Graham Warwick

Some are small, some are big, Airbus¹s are a different shape and some Boeings have them and some don¹t. Ever wondered why?We¹re talking about winglets, of course, and the answer is a combination of style and substance.

Winglets were first developed in the 1960s by NASA aerodynamicist Dr Richard Whitcomb. He had the idea of putting cambered and twisted endplates on a wing to improve its efficiency without increasing its span. Whitcomb also developed the "Coke bottle" area ruling that allows fighters to go supersonic and the supercritical aerofoil that allows transports to fly efficiently at high subsonic speeds.

Winglets reduce the component of drag that is generated by lift, but increasing wing span can achieve the same effect, so designers have a choice to make. Boeing used winglets on the 747-400 because its wing couldn¹t get any longer and still fit airport gates. Learjet first used them to make its business jets look more modern, starting an enduring fashion.

Boeing decided winglets did not offer any advantage on its all-new 777, and for the stretched 767-400ER making its debut here at the show it developed a unique raked wingtip. This increased efficiency without incurring the weight penalty of strengthening the wing to take winglets.

Boeing is leaning toward raked tips for the stretched 747X, but is still evaluating winglets. Under a joint venture with Aviation Partners, Boeing is flight testing 4.4m-tall blended winglets on a 747-200F. These are bigger versions of the winglets fitted to the Boeing Business Jet here at the show and now offered on Next Generation 737s.Seattle-based Aviation Partners says the smoothly curved transition from wing to winglet makes its design more efficient. More than 100 Gulfstream II owners have already retrofitted their aircraft with blended winglets, which will be available next year for Hawker business jets. Dassault Falcons could follow.

Beginning next year, the Aviation Partners Boeing joint venture plans to offer blended winglets for retrofit to "classic" 737s and 747s.Airbus, meanwhile, has added "wingtip devices" to its A3XX large airliner. First seen on the A310 and fitted across the A320-family aircraft, these dart-like devices don¹t improve wing efficiency quite as much as winglets, but behave more predictably "off design", Airbus argues.

Bombardier, starting with the Challenger, has now adopted winglets across its entire range of business and regional jets, and Embraer has revealed that its new ERJ-170/190 regional jet will have blended winglets - similar to those on the airborne early warning version of its ERJ-145.No-one seems immune from the lure of winglets, even nature. Three decades after Whitcomb invented winglets, scientists discovered that flying squirrels raise the tips of their "wings" as they glide from tree to tree. Unfortunately, there are no squirrels in the flying display to demonstrate.

Source: Flight Daily News