Hollow fan blade channel configuration to reduce stress

A fan blade comprising:

• a main body extending between a leading edge and a trailing edge, and having channels formed into said main body from an open side extending toward a closed side, a plurality of ribs extend across the main body intermediate the channels with said fan blade having an airfoil extending radially outwardly from a radially inner end;
• a bottom surface of the channels is defined at the closed side, and sides of the channel merging into sides of the ribs, and there being a compound fillet at the bottom surface, with a first portion having a first radius of curvature along the bottom, and merging into at least a second portion having a second radius of curvature at the rib sides, with the first radius of curvature being larger than said second radius of curvature;
• a skin closing off said channels with the first radius of curvature portion formed along a curve and the second radius of curvature portion formed along a curve and merging from said first radius of curvature portion and into the sides of the ribs;
• and
• wherein a ratio of the second radius of curvature to the first radius of curvature is between 0.03-0.25.