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Design Load Factors on Attack Aircraft

The load factor of an aircraft is a dimensionless figure, commonly measured in "g" forces, that tells you how strong the airplane is designed to be. Design load factor differs from real-world load factor as the airframe ages or as varying stress --- for instance, wing payload --- is placed upon it.

Maximum Load Factor
- Maximum load factor, also known as "limit load factor" or "instantaneous load factor," represents the maximum stress that can be put on the airframe for a short period of time --- on the order of a few seconds. For an attack aircraft, this might represent evasive maneuvers taken in response to an immediate threat, or the pullout at the end of a dive-bombing attack run. Limit load factors are high, and generally not sustainable --- they cause fatigue to the airframe and bleed available energy quickly.
Sustained Load Factor
- Sustained load factor, by contrast, represents the stress that can be placed on the airframe over an extended period of time --- limited by energy depleted in the maneuver. Combat aircraft rely on sustained load factor when engaged in "air combat maneuvering," otherwise known as "dogfighting" --- attempting to get the upper hand with regards to another aircraft. In close encounters, where long-range missiles have diminished effectiveness or cannot be employed, aircraft with a higher sustained load factor are generally likely to emerge victorious.
Load Factors and Agility
- When an aircraft changes directions, the lift vector is changed as well --- the wings are attempting to pull the aircraft along a different course than inertia would keep it on. This places strain on the airframe, meaning that load factors, both limit and sustained, are closely linked to an aircraft's agility. "Transient agility" --- maneuvers an aircraft can perform for one to three seconds --- is related to maximum load factor. Sustained load factor, in combination with the aircraft's drag and power, is tied to "functional agility," which refers to movements an aircraft can perform for up to 20 seconds.
Load Factors and Attack Aircraft
- Because of the increased agility, attack aircraft tend to have higher design load factors than commercial aircraft. Design load for commercial aircraft is a balancing act between making the airframe light and giving it enough strength to carry large amounts of cargo. For this reason, the FAA suggests that commercial airliners should have a limit load factor of 2.5 to 3.8 g. By contrast, the A-10 Thunderbolt, an American attack aircraft, has a limit load factor of 5.0 g, and a sustained load factor of 3.26 g.

Aviation