How do you deal with the uncertainties and variations in the load data and assumptions?

2 Load factors

The second step in dealing with the uncertainties and variations in the load data and assumptions is to apply load factors, which are safety margins that account for the possible errors or deviations in the load analysis or the material properties. Load factors are typically expressed as a ratio of the design load to the nominal load, and they vary depending on the type and category of the aircraft, the design criteria, and the regulatory standards. For example, a civil transport aircraft may have a load factor of 1.5 for limit loads (the maximum loads expected in normal operation) and 1.5 for ultimate loads (the maximum loads expected in extreme or emergency situations), while a military fighter aircraft may have a load factor of 2.0 for limit loads and 1.5 for ultimate loads.

3 Load distribution

The third step in dealing with the uncertainties and variations in the load data and assumptions is to determine the load distribution, which is the way the loads are transferred and shared among the different structural elements of the aircraft. Load distribution depends on the geometry, configuration, and stiffness of the structure, as well as the boundary conditions and constraints. Load distribution can be calculated using methods such as shear flow, shear center, shear lag, or finite element analysis. Load distribution can also be verified or adjusted using experimental methods such as strain gauges, load cells, or photoelasticity.

4 Load cases

The fourth step in dealing with the uncertainties and variations in the load data and assumptions is to define the load cases, which are the combinations of loads that represent the most critical or representative flight conditions for the aircraft design. Load cases can be based on the flight envelope, which is the range of speeds, altitudes, angles of attack, and load factors that the aircraft can operate in safely, or on the mission profile, which is the sequence of events and maneuvers that the aircraft will perform during a typical operation. Load cases can also include special or abnormal conditions such as gusts, turbulence, landing impact, engine failure, or damage.

5 Load testing

The fifth step in dealing with the uncertainties and variations in the load data and assumptions is to conduct load testing, which is the process of applying the load cases to the aircraft structure or components and measuring the resulting stresses, strains, deformations, and failures. Load testing can be done at different stages of the design process, such as during the conceptual, preliminary, or detailed design, or during the prototype, certification, or service life phases. Load testing can be done using static or dynamic methods, or a combination of them. Static methods involve applying constant or gradually increasing loads until a certain level or criterion is reached. Dynamic methods involve applying varying or cyclic loads that simulate the actual flight conditions or environment.

6 Load management

The sixth and final step in dealing with the uncertainties and variations in the load data and assumptions is to implement load management, which is the practice of controlling or modifying the loads or the structural response to improve the performance, efficiency, or safety of the aircraft. Load management can be done using passive or active methods, or a combination of them. Passive methods involve designing the structure or components to have optimal shapes, sizes, materials, or configurations that reduce or distribute the loads. Active methods involve using devices or systems that sense, adjust, or actuate the structure or components to change or alleviate the loads. Examples of load management techniques include winglets, flaps, slats, spoilers, ailerons, rudders, elevators, trim tabs, adaptive wings, morphing structures, or smart materials.