Aircraft design is an activity that leads from an idea to plans for a flying machine. It is a challenging intellectual process involving analysis, integration and aesthetics. Model airplane design can be particularly rewarding because a single person can design and build an entire airplane in a short period of time - short enough that many can be built until a good design is reached! (Cut-and-try is a feasible approach.) Model airplanes often have an entirely aesthetic purpose as flying, four-dimensional art. Subjective judgment of the result is applicable and the design itself is relatively unconstrained.

The principal constraint in model airplane design is Mother Nature. Whatever the designer may wish for, the airplane will do what natural laws dictate. The key to airplane design is to understand natural laws and to apply them so the airplane does what the designer wants.

Natural laws that govern airplane design are divided into disciplines based on related bodies of knowledge. The most broad division might be into aerodynamics, structure and propulsion. An additional discipline of "configuration design" links the other disciplines to define the general arrangement, or "species" of the airplane.

Airplane design is demanding in that the airplane functions as a system. A failure in any element of the airplane's design can ruin the airplane as a whole. Also, it is generally not possible to solve each aspect of the design in a crude way - the resulting airplane is usually unsatisfying. On the other hand, for model airplanes, it is not essential that each element is perfect. Rather, it is important that each element is sufficient and reasonably close to the perfect solution. Airplanes reward refined design with improved performance.

A further characteristic of airplane design is that it is tightly integrated. Any aspect of the design tends to influence the rest of the airplane. This leads to an iterative design process - the design cycle is repeated until it comes together and is good enough. To speed this repetitive process, designers become skilled at doing preliminary designs with limited detail. At each repetition, more detail is added to insure that the design will work. To further speed the process, most designers rely on computers.

Much of each airplane design discipline is now encoded in mathematics, and professional airplane designers do much of their work with computer software. Most of this software requires a strong technical background and a long learning period to use. Furthermore, most programs provide information well beyond the scope of an amateur model airplane design.

Some broader, simpler software has been written for modelers who must work all disciplines, or who need less definition in specific disciplines. "Plane Geometry" is a preliminary design program intended to assist modelers improve and speed the preliminary design process.

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