lecture leading cadet training principles of flight 3 drag
TRANSCRIPT
Lecture
Leading Cadet Training
Principles of Flight
3Drag
Every part of the aircraft over which air flowsproduces drag.
This drag directly opposes thrust.
The more drag there is,the more thrust is needed to overcome it.
DRAGTHRUST
Drag
Anyone on a bicycle knows the faster you go, the more air resistance you encounter.
The force which hinders your progress
is called ‘DRAG’.
Drag
Drag will be least when parallel to the airflow.
What causes Drag ?
Drag is formed by the shape of an object.
When holding a flat plate in an airflow: Drag will be greatest when the plate is at 90°
The object is to reduce this Form Drag.
Drag is formed by the shape of an object.
When an object passes through the air
it is accompanied by a wake.
Wake is the turbulent airflow
immediately behind the aircraft.
Wake produces drag –
the bigger the wake,
the bigger the drag.
Drag
Surface Friction Drag Is caused by the ‘rough’ skinof an object.
Interference DragTwo surfaces meeting at an angle, causes airflow drag.
This is minimized by fairing and filleting to inducesmooth mixing of air past the affected surfaces.
Types of Drag
Drag
Lift Dependent DragIs drag caused by the lift associated with the changein the angle of attack.
Most of the drag caused at take-off is lift-dependent.
Wingtip VorticesAre tubes of circulating air behinda wing as it generates lift.
A wingtip vortex trails from the tipof each wing.
Relatively High Pressure
Low PressureLow Pressure
VORTEX
Types of Drag
Drag
Zero Lift Drag
Streamlined Shape5lbs drag
Form Drag(The Shape) Flat Plate
100lbs drag
Smooth - 4lbs drag
Surface Friction Drag(Smooth/Rough)
Rough - 6lbs drag
Interference Drag(Components)
5lbs drag
11lbs drag
Drag
Wingtip Vortices
LOW SPEED HIGH SPEED
The effects of Speed on Wingtip Vortices.
LARGEVORTEX
SMALLVORTEX
Drag
Wingtip Vortices
HIGH ASPECT LOW ASPECT
The effects of Aspect Ratio on Wingtip Vortices.
LARGEVORTEX
SMALLVORTEX
CHORD CHORD
Drag
How can Drag be minimised ?
By not building in drag at the design stage.
By eliminating as many protruding edges as possible….
By ‘streamlining’ the design.
Drag
How can Drag be minimised ?
Drag
By designing the shape to have a fineness ratioof between 3:1 and 4:1
The fineness ratio is the ratio of the length of a body to its maximum width;
"short and fat" shapes have low ratios, while "long and skinny" have high ratios.
DragDrag and Airspeed
The amount of drag varies with the square of the airspeed -
Twice the airspeed = 4 times the drag.
3 times the airspeed = 9 times the drag.
AIRSPEED DRAG
Drag and Thrust
THRUST DRAG
In un-accelerated straight and level flight:
The aircraft will maintain speed.
Thrust = Drag
If thrust is greater than drag
the aircraft will speed up.
Thrust > Drag
If drag is greater than thrust
the aircraft will slow down.
Drag > Thrust
Drag
An Aircraft in Balance
In straight and level flight, at constant speed, two pairs of forces act on the aircraft.
The thrust opposes the drag and is equal to it,
The lift equally opposes the weight.
WEIGHT
LIFT
DRAGTHRUST
Summary
Check of UnderstandingWhich part(s) of an aircraft produce drag?
Only those parts producing thrust
Only those parts producing lift
Every part that air flows over
The fuselage but not the wings
Check of UnderstandingDrag directly opposes what?
Thrust
Pressure
Lift
Weight
Check of UnderstandingWhich of these objects of equal width,
will produce the least drag?
Airflow
D
A
C
B
Check of UnderstandingHow can drag best be minimised?
By decreasing the airspeed
By increasing the airspeed
By reducing the weight
By streamlining the design
Check of UnderstandingWhat type of drag is formed
when two surfaces meet at a sharp angle?
Interference Drag
Surface Friction Drag
Wingtip Vortex Drag
Lift Dependant Drag
Check of UnderstandingWhen an object passes through the air,
what is it accompanied by?
Wake
Wind
Thrust
Lift
Check of UnderstandingWhat type of drag is dependant upon
the rate of change of velocity through the boundary layer?
Wing Vortex Drag
Interference Drag
Surface Friction Drag
Lift Dependant Drag
Check of UnderstandingWhat is Lift Dependent Drag?
Drag caused by the wingtip vortex
Drag caused by the shape of the object
Drag caused by lift associated withthe change in the angle of attack
Drag caused by the ‘rough’ skin of an object
Check of UnderstandingA streamlined shape with an airspeed of 100 kts
has a drag of 200 n.If the airspeed is increaded to 300 kts
what will the drag be?
3600 n
400 n
1800 n
800 n
Principles of Flight
End of Presentation
Leading Cadet Training