Adjustable Rotor Hub Friction Brake for Pitch-Drop Control
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Solution Overview
Problem
Rotary wing aircraft rotor blades pitch due to the weight of deactivated actuators and their own weight, causing swashplates to settle outside the control volume, leading to vibrations and increased blade loads, especially during ground operations and high wind gusts, and traditional solutions like elastomeric bearings are heavy and inefficient.
Innovation Solution
A friction brake system using tension-torsion straps coupled with adjustable brake assemblies to resist rotor blade pitch when actuators are deactivated, engaging only when the rotor is not rotating, and disengaging with centrifugal force when rotating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If elastomeric bearings are used to resist pitch change of the rotor blade when deactivated, then the rotor blade pitch stability is improved, but the weight of the rotor system increases
Solution Approach 1:
The patent changes the mechanical parameter of torsional resistance by replacing elastomeric bearings with a friction brake system. The friction brake uses adjustable braking force to resist pitch change, providing sufficient stability without the excessive torsional resistance and weight of elastomeric bearings. The friction coefficient and normal force can be adjusted to achieve the desired pitch stability.
Solution Approach 2:
The patent substitutes the elastomeric bearing mechanical system with a friction brake system. Instead of relying on the elastic deformation and torsional resistance of elastomeric materials, the invention uses friction between brake pads and a drum to resist pitch change. This substitution reduces weight while maintaining pitch stability during ground operations.
2Stability of the object's composition
If ground support equipment is used to stop rotor blades from pitching under their own weight, then the pitch drop is prevented, but the device complexity and operational difficulty increase
Solution Approach 1:
The patent merges the pitch stabilization function into the rotor hub structure itself by integrating friction brake assemblies directly into the hub. This eliminates the need for separate ground support equipment and combines the braking function with the existing rotor structure, reducing overall system complexity.
Solution Approach 2:
The friction brake system is self-activating through the weight of the rotor blades themselves. The normal force on the brake pads is generated by the blade weight acting through the tension-torsion strap mechanism, eliminating the need for external power sources or additional support equipment to maintain pitch stability during ground operations.
3Stability of the object's composition
If the tension-torsion strap provides sufficient torsional stiffness to resist pitch drop, then the blade pitch stability is improved, but the control loads increase when the rotor is rotating
Solution Approach 1:
The patent creates a dynamic system where the friction brake assembly automatically engages and disengages based on rotor rotation state. During ground operations, the brake is engaged to resist pitch drop. When the rotor rotates, centrifugal force causes the brake to disengage, eliminating excessive control loads. This dynamic behavior allows the system to provide high torsional resistance when needed without penalizing control loads during flight.
Solution Approach 2:
The patent changes the friction coefficient parameter dynamically by using different brake pad materials or adjusting the normal force through the tension-torsion strap mechanism. This allows sufficient friction force to resist pitch drop during ground operations while reducing the friction force during rotation to minimize control loads, resolving the contradiction between stability and control effort.
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 maintains rotor blade position during ground operations, reducing vibrations and blade loads, while minimizing weight and maintaining efficient control loads during flight.
Implementation Method 1
a brake shoe configured to apply a force on the hub arm
Implementation Method 2
The rotor blade may be coupled to a hub arm of the rotor hub by a tension-torsion strap that provides the centripetal force to retain the rotor blades in position when the rotor is rotating
Implementation Method 3
The tension-torsion strap provides some torsional stiffness that resists the pitching of the rotor blade
Data Source
AI summary
A rotor system of a rotary wing aircraft includes a rotor hub including a hub arm, a rotor blade rotatably coupled to the hub arm about a longitudinal axis of the hub arm, and a first brake assembly. The first brake assembly includes a rod coupled to the rotor blade coupling and a brake shoe coupled to the rod. The brake shoe is configured to apply a force on the hub arm. An axial position of the rod is adjustable to vary the force of the brake shoe on the hub arm.