# Patent

## Title
Propeller balancing using inflight data

## Abstract

There is described herein a propeller balancing system and method that determines a stable cruise condition of an aircraft during flight, and considers vibration data for propeller balancing collected while the aircraft is in the stable cruise condition. Parameters used to determine stable cruise condition may be unique for each flight and/or aircraft, and balancing solutions may be determined based on these unique parameters.

## Background
TECHNICAL FIELD
The disclosure relates generally to a system and method for propeller balancing on propeller-powered aircraft.
BACKGROUND OF THE ART
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.
SUMMARY
There is described herein a propeller balancing system and method that determines a stable cruise condition of an aircraft during flight, and considers vibration data for propeller balancing collected while the aircraft is in the stable cruise condition. Parameters used to determine stable cruise condition may be unique for each flight and/or aircraft, and balancing solutions may be determined based on these unique parameters.
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; determining a time period of the flight using the aircraft data corresponding to a stable cruise condition, the stable cruise condition defined by at least one flight criterion and an associated value for the flight criterion; analyzing the propeller vibration data for the time period of stable cruise condition to assess a vibration level of the propeller; and signaling a balancing need when the vibration level reaches a threshold.
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; determining a time period of the flight using the aircraft data corresponding to a stable cruise condition, the stable cruise condition defined by at least one flight criterion and an associated value for the flight criterion; analyzing the propeller vibration data for the time period of stable cruise condition to assess a vibration level of the propeller; and signaling a balancing need when the vibration level reaches a threshold.
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; determining a time period of the flight using the aircraft data corresponding to a stable cruise condition, the stable cruise condition defined by at least one flight criterion and an associated value for the flight criterion; analyzing the propeller vibration data for the time period of stable cruise condition to assess a vibration level of the propeller; and signaling a balancing need when the vibration level reaches a threshold.



DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures in which:
FIG. 1 is a cross-sectional view of a turboprop engine, in accordance with one embodiment;
FIG. 2 is a schematic diagram of an aircraft system and corresponding ground equipment for performing propeller balancing;
FIG. 3 is a block diagram of an example embodiment of a propeller balancing system;
FIG. 4 is a flowchart of a method for performing propeller balancing, in accordance with one embodiment;
FIG. 5 illustrates an example of various aircraft operating conditions during a flight and corresponding data points acquired for vibration data; and
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
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.
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.
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.
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, ThunderboltTM, Ethernet, ZigbeeTM, BluetoothTM, and the like.
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.
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 (FASTTM) 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 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.
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.
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 form 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.
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.
In other embodiments, the propeller balancing system 216 is implemented using a combination of hardware and software components, as one or more applications 3061 . . . N stored in a memory 302 and running on a processor 304, as illustrated in FIG. 3. The applications 3061 . . . 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 3061 . . . 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.
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.
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.
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.










TABLE 1







FLIGHT CRITERIA
VALUE









MINIMUM ALTITUDE
>12,000 ft



PROPELLER SPEED
880-930 rpm



STABILITY DURATION
120 seconds



MINIMUM CALIBRATED AIRSPEED
160 knots



ENGINE TORQUE
>32%



ENGINE RATING
CLA = 55 + 5



ALTITUDE STABILITY
<+100 feet



CALIBRATED AIRSPEED STABILITY
<+5 knots



ENGINE TORQUE STABILITY
<+1%



PROPELLER SPEED STABILITY
<+0.5%



COMPRESSOR SPEED STABILITY
<+0.2%










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.
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.
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.
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 508A and 508B 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.









TABLE 2





VIBRATION LEVEL
IPS
DESCRIPTION







1
 1.0
VERY ROUGH


2
<1.0
ROUGH


3
<0.5
SLIGHTLY ROUGH


4
<0.25
FAIR


5
<0.15
GOOD


6
<0.07
VERY GOOD


7
<0.04
EXCELLENT









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.
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.
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.
Referring now to FIG. 6, there is illustrated an example application 3061 for implementing the method 400 for propeller balancing. The application 3061 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.
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.
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.
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.
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.
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.
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.

## Claims

1. A method for propeller balancing of an aircraft, the method comprising:
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;
determining a time period of the flight using the aircraft data corresponding to a stable cruise condition, the stable cruise condition defined by at least one flight criterion and an associated value for the flight criterion;
analyzing the propeller vibration data for the time period of stable cruise condition to assess a vibration level of the propeller; and
signaling a balancing need when the vibration level reaches a threshold.

2. The method of claim 1, wherein the at least one flight criterion is customizable per aircraft operator.

3. The method of claim 1, wherein the value associated with the at least one flight criterion is customizable per aircraft operator.

4. The method of claim 1, wherein the at least one flight criterion is customizable per aircraft mission.

5. The method of claim 1, wherein the value associated with the flight criterion is customizable per aircraft mission.

6. The method of claim 1, further comprising determining a balancing solution for the aircraft when the vibration level reaches the threshold.

7. The method of claim 6, wherein determining a balancing solution comprises identifying at least one weight and a placement location for the at least one weight to balance the propeller.

8. The method of claim 1, wherein receiving the propeller vibration data and receiving the aircraft data comprises receiving for multiple flights of the aircraft, and wherein analyzing the propeller vibration data comprises analyzing over the multiple flights to monitor the vibration level of the propeller.

9. The method of claim 1, wherein receiving the propeller vibration data and receiving the engine and aircraft performance parameters comprises receiving at a ground server from the aircraft through a wireless transmission.

10. A system for aircraft propeller balancing, the system comprising:
a processing unit; and
a memory, communicatively coupled to the processing unit and comprising computer-readable program instructions 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;
determining a time period of the flight using the aircraft data corresponding to a stable cruise condition, the stable cruise condition defined by at least one flight criterion and an associated value for the flight criterion;
analyzing the propeller vibration data for the time period of stable cruise condition to assess a vibration level of the propeller; and
signaling a balancing need when the vibration level reaches a threshold.

11. The system of claim 10, wherein the at least one flight criterion is customizable per aircraft operator.

12. The system of claim 10, wherein the value associated with the at least one flight criterion is customizable per aircraft operator.

13. The system of claim 10, wherein the at least one flight criterion is customizable per aircraft mission.

14. The system of claim 10, wherein the value associated with the flight criterion is customizable per aircraft mission.

15. The system of claim 10, wherein the program instructions are further executable for determining a balancing solution for the aircraft when the vibration level reaches the threshold.

16. The system of claim 15, wherein determining a balancing solution comprises identifying at least one weight and a placement location for the at least one weight to balance the propeller.

17. The system of claim 10, wherein receiving the propeller vibration data and receiving the aircraft data comprises receiving for multiple flights of the aircraft, and wherein analyzing the propeller vibration data comprises analyzing over the multiple flights to monitor the vibration level of the propeller.

18. The system of claim 10, wherein receiving the propeller vibration data and receiving the engine and aircraft performance parameters comprises receiving at a ground server from the aircraft through a wireless transmission.

19. 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;
determining a time period of the flight using the aircraft data corresponding to a stable cruise condition, the stable cruise condition defined by at least one flight criterion and an associated value for the flight criterion;
analyzing the propeller vibration data for the time period of stable cruise condition to assess a vibration level of the propeller; and
signaling a balancing need when the vibration level reaches a threshold.