Why do helicopter blades bend during flight?
Spinning at up to 500 RPM, helicopter blades bend and flex during flight due to a constant battle between aerodynamic lift, centrifugal force, and a dynamic motion known as flapping.
Massive lifting forces
As the helicopter rotor spins rapidly, it generates a massive amount of upward lift across the entire surface of the blades. This immense lifting force physically pushes the flexible blades upwards, pulling the entire weight of the heavy aircraft against the pull of gravity.
Centrifugal force counters lift
While aerodynamic lift pulls the rotor blades upwards, the spinning motion creates an immense outward centrifugal force. This centrifugal force pulls the blades straight out horizontally from the central hub, constantly fighting against the upward pull of the generated lift.
The coning effect
Because lift pushes the blades up and centrifugal force pulls them outward, the blades settle into a compromise position. They bend slightly upwards at the tips, creating a shallow V-shape during flight. Aviation engineers refer to this steady upward bending as rotor coning.
Dissymmetry of lift
When flying forward, the blade advancing into the wind moves much faster through the air than the retreating blade on the opposite side. This creates a dangerous imbalance called dissymmetry of lift, where one side of the helicopter generates significantly more lift than the other.
Flapping balances the aircraft
To stop the helicopter from rolling over, the blades are designed on hinges to naturally flap up and down. The advancing blade flaps up, reducing its angle of attack and shedding excess lift, while the retreating blade flaps down to increase lift, balancing the aircraft perfectly.
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