Patent Description:
<CIT>, <CIT> and <CIT> are prior art in this field.

Constant speed propellers are controlled by varying blade angles to maintain the speed of the propeller at a reference speed. In order to do so, the propeller blade angle is increased with increasing engine power and speed and decreased with decreasing engine power and speed. Varying the blade angle is achieved by either adding or removing oil in the propeller dome.

A malfunction of the propeller, and particularly operation of the propeller at fixed pitch, would prevent the propeller speed for being appropriately controlled, which would in turn create a risk to aircraft safety. There is therefore a need for systems and methods for detecting fixed pitch operation of a variable pitch propeller.

In one aspect, there is provided a method for detecting fixed pitch operation of a variable pitch propeller of an engine in accordance with claim <NUM>.

In an embodiment, the command signal is output comprising instructions for causing oil to be exchanged between a blade angle actuator of the propeller and a source of fluid to control the blade angle of the propeller for maintaining the rotational speed of the propeller at the reference speed.

In an embodiment according to any of the previous embodiments, the command signal is output comprising instructions for causing adjustment of a governing current that controls actuation of a valve operable to selectively fluidly connect the blade angle actuator with the source of fluid.

In an embodiment according to any of the previous embodiments, the actual value of at least one of the rotational speed and the blade angle of the propeller is obtained from one or more measurements acquired by one or more sensors coupled to the propeller.

In an embodiment according to any of the previous embodiments, the command signal is output to increase the rotational speed of the propeller, and assessing whether the change in the at least one of the rotational speed and the blade angle of the propeller has occurred comprises assessing whether the blade angle of the propeller has decreased in response to the command signal.

In an embodiment according to any of the previous embodiments, the command signal is output to decrease the rotational speed of the propeller, and assessing whether the change in the at least one of the rotational speed and the blade angle of the propeller has occurred comprises assessing whether the blade angle of the propeller has increased in response to the command signal.

In an embodiment according to any of the previous embodiments, the command signal is output comprising instructions for causing the governing current to be increased, and assessing whether the change in the at least one of the rotational speed and the blade angle of the propeller has occurred comprises assessing whether the rotational speed of the propeller has increased in response to the command signal.

In an embodiment according to any of the previous embodiments, the command signal is output comprising instructions for causing the governing current to be decreased, and assessing whether the change in the at least one of the rotational speed and the blade angle of the propeller has occurred comprises assessing whether the rotational speed of the propeller has decreased in response to the command signal.

In an embodiment according to any of the previous embodiments, the method further comprises determining a period of time for which the change in the at least one of the rotational speed and the blade angle of the propeller has not occurred, comparing the period of time to a pre-determined duration, and detecting operation of the propeller at fixed pitch responsive to determining that the period of time exceeds the pre-determined duration.

In an embodiment according to any of the previous embodiments, operation of the propeller at fixed pitch is detected responsive to determining that the change has not occurred on either of a first controller channel and a second controller channel.

In an embodiment according to any of the previous embodiments, outputting the alert comprises generating a warning message indicative of operation of the propeller at fixed pitch and outputting the warning message for cockpit annunciation.

In another aspect, there is provided a system for detecting fixed pitch operation of a variable pitch propeller of an engine in accordance with claim <NUM>.

In an embodiment, the program code is executable by the processing unit for outputting the command signal comprising instructions for causing oil to be exchanged between a blade angle actuator of the propeller and a source of fluid to control the blade angle of the propeller for maintaining the rotational speed of the propeller at the reference speed.

In an embodiment according to any of the previous embodiments, the program code is executable by the processing unit for outputting the command signal comprising instructions for causing adjustment of a governing current that controls actuation of a valve operable to selectively fluidly connect the blade angle actuator with the source of fluid.

In an embodiment according to any of the previous embodiments, the program code is executable by the processing unit for one of outputting the command signal comprising instructions to increase the rotational speed of the propeller, and assessing whether the blade angle of the propeller has decreased in response to the command signal, and outputting the command signal comprising instructions to decrease the rotational speed of the propeller, and assessing whether the blade angle of the propeller has increased in response to the command signal.

In an embodiment according to any of the previous embodiments, the program code is executable by the processing unit for one of outputting the command signal comprising instructions for causing the governing current to be increased, and assessing whether the rotational speed of the propeller has increased in response to the command signal, and outputting the command signal comprising instructions for causing the governing current to be decreased, and assessing whether the rotational speed of the propeller has decreased in response to the command signal.

In an embodiment according to any of the previous embodiments, the program code is executable by the processing unit for determining a period of time for which the change in the at least one of the rotational speed and the blade angle of the propeller has not occurred, comparing the period of time to a pre-determined duration, and detecting operation of the propeller at fixed pitch responsive to determining that the period of time exceeds the pre-determined duration.

In an embodiment according to any of the previous embodiments, the program code is executable by the processing unit for outputting the command signal comprising instructions for detecting operation of the propeller at fixed pitch responsive to determining that the change has not occurred on either of a first controller channel and a second controller channel.

In an embodiment according to any of the previous embodiments, the program code is executable by the processing unit for outputting the command signal comprising instructions for outputting the alert comprising generating a warning message indicative of operation of the propeller at fixed pitch and outputting the warning message for cockpit annunciation.

Features of the systems, devices, and methods described herein may be used in various combinations, in accordance with the embodiments described herein.

There is described herein systems and methods for detecting malfunction of a propeller for an aircraft, and more specifically for detecting fixed pitch operation of a variable pitch propeller. The aircraft is equipped with at least one engine, such as the exemplary engine <NUM> depicted in <FIG>. In one embodiment, the engine <NUM> is a gas turbine engine of a type typically provided for use in subsonic flight. In this embodiment, the engine <NUM> comprises an inlet <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases.

The turbine section <NUM> comprises a compressor turbine <NUM>, which drives the compressor assembly and accessories, and at least one power or free turbine <NUM>, which is independent from the compressor turbine <NUM> and is coupled with a reduction gearbox (RGB) <NUM>. The power turbine <NUM> rotatingly drives a rotor shaft (also referred to herein as a propeller shaft or an output shaft) <NUM> about a propeller shaft axis 'A' through the RGB <NUM>. Hot gases may then be evacuated through exhaust stubs <NUM>. The gas generator of the engine <NUM> comprises the compressor section <NUM>, the combustor <NUM>, and the turbine section <NUM>.

A rotor, in the form of a propeller <NUM> through which ambient air is propelled, is hosted in a propeller hub <NUM>. The rotor may, for example, comprise the propeller <NUM> of a fixed-wing aircraft, or a main (or tail) rotor of a rotary-wing aircraft such as a helicopter. The propeller <NUM> may comprise a plurality of circumferentially-arranged blades <NUM> connected to the hub <NUM> by any suitable means and extending radially therefrom. The blades <NUM> are also each rotatable about their own radial axes through a plurality of blade angles, which can be changed to achieve modes of operation, such as feather, full reverse, and forward thrust.

The propeller <NUM> converts rotary motion from the engine <NUM> to provide propulsive force to the aircraft (also referred to herein as thrust). In one embodiment, propeller <NUM> is a constant speed variable pitch propeller, meaning that the propeller <NUM> is designed to have its blade angle (also referred to as the "pitch angle" or "pitch") automatically changed to allow it to maintain a constant rotational speed (also referred to herein as a "reference speed"), regardless of the amount of engine torque being produced, the speed of the aircraft, or the altitude at which the aircraft is flying. As used herein, the term propeller blade angle refers to the angle between the propeller blade and the rotational plane of the propeller <NUM>. Other configurations for a turboprop engine may also apply.

Although the examples illustrated herein show a turboprop engine, it will be understood that the methods and systems described herein may be applied to other propeller-based engines, such as piston engines, electrical engines, and the like. It should also be understood that the engine <NUM> may be any suitable aircraft propulsion system, and may include in some embodiments an all-electric propulsion system or a hybrid-electric propulsion system having a propeller driven in a hybrid architecture (series, parallel, or series/parallel) or turboelectric architecture (turboelectric or partial turboelectric). In addition, it will be understood that the engine <NUM> may be found in aircraft as well as in other industrial applications, including, but not limited to, wind power turbines and ship propulsion and electric power generators.

Referring to <FIG> in addition to <FIG>, there is illustrated an example embodiment of a propeller control assembly <NUM>. A controller <NUM> receives, from one or more sensors <NUM> coupled to the engine <NUM> and/or propeller <NUM>, one or more input signals. The input signal(s) comprise measurements of one or more parameters for use in controlling the engine <NUM> and/or propeller <NUM>. As will be discussed further below, based on the received input signal(s), the controller <NUM> regulates, via a Propeller Control Unit (PCU) <NUM>, the flow of fluid (e.g., oil) to the propeller <NUM> in accordance with a reference rotational speed to which the propeller <NUM> is to be set (or equivalently in accordance with a pre-determined propeller blade angle threshold). In other words, the flow of fluid is regulated to maintain the propeller <NUM> at the reference speed (or to prevent the propeller <NUM> from operating at a blade angle exceeding the blade angle threshold). The reference speed (and/or blade angle threshold) is pre-determined and may be obtained by any suitable means, e.g. retrieved from a database, a memory, or other storage medium to which the controller <NUM> may be communicatively coupled. The value of the reference speed (and/or blade angle threshold) may depend on engine configuration and is illustratively set to protect the engine <NUM> from overspeeding.

The sensor(s) <NUM> may comprise one or more speed sensors configured to acquire measurement(s) of the actual (or current) rotational speed (Np) of the propeller <NUM>. The sensor(s) <NUM> may also comprise one or more accelerometers configured to acquire measurement(s) of the actual (or current) acceleration of the propeller <NUM>. The speed and/or acceleration measurement(s) acquired by the sensor(s) <NUM> are then provided to the controller <NUM>. It should however be understood that, in some embodiments, rather than being directly received at the controller <NUM> from the sensor(s) <NUM>, the propeller speed may be calculated based on one or more other engine and/or aircraft parameters measured using the sensor(s) <NUM>.

The sensor(s) <NUM> are also configured to measure the actual blade angle of the propeller <NUM> and to provide this measurement to the controller <NUM>. In one embodiment, the sensor(s) <NUM> comprise one or more sensors configured to magnetically measure the passing of position markers provided on a feedback device (also referred to as a "beta ring") operatively coupled to the propeller <NUM>. Measurement of the markers' position in turn provides, based on the markers' physical geometry, an indication of the position of the feedback device and accordingly an indication of the propeller blade angle. It should be understood that, in some embodiments, a single sensor <NUM> may be used to obtain the propeller blade angle measurements and the propeller speed measurements. Indeed, the same sensor signal may be used to determine the propeller speed and the position of the feedback device, which in turn indicates the propeller blade angle.

When the propeller's actual speed deviates from the reference speed (as determined by the controller <NUM> based on the input signal(s) received from the sensor(s) <NUM>), the controller <NUM> responds with a change in blade angle and commands the PCU <NUM> to direct fluid under pressure to the propeller <NUM> or to release (i.e. remove) fluid from the propeller <NUM>. The change in fluid volume going to the propeller <NUM> causes a change in propeller blade angle, which in turn affects the rotational speed of the propeller <NUM>. Indeed, as known to those skilled in the art, rotational speed of the propeller <NUM> is set via an angle of the blades <NUM>. Fining the blade angle results in a propeller speed increase and coarsing the blade angle results in a propeller speed decrease.

More specifically, in one embodiment, the controller <NUM> transmits a signal or command (also referred to herein as a "PCU command") to the PCU <NUM>, which in turn responds by regulating fluid flow to and from the propeller <NUM> accordingly. The PCU <NUM> illustratively regulates fluid flow to and from the propeller <NUM> via an actuator (also referred to as a "pitch angle actuator" or a "blade angle actuator") <NUM>, which is controlled by the controller <NUM> via the PCU command. The fluid illustratively flows from a fluid source (e.g., a source of oil) provided on the aircraft (e.g. from the engine oil system or from an oil pump of the PCU <NUM>). The actuator <NUM> can be actuated between a closed position and an open position to selectively allow or prevent fluid flow (i.e. supply or drain fluid) to and from the propeller <NUM>. In one embodiment, the actuator <NUM> is an Electrohydraulic Servo Valve (EHSV) and the controller <NUM> is configured to output the PCU command that determines a governing current of the EHSV. The governing current determines the opening of the EHSV for controlling the flow of fluid from the fluid source to the propeller <NUM>. In one embodiment, a positive governing current commands oil supply and a negative governing current commands oil drain. In some embodiments, the controller <NUM> may be configured to set minimum and maximum governing currents for the EHSV, as well as absolute rates of change of the governing current. While the actuator <NUM> is described herein with reference to an EHSV, it should however be understood that the PCU <NUM> may include any suitable component, and any suitable arrangement of components, for regulating fluid flow to and from the propeller <NUM>.

Still referring to <FIG>, the controller <NUM> is configured to detect a malfunction of the propeller <NUM> on the basis of the PCU command and of the input signal(s) received from the sensor(s) <NUM>. In particular, the controller <NUM> is configured to detect that the propeller <NUM> is operating at a fixed pitch (instead of being free in movement) for maintaining the propeller at the reference speed, a condition referred to herein as the propeller being "jammed" in its axial movement. Such a propeller failure condition (resulting in the variable pitch propeller system operating at fixed pitch) can be a result of a failure of the overall propeller system, as well as a mechanical failure of the actuator <NUM> (i.e. seizure at one position), preventing the PCU command from attaining the requested propeller transition due to inability to modulate the mechanical system of the actuator <NUM>. It is proposed herein to detect errors in reading the propeller speed and/or blade angle, as well as to detect errors in the PCU command (e.g., errors in terms of the commanded governing current and in terms of the feedback related to the actuator <NUM>.

For this purpose, the controller <NUM> monitors the input signal(s) received from the sensor(s) <NUM> and assesses whether an expected response from the propeller <NUM> (in terms of blade angle and/or rotational speed) has occurred in response to the PCU command (e.g., in response to the change in EHSV current commanded by the controller <NUM>). A lack of change in propeller blade angle and/or propeller rotational speed in response to the PCU command provides an indication of the propeller <NUM> being jammed.

In some embodiments, the propeller blade angle may be monitored (e.g., by the sensor(s) <NUM>) over the full range of possible blade angles. If this is the case, the propeller jammed condition may be detected based on the propeller blade angle only, by assessing whether a change (i.e. increase or decrease) in propeller blade angle has occurred in response to the PCU command. In embodiments where the propeller blade angle can only be monitored in a specific range, the propeller jammed condition may be detected based on the propeller speed, by assessing whether an expected change (i.e. increase or decrease) in propeller speed has occurred in response to the PCU command. Alternatively, the propeller jammed condition may be detected based on both the propeller blade angle and the propeller speed, with the propeller blade angle being used when the propeller is operating within the specific blade angle range and the propeller speed being used when the propeller is operating outside of the specific blade angle range (i.e. when the blade angle cannot be monitored).

As will be discussed further below, upon detection of the propeller <NUM> being jammed, the controller <NUM> is configured to generate and output an alert, such as a warning indication or message, for annunciation in the aircraft cockpit in order to inform the crew of the propeller malfunction (i.e. of operation with the fixed-pitch propeller <NUM>). The pilot and/or crew may in turn take over control of the aircraft and take appropriate action by applying a specific procedure that is required to protect the aircraft from unsafe flight conditions that can be induced with the propeller <NUM> being jammed. In particular, the crew may modulate the power of the engine <NUM> in a manner that will not expose the propeller <NUM> to the risk of overspeed. In addition, knowledge of the propeller <NUM> being jammed would make the crew aware of the risk arising from shutting down the engine <NUM>, which would result in an inability to feather the propeller <NUM> following a complete loss of power of the engine <NUM>. Moreover, the crew may optimize the availability of the engine power and propeller thrust and accommodation for operation with a fixed pitch propeller may be defined between the airframer, engine manufacturer, and propeller manufacturer.

Referring to <FIG>, there is illustrated an example embodiment of the controller <NUM>. The controller <NUM> may be an Engine & Propeller Electronic Control (EPEC) system, an engine controller, such as a Full Authority Digital Engine Control (FADEC), an Engine Electronic Control (EEC), an Engine Control Unit (ECU), or the like. In the embodiment illustrated in <FIG>, the controller <NUM> comprises an input module <NUM>, a PCU controller module <NUM>, a signal monitoring module <NUM>, a propeller malfunction detection module <NUM>, and an output module <NUM>.

As previously noted and as will be discussed further below, the controller <NUM> is configured to detect a condition of the propeller (reference <NUM> in <FIG>) being jammed by monitoring the change in propeller speed and/or propeller blade angle in relation to the change in the PCU command. For this purpose, the input module <NUM> receives one or more input signals comprising an actual value of the propeller speed and/or propeller blade angle as obtained from measurements acquired by the sensor(s) (reference <NUM> in <FIG>) coupled to the propeller <NUM>. These input signal(s) are then provided to the PCU controller module <NUM> for processing.

The PCU controller module <NUM> is further configured to generate and output the PCU command that would allow to achieve an expected propeller position or speed, based on the sensor signal(s) received from the input module <NUM>. In particular, the PCU controller module <NUM> estimates the PCU actuator command (e.g., the EHSV governing current) that is required to position the propeller blades (reference <NUM> in <FIG>) at a different angle in order to maintain the propeller <NUM> at the reference speed (or equivalently the command required to prevent the propeller <NUM> from exceeding specific thresholds of the propeller blade angle). The PCU controller module <NUM> may then send the PCU command in the output module <NUM> for transmission to the PCU actuator command (reference <NUM> in <FIG>), for use in adjusting the propeller speed and/or angle.

The sensor signal(s) and the PCU command may further be provided to the signal monitoring module <NUM>, which is configured to confirm that the received signals are healthy. In particular, the signal monitoring module <NUM> is configured to assess whether the sensor signal(s) are within range and failure free. This may be achieved by the signal monitoring module <NUM> verifying the speed and/or blade angle reading from multiple sources. For example, the propeller system may comprise a dual channel electronic control system, comprised of control system configured to implement a control system for the propeller and a protection system configured to implement a protection function for the propeller. In this case, the protection system would receive the propeller speed and blade angle reading from a dedicated sensor having dual measuring coils (one for each of two protection channels) and the control system would receive the propeller speed and blade angle reading from a dedicated sensor having dual measuring coils (one for each of two control channels). Redundancy in speed and blade angle reading by the two channels of the protection system and the two channels of the control system allows for accommodation to the value closer to the reading from the two channels of the protection system in the event of a mismatch between the propeller speed and/or blade angle reading from the two channels of the control system.

In one embodiment, reliance on the reading from the protection system as a backup for propeller speed and/or blade angle could be enhanced by the control system monitoring the existence of a deviation in reading between both protection channels as well as by the control system monitoring for deviations between the reading of the propeller speed and/or blade angle of both protection channels and both control channels. As a result of this monitoring, appropriate fault accommodation or fault indication could be perform to allow for correction of any failure conditions as soon as possible after detection thereof.

The signal monitoring module <NUM> may consider a pre-determined range of the propeller speed and/or blade angle as the propeller's operating range. As such, any propeller speed and/or blade angle reading that is out of the expected operating range would be considered by the signal monitoring module <NUM> as a faulty reading.

In addition, the signal monitoring module <NUM> may also consider the rate of change of the propeller speed and/or blade angle in relation to predefined criteria (or thresholds) that may be mechanically achievable by the propeller system. In other words, any propeller speed and/or blade angle reading that is beyond the expected rate of range in propeller speed and/or blade angle would be considered by the signal monitoring module <NUM> as indicative of faulty readings.

The signal monitoring module <NUM> may also compare the propeller speed reading to an expected propeller speed, which may be estimated based on the measurement of the speed of the engine power turbine (reference <NUM> in <FIG>), which, as described herein above, drives the propeller shaft (reference <NUM> in <FIG>) through the RGB (reference <NUM> in <FIG>) or based on other engine operating parameters. Any propeller speed reading that deviates from the estimated propeller speed would be considered by the signal monitoring module <NUM> as a faulty reading.

The signal monitoring module <NUM> may also detect a lost or corrupted propeller speed and/blade angle signal. In particular, a propeller speed and/or angle reading (i.e. signal) that is lost or deviates in a pre-defined manner (e.g., oscillating or intermittent) would be considered by the signal monitoring module <NUM> as a faulty reading.

The signal monitoring module <NUM> considers the propeller speed and/or blade angle reading as healthy if the readings are not detected to be faulty in any of the pre-defined fault detection conditions described herein above.

The signal monitoring module <NUM> is further configured to confirm that the PCU command (i.e. a current request to the actuator, reference <NUM> in <FIG>) is healthy (i.e. failure-free). In one embodiment, the signal monitoring module <NUM> (or alternatively a separate PCU actuator controller) uses feedback from the actuator <NUM> to control the governing current, and for fault detection of the PCU <NUM> and/or of the actuator <NUM>. The signal monitoring module <NUM> performs continuous monitoring of the propeller speed and/or blade angle as well as of the PCU command. The monitoring of the PCU command may be performed after the PCU command is provided from the PCU controller module <NUM>, thus allowing for monitoring of the feedback in relation to the provided command. In particular, the signal monitoring module <NUM> may be configured to compare the commanded governing current (e.g. by monitoring of the feedback current from the actuator <NUM> and/or PCU <NUM>) to the maximum governing current. If the commanded governing current exceeds the maximum governing current, overcurrent is detected and the signal monitoring module <NUM> determines that the PCU command is faulty.

The signal monitoring module <NUM> may be configured to detect a lost, erroneous or corrupted commanded governing current (e.g., lost feedback, intermittent feedback reading, or mismatch between command and feedback). A PCU Command and/or feedback that is lost or deviates in pre-defined manner (e.g. PCU feedback begins to be intermittent, or begins to deviate from the PCU command) would be considered by the signal monitoring module <NUM> (or alternatively a separate PCU actuator controller) as faulty.

The signal monitoring module <NUM> may also be configured to detect any shift from a so-called "zero current setting", which corresponds to a pre-determined value for the governing current that does not change the position of the actuator <NUM> (e.g., of the EHSV), and which is therefore expected to cause no change in the propeller speed or blade angle. The signal monitoring module <NUM>, upon detecting a change in propeller speed and/or blade angle at the "zero current setting" would consider the PCU Command as faulty.

The signal monitoring module <NUM> would consider the PCU Command and PCU Feedback as healthy if no criteria are met for any of the pre-defined fault detection conditions described herein above.

In one embodiment, the controller <NUM> is a dual-channel controller. In this embodiment, when a faulty signal (i.e., a faulty sensor signal and/or a faulty PCU command) is detected using one channel (i.e. on an active channel) of the controller <NUM>, the controller <NUM>, and particularly the signal monitoring module <NUM> switches to the other channel (i.e. a standby channel) and obtains failure free sensor signal(s) and/or PCU command from this other channel. The signal monitoring module <NUM> then provides the failure-free sensor signals to the malfunction detection module <NUM> for use by the malfunction detection module <NUM> in detecting whether the propeller <NUM> is jammed.

Based on the failure-free signals it receives, the malfunction detection module <NUM> compares the actual value of the propeller speed and/or propeller blade angle to the actual value obtained in a previous clock cycle. If an expected change in the propeller speed and/or blade angle is not detected, the malfunction detection module <NUM> concludes to a malfunction of the propeller <NUM>, i.e. that the propeller <NUM> is operating at fixed pitch.

In particular, when the propeller blade angle is used to detect propeller malfunction, if acceleration of the propeller <NUM> (i.e. an increase in the propeller speed) is to be achieved and an expected propeller transition towards lower blade angles (i.e. a decrease in the propeller blade angle) does not occur in response to the PCU command and the propeller blade angle remains unchanged, the malfunction detection module <NUM> detects that the propeller <NUM> is jammed. Conversely, when deceleration of the propeller <NUM> (i.e. a decrease in the propeller speed) is to be achieved, the malfunction detection module <NUM> detects that the propeller <NUM> is jammed when an expected propeller transition towards higher blade angles (i.e. an increase in the propeller blade angle) does not occur in response to the PCU command and the propeller blade angle remains unchanged. When the propeller speed is used to detect propeller malfunction, if the PCU command comprises instructions to increase the governing current of the actuator <NUM> in order to achieve an acceleration of the propeller <NUM>, the malfunction detection module <NUM> detects that the propeller <NUM> is jammed when no expected change in the propeller speed with no added engine power is detected in response to the PCU command. Conversely, when the PCU command comprises instructions to decrease the governing current of the actuator <NUM> in order to achieve a deceleration of the propeller <NUM>, the malfunction detection module <NUM> detects that the propeller <NUM> is jammed when no expected change in the propeller speed with no reduced engine power is detected in response to the PCU command.

In one embodiment, when the malfunction detection module <NUM> detects that there has been no reported change in propeller blade angle and/or propeller speed, the malfunction detection module <NUM> assesses whether the condition has been persisting for a period of time greater than a pre-determined duration, referred to herein as a pre-defined "latch time". The latch time may vary depending on engine configuration and may be obtained by any suitable means, e.g. retrieved from a database, a memory, or other storage medium to which the controller <NUM> may be communicatively coupled. If it is determined that the condition has persisted for a period of time that exceeds the latch time, the malfunction detection module <NUM> confirms that the propeller jammed condition is indeed present.

As discussed herein above, in one embodiment where the controller <NUM> is a dual-channel controller, the malfunction detection module <NUM> may be configured to confirm the detection criteria mentioned above on both controller channels. This may allow for improved robustness and for protection against incorrect or misleading detection of the propeller <NUM> being jammed. In other words, the malfunction detection module <NUM> may be configured to request confirmation of the propeller malfunction detection conditions on both the active channel and the standby channel.

Upon detection of the propeller <NUM> being jammed, the output module <NUM> generates a warning indication or message indicative of operation with propeller jammed and the warning indication is provided to an aircraft output (reference <NUM> in <FIG>) for cockpit annunciation. Cockpit annunciation may be performed using any suitable means, such as by visual rendering of the warning indication on display(s) provided in the cockpit of the aircraft and/or audio output using any suitable audio output device provided in the aircraft. In one embodiment, the aircraft output <NUM> is an Aeronautical Radio Inc. (ARINC) output that uses the ARINC <NUM> data transfer standard for aircraft avionics to output the warning indication. Other data standards may also be used, such as ARINC <NUM>, ARINC <NUM>, and MIL-STD-<NUM>.

<FIG> is an example embodiment of a computing device <NUM> for implementing the controller <NUM> described above with reference to <FIG>. The processing unit <NUM> may comprise any suitable devices configured to cause a series of steps to be performed such that instructions <NUM>, when executed by the computing device <NUM> or other programmable apparatus, may cause the functions/acts/steps specified in the method described herein to be executed. The processing unit <NUM> may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a CPU, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.

The memory <NUM> may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

Referring now to <FIG>, a method <NUM> for detecting fixed pitch operation of a variable pitch propeller will now be described in accordance with one embodiment. The method <NUM> is illustratively performed by a controller (such as the controller <NUM> in <FIG>). The method <NUM> comprises, at step <NUM>, outputting a PCU command. As described above, in one embodiment, the controller <NUM> generates the PCU command required to vary the position of the propeller blades in order to maintain the propeller at the reference speed and outputs the PCU command to the PCU (reference <NUM> in <FIG>). In one embodiment, as discussed herein above, the controller calculates the oil flow required to obtain the desired propeller reference speed and generates the PCU command indicative of the governing current needed to achieve the required oil flow. The method <NUM> further comprises, at step <NUM>, obtaining input signal(s) indicative of an actual value of the blade angle and/or the rotational speed of a propeller. The input signal(s) may be received from one or more sensor(s) coupled to the engine and/or the propeller, in the manner described herein above with reference to <FIG> and <FIG>.

The next step <NUM> comprises a determination as to whether the one or more signals obtained at steps <NUM> and <NUM> are healthy, in the manner described herein with reference to <FIG> and <FIG>. If it is determined at step <NUM> that the one or more signals are not healthy, the method <NUM> ends at step <NUM>. Otherwise, the method <NUM> proceeds with performing a propeller jammed detection logic at step <NUM>, based on the failure-free signal(s). When it is determined that the propeller is functioning properly, the method may end at step <NUM>. Otherwise, an alert indicating that the propeller is malfunctioning (i.e. operating at fixed pitch or jammed) is output at step <NUM> for cockpit annunciation.

Referring now to <FIG> in addition to <FIG>, the step <NUM> of performing a propeller jammed detection logic comprises assessing, at step <NUM>, whether an expected change in the blade angle and/or rotational speed of the propeller has occurred in response to the PCU command. This assessment is illustratively performed on the basis of the input signal(s) received at step <NUM> (i.e. on the basis of the actual value of the blade angle and/or rotational speed of a propeller), in the manner described herein with reference to <FIG> and <FIG>. If it is determined at step <NUM> that the expected change has occurred, no malfunction of the propeller (i.e. no propeller jammed fault condition) is detected (step <NUM>) and the method <NUM> may end (step <NUM>). Otherwise, if it is determined at step <NUM> that the expected change in the blade angle and/or rotational speed of the propeller has not occurred in response to the PCU command, the next step <NUM> is to assess whether this condition has persisted for a period of time longer than (i.e. exceeding) a pre-defined latch time. If this is not the case, the method <NUM> ends (step <NUM>). Otherwise, if it is determined at step <NUM> that the lack of change in the blade angle and/or rotational speed of the propeller has occurred for a time period exceeding the latch time, a propeller jammed condition is detected at step <NUM>. In embodiments where a dual-channel controller is used to perform the propeller malfunction detection logic, step <NUM> entails detecting the propeller jammed condition on the first (i.e. active) channel. The next step <NUM> may then be to obtain a confirmation of the propeller jammed condition from the second (i.e. standby) channel. After the propeller jammed condition has been detected (step <NUM>) and optionally confirmed on both channels (step <NUM>), an alert indicative of this condition is then generated at step <NUM> for output to the cockpit in the manner described herein above.

Claim 1:
A method for detecting fixed pitch operation of a variable pitch propeller (<NUM>) of an engine (<NUM>), the method comprising:
outputting a command signal for maintaining a rotational speed of the propeller (<NUM>) at a reference speed;
obtaining an actual value of at least one of the rotational speed and a blade angle of the propeller (<NUM>);
assessing, from the actual value, whether an expected change in the at least one of the rotational speed and the blade angle of the propeller (<NUM>) has occurred in response to the command signal; and
responsive to determining that the expected change in the at least one of the rotational speed and the blade angle of the propeller (<NUM>) has not occurred in response to the command signal, detecting operation of the propeller (<NUM>) at fixed pitch and outputting an alert accordingly.