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Principles of Flight

2. Learning Outcome 3: Know the principles of stalling
Principles of Flight
Learning Outcome 3: Know the principles of stalling

3. Principles of Flight
Revision

4. Questions What effect does a Trailing Edge Flap have on the Stalling
Speed?
Higher.
Lower.
c. The same.
d. No difference.

5. Questions One type of Leading Edge Flap is: Plain. Slot. c. Split.
d. Krueger.

6. Questions What are some of the High Lift Devices on the Leading
Edge called?
a. Plain Flaps.
b. Ailerons.
c. Slats.
d. Split Flaps.

7. Stalling Objectives: Describe the Stall in terms of Lift.
State the generally used Critical or Stall
Angle of Attack.
Understand the relationship between Stalling and
Airspeed.
State where the Pilot obtains information regarding the
Aircraft’s Stalling Speed.
5. List the Factors which affect the Stalling Speed.

8. What has Stalling got to do with these?
It is ESSENTIAL that a Pilot understands Stalling.
During Take-Off and Landing, the Aircraft is at
Low Speed.
In Aerobatics the Aircraft experiences High “G”.
What has Stalling got to do
with these?

9. Stalling Lift = CLMAX½ρV2MINS Lift = CL½ ρV2S
Remember the Lift Formula?
Lift = CL½ ρV2S
If we slow down (reduce V) we must keep Lift the
same (for Straight & Level Flight) by increasing CL.
The Limit is CLMAX, so the Equivalent speed is
VMIN (stalling speed)
Cl Max
Lift = CLMAX½ρV2MINS α
Crit AOA ~ 15o

10. Stalling Speed Is: The speed at which a clean aircraft (flaps up),
At a stated weight,
With the throttle closed,
Flying straight and level,
Can no longer maintain height.

11. The Mechanism of Stalling

12. BOUNDARY LAYER SEPARATION – Low AoA
TOWARDS HIGHER PRESSURE
PLUS VISCOUS ADHESION -
“ SLOWER”
TOWARDS LOWER
PRESSURE - FASTER
TRANSITION POINT (PERHAPS)
FROM LAMINAR TO TURBULENT
BOUNDARY LAYER

13. BOUNDARY LAYER SEPARATION – Higher AoA
TOWARDS HIGHER PRESSURE
PLUS VISCOUS ADHESION -
“MUCH SLOWER”
TOWARDS LOWER
PRESSURE - FASTER
SEPARATION POINT

14. BOUNDARY LAYER SEPARATION – Wing Stalled
TOWARDS LOWER
PRESSURE - FASTER
SEPARATION
COMPLETE

16. Factors affecting stalling speed
Aircraft Weight

17.  EFFECT OF WEIGHT Lift HEAVY WT = CL MAX½ ρ V2 HEAVY STALL S
Lift BASIC WT = CL MAX½ ρ V2 BASIC STALL S

18. EFFECT OF WEIGHT
Lift BASIC WT CL MAX½ ρ V2 BASIC STALL S
Lift HEAVY WT CL MAX½ ρ V2 HEAVY STALL S =

19. Lift BASIC WT V2 BASIC STALL Lift HEAVY WT V2 HEAVY STALL =
EFFECT OF WEIGHT
Lift BASIC WT V2 BASIC STALL
Lift HEAVY WT V2 HEAVY STALL =
V2BASIC STALL = V2HEAVY STALL X
LIFT HEAVY WT
LIFT BASIC WT
LIFT HEAVY WT
LIFT BASIC WT
V2HEAVY STALL = V2BASIC STALL X

20. V2HEAVY STALL = V2BASIC STALL
EFFECT OF WEIGHT
LIFT HEAVY WT
V2HEAVY STALL = V2BASIC STALL X
LIFT BASIC WT
V STALL HVY = V STALL BASIC X
LIFT HEAVY
LIFT BASIC
V STALL HVY = V STALL BASIC X
Weight HEAVY
Weight BASIC

21. Factors affecting stalling speed
Pulling ‘g’

22. V STALL HVY = V STALL BASIC X
EFFECT OF ‘G’
LIFT HEAVY
LIFT BASIC
V STALL HVY = V STALL BASIC X
SAME FOR PULLING “g”
V STALL MAN’VRE = V STALL BASIC X “g”
e.g. Vstall basic = 90kts, 4g loop
V STALL MAN’VRE = 90 x = 90 x 2
= 180kts

23. EFFECT OF ‘G’ Danger If you pull ‘g’, the stalling speed increases,
e.g. if you pull 4g the stalling speed doubles!

24. Factors affecting stalling speed
Engine Thrust

25. EFFECT OF THRUST ON STALLING
Lift
Thrust
Flight Path
Weight

26. EFFECT OF THRUST ON STALLING
Lift
Lift TR
Thrust
Flight Path
Weight

27. EFFECT OF THRUST ON STALLING
FLIGHT PATH
Aircraft in level flight have a high nose attitude at the stall,
particularly swept wing aircraft.
If the engine is at high power - two thrust components:
1. Along flight path (countering drag).
2. Vertical (opposing weight).
Therefore less lift required from wings, so:
SLOWER STALLING SPEED (V) AT CLMAX

28. NATURAL STALL WARNING
Speed
Nose Attitude
Controls
Light Buffet
Heavy Buffet
Nose Drop
Wing Drop
Descent

29. NATURAL STALL WARNING
TURBULENT
AIR MISSING
TAILPLANE
NORMAL FLIGHT

30. NATURAL STALL WARNING TURBULENT TURBULENT AIR AIR MISSING
TAILPLANE
TURBULENT AIR
JUST TOUCHING
TAILPLANE
NORMAL FLIGHT
STALL WARNING
LIGHT BUFFET

31. NATURAL STALL WARNING Aircraft Descending TURBULENT AIR TURBULENT AIR
JUST TOUCHING
TAILPLANE
TURBULENT AIR
COVERING
TAILPLANE
Aircraft Descending
STALL
HEAVY BUFFET
STALL WARNING
LIGHT BUFFET

32. Synthetic Stall Warning
Firefly/Tutor:
Warning Horn
Warning Light (Firefly only)
Tucano:
AoA Gauge
Stick Shaker
Indexer

33. Typical – Stall Warning Vane
Vane held down by airflow
Micro-switch not made
No stall warning given
Vane lifted up by airflow
Micro-switch made
Stall warning given

34. Example of a Stall Warning Vane

35. EFFECT OF FLAP Basic ‘Clean’ Situation Chord α Relative Airflow
LIFT AUGMENTATION DEVICES
How does each inc cCl , camber etc? α
Relative Airflow

36. EFFECT OF FLAP Basic ‘Clean’ Situation Flap Lowered Chord α
LIFT AUGMENTATION DEVICES
How does each inc cCl , camber etc? α
Relative Airflow
Effective Increase in AoA

37. EFFECT OF FLAP Flap Lowered Maintaining the Same Lift α
LIFT AUGMENTATION DEVICES
How does each inc cCl , camber etc? α
To obtain the same CL the Attitude is Lowered
to Reduce the AoA
Effective Increase in AoA

38. EFFECT OF FLAP CL Cl Max Without Flap Critical Angle AoA
AT STALL: WEIGHT = LIFT = CLMAX ½ρ V2STALL S

39. EFFECT OF FLAP CL With Flap Cl Max Without Flap Nose lower at Stall
Cl Max More
With Flap
Cl Max
Without Flap CL
Nose
lower at
Stall
Critical Angle
AoA
AT STALL: WEIGHT = LIFT = CLMAX ½ρ V2STALL S
IF THIS IS
THIS IS
CONSTANT
MORE
LESS

40. Stall Recovery

41. STANDARD STALL RECOVERY
Move stick Centrally forward until buffet stops.
Open throttle at the same time.
Only then level the wings.
Raise nose at a safe speed and climb.

42. Other Factors Affecting Stalling
Ice:
Alters the ‘Shape’ of the wing, this will reduce Lift.
Damage:
Can also reduce Lift ie after a ‘Birdstrike’.

43. Summary of Stalling Speeds
What happens to the Stalling Speed if:
Aircraft Weight Increases:
Increase.
If we Lower Flap:
Decrease.
If we are “Pulling G”:
If the Aircraft is damaged or had a Birdstrike, it will
probably:
Using Engine Thrust:

44. Stalling REMEMBER: An Aircraft can STALL in any Attitude, level,
turning, upside-down etc.
Where would we find our Stalling Speeds?
Pilot’s Notes/Aircrew Manual etc.

45. Any Questions?

46. Stalling Objectives: Describe the Stall in terms of Lift.
State the generally used Critical or Stall
Angle of Attack.
Understand the relationship between Stalling and
Airspeed.
State where the Pilot obtains information regarding the
Aircraft’s Stalling Speed.
5. List the Factors which affect the Stalling Speed.

47. Questions What happens to Lift when a Wing is Stalled?
Lift Increases as Angle of Attack Decreases.
Lift Decreases as Angle of Attack Increases.
Lift is Greatly Reduced.
Lift Remains unchanged.

48. Questions The Critical Angle of Attack is Generally about? 5o. 15o.

49. Questions Which of the following will NOT REDUCE the Stalling Speed?
Extra Weight.
Larger Wing Area.
Flaps Lowered.
Flaps Raised.

50. Questions Where would you find the information regarding
the Aircraft’s various Stalling Speeds?
Pilot’s Notes.
Air Traffic Control.
Ground Crew.
McDonald’s.