The use of face- -gears in helicopter transmissions was explored. A light- -weight split _torque transmission design
utilizing face – gears is described. Face- -gear design and geometry were investigated. Topics included tooth generation,
limiting inner and outer radi, tooth contact analysis, contact ratio, gear eccentricity, grinding and structural stiffness.
Design charts were developed to determine minimum and maximum face -gear inner and outer radii. An analytical
study showed that the face -gear drive is relatively insensitive to gear misalignment with respect to transmission errors,
but the tooth contact is affected by misalignment. A method of localizing the bearing contact to permit operation with
misalignment was explored. Two new methods for grinding of the face gear tooth surfaces were also investigated. The
proper choice of shaft stiffness enabled good load sharing in the split torque transmission design. Face -gear
experimental studies were also conducted. These tests demonstrated the feasibility of face- -gears in high -speed,
high- -load applications such as helicopter transmissions.