Tail Rotor Actuator Joint With Shear-Pin Torque Release
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Solution Overview
Problem
Conventional tail rotor actuators in rotorcrafts are prone to failure due to excessive torque transfer from the tail rotor, leading to a loss of yaw control and insufficient time for emergency landing, as their joints are not designed to handle increased torque without breaking.
Innovation Solution
A joint with a rotary bearing and shearing elements that remain rotationally fixed until a threshold torque is exceeded, allowing relative rotatability between the inner and outer races to reduce torque transfer and prevent joint failure, featuring a housing, rotary bearing, and shear pins that break to enable rotation when torque exceeds a predetermined value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional rotationally fixed joint is used between the pitch control rod and input lever, then the joint provides structural stability and precise linear movement control, but the joint breaks quickly when excessive torque is transferred from the tail rotor, providing insufficient time for emergency landing
Solution Approach 1:
The joint transitions from a static rotationally fixed design to a dynamic design where the bearing races can rotate relative to each other when excessive torque is detected. This dynamic behavior allows the joint to adapt its stiffness characteristics based on loading conditions, providing both stability during normal operation and protection during failure conditions.
Solution Approach 2:
The invention converts the harmful effect of excessive torque that would normally cause catastrophic joint failure into a beneficial protective mechanism. When torque exceeds the threshold, the shearing elements break and enable race rotation, which dissipates the excessive torque and prevents complete joint failure, thereby extending the time available for emergency landing.
2Reliability
If the joint allows relative rotation between bearing races under excessive torque, then the torque transfer to the actuator is reduced and joint failure is prevented, but the joint structure becomes more complex with additional components
Solution Approach 1:
The joint is segmented into distinct functional components: the housing, the inner and outer bearing races, and the shearing elements. This segmentation allows each component to perform its specific function independently - the shearing elements act as torque-sensing fuses that break at a predetermined threshold, enabling the bearing races to rotate and protect the actuator.
Solution Approach 2:
The shearing elements serve as intermediary components between the bearing races. These elements normally constrain the races to remain rotationally fixed, but when they break under excessive torque, they mediate the transition to a state where the races can rotate relative to each other, thereby protecting the actuator from damage.
3Reliability
If the shearing elements are designed to break at a predetermined torque threshold, then the joint can withstand higher torque without complete failure and maintain control, but the shearing elements must be precisely engineered to break at the correct torque value
Solution Approach 1:
The shearing elements are designed with specific geometric parameters (cross-sectional area, material properties, length) that determine their break torque threshold. By carefully selecting and controlling these parameters during manufacturing, the shearing elements can be made to break at a predetermined torque value that balances actuator protection with sufficient control authority during normal operation.
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
The solution increases the time available for emergency landing by allowing the actuator to withstand higher torque without breaking, maintaining control over the tail rotor blade pitch and yaw angle, as demonstrated by reduced torque transfer after the shearing elements break, thereby preventing critical failure.
Implementation Method 1
If the duplex bearing seizes up or otherwise fails, for example due to contamination of the duplex bearing, an increase in friction at the bearing may cause a high amount of torque to be transferred from the tail rotor
Implementation Method 2
A torque tolerant joint for a tail rotor actuator comprises a housing, a rotary bearing, and at least one shear pin. The shear pin extends through the housing and the bearing and is configured to break between the inner race and the outer race
Data Source
AI summary
A joint for an actuator of a rotorcraft includes a housing configured to be coupled to an input lever of the actuator; and a rotary bearing coupled to the housing, the rotary bearing comprising an inner race and an outer race and configured to be coupled to a control rod, wherein the inner race and outer race are rotationally fixed relative to each other until a torque applied to the joint exceeds a threshold torque value, upon which there is a relative rotatability between the inner race and the outer race.