- Analysis of the Rotorway Drive System -
Properties, Loads, Stresses, FEA, Failures
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The power distribution system in the Rotorway Exec helicopter is a dynamically complex system. Unfortunately, there have been several in-flight failures of the
secondary shaft in this power transmission system.
When discussing the secondary failure issue, it is helpful to have available some technical information about the RotorWay power distribution system. This section
presents some background on the secondary failure problem followed by a technical analysis of the causes. This section describes the key components of the power
distribution system, their mechanical and dynamic characteristics, and presents EPI's detailed dynamic analysis of the system. This analysis covers both the factory
main rotor drive system (roller chain) and the main rotor drive system using the aftermarket Pro-Drive™ tooth-belt system
1. Secondary Failure: An Overview An overview of the in-flight failures of RotorWay secondary transmissions, the results, and
an introduction to an analysis of the causes of the problem.
2. Secondary Failure Database The extent of the problem with hard data about specific secondary failures.
3. Digest of the Failure Analysis A condensation of the detailed analysis presented in the remainder of this section.
4. Analysis Model of the Drive System A description of the system model used to analyze the dynamic properties and
vibration modes of the main rotor drive system.
5. System Excitation from the Engine A description of the engine characteristics which produce the very high torsional
excitation which is seen throughout the rotor drive system.
6. System Properties of the Main V-Belt Drive A description of the power transmission properties of the main V-belt drive,
and the loads this drive generates in the system.
7. System Properties of the Main Rotor Chain Drive A description of the power transmission properties of the main rotor
chain drive, and the loads this drive generates in the system.
8. System Properties of the ProDrive™ Belt System A description of the power transmission properties of the ProDrive main
rotor toothbelt drive, and the loads this drive generates in the system.
9. Very Large Loads from ProDrive™ System An explanation with numbers and pictures of the three reasons the ProDrive belt
system overloads the RotorWay secondary shaft.
10. Drive System Dynamic Properties The level of engine excitation in the drive system, and the inertias and torsional
rates used in the dynamic analysis.
11. Drive System Vibration Modes The determination of the 4-degrees-of-freedom Main Rotor Drive System vibration modes.
12. Metallurgy of the Factory Secondary Analysis of the metallurgy of the factory secondary, with strength, fatigue and
hardness data.
13. Loads on the Secondary Shaft The magnitudes and directions of the various loads the Secondary Shaft carries, and the critical
stresses they generate.
14. FEA of Factory 35mm Shaft Stress analysis of the factory 35mm secondary under various load scenarios.
15. Fatigue Failure of the Shaft An explanation of why the factory secondary shafts are experiencing fatigue failures, and
has some interesting pictures of some failed sections.
16. Secondary Bearing Issues Problems with excessive load and reduced life of both secondary shaft bearings.
17. Gates Toothbelt Issues Clarification of some of the myths, rumors, claims, counterclaims and just plain hype regarding the use
of the Gates toothbelt for a main rotor drive.
18. Autorotation Clutch Issues Description of the operation and construction (with pictures) of the RotorWay autorotation clutch,
with an explanation of its main deficiency.
19. Engine Concerns A brief discussion of several concerns about the RotorWay piston engine (not really related to the main drive system).
20. EPI Secondary Upgrade Status The EPI inspection program and results of inspections, as well as a few problems encountered
by users of the EPI secondary transmission upgrade system.
