Propeller Notes

Shaft Force and Torque

• Shaft force is brake horsepower converted to thrust by the propeller.

• Torque, measured by a torque meter, indicates shaft force.

Propeller Types

• Fixed propellers: Blade angle is constant.

• Variable propellers: Blade angle (pitch) can be adjusted.

Propeller Nomenclatures

• Angle of Attack: Angle between the chord line and the relative wind.

• Blade Angle/Pitch: Angle between the blade and the plane of rotation.

• Effective Pitch: Actual distance the propeller moves forward in one cycle.

• Geometric Pitch: Theoretical distance the propeller should move forward in one cycle (effective pitch + slippage).

Propeller Anatomy

• Leading Edge: Front edge of the propeller blade.

• Tip: Outermost point of the propeller blade.

• Trailing Edge: Rear edge of the propeller blade.

• Shank: The part of the blade near the hub.

Wooden Propeller Maintenance

• Metal Edge: A metal strip protects the leading edge of wooden propellers.

• Drain Holes: Small holes (1/16 inch (\approx 1.6 \text{ mm})) to relieve moisture inside the wood.

• Balancing: Solder is added to the metal tipping for balancing.

• Cracks: Cracks in the tip indicate a major repair is needed.

• Bolt Holes: Oversized or elongated bolt holes in the center hub indicate rejection.

• Sprout Bone Tightness: Check after the first flight and then after 25 hours.

• Coating: Coating applied for final balancing.

Forces Acting on a Propeller During Flight

• Aerodynamic Twisting Force: Pushes the propeller to a lower pitch.

• Centrifugal Twisting Force: Pushes the propeller to a higher pitch; usually greater than aerodynamic twisting force.

  • Centrifugal Twisting Force = Moment

• Centrifugal Force: Tries to pull the propeller apart from the center.

• Torque Bending Force: Bends the propeller tips.

Variable Pitch Propellers

• Used to optimize performance during attitude changes and varying flight conditions.

• Early designs used forces acting on the propeller to counteract hydraulic pressure applied through a three-way propeller valve.

• Basic Positions:

  • Low Pitch

  • High Pitch

  • Reverse Pitch (past low pitch)

  • Feather (past high pitch)

  • Unfeather

Hamilton Standard Counterweighted Propeller

• Utilizes counterweights and a three-way propeller valve.

• Centrifugal force acting on the counterweights pushes the blade angle to high pitch.

• Oil pressure causes the blade pitch to go to low pitch.

• Smaller blade angle means smaller "bites" of air = less load on the engine.

Propeller Governor

• Replaces the three-way propeller valve for automatic pitch adjustment.

• Maintains a specific speed (RPM) set by the pilot, compensating for changes in flight attitude.

Propeller Governor Components

• Speed Adjusting Control Lever & Shaft: Connected to the propeller control lever.

• Drive Gear Shaft: A solid shaft spun by the engine's reduction gearboxes, crankshaft, or turbine rotors; contains a pilot valve in the middle.

• Flyweights: Spinning masses that exert centrifugal force.

• Speeder Spring: Counteracts the centrifugal force of the flyweights; located inside the prop governor.

  • Tension expands or retains the spring's position.

  • Compression squeezes the spring.

• Oil Boost Pump (Idler Gear): Increases oil pressure; located inside the prop governor.

• Relief Valve: A safety feature that releases excessively high oil pressure.

Propeller Governor Operation

• Manufacturers may rename components, but their purpose remains the same.

Overspeed Condition

• Engine speed exceeds the set speed.

• Drive shaft spins faster.

• Flyweights spin faster, increasing centrifugal force.

• Speeder spring compresses.

• Pilot valve moves, redirecting oil flow.

• Blade angle increases to a higher pitch, slowing the engine.

Underspeed Condition

• Engine speed is lower than the set speed.

• Drive shaft spins slower.

• Centrifugal force on the flyweights decreases.

• Speeder spring pushes flyweights inward.

• Pilot valve moves, redirecting oil flow.

• Blade angle decreases to a lower pitch, increasing engine RPM.

Equilibrium

• Flyweights and speeder spring are balanced.

• Pilot valve is in the bypass oil position.

Hamilton Standard Counterweighted Propeller Operation Examples

Setting High RPM (e.g., 2500 RPM)

1. Move the prop control lever forward.

2. Speeder spring rotates to the right, expanding.

3. Flyweights move inwards.

4. Pilot valve moves down, opening the oil path from the sump to the hub.

5. Oil pressure increases in the hub.

6. Cylinder moves forward, decreasing blade angle to low pitch.

7. RPM increases.

8. Flyweights equalize, and the pilot valve closes the oil path from hub to sump.

9. Bypass oil; on-speed, high RPM.

Underspeed Condition

1. Flyweights move inward.

2. Speeder spring expands.

3. Pilot valve moves down.

4. Oil pressure goes inside the hub, increasing oil pressure.

5. Flyweights move back to equilibrium.

6. Pilot valve closes the path from sump to hub, resulting in bypass; back to on-speed.

Setting Low RPM (e.g., 500 RPM)

1. Pull the lever back.

2. Speeder spring screw rotates to the left, compressing the speeder spring.

3. Flyweights move outward.

4. Pilot valve moves up, opening the oil supply from the hub to the sump.

5. Decreasing oil pressure.

6. Centrifugal force acts more on the counterweights.

7. Blade angle goes to high pitch, resulting in low RPM.

8. Centrifugal force decreases.

9. Flyweights equalize.

10. Pilot valve moves down, closing the path of oil from hub to sump.

11. Bypassed on-speed low RPM.

Overspeed Condition (Automatic Correction)

1. Flyweights move outward.

2. Speeder spring compresses.

3. Pilot valve moves up, opening the oil path from hub to sump.

4. Centrifugal force on counterweight experiences more force.

5. Blade angle goes to a high pitch, lowering speed.

6. Decreased centrifugal force of flyweights.

7. Pilot valve starts going down, blocking the flow of oil from hub to sump.

Flight Operations and Propeller Settings

• Consult the engine/aircraft operating manual for specific procedures.

• Propeller settings must be configured for:

  • Takeoff (High RPM)

  • Cruising

  • Power Descent

  • Approach

  • Landing

• The propeller governor maintains constant RPM between these phases.

Oral Review Questions

• Static Propeller Position: Vertical and Horizontal on the arbor.

• Balanced Forces in On-Speed Condition: Speeder spring and flyweights.

• Effect of Centrifugal Force on Counterweights: Increase propeller blade pitch to high pitch.

• Oil Loss Impact: Might cause feathering by going past high pitch.

• Oil Pressure Issues: Could be related to the relief valve not being properly adjusted or if the oil temperature is too high.

• Three Functions of a Typical Governor:

  • Boost oil pressure via an oil boost pump.

  • Control the amount of oil flowing to the propeller (pilot valve).

  • Sense the rotational speed (flyweights).

Non-Counterweighted Propellers

• Takeoff configuration: Low pitch, high RPM.

• Constant reminder: Different types of propeller governance, which changes in propeller control lever.

• Utilizes a single-acting propeller the governor by use of Oil pressure.

Feathering Spring

• Piston spring (another nomenclature).

• Used in single-acting propeller governor.

McCauley Propeller

• Non-counterweighted, non-feathering, constant-speed propeller.

Setting High RPM

1. Move the propeller control lever forward.

2. Rotate the speeder spring screw to the right.

3. Speeder spring compresses and the flyweight moves inwards.

4. Hub to sump opens.

5. Spring and piston to move more forward.

6. Low pitch and increases RPM.

7. Centrifugal and Force Increase , equilibrium the high RPM.

8. Butterfly move up and bye pass

Underspeed Condition

1. Pilot does not move lever

2. Hub to sump draining more oil.

3. Pushing to low angel and high rpm

4. Equilibrium and By-passing.

Low RPM

1. Pull back the proplever.

2. the rotations will rotate to the left tossing speeder spring.

3. Pushing the flyweight outward

4. moving the violet valve up.

5. Piston and spring to pushing

6. Up- pitch equals low RPM