Aeronautical design refers to the multi-part process that precedes the building of an aircraft. Simply put, it's the planning stage of the aircraft building process. The aeronautical design process can be broken down into three phases: conceptual, preliminary and detail.
Issues such as propulsion and aerodynamics — how objects moving through air respond to the forces they encounter — are usually considered throughout all three of these aeronautical design phases. Propulsion, obviously, is not a concern for certain types of aircraft such as gliders. This is because gliders rely on the dynamic action of air on its lifting surfaces to stay aloft.
During the conceptual phase, the requirements that the aircraft must meet are evaluated and different ideas are explored. One of the main factors considered during this phase revolve around the aircraft’s purpose. For example, whether craft is a passenger jet, cargo carrier, bomber or helicopter will have great impact on its design. Technical requirements such as speed and payload capacity are also considered, as are the costs of building and maintaining the aircraft. A major, specific factor considered in this phase is what materials will be used, a choice that will affect both performance and cost.
The aircraft’s major systems — power, navigation, communications, landing, flight control and fuel — are addressed during the conceptual phase. This is especially important to do at this first stage because they greatly impact the aircraft’s overall size and shape.
The second phase is known as the preliminary phase. This phase will usually consist of intensive scrutiny of at least one of the concepts that was hatched during the first stage — the "conceptual" stage. The preliminary phase involves experimentation to ensure that the most promising design can, in fact, hold up to the stresses that are expected to be placed on the future aircraft. This phase often involves the testing of scale models in wind tunnels to study how the design structure responds to powerful air currents and other forces.
By the end of the preliminary phase, a “high-level design” is produced. This means that all the issues concerning the aircraft’s major systems and subsystems have been resolved. It also means that the models and test benches (environments created for the purpose of testing a design) have satisfactorily answered how the aircraft is expected to perform when the prototypes are finally tested.
Aeronautical design's third and final phase is known as the detail phase. The detail phase involves fleshing out the design with all the specific engineering data that will be needed during the manufacturing process. In a sense, this is the fine tuning part of the process.
"Aeronautical" is often used interchangeably with "aviation," although "aeronautical" is actually a more inclusive term because it refers to any type of ship that travels through the air. This includes lighter-than-air craft such as dirigibles and hot-air balloons. The word "aeronautical" is derived from the Greek words aero, meaning air, and nautikos, an adjective referring to ships, sailors and marine navigation.