Lesson 6: Propellers And Governors

1. Lesson 6: Propellers And Governors

2. 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.

3. 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”.

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

5. 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.

6. Propeller Principles • Propeller blade design

7. Propeller Principles • Cross Section (PITCH)

8. Propeller Principles • Forces Acting On The Propeller • Centrifugal • Twisting • Bending

9. Propeller Principles • Forces Acting On The Propeller CENTRIFUGAL THRUST BENDING TORQUE BENDING AERODYNAMIC TWISTING CENTRIFUGAL TWISTING

10. 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.

11. 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.

12. Types Of Propellers • Fixed-Pitch Propeller • Climb Prop (low blade angle) • All Purpose Prop • Cruise Prop (high blade angle)

13. 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

14. 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.

15. 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.

16. 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.

17. 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.

18. Types Of Propellers • Feathering Propellers • Used on multi-engine aircraft to reduce propeller drag during engine failure conditions.

19. 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.

21. 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.

22. Constant-Speed Propellers • Pitch Change Mechanism

23. Constant-Speed Propellers • Propeller Governor

25. Propeller Ice Control Systems • Anti-Icing (Fluid) Systems

26. Propeller Ice Control Systems • Electrical Deicing Systems