- Concepts
- Forces
in flight
i.
Lift
1.
upward force
2.
combination of 2 forces: Newton ’s
3rd law, Bernoulli Effect
ii.
Drag
1.
backward force
2.
a type of air resistance
iii.
Thrust
1.
forward force
2.
generated by propeller, rocket, catapult
iv.
Weight
1.
downward force
2.
caused by gravitational pull
- Lift
and Drag
i.
Can only be seen when there is air moving past
an object
ii.
Bernoulli Effect
1.
Shape & angle of airfoil: force the oncoming
air to curve as it passes the top side of the airfoil
2.
due to the curve: air above the foil moves
faster and farther than the air under the foil
3.
increased speed of air means lower pressure
--> lower pressure on top side of airfoil
4.
--> airfoil is pushed upward
iii.
Third Law
1.
bending airflow: wing redirects the flow of air
downwards --> downward force means there is an equal and opposite force on
the foil, pushing it upwards --> creates lift
iv.
Drag
1.
depends on shape, size, and quality of wing
a.
a thin, streamlined wing will have less drag
than a thick, boxy one
b.
a polished wing will have less drag than a rough
one
v.
Stall
1.
too high angle of attack --> the air flowing
above and below the foil will separate into turbulent eddies
2.
this causes the foil to lose lift and increase
drag
3.
this causes partial or total loss of control
unless the angle of attack is lowered
- Airfoil
Types
i.
High Lift, High Drag
1.
as seen on crop duster planes
2.
pros: extra lift, can take off/land on short
runways
3.
cons: thickness causes a lot of drag --> fly
slowly, cover shorter distances
ii.
Low Lift, Low Drag
1.
as seen in fighter jets
2.
pros: generates low drag; allows for high-speed
movement
3.
cons: because there is not much lift, the
aircraft must move at high speeds in order to keep aloft
iii.
Moderate lift, moderate drag
1.
as seen in small, light propeller aircraft
2.
pros: good for general-purpose aircraft;
inexpensive to build because of the basic, flat-bottom shape of the airfoil
3.
cons: does not allow for high speeds
iv.
moderate lift, low drag
1.
as seen in aerobatic planes
2.
pros: since the airfoil is symmetrical: little
drag, can create lift when flying upside-down
3.
cons: cannot produce lift if angle of attack is
0
v.
Laminar Flow: is the smooth,
uninterrupted flow of air over the contour of the wings, fuselage, or other
parts of an aircraft in flight. Laminar flow is most often found at the front
of a streamlined body and is an important factor in flight. If the smooth flow
of air is interrupted over a wing section, turbulence is created which results
in a loss of lift and a high degree of drag. An
airfoil designed for minimum drag and uninterrupted flow of the
boundary layer is called a laminar airfoil.
vi.
Angle of Attack:
Angle between direction of airflow and the chord; important because it can
cause lift and drag
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