Over-centering Blade Lock for Tiltrotor Aeroelastic Stability
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Solution Overview
Problem
Tiltrotor aircraft face limitations in maximum airspeed during forward flight due to forward airspeed-induced proprotor aeroelastic instability, restricting their high-speed cruising capabilities.
Innovation Solution
The implementation of a blade lock mechanism that enables and disables the folding and pitching degree of freedom of rotor blade assemblies, utilizing a link pivotally connected to a lever and a bellcrank, allowing for gimballing and blade stop assemblies to transition between rotary and non-rotary flight modes, thereby managing the plane of rotation and reducing aeroelastic instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If proprotors are used to enable vertical takeoff and landing, then versatility for VTOL operations is improved, but forward airspeed is limited due to proprotor aeroelastic instability
Solution Approach 1:
The rotor blade assembly incorporates dynamic locking mechanisms that enable the blade to transition between different degrees of freedom based on flight mode. In helicopter mode, the blade allows folding and pitching movements, while in airplane mode, the blade lock mechanism constrains these movements to maintain structural stability at high forward speeds, thus resolving the contradiction between versatility and speed capability
2Power
If proprotors operate in forward flight mode, then forward thrust is generated, but aeroelastic instability limits maximum airspeed
Solution Approach 1:
The blade lock mechanism changes the physical parameters of the rotor blade assembly by transitioning between unlocked and locked states. When locked, the blade's degrees of freedom are restricted, fundamentally changing its structural characteristics to resist aeroelastic instability at high forward speeds while maintaining the ability to generate forward thrust
3Reliability
If blade lock mechanism is implemented to disable folding and pitching degrees of freedom, then aeroelastic stability is improved, but device complexity increases
Solution Approach 1:
The blade lock mechanism is designed to be self-actuating through the existing gimballing and folding linkages of the rotor blade assembly. The mechanism utilizes the natural movements and forces present in the system during mode transitions to automatically engage or disengage the locking action, reducing the need for additional complex actuation systems while maintaining aeroelastic stability
Data Source
AI summary
An exemplary blade lock for a tiltrotor aircraft to enable and disable a folding degree of freedom and a pitching degree of freedom of a rotor blade assembly includes a link pivotally connected to a lever and a bellcrank, where the link is in a center position when the lever is in a locked position disabling the folding degree of freedom and the lever is secured in the locked position when the link is positioned in an over-center position.