Telescopic Hold Open Rod Locking Against Inadvertent Fan Cowl Closure
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Solution Overview
Problem
Existing hold open rods (HORs) for fan cowls in aircraft nacelles face challenges in safely supporting the weight of the cowls while preventing inadvertent closure and ensuring secure locking in the open position.
Innovation Solution
A telescopic hold open rod system with a control sleeve, outer cylinder, lock balls, lock sleeve, piston, piston head, release spring, and lock spring, allowing configurable unlocked and locked configurations through axial and rotational movements to secure the fan cowl in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hold open rod is designed to support considerable fan cowl weight, then the structural strength is improved, but the device complexity increases due to the need for multiple locking mechanisms
Solution Approach 1:
The patent implements a nested telescopic structure where the hold open rod consists of multiple concentric tubes (inner tube, intermediate tube, outer tube) that slide within each other. The locking mechanism is nested within this telescopic structure, with lock balls and locking surfaces integrated into the tube walls. This nesting approach allows the rod to support considerable weight through its robust multi-tube construction while keeping the locking mechanism compact and integrated, thus managing device complexity.
Solution Approach 2:
The hold open rod is divided into multiple functional segments: telescopic sections for length adjustment, locking sections with lock balls and locking surfaces for secure positioning, and spring sections for providing locking force. This segmentation allows each component to be optimized for its specific function, enabling the structure to support weight effectively while maintaining a manageable level of overall complexity through modular design.
2Reliability
If a lock mechanism is added to prevent inadvertent closure, then the safety is improved, but the device complexity increases
Solution Approach 1:
The locking mechanism is designed to be self-actuating through spring force. The springs automatically engage the lock balls with the locking surfaces when the tube reaches the desired extended position, without requiring external control systems or additional actuators. This self-service approach ensures safety against inadvertent closure while minimizing the addition of complex control mechanisms.
Solution Approach 2:
The locking function is merged with the telescopic structure itself. The lock balls are positioned within the tube walls, and the locking surfaces are formed as integral features of the tube structure rather than separate components. This merging of locking functionality into the existing telescopic mechanism provides safety without significantly increasing overall device complexity.
3Reliability
If multiple lock balls are used to secure the hold open rod, then the reliability of locking is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The locking system uses multiple lock balls distributed at different angular positions around the tube circumference, with each lock ball engaging a corresponding locking surface. This segmentation of the locking function across multiple discrete elements provides redundant security - if one locking engagement is imperfect, others compensate. The modular nature of multiple independent locking points reduces the cumulative precision requirement compared to a single complex locking interface.
Solution Approach 2:
The patent employs spring-loaded lock balls that can deform elastically to accommodate minor misalignments between lock ball positions and aperture locations. This use of elastic deformation as a compliance mechanism allows the system to achieve reliable locking even with moderate manufacturing tolerances, reducing the stringency of precision requirements while maintaining locking security.
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 effectively supports the weight of the fan cowl, prevents inadvertent closure, and ensures secure locking in the open position, enhancing safety and operational reliability.
Implementation Method 1
The release spring is disposed between the OC outer radial surface and the first CS inner radial surface and is configured to bias the control sleeve toward the first axial end
Implementation Method 2
The lock spring is disposed between the OC outer radial surface and the lock spring and is configured to bias the lock sleeve toward the second axial end
Data Source
AI summary
A hold open rod has a control sleeve, an outer cylinder, lock balls, a lock sleeve, a piston, a piston head, a release spring, and a lock spring. The control sleeve has first and second cavity sections, an inner radial surface, a CS channel, and a pin. The outer cylinder has an OC inner cavity, OC inner and outer radial surfaces, an OC axial end wall, lock ball apertures, and a pin guide slot. The lock balls are configured to pass through the lock ball apertures. The piston has first and second sections. The piston head has an outer radial surface, a channel, and a piston bore. The piston bore is configured to receive the first section of the piston. The release spring biases the control sleeve toward a first axial end. The lock spring biases the lock sleeve toward a second axial end.