This project presents a conceptual mechanical design of a telescopic Hold-Open Rod (HOR) for aircraft engine nacelle cowl doors, developed as part of the AeroHack 2025 design challenge. The HOR is designed to automatically lock during extension and safely support the full dead weight of the cowl during maintenance operations.
The proposed solution integrates a spring-based passive locking mechanism for automatic engagement, complemented by a threaded secondary lock that requires deliberate rotational and axial motion to unlock, ensuring fail-safe operation under compressive load. A visual lock-status indicator with color-coded feedback enhances operational safety.
 

The design fits within the prescribed cylindrical envelope (Ø60 mm × 1160 mm), weighs only 1.12 kg, and satisfies a 4000-cycle fatigue life requirement. Detailed CAD modeling, assembly design, and finite element meshing were performed, demonstrating structural integrity and manufacturability. This concept emphasizes mechanical simplicity, redundancy, and clear physical reasoning behind the locking behavior.