Editing Propulsion (section)

===Air propulsion===
{{main|Powered aircraft}}
[[File:Tupolev Tu-95 in flight.jpg|thumb|left|A [[turboprop]]-engined [[Tupolev Tu-95]] ]]

An aircraft propulsion system generally consists of an [[aircraft engine]] and some means to generate thrust, such as a [[propeller (aircraft)|propeller]] or a [[propulsive nozzle]].

An aircraft propulsion system must achieve two things. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising. And second, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate. The greater the difference between the thrust and the drag, called the excess thrust, the faster the airplane will accelerate.<ref name=":0" />

Some [[aircraft]], like airliners and [[cargo planes]], spend most of their life in a cruise condition. For these airplanes, excess thrust is not as important as high engine efficiency and low fuel usage. Since thrust depends on both the amount of gas moved and the velocity, we can generate high thrust by accelerating a large mass of gas by a small amount, or by accelerating a small mass of gas by a large amount. Because of the aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large mass by a small amount, which is why high-bypass turbofans and turboprops are commonly used on cargo planes and airliners.<ref name=":0" />

Some aircraft, like [[fighter planes]] or experimental high speed aircraft, require very high excess thrust to accelerate quickly and to overcome the high drag associated with high speeds. For these airplanes, engine efficiency is not as important as very high thrust. Modern [[combat aircraft]] usually have an afterburner added to a [[low bypass turbofan]]. Future [[hypersonic aircraft]] may use some type of [[ramjet]] or rocket propulsion.<ref name=":0" />