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Principles of Flight

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

Principles of Flight Revision

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

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

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

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.

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?

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

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.

The Mechanism of Stalling

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

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

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

Factors affecting stalling speed
Aircraft Weight

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

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

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

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

Factors affecting stalling speed
Pulling ‘g’

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

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

Factors affecting stalling speed
Engine Thrust

EFFECT OF THRUST ON STALLING
Lift Thrust Flight Path Weight

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

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

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

NATURAL STALL WARNING TURBULENT AIR MISSING TAILPLANE NORMAL FLIGHT

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

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

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

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

Example of a Stall Warning Vane

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

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

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

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

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

Stall Recovery

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.

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

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:

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.

Any Questions?

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.

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.

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

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

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