Page 247 - Aircraft Stuctures for Engineering Student

228 Principles of stressed skin construction

Fig. 7.9 British Aerospace 146 (courtesy of British Aerospace).

modern aircraft, coupled with a drop in the structural percentage of the total weight
from 30-40 per cent to 22-25 per cent, gives some indication of the improvements in
materials and structural design.
For purposes of construction, aircraft are divided into a number of sub-assemblies.
These are built in specially designed jigs, possibly in different parts of the factory or
even different factories, before being forwarded to the final assembly shop. A typical
breakdown into sub-assemblies of a medium-sized civil aircraft is shown in Fig. 7.10.
Each sub-assembly relies on numerous minor assemblies such as spar webs, ribs,
frames, and these, in turn, are supplied with individual components from the detail
workshop.
Although the wings (and tailsurfaces) of fixed wing aircraft generally consist of
spars, ribs, skin and stringers, methods of fabrication and assembly differ. The
wing of the aircraft of Fig. 7.7 relies on fabrication techniques that have been
employed for many years. In this form of construction the spars comprise thin
aluminium alloy webs and flanges, the latter being extruded or machined and are