Caudron G.IV, a French bomber/reconnaissance plane, was a twin engine version of the earlier G.III model. It was put into service in 1915, becoming the first mass produced twin engine aircraft in allied service. For several years G.IV served faithfully in several air forces, until becoming completely obsolete and incapable to match newer enemy fighters. In total, more than 1400 planes of the type were built in France, Italy and UK.
This unusual, odd looking plane had always looked to me like a very interesting subject for a model, and since no kit of a twin engine Caudron was available (except for an ancient, hard to find vacuform), I decided to try myself at scratchbuilding – a decision based mostly on an underestimation of complexity of the task ahead.
Right from the beginning I realized that resin casting technology would be essential for the project. Indeed, engines, nacelles, tail booms, wheels, fins, struts – all these parts exist in two, four or eight instances and just beg to be copied. After trying a number of methods and materials I finally mastered a simple technology, allowing to cast epoxy resin in silicone molds. The method is described here
(in Russian). At first I planned to cast only the identical parts, but later decided to make the entire model from resin.
Windsock Datafile 96 was used as a primary source of information, in addition to photos of the surviving G.IVs and scale drawings from an unknown source found on the net. These plans have some major differences compared to a set of drawings from Windsock Datafile, and it's hard to tell which ones are closer to the truth. I decided to stick to more detailed Windsock plans, despite a few questionable areas.
The work started from the wings. I used sheet styrene, giving it a more or less airfoil shape by dragging it over an edge of a table. The ribs (nearly 100 of them) on the front part of the wing were made from thin plastic strips, while on the thinner trailing section they were represented with stretched sprue. While I was mostly satisfied with the look of the finished wings, they turned out to be extremely fragile and prone to deformation, despite knife blades I had inserted for rigidity. The problem was solved by creating a silicone mold and casting the wings in epoxy resin. A wooden block was attached to the leading edge of each wing, acting as a sprue and also holding the wing straight during the molding process. A saw blade was embedded into the lower wing casting, making it extremely tough.
Stabilizer and fins
The stabilizer was also made from styrene sheet, similarly to the wings. Strips of very thin plastic acted as ribs with several layers of putty applied over them and sanded with a rolled sandpaper to create a fabric skin effect. The finished stabilizer was also copied in resin. At first I placed a needle into the casting to improve rigidity, but later found it unnecessary. The fin master was created using the same technique and later cloned four times.
Engine nacelles and cowlings
Engine nacelle was also built from styrene, a skin structure represented with putty. At first I wanted to provide tunnels for the struts, which would penetrate through the nacelle, but later, when I decided to cast all the parts, I abandoned that idea, since it would have been impossible to reproduce this structure in resin.
The front part of the cowling was heat-formed from styrene over the wooden master, while the rear cylindrical part was made from the same material simply bent into shape. Then a characteristic horseshoe shaped cutout was made and nacelle attachment details added.
Engines and propellers
Although probably it was possible to borrow suitable engines from some WWI kit or use aftermarket parts, I really wanted this model to be truly scratchbuilt. As a matter of fact, building a reasonably simplified 1/72 LeRhone engines did not prove to be too difficult. Plastic rods, stretched sprue and copper wire were used to make parts for one engine with one cylinder, later reproduced in resin.
Surprisingly, at least for me, an engine cylinder could be cast as one part. In order to do this I had to stretch a mold considerably — almost turn it inside out — during a resin application, which, of course, caused more rapid mold deterioration. But fortunately, I needed only 18 cylinders.
Dry fitting the assembled engine revealed a very common problem – the engine did not fit into the cowling. This issue was addressed from two directions – first, the cowling was thinned from the inside to an almost scale thickness, and second, the crankcase diameter was reduced a little.
The engine was painted with Alclad II paint (a mix of steel and aluminum for the cylinders and copper for the exhaust pipes).
The propeller, or more precisely, its half, was carved out of styrene and later copied in resin, producing two identical halves, which, when glued together, resulted in a completely symmetrical propeller. The hub was made separate to simplify painting, and together with the finished prop served as a master for a silicone mold.