Have you ever wondered why airplanes fly at high altitudes? Why not just maintain the minimum altitude where there are no obstacles such as buildings and mountains?
For an airplane to an altitude of about 35,000-40,000 feet, significant fuel consumption (to reach this altitude) is required, as well as artificial cabin pressure, so that passengers can breathe normally. So why do they need to fly so high?
When a plane flies at high altitudes, it requires less fuel than what is required at lower altitudes, which means less cost. How does the amount of fuel required by jet engines is reduced as the altitude increases?
For a jet engine to work, there must be a specific proportion of air and fuel molecules. Therefore, if the molecules of air are many, then more fuel molecules are needed, that is, more fuel.
As the altitude rises, the air density decreases. Reduced density means a smaller number of molecules of air entering the engines. Therefore, since the proportion of air and fuel molecules must be constant, then less fuel is needed, which means less total cost!
Moreover, lower air density at high altitudes also increases flight efficiency by decreasing the skin-friction drag produced by the interaction of air molecules with the surface of the aircraft.
The most effective flight altitude for aircraft with jet engines is regarded to be between 35,000 and 42,000 feet and is associated with the weight of each airplane – that is, heavier planes fly lower and lighter higher so that the total amount of fuel required for the flight is the lowest possible!