What is the purpose of winglets?
Refer to figure.
INDUCED DRAG
Whenever a wing produces lift, concentrated vortices form at the wing tips. The vortices are strongest at the wing tips and become progressively weaker toward the centre-line of the aircraft.
It is the production of lift itself which reduces the magnitude of the lift force being generated. To replace the lift lost by the increased downwash, the aircraft must be flown at a higher angle of attack. This increases drag. This extra drag is called induced drag.
The stronger the vortices, the greater the induced drag.
Wing tip modifications reduce the leakage of airflow around the wing tip and limit the size of the vortex.
WINGLETS
These are small vertical aerofoils which form part of the wing tip. Shaped and angled to the induced airflow, they generate a small forward force. Winglets partly block the air flowing from the bottom to the top surface of the wing, reducing the strength of the tip vortex.
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