API's spiroid winglets on its Dassault Falcon 50 test-bed aircraft on AeroShell Square at AirVenture 2010

For the general public, winglets-those smaller vertical surfaces rising from the wingtips of airliners-have become a familiar sight. But they were slow to catch on and find a home in modern aircraft.

The idea was first promulgated by famed NASA aerodynamicist Richard Whitcomb, partly in response to the fuel crisis of 1973.

NASA didn't start testing prototype winglets (on a KC-135, the military tanker version of the Boeing 707) until 1979. Not everyone, however, was so patient.

A young engineer named Burt Rutan read the NASA report and made winglets an integral part of his VariEze, which wowed crowds and changed the whole course of the homebuilt movement, right here at Oshkosh-35 years ago, in 1975.

The purpose of winglets is to control the circulation of air around a wingtip, from the higher pressure below to the lower pressure above; when properly designed and configured, they can actually recover a significant amount of energy from this wingtip vortex-while at the same time making the vortex itself somewhat less of a threat to other following aircraft.

Burt Rutan has always been known for making the most efficient use possible of every element in his designs, so in the Ezes, as well as his later designs like the Defiant and the Beech Starship, the winglets serve the additional function of vertical stabilizers.

Beyond mainstream to the infinite wing
The Seattle, Washington, firm Aviation Partners Inc. pioneered and patented the ideal of "blended" winglets, in which the winglet flows smoothly up as a curved extension of the aircraft wing, rather than being attached at right angles.

Its winglets appeared initially on business jets, but they were soon adopted by airliner builders, most notably Boeing; in an era of ever-increasing prices for jet fuel, a savings of just a few percent in operating cost might mean the difference between an airline's financial success and failure.

This year, API is developing "spiroid winglets," an attempt to approach the Platonic ideal of an "infinite wing"-one with no energy-robbing wingtips at all.

To accomplish this, it's invented a winglet that curves up from the wingtip, then wraps inboard and around to reattach to the wing some distance inboard of the tip.

Recycled, refined, and perfected
Entire "wraparound" wings have actually been built and flown (as long ago as 1904, with the Bleriot Model III), but they aren't practical for high-speed aircraft.

API hopes that its new design can realize a significant improvement in performance and fuel economy over current winglet technology. At present it's in the flight-test stage, with the initial application planned for "one of the bigger bizjets."

If nothing else, the new winglets-with their delicately curved and beautifully polished surfaces-can rank as examples of the finest aviation sculpture.

You can see API's spiroid winglets on its Dassault Falcon 50 test-bed aircraft at the southeast corner of AeroShell Square. Just look for the big three-engine business jet with the strange-looking wingtips.