DynaVibe Blog

Identifying and Resolving Aircraft Vibration

Wednesday, November 18, 2015

There’s nothing about vibration that is good for aircraft, the pilot or the passengers.  In 1973, the Army Air Mobility Research and Development Laboratory commissioned a study to examine the difference in reliability and maintainability of two groups of helicopters with distinctly different vibration characteristics.  One group was fitted with rotor-mounted absorbers to reduce vibration, and the other group did not have the vibration-reducing absorbers.  The study found that the failure rate for the helicopter group fitted with the vibration absorbers was reduced by 48 percent, and corrective maintenance was reduced by 38.5 percent.[1]  Because of the damage it can do, locating the source of vibration and eliminating it should be a high priority.

Propeller or rotor imbalance is the most common cause of vibration, and thanks to innovations like the DynaVibe prop and rotor balancer, dynamic balancing is quick and easy, and it usually resolves most vibration issues.  However, sometimes the source of the vibration is more elusive and when that is the case, a vibration analyzer that does spectral analysis can pinpoint the source. 

Vibration Symptom, Causes and Effects

A vibration issue isn’t always detectable by feel, because often owners and pilots have lived with vibration for a long time and have simply gotten used to it (see our Propeller Vibration Levels Guide for more information). There are always symptoms, however, such as: a panel that shakes, random instrument failure, fatigue cracks that appear or grow, cracked baffling, a compass that won’t “settle”, a rough RPM range and even tingling or numbness in pilot extremities.  These symptoms, such as the fatigue crack pictured below, should not be ignored.

Beyond propeller assembly imbalance, the causes of vibration are many, and the list of possible sources includes: a weak cylinder, a loose or cracked intake hose, an alternator problem, belt resonance, gearbox issues, an oil-canning spinner, prop wash, and other causes.  Because there are many possible sources, troubleshooting vibrations is often problematic, turning into an expensive, trial-and-error process of identifying the source based on someone’s best guess.  The DynaVibe team has seen several forum posts from frustrated aircraft owners who have spent years and lots of their money trying to identify the source of a vibration.

The effects of aircraft vibration are all negative.  When a vibration exists, some of the energy meant for propulsion is directed toward shaking the airplane.  Even a seemingly small vibration can steal enough energy to cause a loss of horsepower.  More troubling, however, is the damage vibration does by creating fatigue that reduces the life of the airframe, engine and instruments.  Dennis Barker, president of Reynolds Aviation, knows well what damage vibrations can do to instruments:  “Vibration can destroy those instruments, so balance is huge!”  Barker uses a DynaVibe Classic to keep the Reynolds fleet of Cessna 172s in balance.

Identifying and resolving vibration is therefore necessary to extend the life of the aircraft and provide a smoother, safer flying experience.

Resolving Complex Vibrations

With the proper diagnostic equipment and approach, the source of a vibration is easily pinpointed.  The approach is spectral analysis, which measures the frequency of vibrations, because vibration frequencies are associated with known causes or sources.  When the frequency of a vibration is known it narrows the list of potential causes to few or one, eliminating the need for speculative maintenance actions. 

Performing spectral analysis is accomplished using a vibration analyzer such as the DynaVibe GX2.  By attaching one or two accelerometers and a photo-tachometer to the aircraft, the DynaVibe computer measures vibrations across the full spectrum of frequencies, producing a graph that displays the magnitude of the detected vibrations.  For example here is a velocity mode spectral chart produced by the DynaVibe GX2 as the result of completing a vibration survey:

Vibration is measured in Inches Per Second (IPS), and this chart reveals a 1.0 IPS vibration at the half-per (H) frequency for this particular aircraft.  The half-per vibration is an indicator of engine health, and in the chart above, the presence of this vibration indicates a combustion problem with one of the cylinders.  To better understand what vibrations in different frequencies signal, view the recorded webinar, “Top 3 Vibration Causes” or contact a DynaVibe team member.

Brian Smith, owner of Stillwater Aircraft Services, gets value from the vibration survey capability of the DynaVibe GX2:  “I can see a half-per vibration using the DynaVibe, and know that it’s caused by a combustion problem.  That information eliminates other vibration sources and narrows it down to the specific problem I need to address.  That’s a home run.  When servicing an airplane, I don’t need to go down as many rabbit trails.”

A vibration analyzer like the DynaVibe GX2 does more than make locating vibration sources easy; it is an excellent preventative maintenance tool.  Performing regular vibration surveys enables early identification of maintenance issues while they’re still relatively small, before the vibration does much damage, or most importantly, before it results in failure.

The DynaVibe GX2 is a dynamic prop balancer and vibration analyzer that is easy and economical to use.  To learn about using DynaVibe to troubleshoot aircraft vibrations, enter your email address below, visit the RPX Technologies online store, or call:  469.708.8779.



[1] “Vibration Effects on Helicopter Reliability and Maintenance”, Angelo C. Veca, April 1973. http://www.dtic.mil/dtic/tr/fulltext/u2/766307.pdf

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DynaVibe Keeps Reynolds Aviation Fleet Flying Smoothly

Saturday, November 14, 2015

Reynolds Aviation provides aerial patrols for pipelines, power lines or any asset that has federal, state, or local reporting requirements.  When on patrol, Reynolds’ highly trained pilots provide security, take aerial photos, respond to emergencies and look for encroachments, leaks, pipeline threats, erosions and construction on right of way assets.   Reynolds uses DynaVibe to help keep its fleet of Cessna 172s flying smoothly while lowering costs of maintenance and operation.

Dennis Barker, president of Reynolds Aviation, has experience with racing engines and therefore knows what damage vibrations can do to an airplane’s engine, its bearings and instruments:  “Vibration can destroy those instruments, so balance is huge!” 

Barker’s partner had previously used a helicopter balancing solution, giving him some frame of reference on the cost of a prop balancer.  When the Aero Performance representative that serves Reynolds Aviation came calling to discuss DynaVibe, Barker expected a pitch for a much more expensive solution costing in the neighborhood of $10,000.  Instead, he learned that he could purchase a DynaVibe Classic and own a dynamic propeller balancing system for less than $2,000, and did so.

Some of the airplanes in the Reynolds fleet were showing signs of fatigue caused by vibration: cracked baffling, new lights that would burn out or instruments that would fail.  Barker knew that eliminating propeller imbalance would stop the damaging vibrations.  “Some of the engines vibrated so badly that we couldn’t even read ‘Lycoming’ that was stamped on the engine.   Now they’re really smooth.“

The prop imbalance on one airplane measured close to 1 Inches Per Second (IPS).  Using DynaVibe, the Reynolds maintenance team was able to balance all the airplanes in the fleet to between .01 and .07 IPS.   The Reynolds pilots often fly long days, spending hours in the air, so eliminating vibration from propeller imbalance not only reduces fatigue on the airplane, but on the pilots as well.  “The pilots were thrilled with how the yoke feels after we balance an airplane,” Barker said.  “They noticed a difference immediately.” 

Barker is confident that using DynaVibe to keep the fleet in balance will also pay dividends in terms of maintenance and operational costs.  “The big enemy of operations like ours is what it costs to keep planes in the air.  Long term, we don’t fully know what the maintenance benefits are, but even cutting these costs by just 10 percent would pay for the DynaVibe system three times over.”

An unexpected bonus from using DynaVibe is the information provided by the photo tachometer, making it possible to determine how accurate the airplane tachometer is.  “An incorrect tach reading can cause us to fly a plane at a cruise RPM that’s actually too high, which can damage the engine,” Barker concludes.  “DynaVibe also tells us if the tach is off.  It’s a phenomenal product.”

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.

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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.

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Dynamic Prop Balancing Adds Service Revenue

Tuesday, November 03, 2015

Our new infographic shows how mechanics, repair stations, shops and service centers can make more money by adding prop balancing to their service mix with DynaVibe:

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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.



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The Bugatti 100P Flies Again

Thursday, October 22, 2015

DynaVibe was on hand to support Scotty Wilson's second flight with the Bugatti 100P when he returned to Oklahoma's Spaceport at Burns Flat to continue flight-testing.  The Bugatti needed new props after its historic first flight due to a brake failure on touchdown.  The DynaVibe team joined Scotty to balance the two, new propellers on the Bugatti and continue the flight-testing program for this innovative and historic airplane.

Having previously balanced the Bugatti (click here to learn why dynamically balancing a prop is important) for its inaugural flight, a location for mounting the accelerometer was already determined.  It was quick work to install the DynaVibe accelerometer and phototach on the Bugatti.  Balancing the contra-rotating propellers started with the rear engine / rear propeller.  The initial balancing run revealed that the rear prop required 27 grams of correction weight, which when added, brought the propeller imbalance down to 0.09 Inches Per Second (IPS).  The front propeller was then balanced down to 0.10 IPS by adding 18 grams of weight.  Shortly afterward, the Bugatti successfully took to the air once again.

DynaVibe has balanced the Bugatti 100P, the world-record breaking Anequim, warbirdsReno Air Racing team aircraft, the AN-2, the world’s largest biplane, and it can balance whatever you fly, delivering better performance and a smoother flying experience.  To learn how easy and economical it is to dynamically balance your prop with DynaVibe, enter your email address below, visit the DynaVibe online store, or call:  469.708.8779.


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DynaVibe Minimizes Equipment Wear-and-Tear for Alaska DOT

Thursday, October 15, 2015

DynaVibe has a long association with aviation as an affordable system for dynamically balancing propellers.  The principles of balancing, however, apply not just to propellers, but any device that spins.  The Alaska Department of Transportation is using a DynaVibe Classic system to keep brush cutting and snow removal equipment operating at peak efficiency. 

The idea to use DynaVibe came from an employee in one of the shops who was an A&P mechanic and had experience using the system to balance propellers and rotors.  Aware of DynaVibe’s ability to achieve precision when balancing, he started using the system to balance a brush cutter that had a rotating head.  When Lon Needles, shop foreman of the Transportation Department's State Equipment Fleet, heard about this, he asked this employee to come and demonstrate how it is done.

“This equipment will hit rocks and things and get out of balance, and it will shake the guys out of the cab,” said Needles.  The balancing demonstration was enough to convince him that they too needed a DynaVibe to balance the brush cutters in their shop.  Once the DynaVibe was in their possession, Needles began to wonder what other equipment they could balance with it.

“We have our snow blowers here,” continued Needles.  “Valdez averages 300 inches of snow a year; Thompson Pass, just up the road a little bit, gets 700 inches per year, so we use the heck out of our snow blowers.  If they hit a rock or something, it can mess them up, so we balance the spinning rotor in there with DynaVibe too.”  

The impellers in these machines are heavy, perhaps weighing as much as a ton.  “When they get out of whack, I’ve seen them sit there and bounce the whole head off the ground.”  Needles shares an experience about a brush cutter that was so out of balance that “it would literally shake the coffee out of the operator’s coffee cup.”  After balancing this equipment, “you could barely see a ripple with it running wide open.” 

The value of keeping these machines in balance is less wear-and-tear – for both the machine and the operators.  “When a machine is not sitting there vibrating, it’s smooth; it takes the fatigue away from the operator, and while I can’t prove it, I think it takes the metal fatigue away from the machine.  Nuts and bolts aren’t trying to come apart.  It’s noticeable.” 

By spending the time to balance, Needles and his team are able to eliminate virtually all the vibration from the spinning components of their machinery.   The snow blowers are balanced about once a year; the brush cutters about twice per year or as needed.  It takes about an hour to balance a machine. “Anything that spins, we seem to be able to balance it,” Needles concludes.  

For a free, no-obligation consult with us about your balancing application, enter your email address below.

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DynaVibe a "Home Run" at Stillwater Aircraft Services

Saturday, October 10, 2015

Stillwater Aircraft Services recently began using a DynaVibe GX2 to provide dynamic propeller balancing and vibration survey services.  Brian Smith, owner of this service center, is using DynaVibe to bring new work in while serving his existing clients better. 

One of Brian’s initial successes with DynaVibe came with a client who flies a Beechcraft Super Musketeer with a 200 horsepower engine and a constant speed prop.  This airplane had a known vibration problem, but it had never been addressed.  The propeller was last statically balanced in 2000. 

The initial propeller-balancing run revealed a severe vibration of 1.5 Inches Per Second (IPS).  This was well above the FAA specified maximum limit for propeller vibration of 1.2 IPS which requires that the prop be removed and statically balanced prior to dynamic balancing on the aircraft.  Even following standard dynamic balancing procedures, Brian could at best reduce the vibration by about half.  It was much better than the starting level of vibration, but still severely out of balance.  Brian pulled the prop off the airplane and took it to a prop shop to have it inspected, where he was surprised to learn that during the last static balancing 15 years ago, the weight had been added to the wrong blade. 

“When they put the prop on the balancing stand, one blade immediately fell to the floor,” said Smith.  It’s unfortunate, but once in a great while, the weights are applied to the wrong blade in the static balancing process, and that was the reason this Musketeer had experienced a vibration problem for 15 years.

After having the prop statically balanced, Brian remounted it on the Musketeer and checked the balance again using his DynaVibe system.  The static balancing had reduced the prop vibration to about .67 IPS.  Brian used the automatic weight solution calculated by the DynaVibe GX2 and almost completely eliminated the vibration, getting it down to .04 IPS.  The owner’s feedback was that his Musketeer felt like a totally new airplane!

Brian sees multiple benefits to offering dynamic prop balancing services with DynaVibe.  “It will help pull more business in, I’ll get more work off of it, but the customer gets something too – a measurable difference in the performance of their airplane.”  In addition to propeller balancing, Brian sees the advantage of the vibration survey capability that the DynaVibe GX2 provides: the ability to identify the type and source of a more complex vibration.  “I can see a half-per vibration using the DynaVibe, and know that it’s caused by a combustion problem.  That information eliminates other vibration sources and narrows it down to the specific problem I need to address.  That’s a home run.  When servicing an airplane, I don’t need to go down as many rabbit trails.”


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Balancing = Profits

Monday, October 05, 2015

At RPX Technologies, we routinely hear stories from service centers, shops, or repair stations that use DynaVibe to deliver service.  These stories have a common theme:  using DynaVibe to offer dynamic balancing service brings in more business, generates greater profit, and increases customer satisfaction.

It doesn’t take much balancing work to create a fast payback on purchasing a DynaVibe GX2 system for balancing and vibration analysis.  Just doing three dynamic balancing jobs per month provides payback in less than 5 months and adds almost $7,000 in profit during the first year.  The following table summarizes the DynaVibe business case:

Under the same balancing workload assumption of three jobs per month, opting for a DynaVibe Classic provides payback in less than two months and delivers over $9,300 in first year profit!

It’s typical for a shop that uses DynaVibe to complete a prop balancing assessment for every airplane that comes in for service.  If the prop is out of balance, owners are given the option to have it dynamically balanced, and often they accept.  What’s also typical is that once a shop begins offering dynamic balancing service, owners will bring their planes in for that reason alone, and often other maintenance issues will surface during the visit. 

Shops, service centers and repair stations that use DynaVibe to offer dynamic prop balancing enjoy a number of benefits:

  • Dynamic balancing is a great “calling card” that attracts business to the shop.
  • Customers are often amazed at how smooth their airplane flies after balancing.  DynaVibe helps create very satisfied, loyal customers.
  • In addition to prop balancing, the DynaVibe GX2 can identify other vibrations from other, more complex sources.
  • Offering dynamic prop balancing improves the status and credibility of the shop or service center.
  • DynaVibe is an excellent preventative maintenance tool, allowing mechanics to get baseline vibration surveys for comparison during future maintenance.

The DynaVibe system is easy and economical to use, adding profit to the bottom line.  To learn about using DynaVibe to dynamically balance propellers, enter your email address below, visit the RPX Technologies website, or call:  469.708.8779.

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Recovering “Lost” Horsepower

Wednesday, September 23, 2015

Vibrations Steal Energy

There are many benefits to dynamically balancing the prop assembly and removing vibrations associated with propeller imbalance.  Often talked about benefits include smoother flying with less wear on the engine, instruments and airframe.  These benefits have enormous value, as they reduce fatigue on the plane, pilot and passengers, while extending the life the airplane.  They are reason enough to keep the prop assembly in good balance, all the time.

Another benefit of dynamic prop balancing is performance.  When an imbalance introduces a vibration, energy is spent shaking the airplane instead of moving it.  With a finite amount of horsepower available to propel the airplane, a vibration uses some of it in a destructive way, leaving less available for propulsion.

The percentage of horsepower lost to vibration may seem small.  Look at it this way: suppose a propeller imbalance is costing 2 percent of an engine’s horsepower.  This 2 percent is going into shaking the airplane.  If that airplane has a 200 HP engine, in this scenario 4 HP is lost due to vibration.  To provide some perspective, this loss is the equivalent of hooking up a lawn mower engine to the airplane’s crankshaft to do nothing more than shake the airplane!  That’s how much energy a propeller imbalance can direct into the crankshaft bearings and the rest of the airplane. 

Fortunately, it’s not difficult to recapture this “lost” horsepower.  Dynamically balancing the prop assembly allows most or all of the horsepower lost to vibration to once again go toward flying the airplane.  Using the DynaVibe GX2, you can easily determine if a prop is out of balance, and also get a solution for how much weight to add, and where to add it to achieve good balance.  To learn about using DynaVibe to dynamically balance propellers, enter your email address below, visit the RPX Technologies website, or call:  469.708.8779.


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