- If you decrease drag by 1% on one 737 it saves $150 000 each year, so
for a company that owns 100 aircraft it makes a
huge difference to reduce drag
- pressure differentials (see overhead #4)
- Low pressure on top, Higher pressure on bottom
- Air wants to move from a high pressure zone to a low pressure zone
--> Balloon Demo
- Since air wants to move into low pressure zone, air pushes the wing up
-
Why is there a pressure differential?
- Newton’s
3rd Law ( For every action there is an equal and opposite reaction)
- Air creates force on wing, so wing puts a force on the air the same way
that as I stand on the floor the floor is holding me up
with the same force I exert on it
- Same as treading water, you are pushing down on the water so the water
is pushing up on you
--> Collision Demo
- P=F/A There is a pressure acting on the area where the force is
applied
- Gives a high pressure on the bottom of wing
- Air moving faster creates a low pressure (Moving air sucks – Bill Nye
the Science Guy) (see overhead #5)
- Can feel this effect when riding a bike and a MAC truck goes by on the
highway
- Air is moving faster on top side of wing then the bottom so there is
a lower pressure on the top surface -> LIFT
--> Flying Disk Demo (see overhead #6)
- Why air moves faster over the wing then under it – Air hits bottom of
wing and slows down as it changes direction
- Stall is when the air is not moving flowing smoothly over the wing ->
Loss of lift
- Speed bump analogy
--> Wind Tunnel Demo
- Reasons to use different airfoils
- Lift is created by a pressure difference on the top and bottom surfaces
of the wing (see overhead #8)
- The theory that we looked at today is only for aircraft that go less
then the speed of sound (343m/s compared to you running at 4 m/s.)
- Supersonic aircraft don’t follow this theory because air behaves differently
once you move faster then the speed of sound so
they use very different types of airfoils
