Abstract: A highly efficient ultra-light weight heavy lift helicopter transmission is disclosed herein which, by these very characteristics, allows greater helicopter payloads and gross weights than now can be attained using present state of the art design approaches. These characteristics are made possible through the use of:1. Multiple vertically mounted engines which allow short power paths and a minimum number of gear meshes in series.2. Many load sharing power paths (three per engine) having fixed load sharing ratios which are unaffected by transmission deflections and manufacturing tolerances.3. A large overall gear reduction through the use of differential planetary meshes (one per engine) and a large gear reduction with many input load paths at its final output herringbone type gear stage.4. A unique final stage, bearingless, floating bull gear support system having an ultra lightweight reaction load path means, and5.