Abstract: An improved variable cycle turbofan-ramjet engine is disclosed. The engine includes a split fan assembly, a bypass channel surrounding a core engine and a mode selector valve for selectively bypassing air around an aft fan and the core engine. In a first, single bypass mode of operation, the mode selector valve allows air to flow through both a forward fan and the aft fan, and a portion of which bypasses the core engine. In a second, double bypass mode of operation, the mode selector valve allows air from the forward fan to bypass the aft fan and a portion of the air from the forward fan to bypass the core engine. In a third, ramjet mode of operation, the mode selector vane bypasses air around the aft fan and the core engine and the core engine is shut down for ramjet operation. In the preferred embodiment, the forward fan is allowed to windmill and powers a fuel pump connected thereto for providing fuel to a ram burner of the engine for ramjet operation.

Abstract: The fan section of a gas turbine engine is divided into a front section and an aft section axially displaced downstream of the front fan section. A duct is provided for bypassing the inlet gas stream around a gas generator. The bypass duct has a first inlet disposed intermediate the front and aft fan sections and a second inlet disposed downstream of the aft fan section. In order to provide increased flexibility in modulating the engine bypass ratio, a diverter valve is provided downstream of the aft fan section to selectively distribute the airflow exhausted from the front fan section between the aft fan section and bypass duct and to selectively distribute the air exhausted from the aft fan section between the bypass duct and gas generator.

Abstract: One or more of the aft stages of the fan section of a gas turbine engine are rotated by the high pressure turbine of a gas generator and the remainder of the fan stages are rotated by a low pressure turbine downstream of the gas generator. This arrangement divides the fan work between the low and high pressure turbines to permit more efficient utilization of the total available turbine capacity, reduction in low pressure turbine workload, increased aft fan stage pressure ratio capability and greater flow and pressure ratio modulation potential for a split fan engine. The invention has a wide range of application for various turbofan configurations including separated and/or mixed flow turbofan engines with separated or close coupled fan sections.