1. Uncontrolled copy not subject to amendment
Principles of Flight

2. Principles of Flight
Learning Outcome 5: Be able to apply the principles of flight and control to rotary wing aircraft Part 1

3. REVISION

4. Questions Name the Forces Acting on a Glider in Normal Flight.
a. Force, Weight and Lift.
b. Drag, Weight and Thrust.
Drag, Weight and Lift.
Drag, Thrust and Lift.

5. Questions How does a Glider Pilot Increase the Airspeed?
a. Operate the Airbrakes.
b. Lower the Nose by pushing the Stick Forward.
Raise the Nose by pulling the Stick Back.
Lower the Nose by pulling the Stick Back.

6. Questions A Viking Glider descends from 1640 ft (0.5 km).
How far over the ground does it Travel (in still air)?
a kms.
b. 35 kms.
70 kms.
8.75 kms.

7. Questions When flying into a Headwind, the distance covered
over the ground will:
a. Be the same.
b. Decrease.
Increase.
No change.

8. Propellers Objectives: Define Blade Angle and Blade Angle of Attack.
Show with the aid of a diagram the Aerodynamic
Forces acting on a Propeller Blade in flight.
Explain Aerodynamic and Centrifugal Twisting
Moments acting on a propeller.
4. Explain the effect of changing forward speed on:
a. A Fixed Pitch propeller.
b. A Variable Pitch propeller.
(and thus the advantages of a variable pitch propeller).
5. Explain the factors causing swings on take-off for:
a. A Nose-Wheel aircraft.
b. A Tail- Wheel aircraft.

9. Propellers
PICTURE
MOD

10. Propellers (Terminology)
Airflow due to rotational velocity
Induced flow This is the air drawn through the disc.
Relative airflow
Where is AOA? (Chord line/relative airflow) Always looking for optimum AOA, which is? (4)
What is other angle? (Chord line/Airflow due to rotational velocity)
Quick look at AOA of blade from hub to tip to maintain 4o AOA
(If prop stationary then the airflow through would be TAS)

11. Propellers (Terminology)
Airflow due
to Rotational
Velocity

12. Propellers (Terminology)
Induced Flow
Airflow due
to Rotational
Velocity

13. Propellers (Terminology)
Induced Flow
Airflow due
to Rotational
Velocity
Relative
Airflow

14. Propellers (Terminology)
Induced Flow
Airflow due
to Rotational
Velocity
Chord
Line
Relative
Airflow

15. Propellers (Terminology)
Induced Flow
Airflow due
to Rotational
Velocity
Chord
Line
Relative
Airflow 
= AofA

16. Propellers (Terminology)
Induced Flow
Airflow due
to Rotational
Velocity
Chord
Line
Relative
Airflow 
= AofA
= Blade Angle 

17. Propellers Blade Twist
Rotational
Velocity
Approx 4o
Angle of Attack
PROPELLER BLADE TWIST
What is the problem with a prop blade?
What is the tip doing relative to the hub?
Total Inflow

18. Effect of Airspeed Induced Flow Airflow due to Rotational Velocity  
At Zero
Airspeed

19. Effect of Airspeed TAS + Induced Flow = Total Inflow Airflow due
to Rotational
Velocity
(Same) - 
EFFECT OF AIRSPEED
Induced flow + TAS does what to AOA? Less efficient
How do we counter this? 
At a Forward
Airspeed

20. Effect of Airspeed TAS + Induced Flow = Total Inflow Airflow due
to Rotational
Velocity
(Same) - 
EFFECT OF AIRSPEED
Induced flow + TAS does what to AOA? Less efficient
How do we counter this? 
At a Forward
Airspeed
Need larger  for same 

21. Effect of Airspeed Fine Propeller Efficiency Coarse at Max Power_
100%
Fine _
75%
Propeller
Efficiency
at Max Power
Coarse _
50% _
25%
True Airspeed

22. Pitch of Propeller Blade_
100%
Variable Pitch
Fine _
75%
Propeller
Efficiency
at Max Power
Coarse _
50% _
25%
True Airspeed

23. Why a different Number of Blades?
EXAMPLES OF PROPS WHY DIFFERENT?
Depends on Power output of the engine

24. Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity

25. Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity
Total
Reaction

26. Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity
Drag
Lift
Total
Reaction

27. Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity
Thrust
Total
Reaction

28. Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity
Thrust
Prop
Rotational
Drag
Total
Reaction

29. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
Slow
Speed
Fixed
Pitch
Total
Reaction

30. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
High
Speed
Fixed
Pitch
Total
Reaction

31. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
High
Speed
Fixed
Pitch
Total
Reaction

32. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
High
Speed
Fixed
Pitch
Total
Reaction

33. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
High
Speed
Fixed
Pitch
NB: Rotational Drag
reduced, RPM ?

34. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
High
Speed
Fixed
Pitch
NB: Rotational Drag
reduced, RPM increases.
Don’t exceed limits.

35. Aerodynamic Forces (Effect of High Speed)
TAS+Induced Flow
Airflow due
to Rotational
Velocity
RAF 
Thrust
Slow
Speed
Variable
Pitch
Total
Reaction

36. Aerodynamic Forces (Effect of High Speed)
Faster TAS+Induced Flow
RAF
Airflow due
to Rotational
Velocity 
Thrust
(eventually
reduces)
High
Speed
Variable
Pitch
Total
Reaction
(same or possibly greater)

37. Windmilling Propeller
Negative

TAS
WINDMILLING PROPELLER
Negative AOA
Normally the prop will fine-off to maintain rpm (rotational drag)
This will even try to drive the engine (oil failure)
Could cause engine failure so:
we want the blade to produce zero torque and reduce drag to a minimum
How is this done?
Airflow
due to
Rotational
Velocity

38. Windmilling Propeller
Negative

TAS TR
Airflow
due to
Rotational
Velocity

39. Windmilling Propeller
Negative

TAS TR
Negative Thrust
(Drag)
Airflow
due to
Rotational
Velocity

40. Windmilling Propeller
Negative

TAS TR
Negative
Rotational
Drag (Driving
The Propeller)
Negative Thrust
(Drag)
Airflow
due to
Rotational
Velocity

41. Windmilling Propeller
Negative

TAS TR
Negative Thrust
(Drag)
Negative
Rotational
Drag (Driving
The Propeller)
This may cause
further damage,
even Fire.
Airflow
due to
Rotational
Velocity

42. Feathered Propeller
SLIDE 40 FEATHERED PROPELLER
The idea is to reduce the drag
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

43. Take-Off Swings All Aircraft: Torque Reaction means greater rolling
resistance on one wheel
Helical slipstream acts more on one
side of the fin than the other
TAKE-OFF SWINGS
Prop rotating clockwise from cockpit
All Aircraft:
Torque Reaction means greater rolling resistance on one wheel. (Newton’s 3rd Law)
More weight supported by wheel  more drag.
USE MODEL
Helical slipstream acts more on one side of the fin than the other
Rotating clockwise from behind -
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?
Don’t forget crosswind effect.
(if yaw to left because of slipstream then get a crosswind from the right)

44. Take-Off Swings

45. Tail wheel aircraft only: Asymmetric blade effect Gyroscopic effect
Take-Off Swings
Tail wheel aircraft only:
Asymmetric blade effect
Gyroscopic effect

46. Take-Off Swings

47. Affect all aircraft on rotate?
Take-Off Swings
Affect all aircraft on rotate?

48. All Aircraft: Don’t forget crosswind effect!
Take-Off Swings
All Aircraft:
Don’t forget crosswind effect!

49. Centrifugal Twisting Moment
This makes it more difficult for the pitch changing mechanism when increasing pitch.
Better to increase the number of blades rather than make larger
Tries to fine blade off

50. Aerodynamic Twisting Moment
Relative Airflow
Total Reaction
AERODYNAMIC TWISTING MOMENT
Tries to increase AOA, this partially offsets CTM
When windmilling in a steep dive the ATM is reversed and enhances CTM. This could prevent pitch mechanism from working
Tries to coarsen blade up

51. Aerodynamic Twisting Moment Windmilling
Total Reaction
Relative Airflow
Tries to fine blade off

52. ANY QUESTIONS?

53. Propellers Objectives: Define Blade Angle and Blade Angle of Attack.
Show with the aid of a diagram the Aerodynamic
Forces acting on a Propeller Blade in flight.
Explain Aerodynamic and Centrifugal Twisting
Moments acting on a propeller.
4. Explain the effect of changing forward speed on:
a. A Fixed Pitch propeller.
b. A Variable Pitch propeller.
(and thus the advantages of a variable pitch propeller).
5. Explain the factors causing swings on take-off for:
a. A Nose-Wheel aircraft.
b. A Tail- Wheel aircraft.

54. PICTURE

55. Questions Blade Angle of Attack is between?
a. The Chord and Relative Airflow.
b. The Rotational Velocity and the Relative Airflow.
The Total Reaction and the Chord.
Lift and Drag.

56. Questions Increasing speed with a fixed pitch propeller will?
a. Be more efficient.
b. Reduce efficiency.
Make no difference.
Increase the Engine speed.

57. Questions The Forces trying to alter the Propeller Blade
Angle of Attack are?
a. ATM and CTM.
b. CDM and ATM.
CTM and REV.
AOA and ATM.

58. Questions The Resultant Forces that a Propeller produce are?
a. Lift and Thrust.
Thrust and Propeller Rotational Drag.
Drag and Total Reaction.
d. Drag and Thrust.