Sentence:  In an aeroplane having superposed aerofoils each provided with a leading edge bar, a trailing edge bar, a central <WSD>wing bar</WSD> designed to resist greater lift than drift stresses and positioned approximately at the most forward center of pressure, a rear wing bar designed to resist greater drift than lift stresses and compression ribs connecting said ribs, diagonal wires to truss drift stresses connecting the leading ege bar with the rear wing bars of each aerofoil, a single row of struts directly connected at their ends to and holding the central wing bars in spaced relation, and brace members having a common connection with the central portion. 
Meaning of the word marked with <WSD> tags:  A support strut on for the wing of an airplane.