Variable Fan Outlet Guide Vanes for Turbofan Engines

The patent applies variable geometry to the fan outlet guide vanes, allowing them to pivot between different angular positions. At take-off, the vanes are positioned to provide high solidity and loading for maximum fan pressure ratio. At high flight Mach numbers, the vanes pivot to an open position to prevent choking and maintain airflow to the ramburner, thus resolving the contradiction between high power at low speed and high productivity at high speed.

Instead of using a fixed high-solidity vane design that would permanently increase weight, the patent employs variable geometry where the vanes can adjust their angle. This allows the fan section to achieve high thrust when needed without permanently increasing weight, as the high-solidity configuration is only active during take-off operations.

The variable geometry design allows the fan outlet guide vanes to provide high aerodynamic loading during take-off when maximum thrust is required. During high Mach number operation, the vanes pivot to an open position that minimizes airflow interruption, thus resolving the contradiction between high force generation and harmful airflow disruption.