Motor-Assisted Fine Pitch Ram Air Turbine Startup
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Solution Overview
Problem
Fine pitch startup Ram Air Turbines (RATs) face a trade-off between steady-state performance and startup performance, resulting in longer start times and controllability issues due to low torque at low airspeeds, which is addressed by mechanisms that increase weight and size while decreasing reliability.
Innovation Solution
A motor-assisted startup assistance apparatus for fine pitch RATs, comprising a generator that operates as a motor at low speeds to provide motive power and switches to generating electricity at higher speeds, utilizing a control unit with a speed sensing unit to manage the operational modes based on sensed frequency conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a small blade pitch angle (5-15 degrees) is used for fine pitch startup RAT, then steady state performance is improved, but startup torque is insufficient leading to long start times
Solution Approach 1:
The system performs preliminary action by using aircraft batteries to drive the RAT blades to a predetermined speed range (300-800 RPM) before aerodynamic torque becomes sufficient. This preliminary mechanical assistance allows the fine pitch blades to reach a speed where they can generate adequate torque without requiring coarse pitch angles.
Solution Approach 2:
The patent introduces an intermediary mechanism (electric motor/generator coupled to the RAT shaft) that bridges the gap between the insufficient startup torque of fine pitch blades and the required torque to overcome aerodynamic resistance. This intermediary provides the necessary torque multiplication during the critical startup phase.
2Speed
If mechanisms are added to allow coarse pitch startup followed by transition to fine pitch, then startup torque is improved, but device weight and size increase while reliability decreases
Solution Approach 1:
The patent applies multi-functionality by designing the RAT to serve dual purposes: as a wind-driven turbine for emergency power generation and as an electric motor during startup. The generator/motor can operate in both motor mode (during startup) and generator mode (during normal operation), eliminating the need for separate startup mechanisms.
Solution Approach 2:
The system achieves self-service by using the RAT's own generator component to provide the startup torque needed to get it running. The aircraft batteries charge the generator, which then operates in reverse as a motor to spin up the RAT, after which the RAT independently generates power without further external assistance.
3Power
If fine pitch blades are used, then torque at operating speed is maximized, but torque at low speed is insufficient compared to load torque
Solution Approach 1:
The system dynamically changes the operational parameters of the generator by switching between motor mode and generator mode based on rotational speed. At low speeds, the generator operates as a motor with high torque output; as speed increases, it transitions to generator mode where it produces electricity. This parameter change allows optimization at both low and high speed regimes.
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
Enables faster startup of RATs by providing additional torque during low-speed conditions without compromising steady-state performance, reducing the need for larger batteries or hydraulic accumulators and improving reliability by optimizing initial blade angle settings.
Implementation Method 1
a generator operable as a motor in a first mode to provide motive power to the RAT
Implementation Method 2
operable in a second mode to generate electricity from RAT operation
Data Source
AI summary
A startup assistance apparatus for a fine pitch Ram Air Turbine (RAT) is provided and includes a generator to provide motive power to the RAT when operating in a first mode and to generate electricity from RAT operation when operating in a second mode and a control unit, including a speed sensing unit configured to sense an operating condition of the generator and a controller operably coupled to the generator and configured to control the generator to operate in the first or the second mode based on the sensed operating condition.