Blade pitch
Encyclopedia
Blade pitch or simply pitch refers to turning the angle of attack
of the blades of a propeller
or helicopter
rotor
into or out of the wind to control the production or absorption of power. Wind turbine
s use this to adjust the rotation speed and the generated power. A propeller
of a ship uses this effect to control the ship's speed without changing the rotation of the shaft and to increase the efficiency of streaming fluids.
In aircraft, blade pitch is usually described as "coarse" for a high angle of attack, and "fine" for a low angle of attack.
Blade pitch is normally described in units of distance/rotation assuming no slip.
Blade pitch acts much like the gearing of the final drive of a car. Low pitch yields good low speed acceleration (and climb rate in an aircraft) while high pitch optimizes high speed performance and economy.
Because the velocity of a propeller blade varies from the hub to the tip, they must be of twisted form in order for the pitch to remain constant along the length of the blade. This is typical of all but the crudest propellers.
It is quite common in aircraft for the propeller to be designed to vary pitch in flight, optimizing both cruise and takeoff performance.
s the pitch control changes the angle of attack of the rotor
blades and thus the vertical acceleration or climb rate of the vehicle. This control is also called collective as opposed to the cyclic control for lateral movement. The collective blade setting is mostly achieved through vertical movement of the swashplate
.
s have interchangeable blades, which enables the blade pitch to be adjusted. Changing the blade pitch in different elevations can be very beneficial to a boater. Typically, using a lower pitch will provide better acceleration and a higher pitch enables better top end speed.
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
of the blades of a propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
or helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...
into or out of the wind to control the production or absorption of power. Wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
s use this to adjust the rotation speed and the generated power. A propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
of a ship uses this effect to control the ship's speed without changing the rotation of the shaft and to increase the efficiency of streaming fluids.
Aircraft
Blade pitch is normally described in units of distance/rotation assuming no slip.
Blade pitch acts much like the gearing of the final drive of a car. Low pitch yields good low speed acceleration (and climb rate in an aircraft) while high pitch optimizes high speed performance and economy.
Because the velocity of a propeller blade varies from the hub to the tip, they must be of twisted form in order for the pitch to remain constant along the length of the blade. This is typical of all but the crudest propellers.
It is quite common in aircraft for the propeller to be designed to vary pitch in flight, optimizing both cruise and takeoff performance.
Helicopter
In helicopterHelicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
s the pitch control changes the angle of attack of the rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...
blades and thus the vertical acceleration or climb rate of the vehicle. This control is also called collective as opposed to the cyclic control for lateral movement. The collective blade setting is mostly achieved through vertical movement of the swashplate
Swashplate (helicopter)
A swashplate is a device that translates input via the helicopter flight controls into motion of the main rotor blades. Because the main rotor blades are spinning, the swashplate is used to transmit three of the pilot's commands from the non-rotating fuselage to the rotating rotor hub and...
.
Feathering
Feathering the blades of a propeller means to minimize their angle of attack by turning the blades to be parallel to the airflow. This minimizes drag from a stopped propeller following an engine failure in flight. Stopped propeller's blade relative wind comes strictly from the forward motion of aircraft through the air. Rotating propeller's blade relative wind comes mainly from rotational speed of the blade vector summed with the aircraft forward motion.Wind turbines
Blade pitch control is a feature of nearly all large modern horizontal-axis wind turbines. While operating, a wind turbine's control system adjusts the blade pitch to keep the rotor speed within operating limits as the wind speed changes. Feathering the blades stops the rotor during emergency shutdowns, or whenever the wind speed exceeds the maximum rated speed. During construction and maintenance of wind turbines, the blades are usually feathered to reduce unwanted rotational torque in the event of wind gusts.Boating
Some composite propellerComposite propeller
Composite propellers are made of an extremely strong, high-tech material. These propellers are produced using an injection molding process, which guarantees a high quality propeller every time. The composite propeller is a lightweight and environmentally friendly boat propeller...
s have interchangeable blades, which enables the blade pitch to be adjusted. Changing the blade pitch in different elevations can be very beneficial to a boater. Typically, using a lower pitch will provide better acceleration and a higher pitch enables better top end speed.