1. 6.07 Stalls References: FTGU pages 18, 35-38
Theory of Flight
6.07 Stalls
References: FTGU pages 18, 35-38

2. 6.07 Stalls Laminar Flow Definition of a Stall Centre of Pressure
Critical Angle of Attack
Stalls
Factors affecting stalls

3. Laminar Flow Boundary Layer – The thin layer of airflow over the wing
Laminar Layer – Smooth portion of the boundary layer nearest the leading edge of the wing
Transition/Separation Point – Point on wing where the boundary layer becomes turbulent
Turbulent layer – Turbulent portion of the boundary layer at the trailing edge of the wing

4. Stall
What is a stall?

5. Stall
When a wing or aerofoil has air flow separation increasing the drag and reducing the lift
No longer capable of producing enough lift to counteract the weight of the aircraft
As a result, can no longer maintain level flight

6. Point on a wing where total aerodynamic pressure acts
Centre of Pressure
Point on a wing where total aerodynamic pressure acts

7. Centre of Pressure
Centre of pressure moves forward as the angle of attack increases to the point of a stall
After a stall the centre of pressure moves rapidly back
If the CoP moves forward of the CG it causes an aeroplane to become unstable, nose of the aeroplane does not drop at the stall

8. Critical Angle of Attack
The AoA above which airflow will separate and become turbulent
The wing stall will occur at any speed

9. Critical Angle of Attack
Most aerofoil or wing designs have a stall angle of 15° to 20°

10. Stall
Centre of pressure and separation point move forward to point of stall and lift production is increased
Angle of attack is increased beyond critical angle of attack
Wing stops producing lift and stalls
Centre of pressure moves rapidly backward

11. Stall
Symptoms of a Stall
Buffeting

12. Factors affecting a Stall
Position of the Centre of Gravity, more forward CG the higher the Vs
Weight, increase in wt = increase in Vs
Turbulence, changes the load factor as well as sudden changes in AoA (greater then the critical AoA)
Turns, increases the load factor which increases the Vs
Snow, Frost, Ice cause early airfoil separation causing an increase in Vs

13. Factors affecting a Stall
Centre of Gravity (CG)
CG forward
Loading on the horizontal tail surfaces increases
Overall weight of aircraft increases
Vs increases
CG aft
Decreased longitudinal stability
Violent stall characteristics
Poor or NO stall recovery (very dangerous!)
Vs decreases

14. Factors affecting a Stall
Weight
The more weight on an aircraft means that it must fly at a higher AoA (for a given speed)
Therefore the critical AoA will be reached at a higher airspeed (instead of stalling at 40 kt stalls at 50 kt)
Attitude to fly straight and level
2500 lbs, at 90 kt (closer to the critical A of A)
1000 lbs, at 90 kt
Start of a trip
End of a trip

15. Factors affecting a Stall
Turbulence
Upward vertical currents cause the aeroplane’s AoA to increase
Could result in the aeroplane stalling of the critical AoA is reached, more likely at reduced speeds (approach)

16. Factors affecting a Stall
Turns
As angle of bank increases the load factor also increases
Therefore, an increased angle of attack is required to maintain level flight in a turn
Subsequently, the stall speed in a turn increases, just like adding more weight to the aircraft

17. Turns and Stall Speeds

18. Factors affecting a Stall
Snow, Frost, and Ice
Accumulation of snow, frost, and ice reduce a wing’s ability to produce lift
Increase in Vs

19. Factors affecting a Stall
Increase Vs
Forward CG
Increased weight
Turbulence
Greater angle of bank
Decrease Vs
Aft CG
Decreased weight

20. Confirmation Check

21. Confirmation Draw the movement of the C of P leading up to the stall.
What are some factors that increase the stall speed?

22. Confirmation 3. When can an aircraft stall?
4. What are the symptoms of a stall?

23. Stall Recovery