In a gas turbine engine of the type having a high-pressure (HP) spool and a low-pressure (LP) spool, methods of increasing surge margin and compression efficiency at a given thrust are provided. One method increases compression efficiency and comprises transferring mechanical power from the HP spool to the LP spool to reduce a corrected speed of a HP compressor therein and raise a working line of a LP compressor therein. Another method increases surge margin and comprises transferring mechanical power from the LP spool to the HP spool to increase a corrected speed of a HP compressor therein and lower a working line of a LP compressor therein.

A variable bypass ratio turbofan engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine, the first electric machine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a fan driven by the LP spool and configured to produce a bypass flow for propulsion and a core flow for delivery to the LP compressor, wherein the ratio of the mass flow rates of the bypass flow and the core flow define a bypass ratio; an engine controller configured to, for a fixed thrust setting, control the degree of electrical power generated by one or both of the first electric machine and the second electric machine so as to vary a mass flow rate of the core flow and to thereby vary the bypass ratio of the engine.

A turbofan engine includes a fan section including a plurality of fan blades, a first spool including a first turbine section, a second spool including a second turbine section, a first electric machine, and a second electric machine. A gear system is coupled between the first spool, the second spool, the first electric machine, the second electric machine and the fan section for driving the fan section.

Aircraft, engine electronic controller systems, and methods for controlling thrust in a no dwell zone are provided. In one example, an aircraft includes a first engine that includes a first compressor fan rotating at a first speed and a second engine that includes a second compressor fan rotating at a second speed. First and second engine electronic controllers receive engine thrust commands and are in communication with the first and second engines, respectively. When the engine thrust commands correspond to an engine response within a no dwell zone, the first engine electronic controller directs the first engine to have the first speed at or below a compressor fan speed lower boundary and the second engine electronic controller directs the second engine to have the second speed at or above the compressor fan speed upper boundary to produce an overall average thrust within the no dwell zone.

At least a selected one of a first and second engine are connected to a drive train for driving an aircraft accessory. A gearbox is connected to a primer mover propulsor and an actuator operatively associated with the selected engine is moveable between a position in which the selected engine drivingly engages the gearbox for driving the propulsor and a position in which the selected engine disengages from the gearbox. A position signal, a status signal, and a request signal respectively indicative of a present position of the actuator, a governing state and present speed of each engine, and a request for movement of the actuator from the present position to the other position are received. If the selected engine's speed differs from a predetermined threshold, a control signal is output for causing the engine's speed to be adjusted towards the threshold. A control signal indicating that movement of the actuator is permitted is then output.

A braking system for the low pressure spool of a gas turbine engine includes a braking assembly connected to the low pressure spool and reversibly configurable between an actuated state and an unactuated state. The braking assembly in the unactuated state allows rotation of the low pressure spool without interference. The braking assembly in the actuated state applies a force opposing the rotation of the low pressure spool. A method of controlling the speed of rotation of a low pressure spool and a method of controlling the speed of rotation of low and high pressure spools are also discussed.

A system for keep out zone control includes a gas turbine engine and a controller operable to determine a closing threshold with respect to an upper limit and an opening threshold with respect to a lower limit of a movement range of an effector of the gas turbine engine based on an on-board model, where the upper limit and the lower limit define a keep out zone of a target parameter of the gas turbine engine. The controller determines a projected state of the target parameter absent a correction command to the effector, applies a closing correction to the effector based on determining that the projected state of the target parameter would result in being above the closing threshold, and applies an opening correction to the effector based on determining that the projected state of the target parameter would result in being below the opening threshold.

A turbine section for a gas turbine engine includes a variable reaction free wheel downstream of the first static vane structure and a turbine rotor downstream of the variable reaction free wheel. A method of generating thrust for a gas turbine engine, includes rotating a variable reaction free wheel located downstream of a combustor and upstream of a turbine rotor to augment a swirl of a core flow combustion gases.

Methods and systems for controlling an engine having a variable geometry mechanism are described. An output power of the engine is determined. A speed of the engine is determined. A temperature-independent position control signal for the variable geometry mechanism is generated based on a power-to-speed ratio, the power-to-speed ratio obtained by dividing the output power by the speed. The position control signal is output to a controller of the engine to control the variable geometry mechanism.

A method is provided of controlling a gas turbine having a shaft connecting a compressor to a turbine, as well as having a reheat system, and a gas turbine. The method includes the steps of: operating the engine using the reheat system to provide a mass flow rate of reheat fuel into a gas flow of the gas turbine engine downstream of an exit of the turbine; detecting a shaft break event in the shaft; and in response to this detection, maintaining the mass flow rate of the reheat fuel being provided into the gas flow downstream of the turbine exit, whereby the maintained mass flow rate of reheat fuel raises a back pressure downstream of the turbine and thereby reduces a rotational speed of the turbine.