Flying Flea Designs Taming the tandem wing requires analysis of the airplane’s stability he first time I saw it was shortly after I arrived at Oshkosh 1976: a tail- less, biplane glider being pushed aloft by a noisy two-stroke engine. John Moody was making the first large-scale public demonstration of his powered Icarus II. The ultralight era had begun. As a teenager with limited financial means, I thought I’d found a T way I could afford to fly. Enthusiasm for ultralights increased yearly as more people, many of whom had never been involved in aviation, Neal Willford also saw the ultralight as their only means of experiencing affordable flight. The ultralight’s popularity continued to increase until December 1983, when the infamous 20/20 episode question- ing its safety and lack of regulation dealt a near-fatal blow to the industry. The past 20 years has shown that ultralight critics were wrong, but the magic was gone, and the ultralight movement was never the same. That was not the first time in aviation history that the bubble had burst on an entire type of airplane. Seventy years ago a Frenchman named Henri Mignet set out to design a safe, easy-to-fly airplane “for the masses.” It caught on like wildfire in Europe and soon was being built in great numbers around the world. Unfortunately, a rash of fatal accidents due to a design flaw in its original configuration resulted in the flying public dropping it like a hot potato—even after the problem had been corrected. Mignet designed KOEPNICK many more airplanes during the rest of his life, but JIM they never achieved large-scale acceptance again. 50 NOVEMBER 2004 050-057 Flea 411.indd 2 10/12/04 10:28:10 PM KOEPNICK JIM Mignet tirelessly promoted his “formula,” as he called it, through- out his life, with the idea evolving through design and technological changes through the years. A spreadsheet for estimating the stability, control, and performance of this unique style of airplane is available to download from the EAA Sport Aviation page on the EAA website at www.eaa.org. Historical Overview Two key features of Mignet’s formula, a pivoting wing for pitch control and the tandem wing arrangement, were invent- ed prior to his involvement in aviation. Octave Chanute, who mentored the Wright brothers during their formative years in aviation, once said he believed the Wrights would succeed in their attempt to fly, but he was afraid that it would not be “in the best way.” Chanute felt the main wing should pivot for pitch control instead of using a separate control surface, as the Wrights were using. He even had a glider with a “rocking wing” built and sent to the Wrights at Kitty Hawk so they could fly it along- side their glider design for comparison. There is no record the Wrights flew that glider, but a mutual friend of Chanute and A smiling Henri the Wrights, Dr. George Spratt, continued developing the pivoting wing Mignet in his HM-14 concept as an alternative means for pitch control. Eventually his son Flying Flea. followed suit and designed a variety of control wing airplanes. Samuel Langley first used the tandem wing arrangement successfully. By flying a powered model in 1896, Langley had shown that powered flight was feasible, and he felt his contribution to aviation was complete. However, President McKinley asked Langley to get funds from the U.S. EAA Sport Aviation 51 050-057 Flea 411.indd 3 10/12/04 11:02:30 PM Army to develop a man-carrying high-wing parasol design, was his problem with a vengeance during version. He did so, and two flight first successful airplane. In 1928 several years of experimenting and attempts of the Aerodrome “A” in he published a book and series of eventually adopted a short-coupled October and December 1903 ended magazine articles describing how tandem wing arrangement. in failure. to build it. His design became a The design was driven in part Langley abandoned his aeronau- huge success among the French, to keep the wingspan and overall tical experiments and just nine and eventually 200 were built. length down. His reason was a days later those two brothers from Though Mignet had succeeded practical one. He wanted custom- Ohio succeeded. in designing a popular airplane, ers to be able to build it in small Henri Mignet’s interest in avia- he had a problem: He couldn’t apartment rooms, where he envi- tion was piqued on the other fly. Mignet had tried and tried sioned many would be built if the side of the Atlantic by the Wright to learn, but he could not master design proved successful. brothers’ flights in France during the three-axis control system. His And successful it was. His 14th the summer of 1908. He started attempts at turns with his instruc- design (the HM-14) was completed experimenting with hang gliders tor would invariably end in a in September 1933 after a one- before World War I engulfed the spin. It was a crash in his HM-8 month building time. The tandem continent. He was a radio opera- that finally convinced him that wing design did not have aile- tor in the Signal Corps during the he needed to design an airplane rons, but relied on a large rudder war, and after the war he made a incapable of a stall/spin. and wing dihedral to accomplish living making radios. He started What Mignet lacked in flying turns. pursuing his aeronautical inter- ability, he more than made up Its biggest deviation from con- ests on the side. for in enthusiasm and persever- ventional aircraft was that the The HM-8, a conventional ance. He attacked the stall/spin front wing pivoted for pitch con- trol. Mignet’s “living wing” was similar in concept to the pivoting ONE CHORD MINIMUM wing promoted by Chanute and (MEASURED FROM 25% CHORD) Spratt 30 years earlier. FRONT WING TRAVEL Mignet reasoned that pivot- ing the wing gave the pilot more HINGE POINT (0 TO 12 DEGREES) (AHEAD OF 25% CHORD) immediate control over pitch than COSANDEY FLAP TRAVEL a separate control surface could 25% CHORD MINIMUM SEPARATION (0 TO 20 DEGREES UP) provide, regardless of whether that surface was a canard or conven- tional tail. He never referred to REAR WING INCIDENCE (6 DEGREES) his unconventional creation as an NACA 23112 AIRFOIL USED ON BOTH WINGS “aeroplane” in his book, but as a powered kite. Figure 1. Historical guidelines for the Flying Flea “Formula.” The HM-14 was further refined over a two-month period, which culminated in Mignet’s first solo flight that included turns. He flew for another 10 hours before return- ing to Paris to write a book detail- ing the new design and to mar- ket plans for others to build their ORIGINAL FLYING FLEA AIRFOIL own. His book was a huge suc- cess, and soon many Frenchmen were building their own copy of Mignet’s Le Pou du Ciel. The lit- eral English translation for this is The Sky Louse, but when his book was translated into English, it was NACA 23112 AIRFOIL USED ON LATER FLEAS dubbed The Flying Flea. Soon Fleas were being built in Figure 2. Comparison of airfoils used on Mignet Flying Fleas. Note very England and other English-speak- sharp leading edge on Mignet’s original Flea airfoil. ing countries. With hundreds 52 NOVEMBER 2004 050-057 Flea 411.indd 4 10/12/04 10:42:06 PM being built worldwide, it is not conventional designs. On Mignet’s ing. This is a useful benefit, because surprising that some were involved Fleas, this ratio was as low as 1- most Fleas have short wingspans in accidents, but between the sum- to-1, indicating that the aircraft’s and small engines. mers of 1935 and 1936 there were horizontal tail would need to be There is no free lunch, however, 11 fatalities involving the Flea. 2.5 to 3 times as large for a given and the rear-lifting wing imposes a Full-size examples were put into level of stability. drag penalty. While producing lift, wind tunnels in both France and Making an airplane’s horizontal the forward wing deflects the air England, and the testing showed tail larger increases its static sta- passing around it downward. The the design’s problem and how to bility and can allow the CG limit rear wing flies in this downwash fix it. English authorities decided to move further aft. This was the and therefore has to continually they would no longer issue flight case with Mignet’s HM-14, which “climb” in this sinking air. This permits for Fleas in the original according to his book had a rec- results in the induced drag of the configuration, and the flying pub- ommended CG of 41 percent MAC rear wing being about three times lic lost faith in the design. The Flea (based on the front wing’s chord). higher than if it were flying in was effectively grounded. His later designs had an aft CG undisturbed air. Though devastated by the turn of 50 percent MAC, and conse- The additional drag can be high of events, Mignet not only per- quently, an even larger tail. Mignet enough to offset the increase in severed with implementing the and his followers typically used the rate of climb due to the lower needed fixes, but continued to same airfoil and chord width on span loading on the forward wing.