Winglets

Winglets

Supercritical airfoils and winglets reshaped commercial aircraft, in the same way delta wings and relaxed stability became common characteristics of combat aircraft. 

The drag-reducing winglet is another aerodynamic improvement now widespread across airliner fleets. It reduces vortex-induced drag by diffusing the tip vortex flow downstream of the wingtip and increases lift at the wingtip by inhibiting the flow of higher-pressure air below the wing to lower-pressure air above. 

Developed initially in response to the 1973 oil crisis, NASA flight tested a Whitcomb-designed winglet on a Boeing KC-135 in 1979. In 1988, a similar-looking feature debuted on the Boeing 747-400. 

Airbus, meanwhile, adopted a lower-profile, end-plate wingtip device that projected above and below the end of the wing. The shape was first introduced on the A310-300 and A320 and in a much larger form, on the A380. 

McDonnell Douglas also tested a form of bifurcated winglet on a DC-10 in 1981 and introduced a 7-ft. tall upper winglet with lower vane on the MD-11 in 1990. 

Larger elliptical or blended winglets are now commonplace on Airbus and Boeing aircraft, though all-new wing designs on the 787, 747-8, 777 and 777X feature raked tips.