In aviation, endurance is the maximum length of time that an aircraft can spend in cruising flight. Endurance is different from range, which is a measure of distance flown. For example, a typical sailplane exhibits high endurance characteristics but poor range characteristics.
Endurance can be defined as:
where W stands for fuel weight, F for fuel flow, and t for time.
Endurance can factor into aviation design in a number of ways. Some aircraft, such as the P-3 Orion or U-2 spy plane, require high endurance characteristics as part of their mission profile (often referred to as loiter time (on target)). Endurance plays a prime factor in finding out the fuel fraction for an aircraft. Endurance, like range, is also related to fuel efficiency; fuel-efficient aircraft will tend to exhibit good endurance characteristics.