Structurally biased proprotor blade assembly

A rotorcraft, comprising:

• a fuselage;
• a wing member extending from the fuselage;
• an engine disposed relative to the wing member;
• and
• a proprotor mechanically coupled to the engine, the proprotor including a plurality of proprotor blade assemblies each comprising:
• a spar having a root section, a main section and a tip section, the spar having a generally oval cross section at radial stations along the main section, the spar having a first edge and a generally oppositely disposed second edge, the first edge having a structural bias relative to the second edge at the radial stations along the main section, the wall thickness of the first edge and the wall thickness of the second edge each having a decreasing spanwise taper as the radial station increases along the main section;
• and
• a sheath extending spanwise along a leading edge of the spar.