DynaVibe Blog

Propeller Vibration Levels Guide

Thursday, January 28, 2016

Many owners and operators ask about what acceptable levels are for propeller vibration and what to do about it.  DynaVibe has prepared the following chart as a guide to understanding prop vibration and when balancing is recommended based on vibration levels:

Aircraft propeller vibration guidelines  

This chart is for information purposes only, and is not intended to replace, supersede or contradict any information in FAA Advisory Circular 20-37E which describes maintenance procedures for owners, operators and FAA certified maintenance personnel for aircraft propellers.  AC 20-37E is a great resource for field propeller maintenance, and it includes a very useful checklist for propeller annual inspection.

Dynamic propeller balancing is easily accomplished using the DynaVibe Classic, for simple balancing, or the DynaVibe GX2 to balance and complete vibration surveys.  The DynaVibe team is always happy to discuss balancing, vibration analysis and resolution, so please contact us if you have questions.  You can reach us by telephone at 469.708.8779, by email at sales@rpxtech.com or simply complete the form below and we'll contact you.  To get pricing or buy a DynaVibe system, visit our online store.

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So, What is a Vibration Survey Anyway?

Saturday, January 16, 2016

Much has been written in this blog about vibration analysis: what it is, how it works and the benefits.  The DynaVibe GX2 is the solution from RPX Technologies that simplifies performing a vibration analysis, or vibration survey as they are often called.  If you’ve never seen the output of a vibration survey, you might find it helpful to see an example. 

The following graph is the actual output of a vibration survey taken using a DynaVibe GX2 of a Rotax 912 engine:

Sample airplane engine vibration survey

This Velocity Mode chart shows the vibrations that were detected, measured in Inches Per Second, during the vibration survey.  We’ve annotated the chart so you can easily see what the presence of these vibrations indicate:

  • A 1-per vibration of about .7 IPS indicates propeller imbalance
  • A 1.2-per vibration of about .8 IPS indicates carburetor imbalance
  • A 2-per vibration of about 1.7 IPS indicates a gearbox issue
  • A 2.43-per vibration of over 2 IPS indicates a front-back cylinder imbalance

The threshold of tolerance for a vibration is about .2 IPS. Anything greater should trigger some action to identify and resolve the vibration(s).  With the information a vibration survey provides, resolving these vibrations becomes much easier because there is certainty about their cause.  Let’s look at each of the vibrations this survey identifies in more detail.

The 1-per Vibration

A 1-per vibration is caused by propeller imbalance.  Dynamically balancing the prop should eliminate a 1-per vibration.  Dynamic prop balancing is always a good place to start when resolving vibrations, because it eliminates the most likely source of vibration.  Because this particular vibration survey reveals multiple vibration sources, dynamically balancing the prop will help, but other vibrations remain. 

The 1.2-per Vibration

The presence of a 1.2-per vibration can mean different things.  On a standard engine, this vibration would appear on the survey as a half-per vibration, but since the Rotax engine in this example is geared, this vibration manifests as a 1.2-per.  Typically, this vibration indicates a combustion problem.  It can also indicate that the carbs are out of balance.  The way to know for sure is to complete at least one more vibration survey at a higher RPM.  If the 1.2-per vibration stays consistent as you vary the RPM, then a cylinder combustion problem is the likely cause.  If, however, the intensity of the 1.2-per vibration varies as RPM changes, a carburetor imbalance is the most probable cause.   Out of balance carbs tend to show the most pronounced vibration at mid-RPM levels.  In this example, a second vibration survey (not shown) confirmed the suspected carb imbalance, so balancing the carbs would resolve this vibration.

The 2-per vibration

The 2-per vibration in this example measured 1.7 IPS, a very significant vibration. A 2-per vibration is related to something that rotates with the prop.  Since this engine had a 1-per vibration, it is known that the prop was out of balance.  The recommended approach is to first dynamically balance the prop and then complete another vibration survey to see if the intensity of the 2-per vibration (or any others) has changed.  In this case, the 2-per vibration persisted even when the prop was balanced.  Since the Rotax 912 is a geared engine, attention fell on the gearbox as the vibration source.  In this example, testing the friction torque of the gearbox revealed that it was well over the manufacturer’s maximum, which led the mechanic to contact the manufacturer for a resolution.

The 2.43-per vibration

The most significant vibration shown on this survey, the 2.43-per, is probably caused by the difference in length of the intake manifold.  This engine is designed with the front cylinder having a longer flow path than the back cylinder.  This difference in front-back airflow causes a torsional vibration in the engine, and the DynaVibe GX2 measure this vibration by utilizes two accelerometers mounted in different places on the engine.  This vibration typically diminishes almost to zero as RPM is increased to standard cruise levels.  This assumption was easily verified by doing another vibration survey at cruise RPM, proving the assumption true.  For this reason, the presence of this engine’s 2.43-per vibration was not a concern.

Summary

Here’s what you should take away from this vibration survey example and discussion:

  • Persistent vibration is never a good thing.  Even small ones, over time, can damage engines, airframes or instruments.
  • Vibrations are often complex.  As this example shows, four different vibrations were revealed in the survey.  It’s nice when the vibration source is an out-of-balance prop and dynamic balancing resolves it, but it doesn’t always work that way.
  • Troubleshooting vibrations can be easy.  With the right equipment, such as the DynaVibe GX2, you can identify the frequency and magnitude of vibrations that exist.  With this information, it becomes easy to pinpoint the source without resorting to trial-and-error, speculative maintenance procedures. 

Vibration surveys are also an excellent preventative maintenance strategy.  Doing vibration surveys at regular intervals can provide an early warning of maintenance issues while they’re relatively small, before they’re noticeable or even better, before they cause a failure.  You can purchase a DynaVibe GX2 by visiting our online store, or if you wish to learn more, just call us at 469.708.8779 or enter your email address in the form below and we’ll respond. 


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Making Money with DynaVibe

Friday, January 08, 2016

Many repair stations and service centers are using DynaVibe to offer prop balancing and vibration analysis services, adding a nice revenue stream to their bottom line.  We’ve shared some of their stories on this blog:  KSFB Aircraft Maintenance Center, Stillwater Aircraft Services, Base Leg Aviation and Skywest Aviation to name just a few.

We’ve collected some insight from listening to how our MRO customers are using DynaVibe to let us share the good, better and best ways to use DynaVibe to boost service revenues, grow your business and create happier customers in the process.  Here is what we have learned:

Good

Simply adding “Dynamic Propeller Balancing” services to your menu of service offerings is a good thing.  You’ll gain some business specifically because some customers need their propellers balanced, and when they learn you offer these services, they'll come to you for them.  Promoting the fact that you offer prop balancing and vibration analysis (something the DynaVibe GX2 can do) will generate some new service revenue for you.  While this approach will generate some service revenue, it is a passive approach as it depends on the customer seeking a provider of these services.

Better

A better approach is to recognize that many owners and pilots don’t realize their prop could be out of balance, or that they have a vibration.  Paul Dye, editor-in-chief of Kitplanes Magazine, in a recent article wrote of this phenomenon of not realizing that over time, vibrations gradually creep in and grow, but go unnoticed.  We covered this phenomenon if a recent blog post, and we regularly hear from those who are amazed at how smooth their airplane is after balancing.  A better approach therefore is to ask every customer that comes in if they want their prop balanced while their airplane is in for service.  A surprising number of them will say “yes” particularly when they understand the benefits.

Best

The best approach, the one that serves the MRO and owner or pilot best, is to use DynaVibe to complete a free baseline vibration survey on every airplane that comes into the shop.  If there is a vibration, whether propeller imbalance induced or caused by something else, the vibration survey will show it.  DynaVibe produces reports that the MRO can share with a customer that show the magnitude and type of vibrations that exist.  When made aware of this information, most customers will want to have these vibrations resolved, and they often are through dynamic prop balancing.  Furthermore, the vibration survey is a great preventative maintenance tool, providing a historical record to compare to a new vibration survey the next time that airplane comes into the shop.

Repair stations, service centers and mechanics can maximize their service revenue using the “Best” approach with DynaVibe.  Furthermore, service revenue opportunities beyond prop balancing and vibration analysis exist.  Ascutney Air uses its DynaVibe system to also offer airplane tire balancing services as well.  To increase your service revenue with DynaVibe, visit our online store to buy your system.  If you have questions about how DynaVibe works or how to use it, please get in touch with us at sales@rpxtech.com, by telephone at 469.708.8779 or by entering your email address in the form below.    

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The Frog in the Kettle: A Prop Balancing Metaphor

Thursday, December 31, 2015

The DynaVibe team can’t help but think of the frog in the kettle as a metaphor for prop balancing.  If you’re not familiar with this anecdote, it tells how a frog reacts to two different situations.  If placed in boiling water, it immediately perceives the danger and jumps out.  But if placed in cold water that is slowly heated, it doesn’t react to the gradual change in its environment and is ultimately boiled to death.  This story is a great metaphor for the inability or unwillingness of people to recognize and respond to gradual change.

Photo © 2010 J. Ronald Lee.

What brought this metaphor to mind was an article recently posted by Paul Dye, editor-in-chief of Kitplanes Magazine.  Paul wrote about his experience using DynaVibe to balance the prop on his RV-3, and he stated:  “It’s the old (probably apocryphal) problem of boiling the frog – if you gradually turn up the heat, it doesn’t know that the temperature is rising. With a slight degradation over time, we don’t realize we are losing balance. Then we reset, and all the smooth magic is back!

Paul nails it.  You just get used to the vibration from imbalance.  It often increases slowly, so a gradual change in vibration isn't noticed.  Many pilots and owners just assume that a certain amount of vibration “comes with the territory.”  It’s the price you pay for combustion engine-powered flight.   But it is wrong.  We get a steady stream of feedback from DynaVibe users and customers of shops that use DynaVibe to provide balancing services.  The feedback follows one of two tracks:

A. Owner whose mechanic or friend talks him into balancing the prop:

  • Owner before: “You can balance the prop if you want, but I don’t have a vibration problem.”
  • Owner after:  “Wow, I can’t believe how smooth it is!

B. Owner who is experiencing a vibration and wants to fix it:

  • Owner before: “The vibration is so bad that it is…. (followed by listing one or more symptoms of the vibration, such as avionics failures, a rough RPM range, fatigue cracks, etc.)
  • Owner after:  “Wow, I can’t believe how smooth it is!

We could go on, but we prefer to let the beneficiaries of prop balancing do the talking for us:

From a FlightLevel Aviation customer:  “While our Bonanza was in for its annual inspection late last year, FL approached us with an option to have the prop balanced. The A36 has the big IO-550, and we felt it ran fairly smooth coupled to a 3 x blade prop. For the relatively small additional price, we opted to try it out anyway. The first time advancing the throttle for take-off after the balancing was complete, I had to look a few times at the MP and Tach gauges to insure the engine was making full power! It ran noticeably smoother through all phases of flight, and the only disappointment was that we didn't do it sooner…."

From a KSFB Aircraft Maintenance Center customer:  “Can’t believe the results!  First run showed it was a long way from acceptable; 0.6 IPS.  The second run we homed in on a better solution; 0.19 IPS.  3rd run was spot on; 0.01 IPS. Compare that with the scale on the LHS [DynaVibe balancing report] which calls 0.05 ‘Excellent’.  The ‘feel’ of the plane, just sitting on the ground in the driver’s seat was remarkably different, too.

From Dennis Barker, President of Reynolds Aviation:  “The pilots were thrilled with how the yoke feels after we balance an airplane. They noticed a difference immediately."

There’s more, and you can read other testimonials on our website.  When it comes to dynamic propeller balancing, perhaps Mark Langford said it best to those who haven’t yet done this procedure on their airplane:  “You guys just don't know what you're missing...

Find out what you’re missing by contacting the DynaVibe team to learn more.  Enter your email address in the form below and we’ll respond to you.  Visit the online store to buy your own DynaVibe unit, email us with your questions at sales@rpxtech.com or just call us if you have questions about the process:  469.708.8779.

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The Top 10 DynaVibe Blog Posts of 2015

Thursday, December 17, 2015

During 2015, the DynaVibe team stayed quite busy creating and publishing new content.  We’ve seen consumption of this content steadily grow, so thanks to everyone who has taken the time to visit our blog and read any of our posts!

Since publishing top 10 lists is in vogue at year-end, we have created one of our own:  the top 10 DynaVibe blog posts from 2015.  We rank them here from 10 to 1, complete with links so you can check them out:

10. Dynamic Prop Balancing: how often to do it?

9.   Airplane Wheel Balancing

8.   Case Study: Complex Vibration Troubleshooting on a Rotax 912

7.   Using DynaVibe to Balance Rotorcraft

6.   Balancing the Antonov 2: the World's Largest Biplane

5.   Identifying and Resolving Aircraft Vibration

4.   Recovering “Lost” Horsepower

3.   Anequim Races to 5 World Records

2.   The Bugatti 100P Flies Again

1.   The Bugatti 100P Flies at Last

We hope you found the content on the DynaVibe blog helpful, and we always welcome comments.  We’ll continue to publish to our blog in 2016, so we hope you’ll follow us there, or on social media:

If you have questions about dynamic propeller balancing or vibration analysis, we're happy to answer them. Please contact us by entering your email in the form below, or by just calling:  469.708.8779. With DynaVibe, we can help you fly safer and smoother next year!

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Interpreting Vibration Analysis Data

Tuesday, December 15, 2015

Pilots, aircraft owners, builders and mechanics are increasingly discovering the benefits of vibration analysis as a way to identify and resolve complex vibrations.  Spectral analysis, vibration analysis or vibrations surveys are very helpful in pinpointing the source of an elusive vibration or simply doing engine trend monitoring as a preventative maintenance approach. 

The DynaVibe GX2 is a prop balancer and vibration analyzer.  When you use it to perform vibration analysis, it detects and reports the various vibrations that are affecting an airplane.  For example, DynaVibe might detect a vibration that is occurring once per prop rotation – what is commonly referred to as a 1-per vibration.  There are also half-per, 1.5-per, 2-per and many other vibrations that can occur.  What do these vibrations indicate?

One way to find out what a vibration means is to contact the DynaVibe team.  We’re always happy to help customers understand how to use DynaVibe for spectral analysis and explain the results of a vibration survey.  We have also put together the following vibration table using the excellent material originally published by John Schwaner of Sacramento SkyRanch.  We hope you find it helpful, with the following disclaimer:  this data is for educational purposes only.  If your engine is exhibiting symptoms of vibration, properly rated professionals using diagnostic equipment should check it.

Table of airplane vibration orders with explanations

This table is a good place to start in understanding the cause of vibrations detected through analysis with the DynaVibe GX2.  If you would like to know more about vibration orders and causes, we can help.  Just reach out to us using the contact information or form below.

The DynaVibe GX2 is he most affordable full-spectrum vibration analyzer on the market.  To learn how to use DynaVibe for vibration analysis, enter your email address in the form below to be contacted by a DynaVibe team member.  To purchase a DynaVibe, visit our online store, or simply call:  469.708.8779.

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EAA Sport Aviation Article

Tuesday, December 08, 2015

RPX Technologies co-founder Matthew Dock contributed an article in the December 2015 edition of Sport Aviation - the Experimenter section (pg. 22) of the magazine: "When Prop Balancing Isn't Enough."

In the article, Matt discusses what to do when dynamic prop balancing isn't enough to eliminate a vibration. Click the cover image above to read the article! If what Matt describes sounds like a problem you're having, DynaVibe can help detect a vibration's source, so you can eliminate it.  

If you'd like to learn how the DynaVibe GX2 can help you troubleshoot complex vibrations, contact RPX Technologies by entering your email in the form below or simply call us at 469.708.8779

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Upgrade your DynaVibe Classic to a GX2!

Monday, December 07, 2015

If you're a DynaVibe Classic owner, RPX Technologies has a limited-time upgrade offer that can put a new DynaVibe GX2 in your hands.  The GX2 supports two accelerometers for simultaneous data acquisition, providing substantially more diagnostic capabilities than the Classic.  The GX2 is a prop balancer and vibration analyzer, and it is the technology platform into which RPX is building product enhancements. 

Here’s the short list of what you get when you upgrade from a Classic to a GX2:

ü  Automated prop balancing solutions. The Autobalance feature of the GX2 saves time, letting you balance in fewer runs, with increased accuracy and to lower vibration levels. 

ü  Vibration spectrum analysis.  When vibrations are not related to prop imbalance, the advanced diagnostic capabilities of the GX2 let you troubleshoot and pinpoint other, complex vibration sources.

ü  Full color report generation.  Save the reports the GX2 generates for record keeping or to give to customers, a very useful feature for mechanics, shops, repair stations and service centers.  These reports show propeller balance and vibration analysis details as well as customer and aircraft information.

Here is how to upgrade your Classic to a GX2:

1. Visit the RPX Technologies online store and purchase the Classic to GX2 upgrade (scroll to the bottom of the store page to see the offer). The cost is $2,995.  You’ll receive a $1,000 trade-in credit for your Classic. We’ll reuse your photo tachometer, accelerometer, and case, then provide you with a new GX2 system and 2nd accelerometer.

2. After you’ve purchased your GX2 upgrade in the online store, you’ll be contacted by DynaVibe and provided with a Return Authorization Number and shipping instructions.

3. Ship your entire DynaVibe Classic kit back to RPX Technologies per instructions. Once we receive it, we can usually turn your upgrade order around the same day.

All DynaVibe GX2 systems come with NIST certification, so you’ll have a new NIST certificate as well!

If you have any questions about upgrading your DynaVibe Classic to a DynaVibe GX2, just enter your email in the form below, or call us:  469.708.8779.


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Mitchell Flying Service Monitors Engine Trends with DynaVibe

Sunday, November 29, 2015

Matthew Mitchell operates Mitchell Flying Service, an agricultural aviation operator based out of Perry Municipal Airport (F22) in Oklahoma.  Mitchell has been flying since 1990 and puts about 250 to 300 hours per year on his Grumman Ag-Cat, for which he has two TPE-331 engines that he rotates as needed.  The rigors of agricultural aviation have shown Mitchell the value of keeping the prop on his Ag-Cat in good balance, which is done using a DynaVibe GX2

Anytime something changes with the prop, such as maintenance or mounting the prop after an engine change, Mitchell likes to have a dynamic balancing performed.  “It is essential to have the prop balanced,” states Mitchell.  Doing so eliminates vibration caused by propeller assembly imbalance, which reduces wear on the engine, airframe and instruments.  Dynamically balancing a propeller is an excellent preventative maintenance approach that can help eliminate future engine problems that might otherwise ground an operator.

Mitchell Flying Service

Another significant benefit to using the DynaVibe GX2 is the vibration survey capability it provides.  “DynaVibe checks other vibration ranges besides the propeller,” says Mitchell.  “It’s a good way to keep an eye on the engine, because you may not feel a vibration that DynaVibe can detect.”  Anytime Mitchell puts an engine together, he likes to have a baseline vibration analysis done.  This allows him to do trend monitoring on the engine with DynaVibe to monitor the health of that engine while it is in use.  Regular vibrations surveys can help operators like Mitchell to identify problems before they cause a shutdown or result in a failure.

The DynaVibe GX2 is a dynamic prop balancer and vibration analyzer that can improve performance and maintain engine health.  To get your own DynaVibe GX2, visit the RPX Technologies online store, enter your email address below or simply call us at:  469.708.8779.


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KSFB Aircraft Maintenance Satisfies Customers with Help from DynaVibe

Tuesday, November 24, 2015

KSFB Aircraft Maintence Center is located in Seminole County, Florida, and is operated by Chris and Lisa Reilly.  Chris is an A&P technician with Inspection Authorization.  He is also a private pilot and aircraft owner.  Included among the many services he provides to his clients is dynamic propeller balancing, which he uses a DynaVibe GX2 to perform. 

Chris recently dynamically balanced a client’s Cozy Mk IV with a Lycoming IO-360 (fuel injected) engine and a Sensenich wooden cruise prop.  His client was pleased with the outcome and sent Chris some feedback email message to share his thoughts:

After finishing the installation of Belleville washers my prop (ask me why), I suspected those huge, new steel lumps under each prop bolt would play havoc with whatever primitive balance I’d achieved during the build, so today I had my local A&P do a dynamic balance.

Can’t believe the results!

First run showed it was a long way from acceptable; 0.6 IPS.

The second run we homed in on a better solution; 0.19 IPS.

3rd run was spot on; 0.01 IPS. Compare that with the scale on the LHS [DynaVibe balancing report] below which calls 0.05 “Excellent”.

The “feel” of the plane, just sitting on the ground in the driver’s seat was remarkably different, too.  I’ll put the cowls back on and fly it at the weekend, but I’m expecting a gross improvement. I’ll report results.

Most engineering exercises are a compromise.  With this result, I drove home with a big smile on my face!

If you haven’t already done this [balance your prop], give yourself a Christmas present!

DynaVibe gives pilots a smoother, safer flying experience, and provides maintenance centers with a new source of revenue.  To get your own DynaVibe system, visit the RPX Technologies online store, enter your email address below or simply call us at:  469.708.8779


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Questions? Contact us at sales@rpxtech.com