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Torque
- resistance to motion in the plane of rotation.
Engine Torque
- Torque Produced by the engine, force that turns the propeller
Propeller Torque
- Caused by drag of the propeller blades, opposes propeller rotation
Principles:
- The combination of the forward velocity and rotational velocity creates a
helical motion of the propeller through the air.
Brief 25
RMIT Flight Training Propellers
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 2
- The tip travels fastest due to greater distance travelled in same time. Root
travels slowest. Therefore varying lift (thrust) forces.
- To even out forces, blade is twisted to compensate. Blade angle at hub needs
to be much greater than blade angle at tip.
- Geometric pitch is how far the propeller would theoretically advance in one
revolution.
- Effective pitch is how far the propeller actually advances in one revolution.
- The difference between geometric and effective pitch is called slip.
Considerations:
Propeller Damage
- usually occurs first on leading edge, cause it hits the air first.
- avoid high power settings on loose surfaces like gravel.
Propeller Fatigue
- most likely to occur on blade face.
Brief 25
RMIT Flight Training Propellers
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 3
Efficiency
- fixed-pitch propellers are most efficient at only one airspeed and RPM
combination. The C172 is fitted with a cruise prop.
Airmanship:
- Always perform thorough pre-flight inspections on the propeller.
- Handle the engine smoothly.
- Low power settings on ground to avoid damage.
Brief 25
RMIT Flight Training Propellers
Propellers Mass Brief
Aim
• To gain an understanding of the principles
and forces acting on a propeller in flight.
Application
• All stages of flight where thrust is required
Overview
• Definitions
• Principles
• Considerations
• Air Exercise
• Airmanship
• Review
Definitions
• Blade
– An aerofoil which converts engine power into thrust.
• Blade Face
– The flat side of the blade (the side the pilot sees).
• Blade Back
– The cambered side of the blade.
• Blade Angle
– The angle between the blade chordline and the plane of rotation.
Spinner
Direction
of flight
Blade
Angle
Plane of
rotation
Propeller Blade
Blade back
Blade Face
Chord
Definitions
• Angle of Attack
– The angle between
the chordline of the
blade and the
relative airflow.
• Helix Angle (Angle
of advance)
– The angle between
the resultant velocity
of the blade and the
plane of rotation.
Angle of
attack
Blade
Angle
Helix
Angle
Resultant velocity
of propeller blade
through the air
Velocity due
to rotation
Velocity due to
forward motion Relative Airflow
Definitions
• Engine Rotation
– The rotational
force produced by
the engine that
turns the
propeller.
• Propeller Torque
– Resistance to
motion in the
plane of rotation.
Direction
of flight
Engine Rotation
Propeller Torque
Definitions
• Fixed pitch
propeller
– A propeller where
the blade angle
cannot be varied
• Variable pitch
propeller
– A propeller where
the blade angle
can be varied
Blade
Angle
Principles
• The combination of the forward velocity
and rotational velocity creates a helical
motion of the propeller through the air.
Principles
• The tip travels fastest due to greater distance travelled in
same time. Root travels slowest. Therefore varying lift
(thrust) forces.
• To even out forces, blade is twisted to compensate.
Blade angle at hub needs to be much greater than blade
angle at tip.
Principles
• Forces on a propeller
Propeller
Torque Force
Thrust
Relative
Airflow
Engine
Torque
Force
Considerations
• Geometric pitch is how far the propeller would
theoretically advance in one revolution.
• Effective pitch is how far the propeller actually advances
in one revolution.
• The difference between geometric and effective pitch is
called slip.
Principles
• Effect of airspeed
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