Why do commercial airplanes typically fly above 30,000 feet?

Question

Why not lower if there are no mountains to contend with?

Answer 1

Fuel economy rises as altitude increases. this is due to the actual mechanism of how jet engines work. Typically air is compressed to some ratio (lets say 30:1) and fuel is added. In order for the mixture to be flammable, you must have a certain ratio of air molecules to fuel molecules. The higher you go, the fewer air molecules you encounter in a given space, to the fewer fuel molecules you require to reach the flammable mixture.

There are also advantages in terms of air resistance. Fewer air molecules bouncing off your airplane means less drag to overcome. But lower air density also affects the angle of attack your wing must operate, so you see an increase in induced drag (drag produced as a byproduct of lift). This is offset easily by the drag savings from air density, and aircraft typically gain approximately 2% of their airspeed for every 1000' they climb. So an aircraft cruising at 30,000' would see an increase in true airspeed of somewhere near 60% over one cruising at sea level. That is a rough "guesstimate" but it works well enough to be used in a practical sense.

Answer 2

Other than using less fuel, they can also take advantage of using the Jet Stream to help propel them, particularly when flying eastward. So with the air being thinner and with the aid of the jet stream, they can really cut down on fuel consumption.

the jet stream usually ranges from 6 to 9 miles above the surface of the earth.

Answer 3

At 30,000 feet the air is so thin that it provides so little drag to the airplane. Because an airliner weighs nearly 100,000 pounds I guess it needs as much help as possible.

Answer 4

The higher one goes, the less dense air becomes. Since air friction and air density are related(the thicker the air the more friction) an aircraft has to fly at an altitude where the air friction is low enough yet the engines will still operate at peak performance

Answer 5

Good answers.

Less air, means less resistance which in turn saves fuel and at that altitude you fly above the weather so there is less turbulence unless, of course, you hit part of the jet stream.

Answer 6

well mate , the higher you go the better it is for any airplane but only to a certain altitude, it is cos of the burners because of so less pressure of air the fuel comsumption is less , , and the planes just float, you fly them near the ground they'll b empty soon, imagine the space shuttles while goin up burn 90% of the fuel just to take off, up there it is fun u can float. but obviously there is no oxygen

Answer 7

When you screw things up there is more room to recover before you smack into the ground.
Two things won't help you when flying:
1) The blue above you
2) The fuel you left on the ground.

Answer 8

maximum commercial plane fly on the better altitudes simply by fact the air is thinner there and the plane run greater effectively. additionally you're generally up greater then the climate and makes for a greater gentle flight for the passengers.

Answer 9

Air is less dense the higher you go so less fuel would be needed and you get out of the weather.

Answer 10

Most "weather." Occurs inside the clouds. over and under where the atmosphere is calmer is preferred. Less turbulence.