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When Frederick Miles flew the original Libellula model, the M.35, in May 1942, it proved to be longitudinally unstable, as a result of the weight concentrated in its tail.  

Dragonfly Dreams

By Robert Guttman
1/15/2018 • Aviation History Magazine

Although Miles Aircraft’s odd-looking Libellula flew well, British officials swatted it down.

The conventional image of an airplane—a tubular fuselage with a pair of wings attached somewhere near the center and a rudder and elevators mounted on tail surfaces—has become ingrained in the public consciousness. A few independent-minded individuals, however, have possessed the imagination to step back and take a fresh look at aircraft design. Among them were British brothers George and Frederick Miles and Frederick’s wife, Maxine.

In 1933 the Miles family began designing airplanes for the Phillips and Powis Aircraft Company. Frederick also became the firm’s managing director, and its products were marketed under the Miles name. That state of affairs persisted until 1943, when Frederick took over the company and its name was officially changed to Miles Aircraft Ltd. Maxine, a draftswoman who in 1935 designed the Sparrowhawk racing plane, became a shareholder and would also serve as director of the Miles Aeronautical Technical School in 1943.

Miles produced a series of successful light sporting monoplanes during the 1930s, including the M.12 Mohawk, an elegant two-seater designed and built in 1936 on special order for Charles Lindbergh (the Mohawk is currently on display at the Royal Air Force Museum outside London). In 1937 Miles introduced the innovative Magister two-seat trainer, which became the first monoplane to be accepted by the British Air Ministry for “ab initio instruction” (primary training). A total of 1,293 Magisters would be manufactured. In 1939 Miles followed up that success with the Master, a high-speed advanced trainer, of which 3,300 were produced. Thousands of British Commonwealth pilots would train in Magisters and Masters during World War II.

In 1941 George Miles learned that the Royal Navy was concerned about the high rate of landing accidents aboard aircraft carriers. Reports indicated that one of the principal issues was poor visibility from the cockpit during final approach. George thought a possible solution might be an airplane configured as a tandem biplane, powered by a pusher engine and equipped with tricycle landing gear. He reasoned that the pilot of such an aircraft could sit in the nose, affording him an unobstructed view during landings. Additional benefits of the configuration would include increased wing area and reduced span, resulting in a slower landing speed while simultaneously eliminating the need for heavy, complex folding wings. In addition, spreading the center of lift between two tandem wings would eliminate the need for tail surfaces, reducing drag. It would also shorten the fuselage, rendering the airplane more maneuverable in flight and easier to stow aboard ship. Miles dubbed this innovative design the Libellula, after a genus of common dragonflies.

To determine whether the proposed configuration was feasible, George Miles and his chief engineer, Ray Bournon, designed a small-scale test version powered by a 130-hp de Havilland Gipsy Major engine. Designated the M.35, the experimental plane was completed in less than six weeks. No more than 12 employees ever worked on it because the factory was so busy filling orders for RAF trainers.

The M.35 had a large, low-set swept wing just ahead of the tail, with end-plate fins and rudders. A smaller, high-set straight wing was mounted just behind the cockpit. The ailerons were fitted to the aft wing, while the elevators were situated on the forward wing. Both wings were fitted with landing flaps. 

The original intention had been to install the Gipsy Major ahead of the rear wing, driving the propeller via an extension shaft. In order to save time and expense, however, the engine was mounted at the tail, without the extension shaft. As a result of all that weight concentrated at the tail, however, when Frederick Miles first flew the aircraft on May 1, 1942, it proved to be longitudinally unstable. Although the problem was alleviated by the installation of ballast, the design was not considered a success. 

The M.35 had been constructed entirely as a private venture, and the Air Ministry criticized Miles for building and flying it without authorization. In any case the Admiralty, for whom it was intended, showed no interest in the design. A projected full-size carrier-based fighter ver-sion, to be powered by a Rolls-Royce Griffon and armed with four 20mm cannons, was never built.

Undeterred by the official disapproval, George Miles designed another Libellula-type aircraft, this time to meet an Air Ministry specification for a high-speed, high-altitude, twin-engine medium bomber. Called the M.39, the bomber variant was intended to be powered by two Rolls-Royce Merlin or Bristol Hercules engines and have a range of 1,500 miles at 30,000 feet while carrying a 4,000-pound bomb load.

Once again Miles built a small-scale flying mock-up of the proposed aircraft, the M.39B. Powered by two 140-hp Gipsy Majors, the M.39B differed from its predecessor in that its rear wing was mounted higher than the front wing, to allow clearance for the twin propellers and also to clear the aft wing from the downwash effect of the forward wing. The endplate fins and rudders were also augmented by a central fixed fin. Flown for the first time on July 22, 1943, the M.39B handled very well, demonstrating that Miles had learned from his mistakes on the M.35. 

Miles again found himself officially censured for building and flying an unauthorized prototype, but this time the Air Ministry was sufficiently interested to purchase the plane for evaluation at the Royal Aircraft Establishment at Farnborough. Official testing was delayed by two accidents that necessitated extensive repairs to the prototype. Neither of those mishaps had anything to do with the airplane’s flying qualities. One occurred when the delivery pilot forgot to lower the landing gear on arrival at Farnborough, the other when the M.39B was blown onto its back by the prop-wash of a nearby aircraft.

While at the R.A.E., the M.39B was flown extensively by Captain Eric “Winkle” Brown, one of the world’s most experienced test pilots. Much of Brown’s work involved testing control and stability with different combinations of the two pairs of flaps. He subsequently wrote that the aircraft exhibited exceptionally mild stall characteristics, and would recover by itself after losing only about 100 feet of altitude. He did criticize its performance with one engine out, during which he found it virtually impossible to maintain straight and level flight. It should be noted, however, that to save money the prototype had been fitted with low-powered engines that turned in the same direction, and with nonfeathering propellers. Brown’s verdict: He found it an interesting and generally pleasant aircraft to fly, and speculated it might have made a good high-speed bomber, though he didn’t believe it would have been suitable as a carrier-based fighter. 

In the end the Air Ministry turned down Miles’ bomber proposal, and the full-sized prototype was never built. The M.39B was eventually returned to Miles Ltd., where it underwent further modifications and tests. The Miles brothers persisted with the Libellula configuration, proposing, among other things, a jet-powered mailplane. Dubbed the M.63, it would have been propelled by three tail-mounted jet engines, similar in configuration to the later Boeing 727. The M.63 was expected to have a range of 1,600 miles at a cruising speed of 500 mph at an altitude of 36,000 feet.

Miles’ most ambitious aircraft—and what would turn out to be its last project—was undoubtedly the M.52, an experimental jet designed by Miles engineer Don L. Brown that was intended to break the sound barrier. The first of three planned aircraft was nearly complete in 1946, but once again the British government stepped in and terminated the project, this time over postwar budget concerns. Data on the M.52’s all-moving, variable-incidence tailplane that Miles shared with America’s National Advisory Committee for Aeronautics (NACA, predecessor of NASA) was reportedly used by Bell Aircraft during its development of the supersonic X-1. In 1947, the same year that Chuck Yeager exceeded the speed of sound in the X-1, Miles Aircraft entered receivership, and the company was subsequently restructured. 

This feature originally appeared in the July 2015 issue of Aviation History. Subscribe today!



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