DynaVibe Blog

Selecting the Right DynaVibe System

Thursday, November 05, 2015

Perhaps you’ve had enough of the vibration that makes flying uncomfortable, or is damaging your airframe, avionics or engine.  Or maybe you want better performance, recapturing horsepower lost to vibration.  Perhaps a friend who has dynamically balanced his or her prop recommended that you do the same.  Whatever the reason, you’re ready to make an investment in a prop balancer, and a Google search has led you here.  Which DynaVibe system is right for you?

RPX Technologies currently offers three models of its DynaVibe propeller balancing system.  Here’s what you need to know about each one in order to choose the one that best addresses your needs.

DynaVibe GX2

The DynaVibe GX2 is the state-of-the-art, flagship solution in the RPX Technologies product line.  This unit comes with two accelerometers, allowing users to dynamically balance propellers while also providing full-spectrum vibration analysis capability.  When prop balancing, the DynaVibe GX2 automatically calculates a recommended weight solution for achieving balance, unlike the DynaVibe Classic.  This feature helps users complete the balancing process faster than is typically possible with the DynaVibe Classic, sometimes in as few as two run-ups. For mechanics, shops, repair stations and service centers where time equals money, this more efficient balancing process is highly desirable.

A more advanced feature of the DynaVibe GX2 is its vibration analysis capability.  When troubleshooting more complex vibrations, those caused by something other than a propeller assembly imbalance, spectral analysis is essential.  It allows users to pinpoint the source, distinguishing between vibrations caused by a combustion issues (e.g. weak cylinder), prop wash induced buffeting, alternator imbalance, and many other sources of vibration.  Instead of wasting time and money on trial-and-error maintenance procedures, the GX2 identifies the vibration source.  The GX2 has a report generation feature to simplify printing or sharing its vibration analysis data.

DynaVibe Classic

The DynaVibe Classic is the original prop balancing system offered by RPX Technologies.  If balancing a propeller or other rotating machinery is the only thing you need to do, the Classic model does an excellent job at the most affordable price.  When it comes to the dynamic balancing process, the main difference between the models is that the Classic does not automatically calculate a weight solution.  The implication is that the user may need a few more run-ups to complete the balancing process.  The DynaVibe Classic does not offer full-spectrum vibration analysis.

DynaVibe Roto

DynaVibe Roto is a version of the DynaVibe Classic with some features specifically for rotorcraft.  This unit comes with two accelerometers, one for lateral vibration and one for vertical vibration.  It also includes an integrated remote control “push-to-talk” switch that can be mounted on the stick for controlling the DynaVibe unit.  The DynaVibe Roto will also dynamically balance propellers on fixed-wing aircraft.

Summary

This table provides a quick reference to help select the right DynaVibe system to meet your needs:

If you would like to learn more about selecting the best DynaVibe model for your needs, simply enter your email address in the form below, email us with your question at sales@rpxtech.com or call: 479.708.8779.

Enter your email address to learn more about selecting the best DynaVibe for your needs:     

Using DynaVibe to Balance Rotorcraft

Monday, October 26, 2015

DynaVibe can balance rotors as well as propellers, and key to accurate rotor balancing is proper placement of the lateral and vertical accelerometers as well as the phototach sensor. 

Lateral Accelerometer Placement

The purpose of the lateral accelerometer is to measure the mass imbalance that occurs once per rotation (1-per) of the rotor.  The best way to measure the mass imbalance is to maximize the sensitivity to the mass imbalance while minimizing sensitivity to other vibrations. 

To do so, mount the lateral accelerometer as high as possible on the rotor mast to maximize sensitivity.  It’s also preferable to mount the accelerometer on a rigid structure.  If the accelerometer is mounted on a bracket or other secondary structure, that structure may absorb vibration or modify the signal due to structural resonance.  Furthermore, to maximize sensitivity, orient the accelerometer so that it is sensitive to the axis of minimum rotational inertia.  For rotorcraft, this is usually the roll-axis, hence the reason for laterally mounting this accelerometer.

To minimize non-mass vibrations, point or align the accelerometer through the rotor shaft.  If the accelerometer is mounted ahead of or behind the main rotor mast, then the accelerometer will receive vibration from the main rotor imbalance plus vibrations from any torsional vibration.  This occurs frequently in analyzing engines: the vibration signature will change if the accelerometer is not pointed through the rotating element.

When measuring mass imbalance, a key area of focus is measuring the vibration when there is minimal forward airspeed.  If the two blades are not identical in lift and drag, then blade asymmetry will cause a 1-per vibration. Measuring the mass imbalance at high forward speeds will cause the sensor to register both the mass imbalance and blade asymmetry.  For this reason, it is best to collect mass imbalance data while in a step decent, power off.

When the lateral accelerometer and phototach are setup correctly, and the forward speed component of the 1-per vibration is eliminated, then balancing the rotor is just like balancing a prop.

Phototach Sensor Placement

Position the phototach so that it has a clear view of the rotor system, making sure that it is at least six inches away from the reflective tape target to get a good signal.  A piece of reflective tape is applied to rotor system so the DynaVibe computer can determine the relative position of the blades to the vibration signal received by the accelerometer.  The phototach position is determined by the polar charts that you will be using, the manufacturer's recommendation, or by talking with a DynaVibe team member.

Vertical Accelerometer Placement

The purpose of the vertical accelerometer is to measure vertical hop and pitch axis vibration.  This requires placing the vertical accelerometer in the forward cabin as pictured.  If vertical hop is present at the 1-per, then its cause is blade asymmetry.  If it is present twice per rotor rotation (at the 2-per), its cause is the advancing blade lift and drag.  It’s usually possible to correct a 1-per vibration through tracking: making tracking better or worse depending on the blades.  The 2-per vibration, however, is generally difficult to eliminate.  For helicopters, DynaVibe engineers recommend using trim tabs to adjust the forward flight 1-per vibration.

For rotorcraft balancing, the full spectrum analysis capability the DynaVibe GX2 provides is excellent for troubleshooting.  However, even the basic balancing capabilities of the DynaVibe Classic provide all that is necessary for rotor smoothing.  The only frequencies requiring analysis are the prop, 1-per rotor, and 2-per rotor, which are within the scope of the DynaVibe Classic feature set.  What also facilitates accurate rotorcraft balancing is expertise and knowledgeable customer service of the DynaVibe team.

Learn more by visiting the DynaVibe Rotorcraft FAQ.

DynaVibe is easy and economical to use for prop and rotorcraft balancing.  For mechanics, shops and service centers, it adds profit to the bottom line.  To learn about using DynaVibe to dynamically balance propellers and rotors, enter your email address below, visit the RPX Technologies website, or call:  469.708.8779.



Enter your email Address here to learn more about using DynaVibe with rotorcraft:     

Questions? Contact us at sales@rpxtech.com