This article continues the description of simple F2A trainer model. The construction notes were published earlier. Here I outline a couple of important design flaws that were discovered during the flight testing.
In order to make the transition to this model easier, it was fitted with a different (less powerful) engine. We acquired a Brodak .15 (2.5 cc) control line motor. The mounting dimensions are exactly like those of the ЦСТКАМ 2.5 but It is much easier to operate than a piped engine. The motor is actually meant for stunt but still turns a 7x5" (180x125 mm) propeller at 19,000 RPM on 10% nitro fuel. The engine startsy easily, does not use a lot of fuel and the glow plug is still good after well over 50 flights. Our model does about 110 kph on standard F2A lines with this engine.
Now about the design issues. First, the nose part of the fuselage had inadequate strength considering the role of the model as a trainer. It actually broke right behind the engine on the first landing, so a reinforcement was applied in the form of 1.8 mm plywood on the engine side and a couple of pinewood planks on top and bottom. Second, as originally trimmed the airplane had a tendency to fly into the circle as the line tension was too weak, especially going against some wind. This was fixed by a) moving the line lead-outs behind by about 15 mm; b) by adding a small vertical stabilizer.
A.Valishev , June 19, 2011
Below are a couple of photos of the model with the Brodak .15: