Fuselage structures and construction

Model Airplane News, Mar 2002 by van Mourik, Dick

Different types of scale model aircraft fuselages require different construction methods. Before you choose a method or combination of methods, first consider the functions you'll need it to perform. A scale fuselage needs to position the model's wing and empennage at a specific distance from each other, hold the engine, provide room for the radio gear and fuel tank and be able to cope with the forces acting on it during takeoff, flight and landing.

Another consideration-especially with girder construction-is to avoid stress points. Abrupt joints, as shown in Figure 1, concentrate stress forces in a small area and tend to break. Because of this, it is a good idea to distribute the forces; I use a triangular filling piece or a thin plywood gusset as shown.

It is nearly impossible to build a bulletproof model, and besides, the lighter the model, the smaller the forces acting on it will be. A low weight is achieved by keeping each individual component as light as possible. You'll be surprised at the results!

Having said that, let's take a look at five different fuselage construction methods:

Basic girder (stick) construction. This basic structure can be used by aircraft that have a square-section fuselage, such as many aircraft of the '30s, as well as recent homebuilts. Here, the outer surface of the girder construction is stiffened with thin sheeting and is used as the final shape in this form (see Figure 2). After you've positioned the half formers to form the turtle deck, you can plank them with single sheets of 164-inch-thick plywood or )12-inch-thick balsa (this avoids the hassle of using strips).

Advantage: simple; easy to build.

Disadvantage: can be used only for square-section fuselages.

Basic girder with half-former sides. This method is based on the same internal crutch previously mentioned, but half formers form the fuselage's final shape (see Figures 3A, 3B and 3C). The basic girder fuselage is easy to build and provides more than enough room for the engine, fuel tank and radio gear. The fuselage structure is cantilevered, so the outer sheeting (covering) is only cosmetic. This also implies that you can sheet the fuselage with thin (light!) materials, as the main structure can handle the flying loads. I use his-inch-thick sheeting, even for bigger models. This construction is well suited to biplanes and lightplanes, and you can create fuselages that are curved all around by placing half formers all around the girder box.

You can build nearly any warbird with this construction method, but a disadvantage is that the girders often cannot be constructed on the most outward sides of the fuselage and may interfere with having a fully detailed cockpit interior. This is why this method is often combined with the classic former construction (described next). In this case, everything aft of the cockpit section is constructed with girders, while the front part of the model is made differently.

Advantage: can be used for fuselages of almost any shape; lightweight.

Disadvantage: labor- intensive.

Classic former construction. Often regarded as obsolete, this construction method can be used by a surprising number of models. One example is an aircraft with formers that are strongly tapered toward the top and/or bottom. In general, the formers are made out of plywood and then sheeted with balsa to form a cantilevered structure (see Figure 4). Note that the sheeting is needed to provide the strength here, so a thicker sheeting is called for (I use ' inch). Because of the accuracy required when using this method, I usually make a jig to hold the parts while I'm building.

Advantage: can be used for every fuselage shape.

Disadvantage: not always easy to line up; you may need to build a jig to hold the parts.

Split fuselage construction (half-shell method). Here, the fuselage is split at a suitable place so the upper and lower (or right and left) fuselage halves are built flat on the drawing board (see Figure 5). This method is especially suited to models that have double-curvature fuselage sides, like many modern designs as well as many warbirds and sport models. It's useful when you need to construct a light model.

A variation of this method is to split the fuselage lengthways to form a left- and righthand shell (see Figure 6). This construction is especially suited to models of larger aircraft, such as the Mosquito, Heinkel 111 and B-17. Also appropriate to many of today's civilian wide-body aircraft, this method allows you to build curved fuselages without using jigs.

Advantage: allows you to more easily build a double-curvature fuselage.

Disadvantage: high degree of precision required, especially when splitting the fuselage from top to bottom.

Building using side flanges. Used on P-51 Mustangs, Hawker Typhoons and many other similar models, this method is ideal for aircraft that have nearly flat fuselage sides. Such side flanges are made out of 4-inch-thick balsa and are doubled with plywood on the inside. I usually use 14- to 112-inch-thick plywood for this, depending on the size of the model. The two sides are then used to construct a box-like fuselage. The upper and lower halves are formed with half formers (see Figures 7A and 713).