two semi-ellipses joined at a common major axis, with the forward semi-ellipse having a smaller minor axis than the rearward one. This geometry is what makes the wing visually distinctive and is the feature that connects most plausibly to Prandtl’s published figures.
Did the elliptical planform make the Spitfire faster?
The retrieved sources do not quantify a causal performance effect attributable to planform alone. A 1940 drag comparison by A. R. Collar indicated that a significant part of the Spitfire’s lower drag relative to the Hurricane came from its thinner aerofoil section, not from the planform by itself. The two features are coupled and difficult to separate.
Who was Beverley Shenstone?
A Canadian-born aeronautical engineer who worked at Supermarine from 1932 and contributed to the aerodynamic design of the Spitfire wing. He later served in the Air Ministry and the Ministry of Aircraft Production, and was President of the Royal Aeronautical Society from 1962 to 1963.
Where can I read the primary sources?
J. A. D. Ackroyd’s papers in the Journal of Aeronautical History — “The Spitfire Wing Planform: A Suggestion” (2013) and “The Aerodynamics of the Spitfire” (2016) — reproduce Shenstone’s statements and analyze the structural and aerodynamic reasoning. Both are available through the Royal Aeronautical Society. The Smithsonian’s Air & Space magazine account adds the gun-fit constraint and a caution about the limits of the ideal ellipse.