Two-lug side-entry turbine blade attachment

A root for attaching a blade to a rotor in a groove having a shape substantially corresponding to a shape of the root, such that the root and groove have a common center line, the root comprising:

• an uppermost neck symmetrically shaped about the center line;
• an uppermost lug formed below the uppermost neck and symmetrically shaped about the center line, and having on each side of the center line a flat bearing surface b.sub.1, a length of which is defined by a beginning point and a terminating point, a radiused fillet surface s.sub.1 of radius R2, an arcuate length of which is defined by a terminating point coexistent with the beginning point of the bearing surface b.sub.1, the bearing surface b.sub.1 being in surface contact with a corresponding flat bearing surface of the groove which is defined by a beginning point and a terminating point, the terminating point being at a greater horizontal distance from the center line than the beginning point, the groove including a radiused fillet surface of radius R3, an arcuate length of which is defined by a beginning point coexistent with the terminating point of the groove bearing surface, a zone of contact between the root bearing surface b.sub.1 and the groove bearing surface extending over a length l.sub.1 from the beginning point of the groove bearing surface to the terminating point of the root bearing surface;
• a lowermost neck formed below the uppermost lug and symmetrically shaped about the center line;
• and
• a lowermost lug formed below the lowermost neck symmetrically shaped about the center line and having on each side of the center line a flat bearing surface b.sub.2 a length of which is defined by a beginning point and a terminating point, a radiused fillet surface s.sub.2 of radius R6, an arcuate length of which is defined by a terminating point coexistent with the beginning point of the bearing surface b.sub.2, the bearing surface b.sub.2 being in surface contact with a corresponding flat bearing surface of the which is defined by a beginning point and a terminating point, the terminating point being at a greater horizontal distance from the center line than the beginning point, the groove including a radiused fillet surface of radius R7, an arcuate length of which is defined by a beginning point and a terminating point, the terminating point being coexistent with the terminating point of the groove bearing surface, a zone of contact between the root bearing surface b.sub.2 and the groove bearing surface extending over a length l.sub.2 from the beginning point of the groove bearing surface to the terminating point of the root bearing surface,
• wherein a ratio of l.sub.2 to l.sub.1 is about 0.76, a ratio of R3 to R2 is about 1.0, and a ratio of R7 to R6 is about 1.55.