An aircraft engine must be:
* reliable, as losing power in an airplane is a substantially greater problem than in an automobile. Aircraft engines operate at temperature, pressure, and speed extremes, and therefore need to perform reliably and safely under all reasonable conditions.
* light weight, as a heavy engine increases the empty weight of the aircraft and reduces its payload.
* powerful, to overcome the weight and drag of the aircraft.
* small and easily streamlined; large engines with substantial surface area, when installed, create too much drag.
* field repairable, to keep the cost of replacement down. Minor repairs should be relatively inexpensive and possible outside of specialized shops.
* fuel efficient to give the aircraft the range the design requires.
* capable of operating at sufficient altitude for the aircraft
Source Obtained: Wikipedia, the free encyclopedia