A balanced propeller assembly is important not just for having a smooth flying experience, but also for the health and longevity of an airplane’s engine, instruments and airframe. Statically balancing a propeller can help reduce vibrations, but to reduce prop imbalance-induced vibration to the minimum, dynamic balancing is recommended.
This story of a Beechcraft Super Musketeer illustrates the importance of dynamic prop balancing, even after static balancing has been performed. This Beech had a 200 horsepower Lycoming engine and a constant speed prop. The airplane had long experienced a vibration problem, but the owner had never attempted to resolve it. The airplane’s propeller was last statically balanced in 2000.
Even though a prop has been statically balanced, once mounted, things can change because the entire propeller assembly comes into play, not just the perfectly balanced, ready-to-mount prop.
It takes just the slightest change in mass anywhere in the propeller assembly to change the balance and introduce a vibration. These numbers illustrate this reality: a perfectly balanced prop, offset by just .0005 inches during installation, can cause a vibration of .6 Inches per Second (IPS)! This scenario occurs more often than most pilots or owners know, because many props don’t have an indexing mechanism to ensure that during mounting, the prop it is perfectly centered with the crankshaft. The dynamic balancing process corrects these “coupling” errors that can result when mounting a prop.
In the case of the Super Musketeer, the prop imbalance was discovered when the owner brought it in for some maintenance. The mechanic had access to a DynaVibe balancing system and did a quick prop balance check. This check revealed a severe vibration of 1.5 IPS, well above the FAA specified maximum limit of 1.2 IPS for prop vibration. A vibration of this magnitude mandates removal of the prop for static balancing. The mechanic pulled the prop off and sent it to a prop shop for inspection and static balancing. The mechanic and owner were surprised to discover that during the previous static balance from 15 years ago, the weight had been added to the wrong prop blade, making the balance and vibration problem worse, not better. The owner had lived with this problem, simply assuming that some level of vibration is a product of combustion.
After the static balancing was complete, the mechanic remounted the prop on the Super Musketeer and dynamically checked the balance. The static balancing process had reduced the prop vibration by about half, to .67 IPS. Using the weight solution provided during the initial dynamic balancing check, the mechanic added the prescribed weight where indicated and did a second balancing run, which showed the vibration had dropped to .04 IPS, well below the level that is discernible by the pilot or passengers. The following report was generated by the DynaVibe GX2 and shows the results of the dynamic balancing runs, including the level of vibration detected and the weight solution calculated to resolve the detected vibration, and where to install it:
The owner’s feedback after dynamic balancing was that his Musketeer felt like a totally new airplane! Static balancing, followed by dynamic balancing, is a great way to get a smoother flying experience and take stress off of the engine, instruments and airframe.
You can get similar results: shop for DynaVibe in our online store, or if you have questions, please call us at 405.896.0026, send email to firstname.lastname@example.org or click on the "Contact Us" tab.
This webinar was part of the EAA webinar series and was originally broadcast on February 24, 2016. It features RPX Technologies co-founder Matt Dock as presenter.
To learn more about using DynaVibe to dynamically balance your prop, or to conduct a vibration survey to pinpoint more complex vibrations, please call us at 405.896.0026 or by email: email@example.com. If you prefer, enter your email address in the form below and we'll contact you! Shop for DynaVibe by visiting our online store.
There's increasing talk about vibrations surveys - what they are, why and how to do them - for good reason: vibrations damage aircraft. A vibration survey will allow you to pinpoint the source of a vibration so that you don't have to pay for speculative maintenance in an effort to resolve it. We've written a lot recently in this blog about vibration surveys, and now we've done one better: we can show you the process in our new video!
We set up an RV-12 with a Rotax 912 engine for balancing and vibration surveying with the DynaVibe GX2, our dynamic prop balancer that also has vibration survey capability. In just over three minutes, the video will show you the process sequence and sensor placement for collecting a vibe survey. You can watch it here:
If you are new to the concept and practice of vibe surveys, please review some of our older posts that discuss this subject. Even better, we welcome your inquiries on how and why to perform vibe surveys, and how to interpret the results you're seeing. Feel free to call us at 405.896.0026, send email to firstname.lastname@example.org or simply fill your email address in the form below to have us contact you. To shop for a DynaVibe system, visit out online store.
David Trotter is Director of Maintenance at Chris Air, an agricultural operator that flies out of Lake Village Municipal Airport (M32) in Lake Village, Arkansas. David recently purchased a DynaVibe Classic, and after using it contacted us to share his experience using the system.
David balanced three of his aircraft, getting the prop imbalance balance on one of them down to .01 Inches Per Second in four run-ups. David shared, “We would normally be flying the airplanes about 40 miles to another shop for prop balancing. By my estimation we have already paid for the unit!”
Props are every bit as critical to the performance of airboats as airplane propellers are to aircraft. DynaVibe balances both equally well, as the principles of balancing don’t differ from airplanes to airboats. The benefits are also similar: less stress on the engine, the propeller, the mounts, instruments and hull.
Here are two stories of airboat prop balancing with DynaVibe.
An owner who had installed a modified 502 V-8 engine in his airboat experienced a problem on the 5-bladed prop he was using. After just 10 hours of use on the prop, the blades cracked, resulting in a catastrophic failure. Because the owner had balanced the prop at installation with DynaVibe, he had the diagnostic data to allow the blade manufacturer to rule out imbalance as the cause of the failure. Instead, the manufacturer determined that there wasn’t sufficient blade surface for the horsepower of the engine: the powerful engine was spinning the blades too fast. The manufacturer provided a new, 6-bladed prop at no charge to this owner. The new prop was also balanced, going from an initial vibration of .65 Inches Per Second (IPS) to .06 IPS on the final run. This owner shared, “It felt really good having the information from the DynaVibe balancing runs to go to the prop manufacturer on a warranty claim, which they quickly honored.”
Another airboat owner got help balancing his prop from a DynaVibe GX2 user. This airboat was running a Whirlwind prop on a Chevy engine with a Rotator brand reduction, and it was experiencing a pretty bad vibration in RPM transition at about 1/3 power. This initial balancing run revealed a severe vibration of 2.35 IPS, which after a series of balancing runs was reduced to .13 IPS. The GX2 owner shared, “At the last weight addition, it (the vibration) cleaned up significantly.” The following photo shows the balancing setup for this airboat:
DynaVibe owners can use their existing systems to balance airboats to get better performance and improve reliability. To learn more about using DynaVibe to balance airboats, call us at 405.896.0026 or enter your email address in the box below and a DynaVibe team member will contact you. Visit the online store to shop for DynaVibe. We welcome your questions!
For any operator, particularly the ag aviation operator, having an engine go out-of-service unexpectedly is not only frustrating, but potentially revenue-impacting, or worse, life-threatening. It’s not possible to predict all engine failures in advance, but it is possible to detect many of them through the use of a full-spectrum vibration survey.
A full-spectrum vibration survey, or vibe survey for short, is a procedure that uses engine-mounted sensors to measure the frequency and magnitude of vibrations emitted by an engine. Certain frequencies of vibrations map to specific problems or potential problems. In other words, a vibe survey can tell you a number of things about what’s going on inside your engine based on the presence of vibrations. Identifying these vibrations early, when they’re relatively small, allows the operator to address them before they result in a failure. For this reason, a vibe survey is an excellent preventative maintenance tool.
Conducting a vibe survey doesn’t take long, and most of the time is spent setting up the airplane with a phototachometer, reflective tape and an accelerometer to measure the vibration. Once the airplane is set up, the engine is run up to operating RPM and with the push of a button, the vibe survey data is captured. The photograph below shows the set up on a Grumman Ag-Cat with a Garrett TPE331 engine and a 3-blade prop:
Vibe surveys measure vibration in Inches Per Second (IPS). In general, the maximum, acceptable level of vibration is .15 IPS. However, vibrations at this level probably escape the notice of the operator, but a vibe survey can detect a vibration that an operator can’t yet feel. Vibrations of .50 IPS are substantial enough that, over time, they can damage the engine, airframe or instruments.
Most of the time, vibrations are the result of propeller assembly imbalance, a condition corrected by dynamically balancing the prop. Typically, a vibe survey is done as part of dynamic propeller balancing. The table below shows the actual result of a series of prop balancing runs performed using a DynaVibe GX2 prop balancer and vibration analyzer on the Ag-Cat.
The second column in the chart above shows the vibration magnitude for each successive prop balancing run. Subsequent columns show the recommended weight and location for adding that weight to balance the prop. At the end of the third balancing run, the vibration was almost eliminated, and was at a low enough level to not require further balancing runs.
Sometimes vibrations are more complex, and the value of a vibe survey is revealing the source of the vibration, particularly if the cause is something other than the prop. In the case of this particular Ag-Cat, the post-prop balancing vibe survey looked like this:
After prop balancing the only significant vibration remaining is the 3-per vibration (100 Hz) caused by the 3-bladed prop passing near the ground. This vibration is not a concern as it will go away once in the Ag-Cat is in the air.
Vibe surveys are a great way to do engine trend monitoring. Conduct a vibe survey on a new engine or anytime an engine has been overhauled. This baseline vibe survey then serves as the benchmark for comparing future vibe surveys done at regular intervals. The approach allows detection of vibrations when they’re relatively slight, before the operator can feel them. The operator is alerted to their presence and can continue to monitor them and address them before they grow to the point where they can damage the engine, or worse, result in a failure.
Matthew Mitchell, who operates Mitchell Flying Service based out of Perry Municipal Airport (F22) in Oklahoma, has been flying since 1990 and puts about 250 to 300 hours per year on his Grumman Ag-Cat. Mitchell has two TPE-331 engines that he rotates as needed. Anytime Mitchell puts an engine together, he likes to have a baseline vibe survey done. This allows him 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 system is the most affordable way to do dynamic propeller balancing and vibration surveys for engine trend monitoring. To learn more, contact the DynaVibe team at 405.896.0026 or email@example.com. You can also enter your email address in the form below if you want us to contact you. If you'd like to shop for a DynaVibe GX2, visit our online store.
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:
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 405.896.0026, by email at firstname.lastname@example.org or simply complete the form below and we'll contact you. To get pricing or buy a DynaVibe system, visit our online store.
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:
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:
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.
Here’s what you should take away from this vibration survey example and discussion:
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 405.896.0026 or enter your email address in the form below and we’ll respond.
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:
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.
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.
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 email@example.com, by telephone at 405.896.0026 or by entering your email address in the form below.
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.
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 firstname.lastname@example.org or just call us if you have questions about the process: 405.896.0026.