Back to Race Tech Start Page
Angle of Attack
Angle of Attack
The difference between where the wing is pointed and the direction
of the air flowing over the wing is the angle of attack as shown
in this schematic.
The graph below shows how lift and drag changes with the angle
of attack for a typical wing design.
Where the curve crosses the Drag axis is where the wing is
generating zero lift. Notice the angle of attack at that point
is a negative value. That means a typical wing has to point down
to get to zero lift. Notice, also, there is some drag at zero
lift. There is, truly, no free lunch.
As the nose of the wing turns up, angle of attack increases,
and lift increases. Drag goes up also, but not as quickly as
lift. Think about the last time you took a trip on an airplane.
During take-off an airplane builds up to a certain speed and
then the pilot rotates the plane; that is, the pilot
manipulates the controls so that the nose of the plane comes
up and, at some angle of attack, the wings generate enough lift
to take the plane into the air. Since an airplane wing is fixed
to the fuselage, the whole plane has to rotate to increase the
wing's angle of attack.
A wing is fairly efficient. You get a lot of lift without
much draguntil you get to about 12 degrees angle of attack
on this curve. Then drag goes way up, without creating much more
lift. As the angle of attack increases from 12 to 19 degrees
for this particular design, there isnt much increase in
lift but you have a lot more drag. We say the wing is stalled
when lift decreases at increasingly higher angles of attack.
The shape of this curve is why you read about airplane crashes
during stormy takeoffs and landings. Under conditions of low
speed and high lift, the plane is rotated up there near the top
of the curve. If the plane has to climb and the pilot tries to
bring the nose up, he gets more drag and not much more lift.
What he really needs is more airspeed. A few years ago most airlines
changed their procedures and you don't see planes landing at
high angles of attack any more.
Front wings on racecars are fabricated so the angle of attack
is easily adjustable to vary the amount of downforce needed to
balance the car for the driver. You see that happening at pit
stops during a race. Rear wings are also adjusted by changing
the angle of attack but that takes too much time for a pit stop.
Sometimes you'll see a team change a Gurney flap during a pit
stop and that's the next Race Tech story coming soon.