Lesson 6: 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 CENTRIFUGAL TWISTING AERODYNAMIC 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