Safari users please note that the PB-4 is not compatible with Safari's “Private Mode”.

Accessing the PB-4 user interface from your tablet's browser requires the PB-4 and the tablet to be using the same Wi-Fi network.

When you load the PB-4 user interface into your browser, after showing the splash screen for a few seconds it will show an initial screen, like Figure 1.1, “Initial screen”

This shows a polar chart and a list of captured points (both empty as no points have been captured yet). At the top of the screen, are the Menu and Connect buttons and the name of the current job.

Most of the screen is used to display the PB-4 data. At the top of the region are three tabs (Polar, Spectrum & Data) which you use to select the data you wish to see.

Figure 1.1. Initial screen

The PB-4 user interface is "responsive" - the layout changes depending on the resolution and orientation of the user interface's screen. It should be usable on many different user interface devices. For in-cockpit use, a 7" form factor tablet is ideal. For lower resolution devices, you may find that changing the orientation to landscape is beneficial.

The PB-4 supports the notion of a "job".

Clicking the menu button pops up a menu with these items:

The connect button toggles the user interface - PB-4 connection state. The current state is indicated by the colour of the button:

If the browser page is reloaded from the PB-4 while connected or the browser is closed, the connection will be dropped.

The PB-4 will turn itself off automatically after 30 minutes of not being connected.

The polar chart shows the points that were captured during the balancing process. The chart may be panned and zoomed^[1]. If the PB-4 is connected and the Update checkbox is checked, the chart will be updated in real-time to show the current balance condition.

The current point is simply the most recent point sent from the PB-4 when the display is being updated in real-time or the point that has been selected in the points list when the display is not being updated in real-time.

Each point is plotted as a circle^[2], the colour coding of the plotted points are:

Figure 2.2. Polar chart - propeller balancing

The chart shows some text in yellow boxes that describes the current point:

The top-left box contains the tacho channel name (A or B) and the current point's propeller RPM.

The top-right box contains the accelerometer channel name (X, Y, X2 or Y2) and the current point's IPS and DEG values.

The bottom-right box contains the date & time the current point was measured.

The bottom-left box is only visible if there is a start point defined for the axis. It shows a “solution”, i.e. what adjustment needs to be made to the balance weight to improve the balance. The adjustment has the form ANGLE × SCALE. ANGLE is signed; a positive value means move the weight forward (in the direction of propeller rotation) that many degrees and a negative value means move the weight backward (opposite to the direction of propeller rotation). SCALE is a multiplier that specifies the required change in weight; e.g. a value of 1.2 means increase the weight by 20%, a value of 0.5 means halve the weight. So in the chart above, the solution is saying move the weight backwards 5° and keep the amount the same.

To the right of the polar chart are the Update check box, the points visibility menu and the points list.

To the right of the points list are a drop down menu and some buttons:

This dialog displays the detailed information for the selected point along with some text input boxes and buttons as shown in Figure 2.5, “Point details dialog - propeller mode”. To open this dialog simply click the selected point's row in the point list a second time. The buttons are:

Figure 2.5. Point details dialog - propeller mode

The text input boxes are:

The polar chart can optionally display a "spider" that may help the operator visualise where the balance weights need to be added. The spider's body is the start point and it has one leg for each weight site. The legs are numbered to match the weight sites and their orientation is derived from the polar points that have previously been captured for this job.

The idea is that just by looking at where the middle of the chart falls between the spider's legs you can see where the weight needs to be positioned. In the example below, leg 5 crosses the middle of the chart so the weight needs to be located at site 5.

Figure 2.6. Weight site spider

The spider is displayed after the start point has been set and at least one other point has been captured that has weight assigned to a site. To enable the spider, open the UI configuration dialog and in the Polar Chart section there is an option to set the prop mode weight site lines colour. Enter a colour, i.e. blue, save the configuration and reload the page.

The polar chart shows the points that were captured during the balancing process. The chart may be panned and zoomed^[3]. If the PB-4 is connected and the Update checkbox is checked, the chart will be updated in real-time to show the current balance condition.

The chart may show move lines (the red, green and blue lines in the above figure).

The current point is simply the most recent point sent from the PB-4 when the display is being updated in real-time or the point that has been selected in the points list when the display is not being updated in real-time.

Each point is plotted as a circle^[4], the colour coding of the plotted points are:

Figure 3.2. Polar chart - rotor balancing

The chart shows some text in yellow (or gold) boxes that describes the current point:

The top-left box contains the tacho channel name (A or B) and the current point's rotor RPM.

The top-right box contains the accelerometer channel name (X, Y, X2 or Y2) and the current point's IPS and DEG values.

The bottom-right box contains the date & time the current point was measured.

To the right of the polar chart are the Update check box, the point visibility menu and the points list.

To the right of the points list are a drop down menu and some buttons:

A profile configures the user interface for a particular type of aircraft or scenario. Each profile specifies a few values that can modify how jobs are displayed. Profiles can currently contain these values:

If a second accelerometer is mounted near the front of the machine, it is expected to be orientated such that its X axis is pointing to the right and its Y axis is pointing vertically upwards.

The following table lists the supplied profiles. The user can also define their own profiles (see Appendix B, User Interface Configuration).

Figure 3.6. Standard accelerometer orientation (top view)

This dialog shows the detailed information for the selected point along with some text input boxes and buttons as shown in Figure 3.7, “Point details dialog - rotor mode”. To open this dialog simply click the selected point's row in the point list a second time. The buttons are:

Figure 3.7. Point details dialog - rotor mode

The text input boxes are:

This dialog shows you the changes you have to make to the state of the rotor compared to the state at the time that point was captured.

Figure 3.8. Rotor balance solution dialog

	The suggested changes are relative values not absolute In words, the dialog in the above figure is saying reduce the weight on the master blade by 1 unit (or, equivalently, add 1 unit to the slave blade), reduce the chord adjustment by 9 units and reduce the pitch adjustment by 1 unit. The dialog also shows the absolute state of the rotor after the suggested changes have been applied.

The dialog shows how the polar points should move when the changes in the solution have been applied to the rotor. The white points indicate the initial positions and the orange points indicate the final positions. The effect of each adjustment (Span, Chord or Pitch) is shown as an appropriately coloured line.

There are checkboxes provided to select which adjustments and move lines are used when calculating the solution. You must have at least one adjustment and one move line enabled to be able to calculate a solution. Click the Recalculate Solution button to get a new solution after you have altered the selected adjustments or move lines.

The Apply Changes To Current Adjustments button does exactly that, it updates the current adjustments in the polar point list header with the calculated changes. Obviously, you still have to physically make those adjustments to the rotor!

The edit move line dialog is where you define your move lines. It shows a simplified polar chart so you can immediately see the effects of the changes you make. The orientation of the move line is defined by the positions of two nodes which are specified in this dialog along with their adjustment values. Each node has a position (given as Deg and IPS) and a value. The nodes are drawn as filled circles and their values are displayed in a small box.

Figure 3.9. Edit move line dialog

Normally, the move lines (and their nodes) are drawn on top of the polar points. This ensures that the node values are not obscured by any points. Obviously, this can mean that some points are hidden behind the move line nodes and so to make it possible to see those hidden points, while the chart is being panned, the points are drawn on top of the move lines.

On the right hand side of the dialog are various text entry boxes and a couple of checkboxes:

Name	Enter here the name of the move line (the software doesn't require it to be unique but you will get confused if it isn't!)
Adjustment	The adjustment this move line is associated with. One of None[a], Span, Chord or Pitch. When a move line is associated with an adjustment, the move line's colour, units and step are inherited from the specified adjustment and cannot be altered in this edit move line dialog. See Section 8, “Changing adjustment settings” for more information on changing adjustment settings.
Solidity	The percentage solidity of the move line (20, 50, 80 or 100%).
Colour	The colour used to draw the move line. What you will get when you click on this depends on the browser you are using. Some browsers will present a colour chooser widget when you click on this. If you're not so lucky it will probably get the chance to enter the colour as a number like #008000 (that's the value for the green move line shown above).
Units	The units of adjustment for this move line. This is just text, it doesn't feature in any calculations.
Step	When the solution is calculated, the resulting adjustment will be a multiple of this value. So if you are using washers for the units of adjustment and you only have washers of one size, then a step of 1 would be appropriate but if you also had some washers that weighed half as much, then a step of 0.5 would be appropriate because then the suggested amount of adjustment would be to the nearest 1/2 washer.
Visible	This needs to be checked to see the move line on the polar chart.
Active	This needs to be checked for the software to use this move line when calculating the balance solution.
[a] The None adjustment is provided for compatibility with jobs that were created by earlier versions of the PB-4 UI firmware that didn't support adjustments.

The three inbuilt adjustments (span, chord and pitch) are defined with sensible default settings. You may, however, alter these settings if you wish. To do so, click on the appropriate adjustment in the polar point list header and in the dialog that pops up, click Show Adjustment Settings. The dialog expands to show the settings.

Figure 3.10. Span Adjustment Settings

The adjustment's settings are:

The spectrum display shows vibration level (in IPS) plotted against RPM. If the PB-4 is connected and the Update checkbox is checked, the display will be continuously updated to show the latest spectrum received from the PB-4. The Axis 1 menu (see below) controls which axis the displayed spectrum is sourced from.

In the top right-hand corner are shown:

Figure 4.2. Rotor spectrum with line info box

If the rotor/propeller RPM is known, the region of the spectrum around that RPM is displayed in red and if any line labels have been defined, they will be displayed in a box above their respective lines. Line labels x1 and x2 are shown in the figures.

The bottom 1/3 of the display is the scroll zone. When zoomed into the display, the spectrum may be scrolled left or right by clicking and moving in the scroll zone. On computers with a keyboard and a mouse you can also scroll using shift-mousewheel.

Clicking above the scroll zone displays a cursor line and an info box which contains information about the spectral line below the cursor. The information displayed is the line's vibration level (IPS), frequency (RPM) and ratio of the line's RPM and the propeller/rotor RPM.

Clicking in the middle 1/3 of the display moves the cursor line to the position of the click. Clicking in the top 1/3 of the display moves the cursor one line left or right depending on which side of the cursor you clicked.

To the right of the spectrum display are the Update and Show All checkboxes and the lines and spectra lists.

To the right of the spectra list are some buttons:

The Data Options button toggles the display of the data options box (visible above), the options are:

The section expands to show a list of jobs known to the PB-4, click on one to load it into the browser so it becomes the current job.

The section expands to show 3 controls:

The section expands to show a text input box into which you enter the new name for the current job - it must not be the same as an existing job name. Press enter to action the rename.

The section expands to show 2 sub-sections. The first sub-section contains 3 buttons:

Pressing one of those buttons will ask you to confirm your action. Think twice here because the deleted data cannot be un-deleted. However, the data stored on the PB-4 can be exported (before you delete it, not after!) and subsequently imported again. So it is possible to back up your data to your computer.

The second sub-section contains a selector that lets you choose which jobs you wish to delete and a button to carry out the action which you will be asked to confirm. Once confirmed, all data associated with the selected jobs will be deleted from the PB-4. Be very careful!

	Due to limitations in iOS, it is not possible to save/restore data to/from an ipad or iphone unless 3rd party software (e.g. Dropbox) is installed on the UI device.

The section expands to show controls to save and restore PB-4 data.

A drop-down list of known jobs is provided so you can select the jobs whose data is to be saved. Multiple jobs can be saved at the same time. When the jobs to be saved have been selected, press the Save Selected Jobs To File button.

Pressing the Select PB-4 Archive To Restore button will pop-up a file chooser that lets you select the PB-4 data archive that you wish to load onto the PB-4. Because all job names must be unique, if the archive file contains any jobs with the same name as existing jobs, the name of the new job will have a # character appended.

This section expands to show several sub-sections:

6.2. PB-4 hardware configuration

This sub-section contains controls for configuring various aspects of the PB-4 hardware.

6.2.1. Set the battery level to 100%

Normally, when the exhausted batteries are replaced with a fresh set, the PB-4 detects that they have been changed and resets the battery level to 100%. If it fails to detect the changed batteries, pressing the New Batteries Installed button will reset the battery level to 100%.

6.2.2. Selecting the tachometer input

The PB-4 supports two tachometer inputs (A and B), clicking the Select Tacho Input button lets you choose which tacho input will supply the tacho signal. Input A corresponds to the 3 pin socket tacho input and input B corresponds to the jack socket tacho input. Unless you have a second tacho connected through the jack socket this should always be set to A.

6.2.3. Accelerometer axis calibration

Clicking the Select Axis To Calibrate button pops up a menu of accelerometer axis names (X, Y, X2 and Y2). Select one of those names to start the accelerometer axis calibration procedure. As the accelerometers are sensitive to gravity, we can use the force of gravity (1 G) to calibrate the accelerometer using the following steps:

1. Measure the output from the accelerometer with the axis being calibrated pointing straight upwards (+1 G applied).

2. Invert the accelerometer so that the axis being calibrated is now pointing downwards and measure the output again (-1 G applied).

3. Subtract the second value from the first and divide by 2 and that gives the accelerometer output for 1 G of acceleration which can be saved as the calibration value.

The user interface takes you through these 3 steps. At each step, a dialog box appears telling you what to do. It's very easy.

Figure 6.2. Accelerometer orientation during calibration

6.4. Firmware upload

	Due to limitations in iOS, it is not possible to load firmware files from an ipad or iphone unless 3rd party software (e.g. Dropbox) is installed on the UI device.

This section expands to show two buttons:

• Pressing the Select PB-4 CPU Firmware File To Upload pops up a file chooser that lets you select the file containing the new PB-4 CPU firmware you wish to install. Select the required file and the contents will be uploaded to the PB-4 and installed.

• Pressing the Select PB-4 Wi-FI Firmware File To Upload pops up a file chooser that lets you select the file containing the new PB-4 Wi-Fi firmware you wish to install. Select the required file and the contents will be uploaded to the PB-4 and installed.

Please see the PB-4 hardware manual for more information regarding the uploading of firmware.

	Due to limitations in iOS, it is not possible to load user interface files from an ipad or iphone unless 3rd party software (e.g. Dropbox) is installed on the UI device.

The section expands to show two buttons and a checkbox:

This section expands to show a text input box into which you can enter the IP address (network address) that will be used to connect the browser to the PB-4 when you click on the connect button. You do not normally need to do this because the browser knows the PB-4's IP address because that's where the user interface web files (HTML, etc.) you are currently viewing were loaded from. The only time you would enter an IP address here is when you are loading the user interface web pages from a different server than the PB-4.

Propeller mass imbalance can be a major source of vibration. However, there are other sources of vibration as well. To minimise the overall vibration level and to make the dynamic balancing process more effective, all other sources of vibration must be minimised before dynamic balancing is carried out.

	Unless the engine is running smoothly, there is little point in trying to balance the propeller. Carburettor imbalance, dirty plugs, loose engine mounts and general wear and tear are just some of the reasons why the engine could be producing excess vibration.

Propellers with an adjustable blade pitch will produce a lot of vibration if all the blades are not set to the same pitch. This is critical: if a blade's pitch differs from its neighbours' by even a fraction of a degree, it will produce vibration that appears to be caused by mass imbalance but cannot actually be removed by mass balancing.

	Before attempting to dynamically balance a variable pitch propeller (either ground adjustable or in-flight adjustable), confirm that the blades' pitch are equal to within the tolerance specified by the propeller's manufacturer (typically, 0.25°).

When an object rotates around an axis, if the mass of the object is not uniformly distributed around that axis, a force (the centripetal force) will be generated and will cause vibration. As the magnitude of the force is proportional to the square of the rotational velocity, at high RPMs (high rotational velocity) even a small mass imbalance in a propeller will generate an appreciable amount of force (and hence vibration). This vibration can be measured by mounting a sensor on the engine as close to the propeller as possible. Conventionally, the magnitude of a propeller's vibration is reported as a peak velocity in units of Inches Per Second (IPS).

A propeller can be statically balanced in the workshop using a static balancing tool. This often involves suspending the propeller from its central axis. If the propeller is statically balanced, the blades should be level^[9]. If one blade is heavier than the others (or its centre of mass is further from the centre of the propeller), it will dip towards the floor. If this occurs, weight can be added to the hub on the opposite side of the central axis to the dipping blade to bring the propeller level.

All propellers should be manufactured with blades that have equal mass (and mass distribution) and so a new propeller should not require static balancing. Propellers that have suffered damage to the blades (stone chips or tip abrasion) may well benefit from being statically balanced.

While statically balancing a propeller is worthwhile, the best results will be obtained if the propeller is dynamically balanced together with the spinner.

Dynamic propeller balancing involves measuring the actual rotational vibration generated at a realistic propeller RPM and then adding weights to the propeller hub or spinner backplate to minimise the measured vibration level. Because the balancing operation is carried out with the propeller and spinner attached to the engine, the best possible solution is obtained.

The vibration is measured using a sensor known as an accelerometer. The accelerometer is securely attached to the engine as close to the propeller as possible and it measures the acceleration of the front of the engine in one direction (normal to the propeller shaft). If the propeller is out of balance, as the centre of mass rotates around the axis of rotation, the resulting centripetal force tries to pull the propeller (along with the spinner and engine) towards the centre of mass. This rotating imbalance force acts on the mass of the engine/propeller combination and accelerates it. It is this acceleration that is measured by the accelerometer.

Figure 7.1. Sine wave

If the accelerometer was very selective and measured only the vibration caused by the rotating out-of-balance propeller, the signal it produced for one rotation of the propeller would look like a sine wave as shown here. In reality, the measured acceleration waveform is much more complex than a simple sine wave. This is mainly because of the vibration generated by the engine and also the turbulence generated by the rotating propeller blades. The dynamics of the engine mountings also affect the waveform.

The balancer's processing unit digitises the measured acceleration waveform and uses the resulting numbers to calculate the magnitude of the vibration signal. This magnitude is reported as a peak velocity in units of Inches Per Second (IPS).

The accelerometer senses the magnitude of the vibration but more information is required to carry out the balancing process. This is because it is not sufficient to know just the magnitude of the vibration signal. It is also necessary to know the phase of that signal. The phase of the signal is the relationship of the signal waveform to the angular position of the propeller. Given the phase information, it is possible to determine where the weight is required to be added to reduce the vibration. By detecting when one particular propeller blade passes an optical sensor, the balancer can measure and report the phase of the vibration waveform. The optical sensor also works as a tachometer to measure the propeller RPM.

	Propellers can kill. Make sure that the engine ignition is switched off before touching the propeller. Always assume that the engine could fire when the propeller is being moved. Make sure that the aircraft is securely chocked or tied down while carrying out the balancing process.

Please see the PB-4 Hardware Manual for a description of the PB-4 sensors and how they are attached to the aircraft.

For maximum accuracy, the dynamic balancing process should only be carried out in light winds. Ideally, the wind should be less than 5 kts. The aircraft should be positioned so that it is pointing into any wind.

	Before you start the engine, check that the Polar Options are all set appropriately. Propeller mode should be selected and the point smoothing, number of weight sites and PSRU ratio set to suitable values.

Make sure the engine is thoroughly warm before taking any readings.

Firstly, you need to decide what propeller RPM you are going to use while balancing. For a typical propeller, an RPM in the range 1500-2000 is often a good choice. Using the polar tab, observe the movement of the current polar point. If you think it is necessary, adjust the throttle to find the RPM that minimises the variation in the current point's position. When you adjust the throttle it will take a few seconds for the point to settle down enough to allow you to capture a reading.

	Once you have determined the best RPM to use, it is important to use the same RPM for each balancing run so that you get consistent results.

With a steady RPM being reported by the balancer, press the Capture button to capture a polar point. The point's data will be entered into the list of polar points for the current job.

Capture a few points – if the propeller is obviously out of balance, the points will be clustered together some distance away from the centre of the chart.

Now stop the engine and double-check that the ignition is switched off.

If the vibration level is already 0.15 IPS or less, the propeller can be considered reasonably well balanced – in ideal conditions, the balancer is capable of balancing a propeller down to about 0.03 IPS so you may wish to continue the process to achieve a better result. If you want to improve the balance, you must carry out the balancing procedure as described in the next section.

	To reduce battery drain in the PB-4 and the tablet, it is best to disconnect the user interface from the PB-4 when you are not actually capturing points or viewing the live data. When you are ready to capture a new point, just reconnect.

It is the operator's responsibility to ensure that any procedures or guidelines that have been issued by the manufacturers of the propeller, engine or aircraft or some other agency (e.g. the FAA/CAA/LAA/BMAA), that specify how the propeller is to be balanced, are adhered to. The following instructions describe the balancing process from the point of view of operating the balancer and determining where balance weights are to be attached. The exact detail of how balance weights are attached to the hub or spinner backplate is beyond the scope of this document. If you have any doubt, please consult your inspector/engineer.

	Weight sites are numbered from 1 to the number of sites. Considering the direction of normal propeller rotation, site 1 will pass a fixed point (e.g. the tacho) before site number 2, and so on.

The position and the mass of the required balance weight(s) is determined as follows:

When the balancing has been completed, double-check that all balance weights are securely attached. If you have been using temporary weights to carry out the balancing, they should be replaced with permanent weights whose mass and position are such that they have the same effect as the temporary weights. If in doubt, recheck the balance once the permanent weights are installed.

Remove the sensors and the tape from the propeller blade. Make an entry in the appropriate log book to record the vibration level achieved and the RPM used.

This section provides answers to common problems that can arise when balancing.

Mass imbalance is one of the causes of rotor vibration and the PB-4 system can help you balance the rotor to eliminate that vibration. Other vibrations may also be present. In particular, gyroplanes often suffer strong vibration at twice the rotor frequency. This “× 2” (times 2) vibration is often much larger than the vibration due to imbalance and so even when the rotor has been mass balanced satisfactorily, vibration will still be noticeable to the occupants.

Figure 8.1. Rotor spectrum with large × 2 peak

The above spectrum is from a gyroplane rotor that shows the very large × 2 vibration still present after the rotor was balanced. You can see that the vibration at the rotor RPM (372) was only 0.08 IPS but the × 2 vibration at 750 RPM was 4.23 IPS, that's around 50 times larger!

Unlike, rotor mass imbalance, the × 2 vibration cannot be suppressed by simply adding weights. It is fundamental to the geometry of a (2 bladed) rotor system and the physical properties of its components (blades, hub, mast, etc.) The × 2 vibration can be caused by a variety of reasons. Some possibilities are:

Furthermore, the amount of × 2 vibration being produced is influenced by the flight conditions (rotor speed, airspeed, etc.) At this time, the PB-4 system can only report the magnitude of the × 2 vibration and it does not offer any suggestions as to how the level of vibration can be reduced. Perhaps in the future when the causes of the × 2 vibration are better understood, it will be able to make helpful suggestions.

Gyroplane rotors are balanced by making these adjustments:

Figure 8.2. Rotor Adjustments

What you need to know to balance the rotor is how much change (magnitude and sense) is required for each of these adjustments. You can determine that information using a polar chart that has been augmented with move lines. A move line is literally a line drawn on a polar chart that shows the direction a polar point would move when a particular adjustment is made to the rotor. A move line is required for each adjustment you are going to alter. Each accelerometer axis (X and Y) requires its own set of move lines.