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Principles of Flight

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?

a. Higher.

b. Lower.

c. The same.

d. No difference.

Questions

One type of Leading Edge Flap is:

a. Plain.

b. 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:

1. Describe the Stall in terms of Lift.

2. State the generally used Critical or Stall

Angle of Attack.

3 Understand the relationship between Stalling and Airspeed.

4. State where the Pilot obtains information regarding theAircraft’s Stalling Speed.

5. List the Factors which affect the Stalling Speed.

Stalling

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?

Remember the Lift Formula?

Lift = CL½ ρV2SIf 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)

Lift = CLMAX½ρV2MINS

Cl Max

α

Stalling

Crit AOA ~ 15o

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.

Stalling Speed

The Mechanism of Stalling

BOUNDARY LAYER SEPARATION – Low AoA

TOWARDS LOWERPRESSURE - FASTER

TOWARDS HIGHER PRESSUREPLUS VISCOUS ADHESION - “ SLOWER”

TRANSITION POINT (PERHAPS)FROM LAMINAR TO TURBULENT BOUNDARY LAYER

BOUNDARY LAYER SEPARATION – Higher AoA

TOWARDS LOWERPRESSURE - FASTER

TOWARDS HIGHER PRESSUREPLUS VISCOUS ADHESION - “MUCH SLOWER”

SEPARATION POINT

BOUNDARY LAYER SEPARATION – Wing Stalled

TOWARDS LOWERPRESSURE - FASTER

SEPARATIONCOMPLETE

Factors affecting stalling speed

Aircraft Weight

EFFECT OF WEIGHT

Lift BASIC WT = CL MAX½ ρ V2 BASIC STALL S

Lift HEAVY WT = CL MAX½ ρ V2 HEAVY 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

EFFECT OF WEIGHT

Lift BASIC WT V2 BASIC STALL

Lift HEAVY WT V2 HEAVY STALL=

V2BASIC STALL = V2

HEAVY STALLX

LIFT HEAVY WT

LIFT BASIC WT

LIFT HEAVY WT

LIFT BASIC WT

V2HEAVY STALL = V2

BASIC STALL X

LIFT HEAVY WTV2HEAVY STALL = V2

BASIC STALL XLIFT BASIC WT

V STALL HVY = V STALL BASIC XLIFT HEAVY

LIFT BASIC

EFFECT OF WEIGHT

V STALL HVY = V STALL BASIC XWeight HEAVY

Weight BASIC

Factors affecting stalling speed

Pulling ‘g’

V STALL MAN’VRE = V STALL BASIC X “g”

V STALL HVY = V STALL BASIC XLIFT HEAVY

LIFT BASIC

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

EFFECT OF ‘G’’

Danger

Danger Danger

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

Weight

Lift

Thrust

Flight Path

EFFECT OF THRUST ON STALLING

Weight

Thrust

LiftLift TR

Flight Path

EFFECT OF THRUST ON STALLING

EFFECT OF THRUST ON STALLING

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

FLIGHT PATH

NATURAL STALL WARNINGSpeed

Nose Attitude

Controls

Light Buffet

Heavy Buffet

Nose Drop

Wing Drop

Descent

NATURAL STALL WARNING

NORMAL FLIGHT

TURBULENTAIR MISSINGTAILPLANE

NATURAL STALL WARNING

NORMAL FLIGHT

TURBULENTAIR MISSINGTAILPLANE

TURBULENT AIR JUST TOUCHINGTAILPLANE

STALL WARNINGLIGHT BUFFET

NATURAL STALL WARNING

TURBULENT AIR JUST TOUCHINGTAILPLANE

STALLHEAVY BUFFETSTALL WARNINGLIGHT BUFFET

TURBULENT AIRCOVERINGTAILPLANE

Aircraft Descending

Synthetic Stall Warning

Firefly/Tutor:Warning HornWarning Light (Firefly only)

Tucano:Warning HornAoA GaugeStick ShakerIndexer

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

Relative Airflow

Chord

Basic ‘Clean’ Situation

α

EFFECT OF FLAP

Relative Airflow

Chord

Flap Lowered

α

Basic ‘Clean’ Situation

Effective Increase in AoA

EFFECT OF FLAP

Flap Lowered

α

Maintaining the Same Lift

Effective Increase in AoATo obtain the same CL the Attitude is Lowered to Reduce the AoA

Cl Max

AT STALL: WEIGHT = LIFT = CLMAX ½ρ V2

STALL S

EFFECT OF FLAP

Critical Angle

Without Flap

AoA

CL

AT STALL: WEIGHT = LIFT = CLMAX ½ρ V2

STALL SIF THIS IS THIS IS

CONSTANT MORE LESS

EFFECT OF FLAP

Critical Angle

With FlapCl Max More

AoA

CL

Nose lowerat Stall

Without Flap

Cl Max

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”:Increase.If the Aircraft is damaged or had a Birdstrike, it willprobably:Increase.Using Engine Thrust:Decrease.

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:

1. Describe the Stall in terms of Lift.

2. State the generally used Critical or Stall

Angle of Attack.

3 Understand the relationship between Stalling and Airspeed.

4. State where the Pilot obtains information regarding theAircraft’s Stalling Speed.

5. List the Factors which affect the Stalling Speed.

Questions

What happens to Lift when a Wing is Stalled?

a. Lift Increases as Angle of Attack Decreases.

b. Lift Decreases as Angle of Attack Increases.

c. Lift is Greatly Reduced.

d. Lift Remains unchanged.

Questions

The Critical Angle of Attack is Generally about?

a. 5o.

b. 15o.

c. 25o.

d. 35o.

Questions

Which of the following will NOT REDUCE the Stalling Speed?

a. Extra Weight.

b. Larger Wing Area.

c. Flaps Lowered.

d. Flaps Raised.

Questions

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.