lesson 6: propellers and governors. propeller principles consists of two or more blades and a...
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Lesson 6: Propellers And Governors
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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.
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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”.
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Propeller Principles
• Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch.
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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.
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Propeller Principles
• Propeller blade design
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Propeller Principles
• Cross Section
(PITCH)
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Propeller Principles
• Forces Acting On The Propeller
• Centrifugal• Twisting• Bending
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Propeller Principles
• Forces Acting On The Propeller
CENTRIFUGAL THRUST BENDING TORQUE BENDING
AERODYNAMIC TWISTINGCENTRIFUGAL TWISTING
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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.
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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.
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Types Of Propellers
• Fixed-Pitch Propeller
• Climb Prop (low blade angle)• All Purpose Prop• Cruise Prop (high blade angle)
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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
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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.
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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.
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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.
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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.
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Types Of Propellers
• Feathering Propellers
• Used on multi-engine aircraft to reduce propeller drag during engine failure conditions.
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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.
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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.
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Constant-Speed Propellers
• Pitch Change Mechanism
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Constant-Speed Propellers
• Propeller Governor
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Propeller Ice Control Systems
• Anti-Icing (Fluid) Systems
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Propeller Ice Control Systems
• Electrical Deicing Systems
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