The PB-4 balancing system has these main components:

The PB-4 uses Wi-Fi to communicate with the user interface device which can be any computer that supports a modern browser and Wi-Fi. Obviously, the most suitable devices for use in aircraft are lightweight tablets. A 7" format tablet is a good choice for use while balancing as it is not too bulky but still has reasonable screen resolution. Later, you can look at the results on a device with a bigger screen, e.g. a laptop computer. The following text simply calls the user interface device a tablet.

1.1. Wi-Fi network components

The PB-4 uses a Wi-Fi network to communicate. Most commonly, a Wi-Fi network consists of an access point and one or more stations. The network traffic to and from the stations is routed through the access point. The PB-4 can operate as either a Wi-Fi station or as a Wi-Fi access point depending on where you are located at the time.

1.1.1. PB-4 is the Access Point

When you are at the airfield doing the balancing, you would not normally have an access point available. Fortunately, the PB-4 can be the access point (as well as being a balancer). By starting the PB-4 in AP mode, it will be an access point and the tablet will be able to communicate with it directly as shown below. Note that unless the tablet has some other means of accessing the internet, it will only be able to talk to the PB-4 in this configuration.

Figure 1.1. Wi-Fi roles when PB-4 is in AP mode

1.1.2. PB-4 is a station

When you are back indoors, your tablet will most likely be already configured to use an existing access point at that location. The PB-4 can be started as a station (STA mode) and it will then use the same access point as the tablet so they will be able to communicate. In this configuration, your tablet will be able to access the network (internet, printers, etc.) as normal.

Figure 1.2. Wi-Fi roles when PB-4 is in STA mode

For the PB-4 to be able to talk to the access point, it needs to know the access point's SSID (Wi-Fi network name) and password. The PB-4 supports Wi-Fi Protected Setup (WPS) which makes setting up the access point credentials easy. The SSID and password may also be entered into the PB-4 manually if required.

	One way of remembering which mode you need to use is that when you are "at the AirPort" use AP mode and when you "STAy at home", use STA mode!

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.

The PB-4 is powered by 4 x 1.2V AA NiMH rechargeable batteries. The batteries are easily accessible via a hatch in the bottom of the PB-4 case. The PB-4 itself cannot charge the batteries, they have to be removed and charged in an external charger. It is also possible to use non-rechargeable 1.5V AA batteries in the PB-4.

The PB-4 also contains a CR2032 3V coin cell which provides backup power. This battery will require replacing every now and then.

See Appendix A, Battery Charging & Replacement for more information on battery charging and replacement.

Figure 1.3. PB-4 panel

The panel contains:

Please operate the PB-4 within the following environmental limits:

To carry out the balancing process, you will need the following items in addition to the balancer kit:

The following points should be observed regarding positioning the aircraft for a propeller balancing session:

Remove sufficient cowlings to gain access to the front of the engine. Mount the accelerometer (40mm square with a 6mm hole through the middle) as near to the front of the engine as possible with the accelerometer's sensing axis pointing directly at the propeller's centre line.

The accelerometer's X axis coincides with the direction of the sensor's cable socket and its Y axis is at 90° to the direction of the cable socket.

Figure 2.1. Accelerometer axes and orientation

	The sensing axis used must intersect the axis of rotation of the propeller. Remember to configure the job to use the correct axis.

Note that the accelerometer does not have to be directly above the propeller's axis of rotation. However, to get the best results you should not mount the accelerometer such that the sensing axis is parallel with the engine's cylinders.

On a Rotax 4-stroke engine that doesn't have a vacuum pump attached, the best place to mount the accelerometer is on the rear of the gearbox using one of the available tapped holes and the supplied M6 screw and washer.

Figure 2.2. Accelerometer mounted on a Rotax 912 gearbox

If the accelerometer cannot be bolted directly to the engine, some form of bracket will be required. Obviously, the details of this are engine specific but it could be as simple as a strip of metal with a hole drilled at each end. If a bracket is used, it must be sufficiently stiff to ensure that the accelerometer does not move with respect to the engine.

However the accelerometer is mounted, it must not be subjected to excessive temperatures. The temperature of the sensor should not exceed 85° C. If necessary, thermally insulating material can be sandwiched between the accelerometer and the engine (or bracket) to reduce the amount of heat conducted to the accelerometer. If the surrounding area will be very hot, the accelerometer could be wrapped in thermally insulating material (once the cable has been attached).

	The accelerometer is robust but may be damaged if dropped on a hard surface.

It is preferable to refit the engine cowling to minimise the turbulence generated by the airflow from the propeller. For some aircraft, the cowling will have to be refitted to provide a suitable mounting position for the optical sensor. However, if the balance weights are to be added to the rear of the spinner backplate, it may pay to leave the cowling off (if possible) during the balancing process so that it is easier to gain access to the weights. Once the balancing has been completed, the cowling could be replaced and a final reading taken to determine the level of vibration achieved.

Owing to the variation in aircraft cowling shapes and sizes, only generic instructions can be provided here. You may find that a little experimentation is required to obtain the best results.

The tacho sensor is drilled for a 6mm fastener and so it may be securely bolted to the airframe using a suitable bracket. With an adequately strong bracket, it would be safe for the aircraft to be flown with the sensor attached in this way (assuming no other safety issues arise).

For ground use only, a flexible plastic mounting plate is provided. The sensor is bolted to the plate and then the plate may be taped to the aircraft cowling. The supplied soft washer should be placed between the tacho sensor and the mounting plate to increase the friction as this will reduce the fastener torque required.

Figure 2.3. Tacho sensor with flexible mounting plate

	This method of mounting the tacho sensor on the cowling is perfectly adequate when the aircraft is stationary on the ground. Under no circumstances should the aircraft be flown with the tacho sensor attached using the flexible mounting plate.

If the propeller is a pusher, i.e. the cowling is in front of the propeller rather than behind, extra care should be taken to ensure that the tacho sensor cannot become detached from the cowling and hit the propeller blades. As a minimum, tape the accelerometer cable to the cowling so that it will restrain the tacho sensor in the event of it becoming detached from the cowling. If you have any doubt as to the security of the tacho sensor, don't risk destroying it and the propeller.

Position the tacho sensor such that the sensor block is pointing towards the propeller. If the sensor's orientation is correct, the blades will sweep across the sensor block as the propeller rotates. The distance from the front of the sensor to the propeller should be in the range 5-75cm.

Figure 2.4. Tacho sensor mounted on cowling

Figure 2.4, “Tacho sensor mounted on cowling” shows the tacho sensor mounted an aircraft cowling.

To detect the propeller RPM reliably when the propeller blades are reflective, the tacho sensor should be positioned such that the angle of the LED beam is not normal to the faces of the propeller blade. Rotate the tacho sensor so that it is approximately 30° from the normal (either in front of or behind the normal). Figure 2.5, “Tacho sensor angle of incidence” illustrates this. Figure 2.5. Tacho sensor angle of incidence If the angle is too small, the tacho sensor will tend to detect the other blades (especially if they are highly reflective) and the RPM will appear erratically too high. If the angle is too large, the blade with the reflective tape will not be reliably detected and the RPM will appear zero or erratically too low.

With the engine ignition switched off, rotate the propeller so that one blade lies directly on the sensing axis of the tacho sensor. Make sure that the area on the back of the blade where the tape is going to be attached is clean. Apply a strip of 25mm wide masking tape to the back of the propeller at the point that the red beam will hit the blade. Wrap the tape a short distance around the leading edge of the blade but don't wrap it around the trailing edge.

	The tape must be oriented such that it is parallel to the tacho sensor's body. This ensures that as the blade sweeps across the tacho sensor, the maximum length of reflective tape will be seen by the sensor. This may mean that the tape is not at 90° to the leading edge of the blade but that doesn't matter.

Now put a strip of the reflective tape on top of the masking tape, it should extend to close to the leading edge but not actually wrap around the leading edge.

If you subsequently find that the tacho sensor cannot reliably detect the RPM, verify that the tape really is in the correct position. You may find that adding another strip of reflective tape next to the first strip will improve the situation.

When the tacho sensor is connected and the PB-4 is powered up and connected to the tablet, the red LED will flash regularly. If the tacho sensor is receiving a large amount of reflected light, the LED will stop flashing. To check that the sensor is correctly orientated, move the propeller so that the tacho sensor's beam is pointing at the most reflective portion of the background (but not the tape). If the LED is continuously on, rotate the sensor until the LED starts flashing. Check that the tape still passes through the LED beam.

Connect the accelerometer and tacho sensor to the PB-4 using the supplied cables (4 pin connectors for the accelerometer and 3 pin connectors for the tacho sensor). Make sure the connectors' retaining collars are screwed down (take care to only rotate the metal retaining collar and not the plastic body of the connector).

Any slack in the cables should be taken up by coiling the cable and then applying a few strategically placed pieces of masking tape to stop the cable flapping around in the propeller breeze.

Figure 2.6. Cable taping

If you tape the cables as shown in the above figure, they are unlikely to come adrift.

	To obtain the best results, the cables should be kept away from sources of electrical interference such as ignition leads, magnetos/ignition units, generators/alternators/regulators and their associated wiring. Be especially careful to ensure that the cable cannot get close to rotating components or very hot surfaces.

The PB-4 enclosure can be positioned in the cockpit if the cables are long enough or even just on the ground. Remember that Wi-Fi signals cannot pass through metal and so if the aircraft has a metal fuselage the person operating the tablet will have to be able to see the PB-4 enclosure.

For gyroplane rotor balancing, the accelerometer and the tacho sensor must be mounted on the rotor head using one or more brackets. Exactly how this is achieved is dependent on the design of the rotor head. A common configuration (e.g. for AutoGyro & ELA gyros) is to position the reflective tape on the underside of the prerotator disk with the tacho sensor mounted below the disk. Another common configuration (e.g. for Magni gyros) is to mount the sensors aft of the mast with the reflective tape attached to the slave rotor blade. However the sensors are mounted, you must ensure that the reflective tape is always aligned with the beam from the tacho sensor whatever the position of the rotor head. i.e. moving the aircraft's control stick should not affect the alignment.

The following general points should be observed:

The standard accelerometer orientation advocated by Smart Avionics is to point the X axis to the right (when viewed from above) and point the Y axis forward.

Figure 3.1. Standard sensor orientation (top view)

The PB-4 is supplied with sensor mounts for popular gyro types, they are described below.

1.1. ELA / AutoGyro sensor mount

This mount is fastened to the right hand side of the rotorhead. It is compatible with ELA and early AutoGyro (MTO) rotorheads. The accelerometer is orientated such that the X axis is pointing to the right of the machine and the Y axis is pointing forward. Note that the tacho sensor has been rotated to approximately 30° from the normal to avoid spurious reflections from the prerotator disk.

	The reflective tape is attached to the bottom of the prerotator disk with the master blade in the 12 o'clock position.

	Use one of the ELA, AutoGyro or Standard rotor profiles with this mount to match the orientation of the sensors.

Figure 3.2. Sensors mounted on an MTO rotor head (rear-right view)

1.2. Magni sensor mount

This mount is used with Magni gyroplanes. It is strapped to the rear of the prerotator drive. The accelerometer is orientated such that the X axis is pointing to the right of the machine and the Y axis is pointing forward.

	The reflective tape must be attached to the bottom of the slave blade.

	Use either the Magni or Standard rotor profiles with this mount to match the orientation of the sensors.

Figure 3.3. Sensors mounted on a Magni prerotator drive

1.3. AutoGyro Mk2 sensor mount

This mount is used for AutoGyro gyroplanes fitted with the Mk2 rotor head. The accelerometer is orientated such that the X axis is pointing to the left of the machine and the Y axis is pointing rearward. This is different from the standard accelerometer orientation described above but as long as the correct rotor profile (AutoGyro-RH2) is used, all will be OK.

	The reflective tape must be attached to either the bottom of the slave blade or to the bottom of the prerotator disk immediately below the slave blade.

	Use the AutoGyro-RH2 profile with this mount to match the orientation of the sensors and the position of the tape.

Figure 3.4. Sensors mounted on an AutoGyro Mk2 rotor head (front-left view)

Figure 3.5. Sensors mounted on an AutoGyro Mk2 rotor head (rear view)

Figure 3.6. Sensors mounted on an AutoGyro Mk2 rotor head (left view)

This sensor mount is attached to the AutoGyro Mk 2 rotor head using two 50mm M6 cap screws.

Figure 3.7. Exploded view of the AutoGyro Mk 2 rotor head sensor mount

Use soft washers between the sensors and the mount to increase the friction so that less fastener torque is required.

When using the ELA / AutoGyro mount, the tape is attached to the bottom of the prerotator disk.

When using the Magni mount, the tape is attached to the bottom of the slave blade.

When using the AutoGyro Mk2 mount, you have the option of attaching the tape to either the bottom of the slave blade or the bottom of the prerotator disk.

A simple procedure for positioning the reflective tape is:

Figure 3.8. Tacho shining onto reflective tape attached to prerotator disk

The PB-4 enclosure must be constrained so that it cannot become loose in flight. Preferably, it will be located inside the aircraft's cockpit where it could be held (but not by the pilot!) or tucked into a pocket, etc. If it is to be mounted outside of the cockpit, it must be securely attached to a properly designed and constructed mount.

	It is the operator's responsibility to ensure that the PB-4 enclosure is safely constrained and that it cannot become a flight hazard.

	When the sensors, cabling and PB-4 have been installed, verify that the normal range of movement of the rotor head is still available and that the cables cannot become tangled in the controls, engine or propeller.

The PB-4 kit includes a push button with cable that can be plugged in the PB-4's jack socket. Pressing the push button will capture a polar point and/or a spectrum even if the tablet is not connected to the PB-4. This means that you can capture data simply with the push button without even taking the tablet flying. The capture button is equipped with a velcro strap which can be used to attach it to the control stick or some other convenient location.

Please see the user interface manual for details of how the offline capture button is configured and enabled.

Just a few words here to get you started. When you load the PB-4 user interface into your browser, it will display a splash screen for a few seconds and then show an initial screen similar to Figure 4.1, “Initial screen”.

Figure 4.1. 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, a couple of important buttons are displayed along with the name of the current job. The buttons are:

For the full description of how to use the PB-4 browser based user interface, please go to Menu / Help.

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 lower resolution devices, you may find that changing the orientation to landscape is beneficial.

The UI firmware consists of the web files (HTML, CSS, Javascript) that are loaded into the tablet's browser. New UI firmware will be packaged as a file named pb4ui-version.zip.

To install new UI firmware, load the PB-4 UI into a browser and then go to Menu / Options / Upload UI Files where you can select the zip file to upload. The contents of the zip file will be uploaded to the PB-4 and the next time you load the UI into your browser, you will be using the new files.

In the unlikely event of this procedure failing and rendering the unit unusable, please contact Smart Avionics for instructions on how to recover.

The PB-4 CPU firmware is responsible for digitising the vibration signals, calculating the IPS/DEG values, doing the spectral analysis, storing the results, etc. New CPU firmware will be packaged as a file named pb4-version.fw.

To install new CPU firmware, load the PB-4 UI into a browser, connect to the PB-4 and then go to Menu / Options / PB-4 Configuration / Upload PB-4 CPU Firmware where you can select the .fw file to upload. The contents of the .fw file will be uploaded to the PB-4 and the unit will restart and then program the CPU with the new firmware. Do not turn the PB-4 off while this is being done! When the programming has finished, LED 1 should flash green quickly. Press the on/off switch and the PB-4 will turn off. Next time you turn it on, the new firmware will be used.

In the unlikely event of this procedure failing, LED 1 will flash red quickly. Press the on/off switch and the PB-4 will turn off. Because the update failed, the PB-4 will revert to using the firmware that was installed when it was made. You can retry the procedure and if it fails again, please contact Smart Avionics for advice.

The Wi-Fi Firmware is installed into the PB-4's Wi-Fi module. New Wi-Fi firmware will be packaged as a file named wifi-date.dfu.

To install new Wi-Fi firmware, load the PB-4 UI into a browser, connect to the PB-4 and then go to Menu / Options / PB-4 Configuration / Upload PB-4 Wi-Fi Firmware where you can select the .dfu file to upload. The contents of the .dfu file will be uploaded to the PB-4 and the Wi-Fi module will be programmed with the new firmware. Do not turn the PB-4 off while this is being done! When the programming has finished, LED 1 should flash green quickly. Press the on/off switch and the PB-4 will continue.

In the unlikely event of this procedure failing, LED 1 will flash red quickly. Press the on/off switch and the PB-4 will continue. Because the update failed, the PB-4 may now not be accessible via the Wi-Fi. If that happens, it is likely that the unit will need to be returned to Smart Avionics to be made usable again.