Winglets - Making of A New Era

On November 30, 2011, Airbus test A320 took to the skies on a five-hour flight from Toulouse initiating an elaborate test schedule to validate the performance of its new pair of winglets called, the Sharklets. The test A320, fitted with Sharklets, was to study the aerodynamic behaviour of the new winglets and gather data for certification. Sharklets, the Airbus lingo for its new wingtip design for the Airbus A320 family, were launched in November 2009. The first aircraft fitted with these are slated for delivery to the launch customer Air New Zealand by the end of 2012. The 2.5-metre-tall winglets will replace the aircraft’s current wingtip fence. Offered as an option for newly-built aircraft, Sharklets have been specially designed for the Airbus A320 family to reduce fuel burn by up to an additional 3.5 per cent on long routes of around 3,000 nm.

Winglets: An Inspiration from Nature

The high pressure on the lower surface of the wing creates lateral airflow outwards or away from the fuselage towards the wingtip where on account of relatively lower air pressure above the wing, it tends to spill over and swirl around the wingtip to form a vortex creating additional drag described as “induced drag”, thereby reducing aerodynamic efficiency of the wing. NASA engineer Richard Whitcomb, who developed the supercritical airfoil, a fuelefficient wing design adopted for Airbus aircraft, is also credited with the development in the 1970s of aerodynamically efficient winglets that had a profound impact on the operating economics of airliners. In response to the 1973 oil crisis, NASA’s Aircraft Energy Efficiency (ACEE) programme sought ways to conserve energy in aviation. Whitcomb’s winglet design was predicted to reduce induced drag by approximately 20 per cent and improve the overall aircraft lift-drag ratio by six to nine per cent.

Winglets are small aerodynamic surfaces mounted almost vertically at the wingtips. Inspiration for the design came from birds observed to curl their wingtip feathers upward when in need of high lift. A well-designed winglet rises vertically and is swept back so that it significantly reduces the size of the wingtip vortex thus reducing induced drag.

Winglets: Their Evolution

In 1988, the Boeing 747-400 became the first airliner to fly with winglets (the design similar to Fig. 1A). In 1993, Dr Louis Gratzer, Professor of Aeronautics at the University of Washington, the erstwhile Chief of Aerodynamics for Boeing, filed a patent application for an aerodynamically effective winglet termed “blended winglet” which provides a smooth transition between the wing and the winglet (Fig. 1B). Highly blended winglets have demonstrated more than 60 per cent greater effectiveness over conventional winglets with an angular transition. Blended winglet technology made its debut in 1993, as a performance enhancement programme for the Gulfstream II by Aviation Partners Inc, a company established in 1991 at Seattle by Joe Clark and Montana businessman Dennis Washington.

Boeing’s attention was drawn to the fuel efficiency and range enhancement on the Gulfstream II leading to a joint venture with Aviation Partners Inc to develop blended winglets for Boeing airplanes. Boeing helped Aviation Partners pioneer the technology that is available as options on 737NG airplanes and as retrofit options on the older 737, 757 and 767 models. In 2000, Dr Fort F. Felker, a former NASA wind-tunnel researcher and expert in computational fluid dynamics, filed a patent for “elliptical winglets”, wherein the curvature of the winglets as they extend outwards from the intersection with the wings approximates part of an ellipse (Fig. 1C). This apparently ensures an elliptical distribution of lift both horizontally and vertically, resulting in lower induced drag. The very next year, Winglet Technology LLC was founded by Robert Kiser and Dr Fort Felker at Wichita, Kansas.

In 2002, a European Union funded four-year technology programme entitled Aircraft Wing with Advanced Technology Operation (AWIATOR) was launched with focus on reduction in drag, noise, aircraft wake and improved fuel consumption. It brought together 23 European manufacturers, universities and research institutes with Airbus contributing 60 per cent of the Euro 80 million budget. Very large wingtip devices which include winglets were also looked into by the programme and a resin film-infused composite winglet was test flown onboard an Airbus A340 in 2003. Flight testing was completed in early 2006.

Airbus A320: A Drive for Improvement

Airbus was working on an “A320 enhanced” which was to include winglets, an aerodynamic tidy-up (to the engine pylons, surge tank ducts and upper belly fairing), engine improvements, weight savings and a new cabin, all aimed at reducing fuel burn by four to five per cent with significant contribution by the winglets. Since this was in line with the activity at the Aircraft Wing with Advanced Technology Operation (AWIATOR) programme, in April 2006, after the results of the AWIATOR winglet that flew on the A340-300, Airbus tested similar angular winglets on its prototype A320 and another newly produced A320 that was meant for Jet-Blue (Image 1). Closely following these tests, in July 2006, Airbus began flight testing “elliptical winglets” from Winglet Technology LLC (Image 2). But in the October 2006, Airbus appeared somewhat unsure about the efficacy of winglets. The results of the latest tests on the A320 winglet indicated that although improvements were found in terms of cruise drag, the increase in structural weight that would be necessary to support the winglets largely offset the gain.

In late 2008, Aviation Partners Inc. and Airbus announced that blended winglets specially made for the A320 were being tested on the aircraft. In this design, the winglets had a unique shape (Image 3).

There was no further news of the test until in January 2010, when JetBlue provided an A320 for testing with winglets from Aviation Partners Inc. This time, however, the test conducted in the US, was between the airline and the winglet manufacturer with cooperation from Airbus and five per cent fuel savings was claimed to have been achieved.