Variable Pitch Fan Blade Retention via Timing Ring and Gear Mechanism
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Solution Overview
Problem
Current systems for variable pitch in aircraft engine fan blades face challenges such as high weight, instability due to centrifugal forces, and the risk of rotor overspeed and loss of control, which are not effectively addressed by existing solutions like counter-weights or backup pitch-change systems, limiting efficiency and fuel savings in turbofan engines.
Innovation Solution
A system comprising a rotatable hub, gear mechanism, timing ring, and pitch arm that allows for variable pitch control of fan blades, using flexible support tennons to balance centrifugal and aerodynamic forces, reducing the need for counter-weights and enabling efficient pitch adjustment, with a drive motor for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If counter-weights are added to balance centrifugal forces and prevent blade pitch instability, then blade pitch stability is improved, but rotor weight and device complexity increase
Solution Approach 1:
The patent applies counter-weights mounted on the rotor hub to counteract centrifugal forces that cause blade pitch instability. These counter-weights create opposing moments that balance the twisting forces generated by centrifugal loads, preventing the blades from rotating toward low pitch positions and ensuring stable pitch control during operation.
Solution Approach 2:
The patent modifies the mass distribution parameters of the rotor system by adding counter-weights at specific positions and masses calculated to balance centrifugal forces. This parameter change transforms the unstable pitch control problem into a stable system where the counterbalancing moments offset the centrifugal twisting moments, achieving pitch stability without compromising structural integrity.
2Reliability
If backup pitch-change systems are added to prevent rotor overspeed, then safety is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements backup pitch-change systems with latching mechanisms that automatically engage if the primary pitch control system fails. These backup systems are designed to prevent rotor overspeed by maintaining blade pitch at safe angles, providing a safety net before dangerous conditions can develop. The latching mechanisms ensure that even if the primary control system malfunctions, the rotor cannot overspeed under any operating condition.
3Measurement precision
If frictional resistance is increased in retention bearings to control blade pitch, then pitch control precision is improved, but force required for pitch change increases
Solution Approach 1:
The patent employs frictional retention bearings with latching mechanisms that provide feedback control for blade pitch. The frictional force in the bearings creates a self-regulating system where the pitch position is maintained through elastic deformation of the bearing elements. This feedback mechanism ensures precise pitch control by automatically adjusting the retention force to match the centrifugal loading conditions, preventing both excessive pitch changes and loss of pitch control.
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 simplifies variable pitch systems, reduces weight and cost, enhances rotor efficiency, and allows for significant fuel savings of 15-20% in turbofan engines, while maintaining operational safety and serviceability, making it suitable for large, ducted high-bypass fans.
Implementation Method 1
flexible support tennons to balance centrifugal and aerodynamic forces
Data Source
AI summary
A system for providing variable pitch to a rotor blade of an aircraft engine includes a rotatable hub; at least one blade mounted on the rotatable hub; a gear mechanism operably connected to the rotatable hub; a timing ring rotatably and operably connected to the gear mechanism; and a pitch arm operably connecting the timing ring and the at least one blade mounted on the rotatable hub. In the operation of the system, the gear mechanism facilitates the rotation of the timing ring to vary the pitch of the at least one blade mounted on the rotatable hub.