I've started to build new Bellanca Xtreme Decathlon model. Despite having about the same dimensions as the previous Bellanca Super Decathlon, it's a completely different model. The fuselage construction is identical with the real aircraft. It has been built using thin wall steel tubes connected together by brassing. I spent a lot of time trying to find a supplier of the thin wall tubes. While it is possible to find such tubes in the catalogues of many suppliers, they manufacture them mostly against a received order. A typical question asked by the manufacturers was: "How many tons do you need, sir?"... Finally I found a distributor that was willing to sell small amount of tubes, unfortunately the offer was beyond all acceptable limits for me.The offered price was €1,200 for 35 meters of tubes. After that I just visited the local hobby shop (Hornbach} and looked around if I'd be able to find some usable tubes. I ended up in the garden section looking at the garden stakes which are used as supportive structure for tomatos, flowers, trees etc. They looked like a bamboo stakes, but it was just plastic coat imitating bamboo design. The tube inside is made from 0.3 mm thin welded steel sheet. They had two diameters, 10 and 15 mm. The price was about €3 for 1.8 meters 15 mm tube and bit less for 10 mm tube. I just removed the plastic coat using a sharp knife at home and could start brassing the fuselage together. Some
were placed in the local gallery.
Then, I have added the tubes to the drawing adding real dimensions of the steel tubes bought.
Knowing what engine is going to be used, I have drawn the fuselage frame so the engine has both the right and down angles right.
The thinwall steel tubes tend to bending when heated. It was absolutelly mandatory to keep the tubes in place while brassing them together. To do so I have drawn a plywood jig that held the tubes in place. Of course the jig suffered from heat and got partially burned during the brassing. However it was made for a single use only and at the end of brassing the jig had to be broken in parts to be removed from a finished frame anyway.
The drawing of the Xtreme Decathlon with a steel tube fuselage has been almost finished. The goal to design a model with a significantly reduced weight looks reachable. It seems to be possible to build the model at around 25 kgs. The estimated weight of all the parts included in the drawing is 21.8 kg. The missing parts are the motor cowl, covering, silencer, tank, accumulators, receivers, power box, ignition, towing hook, rear wheel, ... Some images have been added to the
surprisingly, the weight of the steel construction is lower than the weight of the wooden construction. The steel construction model hasn't been finished yet. The fuselage is mostly ready for covering, I've started to build the wings, producing the main wing beams during last weekend. Based on my estimate the weight might be below 30 kg. This time I'm trying to reduce the weight as much as possible, making the construction really light. My goal is to reach 25 kg as well (current no-certification limit in my country), however with the planned motor
this would be really challenging.