All that is necessary to create lift is
to turn a flow of air. An aerodynamic, curved airfoil will turn a
flow. But so will a simple flat plate, if it is inclined to the flow. The
fuselage
of an airplane will also generate lift if it is inclined
to the flow. For that matter, an automobile body also turns the flow
through which it moves, generating a lift force. Lift is a big problem
for NASCAR racing machines and race cars now include
spoilers
on the roof to kill lift in a spin. Any physical body
moving through a fluid can create lift if it produces a net turning
of the flow.
There are many factors that affect the turning of the flow, which
creates lift. We can group these factors into(a) those associated
with the object, (b) those associated with the motion of the object
through the air, and (c) those associated with the air itself:
- Object: At the top of the figure, aircraft
wing geometry has a large effect on the
amount of lift generated. The airfoil
shape and wing size will both affect
the amount of lift. The ratio of the wing span to the wing area also
affects the amount of lift generated by a wing.
- Motion: To generate lift, we have to move
the object through the air. The lift then depends on the
velocity of the air and how the object is
inclined to the flow.
- Air: Lift depends on the mass
of the flow. The lift also depends in a complex way on two other
properties of the air: its viscosity and
its compressibility.
We can gather all of this information on the factors that affect
lift into a single mathematical equation called the Lift
Equation. With the lift equation we can predict how much lift
force will be generated by a given body moving at a given speed.
You can investigate the various factors that affect lift by using
the FoilSim II Java Applet. Have fun! You
can use the browser "Back" button to return to this page. If your
want your own copy of
FoilSim to play with, you can download
it at no charge.
Activities:
Guided Tours
-
Factors that Affect Lift:
-
FoilSim:
-
Wings:
-
Spoilers:
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