lecture leading cadet training principles of flight 6 stalling and gliding
TRANSCRIPT
Lecture
Leading Cadet Training
Principles of Flight
6Stalling
and Gliding
The StallIn 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.
α15o
The critical angle of attack(the stalling angle)
varies from one type of wing to another,as does the stalling speed.
The Stall
α15o
The airflow turbulence is calledBoundary Layer Separation
The Stall
TRTOWARDS LOWER PRESSURE -
FASTER
TOWARDS HIGHER PRESSUREPLUS VISCOUS ADHESION –
“SLOWER”
AIRFLOW
TRANSITION POINT FROM LAMINAR TO TURBULENT BOUNDARY LAYER
Boundary Layer Separationat a
Low Angle of Attack
The airflow turbulence is calledBoundary Layer Separation
The Stall
TRTOWARDS LOWER PRESSURE – FASTER
TOWARDS HIGHER PRESSUREPLUS VISCOUS ADHESION –
“MUCH SLOWER”
AIRFLOW
SEPARATION POINT
Boundary Layer Separationat a
High Angle of Attack
The airflow turbulence is calledBoundary Layer Separation
The Stall
TR
TOWARDS LOWER PRESSURE –
FASTERAIRFLOW
COMPLETE SEPARATION
Boundary Layer Separationat a
Stall !!
The main factors which affect the stalling speed are:
Speed
Weight
‘G’ Force
Thrust
Flaps
Ice & Damage
The Stall
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 speedsare found in the Pilot’s Notes/Aircrew Manual etc.
Stalling Speed
The Stall
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 -
Stalling Speed
The Stall
Lift = CLMAX ½ρ V2MIN S
CL = Coefficient of Lift(the ratio between lift and dynamic pressure).ρ = Density V = True Airspeed S = Surface Area
The Effect of Speed
S
S
CL MAX ½ρCL MAX ½ρ=
=
Lift HEAVY WT
Lift BASIC WT
Stalling Speed
The Stall
The Effect of Weight
=V2
BASIC STALL
V2 HEAVY STALL
=
V2HEAVY STALL
XLift HEAVY WT
Lift BASIC WT
Lift BASIC WT
Lift HEAVY WT
V2BASIC STALL =
and so
CL = Coefficient of Lift(the ratio between lift and dynamic pressure).ρ = Density V = True Airspeed S = Surface Area
CANCELLATION
V2 BASIC STALL
V2 HEAVY STALL
V2 BASIC STALL
V2 HEAVY STALL
Lift HEAVY WT
Lift BASIC WT
= X
THEREFORE
THEREFORE
Stalling Speed
The Stall
The Effect of Weight
V2HEAVY STALL X
Lift HEAVY WT
Lift BASIC WT
V2BASIC STALL =
V HEAVY STALL = V BASIC STALL X
Lift HEAVY WT
Lift BASIC WT
V HEAVY STALL = V BASIC STALL X
Weight HEAVY
Weight BASIC
2 2
CONVERSION
CANCELLATION
CL = Coefficient of Lift(the ratio between lift and dynamic pressure).ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Stall
The Effect of Weight
V HEAVY STALL = V BASIC STALL X
Weight HEAVY
Weight BASIC
CL = Coefficient of Lift(the ratio between lift and dynamic pressure).ρ = Density V = True Airspeed S = Surface Area
Load (200 ton)
Empty (50ton) Basic Stall Speed (90kts) X
e.g. V BASIC STALL (90kts) X 4 ton
V HEAVY STALL = 90 X ( = 90 x 2 )
= 180kts
4 (= 2)
Stalling Speed The Effect of ‘G’
V STALL MAN’VRE = V BASIC STALL X ‘g’
SAME FOR PULLING “g”
e.g. V BASIC STALL (90kts) X
V STALL MAN’VRE = 90 X 4 ( = 90 x 2 )
= 180kts
The Stall
V HEAVY STALL XV BASIC STALL = Weight HEAVY
Weight BASIC
4g loop
(= 2)
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’
The Stall
= 180kts
V STALL MAN’VRE = 90 X 4 ( = 90 x 2 )(= 2)V STALL MAN’VRE = 90 X 9 ( = 90 x 3 )(= 3)
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 !!!
= 270kts
CL = Coefficient of Lift(the ratio between lift and dynamic pressure).ρ = Density V = True Airspeed S = Surface Area
Stalling Speed
The Stall
The Effect of Thrust
Flight PathWeight
Lift
Thrust
Lift TR
Aircraft in level flight have a high nose attitude at the stall,
particularly swept wing aircraft.
Stalling Speed
The Stall
The Effect of Thrust
Flight Path
Thrust
If the engine is at high powerthere 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
TRLift
Weight
Stalling Speed
The Stall
The Effect of Flaps
Relative Airflow
Basic ‘Clean’ Situation
Chord Line
α
Flap Lowered
Effective Increase in Angle of Attack
α
Maintaining the Same Lift
To obtain the same CL, the Attitude is Lowered,
and the Angle of Attack is reduced.
Stalling Speed
The Stall
Other Factors
Ice:Alters the ‘Shape’ of the wing, this will reduce Lift.
Damage:Can also reduce Lift ie after a ‘Birdstrike’.
Natural Stall Warning
NORMAL FLIGHT
Turbulent AirMissingthe tailplane
The Stall SpeedNose Attitude
ControlsLight Buffet
Heavy BuffetNose DropWing Drop
Turbulent Airjust touchingthe tailplane
Natural Stall Warning
STALL WARNINGLIGHT BUFFET
The Stall SpeedNose Attitude
ControlsLight Buffet
Heavy BuffetNose DropWing Drop
Turbulent AirCoveringthe tailplane STALL WARNING
HEAVY BUFFET
Natural Stall Warning
Aircraft Descending
The Stall SpeedNose Attitude
ControlsLight Buffet
Heavy BuffetNose DropWing Drop
Synthetic Stall Warning
The Stall
Firefly/Tutor:Warning HornWarning Light (Firefly only)
Tucano:Warning HornAoA GaugeStick ShakerIndexer
Synthetic Stall Warning
The Stall
Stall Warning Vane
Vane held down by airflow
Micro-switch not made
No stall warning given
Vane lifted up by airflow
Micro-switch is made
Stall warning given
Synthetic Stall Warning
The Stall
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.
Gliding
Balance of ForcesIn 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
Lift
Speed
Lift and Speed reduce.
The Rate of Descent also reduces!
If the Nose is raised,
What happens to Lift and Speed?
Balance of Forces
Speed
Lift
Balance of Forces
If the Nose is lowered,
What happens to Lift and Speed?
Lift and Speed increase.
The Rate of Descent also increases!
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.
Lift
Weight
DragPath of Glider
Balance of Forces
The Lift reduces the rate of descent,and to increase airspeed the nose must be lowered.
So in order to maintain steady flightthe glider must be constantly descending.
Lift
Weight
DragPath of Glider
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 and Drag
α
CL CD
α0°0°
Lift Drag
Lift and Drag Lift / Drag Ratio
25
20
15
10
5
0
-5
0 5 16
-5 0 5 10 15 20 25o o o o o o
ooo
UsualAngles of flight
Mo
st e
ffic
ien
tA
ng
le o
f at
tack
CL
CDLess LiftMore Drag
Lift and Drag Flight Speed
VIMD
ZERO LIFT DRAG
LIFT DEPENDENT DRAG
DRAG
IAS
We know the best Angle to fly, but what is the best Speed to fly?
Minimum Drag Speed
VIMD
This depends upon the gliding angle and the wind.
The flatter the gliding anglethe further the glider will travel.
A glider with a steep angle does not travel far.
A glider with a shallow angle travels much further.
How Far will a Glider go ?
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.
Downwind
Upwind
Equally,
a glider travelling downwind,
will cover a greater distance over the ground
than a glider travelling into the wind.
How Far will a Glider go ?
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
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
Air Brakes
Check of UnderstandingAt the stall of any particular wing
which of these factors is not variable?
The airspeed across the wing
The amount of weight supported by the wing
The amount of lift produced by the wing
The angle of attack of the wing
Check of UnderstandingWhich of the following statements is true?
The airspeed at which an aircraft stallsdoes vary
The stall is the same for all aircraft
The airspeed at which an aircraft stallsdoes not vary
An aircraft can stall at any angle of attack
Check of UnderstandingWhich of the following will increase
the stalling speed of an aircraft?
Lowering the flaps
Putting it into a turn
Increasing the power
Reducing the weight
What happens to Stalling Speed :
If Aircraft Weight Increases ?Stalling Speed Increases.If we Lower Flaps ?Stalling Speed Decreases.If we are “Pulling G” ?Stalling Speed Increases.If damaged by a Birdstrike ?Stalling Speed probably Increases.If Using Engine Thrust ?Stalling Speed Decreases.
Check of Understanding
Check of UnderstandingWhat are the three forces acting on a glider
during normal flight?
Force, Thrust and Lift
Drag, Weight and Thrust
Drag, Thrust and Lift
Drag, Weight and Lift
Check of UnderstandingHow does a glider pilot increase airspeed?
Pull the stick back to lower the nose
Push the stick forward to raise the nose
Push the stick forward to lower the nose
Pull the stick back to raise the nose
Check of UnderstandingA Viking glider descends from 1640 ft (0.5 km).
How far over the ground does it travel (in still air)?
8.75 kms
70 kms
17.5 kms
35 kms
Check of UnderstandingWhen flying into a Headwind,
the distance covered over the ground will:
Be the square of the height
Decrease
Increase
Remain the same
Check of UnderstandingDuring flight if the nose of a glider is lowered,
What happens to Lift and Speed?
Both lift and speed increase
Both lift and speed decrease
Lift decreases, speed increases
Lift increases, speed decreases
Check of UnderstandingIn order to maintain steady flight
What must a glider be constantly doing?
Travelling upwind
Descending
Ascending
Spiralling
Principles of Flight
End of Presentation
Leading Cadet Training