Weight and CoG Estimation
To estimate the total weight of the aircraft, a list must be made of all items carried (such as individual components of the avionics, including the wiring harness, undercarriage components, fuel tanks, servos, engine, etc.) and the locations of each item relative to the chosen datum noted, typically on a separate weights sheet (a relatively detailed example of a weights table is given in Chapter 15). For wing and fuselage structure, some construction method must be chosen and then estimates made using projected areas and lengths. Any spars or booms must be suitably sized with simple beam theory calculations as noted above. Monocoque areas subject to significant structural loads are difficult to estimate weights for accurately during concept sizing, but typically a surface area and thickness plus allowance for any rib stiffening has to suffice. Typical materials for stressed monocoques are carbon-fiber lay-up (possibly using foam sandwich techniques) or selective laser sintered (SLS) Nylon - in this chapter we restrict designs to SLS nylon or glass-fiber-covered hot-wire-cut foam. Tables 11.4 and 11.5 list some of the variables that might be used to scale weights and the items which might be scaled from them, respectively. Table 11.6 lists items whose weights are rather less easy to estimate, but which nonetheless may vary with aircraft size and must be allowed for.