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Questions and Answers about Wills Wing Winglets

General Information
The Wills Wing Cross Country 155 has been HGMA Certified both with conventional wing tip fairings and with optional winglets. It is the first, and only glider to date to be HGMA certified with winglets. The Wills Wing winglets were originally designed by Wills Wing team pilot Jim Lee, and Jim put more than three years of flight testing and development into various winglet configurations before arriving at his final design. Wills Wing designer Steve Pearson developed the final production versions of the winglets, which are based on Jim’s design, and are further refined aerodynamically and optimized for economical large scale production. Below are some common questions and answers about the winglets.

The Winglets are no longer available, and further are not compatible with curved-tip gliders or any Wills Wing hang gliders not mentioned below. Pilots interested in increasing a glider's yaw stability should consider Wills Wing's Vertical Stabilizer.

Q) What are winglets?
A) Winglets are small vertical wings, attached at the extreme outboard end of the wing span.

Q) What do they do?
A) In theory, they inhibit the formation of wing tip vortices, which form due to circulation at the tip. As a result, they reduce induced drag and increase performance. We have observed improvements in performance from the winglets in controlled performance comparisons across the speed range. The same reduction in induced drag can be achieved by increasing the span of the wing, however increasing the span increases the structural demands on the wing, and slows down the roll rate. On a swept wing like a hang glider, winglets can also increase both pitch and yaw stability. The increase in yaw stability can also be a source of increased performance. In our flight testing of the Cross Country, the winglets also seem to make the glider more resistant to spinning.

Q) How are they installed?
A) The winglets attach to the tip of the sail in the same manner as the conventional wing tip fairings - there are velcro surfaces inside the tip of the sail, and on the outside surface of the winglet. The attachment is quite secure, and we have performed high speed vehicle and flight tests (speeds greater than 80 mph) without any incidents of the winglets becoming detached from the wing.

Q) How much do they weigh?
A) The final production winglets weigh just under 6/10s of a pound each. That is about 3/10s of a pound more than the conventional wing tip fairings. Other lighter, more expensive, and heavier less expensive winglets may be available in the future.

Q) Can they be used on other gliders?
A) The Winglets were designed for the Cross Country series of gliders and were fully HGMA certified (substantial additional vehicle and flight tests were done) on the 155 XC. They fit all sizes of the XC, and also fit both sizes of the RamAir, both sizes of the Fusion, and all three sizes of the Ultra Sport. We have flight tested them on all these models, and done vehicle testing as well on the Fusion 150, and have found the winglets to work well and provide the expected benefits on all of the above gliders. The HP AT and Super Sport models share the same size tip fairing as all the models listed above, and because of that the winglets can be attached to these models as well. However, the cut of the sail at the tip will not necessarily place the winglets at the optimum incidence angle on these models, and as a result they may not work as well. We have had reports from the field from pilots who have flown the winglets on HP AT's and Super Sports, and they have not reported any negative effects.

Last Modified: 12 November, 2002