Ever wondered why airplanes fly at high altitudes? Why not maintain the minimum altitude that clears all obstacles – why the excess climb?
For an airplane to fly at high altitudes, the aircraft must first climb to that altitude, which requires additional lift and a certain minimum forward velocity. To attain these two, the aircraft engines rotate at high rpms during the climb, thus leading to a higher fuel flow into the engines.
Moreover, flight at higher altitudes requires artificial pressurization that enables us to breathe freely at that altitude where the air pressure has dropped drastically. Due to this lower atmospheric pressure outside the aircraft and higher artificial pressure inside the plane, any event that punctures the fuselage would be catastrophic! With all this in mind, the question arises…
Why do Jet Airplanes Fly at High Altitudes?
To answer the question plainly, it’s a matter of cost-effectiveness. The purpose of a jet aircraft operating in an airline is to carry payload (passengers/cargo) from one place to another. For an airline operator, using the minimum amount of fuel required to transport the payload from point A to point B would translate into cost-effectiveness.
The Role of Air Density in Increasing Flight Efficiency
When an airplane is flying at high altitudes, it requires less fuel than the amount that is required at lower altitudes. How does fuel quantity required by the engines decrease with altitude?
Jet engines function when supplied with a stoichiometric fuel/air mixture. The fuel/air mixture introduced into the core engine must have a specified ratio between the air molecules and fuel molecules. The provision of this stoichiometric ratio results in high efficiency of the jet engine.
With the increase in altitude, the density of air decreases. The reduced density means a lower number of air molecules entering the core engine. For the fuel/air mixture to maintain its stoichiometric ratio, the required number of fuel molecules must decrease to cater for the decreased number of air molecules. This results in a lower amount of fuel required at higher altitudes.
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.
Pages: 1 2