1. Leading Cadet Training
Principles of Flight
Leading Cadet Training
Stalling
and Gliding
Lecture 6

2. The Stall α In normal flight a wing meets the oncoming air
at a small angle of attack,
The more the pilot increases the angle of attack,
the more lift there will be,
until an angle of about 15° is reached,
when the airflow becomes turbulent, lift is lost –
so the aircraft STALLS.
15o α

3. The Stall α The critical angle of attack (the stalling angle)
varies from one type of wing to another,
as does the stalling speed.
15o α

4. The Stall The airflow turbulence is called Boundary Layer Separation
at a
Low Angle of Attack TR
TOWARDS HIGHER PRESSURE
PLUS VISCOUS ADHESION –
“SLOWER”
TOWARDS LOWER PRESSURE -
FASTER
AIRFLOW
TRANSITION POINT FROM LAMINAR
TO TURBULENT BOUNDARY LAYER

5. The Stall The airflow turbulence is called Boundary Layer Separation
at a
High Angle of Attack
TOWARDS LOWER PRESSURE –
FASTER TR
TOWARDS HIGHER PRESSURE
PLUS VISCOUS ADHESION –
“MUCH SLOWER”
AIRFLOW
SEPARATION POINT

6. The Stall The airflow turbulence is called Boundary Layer Separation
at a
Stall !! TR
COMPLETE
SEPARATION
TOWARDS LOWER
PRESSURE –
FASTER
AIRFLOW

7. The main factors which affect the stalling speed are:
Weight
‘G’ Force
Thrust
Flaps
Ice & Damage

8. The Stall Stalling Speed The Effect of Speed
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.
Details of individual aircraft stalling speeds
are found in the Pilot’s Notes/Aircrew Manual etc.

9. The Stall Stalling Speed The Effect of Speed Lift = CL ½ρ V2 S
CL = Coefficient of Lift
(the ratio between lift and dynamic pressure).
ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Effect of Speed
Remember the Lift Formula?
Lift = CL ½ρ V2 S
If we slow the speed down (reduce V)
we must keep Lift the same (for Straight & Level Flight)
by increasing CL.
The limit therefore becomes CLMAX,
so the equivalent speed is VMIN (Stalling Speed)
The formula for the Stalling Speed is therefore -
Lift = CLMAX ½ρ V2MIN S

10. The Stall Stalling Speed The Effect of Weight so Lift HEAVY WT
CL = Coefficient of Lift
(the ratio between lift and dynamic pressure).
ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Effect of Weight
Lift HEAVY WT
CL MAX ½ρ =
V2 HEAVY STALL
V2 HEAVY STALL S
and so =
Lift BASIC WT
CL MAX ½ρ =
V2 BASIC STALL
V2 BASIC STALL S
Lift HEAVY WT
CANCELLATION
V2 HEAVY STALL =
Lift BASIC WT
V2 BASIC STALL
THEREFORE
Lift HEAVY WT
Lift HEAVY WT
V2BASIC STALL X =
V2HEAVY STALL
Lift BASIC WT
Lift BASIC WT
THEREFORE = X

11. The Stall Stalling Speed The Effect of Weight Lift HEAVY WT
CL = Coefficient of Lift
(the ratio between lift and dynamic pressure).
ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Effect of Weight
Lift HEAVY WT
V2HEAVY STALL 2
V2BASIC STALL 2 = X
Lift BASIC WT
CONVERSION
Lift HEAVY WT
V HEAVY STALL = V BASIC STALL X
Lift BASIC WT
CANCELLATION
Weight HEAVY
V HEAVY STALL = V BASIC STALL X
Weight BASIC

12. Basic Stall Speed (90kts) X
The Stall
CL = Coefficient of Lift
(the ratio between lift and dynamic pressure).
ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Effect of Weight
Load (200 ton)
Basic Stall Speed (90kts) X
Empty (50ton)
e.g. V BASIC STALL (90kts) X
4 ton
V HEAVY STALL = X 4
(= 2)
( = 90 x 2 )
V HEAVY STALL = V BASIC STALL X
Weight HEAVY
Weight BASIC
= 180kts

13. The Stall Stalling Speed The Effect of ‘G’ = 180kts V HEAVY STALL
CL = Coefficient of Lift
(the ratio between lift and dynamic pressure).
ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Effect of ‘G’
V HEAVY STALL X
V BASIC STALL =
Weight HEAVY
Weight BASIC
SAME FOR PULLING “g”
V STALL MAN’VRE = V BASIC STALL X
‘g’
e.g. V BASIC STALL (90kts) X
4g loop
V STALL MAN’VRE = X 4
(= 2)
( = 90 x 2 )
= 180kts

14. The Stall Stalling Speed The Effect of ‘G’ = 180kts = 270kts
CL = Coefficient of Lift
(the ratio between lift and dynamic pressure).
ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Effect of ‘G’
When you pull ‘g’, the stalling speed increases,
e.g. if you pull 4g the stalling speed doubles !!
If you pull 9g the stalling speed triples !!!
V STALL MAN’VRE = X 4
( = 90 x 2 )
(= 2)
V STALL MAN’VRE = X 9
( = 90 x 3 )
(= 3)
= 180kts
= 270kts

15. The Stall Stalling Speed The Effect of Thrust Lift Lift Thrust WeightTR
Thrust
Flight Path
Weight
Aircraft in level flight
have a high nose attitude at the stall,
particularly swept wing aircraft.

16. The Stall Stalling Speed The Effect of Thrust Lift Thrust WeightTR
Thrust
Flight Path
Weight
If the engine is at high power
there are two thrust components:
One acts along the flight path (countering drag).
and the other is vertical (opposing weight).
Therefore less lift is required from wings, so:
SLOWER STALLING SPEED (V) AT CLMAX

17. The Stall Stalling Speed The Effect of Flaps To obtain the same CL,
Flap Lowered
Basic ‘Clean’ Situation
Maintaining the Same Lift
Chord Line α α
Relative Airflow
To obtain the same CL,
the Attitude is Lowered,
and the Angle of Attack is reduced.
Effective Increase in Angle of Attack

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

19. The Stall Natural Stall Warning Speed Nose Attitude Controls
Light Buffet
Heavy Buffet
Nose Drop
Wing Drop
Natural Stall Warning
Turbulent Air
Missing
the tailplane
NORMAL FLIGHT

20. The Stall Natural Stall Warning Speed Nose Attitude Controls
Light Buffet
Heavy Buffet
Nose Drop
Wing Drop
Natural Stall Warning
Turbulent Air
just touching
the tailplane
STALL WARNING
LIGHT BUFFET

21. The Stall Natural Stall Warning Speed Nose Attitude Controls
Light Buffet
Heavy Buffet
Nose Drop
Wing Drop
Natural Stall Warning
Turbulent Air
Covering
the tailplane
STALL WARNING
HEAVY BUFFET
Aircraft Descending

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

23. The Stall Synthetic Stall Warning Stall Warning Vane
Vane held down by airflow
Micro-switch not made
No stall warning given
Stall Warning Vane

24. The Stall Synthetic Stall Warning Vane lifted up by airflow
Micro-switch is made
Stall warning given

25. STANDARD STALL RECOVERY
The Stall
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.

26. Gliding

27. Balance of Forces In straight and level flight, at constant speed,
two pairs of forces act on the aircraft.
Thrust opposes Drag and Lift opposes Weight.
To maintain a steady airspeed if thrust is removed,
pitch the nose down and use weight to descend.
The aircraft is now GLIDING.
WEIGHT
LIFT
DRAG
THRUST

28. Balance of Forces Lift Speed If the Nose is raised,
What happens to Lift and Speed?
Lift and Speed reduce.
The Rate of Descent also reduces!

29. Balance of Forces Lift Speed If the Nose is lowered,
What happens to Lift and Speed?
Lift and Speed increase.
The Rate of Descent also increases!

30. Balance of Forces Three forces act on a Glider –
Due to Gravity a glider descends in a controlled way.
Drag acts along the flightpath,
and as the glider descends air flow produces Lift.
The Lift reduces the rate of descent,
and to increase airspeed the nose must be lowered.
So in order to maintain steady flight
the glider must be constantly descending.
Lift
Drag
Path of Glider
Weight

31. Balance of Forces Remember: If you fly too slowly
Lift will be lost and the glider will Stall.
If you fly too fast
the Rate of Descent will be High.
Lift
Drag
Path of Glider
Weight

32. Lift and Drag
Lift
Drag CL CD α α 0° 0°

33. Lift and Drag Lift / Drag Ratio CL CD Usual Angles of flight Less Lift
Angle of attack
Most efficient
Less Lift
More Drag

34. Lift and Drag Flight Speed We know the best Angle to fly,
but what is the best Speed to fly?
Minimum
Drag Speed
VIMD
DRAG
VIMD
ZERO LIFT
DRAG
LIFT DEPENDENT
DRAG
IAS

35. How Far will a Glider go ?
This depends upon the gliding angle and the wind.
The flatter the gliding angle
the further the glider will travel.
A glider with a steep angle does not travel far.
A glider with a shallow angle travels much further.
A Viking Glider’s angle is about 1 in 35.
Therefore, from a height of 3,280 ft (1 kilometre),
in still air, it will travel about 35 kilometres.

36. How Far will a Glider go ? Equally, a glider travelling downwind,
will cover a greater distance over the ground
than a glider travelling into the wind.
Upwind
Downwind

37. Air Brakes Most gliders do not have Flaps in their wings.
Instead they are fitted with airbrakes.
Airbrakes are panels which lie in the wings,
and can extend to 90°
from the upper and/or lower surfaces of the wings

38. Air Brakes A glider with Airbrakes IN. A glider with Airbrakes OUT
produces more drag and must therefore
lower the nose to maintain airspeed
= Steeper Descent + Shorter Ground Distance

39. Check of Understanding
At the stall of any particular wing
which of these factors is not variable?
The amount of weight supported by the wing
The angle of attack of the wing
The amount of lift produced by the wing
The airspeed across the wing

40. Check of Understanding
Which of the following statements is true?
The stall is the same for all aircraft
An aircraft can stall at any angle of attack
The airspeed at which an aircraft stalls
does not vary
The airspeed at which an aircraft stalls
does vary

41. Check of Understanding
Which of the following will increase
the stalling speed of an aircraft?
Putting it into a turn
Reducing the weight
Increasing the power
Lowering the flaps

42. Check of Understanding
What happens to Stalling Speed :
If Aircraft Weight Increases ?
Stalling Speed Increases.
If we Lower Flaps ?
Stalling Speed Decreases.
If we are “Pulling G” ?
If damaged by a Birdstrike ?
Stalling Speed probably Increases.
If Using Engine Thrust ?

43. Check of Understanding
What are the three forces acting on a glider
during normal flight?
Drag, Weight and Thrust
Drag, Weight and Lift
Drag, Thrust and Lift
Force, Thrust and Lift

44. Check of Understanding
How does a glider pilot increase airspeed?
Push the stick forward
to raise the nose
Pull the stick back
to raise the nose
Push the stick forward
to lower the nose
Pull the stick back
to lower the nose

45. Check of Understanding
A Viking glider descends from 1640 ft (0.5 km).
How far over the ground does it travel (in still air)?
70 kms
35 kms
17.5 kms
8.75 kms

46. Check of Understanding
When flying into a Headwind,
the distance covered over the ground will:
Decrease
Remain the same
Increase
Be the square of the height

47. Check of Understanding
During flight if the nose of a glider is lowered,
What happens to Lift and Speed?
Both lift and speed decrease
Lift increases, speed decreases
Lift decreases, speed increases
Both lift and speed increase

48. Check of Understanding
In order to maintain steady flight
What must a glider be constantly doing?
Descending
Spiralling
Ascending
Travelling upwind

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