Contra-rotating Propeller Torque Balance via Planetary Gear Train
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Solution Overview
Problem
Turbomachines with contra-rotating propellers face inefficiencies due to unequal torque ratios between propellers, leading to reduced propulsion efficiency, increased acoustic levels, and excessive mechanical stress on mounting systems, which are exacerbated by the need for a high reduction ratio and increased mass.
Innovation Solution
Incorporating a second contra-rotating rotor within the free power turbine to balance torque transmission between propellers through a planetary gear train, allowing the second propeller to be partly driven by the ring, achieving equal torque ratios and reducing the rotational speed of the first rotor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single planetary gear train is used to drive contra-rotating propellers, then the structure is simple, but the torque ratio between propellers cannot be equalized
Solution Approach 1:
The single planetary gear train is segmented into two independent planetary gear trains, each driving one propeller. This allows independent torque control to each propeller while maintaining a relatively simple overall structure, resolving the contradiction between structural simplicity and propulsion efficiency.
Solution Approach 2:
Two planetary gear trains are merged into a unified transmission system that shares common components (such as the sun gear driven by the turbine), achieving equal torque distribution to both propellers while avoiding the complexity of completely separate transmission systems.
2Productivity
If the reduction ratio R is increased to approach equal torque ratio, then the torque balance improves, but the overall mass of the propeller system increases
Solution Approach 1:
The invention changes the fundamental parameter of torque transmission by using two separate planetary gear trains with independent control, rather than trying to achieve torque balance through extreme reduction ratios. This allows optimal reduction ratios that balance torque equality with acceptable system mass.
3Weight of moving object
If unequal torque ratio is accepted, then the system mass is reduced, but the acoustic level increases and mounting stress increases
Solution Approach 1:
The invention applies different local qualities to each propeller drive path by using independent planetary gear trains that can be individually optimized. This allows each propeller to receive precisely the torque it needs, minimizing residual gyration and associated acoustic emissions while keeping system mass acceptable.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution balances torque ratios, enhancing propulsion efficiency, reducing acoustic levels, and minimizing mechanical stress and mass, while also reducing the size and complexity of the reduction gear system, leading to a more efficient and lighter turbomachine design.
Implementation Method 1
a mechanical transmission system including a planetary gear train fitted with a sun gear centred on the said lengthways axis and driven by the said first rotor of the free power turbine
Implementation Method 2
a free power turbine including a first rotor; a second contra-rotating rotor intended to be rotated in the opposite sense to that of the first rotor
Data Source
AI summary
A system of contra-rotating propellers for an aircraft turbomachine, including: a free power turbine including a first rotor; first and second propellers; and a mechanical transmission system including a planetary gear train fitted with a sun gear driven by the rotor, at least one planet gear driving the first propeller, and a ring driving the second propeller. The free power turbine also includes a second rotor that is contra-rotating relative to the first rotor, and rotating the ring.