START…
Lesson Presentation for Transportation
FORCES
Lift
Gravity
Drag Thrust
LIFT
Pushes up on bottom of wing Pulls up on top of wing Created by airfoils, Opposes gravity Requires power
Engine Gravity Rocket
GRAVITY
Pulls planes toward earth Opposes lift Gives gliders their source of power
THRUST
Force pushing plane forward Opposes drag Created by engine driven props, rockets or jet engines
DRAG
Force pulling back on a plane Opposes thrust Every surface adds more
DRAG
Parasitic drag:
The “Stuff” that causes more drag
Antenna Landing gear Wing struts
DRAG
More drag on one wing results in turns
BERNOULI’S PRINCIPAL
The pressure of a fluid (liquid or gas) decreases at points where speed increases
High speed = Low pressure Low speed = High pressure
AIRFOIL
Increases velocity of airflow on top Decreases velocity on bottom As air is pulled around the top of a wing it accelerates air down (creating lift)
Knowing Newton!
(Great Old Guys in History)
Newton’s third law:
For every action there is an equal and opposite reaction
Wings move through the air accelerating the air above them down. The change in momentum of the air accelerated down is equal to the lift created by a wing ……. F=MA
FANS IN THE SKY
If ………..a fan creates a tunnel of
air,
Then …...from one blade’s perspective it Think…..of wings as blades on a fan,
or a propeller (all are airfoils)
MORE
is pushing back a steady stream of air at a 90o to it’s self
Air is diverted from blades at 90o Wings are like horizontal fan blades The fan blade creates a vacuum ahead of it The blade creates a pressure behind it
COANDA EFFECT
(How wings divert air down)
Tendency for fluids to follow a curved surface Air has viscosity
COANDA EFFECT
The further from the surface the greater the air flow The change in velocity bends fluids(air) toward the surface As a result of the coanda effect Air follows surface of airfoil
DOWNWASH
Downward velocity of the air off the trailing edge of a wing To gain more lift wings can either:
Move more volume of air Increase the velocity of the air
UPWASH
Adds complication to airfoils Air is diverted up at the leading edge of a wing Negates some of the lift created by a wing
ANGLE OF INCIDENCE
The angle formed by the longitudinal axis of the plane and the chord of the wing
BIG NUMBERS
IF
•Air weighs approx. 2lbs./yard at sea level
•A Cessna 172 needs approx. 2300 lbs of lift to keep it up
Then
•A Cessna wing must pump almost 2.5 tons/sec of air
•This # might be as much as 2x too low because of up wash
•The vertical component of the downwash at 110 knots is 9 knots
End