Tiltrotor Conversion Actuation With Passive Backlash Preload
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Solution Overview
Problem
Tiltrotor aircraft experience mechanical backlash during mode conversion from hover to aircraft mode, leading to undesirable effects like aero-servo-elastic coupling due to aerodynamic and other loads, which existing actuation systems fail to adequately address.
Innovation Solution
The method involves pre-loading a rod connected to a spindle using a passive friction device and a downstop mechanism, where the rod is displaced to apply a load against the downstop, and the passive friction device maintains this load, reducing mechanical backlash by engaging without active energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If linear actuators (screw jacks or hydraulic jacks) are used to rotate the pylon, then the pylon can be rotated between hover mode and aircraft mode, but mechanical backlash occurs during mode conversion leading to aero-servo-elastic coupling
Solution Approach 1:
The patent applies preliminary anti-action by pre-loading the actuator rod against a downstop before mode conversion occurs. This pre-load creates an initial compressive force that eliminates clearance and backlash in the actuator mechanism, preventing the harmful effects of mechanical play during the critical mode conversion phase. The downstop provides a fixed reference point that ensures the rod maintains constant contact and pressure throughout the operation.
Solution Approach 2:
The patent implements preliminary action by establishing the pre-load condition on the actuator rod before the actual mode conversion begins. The rod is displaced to apply load against the downstop in advance, ensuring that the actuation mechanism is primed and free of backlash before the pylon rotation starts. This preparatory action ensures smooth and precise control during the subsequent mode conversion.
2Reliability
If active brakes or sensors are used to maintain rod position, then mechanical backlash can be reduced, but device complexity increases
Solution Approach 1:
The patent applies self-service by using a passive friction device that automatically maintains the pre-load on the actuator rod without requiring external control systems. The friction device self-regulates to prevent rod displacement and maintain position stability through inherent friction forces, eliminating the need for active brakes, sensors, or control algorithms. This passive approach reduces system complexity while maintaining reliability.
Solution Approach 2:
The patent introduces a passive friction device as an intermediary element between the actuator rod and the surrounding structure. This friction device acts as a mediator that provides continuous positional stability through controlled friction forces, preventing backlash without requiring complex active control systems. The friction device translates the pre-load force into stabilizing resistance against unintended rod movement.
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
This solution effectively reduces mechanical backlash and maintains the pre-load, preventing unwanted mode conversions during forward flight, thereby enhancing the stability and reliability of tiltrotor aircraft actuation systems without the need for additional active brakes or sensors.
Implementation Method 1
an actuator with a rod displaceable by a drive mechanism, the rod mounted to the linking member such that displacement of the rod causes the spindle to rotate about the spindle axis, the actuator having a passive friction device engaged with the rod to stop displacement thereof
Data Source
AI summary
A method of displacing rotors of an aircraft between a hover mode and an aircraft mode includes rotating a spindle drivingly connected to the rotors about a spindle axis to displace the rotors between the hover and aircraft modes until a component displaceable with the spindle abuts against a downstop of the aircraft and applies a load against the downstop. The method includes passively maintaining the component against the downstop to maintain the load applied against the downstop. An aircraft is also disclosed.