Patent Description:
Modern large commuter turbofan-powered aircraft incorporate a high level of automation in regards to flight management. This includes autopilot, flight director, and autothrust systems. Similar systems exist in high-end business jet aircraft.

The increased complexity of dealing with the two powerplant components that make up the turboprop powerplant system, namely the engine and the propeller, have made it more difficult to introduce such systems. Therefore, there is a need for improvement.

<CIT> discloses a prior art aircraft control system.

In one aspect, there is provided an aircraft control system according to claim <NUM>.

In another aspect, there is provided a method of controlling an aircraft according to claim <NUM>.

There is described herein systems and methods for an autothrottle system on a propeller-driven aircraft. With reference to <FIG>, there is illustrated a powerplant <NUM> for a propeller-driven aircraft, generally comprising an engine <NUM> and a propeller <NUM>. The propeller <NUM> converts rotary motion from a shaft of the engine <NUM> to provide propulsive force, i.e. thrust, for the aircraft. The thrust generated by the powerplant <NUM> can be broken down into two contributors: the propeller thrust (FNP) and the engine jet thrust (FENJ). For a turboprop engine, about <NUM>% to <NUM>% of the total thrust is attributable to FNP while <NUM>% to <NUM>% of the total thrust is attributable to FENJ. The propeller thrust is a function of many factors, such as ambient temperature, ambient pressure/altitude, airspeed, propeller rotational speed, and power input to the propeller by the engine, and the airfoil design of the propeller blades.

The powerplant <NUM> of <FIG> is a turboprop engine, but it could also be any other type of engine comprising a propeller <NUM>, such as a piston engine, a turboshaft engine, and the like.

In regular operation, the engine <NUM> and the propeller <NUM> are regulated by a pilot or other operator by way of various control inputs. With reference to <FIG>, there is illustrated an example aircraft control system <NUM> comprising a powerplant control system (PCS) <NUM>. The PCS <NUM> is configured for controlling operation of the powerplant <NUM>, comprising engine <NUM> and propeller <NUM>. An engine controller <NUM> regulates fuel flow to the engine <NUM> in order to generate a desired engine output power. A propeller controller <NUM> sets blade pitch angle and/or propeller rotational speed of the propeller <NUM>, so as to convert the engine output power from the engine <NUM> into thrust.

A power throttle <NUM> is controlled by the pilot or other operator in order to provide engine and propeller settings to the powerplant <NUM> via the PCS <NUM>. In examples falling outside the wording of the claims, the power throttle comprises a throttle lever <NUM> to regulate the output power of the engine <NUM> and a condition lever <NUM> to regulate the thrust produced by the propeller <NUM>.

According to the invention, the power throttle comprises a single lever <NUM> to control both the engine <NUM> and the propeller <NUM>.

An autothrottle controller <NUM> is operatively connected to the PCS <NUM> and the power throttle <NUM>. The autothrottle controller <NUM> modulates engine power without pilot input. It may be used, for example, when the aircraft is set to autopilot, but may also be used outside of the autopilot mode. In some embodiments, the autothrottle controller <NUM> is integrated into aircraft avionics <NUM>, for example as part of an aircraft computer. Alternatively, the autothrottle controller communicates with the aircraft avionics <NUM> but is provided externally thereto, such as in the PCS <NUM> or as another separate component of the aircraft control system <NUM>.

Referring to <FIG>, there is illustrated a flowchart of an example method <NUM> for autothrottle as performed by the autothrottle controller <NUM>. At <NUM>, a required thrust change is obtained. The thrust change corresponds to a difference between an actual thrust generated by the powerplant <NUM> and a desired thrust in accordance with the inputs provided to the powerplant <NUM>. For example, in a single lever configuration, the current position of the power throttle <NUM>, also referred to as the power lever angle (PLA), will dictate a requested engine power and a corresponding reference propeller governing speed, which may be used to determine the desired thrust. Similarly, the actual thrust may be determined using a measured engine output power and a measured propeller speed. It should be understood that all thrust determinations are estimated thrust as thrust has no measurement system per se on an aircraft.

In some embodiments, the autothrottle controller <NUM> receives the thrust change as already determined, for example from an aircraft computer <NUM>. Alternatively, the autothrottle controller <NUM> calculates the thrust change based on various parameters as received from the aircraft computer <NUM>, the PCS <NUM>, the power throttle <NUM>, and/or various sensors on the aircraft and/or powerplant <NUM>. For example, the actual thrust is determined from the measured engine output power and the measured propeller speed as received from sensors provided on the engine <NUM> and/or propeller <NUM>. The desired thrust is determined from the requested engine power and the corresponding reference propeller governing speed, as determined from the PLA. In yet another embodiment, the autothrottle controller <NUM> receives the actual thrust and the desired thrust and determines the difference in order to obtain the thrust change.

In some embodiments, the autothrottle controller <NUM> receives as input one or more aircraft operating condition, such as aircraft speed, ambient temperature, ambient temperature, altitude, and the like. The operating conditions may also be used to calculate an estimated thrust, for example using the following equation: <MAT>.

Where ηprop is the propeller efficiency, which is determined by the propeller supplier and may vary as a function of flight phase and speed of the aircraft. Other factors that may affect propeller efficiency are aircraft angle of attack, propeller speed, power, altitude, and ambient temperature. Other factors may also apply. For example, ηprop may be in the order of <NUM>% at takeoff power and typical V1 speed of the aircraft, in the range of <NUM>% to <NUM>% in climb rotational speed and power, and <NUM>% to <NUM>% in cruise rotational speed and power. Other values may also apply, as propeller efficiency is specific to propeller blade design and the design points that the propeller blade has been optimized for.

Referring back to method <NUM>, optionally at <NUM>, the thrust change is converted to a power value. In other words, a conversion is made to determine what difference in input power is needed to cause the thrust change. Indeed, while the output of the engine may be measured via the propulsion force, what is input to the engine is measured in terms of power. The power generated by the engine <NUM> is then converted into thrust by the propeller <NUM>. Therefore in order to speak to the engine <NUM>, the autothrottle controller <NUM> communicates in terms of power. Note that method <NUM> may be performed without step <NUM>. The conversion from thrust to power allows for an easier determination of a setting change at step <NUM>, due to the mapping of engine power and throttle position.

At <NUM>, a setting change is determined for at least one control input of the powerplant <NUM> when the thrust change or power value is greater than a threshold. The setting change corresponds to a change in one or more powerplant input control so as to cause a change in engine power proportional to the thrust change or power value. The setting change may cause an increase or a decrease to a currently requested engine power.

In some embodiments, the input control is for the power throttle <NUM> associated with the PCS <NUM>. For example, the input control may be the position of the power throttle, i.e. the PLA. <FIG> illustrates an example lookup table <NUM> for mapping requested engine power to PLA. A curve <NUM> shows a relationship between the PLA (horizontal axis) and the requested power (vertical axis). Another curve <NUM> shows the relationship between the lever angle (horizontal axis) and the reference propeller governing speed (vertical axis). The curve <NUM> is aligned with the curve <NUM>, which share a common horizontal axis, and points on the curve <NUM> can be mapped with points on the curve <NUM>.

As defined above, the power value as converted from the thrust change corresponds to a change in requested power to be applied to the engine. For a given power value, a new requested power is found by adding the power value to the current requested power. For example, if the power value is +<NUM> hp and the current requested engine power is <NUM> hp, then the new requested power used in the table <NUM> to determine PLA is <NUM> hp. If the power value is -<NUM> hp and the current requested engine power is <NUM> hp, then the new requested power used in the table <NUM> to determine PLA is <NUM> hp. The corresponding PLA is found on the horizontal axis using the curve <NUM>.

In some embodiments, the input control corresponds to a PLA trim, which is a fine adjustment of the PLA sent to the controller PCS <NUM> that does not require a physical change in the position of the throttle <NUM>. PLA trim is used for small adjustments in commanded power in order to achieve the requested engine power. <FIG> illustrates an example lookup table <NUM> for mapping PLA trim to PLA. In this example, the autothrottle controller <NUM> may adjust PLA trim only when the PLA is between two defined settings, identified as <NUM> and <NUM> on the horizontal axis, for example Flight Idle (FI) and maximum climb (MCL). These settings may be customizable. In some embodiments, PLA trim may be enabled/disabled by a pilot or other operator through a cockpit command. PLA trim may also be disabled in circumstances where fault accommodation is activated for loss of inputs.

In some embodiments, the input control corresponds to both PLA and PLA trim. In other embodiments, the input control corresponds to engine fuel flow and/or propeller pitch angle. Any control input that affects the amount of power generated by the engine <NUM> and converted into thrust by the propeller <NUM> may be varied in accordance with the power value. If the power value is lower than the threshold, the method <NUM> returns to <NUM> where a new thrust change is determined.

Once the setting change is determined, at least one command is output by the autothrottle controller <NUM> to cause the setting change, as per <NUM>. The command may be one or more of a PLA command, a PLA trim command, a fuel flow valve command, a propeller speed command, a propeller blade pitch angle command, and the like.

The autothrottle controller <NUM> is configured to output a PLA command directly to a throttle quadrant controller (TQC) comprising a servo-motor and a rotary variable differential transformer (RVDT), which in turn controls the power throttle <NUM>. The servo-motor physically moves the power throttle <NUM> to a given position in accordance with the control command. The RVDT sends electrical signals of the throttle position to the engine controller <NUM>.

A PLA trim command may be sent to the PCS <NUM>, for example to the engine controller <NUM>. The use of the PLA trim added to the physical PLA position modulated with servo-motors is to minimize the throttle movement to accommodate for the uncertainties and variability related to the propeller efficiency ηprop determination. In some embodiments, the autothrottle controller <NUM> only interfaces with the engine controller <NUM> and no direct communication is needed with the propeller controller <NUM>. In some embodiments, the PLA trim is added to the electrical signals sent by RVDT containing the PLA position. The resulting signal is used to determine a power request command to the engine controller <NUM>. The PLA setting will also set the propellers to govern at a corresponding reference rotational speed.

In some embodiments, the autothrottle controller <NUM> is activated by the pilot upon confirmation that the system is capable of operating in an autothrottle mode. System capability may be dictated by various conditions. For example, the local throttle position is within specified boundaries, such as flight idle and maximum climb. Local and remote throttles are within a specified tolerance of each other, and the take-off phase of the aircraft is complete and the aircraft is safely in the air. In some embodiments, certain functionalities are also tested before the system is deemed capable of operating in autothrottle mode, such as the data input interface with the aircraft, the channels of the engine controller <NUM> (in a multi-channel controller), and the throttle position signal to the engine controller <NUM>.

The pilot may set aircraft operating targets for autothrottle. These commands are sent from the pilot interface to the autothrottle controller <NUM>. In some embodiments, this is done through the aircraft avionics. Alternatively, the autothrottle controller <NUM> may be connected directly to the pilot interface. Once operating targets are set, the pilot may enable autothrottle through an autothrottle request signal sent from the pilot interface to the autothrottle controller <NUM>.

Additional indications provided by the engine controller <NUM> may be used to dictate whether the autothrottle controller <NUM> is limited by either an engine limitation or a trim limitation. An engine limitation prevents and increase and/or decrease of requested engine power due to a high/low end engine limit being attained. A trim limitation prevents and increase and/or decrease of requested engine power due to a high/low end trim limit being attained.

In some embodiments, the PLA trim value is set to a default value of <NUM>° when autothrottle is not enabled or when the system is not capable of operating in an autothrottle mode.

In some embodiments, the PLA trim value is frozen, i.e. held constant to a last value, during propeller reference speed setting changes when the autothrottle is engaged, or if the PLA signal is moving at a rate greater than a predetermined amount.

In some embodiments, the PLA trim value is rate limited to a rate deemed necessary to maintain a smooth aircraft operation when transitioning to/from an engaged to a disengaged autothrottle mode, or when unfrozen following propeller speed reference changes or following the PLA signal moving at rate greater than a predetermined amount.

In some embodiments, the engine controller <NUM> is implemented as a single-channel or dual-channel full-authority digital engine controls (FADEC), an electronic engine controller (EEC), an engine control unit (ECU), or any other suitable engine controller. In some embodiments, the propeller controller <NUM> is implemented as a propeller electronic control (PEC) unit.

<FIG> illustrates an example embodiment to implement the autothrottle controller <NUM>, so as to perform the method <NUM>. A computing device <NUM> comprises a processing unit <NUM> and a memory <NUM> which has stored therein computer-executable instructions <NUM>. The processing unit <NUM> may comprise any suitable devices configured to implement the autothrottle controller <NUM> such that instructions <NUM>, when executed by the computing device <NUM> or other programmable apparatus, may cause the functions/acts/steps attributed to the autothrottle controller <NUM> as described herein to be executed.

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), compact disc read-only memory (CDROM), 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.

The methods and systems for autothrottle in a propeller-driven aircraft described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device <NUM>. Alternatively, the methods and systems for autothrottle in a propeller-driven aircraft may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems for controlling operation of aircraft engines may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems for autothrottle in a propeller-driven aircraft may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit <NUM> of the computing device <NUM>, to operate in a specific and predefined manner to perform the functions described herein.

Claim 1:
An aircraft control system (<NUM>) comprising:
a powerplant control system (<NUM>) configured for controlling operation of a powerplant (<NUM>) comprising an engine (<NUM>) and a propeller (<NUM>);
an engine controller (<NUM>) configured to regulate a fuel flow to the engine (<NUM>) in order to generate a desired engine output power;
a propeller controller (<NUM>) configured to a set blade pitch angle and/or a propeller rotational speed of the propeller (<NUM>), so as to convert the engine output power from the engine (<NUM>) into thrust;
a power throttle (<NUM>) comprising a single throttle lever (<NUM>) to regulate both: the engine output power; and the thrust produced by the propeller (<NUM>);
an autothrottle controller (<NUM>) operatively connected to the powerplant control system (<NUM>) and the power throttle (<NUM>), and configured to modulate engine power without pilot input and to output a command to cause a setting change of the power throttle (<NUM>), wherein the setting change corresponds to a power lever angle of the power throttle (<NUM>); and
a throttle quadrant controller comprising a servo-motor configured to physically move the power throttle (<NUM>) in accordance with the command from the autothrottle controller (<NUM>).