A method of estimating a parameter of a fluid flowing in a passage includes: having a plurality of instruments operable to measure one or more fluid properties flowing in the passage, the plurality of instruments being disposed in the passage and arranged within a common measurement plane; assigning a stream tube to each instrument, each stream tube represents a region of space in the common measurement plane within the passage and each stream tube surrounds one of the plurality of instruments, the stream tubes together correspond to the cross-sectional shape and area of the passage in the common measurement plane; measuring the one or more fluid properties using the instruments to obtain one or more measured values for each stream tube; using the measured value(s) for each stream tube to calculate a derived value for each stream tube; and summing the derived values across all of the stream tubes.

A propulsion system for an aircraft includes (1) an engine configured to generate a mass flow, (2) a nozzle having a pathway having a throat and a trailing edge, one of the throat and the trailing edge configured to enlarge and contract, (3) a heat source disposed in the nozzle, (4) a first pressure sensor to sense the static pressure of the mass flow at the nozzle exit, (5) a second pressure sensor to sense the ambient pressure proximate the aircraft, and a (6) controller. The controller is coupled with the first and second pressure sensors, the heat source, and the throat or the trailing edge (whichever is configured to enlarge and contract). The controller receives the static and ambient pressures and when there is a disparity, the controller controls at least one of the heat source, the throat, and the trailing edge in a manner that reduces the disparity.

A control system for a gas turbine engine, a method for controlling a gas turbine engine, and a gas turbine engine are disclosed. The control system may include a nozzle scheduler for determining an exhaust nozzle position goal based on a nozzle schedule of exhaust nozzle positions related to flight conditions. The control system may further include a control module for determining a control command for the gas turbine engine. The control command may include, at least, a fuel flow command and an exhaust nozzle position command and the control command may be based on, at least, the exhaust nozzle position goal and an estimated thrust value. The control system may further include an actuator for controlling the gas turbine engine based on the control command.

A control system for a gas turbine engine, a method for controlling a gas turbine engine, and a gas turbine engine are disclosed. The control system may include a nozzle scheduler for determining an exhaust nozzle position goal based on a nozzle schedule of exhaust nozzle positions related to flight conditions. The control system may further include a control module for determining a control command for the gas turbine engine. The control command may include, at least, a fuel flow command and an exhaust nozzle position command and the control command may be based on, at least, the exhaust nozzle position goal and an estimated thrust value. The control system may further include an actuator for controlling the gas turbine engine based on the control command.

Systems and methods for limiting power of a gas turbine engine for an aircraft are described herein. A blade angle of a propeller blade of the engine and a commanded power for the engine are obtained. A thrust transition direction is determined. The commanded power is compared to a selected threshold based on the blade angle and the thrust transition direction. Power to the engine is limited when the commanded power exceeds the selected threshold.

Systems and methods for limiting power of a gas turbine engine for an aircraft are described herein. A blade angle of a propeller blade of the engine and a commanded power for the engine are obtained. A thrust transition direction is determined. The commanded power is compared to a selected threshold based on the blade angle and the thrust transition direction. Power to the engine is limited when the commanded power exceeds the selected threshold.

In accordance with at least one aspect of this disclosure, a variable displacement pump system can include, a variable displacement pump disposed in a main line and configured to supply pressure to receive a low pressure fluid and to output a high pressure fluid. The main line can connect a hydraulic fluid source to a plurality of system actuators, where the variable displacement pump is disposed in the main line between the hydraulic fluid source and the plurality of system actuators to pressurize the hydraulic fluid.