Aerodynamics
How Jetliners Fly
Commercial jetliners -- like all airplanes -- fly according to basic physical principles. To find out how they work, following the links below:
- Airplane Parts
- Aerodynamics
- Propulsion
For an interactive version (Flash required), click here.
Aerodynamic Lift
Four forces come into play during a jetliner flight:
- Lift -- The upward force generated by the wings.
- Gravity -- The downward force opposing lift
- Thrust -- The forward force produced by the engines
- Drag -- The rearward pull as air resistance seeks to slow the airplane down
Wings
An airplane wing has a distinctive shape called an airfoil. Seen from the side, an airfoil is curved on top and relatively flat on the bottom.
As a wing moves through the air, it splits the airflow. Some of the air passes above the wing and some below. But because the wing's upper surface is curved, the air rushing over the top is forced to speed up.
The result is decreased air pressure above the wing. In contrast, the air flowing below the wing is slower and its pressure is higher.
The wing is lifted because the air pressure on the top of the wing is lower than the air pressure on the bottom. The faster the airplane flies forward, the more of this aerodynamic "lift" it creates. Flight occurs when the force of lift exceeds the weight of the airplane.
Note:
Aerodynamic lift is based on the Bernoulli principle, which states that the pressure of a flowing fluid decreases as its velocity increases. Daniel Bernoulli (1700-1782) was the first person to define the fundamental relationship between pressure, density and velocity in fluid flows.
Glide
Finally, jetliners are highly efficient gliders. Even without engine thrust, they can glide about 20 feet forward for each 1 foot of altitude they lose. If all engine power were lost at cruise altitude, a typical jet could glide more than 100 miles (160 kilometers) before landing at sea level.