Fluid Mechanics-II Project Farhan Akram Department of Mechanical Engineering College of Electrical & Mechanical Engineering National University of Sciences & Technology Rawalpindi, Pakistan farhanakram@outlook.com Question - Large commercial airplanes cruise at high altitudes (up to about 40,000 ft) to save fuel. Discuss how flying at high altitudes reduces drag and saves fuel. Also discuss why small planes fly at relatively low altitudes. (Cengel 11-112) Index Terms – Plane, Altitude. SOLUTION The pilot needs to know how high above the earth the plane is traveling, i.e. altitude. For measuring altitude, there is a gauge inside cockpit called an altimeter which measures air pressure, to determine how high the plane is flying at any given time. Inside the altimeter there is a barometer that contracts or expands …show more content…
Air density: Increase of altitude means decrease of air density. The range and endurance increases with altitude because the efficiency of jet engine increases. Temperature: Increase of temperature (of air) will reduce efficiency of jet engine, giving increased fuel flow SUMMARY There are a few reasons the commercial airplanes cruise at high altitudes. • The air is less dense at higher altitudes. With less air in the way there is less drag on an airplane. Traveling in thin air requires much less energy compared to thicker air levels, hence less fuel is needed to hit the same speed. • As the air is cooler at high altitudes, which expands more when heated than warm air. It is the expansion of the air that drives combustion engines. • Also at higher altitudes there is less turbulence because of less weather differentiation. So commercial flights benefit from flying at higher altitudes; the thinner air reduces drag, increases engine efficiency, and saves