1. Leading Cadet Training
Principles of Flight
Leading Cadet Training
Propellers
Lecture 7

2. A propeller is essentially an aerofoil
Propellers
A propeller is essentially an aerofoil
Leading Edge
Trailing Edge
Chord Line

3. This rotational airflow
Propellers
At a Zero Airspeed
As the blade
produces lift,
air is projected
vertically,
known as the
Induced Flow.
Induced Flow
The blade generates
Rotational Airflow,
parallel to and
opposite the blade’s
plane of rotation.
This rotational airflow
generates lift.
Relative
Airflow
(RAF)
Chord
Line 
= AofA
Airflow due to
Rotational Velocity
= Blade Angle 

4. Propellers Blade Twist Rotational Velocity Approx 4o Angle of Attack
Total Inflow

5. -  Propellers Airspeed Effects At a Forward Airspeed Need larger 
True Air Speed +
Induced Flow
Total Inflow =
- 
Chord
Line
Relative
Airflow
(RAF)
Airflow due to
Rotational Velocity 
= AofA
Need larger 
for same 
= Blade Angle 

6. Propellers Airspeed Effects Propeller Pitch Course Pitch Feathered 90o
Fine Pitch
Feathered
90o
Ground Pitch 0o
Reverse Pitch 20o

7. Propellers Airspeed Effects Propeller Pitch Propeller Efficiency
at Max Power _
100%
Fine
Variable Pitch _
75%
Coarse _
50% _
25%
True Airspeed

8. Aerodynamic Forces Feathered Propeller Therefore drag at minimum.
Although twisted, in aggregate, blade at “Zero Lift α”.
Therefore drag at minimum.
Note that in Firefly/Tutor prop goes to “Fine Pitch”
if engine rotating, “Coarse Pitch” if engine seized

9. Aerodynamic Forces Total Inflow  (RAF) Airflow due to
Relative
Airflow
(RAF) 
Airflow due to
Rotational Velocity
Chord Line
Lift
Drag 
Total Reaction

10. Aerodynamic Forces High Slow speed fixed pitch TAS + Induced Flow 
Relative
Airflow
(RAF) 
Airflow due to
Rotational Velocity
Chord Line
Thrust
Thrust reduced
Total Reaction reduced
RPM increases,
Rotational Drag reduced 
Prop
Rotational
Drag
Total Reaction

11. Aerodynamic Forces High Slow speed variable pitch Faster TAS +
Induced Flow
Relative
Airflow
(RAF) 
Airflow due to
Rotational Velocity
Chord Line
Thrust
(eventually reduces)
RPM increases,
Rotational Drag
increased 
(same or greater)
Prop
Rotational
Drag
Total Reaction

12. (Driving the propeller)
Aerodynamic Forces
Windmilling
TAS
Chord Line
Total Reaction
Negative
AOA 
Negative
Rotational Drag
(Driving the propeller)
Negative Thrust
(Drag)
Relative
Airflow
(RAF)
This may cause
further damage,
even Fire.
Airflow due to
Rotational Velocity

13. Take Off Swings Yaw due to torque reaction
Yaw due to slipstream effect
Torque Reaction means
more rolling
resistance on one wheel
Helical slipstream acts
on one side of fin
more than the other

14. Take Off Swings Tail wheel aircraft only: Asymmetric blade effect
Top picture both propeller sections are equal also distance travelled are equal.
Picture exaggerated but downgoing blade has greater AOA more thrust.
Distance travelled by downgoing blade greater.
Gyroscopic effect
When tailwheel raised all effects are zero (until rotate?)
But, force applied to top of disc (gyro) then clockwise rotation will cause yaw to the left
Obviously anticlockwise all reversed.
Affect all aircraft on rotate?
All Aircraft:
Don’t forget crosswind effect.
(if yaw to left because of slipstream then get a crosswind from the right)

15. Centrifugal Twisting Moment
Tries to fine blade off
This makes it more difficult for
the pitch changing mechanism
when increasing pitch.

16. Aerodynamic Twisting Moment
Relative Airflow
Total Reaction
Tries to coarsen blade up
Aerodynamic Twisting Movement
(ATM)
tries to increase the AOA,
this partially offsets
Centrifugal Twisting Moment (CTM)

17. Aerodynamic Twisting Moment
Total Reaction
Relative Airflow
Windmilling
Tries to fine blade off
When windmilling in a dive the
Aerodynamic Twisting Movement
(ATM)
is reversed and enhances the
Centrifugal Twisting Moment CTM.
This could prevent the pitch mechanism
from working.

18. Check of Understanding
What is the blade angle of attack
measured between?
The chord line and the total reaction
The chord line and the relative airflow
The relative airflow and the rotational velocity
The rotational velocity and the induced flow

19. Check of Understanding
What are the Resultant Forces
that a propeller produces?
Total Reaction and Drag
Thrust and Propeller Rotational Drag
Total Reaction and Lift
Lift and Propeller Rotational Drag

20. Check of Understanding
What effect will increasing speed
with a fixed pitch propeller have?
Reduce efficiency
Increase efficiency
Reduce the engine speed
Increase the engine speed

21. Check of Understanding
What are the two main forces
trying to alter the propeller blade Angle of Attack?
RAF and ATM
CTM and REV
ATM and CTM
REV and ATM

22. Check of Understanding
Which of the following statements regarding
take off swing is true?
Equal helical stripstream on the fin
Equal rolling resistance on all wheels
Less rolling resistance on all wheels
More rolling resistance on one wheel

23. Check of Understanding
What is the expression that makes it more difficult
for the pitch changing mechanism to work
when increasing pitch?
Centrifugal twisting moment
Aerodynamic twisting motion
Windmilling
Rotational velocity

24. Leading Cadet Training
Principles of Flight
Leading Cadet Training
End of Presentation