Propellers And Governors

Propeller Principles

• Consists of two or more blades and a central hub to which the blades are attached.

• Propeller blades produce forces that create thrust to pull or push the airplane through the air.

Propeller Principles

• The engine supplies brake horsepower through a rotating shaft.

• The propeller converts the brake horsepower into thrust horsepower.

• Propeller efficiency is the ratio of thrust horsepower to brake horsepower.

• Propeller efficiency depends on how much the propeller “slips”.

Propeller Principles

• Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch.

Propeller Principles

• Geometric pitch is the distance a propeller should advance in one revolution.

• Effective pitch is the distance the propeller actually advances in one revolution.

Propeller Principles

• Propeller blade design

Propeller Principles

• Cross Section

(PITCH)

Propeller Principles

• Forces Acting On The Propeller

• Centrifugal• Twisting• Bending

Propeller Principles

• Forces Acting On The Propeller

CENTRIFUGAL THRUST BENDING TORQUE BENDING

AERODYNAMIC TWISTINGCENTRIFUGAL TWISTING

Propeller Operation

• The angle at which the air strikes the propeller blade is called the angle of attack.

• The air deflection produced by this angle causes the dynamic pressure behind the propeller blade to be greater than the atmospheric, thus creating thrust.

• The shape of the blade also creates thrust. As air flows past the propeller, the pressure on one side is less than that on the other.

• Aerodynamically, thrust is the result of the propeller shape and the angle of attack of the blade.

Types Of Propellers

• Fixed-Pitch Propeller

• Has the blade pitch, or blade angle, built into the propeller.

• One piece and constructed of wood or aluminum.

Types Of Propellers

• Fixed-Pitch Propeller

• Climb Prop (low blade angle)• All Purpose Prop• Cruise Prop (high blade angle)

Types Of Propellers

• Ground-Adjustable Propeller

• The pitch or blade angle can be changed only when the propeller is not turning.

• Operates as a fixed-pitch propeller

Types Of Propellers

• Controllable-Pitch Propeller

• Permits a change of blade pitch, or angle, while the propeller is rotating.

• Number of pitch positions may be limited, or the pitch may be adjusted to any angle between min and max.

• Lacks a propeller governor.

Types Of Propellers

• Constant-Speed Propeller

• A propeller governor is used to increase or decrease the propeller pitch.

• The governor is used to control the hydraulic propeller pitch-changing mechanism.

• The governor is geared to the crankshaft so it is sensitive to changes in RPM.

Types Of Propellers

• Constant-Speed Propeller

• As engine RPM increases blade angle increases thus decreasing RPM.

• As engine RPM decreases blade angle decreases thus increasing RPM.

Types Of Propellers

• Reverse-Pitch Propellers

• Blade angle can be changed to a negative value during operation.

• Used as an aerodynamic brake to reduce ground roll after landing.

Types Of Propellers

• Feathering Propellers

• Used on multi-engine aircraft to reduce propeller drag during engine failure conditions.

Types Of Propellers

• Tractor Propeller

• Mounted on the upstream end of a drive shaft in front of the supporting structure.

• Pusher Propeller

• Mounted on the downstream end of a drive shaft behind the supporting structure.

Constant-Speed Propellers

• Single-Engine

• Oil pressure from the governor usually increases blade pitch and centrifugal and aerodynamic pitching moments decrease blade pitch.

• Multi-Engine

• Oil pressure from the governor decreases blade pitch while centrifugal force acting on counterweights increases blade pitch.

Constant-Speed Propellers

• Pitch Change Mechanism

Constant-Speed Propellers

• Propeller Governor

Propeller Ice Control Systems

• Anti-Icing (Fluid) Systems

Propeller Ice Control Systems

• Electrical Deicing Systems