Abstract:
There is described herein a propeller balancing system and method that selects at least a portion of received propeller vibration data by comparing received aircraft data collected concurrently with the propeller vibration data with at least one customizable flight criterion, and identifying the portion of the vibration data acquired at a time when the aircraft data meets the at least one customizable flight criterion. The selected portion of the propeller vibration data is analyzed to assess a vibration level of the propeller and a balancing need is signaled when the vibration level reaches a threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 15/078,394 filed on Mar. 23, 2016, the contents of which are hereby incorporated in their entirety by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates generally to a system and method for propeller balancing on propeller-powered aircraft. 
       BACKGROUND OF THE ART 
       [0003]    Propeller powered aircraft, small and large, require propeller balancing at some point in time. Some require balancing more often than others. 
         [0004]    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. 
         [0005]    Therefore, there is room for improvement. 
       SUMMARY 
       [0006]    In one aspect, there is provided a method for propeller balancing of an aircraft. The method comprises receiving propeller vibration data comprising speed, phase, and magnitude of vibration, the propeller vibration data having been collected in-flight; receiving aircraft data collected in-flight concurrently with the propeller vibration data; selecting at least a portion of the propeller vibration data by comparing the aircraft data with at least one customizable flight criterion and identifying the portion of the vibration data acquired at a time when the aircraft data meets the at least one customizable flight criterion; analyzing the selected portion of the propeller vibration data to assess a vibration level of the propeller; and signaling a balancing need when the vibration level reaches a threshold. 
         [0007]    In another aspect, there is provided a system for aircraft propeller balancing. The system comprises a processing unit and a memory, communicatively coupled to the processing unit and comprising computer-readable program instructions. The instructions are executable by the processing unit for receiving propeller vibration data comprising speed, phase, and magnitude of vibration, the propeller vibration data having been collected in-flight; receiving aircraft data collected in-flight concurrently with the propeller vibration data; selecting at least a portion of the propeller vibration data by comparing the aircraft data with at least one customizable flight criterion and identifying the portion of the vibration data acquired at a time when the aircraft data meets the at least one customizable flight criterion; analyzing the selected portion of the propeller vibration data to assess a vibration level of the propeller; and signaling a balancing need when the vibration level reaches a threshold. 
         [0008]    In a further aspect, there is provided a non-transitory computer readable medium having stored thereon computer-readable program instructions executable by a processor for receiving propeller vibration data comprising speed, phase, and magnitude of vibration, the propeller vibration data having been collected in-flight; receiving aircraft data collected in-flight concurrently with the propeller vibration data; selecting at least a portion of the propeller vibration data by comparing the aircraft data with at least one customizable flight criterion and identifying the portion of the vibration data acquired at a time when the aircraft data meets the at least one customizable flight criterion; analyzing the selected portion of the propeller vibration data to assess a vibration level of the propeller; and signaling a balancing need when the vibration level reaches a threshold. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]    Reference is now made to the accompanying figures in which: 
           [0010]      FIG. 1  is a cross-sectional view of a turboprop engine, in accordance with one embodiment; 
           [0011]      FIG. 2  is a schematic diagram of an aircraft system and corresponding ground equipment for performing propeller balancing; 
           [0012]      FIG. 3  is a block diagram of an example embodiment of a propeller balancing system; 
           [0013]      FIG. 4  is a flowchart of a method for performing propeller balancing, in accordance with one embodiment; 
           [0014]      FIG. 5  illustrates an example of various aircraft operating conditions during a flight and corresponding data points acquired for vibration data; and 
           [0015]      FIG. 6  is a block diagram of an example application running on the propeller balancing system, for performing the method of propeller balancing. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  illustrates an example engine  100  comprising a propeller  102 . The propeller  102  converts rotary motion from the shaft  104  to provide propulsive force to an aircraft. The engine  100  of  FIG. 1  is a turboprop but it could also be any other type of engine comprising a propeller  102 , such as a piston engine, a turboshaft engine, and the like. 
         [0017]      FIG. 2  illustrates an example aircraft  200 , which may be any type of propeller-driven aircraft  200 . At least one accelerometer  204  is provided per engine  100  of the aircraft  200 , for collecting measurement data from the propeller  102 . The measurement data corresponds to the acceleration of the front of the engine  100  in a direction normal to the shaft  104  of the propeller  102 . When the propeller  102  is out of balance, as the center of mass rotates around the axis of rotation, the resulting centripetal force tries to pull the propeller  102  towards the center of mass. This rotating imbalance force acts on the mass of the engine  100  and propeller  102  and accelerates it. This acceleration is measured by the accelerometer  204 . 
         [0018]    The accelerometer  204  may be mounted directly on the engine  100 , proximate to the propeller  102 , in order to measure the acceleration of the propeller  102 . The installation may be permanent or temporary. A permanent mount may be performed during manufacture of the engine  100 . When the aircraft is assembled, the accelerometer  204  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  204  to the existing aircraft harness. A temporary mount may be performed after manufacture of the engine  100  and/or after aircraft assembly, such as during aircraft maintenance. 
         [0019]    The measurement data collected by the accelerometer  204  may be transmitted to a vibration data processing unit  206 , via the existing aircraft harness and/or additional cables, adapters, connectors, and/or harnesses. Alternatively, transmission of the data collected by the accelerometer  204  is performed wirelessly. Therefore, the accelerometer  204  may be configured for providing the measurement data to the vibration data processing unit  206  via any suitable wired or wireless communication path, including RS-232, USB, USB 2.0, USB 3.0, USB-C, SATA, e-SATA, Thunderbolt™, Ethernet, Wi-Fi, Zigbee™, Bluetooth™, and the like. 
         [0020]    The vibration data processing unit  206  is configured to determine, from the measurement data, vibration data for the engine  100  and/or the propeller  102 . 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  102 . The accelerometer  204  may act as a tachometer to measure the propeller  102  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  204 , and corresponds to the relationship between the waveform of the vibration magnitude signal to the angular position of the propeller  102 . The vibration data processing unit  206  may be configured to digitize the measurement data if received in analog form, and determine the vibration data from the digitized data. 
         [0021]    The vibration data determined by the vibration data processing unit  206  is transmitted to a data acquisition and transmission unit  208 . The data acquisition and transmission unit  208  may take various forms, such as a Flight-data Acquisition, Storage, and Transmission (FAST™) box, as manufactured by Pratt &amp; 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  214 . For example, the data acquisition and transmission unit  208  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  214 . The processor may be coupled to a data bus of the aircraft  200  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  206  to the data acquisition and transmission unit  208  using the Aeronautical Radio Inc. (ARINC) 429 data transfer standard for aircraft avionics. Other data standards may also be used, such as ARINC 615, ARINC 629, and MIL-STD-1553. 
         [0022]    In some embodiments, the data acquisition and transmission unit  208  is also configured to convert received data into digital form. As illustrated, unit  208  also receives data from an engine computer  212  and/or an aircraft computer  210 . This data will be collectively referred to as aircraft data, and denote engine and/or aircraft performance parameters. The aircraft computer  210  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  200 . The engine computer  212  may be any type of computing unit of an engine  100 , 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  212  and/or the aircraft computer  210  to the data acquisition and transmission unit  208  may be provided over a dedicated communication bus or any other existing communication system of the aircraft  200 . Example data provided by the aircraft computer  210  comprises airspeed, altitude, stability, and position of the aircraft  200  at any point in time during a flight. Example data provided by the engine computer  212  comprises torque, speed, rating, torque stability, propeller speed stability, and compressor speed stability of the engine  100  at any point in time during engine operation. 
         [0023]    In some embodiments, the vibration data processing unit  206  is integrated with the data acquisition and transmission unit  208 . The accelerometer  204  may thus be connected directly to the data acquisition and transmission unit  208  for providing measurement data thereto, and the data acquisition and transmission unit  208  may be configured to determine the vibration data from the measurement data. The data acquisition and transmission unit  208  is configured to transmit both the vibration data and the aircraft data to the ground server  214  via a wireless communication link. 
         [0024]    Once received by the ground server  214 , the aircraft data and the vibration data are provided to a propeller balancing system  216  for further processing. The propeller balancing system  216  may be provided directly on the ground server  214  or separately therefrom. In some embodiments, the propeller balancing system  216  may be implemented in hardware, using analog and/or digital circuit components. For example, the propeller balancing system  216  may be provided as an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA). In some embodiments, the propeller balancing system  216  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. 
         [0025]    In other embodiments, the propeller balancing system  216  is implemented using a combination of hardware and software components, as one or more applications  306   1 . . . N  stored in a memory  302  and running on a processor  304 , as illustrated in  FIG. 3 . The applications  306   1 . . . N  are illustrated as separate entities but may be combined or separated in a variety of ways. The memory  302  accessible by the processor  304  may receive and store the vibration data and the aircraft data. The memory  302  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  302  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  304  may access the memory  302  to retrieve the data. The processor  304  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  306   1 . . . N  are coupled to the processor  304  and configured to perform a method  400  for propeller balancing, which will be described with reference to  FIG. 4 . 
         [0026]    At step  402  of the method  400 , the propeller vibration data and the aircraft data are received by the propeller balancing system  216 . The data may be received sequentially or concurrently. When received sequentially, the order of reception is irrelevant. 
         [0027]    At step  404 , the propeller balancing system  216  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. 
         [0028]    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 1 is an example of a set of flight criteria with operator-specific parameters for a flight operator X. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 FLIGHT CRITERIA 
                 VALUE 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 MINIMUM ALTITUDE 
                 &gt;12,000 
                 ft 
               
               
                   
                 PROPELLER SPEED 
                 880-930  
                 rpm 
               
               
                   
                 STABILITY DURATION 
                 120  
                 seconds 
               
               
                   
                 MINIMUM CALIBRATED AIRSPEED 
                 160 
                 knots 
               
             
          
           
               
                   
                 ENGINE TORQUE 
                    &gt;32% 
               
               
                   
                 ENGINE RATING 
                 CLA = 55 + 5 
               
             
          
           
               
                   
                 ALTITUDE STABILITY 
                 &lt;+100  
                 feet 
               
               
                   
                 CALIBRATED AIRSPEED STABILITY 
                 &lt;+5  
                 knots 
               
             
          
           
               
                   
                 ENGINE TORQUE STABILITY 
                   &lt;+1% 
               
               
                   
                 PROPELLER SPEED STABILITY 
                 &lt;+0.5% 
               
               
                   
                 COMPRESSOR SPEED STABILITY 
                 &lt;+0.2% 
               
               
                   
                   
               
             
          
         
       
     
         [0029]    In this example, flight operator X has selected eleven (11) 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 (11) flight criteria. These values may be set for aircraft A or fleet A comprising multiple aircraft A, which is for example an ATR 42 aircraft. Operator X may select different values for aircraft B or fleet B comprising multiple aircraft B, which is for example an ATR 72 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. 
         [0030]    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 1050 RPM wile aircraft C flies at a propeller speed of 975 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 1 may be used. 
         [0031]      FIG. 5  illustrates an example timeline  502  showing the different operating conditions throughout a flight for an aircraft  200 . 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  200  experiences turbulence, this may cause it to exit stable cruise condition. Once the aircraft  200  stabilizes, it may re-enter stable cruise condition. 
         [0032]    As per step  406 , a vibration level of the propeller  102  is assessed using vibration data captured while the aircraft  200  operates in stable cruise condition. Referring again to  FIG. 5 , an example timeline  504  illustrates the capture of data points  506  corresponding to the measurement data collected by the accelerometer  204  throughout the flight. The data points  506  may be captured at any predefined interval, such as 10 seconds, 15 seconds, 30 seconds, 1 minute, and the like. In order to use data points  506  that correspond to stable cruise condition, only the data points obtained during the period defined by cutoff lines  508 A and  508 B are used. From these data points, a vibration level of the propeller  102  is calculated using the propeller  102  rotational speed, the vibration phase, and the vibration magnitude of the aircraft  200 . Multiple vibration levels may be used, as illustrated in the example of TABLE 2. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 VIBRATION  
                   
                   
               
               
                 LEVEL 
                 IPS 
                 DESCRIPTION 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 ≧1.0 
                 VERY ROUGH 
               
               
                 2 
                 &lt;1.0 
                 ROUGH 
               
               
                 3 
                 &lt;0.5 
                 SLIGHTLY ROUGH 
               
               
                 4 
                 &lt;0.25 
                 FAIR 
               
               
                 5 
                 &lt;0.15 
                 GOOD 
               
               
                 6 
                 &lt;0.07 
                 VERY GOOD 
               
               
                 7 
                 &lt;0.04 
                 EXCELLENT 
               
               
                   
               
             
          
         
       
     
         [0033]    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 3, 4, or 5. The threshold may be determined by an operator of the aircraft  200 , 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 1 may be used. 
         [0034]    When the vibration level of the propeller  102  reaches or exceeds the threshold, a balancing need is signaled by the propeller balancing system  216 , as per step  408 . 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. 
         [0035]    In some embodiments, the method  400  also comprises a step of determining a balancing solution, as per step  407 . 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  102 . 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  408  of signaling a balancing need may also comprise providing the balance solution. 
         [0036]    Referring now to  FIG. 6 , there is illustrated an example application  306   1  for implementing the method  400  for propeller balancing. The application  306   1  illustratively comprises a stable cruise condition unit  602 , a vibration data extraction unit  604 , and a vibration level unit  606 . Optionally, a balancing unit  608  may also be provided. 
         [0037]    The stable cruise condition unit  602  may retrieve the aircraft data from a data storage  610 , or it may receive it directly from the ground server  214  or the data acquisition and transmission unit  208 . The data storage  610  may correspond to the memory  302  or it may be another storage device, local to the propeller balancing system  216  or remote therefrom. The stable cruise condition unit  602  is configured to perform step  404  of method  400 , 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  610 , memory  302 , or any other storage device. 
         [0038]    The vibration data extraction unit may retrieve the vibration data from the data storage  610 , or it may receive it directly from the ground server  214  or the data acquisition and transmission unit  208 . 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  602 , this information is provided to the vibration data extraction unit  604  for selection of data points collected during the same time period. The selected data points may be stored in the data storage  610  for retrieval by the vibration level unit  606 , or they may be provided directly to the vibration level unit  606  by the vibration data extraction unit  604 . 
         [0039]    The vibration level unit  606  is configured for assessing the vibration level of the propeller  102 , as per step  406  of the method  400 , and signaling a balancing need when the vibration level reaches a threshold, as per step  408 . In some embodiments, the vibration level unit  606  may also be configured to trigger the balancing unit  608  to compute a balancing solution. The balancing unit  608  may retrieve vibration data, aircraft data, and/or any other parameters needed for computing the balancing solution from the data storage  610 . The balancing solution may be stored in the data storage  610  and retrieved by the vibration level unit  606  for transmitting to an operator and/or maintenance service, or it may be provided to the vibration level unit  606  directly. Operator and/or aircraft and/or mission specific parameters may also be retrieved from the data storage  610  by the balancing unit  608  and used to compute a unique balancing solution. 
         [0040]    In some embodiments, the vibration level unit  606  and/or the balancing unit  608  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  216  and signaled to an operator and/or maintenance service of the aircraft by the vibration level unit  606 . Other trends may also be observed from the vibration data and/or aircraft data. 
         [0041]    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. 
         [0042]    While illustrated in the block diagrams as groups of discrete components communicating with each other via distinct data signal connections, it will be understood by those skilled in the art that the present embodiments are provided by a combination of hardware and software components, with some components being implemented by a given function or operation of a hardware or software system, and many of the data paths illustrated being implemented by data communication within a computer application or operating system. The structure illustrated is thus provided for efficiency of teaching the present embodiment. The present disclosure may be embodied in other specific forms without departing from the subject matter of the claims. Also, one skilled in the relevant arts will appreciate that while the systems, methods and computer readable mediums disclosed and shown herein may comprise a specific number of elements/components, the systems, methods and computer readable mediums may be modified to include additional or fewer of such elements/components. The present disclosure is also intended to cover and embrace all suitable changes in technology. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.