How are helicopter blades designed?
Air flows more slowly at the hub of a rotor, than at the faster moving tip. That’s achieved by making the rotor with a twist along its length. Aerodynamics determines the optimum design, as the angle of attack increases, the flow above an aerofoil becomes turbulent. This increases drag and reduces lift.
What is a rotorcraft with unpowered blades called?
An autogyro (sometimes called gyrocopter, gyroplane, or rotaplane) utilizes an unpowered rotor, driven by aerodynamic forces in a state of autorotation to develop lift, and an engine-powered propeller, similar to that of a fixed-wing aircraft, to provide thrust. The autogyro was invented in 1920 by Juan de la Cierva.
Why do you need so many blades on a helicopter?
The blades, like wings, affect air to a significant distance above and below them, so you don’t need many blades to use all air within the rotor area. But no matter how many blades you add, they will still only affect the air within the rotor area, so the efficiency won’t change much.
Why are longer rotors better for a helicopter?
My understanding of helicopters is that, despite theoretically increasing efficiency, longer blades are worse in practice than short ones in every respect (except, perhaps, cost): Longer blades are more prone to vibration and resonance dynamics, if for no reason other than that their rigidity is reduced by length, holding all else constant.
What was the first helicopter with fixed rotors?
One of the first helicopters was the Petróczy-Kármán-Žurovec PKZ 2 Helicopter, fitted with two contrarotating, coaxial rotors that had fixed blades, with no provisions for flapping or pitch change:
Can a rotor system have more than two blades?
However, from the day of that accident, lead lag hinges were used on all rotor systems with more than two blades. Even in rigid rotor systems in which the blades are supposed to be mounted rigidly at the hub, a small amount (0.5 to 1.0 degrees) of lead and lag must be allowed.