RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 1 Brief 8
STALLING
Aim: To learn the principles and considerations of an aircraft approaching a stall, to
recognize the symptoms, and how to correctly recover with a minimum of height loss.
Application: - Inadvertent stall recovery, high AoA / low IAS operations such as
take-off and landing.
Revision:
Aerofoil and Lift
Drag
Lift Distribution
A S
I A O A
Relative airflow
Angle of attack
Chordline
Slow Fast
DRAG
AIRSPEED
Induced Drag
Parasite drag
Minimum Drag TOTAL DRAG
Best L/D Ratio
Pressure distribution
+
_
Aerodynamic Force
Centre of pressure
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 2 Brief 8
Definitions:
Critical Angle
- The AoA where the CL (the lifting ability of the wing) is at a maximum;
beyond that CL decreases markedly.
Stall
- Occurs when the AoA exceeds the critical angle.
Stall Speed (VS )
- The speed at which the aircraft stalls in the following configuration:-
MTOW @ mean sea level, idle power, straight and level altitude and the
most forward CoG position.
Streamline Airflow
- Smooth airflow that remains attached to the surface of the aerofoil.
Turbulent Airflow
- Airflow that cannot remain attached to the aerofoil, creating drag.
Separation Point
- Where the streamline airflow becomes turbulent airflow.
Boundary Layer
- The closest layers of air to the surface of the aerofoil which have reducing
velocities due to both the skin friction and the viscosity of the air. It is
initially laminar then transitions to become turbulent.
Transition Region
- Where the laminar boundary layer becomes a turbulent boundary layer.
Stagnation Point
- Point on the aerofoil where the airflow comes to rest relative to the
aerofoil. Normally occurs at the LE and the TE.
Load Factor
- LF = L/W, measured in ‘g’ numbers.
AoA
CL
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 3 Brief 8
Principles:
Let’s take a closer look at an aerofoil at varying AoA’s:
4 AoA
- Airflow is streamlined with the transition and separation occurring well aft.
Referring to the pilot’s lift formula, most of the lift produced is due to high
airspeed, whilst only a small amount is due to the AoA.
8 AoA
- With the increased AoA comes a further decrease in Pstatic over the
leading section of the aerofoil. Hence the average pressure moves
forward (acting through the CoP), thereby causing an earlier transition
region and separation point.
16 AoA
- At the critical AoA, the lift produced due to the AoA is a maximum and the
CoP is the furthest forward. This causes even earlier separation, creating
more drag and an adverse pressure gradient towards the trailing edge.
16 AoA
- Whilst the aerofoil is still creating some lift, but is insufficient to sustain the
weight. Most of the airflow is turbulent with a rearwards shift in CoP
position, causing a nose drop and loss of altitude
IAS
IAS IAS IAS
CL
CL
CL
CL
L
L L L
W W W W
110kt
4o
70kt
8o
44kt
16o
<44kt
>16o IAS
AoA
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 4 Brief 8
RMIT Flight Training Stalling
RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 5 Brief 8
The stall AoA can be associated with a particular airspeed, since we can’t directly
read AoA (Performance = Power + Attitude):
VS0 = 33KIAS (full flap)
VS1 = 44KIAS (clean)
Usual Symptoms:
1. High nose attitude
2. Low IAS
3. Reduced control effectiveness
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