Following is a short article I wrote for Kitplanes magazine on the evolution of aircraft blueprints (plans) over the years:

Aircraft plans (also called drawings or blueprints) are the single most important and valuable resource available to an airplane builder. The blueprints contain the “genetic code” of an airplane, allowing the builder to “clone” an airplane from the information contained in the drawings. All airplanes (including kits and factory-builts) started their existence on a flat piece of paper (or, more recently, on a flat monitor). A plans builder (sometimes called a scratch-builder) not only assembles the aircraft, but first sources the materials and then makes (manufactures) the parts and pieces that are later assembled to form the various sections of the airframe. Obviously it takes time, tools and skills to source and manufacture the parts, but this can potentially be a significant cost saver and provide a good learning opportunity, while also allowing a builder to develop new skills.

As the kit has become more complete and the level of completion of individual parts has increased, so has the definition of the individual parts as shown in the drawings. Twenty years ago, a purchaser received a hand-drawn set of blueprints covering the basic airframe structure, with somewhat scant details on finishing the aircraft (only rudimentary information on firewall forward, fuel system, cabin details and other finishing touches). Today’s CADD drawings take the builder much closer to the completed aircraft with more information on finishing the project, and they are revised on a regular basis (we typically update the drawings at least once a year).

As an example, the Zenith STOL wing fuel-tank diagrams show much more detail and clarity in the 2012 version than the hand-drawn diagram from 1990 (see diagrams above "The old [bottom half] vs. the new [top diagram] approach, much improved thanks to CADD."). 

Zenith plans come with an aircraft serial number and are supplied on 11x17-inch paper sheets (a size that is much more transportable than larger blueprint sheets), with the photo assembly guides supplied on a CD-ROM disk (with easy-to-print PDF files with high-resolution color photos). The plans are split into logical sections (such as wings, tail, etc.) with details on both the individual parts and the assemblies of the individual parts. The parts drawings contain full details to build the parts, starting with the material (such as type and thickness of the aluminum alloy sheet) and also details on making the part. For example, for a wingrib, the exact dimensions of the finished part are supplied, as well as the dimensions of the rib-forming block, bend radius and flat dimensions of the part before forming.

As shown on right, today’s drawings can be much more detailed than in years past [thanks to CADD]. 

While building an airplane from plans is not for everyone, it is an affordable way to begin the adventure of building your own airplane (whether or not you decide to later purchase a full kit or various components). Our plans (and included manuals) are chock-full of useful information and also include full access to Zenith’s online builder resources (which include an online community with active discussions and bulletin boards where builders help each other). They also include unlimited access to the factory for technical support. (Furthermore, a builder may apply the cost of the plans toward the purchase of a kit.) 

Zenith designs are well suited for plans building, requiring relatively few specialty tools (and corresponding skills). Sheet-metal skins are single-curvature bends, and many sections (such as wing leading edge airfoil) are constant chord, requiring fewer forming blocks. The raw materials, such as 6061-T6 aluminum sheets, and hardware are also readily available from multiple sources, and, importantly, a builder may purchase any individual finished part or component kit from the factory. (Let’s face it, some individual parts are just not worth the time and effort to build when the company can have the finished part shipped to you at an affordable price.)

Once the aircraft is finished and flying, having a set of plans for the aircraft continues to be an advantage: You’ll never have to fully rely on the (kit) manufacturer (assuming a kit is also available), and you won’t have to reverse-engineer for spares or replacement parts.

— Sebastien Heintz

View PDF document from Kitplanes magazine (January 2013 issue):
The Evolution of Plans Making, by Sebastien Heintz, Kitplanes magaz...