Commonly manufactured rotor blade

A rotor blade configured to be installed on a rotary wing aircraft, the rotor blade comprising:

• a spar comprising:
• an inboard portion extending from a root of the rotor blade to a first spanwise position of the rotor blade;
• and
• an outboard portion meeting the inboard portion at the first spanwise position;
• and
• an upper skin and a lower skin coupled to the outboard portion of the spar,
• wherein the first spanwise position is defined by a most inboard point at which the upper and lower skins are coupled to the spar,
• wherein the inboard portion comprises a top layer, a bottom layer, and an inner cavity between the top layer and the bottom layer, wherein the top layer has a constant first thickness and the bottom layer has a constant second thickness, and wherein the distance between an outer surface of the top layer and an outer surface of the bottom layer is constant, the outer surface of the top layer and the outer surface of the bottom layer each extending from a leading edge conic to a trailing edge conic.