Stowed Blade Active Restraint 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, which restricts their high-speed cruising capabilities.
Innovation Solution
A clamp system with opposing pads and a rotary actuator is used to securely fold and stow proprotor blades during non-rotary flight modes, reducing drag and stabilizing the aircraft, allowing for higher forward airspeeds by transitioning from rotary to non-rotary flight modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If proprotors are used for vertical thrust during takeoff and landing, then vertical takeoff and landing capabilities are achieved, but forward airspeed is limited due to proprotor aeroelastic instability
Solution Approach 1:
The proprotor blades are designed to be dynamically reconfigurable, transitioning from a horizontal plane of rotation during vertical flight to a vertical plane of rotation during forward flight. This dynamic reconfiguration allows the same blade structure to serve dual purposes, enabling the aircraft to overcome the speed limitation imposed by proprotor aeroelastic instability in forward flight while maintaining vertical flight capabilities
2Power
If proprotors are operated in forward flight mode, then forward thrust is provided, but aeroelastic instability limits maximum airspeed
Solution Approach 1:
The system dynamically changes the plane of rotation of the proprotors from horizontal to vertical based on flight mode. In forward flight, the vertical plane of rotation eliminates the aeroelastic instability that plagues horizontal rotation at high speeds, while still providing the necessary forward thrust through the propeller action of the blades
Solution Approach 2:
The invention changes the operational parameters of the proprotor system by rotating the entire proprotor assembly 90 degrees. This parameter change transforms the system from a configuration susceptible to aeroelastic instability to one that is stable at high forward speeds, while maintaining the ability to generate required thrust
3Force
If proprotor blades are extended for rotary flight, then vertical lift is generated, but drag increases during non-rotary flight
Solution Approach 1:
The proprotor blades are designed to dynamically reconfigure their orientation based on flight mode. During non-rotary flight, the blades rotate to a vertical plane alignment that minimizes their cross-sectional area presented to the oncoming airflow, thereby reducing aerodynamic drag while maintaining the structural capability to generate vertical lift when needed
4Reliability
If a clamp system is added to secure proprotor blades, then blade stability is improved, but device complexity increases
Solution Approach 1:
The clamp system is designed to automatically engage and secure the proprotor blades in their stowed position without requiring manual intervention. The system uses the existing motion of the pylon and blade folding mechanism to trigger automatic clamping, thereby providing enhanced blade stability while minimizing the added complexity through self-actuating design
Data Source
AI summary
An exemplary clamp system for securing a proprotor blade in a stowed position includes a clamp having a pair of opposing pads operable between an open position to receive a portion of a proprotor blade between the pair of opposing pads and a closed position to grip the portion of the proprotor blade with the pair of opposing pads and a rotary actuator in connection with the clamp to operate the clamp between the open and the closed position.