Lecture Leading Cadet Training Principles of Flight 2 Lift and Thrust.
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Lectur e Leading Cadet Training Principles of Flight 2 Lift and Thrust
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Resulting in an upward force which adds to the lift needed to hold up the aircraft in flight. This deflects some of the lower airflow downwards. Lift
Transcript of Lecture Leading Cadet Training Principles of Flight 2 Lift and Thrust.
Lecture
Leading Cadet Training
Principles of Flight
2Lift and Thrust
Lift
Free Stream Flow
Leading Edge
Trailing Edge
Chord Line
Angle of Attack α
In most flight conditions, the wing is inclined to the airflow
at a slight positive angle (The Angle of Attack)
This is the angle between the Chord Line, and the oncoming air or Free Stream Flow.
Resulting in an upward force which adds to the lift needed to hold up the aircraft in flight.
This deflects some of the lower airflow downwards.
Lift
How Lift VariesWe know that pressure difference between
the air above and below the wing, tends to lift the wing up.
But lift is not evenly distributed over the wing.
How Lift VariesAll lift forces act at 90o to the airflow,
but the top of the wing generates more lift than the bottom.
The greatest amount occurswhere the surface is most curved,
towards the leading edge.
Oncoming Air
How Lift VariesAirspeed
Altering the airspeed will vary the amount of lift.Lift increases at the square of the speed.
Double the airspeed gives four times the lift;
Treble the airspeed gives nine times the lift.
Airspeed Lift
How Lift Varies
Lift
Air DensityIf the air becomes ‘thinner’ or less dense,
the amount of lift is reduced.
Consequently the higher you go, the less the lift.
Air Density
+
+
_+
+
_
++
_
How Lift VariesAngle of Attack and the Pressure Envelope
Free Stream FlowAngle of Attack
α
0o5o10o15o
+ +
_
The Angle of Attack alters the Pressure Envelope.
As the Angle of Attack increases, the pressure above decreases,
and the wing produces more LIFT.
How Lift VariesWing Shape
General Purpose High Lift
High Speed High Speed
High Speed High Speed
How Lift VariesWing Shape and Area
Low aspect ratio 2.4:1
High aspect ratio 16:1
ASPECT RATIO The ratio of : wing span
mean chordor
wing span2
wing area
When all the ‘variables’ are put together we can derive a formula for lift:
Lift = CL ½ρ V2 S
CL = Coefficient of Lift(the ratio between lift and dynamic pressure).ρ = Density (rho)V = True AirspeedS = Surface Area
Lift Formula
Coe
ffici
ent o
f Lift
C
L
Angle of Attack α
2
1.5
0
.25
.5
.75
1
1.25
1.75
-10o -5o 0o 5o 10o 15o 20o 25o 30o
MaximumCL
StallingAngle
Besides the forces of lift and weight, which act on an aircraft in flight,
there are other forces to consider.
Initially, how to propel the aircraft,and for this we need –
ThrustThrust
Thrust
To produce lift, a wing needs airflow over the top of it …..
This airflow is increased by the engine
‘thrusting’ the aircraft forwardsby “pushing” the air backwards
Thrust
The aircraft engine thrusts air backwards, by either:
A propeller - which ‘screws’ the air backwards …
or
A jet engine – expelling air backwards
Thrust
In both cases, throwing the air backwards,thrusts the aircraft forward.
Thrust
Check of UnderstandingWhere is the greatest amount of lift normally generated on an aerofoil?
The Trailing Edge
The Top Surface
The Leading Edge
The Bottom Surface
Check of UnderstandingIf the air density in an airflow is reduced,
and all other factors are unchanged,What happens to the lift generated by the wing
in that airflow?
The lift becomes unpredictable
The lift is reduced
The lift is increased
The lift stays the same
Check of UnderstandingIf the airspeed is increased,
what happens to the lift?
It fluctuates
It decreases
It increases
It remains constant
Check of UnderstandingIf you double the airspeed,
the lift would increase by a factor of what?
Eight (8)
Two (2)
Six (6)
Four (4)
Check of UnderstandingWhich of these wing sections
is for general purpose?
D
A
C
B
Check of UnderstandingWhat is the force called
that drives an aircraft forwards?
Drag
Thrust
Weight
Lift
What name is given to the termif the wing is inclined to the airflow
at a slight positive angle?
The Angle of Attack
The Free Stream Flow Angle
The Chord Line Angle
The Angle of Pressure
Check of Understanding
What is meant by the termAngle of Attack?
The angle the wing is swept-back
The angle between the chord lineof the wing and the oncoming air
The angle at which the wing is fixed to the fuselage
The angle between the chord line of the wing and the leading edge
Check of Understanding
Principles of Flight
End of Presentation
Leading Cadet Training
