Blade Design
The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape which minimises drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout to reduce the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. Rotor blades are made out of various materials, including aluminium, composite structure and steel or titanium with abrasion shields along the leading edge. Rotorcraft blades are traditionally passive, but research into active blade control trailing edge flaps is performed.
The tips of some blades found in helicopters can be especially designed to reduce turbulence and thus also noise (and also allow the helicopter to fly more efficiently). An example of such tips are the tips of the BERP_rotor.
Read more about this topic: Helicopter Rotor
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