Aircraft loads are the forces and moments applied to the airplane structural components to establish the required strength level of the complete airplane. These loadings may be caused by air pressure, inertia forces or ground reactions during take offs and landings. Determining design loads involves a full aircraft analysis of the air pressure and inertia forces during prescribed maneuvers, either in the air or on the ground. Aircraft loads are needed at all design phases, from day one through certification and product lifecycle support. Early in preliminary design, structural designers need initial loads to size the preliminary structure. As the design iterations progress, the detail and fidelity of the loads increases. The final step for an aircraft is a full set of certification loads for submission to government agencies such as the FAA and European Aviation Safety Agency (EASA).
The loads analysis needs to cover all possible combinations of speed, altitude, flap angle, airplane gross weight, airplane center of gravity, passenger and payload distribution, fuel quantities, engine thrust and airbrake positions for each of the required maneuver and load cases for each part of the airplane. Static loads are calculated for conditions in which the aircraft is assumed to be at steady state and range from high speed dives to low speed stalls. The dynamic loads are how the airplane responds to gusts and bumps, including landing.
The input data to the loads analyses are accurate airplane geometry, aerodynamic data, weight (inertia) data, design speeds, stiffness data, operational data and regulations and requirements. This makes loads a multidisciplinary process. Early in a design program, these parameters can be estimated from various methods. As the design becomes more detailed and defined, the inputs will be more refined, and for the final certification level, verified by test.
TLG Aerospace is an aerospace engineering services company that specializes in full vehicle analysis and optimization including static and dynamic loads, flutter, stability and control, aerodynamic design, Computational Fluid Dynamics (CFD), FAA certification and aircraft performance and handling qualities. TLG has developed an extensive set of tools to facilitate quickly setting up and running a large number of static and dynamic loads cases and then rapidly post-processing to obtain the most critical load cases, and then providing “loads envelopes” to the stress and structural engineers. TLG uses MSC Nastran as the core aeroelastic solver for both static and dynamic loads for these surveys. Scenarios in which MSC Nastran is used at TLG include:
- Engine thrust
- Aerodynamic effects of deployed spoilers
- High trailing edge flap deflections
- Balancing the airplane in any way needed for particular calculations
- Defining control surface relationships such as control wheel to aileron gearing
- Providing loads to stress engineers
- Flutter analysis
To learn more about the use of FEA in aircraft certification, watch our on-demand webinar: http://bit.ly/295uqeN