Transcript Basic Nav tests - Chelmsford Air Cadets

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Principles of Flight
Principles of Flight
Learning Outcome 1:
Know the principles of lift, weight, thrust and drag
and how a balance of forces affects an
aeroplane in flight
Part 2
Principles of Flight
Revision
Questions
Newton’s 3rd Law States:
a. Every object has weight.
b. Weight equals lift during flight.
c. Every action has an equal and opposite reaction.
d. Every force causes an object to move.
Questions
In which direction does LIFT operate relative to airflow?
a. Parallel to it.
b. Perpendicular (at 90o) to it.
c. Straight up.
d. Straight down.
Questions
What has happened to the air pressure at point ‘B’?
C
A
B
a. It is greater than at point ‘A’.
b. It is greater than at point ‘C’.
c. It is the same as point ‘C’.
d. It is lower than at point ‘A’.
Drag and Thrust
Objectives:
1. Explain Drag and Thrust.
2. Describe the effect that Streamlining has on Drag.
3. State the effect that Airspeed has on Drag.
4. Describe the relationship between Drag and Thrust
when an aircraft is:
a. At Constant Speed.
b. Accelerating.
c. Decelerating.
Drag and Thrust
Lift
Thrust
Drag
Weight
Thrust
How do we produce Thrust?
Propellers
Jet Engines
Thrust
Remember Newton’s 3rd Law?
The engine achieves this by “pushing” the air backwards
from either through a propeller or from the rear of a jet
engine. The amount of Thrust depends on engine size,
etc.
Drag
What is Drag?
Remember riding a bicycle into a wind or riding faster?
PHEW!
!
Variation of Drag with Airspeed
The amount of Drag varies with the square of the Airspeed.
So,
Double the Airspeed, then Drag is Four times as much!
Triple the Airspeed, then Drag is Nine times as much!
Drag
Airspeed
Drag
Drag is the force which hinders your progress.
The faster you go the more drag you feel.
We need Thrust to overcome the Drag.
Consider:
Airflow
Maximum Drag.
20 “people” needed on “the team”.
Drag
What happens we pull a ball of the same diameter as the
plate?
Airflow
Drag is reduced by 50%.
Now only 10 “people” needed on “the team”.
Drag
What happens we ‘streamline’ a shape of the same
diameter?
Airflow
Drag is reduced to 5%.
Only 1 “person” needed on “the team”.
Form Drag
VERY TURBULENT WAKE
REDUCTION IN FORM DRAG
50%
85%
90 - 95%
Drag
This type of drag is “Form Drag”, ie the shape of the
object.
So do we need:
This Shape?
OR?
This Shape?
Reducing Drag, reduces the amount of Thrust required!
Examples of Streamlining
Surface Friction Drag
Boundary layer
Total surface area
Viscosity of the air
Thickness of the boundary layer
Surface friction drag is reduced by
smooth surfaces
Interference Drag
Reduced by adding fairings
JSF
Zero Lift Drag
1. Form Drag (The Shape)
Streamlined Shape
5lbs drag
Flat Plate
100lbs drag
Smooth - 4lbs drag
Rough - 6lbs drag
2. Surface Friction Drag (Smooth/Rough)
3. Interference Drag
11lbs drag
5lbs drag
Lift Dependent Drag
Low Pressure
Low Pressure
Relatively High Pressure
Formation of Wingtip Vortices
TIP VORTEX
SPILLAGE
Effect of Speed on Wing Tip Vortex
LOW SPEED
LARGE VORTEX
HIGH SPEED
SMALL VORTEX
Effect of Aspect Ratio on Wing Tip Vortex
HIGH ASPECT RATIO
LOW ASPECT RATIO
CHORD
CHORD
SMALL VORTEX
LARGE VORTEX
Vortex Drag
Drag
Drag has several components as the following “Tree”
will illustrate:
Surface
Friction
Drag
Form
Drag
Zero
Lift
Drag
Interference
Drag
Total
Drag
Vortex
Drag
Lift
Dependent
Drag
Increments of
Zero Lift Drag
Drag
Drag can be represented by the following
graph:
TOTAL DRAG
DRAG
ZERO LIFT DRAG
LIFT DEPENDENT DRAG
IAS
VIMD
Thrust and Drag in Straight & Level Flight
Aircraft Accelerating:
What is the difference between Thrust and Drag?
Thrust is Greater than Drag
Thrust and Drag in Straight & Level Flight
Aircraft Decelerating:
What is the difference between Thrust and Drag?
Drag is Greater than Thrust
Thrust and Drag in Straight & Level Flight
Aircraft Constant Speed:
What is the difference between Thrust and Drag?
Thrust = Drag
Straight & Level Flight
For Straight & Level Flight at Constant Speed
ALL Forces are in Balance
Lift
Thrust
Drag
Weight
ANY QUESTIONS?
Drag and Thrust
Objectives:
1. Explain Drag and Thrust.
2. Describe the effect that Streamlining has on Drag.
3. State the effect that Airspeed has on Drag.
4. Describe the relationship between Drag and Thrust
when an aircraft is:
a. At Constant Speed.
b. Accelerating.
c. Decelerating.
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 you 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 and Decelerating
Flying Straight & Level at Constant Speed