Control system

A control system operable to provide a modified primary control parameter for an aircraft, the control system comprising:

• a primary control parameter leg configured to output a demand in a primary control parameter of the aircraft;
• a primary control parameter compensation leg configured to receive a detected change in absolute levels and/or spatial distributions of swirl angle and/or fan pressure at the primary control parameter relative to a reference and convert the detected change into a change to the primary control parameter;
• a processor adapted to:
• receive the demand in the primary control parameter output from the primary control parameter leg and the change to the primary control parameter output from the primary control parameter compensation leg;
• compare the demand in the primary control parameter output from the primary control parameter leg and the change to the primary control parameter output from the primary control parameter compensation leg;
• and
• generate a modified primary control parameter for the aircraft;
• an apparatus for estimating a parameter of a fluid flowing in a bypass duct, the apparatus comprising a plurality of instruments operable to measure one or more properties of the fluid flowing in the bypass duct, the plurality of instruments being disposed in the bypass duct and arranged within a common measurement plane;
• and
• a computer adapted to communicate with the plurality of instruments and to:
• receive measured values of the one or more properties of the fluid measured by the plurality of instruments;
• assign a stream tube to each instrument, wherein each stream tube represents a region of space in the common measurement plane within the bypass duct and each stream tube surrounds one of the plurality of instruments, wherein the stream tubes together correspond to the cross-sectional shape and area of the bypass duct in the common measurement plane;
• use the measured value(s) for each stream tube to calculate a derived value for each stream tube;
• and
• sum the derived values across all of the stream tubes.

A method of operating an aircraft comprising:

• providing a demand in a primary control parameter of the aircraft;
• receiving a detected change in absolute levels and/or spatial distributions of swirl angle and/or fan pressure at the primary control parameter relative to a reference wherein the detected change is obtained based on measurement information acquired from a plurality of instruments operable to measure one or more properties of a fluid flowing in a bypass duct, the plurality of instruments being disposed at one or more leading edges of outlet guide vanes which are spaced circumferentially around the bypass duct;
• converting the detected change into a change to the primary control parameter;
• comparing the demand in the primary control parameter and the change to the primary control parameter;
• and
• generating a modified primary control parameter for the aircraft.