Ahsanullah University of Science & Technology Department of Mechanical & Production Engineering

Design Analysis of Winglets

When an aircraft takes off, high pressure air from the bottom of aircraft’s wing escapes around the wingtip, moving up towards the lower pressure area on the top of the wing. This movement creates a vortex or tunnel of air, rotating inwards behind the wing. They're strongest when the air pressure difference between the top and the bottom of the wing is the greatest. This occurs when the aircraft is at high angles of attack which generates the most induced lift.

Fig: Vortex Generation.

Aircraft wing generates lift perpendicular to the relative wind. The wingtip vortices curve up and around the wingtips, pushing the air flowing over the wing downward. That angles the relative wind downward and tends to tilt the wing making the lift backward which as a result turns some lift into drag.

Fig: Change of angle due to wingtip vortices.

This causes two problems – some of lift is now pointing backward, adding to drag. And as the backward lift increases and adding drag, the counter weight increases. So, to maintain level flight, it is needed to increase angle of attack and generate more lift. And generating more lift means generating more induced drag. This extra angle of attack you need is called the induced angle of attack.

Winglets are vertical projection on the tip of an aircraft wing for reducing drag. It helps to prevent the formation of vortices and thus eliminating the alteration of airflow behind the wing. But total prevention of vortices is not possible. So, it moves the downward vortices up, over the wing and creates weaker vortices to reduce drag.

Fig: Comparison of Vortex Generation

Fig: Different popular winglets, A. the conventional winglet, B. a blended winglet, C. an elliptical winglet

The purpose of this thesis is to study on different types of winglets and to compare between their performance on reducing drag and to develop a conceptual winglet design in a simulation software.