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All current Wills Wing models use 7075 aluminum in the leading edges, except for the Sport 2 175 and the Falcon Tandem. Why do these gliders use 6061 leading edges? The answer lies in understanding what is different between the two materials, along with what is not different. The 7075 T6 alloy is approximately 75% stronger than 6061-T6. This allows the designer to use 7075 in a thinner wall tubing, typically .035 inches instead of .049 inches, and thus achieve substantial weight savings - typically six lbs in an entire glider airframe. Because of this significant advantage, Wills Wing designer Steve Pearson pioneered the large scale production use of 7075 in hang glider airframes twenty years ago, when 6061 was the universal industry standard, an innovation that some manufacturers have only recently adopted, and in most cases only on their competition class gliders. At the same time, while 7075 is inherently much stronger than 6061, it has the same "modulus of eslaticity" or inherent material stiffness. As a result, a leading edge made to the same strength in 7075 will be, because of the thinner wall, somewhat more flexible than an equivalent strength, thicker wall, 6061 leading edge. In most design applications, this is not a problem. However, when designing a wing for the broadest possible range of load carrying capacity, the ability to retain aerodynamic performance and optimum handling qualities across a wide range of loadings can depend very significantly on the degree of stiffness of the airframe. The stiffer 6061 leading edges used on the Sport 2 175 and Falcon Tandem allow these gliders to preserve the designed wing shape more effectively to very high wing loadings, which in turn allows these gliders to more effectively retain their intended flight performance and handling qualities across their larger than normal range of recommended pilot weights.
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