How is ultimate load typically calculated from limit load in aircraft design?

In aircraft design, the ultimate load is calculated to ensure that the structure can withstand unexpected loads beyond the operational limits. This is achieved by applying a safety measure that accommodates for possible overloads and material imperfections. The industry standard for calculating the ultimate load is by multiplying the limit load by a specific factor, typically set at 1.5.

The limit load is the maximum load that the aircraft is expected to encounter in normal operations, while the ultimate load represents a higher threshold, which provides a margin of safety up to 1.5 times that limit. This method not only ensures structural integrity under normal operating conditions but also allows for a buffer against extreme situations that could occur during flight.

This approach is part of the rigorous certification standards set forth by aviation authorities, ensuring that aircraft can handle a certain level of unexpected stresses without failure. The other methods, such as subtracting a safety factor or averaging multiple limit loads, do not adhere to this standardized practice, and adjusting the limit load by a fixed percentage does not accurately incorporate the necessary level of safety intended in ultimate load calculations.