Partial Coarse Pitch Ram Air Turbine Spring Support
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Solution Overview
Problem
Ram Air Turbine (RAT) systems with cantilevered springs experience vibration and sticky operation due to full coarse pitch start angles, which can result in the governor mechanisms staying in coarse pitch at low airspeeds, failing to shift to fine pitch efficiently.
Innovation Solution
A partial coarse pitch start RAT design with a hub assembly that biases the governor shaft to adjust turbine blades from a partial coarse pitch angle at low rotational speeds to a fine pitch angle at high rotational speeds, using a combination of governor springs, flyweights, and a cam follower system to optimize torque generation and operational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If full coarse pitch start angles are used, then startup torque is enhanced, but the governor mechanisms may stay in coarse pitch at low airspeeds and fail to shift to fine pitch efficiently
Solution Approach 1:
The patent applies local quality by using a partial coarse pitch angle (30-40 degrees) rather than full coarse pitch, creating a localized optimization where the blade angle is sufficient for startup torque but not excessive. This allows the governor mechanism to transition smoothly to fine pitch at higher speeds without being stuck in coarse pitch position.
Solution Approach 2:
The system dynamically adjusts blade pitch angle based on operational conditions. At startup, partial coarse pitch provides necessary torque, then the mechanism transitions to fine pitch as speed increases. The spring force and flyweight centrifugal force dynamically balance to enable this smooth transition.
2Ease of operation
If cantilevered springs are used in governor mechanisms, then blade pitch control is achieved, but vibration and sticky operation occur
Solution Approach 1:
The patent uses flyweights that generate centrifugal force to counterbalance the spring force acting on the governor mechanism. This counterweight approach eliminates the sticky operation and vibration problems associated with cantilevered springs alone, as the outward centrifugal force on the flyweights balances the inward spring force, enabling smooth pitch transitions.
3Force
If coarse pitch is maintained at low airspeeds, then startup torque is sufficient, but maximum speed performance is reduced
Solution Approach 1:
The blade pitch angle is dynamically adjusted based on rotational speed. At low speeds, partial coarse pitch (30-40 degrees) provides sufficient torque for startup. As speed increases, centrifugal force on flyweights overcomes spring force, transitioning blades to fine pitch (approximately 9 degrees) for optimal high-speed performance.
Solution Approach 2:
The system changes the blade pitch angle parameter according to operational conditions. The governor mechanism automatically adjusts the pitch angle from partial coarse (30-40 degrees) at low speeds to fine (9 degrees) at high speeds, optimizing performance across the entire operating range.
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 design reduces vibration and sticky operation, ensuring sufficient startup torque at low speeds and increased maximum torque at higher speeds, while maintaining efficient operation by transitioning to fine pitch at higher rotational speeds, enhancing overall power generation capabilities.
Implementation Method 1
the hub assembly biases the governor shaft toward the first position at low rotational speeds such that the turbine blades assume a partial coarse pitch angle
Implementation Method 2
the second position at high rotational speeds such that the turbine blades assume a fine pitch angle
Data Source
AI summary
A Ram Air Turbine (RAT) is provided and includes a turbine hub having an end plate and a nose cone attached thereto at trailing and leading ends, respectively, a governor shaft, to which turbine blades are connected, which is coupled to the end plate and supported within the nose cone to be rotatable with the turbine blades about a central axis thereof and axially movable from a first position relative to the turbine hub to a second position relative to the turbine hub and a hub assembly operably coupled to the turbine hub, the governor shaft and the turbine blades whereby the hub assembly biases the governor shaft toward the first position at low rotational speeds such that the turbine blades assume a partial coarse pitch angle, and the second position at high rotational speeds such that the turbine blades assume a fine pitch angle.