Negative Hinge Offset Rotor Head for Helicopter
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Solution Overview
Problem
Conventional coaxial helicopters with flapping hinges are limited in top speed due to the pitching moment generated by the offset thrust vector and flapping hinge offset, which can be counterproductive to achieving higher speeds.
Innovation Solution
A negative hinge offset rotor head system is introduced, where the hinge attachment is configured such that the driveshaft is disposed between the hinge axis and the outer tip of each rotor blade, allowing each rotor blade to rotate orthogonally about a hinge axis, effectively canceling out the undesirable nose-up pitching moment and enhancing forward thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a positive flapping hinge offset is used, then pitch and roll control is improved, but top speed is limited due to nose-up pitching moment
Solution Approach 1:
The patent inverts the conventional positive hinge offset configuration by implementing a negative hinge offset, where the hinge axis is positioned on the opposite side of the rotor blade relative to the driveshaft axis. This inversion reverses the direction of the pitching moment generated by the offset, transforming the harmful nose-up moment into a beneficial or neutral effect, thereby enabling higher top speeds while maintaining control effectiveness.
Solution Approach 2:
The patent changes the sign parameter of the hinge offset from positive to negative, fundamentally altering the aerodynamic characteristics of the rotor system. This parameter change modifies the pitching moment direction and magnitude, allowing the system to achieve higher speeds by eliminating the speed-limiting nose-up moment while preserving pitch and roll control capabilities through adjusted hinge positioning.
2Speed
If the driveshaft is positioned between the hinge axis and rotor blade tip, then the nose-up pitching moment is canceled, but the structural configuration becomes more complex
Solution Approach 1:
The patent employs asymmetric positioning of the driveshaft relative to the hinge axis and rotor blade tip, creating an unbalanced configuration that generates a counteracting pitching moment. This asymmetric arrangement places the driveshaft between the hinge axis and blade tip, producing a moment that cancels the nose-up pitching moment, thereby enabling improved forward thrust and speed performance.
Data Source
AI summary
A negative hinge offset rotor head for a coaxial helicopter, the rotor head having two or more flapping rotor blades having outer and inner tips, the inner tips rotatably attached to a hinge attachment rotated by a driveshaft where the driveshaft is positioned between the rotor blades and the rotor blades' respective hinge attachment.