The Instantaneous Efficiency of Epicyclic Gears in Flight Control Systems

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Anngwo Wang ◽  
Seth Gitnes ◽  
Lotfi El-Bayoumy
Keyword(s):  
Control Systems ◽  
Flight Control ◽  
The Sun ◽  
Large Fluctuation ◽  
Planetary Gears ◽  
Average Efficiency ◽  
Rotary Actuator ◽  
Epicyclic Gear ◽  
Gear Trains

The instantaneous efficiency of an epicyclic gear rotary actuator is an important factor in sizing flight control systems where compound epicyclic gear trains are typically used. The efficiency variation can be smooth or fluctuating depending on the combination and timing of the teeth of ring, planet, and sun gears. In this paper, the instantaneous efficiency characteristics of synchronous and nonsynchronous actuators under forward-driving with opposing load and reverse-driving with aiding load are investigated. The emphasis will be on instantaneous, rather than average efficiency of gears. Several gear arrangements are considered: external and internal gears, simple planetary gears and compound planetary gears. Efficiency will be discussed considering not only the geometry of the mating gears, but also the relative phasing of the planet gears relative to the sun and ring gears. Synchronous compound epicyclic gears are shown to have large fluctuation in their instantaneous efficiency. When reverse-driving efficiency falls below 0%, the unit cannot be back-driven and will chatter. Nonsynchronous compound gears have a smaller variation in instantaneous efficiency. However, extra care must be taken in timing the compound planet gears, as well as clocking position of compound planet gears relative to ring gears and the sun gear.

Synthesis of Single-Ratio and Multi-Ratio Epicyclic Gear Trains

1971 ◽  
Vol 13 (6) ◽  
pp. 404-415 ◽  
Author(s):  
D. Fitzgeorge
Keyword(s):  
Single Equation ◽  
Planetary Gears ◽  
Input And Output ◽  
Epicyclic Gear ◽  
Letter Code ◽  
Gear Trains

A class of epicyclic gears based on coaxially mounted plane trains is defined. The class is restricted to those gears in which planetary gears of adjacent trains are coupled. The type of epicyclic multi-ratio gearbox in which the input and output members are always the same is selected for consideration. The basic kinematics of the planetary member are then reduced to a single equation which is subsequently expressed as a chart, covering all ratio possibilities and directly applicable as the basis of synthesis. The chart is shown to offer an arbitrary means of describing the various forms of gear by a number-and-letter code. The application of the chart to the synthesis of trains incorporating planetary idlers and multi-ratio trains is explained.

scholarly journals An Analysis of the Gear Meshing Characteristics of the Main Planetary Gear Trains of Helicopters Undergoing Shafting Position Changes

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Li Xuejun ◽  
Jiang Lingli ◽  
Hua Dengrong ◽  
Yin Daoxuan ◽  
Yang Dalian
Keyword(s):  
Planetary Gear ◽  
The Sun ◽  
Mass Center ◽  
Main Rotor ◽  
Transmission Systems ◽  
Planetary Gears ◽  
Planetary Gear Trains ◽  
Gear Trains ◽  
Meshing Characteristics ◽  
Helicopter Transmission

The complex three-shaft three-reducer structural designs of helicopter transmission systems are prone to changes in the relative positions of shafting under the conditions of main rotor and tail rotor loads. These changes will affect the transmission characteristics of the entire transmission system. In this study, the planetary gear trains of helicopters were examined. Due to the fact that these structures are considered to be the most representative structures of the main reducers of helicopters, they were selected as the study objects for the purpose of examining the meshing characteristics of planetary gear trains when the relative positions of the shafting changed due to the position changes of the main rotor shafts under variable load conditions. It was found that by embedding the comprehensive time-varying meshing stiffness values of the main rotor shafts at different positions, a dynamic model of the relative position changes of the planetary gear trains could be established. Then, combined with the multibody dynamics software, the meshing characteristics of the sun gears, and the planetary gears, the planetary gears and the inner ring gears were simulated and analyzed under different inclinations and offsets of the shafting. The results obtained in this study revealed the following: (1) the average meshing force of the gears increased with the increases in the angle inclinations, and the meshing force between the sun gears and the planetary gears increased faster than the meshing force between the planetary gears and the inner ring gears. It was observed that during the changes in the shafting tilt positions, obvious side frequency signals had appeared around the peak of the meshing frequency in the spectrum. Then, with the continuous increases in the tilt position, the peak was gradually submerged; (2) the average meshing force of the gears increased with the increases in the offset, and the increasing trend of the meshing force between the sun gears and the planetary gears was similar to that observed between the planetary gears and the inner ring gears. It was found that when the shafting offset position changed, there were obvious first and second frequency doubling in the spectrum; (3) the mass center orbit radii of the sun gears increased with the increases in the shafting position changes, and the changes in the angular tilt position were found to have greater influencing effects on the mass center orbit radii of the sun gears than the changes in the offset positions. This study’s research findings will provide a theoretical basis for future operational status monitoring of the main transmission systems of helicopters and are of major significance for improvements in the operational stability of helicopter transmission systems, which will potentially ensure safe and efficient operations.

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