Aircraft Actuator Screw-Nut Jamming Redundancy
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Solution Overview
Problem
Conventional electric actuators used in aircraft safety-critical components, such as landing gear and flight control devices, face high failure risks due to the interface between the threaded screw and nut, leading to bulkiness and reduced reliability, especially when hydraulic systems are being phased out.
Innovation Solution
A compact and lightweight actuator system utilizing a threaded screw and nut with a main prime mover for normal operation and an emergency prime mover to address jamming issues, ensuring torque application in opposition to or in the same sense as external loads, featuring a set of rolling elements and direct-drive motors for efficient movement between positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electric actuators with threaded screw and nut are used in safety-critical components, then they can replace hydraulic systems, but the interface between screw and nut has high failure risk leading to bulkiness and reduced reliability
Solution Approach 1:
The actuator is divided into two independent drive systems: a main drive system for normal operation and an emergency drive system for failure conditions. Each system has its own motor and can independently operate the screw-nut interface, providing functional redundancy without requiring a single complex over-engineered system. This segmentation allows each subsystem to be simpler while the overall system achieves high reliability through redundancy.
2Reliability
If redundant actuator systems are implemented to tolerate failure, then reliability improves, but the actuators become large and bulky
Solution Approach 1:
The emergency drive system shares the same screw and nut mechanical interface with the main drive system, rather than having completely separate redundant mechanisms. The emergency motor can directly engage the existing screw-nut interface, merging the emergency function with the main mechanical transmission path. This reduces overall weight compared to fully independent redundant systems while maintaining failure tolerance.
Solution Approach 2:
The screw-nut interface serves dual purposes: it is the mechanical transmission element for both the main drive system during normal operation and the emergency drive system during failure conditions. This multi-functional use of the same mechanical components allows the actuator to achieve redundancy without duplicating the entire mechanical transmission path, reducing weight and size.
3Device complexity
If a single actuator system is used without redundancy, then the design remains compact, but the risk of complete failure increases
Solution Approach 1:
The emergency motor acts as an intermediary backup that can engage the existing screw-nut mechanical interface when the main motor fails. Rather than requiring a completely separate redundant mechanism, the emergency motor serves as a mediator that can take over the same mechanical path, providing failure tolerance while maintaining system simplicity and compactness.
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 system achieves a low probability of complete jamming, allowing for a lightweight and compact design with reduced reliance on hydraulic systems, maintaining high integrity and reliability even under emergency conditions.
Implementation Method 1
a set of rolling elements arranged between the threaded screw and the threaded nut
Implementation Method 2
a main prime mover arranged to rotate the screw or the nut in order to impart relative linear motion between the screw and the nut
Implementation Method 3
an emergency prime mover arranged to rotate the screw or the nut in order to impart relative linear motion between the screw and the nut
Data Source
AI summary
An actuator is arranged to move an aircraft component such as a landing gear leg, flap or aileron between a first position and a second position, net load from external forces acting on the aircraft component tending to drive it towards the first position. The actuator comprises a threaded screw and a threaded nut. A main prime mover is configured to apply torque to the screw or nut acting in opposition to the net load under normal operating conditions. An emergency prime mover is configured to apply torque to the screw or nut acting in the same sense as the net load under emergency operating conditions in which the interface between the nut and the screw has become partially jammed to the extent that the component cannot be moved from the second position to the first position by operation of the net load alone.