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Principles of Flight
Principles of Flight
Learning Outcome 2:
Understand how the stability of an aeroplane is
maintained in flight and how manoeuvrability
is controlled
Part 1
Principles of Flight
A Ship
C Tower
A Bourne
H Copter
B Loons
R Way
Dan
Winterland
S Huttle
I Flyum
Revision
Questions
What is the force called that drives an aircraft forwards?
Lift
Weight
Drag
Thrust
Questions
What is the force called that resists the forward motion of
an aircraft?
Lift
Weight
Drag
Thrust
Questions
If your speed is doubled, by how much would the
Drag be increased?
x2
x4
x6
x8
Questions
If Thrust = Drag and Lift = Weight
then the aircraft is:
Climbing
Flying Straight & Level and Accelerating
Flying Straight & Level an Decelerating
Flying Straight & Level at Constant Speed
Stability
Objectives:
1. Identify the Axes of Rotation for an Aircraft.
2. Identify the Planes of Movement for an Aircraft.
3. Describe and Explain Stability in the 3 Planes of
Movement.
4. Explain Dihedral and Anhedral and how they affect
Stability.
OW!!
Stability
What would happen to this dart when thrown?
What would happen now?
Something is needed to “Stabilise” the Dart (Aircraft).
Stability
Airflow
Centre of Gravity (CG)
Airflow
‘Body’ Ahead of CG is Destabilising.
‘Body’ Behind CG is Stabilising.
Basic Stability
Stable
Unstable
Neutral
Basic Stability
Stable
Forms of stability
•Static
•Dynamic
- initial reaction
- subsequent reaction
Basic Stability
Stable
Forms of stability
•Static
•Dynamic
- initial reaction
- subsequent reaction
Basic Stability
Stable
Forms of stability
•Static
•Dynamic
- initial reaction
- subsequent reaction
Basic Stability
Stable
Forms of stability
•Static
•Dynamic
- initial reaction
- subsequent reaction
Basic Stability
Stable
Forms of stability
•Static
•Dynamic
- initial reaction
- subsequent reaction
Application to Aircraft
Static Stability
Unstable
Neutral
Stable
Application to Aircraft
Statically Stable
Dynamic Stability
Dynamically Neutral
Dynamically Unstable
Dynamically Stable
Planes of Stabilisation
Pitch
(Longitudinal)
Yaw
(Directional)
Longitudinal
Axis
Roll
(Lateral)
Lateral
Axis
Normal
Axis
Stabilisation
Axis
Longitudinal
Plane
Stability
Rolling
Lateral
Stability
Stabilisation
Axis
Plane
Stability
Longitudinal
Rolling
Lateral
Lateral
Pitching
Longitudinal
Stability
Stabilisation
Axis
Plane
Stability
Longitudinal
Rolling
Lateral
Lateral
Pitching
Longitudinal
Normal
Yawing
Directional
Stability
Directional Stability
Directional Stability
Stabilising
Influence
of fin:
1. Value of Lift
2. Moment Arm
CG
Flight
Path
Lift
Enhancement features:
A large finSomething
and/or a long
moment
arm to yaw
causes
the aircraft
CofG Considerations
An aft CofG requires a large Fin
The strange case of the ever growing fins
MOD
Longitudinal Stability
Longitudinal Stability
Lift
Flight
Path
Weight
To explain this stability, we assume that the CP and CG
are coincident.
Longitudinal Stability
Lift
Lift
Flight
Path
Weight
Something causes
the nose
to rise
Lift wings - Destabilising
Stabilising
influence
of Tailplane:
Lift tailplane - Stabilising
Area x Moment Arm = Tail Volume
Lateral Stability
Lateral Stability
Lift
Resultant Sideslip
Weight
Lateral Stability
Hdg
Aircraft sideslips
in this direction
All design features for lateral stability rely
on the fact that bank results in sideslip
Lateral Stability Methods
1. Large Fin of high aspect ratio (a big tall fin).
Lift from fin
rolls wings level
Lateral Stability Methods
2. Dihedral: Due to new direction of relative airflow –
lower wing has higher AoA than upper - more lift - tends
to roll wings level.
Lift
Lateral Stability Methods
3. Sweepback
Span
More
Chord
Less
Aspect Ratio
Lift
Higher
Less
More
Lower
More
Less
LOW WING
Lateral Stability Methods
4. High wing
Less Lift
More Lift
Air flow near wing roots affected
by fuselage - Increases AoA on
Low Wing -Decreases AoA
on High Wing
Relative Airflow
Lateral Stability Methods
1. High Fin.
2. Dihedral.
3. Sweepback.
4. High Mounted Wing
But too much Lateral Stability
(High wing and Sweepback)
very undesirable in fighter aircraft.
Therefore anhedral to reduce the excess
Any Questions?
Stability
Objectives:
1. Identify the Axes of Rotation for an Aircraft.
2. Identify the Planes of Movement for an Aircraft.
3. Describe and Explain Stability in the 3 Planes of
Movement.
4. Explain Dihedral and Anhedral and how they affect
Stability.
Questions
What are the 3 planes of an aircraft’s movement?
a. Pitching, Lateral and Rolling.
b. Pitching, Rolling and Yawing.
c. Yawing, Longitudinal and Rolling.
d. Longitudinal, Lateral and Normal.
Questions
Which one of the following will REDUCE Lateral Stability?
Dihedral.
A Large Fin.
Sweepback.
Anhedral.
Questions
What are the 3 Axes about which an Aircraft can move?
a. Pitching, Lateral and Longitudinal.
b. Pitching, Rolling and Yawing.
c. Yawing, Longitudinal and Normal.
d. Longitudinal, Lateral and Normal.
Questions
Which 3 Terms describe Static Stability?
a. Stable, Neutral and Unstable.
b. Stable, Rolling and Unstable.
c. Yawing, Neutral and Stable.
d. Neutral, Unstable and Pitching.

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