Make it safe...
The preliminary design incorporates the 3D lofted bodies. Suspected parts are determined and the weight and balance is conducted. Construction materials are identified. The static and dynamic stability is analyzed. The performance is estimated. Mold surfaces are ready for tooling quotes.
Design loads need to be identified based on the mission whether flying through the air or motoring across the Salt Flats. Design loads determine the required strength of the structure. The structure must withstand all design loads multiplied by an additional factor of safety.
Using the power of finite elements, a structure can be analyzed at the simple part level or at the complete assembly level. Stresses are easily identified along with resulting displacements. Modal shapes can be identified along with the natural frequencies. The stiffness as well as the the margin of safety can be determined before the first part is built.
Most designs require complex sub-assemblies. Landing gear, control systems, firewall forward packages are all part of the total design process. Some systems are more complex than others but the level of analysis and documentation should remain constant.for both.