Before start building i'm trying to figure out the best approach to building process and i'm checking all the measures. I drew in 3D the basic fusolage (Scale 1/7) to better understand the fusolage layout and these allowed me to check at ones all the measure.The project is quite hard, and would be difficult to build it all at once, so i decided to divide it in smaller projects which i will join later. Work will consist in four phases: Top truss, Bottom truss, join top to bottom and finally built the empennage.In these way i can better focus on a specific area in a bigger contest. These way to operate, also allows, a better evaluation about the Bill of Material required, that i want buy all at once, to reduce at least shipping fees.The basic structure is all made of tubolar 4130 Crome-Moly Aeronautic quality steel.Steel alloy 4130 is typically used for structural applications. This stell alloy finds many uses in the aviation industry due to its good strenght, ductility and corrosion resistance.
The physical properties of 4130 steel derive from its chemical composition. This grade of steel includes about 0.30 percent carbon, making it a low-carbon alloy. The superior mechanical properties of the material derive from the addition of chromium and molybdenum ions. About 1.0 percent chromium and 0.20 percent molybdenum are used in standard 4130 steel materials.
The structure is mostly composed by ¾ - 5/8 and ½ inch tubes whit 0.350 thickness, so I’m preparing to work with this order of dimension.
4130 is used in the normalized or near normalized condition and does not require heat treatment. In the normalized state the maximum allowable tension stress is 95 ksi. At this value 4130 has good toughness and excellent elongation. Toughness means resistance to crack propagation and elongation means it can absorb energy in deformation without breaking (useful in a fuselage safety cage).
By letting weld joints air cool, the joint becomes normalized. Further normalizing and evening of the internal stresses can be accomplished by heating the general area of the weld (cluster) to a straw color (light yellow) and letting the area air cool.This is not absolutely necessary (because the internal stresses of the weld are not that much higher) like it would be with a higher carbon content steel, therefore i will not do it.
