RPX Technologies DynaVibe Classic User manual

DynaVibe Classic
User Manual
Version 1-09
Aug 2015
WWW.RPXTECH.COM

Table of Contents
Introduction..................................................................2
Pre-Balance Inspection.................................................3
Equipment Performance and Calibration......................6
Precautions ...................................................................6
Secure Cabling .............................................................6
Installation of Equipment .............................................8
Remove Cowling..........................................................8
Mount the Accelerometer and Optical Pickup..............8
Mount Reflective Tape on the Propeller.......................9
Using the DynaVibe ...................................................12
Attach the DynaVibe..................................................12
Start Your Engine.......................................................13
Averaging...................................................................14
Limitations..................................................................14
Balance / Analysis......................................................15
Clock the Prop and Change Weight............................15
Completing Balance ...................................................17
Documentation ...........................................................17
Troubleshooting..........................................................18

Important Notice
Any system that distracts a pilot while operating an aircraft is a safety
hazard.
During the balancing procedure please use extreme caution. Be very
careful with cables and components, especially on pusher type
aircraft. ALWAYS confirm the ignition is off before rotating the
propeller.
Areas of this manual will highlight specific safety concerns while
operating the dynamic balancing system. Please review these before
operating the system.

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Introduction
A rotating mass such as an engine crank, propeller, propeller extension, or
starter ring will always have small imbalances and tolerance variations. Those
variations, upon assembly, may cause eccentricity in the mass of the rotating
components, which generates vibration in the engine and airframe. In most
cases, those mass eccentricities are designed to cancel and provide a smooth
operation.
Vibration can cause damage throughout the aircraft, including; the crank
bearings, engine mounts, firewall, instrument panel, etc. Vibration causes
accelerated wear and fatigue on equipment and passengers. The negative
effects of vibration can be reduced by dynamically balancing the aircraft’s
rotating assembly, balancing the crank, prop extension, propeller, spinner, all
as one unit.
Dynamic balancing is accomplished by attaching a sensor to the unbalanced
equipment. By using a device to monitor the speed and position of the
rotating mass (propeller - crank) the dynamic balancer is capable of
determining the vibration caused by the unbalanced assembly. Corrections to
the assembly can then reduce the vibration.
While not all vibration can be eliminated, any reduction in vibration will
reduce fatigue and damage. Some vibration from engine combustion, gear
reductions, and accessories will not be affected by dynamic balancing.

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Pre-Balance Inspection
The pre-balance inspection is very important. An initial evaluation of the
propeller and engine can greatly reduce troubleshooting later in the process.
Most dynamic balancing issues can be resolved by a good pre-balance
inspection.
Airworthiness Directives / Service Bulletins
The first step in the pre-balance inspection is to review all available
Airworthiness Directives (AD) and service bulletins for the propeller and
powerplant. ADs and service bulletins will often contain specific information
about problems, updates, or other issues pertaining to the particular propeller
and powerplant.
Determine Applicable procedure
For aircraft or propeller manufacturers that provide procedures for dynamic
balancing, propeller balancing is not considered a major airframe alteration.
When approved aircraft and propeller manufacturer's procedures are not
available, there are other acceptable dynamic balancing procedures. Dynamic
balancing of propellers using FAA-approved or FAA -accepted dynamic
propeller balancing procedures is not considered a major propeller repair
unless the propeller static balance weights are altered. Reference FAA
Advisory Circular 20-37E “Aircraft Propeller Maintenance.”
Blade Inspection
The propeller blade should be closely inspected for any damage to the
propeller and general condition. Any maintenance that needs to be performed
Example: Certain combinations of engines and
propellers may require modified dampers due
to increased torque impulses.

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should be completed prior to dynamic balancing. Any dent or chip repair,
painting, or finish treatments should be completed before proceeding.
Reference FAA Advisory Circular 20-37E “Aircraft Propeller Maintenance”
and FAA Advisory Circular 43.13-1B “Acceptable Methods, Techniques, and
Practices - Aircraft Inspection and Repair”Chapter 8.
Spinner Installation
Prior to dynamic balancing, the spinner should be removed and inspected.
The spinner should be checked for any mass imbalances caused by foreign
material, missing screws, or damage. The attachment bulkheads should be
inspected for cracks or damage and repaired as required.
There are instances where spinners have been installed in such a manner as to
allow the front of the spinner to move relative to the propeller. If the spinner
structure has any flexibility, it will move from one side to another at high
RPM, causing the out-of-balance location to shift periodically. The spinner
should be firmly mounted and should not move when laterally loaded.
Blade Track and Pitch
It is important to determine that the blade is tracking correctly. If the blade is
mounted on an irregular surface, if there is debris under the blade, or the blade
is bent it will be impossible to balance the aircraft because the blade will be
aerodynamically out of balance. An aerodynamic imbalance is similar to P-
factor, an asymmetric lift between the blades.
Example: Mud daubers, wasps, and other
insects may nest inside the spinner housing
in only a few weeks.

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Check blade track and pitch
The simplest way to check for blade track is to position a wood block or other
rigid structure next to a blade tip. Then rotate the blade carefully (avoid
moving the aircraft) to the next blade and verify that the blade tip is in the
same relative position as the previous blade. You may need to remove the
spark plugs to allow the engine to rotate freely. If one blade is positioned
differently from another, this indicates that either the blade is bent or the
installation is unacceptable. Again, a dynamic balancer will not adequately
correct an aerodynamic imbalance. According to FAA Advisory Circular
43.13-1B, each blade track should be within 1/16 of an inch.
Example: If a small metal chip or burr is
allowed between the propeller and prop flange,
then one blade will have a higher angle-of-
attack than another blade, causing a vibration.
CAUTION:
Verify ignition and fuel are off
prior to moving propeller

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Any error in blade track should be investigated thoroughly and eliminated.
This may require that the propeller be pulled off the aircraft and sent to a
propeller repair station.
Existing dynamically balanced weights
Once the pre-balance inspection is complete, record the position and weight of
each dynamic balance correction weight previously mounted. Remove any
existing dynamic balancing weights.
Static balance weights, installed by a propeller repair station, should not be
removed. Only a propeller repair station may modify static balance weights.
Equipment Performance and Calibration
Equipment used on certified aircraft must be inspected and calibrated. The
DynaVibe is available with National Institute of Standards and Technology
(NIST) traceable calibration. Contact RPX for further information.
Precautions
Secure Cabling
Secure all cabling from the accelerometer and the optical pickup to the engine
and aircraft using tape and zip ties as needed. Route the cabling into the cabin
of the aircraft. Cables should not be allowed to hang free as they may become
entangled in rotating equipment. For pusher aircraft and rotorcraft, this can be
particularly dangerous. The cabling must always be secured and any doors or
loose cowlings should be thoroughly secured to prevent damage during engine
run-up.

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Secure all cabling
CAUTION:
Verify ignition and fuel are off
prior to moving propeller
CAUTION:
Rotate the propeller slowly to confirm clearance of
all components.
When you add weight, confirm that you have not
introduced any clearance issues.
Confirm that bolts are not protruding into the
cowling, starter, alternator, or other components!

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Installation of Equipment
Remove Cowling
Remove the cowling, if needed, to gain access to the area immediately behind
the propeller. For typical power plant installations, this would require
removing the upper cowling of the aircraft, giving access to the top of the
engine.
While you have the cowling off, check all the accessories for secure
mounting. Any loose components such as an alternator, starter, etc
Mount the Accelerometer and Optical Pickup
The accelerometer and optical pickup are typically mounted on the top of the
engine. The optical pickup should be mounted approximately six inches
behind the back of the propeller. The accelerometer should be mounted as far
forward as possible for maximum sensitivity.
A common mounting technique is to remove one of the case bolts along the
top of the engine. Replace the bolt with the accelerometer and optical pickup
bracket installed under the bolt. Position the optical pickup such that the beam
projects onto the back of the blade or spinner backplate.
The following Figure shows the relationship between the optical pickup,
accelerometer, and the propeller. The optical pickup is pointing to the back of
the propeller onto the reflective tape (to be put on in the next step). The
accelerometer is mounted vertically, perpendicular to piston travel.

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Relationship between optical pickup, accelerometer, and propeller.
Showing a typical installation for a Lycoming engine.
The optical sensor should be at least 6” from the reflective tape, but not so far
that the optical sensor cannot obtain a reading from the tape.
Mount Reflective Tape on the Propeller
By placing the small piece of reflective tape (provided in the kit), on only one
propeller, that propeller can now be considered the “Master” blade. Cut off
approximately 2 inches of tape from the provided roll. Position the tape such
that the optical pickup strikes the reflective tape and turns on the small light at
the back of the optical pickup

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A simple way to verify that the system is working is to position the “Master”
blade so that the light on the back of the optical pickup is illuminated. Pass
your finger between the beam to cause the light to turn on and off rapidly.
It is also beneficial to move your finger from top to bottom of the tape to
verify that the optical pickup is reading the center of the tape. If the optical
pickup is reading from one edge of the tape, it is best to readjust the optical
pickup to measure in the center of the tape.
The photo pickup is configured to pulse a small light on the back of the photo
pickup. When the photo pickup is correctly illuminating the reflective tape,
the back of the photo pickup should have a pulsing red LED.
The faster the pulse rate, the better the returned signal. If the light is
illuminated when not viewing the reflective tape, then the optical contrast may
be insufficient to correctly determine RPM. It will be best to move the tape to
a location with greater contrast.
Experimental installation, showing reflective tape on spinner backing plate.
Example: Some chromed spinner backplates
may confuse the photo pickup. Relocate the
tape to the starter ring, propeller, or paint the
back of the spinner backplate.

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For an expected RPM and distance from hub / rotation center, there is a
minimum tape width required.
For instance, if the engine cruise RPM is 2400 RPM, we look at the 2500
RPM line (next RPM greater) and we place the reflective tape 6 inches from
the center of the hub, the minimum tape length is 1". If the RPM is 2400 with
the tape 8 inches from the center of the hub, the minimum tape width required
would be 1.9 inches.
Tape Length Required
RP 6" from hub center 12" from hub center 24" from hub center
500 0.2" 0.4" 0.8"
1000 0.4" 0.8" 1.6"
1500 0.6" 1.2" 2.3"
2000 0.8" 1.6" 3.1"
2500 1" 1.9" 3.8"
3000 1.2" 2.3" 4.6"
3500 1.4" 2.7" 5.3"
4000 1.6" 3.1" 6.1"
4500 1.7" 3.4" 6.8"
5000 1.9" 3.8" 7.6"
Alternately, to use a particular tape width, table 2 shows maximum distances
from hub center.
aximum Distance From Hub Center
RP
1" Tape 2" Tape 3" Tape
500 31" 62" 95"
1000 15" 31" 47"
1500 10" 21" 31"
2000 7" 15" 23"
2500 6" 12" 19"
3000 5" 10" 15"
3500 4" 9" 13"
4000 3" 7" 11"
4500 3" 7" 10"
5000 3" 6" 9"
Insufficient tape width will cause engine RPM to fluctuate and provide erratic
readings.

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Using the DynaVibe
Attach the DynaVibe
Attach the DynaVibe dynamic balancer to the accelerometer and optical
pickup cables from the engine compartment. The cables are keyed, so look
closely at the connectors before plugging them into the DynaVibe.
Back of DynaVibe
CAUTION:
Verify that the area around the
propeller is clear of obstructions.
Verify that all cabling is secure.
Accelerometer
Optical Pickup
Power
Button
Averaging
Button

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Start Your Engine
Check with your engine manufacturer for specific information about ground
running aircraft engines.
Start the engine normally, watching for any shifting of cabling or equipment.
Let the engine warm up to reduce wear during the high RPM data collection.
Slowly increase the RPM of the engine until it has reached the desired RPM
(usually peak static RPM, or cruise RPM).
Verify that the DynaVibe RPM reading is accurate relative to the displayed
RPM. If the RPM is erratic or incorrect, this may indicate that the optical
sensor is not properly in-line with the reflective tape.
The DynaVibe will now display the measured RPM and IPS-phase. Be sure
the engine RPM remains constant during this process.
CAUTION:
Improper ground running of engines
can cause significant damage to the
engine.
Example: Lycoming recommends that the
engine be warmed up at 1000 RPM until oil
temperatures have stabilized or reach 140° F.
Full-static RPM should be maintained for not
more than 10 seconds. After operating at full
power, allow the engine to cool down
moderately.

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Averaging
Press the averaging button momentarily to have the DynaVibe average
multiple rotations. This process will take a few seconds at high RPM, and
longer at lower speeds. The DynaVibe will then display the averaged value.
This is the number that you will want to record on your datasheet. It is usually
best to record two averages to verify repeatable operation.
Slowly return the engine to idle. Allow the engine to run at the lower RPM for
a short period of time to cool.
Limitations
Correction weights should not be attached to a damaged or cracked spinner or
spinner backplate.
Trial weights mounted on the outside of the spinner should be moved to the
spinner backplate for permanent installation.
Do not use automotive stick-on weights. Only aircraft hardware should be
used for balancing.
Propeller assemblies with initial readings above 1.2 IPS should be removed
and static balance performed.
All hardware used should be aircraft quality. Hardware should be a minimum
#10 size. Retaining nut should be self-locking.

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Balance / Analysis
Clock the Prop and Change Weight
Confirm that the ignitions are off and mixture is full lean. Rotate the propeller
carefully until the small light at the back of the optical pickup comes on. This
is the 0° position relative to the accelerometer. The angle indicated by the
DynaVibe is the angle where the prop assembly is heavy.
The angle is measured from the zero position of the accelerometer to the
indicated angle in the direction of propeller rotation.
When the heavy point is identified, remove weight from this point. If there is
no weight to remove from the heavy location, add weight on the opposite side
of the propeller (indicated angle +/-180°).
For instance, if the system is displaying 0.25IPS @ 90°, this is the position of
excess weight. If there are no extra washers to remove from the spinner, then
weight must be added to the opposite side (270°, 90°+180°). A typical O-320
installation with fixed pitch prop and spinner may require two to four AN970
washers to correct this type of vibration.
Every installation is different due to the weight of the engine, propeller,
spinner, etc. Therefore, adding weight should be done in small increments
and by making notes on the datasheet, the step-by-step correction gives you an
indication of future changes.
A good starting point is 50 grams / IPS.
CAUTION:
Verify ignition and fuel are off
prior to moving propeller

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For instance, if in the above example, one AN970 washer is added at the 270
degree position and the system is run again, it is likely that the readout would
be 0.17IPS @ 90°. This gives a good indication that the single washer
corrected approximately 0.07IPS of vibration. While this would imply that
one could quickly add two additional washers to correct the system down to
0.03IPS, it usually isn’t that simple.
Take small steps and document as you go.
Showing the phase angle relative to the master blade.

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Completing Balance
To move test weights outward or inward, the moment of the weight correct
must remain constant. The mass times the radius of the position must remain
the same between the trial weights and permanent weights.
For instance, if a trial weight correct is 10 grams at 12 inches, the total
moment of the system is (10 grams x 12 inches) 120 gram inches. To move
this amount of correction inboard to the spinner backplate, at a radius of 6
inches, the total mass must be increased to 20 grams (20 grams x 6 inches)
120 gram inches.
The table below shows the weight of common AN hardware.
Part Number
Weight,
Grams Description Type
AN960-10L 0.5 Flat Washer 3/16 Light washer
AN960-10 0.9 Flat Washer 3/16 washer
AN970-3 3.9 Flat Washer 3/16 washer
AN365-1032A 2.2 Elastic Stop Nut 10-32 nut
AN525-10R6 2.1 Washer Head Screw 10-32 x 3/8 screw
AN525-10R7 2.3 Washer Head Screw 10-32 x 7/16 screw
AN525-10R8 2.6 Washer Head Screw 10-32 x 1/2 screw
AN525-10R9 2.7 Washer Head Screw 10-32 x 9/16 screw
AN525-10R10 3.0 Washer Head Screw 10-32 x 5/8 screw
AN525-10R12 3.4 Washer Head Screw 10-32 x 3/4 screw
AN525-10R14 4.1 Washer Head Screw 10-32 x 7/8 screw
AN525-10R16 4.4 Washer Head Screw 10-32 x 1 screw
AN525-10R18 4.8 Washer Head Screw 10-32 x 1 1/8 screw
AN525-10R20 5.4 Washer Head Screw 10-32 x 1 1/4 screw
Documentation
The dynamic balance solution should be documented in the logbook
with the mass and location of the corrective weights. A decal should
be applied to the spinner or propeller hub to show that the assembly
has been dynamically balanced.