Building without plans

Model Airplane News, Jul 1999 by Fawcett, Guy

A budding scale modeler wanders along the flightline at the field, and a gorgeous but totally obscure scale model rivets his attention: the local scale guru has shown up with another original. The resulting conversation usually goes like this: "Beautiful plane. Whose kit is it?" Guru (beaming with pride): "It's not from a kit; I designed it myself." "Neat; is there any way I can get a set of plans?" "Plans? I don't use plans; I built it from the 3-views."

Our scale-modeler wannabe's mind fogs over as he tries to contemplate a world without directions. If his grand sum of modeling skill comes from having recently assembled an ARF, building from 3-views may not be for him, but anyone with a few scratchbuilt airplanes to his credit can take on this task with a good chance of success, and I encourage everyone to try i

Once an aircraft has grabbed you by the throat, you at least need drawings that show the plane from the top, the side and the front. The more information the drawing displays, the less you'll have to guess and extrapolate. A common example that comes to mind is that of crosssections, or lack of them. If the plane in question is a simple box, the absence of crosssections is of no real consequence, but take a gracefully curved fighter from WW II, and that same dearth of information becomes a hurdle. The work can be done, but it becomes that much harder.

With a 3-view in hand, you have what I consider to be a reduced-size set of plans. I know; you're looking at this aircraft outline with a glazed expression. Where are the wing mounts? How do I mount the engine? What's the thickness of the landinggear wire, the fuselage sides, the wing ribs? The questions seem to stretch to infinity (and beyond). The knowledge needed to answer these questions must be acquired. If you don't have enough building experience, answer these questions by studying plans of similar aircraft by successful designers (the old standingon-the-shoulders-of-giants routine). This doesn't mean buying every plan on the market. Most magazine construction articles show a reduced-size version of their plans for reference; use these for guidance. Failing that, buying a plan for a similar aircraft might be useful to obtain construction ideas to build your dream ship.

SELECTING A SIZE

The neophyte designer's first big decision is: what size? The answer again lies with the vast collection of plans available from various sources and model magazines. Find a plan with a similar power source and layout; if your subject is a fast monoplane, look for a plan of a fast monoplane, a biplane for biplane, etc.

Let's say you decide to build an Armstrong Witworth Siskin III (a between-the-Wars British biplane fighter) and you have a good, .60 2-stroke lying about looking for a home. Through research, you've found that the only information available for this airplane is a decent set of 3-views and some small, rubber-powered, free-flight plans (another good source of cross-sections). Lo and behold, the catalog also lists a plan for a .60-powered Bristol Bulldog. A contemporary of the Siskin, the Bulldog makes a good match and will provide endless clues for structural components. So, by using the information about the Bulldog, you can decide which size is required for the Siskin drawings and go to it.

ENLARGING THE 3-VIEW

Having chosen a size, you can enlarge the drawing following one of these methods:

Laboriously measure, multiply and transfer all points with paper and pencil-the timehonored way.

Photocopy the drawing onto a transparency and project the image for tracing onto large sheets of paper.

Use a conventional photocopier to enlarge the drawing to the size you want, then cut and paste the resulting parts together.

Digitally scan the drawing, insert it into a computer paint program that allows enlargement, then print out the results.

Digitally scan the drawing, then insert the image into a CAD program and trace over the bitmap to produce a drawing suitable for printing.

FUSELAGE CONSTRUCTION

When you've enlarged the 3-views to the appropriate size, you can start construction. As an example of the process, I have included pictures of a recent project of mine-a WW I German biplane fighter known as the Halberstadt D.II (see "Final Approach" in the June issue). I began with the construction of the fuselage, which is generally the most complicated part of any aircraft to design. The fuselage has many intricate shapes and model requirements; after tackling this, the wings and stabs seem effortless. The sides are framed directly over the large drawing's outline. Uprights are positioned to correspond with actual points on the full-size structure-landing-gear attachments, cabane attachments, end of the full-size aircraft's plywood sheeting and whatever else is shown in the drawing. These items hint at the underlying structure.

Be aware that designers of full-size aircraft try, as much as they can, to integrate the wing-mounting points, motor mounts and landing gear into the fuselage frame. Using this information and the structural hints on the drawing, connect the dots. Run uprights between these mounting points. Areas that need to be hardened with ply and spruce, such as the landinggear mounts, can do double-duty if you use reinforcements to connect the high-load points. For instance, I placed a bulkhead on the Halberstadt where the forward leg of the landing gear is attached. This can be beefed up to serve as the rear support for beam motor mounts and, if angled to the rear, it will also act as the attachment point for the forward cabane struts at the top of the fuselage. It must be emphasized that if your drawings are detailed enough, they may show the bare structure, and guessing won't be required. With these points taken care of, the builder/designer must position other structural members to provide sufficient strength and rigidity. This is where design talents enter the picture; if you don't have experience, refer to successful designs of similar aircraft.