Since the first bird-watching human thought of trying a little flying of his own, the idea of wings has fascinated mankind. Through myth and magic, from Daedalus through the “Hawk Men” of Flash Gordon, avid inventors have repeatedly sought to soar with subtly shaped wings.
Things didn’t change at all after Orville and Wilbur Wright demonstrated the correct way to approach building wings. They carefully analyzed wing shapes and airfoils in a wind tunnel and followed that up with practical tests. Ironically, after the Wrights had incontrovertibly established that heavier-than-air flight was possible, inventors were even more intent on evolving new wing shapes that would avoid infringing on the Wright patent and improve on the flying characteristics of aircraft. One who succeeded was Commandant Maurice Hurel, a pilot and adventurer who began his career in the French navy and established a company that became an important part of the modern French aviation industry.
Before Hurel’s attempt, pioneers explored many avenues of approach. Some favored a multiplicity of wings— triplanes, quadruplanes and, in the case of an unusual Fokker design, a quintaplane. The idea roughly was that if two wings are good, more wings are better. Later efforts, including the five-wing Johns Multiplane and the nine-wing Caproni Ca-60 triple-triplane flying boat (“Aerial Oddities,” July 2000) demonstrated that while more wings generated more lift, they also produced much more drag.
The goal of increasing lift while reducing drag led to several advanced ideas, such as a design by Mikhail Makhonine in France in 1931. His good-looking aircraft featured extendable outer wing panels that could increase the wingspan from 43 to 69 feet and the wing area from 226 to 335 square feet. The idea was to take off with the wings extended for greater lift, then retract them at altitude for increased speed. (The idea was probably picked up from the prewar American comic strip Scorchy Smith.)
The idea of variable-span wings was succeeded by variable geometry wings, with greater success. The first of these was the design for the German Messerschmitt P.1011—a plane that never flew—followed by the Bell X-5, Grumman F-14, General Dynamics F-111 and Rockwell B-1A. There were, of course, similar developments in the United Kingdom, Europe and the Soviet Union.
Some designers sought to enhance the wing’s efficiency by directing airflow from either propellers or jet engines over it. Willard R. Custer’s Channel Wing design, for example, almost entered production at mid-century, and many who saw his later versions in flight regret that it did not. Boeing and McDonnell Douglas experimented with blowing jet engine air over the wings with their YC-14 and YC-15 models, respectively. The experience gained on the latter was incorporated into the McDonnell Douglas (now Boeing) C-17A Globemaster III.
Many other avenues were investigated as well, including forward and rearward swept wings, mission-adaptive wings and the blended wing and body pioneered by Vincent Burnelli so many years ago, and now reappearing in forecasts of future transports. Pioneered by the Horten brothers, Anthony Stadlman and John K. Northrop, the flying wing somehow sparked a romantic sense in the aviation public, which was delighted when the Northrop Grumman B-2A Spirit stealth bomber was picked for production.
Yet of all the approaches to wing design, two relatively simple types have been around for almost a century—the low aspect ratio and the high aspect ratio wing. (Aspect ratio is the ratio of the length and span of a wing to its meanwidth and chord.)
The first application of a relatively high aspect ratio wing came in the Wright glider of 1902, whose higher aspect ratio wing was far superior to the otherwise similar 1901 glider’s not only in appearance but in performance. One of the first ultra-low aspect ratio designs was the McCormick Romme “Umbrella plane,” which first flew on March 11, 1910. Designed by 20-year-old Chance Vought, it had a circular wing that was absolutely devoid of camber. Nicknamed the “Doughnut,” the aircraft not only got airborne but also made controlled flights around its home field at Cicero, Ill. About that same time in Britain, Lee Richard built a circular-wing monoplane with a conventional two-place fuselage reaching across the gap in the center. (A version of this aircraft flew in the great film Those Magnificent Men in Their Flying Machines.)
In 1932 Cloyd L. Snyder teamed with Raoul Hoffman (who would become Matty Laird’s chief engineer) to create three circular aircraft. Each called the Arup, they progressed from glider models to a really handsome plane, the S-4, which featured a tricycle landing gear and an enclosed cockpit. Seen as a novelty, it was documented in the newsreels of the day.
Long after Chance Vought’s premature death in 1930, another Vought low aspect ratio aircraft appeared in the form of Charles Zimmerman’s Vought V-173 “Flying Pancake” (see Aviation History, September 1997), currently being restored by Vought retirees for the National Air and Space Museum. It led to the Vought XF-5U1 Navy fighter, which never flew.
A far more successful champion of low aspect ratio wings was Alexander Lippisch, whose experiments led to the world’s first rocket-powered fighter, the Messerschmitt Me-163, as well as to the later Convair series of delta-wing aircraft that included the XF-92A, F-102, F-106, Seadart and B-58. Many foreign manufacturers adopted some variation of the delta wing, including Dassault, Avro, Fairey, Saab, Tupelov and the MiG design bureau. And low aspect ratio aircraft designs got a new lease on life in the quest not to reduce drag but to reduce radar signature, as in the Lockheed Martin F-117A (Aviation History, March 1996).
But success proved to be easier at the high end of the aspect ratio spectrum. High aspect ratio wings were relatively more efficient, and in the biplane format such wings were also relatively strong. The monoplane high aspect ratio wing was given a boost with the introduction of Gottlob Espenlaub’s Mü-2 Kakadu sailplane of 1927. With its 65-foot wingspan, the Kakadu (which was launched by a tow plane) introduced the era of the elegant super-high aspect ratio sailplane.
It was far easier to impart structural strength to low aspect ratio aircraft because they usually made up partially in chord what they lacked in span. Sailplanes could be built with sufficiently strong ultra-high aspect ratio wings without too much difficulty, because they were normally required to lift only the fuselage and the pilot.
Using a high aspect monoplane wing to lift large loads usually meant the incorporation of many drag-producing struts, which more or less defeated the idea. However, Maurice Hurel was obsessed with that concept and ultimately succeeded in his quest. A record-setting test pilot and a competitor in Schneider Trophy races, Hurel reportedly made history in 1943 when he flew the six-engine Potez (CAMS) 161, a 43-ton flying boat, from occupied France to Bizerte in North Africa on its first flight, much to the chagrin of the Nazis.
After World War II, Hurel formed his own firm, Hurel-Dubois. His wind tunnel tests demonstrated that the induced drag of a monoplane braced by suitably designed lifting struts was less than that of a cantilever monoplane of the same span and area. The research led him to believe that the use of lifting struts permitted doubling or even tripling the aspect ratio without any weight penalty.
The first practical demonstration of his ideas was the Hurel-Dubois H.D.10, a research plane with an aspect ratio of 32.5-to- 1. A small monoplane with its very long, narrow-chord wing braced externally by lifting struts, the H.D.10 demonstrated Hurel’s belief that such a wing would generate greater lift at lower weight.
The H.D.10 had a wing area of only 48.3 square feet—about the same as an average dining room table—and was powered by a 40-hp Mathis 2-cylinder engine. The 39-foot 4-inch wing was built out of two longitudinal half-shells of Alumag, reinforced with electrically welded stiffeners, and riveted together along the leading and trailing edges. It used large Fowler-type flaps. The fuselage was built of steel tubing, fabric covered. The cockpit was enclosed, and the tricycle landing gear was retractable, remarkable in an aircraft with an all-up weight of only 1,056 pounds. With the Mathis engine, the H.D.10 achieved a 1331⁄2 mph top speed, but when a 75-hp Praga D engine was installed, its speed went up to 161 mph.
Hurel intended his aircraft as a freight carrier from the start, and he was backed in his efforts by the French government, which then and now is supportive of experimental aircraft. An order was placed for two aircraft, the H.D.31 and H.D.32, which featured an extraordinary wingspan of 148 feet 71⁄2 inches. The aspect ratio was 20.2-to-1, less than that of the H.D.10, but still remarkable for an airplane intended for the same role as the Douglas DC-3, which has a wingspan of 95 feet.
The H.D.31 was first flown on January 27, 1953, while the H.D.32 was first flown on December 29, 1953. The aircraft were almost identical, with the exception of the H.D.32 having 1,200-hp Pratt & Whitney R 1830 engines instead of 800-hp Wright Cyclone engines. The H.D.32’s airframe was strengthened, and the fuselage was increased in length by a little over 4 feet.
Both aircraft were of all-metal construction, and both reverted to fixed landing gear. Maximum takeoff weight was 41,985 pounds, with an empty weight of 24,700 pounds. The payload for a 620-mile stage was estimated at a noteworthy 14,000 pounds.
A second H.D.32 prototype was flown on February 11, 1955, and both H.D.32s were updated in an extensive test program. The Institut Géographique Nationale placed two orders for a total of eight H.D.34s, which were modified to have a slightly longer front fuselage adapted for photographic purposes.
But it was not in France that the Hurel-Dubois concept would reach its zenith. The British company of F.G. Miles Ltd. licensed the Hurel-Dubois wing from its Aerovan Mk. VI in 1957. This concept was adapted by Shorts (which properly claimed it was “the first manufacturers of aircraft in the world”) in the United Kingdom. Shorts’ marketing experts found a requirement for a short-haul freighter aircraft, and adapted the Miles/Hurel design to what became the famous Shorts Skyvan, which flew for the first time on January 17, 1963. The slab-sided, twin-tailed aircraft was originally powered by two 390-hp Continental engines, but was intended all along for turboprops, which it received in the Skyvan Series 1A. The production version of this aircraft, the Skyvan Series 2, had two healthy 730- shaft-horsepower Astazou turboprops that—combined with the Hurel-Dubois wing—resulted in remarkable performance. A whole series of cargo and passenger aircraft followed, with a total of 153 built and in service around the world.
The Hurel-Dubois wing concept was retained by Shorts through a long series of better streamlined light transports. The U.S. Air Force purchased 18 Short Sherpas in 1983, designating them C-23As. Further U.S. and foreign orders followed, and ultimately about 180 of the slick-looking Short 330 series were built, followed by more than 160 of the single vertical stabilizer Short 360. This led in turn to a project for a small jet airliner just before Shorts was acquired by Bombardier.
Maurice Hurel proved to be one of the few designers who could bend the dream of wings to his own vision—and make it work.
Originally published in the March 2006 issue of Aviation History. To subscribe, click here.