An ultra-safe, high ratio planetary transmission, for application as a helicopter main rotor drive, has been
designed, fabricated and tested under the sponsorship of NRTC-RITA. The anticipated improvements
offered by this new planetary transmission are reduced weight, reduced transmitted noise and improved
fail-safety. This paper discusses the fabrication assembly and test results for the subject planetary
transmission. The design and analysis of this transmission system have been discussed in a previous paper
presented at the AGMA FTM in 2004.
The ultra-safe, high ratio planetary transmission design utilizes a compound planetary configuration with a
17.5:1 reduction ratio which would replace a conventional two stage simple planetary transmission. The new
design uses ultra-safe principles such as split-torque paths and high combined contact ratio gearing. Double
helical gears in the planet/ ring meshes balance axial tooth forces so that axial bearing reactions are not
required. The spur gear sun/planet meshes are staggered to achieve a compact spatial arrangement.
Fabrication and assembly of the components for this transmission are complicated by their configuration. The
grinding process for the helical gears must use small diameter wheels due to the proximity of the adjacent
helix, since most the gears in this configuration are integrated designs. Assembly procedures also require
special consideration because of the integrated design and helical gears. Test results are presented to
support the goals of this project, including, concept verification, weight reduction, noise reduction and
determination of the operating characteristics of the test transmission.