They were aluminium
Titanium or composites. There are also steel and aluminum rotors.
The rotors are used for lift and thrust on a helicopter.
The first helicopter was made in 1909.
Just looking at the gyrations of the helicopter rotors made me dizzy.
The first Helicopter was made by Igor Sikorsky, in 1939.
No, the first practical helicopter was made in 1941.
Rotating rotors on a helicopter create lift by generating airflow over the blades, allowing the helicopter to take off, hover, and maneuver in different directions.
Because at present rotors are more efficient
it is probably 1-3 feet depending on the helicopter
READ THIS - GOOD INFORMATION The wings of an airplane and the rotors of a helicopter both help the object fly. Without those the object could not fly because the wings of an airplane have wind going past it which keeps the airplane in the air. The rotors of a helicopter spin in the wind and help the helicopter fly.
That is the Chinook.
The rotor blades on a helicopter work the same way as wings on a fixed wing aircraft. The air passing faster over the top of the airfoil generates lift. Helicopter rotors spin so that the lift is generated without having to have forward airspeed like a fixed wing aircraft.