In the late 1990s Aviation Partners Inc. (API), the developer of the blended winglet, began to flight test on a Gulfstream II a completely different winglet shape than anything that had flown before, the spiroid winglet. The original patent of the closed-loop shape winglet was originally filed in 1992 by one of API's founders. The basic idea of the spiroid winglet is to take the benefits of the blended winglet to their fullest by essentially bringing the blended winglet to loop back onto the wing. The vortices that stream off the wingtips of aircraft are a major source of drag and in the blended winglet, they have resulted in 5-7% increase in fuel efficiency by attenuating those vortices.
The first version of the spiroid winglets flown in the 1990s on the Gulfstream II were more circular in shape than the current incarnation. Flight testing of the first version resulted in refinements to the design that leads to more of an arch design with the inboard section of the spiroid moved farther aft and outboard to bring it closer to the wingtip vortex. The resultant design is now in flight testing on a Dassault Falcon 50 and the winglets and structural strengthening needed add 500 pounds to the empty weight of the jet. It was this Falcon 50 that made its first public appearance at the recent Oshkosh air show. Constructed of polished aluminum and approximately six feet in height, the new spiroids are not just intended to attenuate the wingtip vortex but to attempt to eliminate them altogether. Should this be the case, the leap in fuel savings and efficiency would be tremendous- on the order of 30% over the existing blended winglet design.
One of the side benefits of the spiroid winglet's possible ability to nearly eliminate the wingtip vortex would be in air traffic flow management at major airports. As it is right now, aircraft spacing is necessary to allow for wake vortex dissipation for the following aircraft. Aircraft with spiroid winglets would allow following aircraft to be spaced closer, in effect easing some of the congestion at major airports and improving flow efficiency.
The Dassault Falcon 50 testbed is to begin its formal flight test program this month to explore flutter, stability, and allow precise measurements of the degree of drag reduction. The aircraft will be initially limited to 250 KIAS and 0.70 Mach but as the tests progress, the flight envelope is anticipated to be expanded and may include icing tests.
Source: Aviation Week & Space Technology, August 2, 2010. "Head Turning Tip" by William Garvey, "Inside Business Aviation" column, p60.