Winglet on Aircraft

Inspired from eagle's wings, winglets are applied on aircraft's wings. Same principle applies to eagles, winglets reduce wintip vortices, small wing vortex that formed at the wing tips due to air pressure difference. High pressure on the lower wing works its way up to the low pressure on the upper wing and curls around it. Having these vortices on the wings reduce flight efficiency and enhance drag. 

Winglets reduce drag and result in better cruising speed. Not only that, operators take advantage of this drag reduction by controlling cruising speed, reducing fuel consumption. In general, longer wings would generate better lift for aircrafts. However, longer wings would mean weight addition and it's not ideal. Installing winglets would result in same lifting force as longer wing would. The advantage is that wings with winglet would generate the same amount of lift force than ones with longer wings and without winglet. 

Winglets on aircraft reduce drag making flying more efficient. This include fuel saving up to 5% with carbon dioxide emission reduction up to 5%. The percentage may not be magnitude but 500,000 gallons of fuel is saved per airline per year just by adding winglets on aircraft's wings.

Reference

http://www.airspacemag.com/flight-today/how-things-work-winglets-2468375/
http://www.airspacemag.com/flight-today/how-things-work-winglets-2468375/