1. Uncontrolled copy not subject to amendment Principles of Flight Learning Outcome 2 Understand how the stability and manoeuvrability of an aeroplane are controlled Part 3: Explain factors which cause an aeroplane to stall Revision 2.00

2. Principles of Flight Revision

3. Questions for you …..

4. 1.What effect does a trailing edge flap have on the stalling speed? a.Higher b.Lower c. The same d. No difference

5. 2.One type of leading edge flap is ….. a.Plain b.Slot c. Split d. Krueger

6. 3.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: 1.Describe the stall in terms of lift 2.State the generally used critical or stall angle of attack 3Understand the relationship between stalling and airspeed 4.State where the pilot obtains information regarding the aircraft’s stalling speed 5.List the factors which affect the stalling speed

8. 1.It is essential that a pilot understands stalling 2.During take-off and landing, the aircraft is at low speed 3.In aerobatics the aircraft experiences high “G” What has stalling got to do with these?

9. Remember the lift formula? Lift = C L ½ ρV 2 S If we slow down (reduce V) we must keep lift the same (for straight and level flight) by increasing C L The limit is C LMAX, so the equivalent speed is V MIN (stalling speed) Lift = C LMAX ½ρV 2 MIN S Cl Max α Crit AoA ~ 15 o

10. Stalling speed is when: The speed at which a clean aircraft (flaps up) 2. At a stated weight 3. With the throttle closed 4. Flying straight and level 5. Can no longer maintain height Stalling speed

11. The mechanism of stalling

12. Boundary layer separation – low AoA Towards lower pressure - faster Towards higher pressure plus viscous adhesion - slower Transition point (perhaps) from laminar to turbulent boundary layer

13. Towards lower pressure - faster Towards higher pressure Plus viscous adhesion - much slower Separation point

14. Separation complete Towards lower pressure - faster

16. Factors affecting stalling speed 1.Aircraft weight

17. The effect of weight Lift BASIC WT = C L MAX ½ ρ V 2 BASIC STALL S Lift HEAVY WT = C L MAX ½ ρ V 2 HEAVY STALL S 

18. = Lift BASIC WT = C L MAX ½ ρ V 2 BASIC STALL S Lift HEAVY WT C L MAX ½ ρ V 2 HEAVY STALL S

19. Lift BASIC WT V 2 BASIC STALL Lift HEAVY WT V 2 HEAVY STALL = V 2 BASIC STALL = V 2 HEAVY STALL X LIFT HEAVY WT LIFT BASIC WT LIFT HEAVY WT LIFT BASIC WT V 2 HEAVY STALL = V 2 BASIC STALL X

20. LIFT HEAVY WT V 2 HEAVY STALL = V 2 BASIC 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. 2.Pulling ‘G’

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

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

24. 3. Engine thrust

25. Weight Lift Thrust Flight path The effect of thrust on stalling

26. Weight Thrust Lift TR Flight path

27. 1.Aircraft in level flight have a high nose attitude at the stall, particularly swept wing aircraft 2.If the engine is at high power there are two thrust components: a. Along the flight path (countering drag) b. Vertical (opposing weight) Therefore less lift is required from the wings, so: SLOWER STALLING SPEED (V) AT C LMAX Flight path

28. Natural stall warning Speed Nose attitude Controls Light buffet Heavy buffet Nose drop Wing drop Descent

29. Normal flight Turbulent air missing tailplane

30. Normal flight Turbulent air missing tailplane Turbulent air Just touching tailplane Stall warning Light buffet

31. Turbulent air just touching tailplane Stall Heavy buffet Stall warning Light buffet Turbulent air covering tailplane Aircraft descending

32. Synthetic stall warning Firefly and Tutor: Warning horn Warning light (Firefly only) Tucano: Warning horn 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. The effect of the flap Relative airflow Chord Basic ‘clean’ situation α

36. Relative airflow Chord Flap lowered α Basic ‘clean’ situation Effective increase in AoA

37. Flap Lowered α Maintaining the same lift Effective Increase in AoA To obtain the same C L the attitude is lowered to reduce the AoA

38. Cl Max At stall: Weight = Lift = C LMAX ½ρ V 2 STALL S Critical angle Without flap AoA CLCL

39. AT STALL: WEIGHT = LIFT = C LMAX ½ρ V 2 STALL S IF THIS ISTHIS IS CONSTANT MORELESS Critical angle With flap Cl Max More AoA CLCL Nose lower at stall Without flap Cl Max

40. Stall recovery

41. Standard stall recovery 1.Move stick centrally forward until buffet stops 2. Open throttle at the same time 3. Only then level the wings 4. Raise nose at a safe speed and climb

42. Other factors affecting stalling 1. Ice: Alters the shape of the wing, this will reduce lift 2. Damage: Can also reduce lift, for example after a bird strike

43. Summary of stalling speeds What happens to the stalling speed..... 1. If aircraft weight increases? The stalling speed will increase 2. If we lower the flap? The stalling speed will decrease 3. If we are pulling “G”? The stalling speed will increase 4. If the aircraft is damaged or has had a birdstrike? The stalling speed will probably increase 5. If using engine thrust? The stalling speed will decrease

44. Remember: 1.An aircraft can stall in any attitude – level, turning, upside-down etc. 2. Where would we find our stalling speeds? Pilot’s Notes or Aircrew Manual

45. Any questions?

46. Questions for you …..

47. 1.What happens to lift when a wing is stalled? a.Lift increases as the angle of attack decreases b.Lift decreases as the angle of attack increases c.Lift is greatly reduced d.Lift remains unchanged

48. 2.The critical angle of attack is generally about: a. 5 o b.15 o c.25 o d.35 o

49. 3. Which of the following will not reduce the stalling speed? a.Extra weight b.Larger wing area c.Flaps lowered d.Flaps raised

50. 4.Where would you find the information regarding the aircraft’s various stalling speeds? a.Pilot’s Notes b.Air Traffic Control c.Ground crew d.McDonald’s