Lesson 6: Propellers And Governors

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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 TWISTING
CENTRIFUGAL 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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