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Wing Tip Drag Reduction Devices
From SKYbrary Wiki
Winglet / Wing Tip Fence / Raked Wing Tip / Blended Winglet
The intent of any Wing Tip Drag Reduction Device is to improve the efficiency of a fixed wing aircraft by reducing induced drag resulting from lift-induced wing tip vortices. By smoothing the airflow across the wing and reducing the wing tip vortex effects, the wing tip devices serve to increase lift production at the wing tip, reduce total drag, improve takeoff and climb performance, and reduce fuel consumption. A further benefit of wing tip devices is that they reduce the strength of wingtip vortices, which trail behind the aeroplane and pose a hazard to other aircraft.
Induced drag is an inevitable consequence of lift production. Air flowing over the top of a wing tends to flow inwards because the deceased pressure over the top surface is less than the pressure beyond the wing tip. Below the wing, the air flows outwards because the pressure below the wing is greater than that beyond the wing tip. A direct consequence of this differential pressure and airflow pattern is that there is a continual spilling of air upwards around the wing tip, a phenomenon referred to as "tip effect" or "end effect". Although wing tip devices do not eliminate tip effect, they reduce it considerably.
There are many different wing tip device configurations in production inclusive of winglet, blended winglet, wing tip fence and raked wing tip. Each designs has its own advantages with some providing the most benefit whilst in cruise while others help optimise takeoff and climb performance. Where possible, the design chosen for installation on a given aircraft will reflect the best option for the normal flight profile of the aircraft type. For example it is likely that the wing tip devices chosen for a long range aircraft would be of a design providing optimum cruise performance.