RAT Flyweight Cam Follower Variable Pitch Startup
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Solution Overview
Problem
Ram Air Turbines (RATs) face inefficiencies during startup, particularly at low RPMs, due to low centrifugal forces and high dynamic pressure losses in turbulent zones, leading to slow startup and inadequate torque for overcoming blade inertia and tare losses.
Innovation Solution
The integration of a cam follower system with an axially movable plate and rotatable flyweight that positions the cam follower at different angles based on RPMs, allowing for increased torque during startup by transitioning to a coarser pitch at low RPMs and adjusting to finer pitches as RPMs increase, utilizing a flyweight spring and detent mechanism to balance forces and maintain optimal blade angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fine pitch RAT architecture is used, then reliability and weight are improved, but startup efficiency deteriorates due to insufficient torque at low RPMs
Solution Approach 1:
The patent applies dynamics by making the blade pitch angle variable during startup. The flyweight mechanism automatically transitions the blade pitch from coarse (higher torque) to fine (operational) as RPM increases, optimizing performance across different operating phases without manual intervention or complex control systems
Solution Approach 2:
The patent changes the pitch angle parameter dynamically during startup. By varying the blade pitch angle from coarse to fine as a function of RPM, the system overcomes the insufficient torque problem at low speeds while maintaining the reliability benefits of fine pitch architecture throughout the operational range
2Productivity
If coarse pitch RAT architecture is used, then startup efficiency is improved, but device complexity and weight increase
Solution Approach 1:
The patent merges the startup mechanism with the existing governor mechanism. The flyweight that controls blade pitch during startup is integrated into the governor assembly, eliminating the need for separate startup components and reducing overall system complexity while achieving coarse pitch startup performance
Solution Approach 2:
The system performs self-service through the automatic flyweight mechanism that transitions blade pitch based on centrifugal force at different RPMs. This eliminates the need for external control systems, actuators, or complex electronics, achieving coarse pitch startup benefits with minimal added complexity
3Reliability
If fine pitch blade orientation is maintained at low RPMs, then operational reliability is improved, but torque availability deteriorates due to high blade inertia
Solution Approach 1:
The patent applies preliminary action by positioning the blades at coarse pitch before and during early startup. This preliminary coarse pitch orientation generates higher torque to overcome blade inertia and get the turbine rotating, after which the blades transition to fine pitch for reliable operation once operational speed is reached
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 enables faster RAT startup, comparable to coarse pitch turbines, while maintaining reliability and reducing complexity, with automatic reset and minimal weight increase, allowing for efficient torque production across the RPM range.
Implementation Method 1
The counterweights require centrifugal forces to develop their restraining forces. During startup, centrifugal forces are low... at low RPMs, the system prevents flyweight rotation... at medium RPMs, the system permits flyweight rotation
Data Source
AI summary
A turbine having a cam follower operable to control turbine blade pitch in association with a position thereof is provided and includes an axially movable plate, a rotational and axially movable flyweight and a system operably coupled to the plate and the flyweight whereby, at low RPMs, the system prevents flyweight rotation such that the plate and the flyweight position the cam follower at a first position, at medium RPMs, the system permits flyweight rotation such that the plate and the flyweight position the cam follower at a second position, and, at high RPMs, the system prevents further flyweight rotation and permits initial axial movement of the plate and the flyweight such that the plate and the flyweight position the cam follower at a third position.