This information is offered in the hope that it will aid some of our readers in understanding the nature of wooden aircraft construction.

We emphasize that this piece is intended as an overview, not a Construction Manual or "How To" article. Specific information, such as should we or should we not sand a piece of plywood in the area where it will be glued to another member, is typically found in the Construction Manual for the kit. Several excellent publications are also available from the EAA Library. Your lot supplier will willingly supply you with addresses and phone numbers.

Right off the bat with wooden kits you often have the choice of plans building or kit building. Available expertise, equipment, building technique, and working space are all ingredients in figuring out your direction.

Expertise

Wood is a most user friendly material for building kit airplanes. Wood structures do not demand the close tolerance fits and elaborate alignment fixtures that other methods do. Building a wood aircraft does not demand the investment in specialized shop equipment, nor the need to acquire new skills typical of other materials. In general, if a prospective builder can maintain the things around the house that need maintenance, he or she has the necessary skill and the tools required to successfully complete a wood and fabric aircraft project.

Building from plans or kit will vary what is required of your expertise and the tools you will need.

If you plan to "plans build," first you need to understand how to read and grade wood. Obviously, you need to know the type of wood you're looking at. The more common woods in wooden aircraft are Spruce and White Pine. Some Firs and Ash are not uncommon. Once this is established there are certain characteristics the wood should have. The wood should be free of knots and major deviations in the grain. You may be able to work around (or cut out) bad areas.

The next thing to at will be the grain density or "rings per inch". Generally, there should be at least six to eight grains or rings per inch. Ten to twelve is usually better

Grain run out is another important aspect. This is a ratio of how far the grain runs as it deviates from a straight line. 10:1 means for every ten units (inches of length) the grain strays one unit (inch) from a straight centerline. Airplanes generally like at least 12:1. Of course, the straighter (less run out) the better.

Be sure to note these things as you look at various planes (or kits) to help you determine the level of quality you demand

There are other things like moisture content and specific gravity that the engineers look at. You probably don't need to be too concerned with these unless the wood has been living in an extreme condition of very high humidity (which could affect the weight) or in an unusually hot and dry environment (which could make the wood brittle and weak).

Another concern for the plans builder is an ability to source the items in the plans. This includes where to look for which materials, in what quantity they are available, and how they are shipped. Once you know these, your creativity will likely affect price.

If the previous paragraphs made you feel a little uneasy, you may want to consider building from a kit instead of plans. In so doing, you eliminate a time consuming and potentially error ridden processes involved in building an aircraft - that of material location and selection.

Materials

If you are dealing with a reputable kit manufacturer, the materials supplied in the kit will be carefully selected, continually tested, and inspected for defects.

Plywood and other parts supplied in your kit should be subject to the same scrutiny as the "plank" wood just described. By dealing with a reputable company, you will be comfortable that the material you use is indeed suitable for the purpose. Hopefully your kit supplier has also invested many, many hours in structural analysis of the finished aircraft. Ask if you can obtain a copy of it. This relieves you of the concern over its safety. As a kit builder, you need only use the material in the kit (before you decide on a kit find out exactly what does and does not come with the kit - you may be surprised! ), assemble that material according to the plans, and the integrity of the finished product will be increased.

Equipment

Plans building will require more specific tools than kit building. A pretty good table saw and/or radial arm saw with table extensions and guides, and planer are the most critical tools the plans builder would need beyond a kit builder.

Otherwise, simple hand tools are all that's really needed. You probably have most of what you need such as some "C" clamps, but you'll be amazed to discover that, in many places, a modified clothes pin makes a good clamp. The epoxy resin supplied in kits does not require huge amounts of pressure to yield a good glue joint. You will need a small staple gun (hand operated) and lots of staples. You'll need some kind of staple puller (you can make one out of a bearing scraper or screwdriver), unless you don't pull the staples. You can do it either way. The only staples that must be pulled are those that will be in contact with the fabric. You'll need some sort of sander - block, disc, belt.

Among the neat things to own, but not necessary, are a drill press, a small table saw, and a small band saw. An electric or air operated stapler is nice, but not necessary. All of the operations required can be accomplished without these -- it just takes a little longer.

Work Space

How much shop space do you need for this project? The obvious answer is, the more the better. And it would be keen if this huge shop was as bright as day, heated, air conditioned and the like - but, that's not necessary. Many builders are presently building great planes in one half of a two-car garage, and can still put the car in at night.

Construction Technique

As a first time kit builder, you will learn a little bit about reading plans. The size of the drawings directly relates to how much detail is provided and therefore how easy the plans are understood. Written text or construction notes which complement the drawings are a great benefit.

You will likely need a workbench on which all is built. Imagine the biggest single part of the plane. That's about the size of the bench. Two 4' x 8' sheets of ply or particle board make a typical bench 4' x 16'

Now, let's consider building a wing rib for a popular wooden kit offered as both kit and plans, the JDT Mini-Max. In doing so, we can introduce some terminology, and also show how the entire aircraft is built, piece by piece.

Since a rib must be an exact shape, it is built over a full size drawing furnished with the plans. In this case, we are only using the drawing to construct a simple fixture. The ribs built in this fixture will all be the same size .

The rib fixture should be built on a flat board about 12 inches wide and 50 inches long. This will allow the builder to move it around as required. The rib drawing is laid out on the board and secured at the edges. Then it is covered with clear plastic (unless a Mylar template is used) to prevent glue squeezed out from sticking to the pattern.

The upper and lower horizontal members of the rib are called "caps" and are 1/4" square pine. The lower cap is straight and held in position over the drawing by nailing small blocks at appropriate locations to hold it in position. The upper and lower caps can be cut to length on assembly or left long at the front of the rib and trimmed later.

The upper cap is now located over the drawing. This one is curved in shape but is still secured in the same manner. The vertical and diagonal members are now cut, fitted and glued in position over the drawing.

The joint attained where the vertical and diagonal members meet the cap strips is called a "butt" joint, and, by itself, has little structural integrity. This joint is, therefore, reinforced by the addition of a "gusset", which is cut to shape from light plywood, and glued in position over the outside of the joint. Staples are driven in appropriate positions to hold the gusset until the glue cures.

Gussets come in various shapes and sizes throughout the aircraft structure. The light plywood from which they are formed is very easily cut with tin snips.

In some areas, such as fuselage sides where further strengthening of butt joints is required, members known as "corner blocks" are cut to fit, and glued in place on one or both sides of the butt joint. This whole area is then overlaid with a gusset, yielding a glue joint with great strength! We have seen welds broken at the weld in welded aircraft, and rivets popped out of aluminum aircraft, but never. even in a wrecked wood aircraft have we seen one of these joints broken.

Back to our rib. When all the gussets are stapled in place, the rib may be immediately removed from the fixture and set aside to cure. Ribs can be built one behind the other in this fashion, as quickly as you want to work. Gussets are cut and glued to the back side of each rib at your convenience.

A finished rib of this type weighs just ounces. When installed in the wing and supported by spars and other structure, it is infinitely stronger than it needs to be to withstand any flight loads you might possibly inflict on it. While it is made of different material, this rib is the same type of structure that is used in the construction of wooden railroad bridges!

The entire aircraft is built in the same manner as that just described -- one subassembly attached to another. until a complete aircraft emerges from your shop. There are holes to drill and parts made to fit together and work. With wood, it's very difficult to make a mistake that cannot be easily rectified. In what other type structure can you drill a hole in the wrong place and, when the error is discovered, simply plug the hole by gluing in a piece of dowel, then moving over and re-drilling the hole in the proper location, without weakening the structure?

You may have an impression at this point that nothing about this project is cast in stone, and in a sense, that is true. That's part of the beauty of wood aircraft construction. Shop temperatures are not extremely critical, and precisely how you elect to do a particular operation is up to you. The important thing is not how you do it, but that the finished product is exactly as shown on the prints, with nothing added and nothing left out.

Whether you build from plans or from a kit, few rewards in life can match the pride attained from building your own aircraft, and few companies can match JDT Mini-Max's experience and proven aircraft designs. Whether you are a first time builder or an experienced craftsman you will appreciate the quality and support afforded to all of JDT Mini-Max's products.