Patent Description:
Propeller powered aircraft, small and large, require propeller balancing at some point in time. Some require balancing more often than others.

Many systems require the aircraft to be on the ground to perform engine runs in order to collect the data needed for propeller balancing. This is not an effective solution as the ground data is not truly representative of inflight conditions. Other systems will collect data inflight and provide it to a ground station post-flight for analysis. However, such systems are programmed to gather data at specific points in time, which again does not consider specific operational conditions of the flight.

Therefore, there is room for improvement.

<CIT> discloses prior art devices, systems, and methods for balancing closely coupled rotating machinery.

In one aspect of the present invention, there is provided a method for propeller balancing of an aircraft as set forth in claim <NUM>.

In another aspect of the present invention, there is provided a system for aircraft propeller balancing as set forth in claim <NUM>.

Further embodiments of the present invention are provided in dependent claims <NUM> to <NUM> and <NUM> to <NUM>.

Features of the systems, devices, and methods described herein may be used in various combinations, in accordance with the embodiments described herein. In particular, any of the above features may be used alone, together in any suitable combination, and/or in a variety of arrangements, as appropriate.

<FIG> illustrates an example engine <NUM> comprising a propeller <NUM>. The propeller <NUM> converts rotary motion from the shaft <NUM> to provide propulsive force to an aircraft. The engine <NUM> of <FIG> is a turboprop 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.

<FIG> illustrates an example aircraft <NUM>, which may be any type of propeller-driven aircraft <NUM>. At least one accelerometer <NUM> is provided per engine <NUM> of the aircraft <NUM>, for collecting measurement data from the propeller <NUM>. The measurement data corresponds to the acceleration of the front of the engine <NUM> in a direction normal to the shaft <NUM> of the propeller <NUM>. When the propeller <NUM> is out of balance, as the center of mass rotates around the axis of rotation, the resulting centripetal force tries to pull the propeller <NUM> towards the center of mass. This rotating imbalance force acts on the mass of the engine <NUM> and propeller <NUM> and accelerates it. This acceleration is measured by the accelerometer <NUM>.

The accelerometer <NUM> may be mounted directly on the engine <NUM>, proximate to the propeller <NUM>, in order to measure the acceleration of the propeller <NUM>. The installation may be permanent or temporary. A permanent mount may be performed during manufacture of the engine <NUM>. When the aircraft is assembled, the accelerometer <NUM> may be connected to an existing aircraft harness (not shown). One or more additional cables, adapters, connectors, and/or harnesses may be added in order to connect the accelerometer <NUM> to the existing aircraft harness. A temporary mount may be performed after manufacture of the engine <NUM> and/or after aircraft assembly, such as during aircraft maintenance.

The measurement data collected by the accelerometer <NUM> may be transmitted to a vibration data processing unit <NUM>, via the existing aircraft harness and/or additional cables, adapters, connectors, and/or harnesses. Alternatively, transmission of the data collected by the accelerometer <NUM> is performed wirelessly. Therefore, the accelerometer <NUM> may be configured for providing the measurement data to the vibration data processing unit <NUM> via any suitable wired or wireless communication path, including RS-<NUM>, USB, USB <NUM>, USB <NUM>, USB-C, SATA, e-SATA, Thunderbolt™, Ethernet, Wi-Fi, Zigbee™, Bluetooth™, and the like.

The vibration data processing unit <NUM> is configured to determine, from the measurement data, vibration data for the engine <NUM> and/or the propeller <NUM>. The vibration data comprises propeller speed as well as phase angle and magnitude of engine vibration. Speed may be denoted as a Rotation Per Minute (RPM) of the propeller <NUM>. The accelerometer <NUM> may act as a tachometer to measure the propeller <NUM> RPM. One or more additional sensors may also be provided for this purpose. Magnitude may be denoted as a peak velocity in units of Inches Per Section (IPS). The phase angle is found by detecting when one particular propeller blade passes the accelerometer <NUM>, and corresponds to the relationship between the waveform of the vibration magnitude signal to the angular position of the propeller <NUM>. The vibration data processing unit <NUM> may be configured to digitize the measurement data if received in analog form, and determine the vibration data from the digitized data.

The vibration data determined by the vibration data processing unit <NUM> is transmitted to a data acquisition and transmission unit <NUM>. The data acquisition and transmission unit <NUM> may take various forms, such as a Flight-data Acquisition, Storage, and Transmission (FAST™) box, as manufactured by Pratt & Whitney Canada, or any other computer-controlled unit that receives data from various aircraft systems and sensors, and transmits the received data off-aircraft to a ground server <NUM>. For example, the data acquisition and transmission unit <NUM> may comprise one or more antenna, a processor, and a memory. The one or more antenna enable establishment of a wireless connection with the ground server <NUM>. The processor may be coupled to a data bus of the aircraft <NUM> for receiving the vibration data and any other data from the aircraft systems and sensors. In some embodiments, the vibration data is transmitted from the vibration data processing unit <NUM> to the data acquisition and transmission unit <NUM> using the Aeronautical Radio Inc. (ARINC) <NUM> data transfer standard for aircraft avionics. Other data standards may also be used, such as ARINC <NUM>, ARINC <NUM>, and MIL-STD-<NUM>.

In some embodiments, the data acquisition and transmission unit <NUM> is also configured to convert received data into digital form. As illustrated, unit <NUM> also receives data from an engine computer <NUM> and/or an aircraft computer <NUM>. This data will be collectively referred to as aircraft data, and denote engine and/or aircraft performance parameters. The aircraft computer <NUM> may be an aircraft management controller (AMC), a flight management system (FMS), an aircraft digital computer system, or any other device used for computing inside an aircraft <NUM>. The engine computer <NUM> may be any type of computing unit of an engine <NUM>, such as an engine control unit (ECU), an engine electronic controller (EEC), an engine electronic control system, and a Full Authority Digital Engine Controller (FADEC). Data transmitted from the engine computer <NUM> and/or the aircraft computer <NUM> to the data acquisition and transmission unit <NUM> may be provided over a dedicated communication bus or any other existing communication system of the aircraft <NUM>. Example data provided by the aircraft computer <NUM> comprises airspeed, altitude, stability, and position of the aircraft <NUM> at any point in time during a flight. Example data provided by the engine computer <NUM> comprises torque, speed, rating, torque stability, propeller speed stability, and compressor speed stability of the engine <NUM> at any point in time during engine operation.

In some embodiments, the vibration data processing unit <NUM> is integrated with the data acquisition and transmission unit <NUM>. The accelerometer <NUM> may thus be connected directly to the data acquisition and transmission unit <NUM> for providing measurement data thereto, and the data acquisition and transmission unit <NUM> may be configured to determine the vibration data from the measurement data. The data acquisition and transmission unit <NUM> is configured to transmit both the vibration data and the aircraft data to the ground server <NUM> via a wireless communication link.

Once received by the ground server <NUM>, the aircraft data and the vibration data are provided to a propeller balancing system <NUM> for further processing. The propeller balancing system <NUM> may be provided directly on the ground server <NUM> or separately therefrom. In some embodiments, the propeller balancing system <NUM> may be implemented in hardware, using analog and/or digital circuit components. For example, the propeller balancing system <NUM> may be provided as an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA). In some embodiments, the propeller balancing system <NUM> is provided as a non-transitory computer readable medium having stored thereon program code executable by a processor for carrying out the instructions of the program code.

In other embodiments, the propeller balancing system <NUM> is implemented using a combination of hardware and software components, as one or more applications <NUM><NUM>. N stored in a memory <NUM> and running on a processor <NUM>, as illustrated in <FIG>. The applications <NUM><NUM>. N are illustrated as separate entities but may be combined or separated in a variety of ways. The memory <NUM> accessible by the processor <NUM> may receive and store the vibration data and the aircraft data. The memory <NUM> may be a main memory, such as a high speed Random Access Memory (RAM), or an auxiliary storage unit, such as a hard disk, a floppy disk, or a magnetic tape drive. The memory <NUM> may be any other type of memory, such as a Read-Only Memory (ROM), or optical storage media such as a videodisc and a compact disc. The processor <NUM> may access the memory <NUM> to retrieve the data. The processor <NUM> may be any device that can perform operations on data. Examples are a central processing unit (CPU), a front-end processor, a microprocessor, and a network processor. The applications <NUM><NUM>. N are coupled to the processor <NUM> and configured to perform a method <NUM> for propeller balancing, which will be described with reference to <FIG>.

At step <NUM> of the method <NUM>, the propeller vibration data and the aircraft data are received by the propeller balancing system <NUM>. The data may be received sequentially or concurrently. When received sequentially, the order of reception is irrelevant.

At step <NUM>, the propeller balancing system <NUM> determines from the aircraft data a time period during which the aircraft operated in a stable cruise condition. Stable cruise condition corresponds to an operating condition of the aircraft during which certain flight criteria are attained. The flight criteria may correspond to engine parameters and/or aircraft parameters. Example aircraft parameters are minimum altitude, stability duration, minimum calibrated airspeed, altitude stability, and calibrated airspeed stability. Example engine parameters are propeller rotational speed, engine torque, engine rating, engine torque stability, engine propeller speed (Np) stability, and engine compressor speed (Nh) stability.

In some embodiments, stable cruise condition is operator-specific, that is to say that the flight criteria which determine whether an aircraft is operating in stable cruise condition are set by the aircraft operator. The operator may select which flight criteria are to be considered, and/or may set values for the flight criteria considered. TABLE <NUM> is an example of a set of flight criteria with operator-specific parameters for a flight operator X.

In this example, flight operator X has selected eleven (<NUM>) flight criteria used to determine stable cruise condition of an aircraft during a flight, and has set a value for each one of the eleven (<NUM>) flight criteria. These values may be set for aircraft A or fleet A comprising multiple aircraft A, which is for example an ATR <NUM> aircraft. Operator X may select different values for aircraft B or fleet B comprising multiple aircraft B, which is for example an ATR <NUM> aircraft. Operator X may also select more or less flight criteria, with the same or different values, for aircraft C or fleet C comprising multiple aircraft C, which is for example a Q400 aircraft. Therefore, operator X may operate fleets of aircraft with aircraft A, B, and C, and each aircraft may have its own set of flight criteria and associated values for establishing stable cruise condition.

Operator X may also set the parameters for stable cruise condition as a function of the specific mission of each aircraft. A "mission" should be understood as a flight to perform a specific task. The mission may be defined by various parameters, such as duration, destination, cargo, and any flying parameters to be used during the mission, such as propeller speed or maximum altitude. For example, operator X may have aircraft A and B fly at a propeller speed of <NUM> RPM wile aircraft C flies at a propeller speed of <NUM> RPM. The value associated for the flight criteria "propeller speed" may therefore differ between aircraft A and B and aircraft C. In some embodiments, operator X may define a unique set of flight criteria and associated values for each flight of an aircraft as a function of the specific flight parameters of a given flight, such as propeller speeds, cruising altitudes, etc. Therefore, aircraft specific and/or mission specific flight criteria and/or associated values may be used to determine stable cruise condition for any given flight. More or less than the specific flight criteria of Table <NUM> may be used.

<FIG> illustrates an example timeline <NUM> showing the different operating conditions throughout a flight for an aircraft <NUM>. In this example, stable cruise condition occurs after takeoff and ascent and before descent and landing. In certain circumstances, there may be more than one instance of stable cruise condition, interspaced by ascent, descent, and/or one or more other condition, such as turning or unsteady. For example, when the aircraft <NUM> experiences turbulence, this may cause it to exit stable cruise condition. Once the aircraft <NUM> stabilizes, it may re-enter stable cruise condition.

As per step <NUM>, a vibration level of the propeller <NUM> is assessed using vibration data captured while the aircraft <NUM> operates in stable cruise condition. Referring again to <FIG>, an example timeline <NUM> illustrates the capture of data points <NUM> corresponding to the measurement data collected by the accelerometer <NUM> throughout the flight. The data points <NUM> may be captured at any predefined interval, such as <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> minute, and the like. In order to use data points <NUM> that correspond to stable cruise condition, only the data points obtained during the period defined by cutoff lines 508A and 508B are used. From these data points, a vibration level of the propeller <NUM> is calculated using the propeller <NUM> rotational speed, the vibration phase, and the vibration magnitude of the aircraft <NUM>. Multiple vibration levels may be used, as illustrated in the example of TABLE <NUM>.

In this example, the vibration level is expressed in units of Inches Per Second (IPS). The threshold for balancing the propeller may be set to any one of the vibration levels, such as <NUM>, <NUM>, or <NUM>. The threshold may be determined by an operator of the aircraft <NUM>, or it may be set according to regional and/or other types of aircraft regulations. The threshold may be set as a function of the mission of the aircraft. For example, a cargo plane carrying only goods may have a lower threshold than an aircraft carrying passengers. Similarly, the threshold may be set as a function of various aircraft parameters, such as size of the aircraft, type of engine, etc. More or less threshold levels than those illustrated in TABLE <NUM> may be used.

When the vibration level of the propeller <NUM> reaches or exceeds the threshold, a balancing need is signaled by the propeller balancing system <NUM>, as per step <NUM>. In some embodiments, signaling a balancing need comprises sending a signal to an external system, so as to trigger an alert and/or alarm message. In some embodiments, signaling a balancing need comprises sending an electronic message to an operator of the aircraft or to a maintenance service. Other forms of signaling a balancing need may also be used.

In some embodiments, the method <NUM> also comprises a step of determining a balancing solution, as per step <NUM>. Determining a balancing solution may comprise identifying a value and a location for at least one weight (or mass) to be added to the propeller <NUM>. Other balancing solutions may include removing mass, radial drilling, milling, providing balancing rings, providing sliding blocks, and/or providing radial set screws. In such instances, step <NUM> of signaling a balancing need may also comprise providing the balance solution.

Referring now to <FIG>, there is illustrated an example application 306i for implementing the method <NUM> for propeller balancing. The application <NUM><NUM> illustratively comprises a stable cruise condition unit <NUM>, a vibration data extraction unit <NUM>, and a vibration level unit <NUM>. Optionally, a balancing unit <NUM> may also be provided.

The stable cruise condition unit <NUM> may retrieve the aircraft data from a data storage <NUM>, or it may receive it directly from the ground server <NUM> or the data acquisition and transmission unit <NUM>. The data storage <NUM> may correspond to the memory <NUM> or it may be another storage device, local to the propeller balancing system <NUM> or remote therefrom. The stable cruise condition unit <NUM> is configured to perform step <NUM> of method <NUM>, namely determine the stable cruise condition time period for the flight. The flight criteria and associated values for determining stable cruise condition may be retrieved from the data storage <NUM>, memory <NUM>, or any other storage device.

The vibration data extraction unit may retrieve the vibration data from the data storage <NUM>, or it may receive it directly from the ground server <NUM> or the data acquisition and transmission unit <NUM>. When the time period of the flight during which the aircraft was operating in stable cruise condition is identified by the stable cruise condition unit <NUM>, this information is provided to the vibration data extraction unit <NUM> for selection of data points collected during the same time period. The selected data points may be stored in the data storage <NUM> for retrieval by the vibration level unit <NUM>, or they may be provided directly to the vibration level unit <NUM> by the vibration data extraction unit <NUM>.

The vibration level unit <NUM> is configured for assessing the vibration level of the propeller <NUM>, as per step <NUM> of the method <NUM>, and signaling a balancing need when the vibration level reaches a threshold, as per step <NUM>. In some embodiments, the vibration level unit <NUM> may also be configured to trigger the balancing unit <NUM> to compute a balancing solution. The balancing unit <NUM> may retrieve vibration data, aircraft data, and/or any other parameters needed for computing the balancing solution from the data storage <NUM>. The balancing solution may be stored in the data storage <NUM> and retrieved by the vibration level unit <NUM> for transmitting to an operator and/or maintenance service, or it may be provided to the vibration level unit <NUM> directly. Operator and/or aircraft and/or mission specific parameters may also be retrieved from the data storage <NUM> by the balancing unit <NUM> and used to compute a unique balancing solution.

In some embodiments, the vibration level unit <NUM> and/or the balancing unit <NUM> is configured to perform trending of vibration data received over multiple flights for a given aircraft. Vibration levels may be compared over time from the multiple flights in order to monitor a progression of the vibration levels. Significant and/or sudden changes in vibration level may be noted by the propeller balancing system <NUM> and signaled to an operator and/or maintenance service of the aircraft by the vibration level unit <NUM>. Other trends may also be observed from the vibration data and/or aircraft data.

With reference to <FIG>, and additional reference to <FIG>, an embodiment of the vibration data processing unit <NUM>, which forms part of the aircraft <NUM>, is illustrated. The vibration data processing unit <NUM> is composed of a filter <NUM>, and optionally includes a signal pre-processor <NUM> and/or a signal post-processor <NUM>. The accelerometer <NUM>, as described hereinabove, can be any suitable type of accelerometer, which can be coupled to any suitable part of the engine <NUM>, or to any suitable part of the aircraft <NUM>. In the embodiment of <FIG>, it is considered that the accelerometer <NUM> is a singular accelerometer coupled to the engine <NUM> or the aircraft <NUM>. For instance, the embodiment illustrated in <FIG> may be part of a propeller balancing or vibration monitoring system which is provided as a lower-cost solution, and thus includes only a single accelerometer <NUM>.

The accelerometer <NUM> is configured for producing acceleration data indicative of accelerations which occur within the aircraft <NUM> and/or within the engine <NUM>, for instance in the form of an acceleration data signal. The acceleration data signal is, for example, an analog signal which encodes information relating to the accelerations measured by the accelerometer in the form of pulses of different frequency. Other embodiments are also considered. The acceleration data produced by the accelerometer can concurrently provide information regarding the accelerations and/or vibrations experienced by various components within the aircraft <NUM> and/or the engine <NUM>. For example, the acceleration data can be indicative of the vibrations experienced by the propeller <NUM>, the propeller <NUM>, and/or other elements of the engine <NUM> and/or the aircraft <NUM>. Although the information indicative of these different vibrations are all encoded as part of the acceleration data produced by the accelerometer <NUM>, the vibration data processing unit <NUM> illustrated in <FIG> is configured for isolating propeller-specific vibration data, as detailed hereinbelow.

The accelerometer <NUM> provides acceleration data to the vibration data processing unit <NUM>. In embodiments in which the vibration data processing unit <NUM> includes the signal pre-processor <NUM>, the acceleration data can be provided as part of a signal to the signal pre-processor <NUM>. The signal pre-processor <NUM> can include one or more amplifiers, one or more noise filters, or the like, and can transform or otherwise perform signal processing on the acceleration data in any suitable fashion. The signal pre-processor <NUM> can then provide the acceleration data to the filter <NUM>. In embodiments in which the signal pre-processor <NUM> is not included within the vibration data processing unit <NUM>, the acceleration data can be provided from the accelerometer <NUM> to the filter <NUM>.

The filter <NUM> is configured for filtering the acceleration data obtained from the signal pre-processor <NUM>, or from the accelerometer <NUM>, to obtain propeller-specific vibration data. The filter <NUM> defines a range of acceptable frequencies, also known as a passband, which are associated with a frequency of rotation of the propeller <NUM>. By applying the filter <NUM> to the acceleration data, portions of the acceleration data not relevant to propeller vibration can be discarded, and the output of the filter <NUM> is a modified signal which is indicative of the vibrations experienced by the propeller <NUM>.

For example, the propeller <NUM> is known to rotate at a particular frequency. In some cases, the vibration data processing unit <NUM> is preprogrammed with a predetermined frequency of rotation, or range of frequencies of rotation, for the propeller <NUM>. In some other cases, the vibration data processing unit <NUM> can obtain data substantially in real-time, for instance from a sensor, which indicates the frequency of rotation of the propeller <NUM>. The vibration data processing unit <NUM> can then alter the operation of the filter <NUM> to shift the range of acceptable frequencies in order to filter the acceleration data to obtain the propeller-specific vibration data. In some embodiments, the filter <NUM> is a band-pass filter, which defines a passband having a central frequency which is based on the frequency of rotation of the propeller. Other approaches for filtering the acceleration data signal provided by the accelerometer <NUM> to obtain propeller-specific vibration data is also considered.

Optionally, the filter <NUM> provides the propeller-specific vibration data, in the form of a signal, to the signal post-processor <NUM>, which can perform various post-processing operations on the propeller-specific vibration data. In some embodiments, the signal post-processor <NUM> performs an analog-to-digital conversion, converting the analog signal output by the filter <NUM> to a digital signal, which is then transmitted to the DAT unit <NUM>. For example, the analog-to-digital conversion can be performed by a remote-sensing node or other similar device, which can then be output by any suitable interface, for instance an ARINC <NUM> interface. In some other embodiments, the signal post-processor <NUM> performs a different type of conversion, for instance a conversion between a root-mean-squared signal to a DC (direct current) signal. Other types of signal conversions, for instance to facilitate the interpretation of the propeller-specific vibration data by the DAT unit <NUM>, are considered. In some embodiments, the signal post-processor <NUM> can perform noise reduction, amplification, or other types of signal processing, as appropriate.

The propeller-specific vibration data is then provided to the DAT unit <NUM>, whether from the filter <NUM> or from signal post-processor <NUM>. The DAT unit <NUM> can then use the propeller-specific vibration data to perform trend analysis of vibration data received over multiple flights for a given aircraft. The propeller-specific vibration data obtained during a particular flight mission can be compared with trend data associated with the propeller <NUM>, for instance to assess whether the propeller-specific vibration data indicates a change in the behavior of the propeller <NUM> vis-à-vis the trend data. In some embodiments, the trend data is preprogrammed into the DAT unit <NUM>. In some other embodiments, the trend data is based on previously-acquired propeller-specific vibration data, for instance from one or more previous flight missions for the aircraft <NUM>. The previously-acquired propeller-specific vibration data can be used, for instance, to augment preprogrammed trend data, or to build the trend data.

The trend analysis for the propeller-specific vibration data performed by the DAT unit <NUM> can include comparing the propeller-specific vibration data for a given flight mission against the trend data to determine whether the propeller-specific vibration data substantially aligns with the trend data, or whether the propeller-specific vibration data indicates a departure from the trend data. For example, the trend data can be associated with a predetermined range or other threshold, and when the propeller-specific vibration data is within the predetermined range, the DAT unit <NUM> can determine that the vibrations experienced by the propeller <NUM> are acceptable. Alternatively, when the propeller-specific vibration data is outside the range, the DAT unit <NUM> can determine that the propeller <NUM> is operating with unacceptable levels of vibration, and can issue an alert, for instance to the ground server <NUM>, to indicate a balancing need for the propeller <NUM>. The alert can indicate that a particular maintenance operation should be performed, for instance a propeller balancing operation, and/or provide relevant information for a maintenance crew assigned to the aircraft <NUM> and/or the engine <NUM>. The alert indicates a remaining flight time for the aircraft <NUM> (and, optionally, for the engine <NUM>) before a maintenance operation is required. The DAT unit <NUM> can also identify instances where the propeller-specific vibration data quickly departs from the trend data as an indication of a mechanical failure or other event requiring a maintenance operation, and provide an indication thereof via the alert.

The trend analysis can also include comparing the propeller-specific vibration data against one or more predetermined threshold values for vibrations experienced by the propeller <NUM>. For example, the DAT unit <NUM> can be preprogrammed with an expected vibration level for the propeller, for instance <NUM>,<NUM>/s or <NUM> inches/second (in/sec), or with an expected range of vibration levels for the propeller, for instance <NUM>,<NUM>-<NUM>,<NUM>/s or <NUM>-<NUM> in/sec. When the DAT unit <NUM> determines, based on the propeller-specific vibration data, that the vibrations experienced by the propeller <NUM> are beyond the expected vibration level or range, the DAT unit <NUM> can issue an alert for maintenance and/or propeller balancing.

In some embodiments, the DAT unit <NUM> is configured for updating the trend data based on the propeller-specific vibration data obtained during flight missions. The propeller-specific vibration data can be recorded or otherwise stored in a memory store, for instance within the DAT unit <NUM>, and can then be used to update the trend data. The trend data can be updated substantially in real-time, or periodically, for instance following review of the propeller-specific vibration data by a maintenance crew assigned to the aircraft <NUM> and/or the engine <NUM>, or by an operator of the aircraft <NUM> and/or the engine <NUM>.

In some embodiments, the acceleration data obtained by the accelerometer <NUM> is subdivided into a plurality of acceleration data sets associated with different flight stages with the flight mission. For instance, different levels of vibration are experienced by the propeller <NUM> during takeoff, ascent, cruise, descent, and landing, and the vibration processing unit <NUM> and/or the DAT unit <NUM> can be configured to subdivide the acceleration data and the propeller-specific vibration data into sets of data for different flight stages. Similarly, different sets of trend data can be maintained by the DAT unit <NUM> for different flight stages, and comparisons to the trend data sets can be performed on a per-flight-stage basis. Other variations are also considered. For instance, portions of the acceleration data can be discarded: acceleration data collected during ground operation of the aircraft <NUM> can be less indicative of the actual vibrations experienced by the propeller <NUM>, and the DAT <NUM> can discard the associated propeller-specific vibration data.

With reference to <FIG>, there is illustrated a method <NUM> for performing propeller balancing of an aircraft having a propeller, for instance the aircraft <NUM> having the propeller <NUM>. At step <NUM>, acceleration data is obtained from an acceleration sensor, for instance the accelerometer <NUM>. The accelerometer <NUM> can be coupled to the aircraft <NUM>, for instance to the engine <NUM>, or to another element of the aircraft <NUM>. The acceleration data obtained from the accelerometer <NUM> can be in the form of an analog electrical signal, for instance, which encodes acceleration data therein.

At step <NUM>, the acceleration data is filtered to obtain propeller-specific vibration data, for instance using the filter <NUM>. The propeller-specific vibration data can be obtained by filtering the acceleration data through the filter <NUM>, which has a passband associated with a frequency of rotation of the propeller <NUM>.

Optionally, at step <NUM>, portions of the propeller-specific vibration data which are associated with a period of ground operation for the aircraft <NUM> are discarded. For instance, information from other systems, including the aircraft computer <NUM> and/or the engine computer <NUM>, can provide information to indicate periods of ground operation for the aircraft <NUM>.

At step <NUM>, the propeller-specific vibration data is compared to trend data associated with the propeller <NUM>. At decision step <NUM>, an evaluation is performed to assess whether the propeller-specific acceleration data differs from the trend data beyond a predetermined threshold. When the propeller-specific acceleration data does differ from the trend data beyond the predetermined threshold, the method <NUM> proceeds to step <NUM>. When the propeller-specific acceleration data does not differ from the trend data beyond the predetermined threshold, the method <NUM> optionally proceeds to step <NUM>, or returns to some previous step, for instance, step <NUM>.

At step <NUM>, an alert indicative of a balancing need for the propeller <NUM> is issued. For example, the alert is issued by the DAT unit <NUM> to the ground server <NUM>, or to an operator or maintenance crew for the aircraft <NUM>. In some embodiments, the alert is indicative of a maintenance operation to be performed, for instance for the propeller <NUM>. The alert is indicative of a remaining flight time for the aircraft <NUM> (and, optionally, for the engine <NUM>) before a maintenance operation is to be performed.

Optionally, at step <NUM>, the propeller-specific vibration data is stored in a memory store and used to update the trend data. Step <NUM> is optionally performed after step <NUM>, or when the propeller-specific acceleration data does not differ from the trend data beyond the predetermined threshold, as assessed at step <NUM>. The updating of the trend data can include determining a new average, rolling average, or other trend information for the level of vibration experienced by the propeller <NUM>. Other approaches are also considered. For example, a trend line slope for the level of vibration experienced by the propeller <NUM> can be updated based on the propeller-specific vibration data.

The above description is meant to be exemplary only, and one skilled in the relevant arts will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the blocks and/or operations in the flowcharts and drawings described herein are for purposes of example only. There may be many variations to these blocks and/or operations without departing from the teachings of the present disclosure. For instance, the blocks may be performed in a differing order, or blocks may be added, deleted, or modified.

Claim 1:
A method for propeller balancing of an aircraft comprising a propeller (<NUM>), the method comprising:
obtaining acceleration data from an acceleration sensor (<NUM>) coupled to the aircraft;
filtering the acceleration data using a filter (<NUM>) to obtain propeller-specific vibration data, the filter (<NUM>) defining a range of acceptable frequencies associated with a frequency of rotation of the propeller (<NUM>);
comparing the propeller-specific vibration data to trend data associated with the propeller (<NUM>); and
when the propeller-specific vibration data differs from the trend data beyond a predetermined threshold, issuing an alert indicative of a balancing need for the propeller (<NUM>),
characterised in that:
issuing an alert comprises indicating a remaining flight time for the aircraft until a maintenance operation is required.