As the creators and inventors of DynaVibe – the RPX Technologies dynamic balancing system – we’re naturally proud of the innovation it represents, as well as its affordability. DynaVibe with its accessory DynaTrack optical tracker, or the optional turbine kit, is a leading-edge, state-of-the-art system for prop balancing, blade tracking and turbine vibration surveys. So what?
In the 10 years since RPX was founded, we’ve learned some important truths about how customers perceive and evaluate solutions. We can make some wonderful claims about how affordable DynaVibe is, how easy it is to use, how it makes quick work of prop balancing, or even how differently an airplane or helicopter flies once props are balanced or blades are in track. But, despite the claims we can make about DynaVibe, we’ve learned there’s just one customer question we must answer: “Why should I care?”
In the decade we’ve served the aviation industry, we’ve collected a lot of prop balancing data. We know this: there’s an 80% chance that the general aviation aircraft you are flying has an unbalanced prop. What does that mean? From a technical sense, it means that the measurable vibration exceeds .15 Inches Per Second (IPS), the maximum acceptable vibration level after dynamic balancing. At .15 IPS vibration may not seem like much, but it is not a lack of vibration. Four out of five GA aircraft are flying with vibration levels of .15 IPS or greater.
What’s the problem with this? Vibration only has negative consequences. Your unbalanced prop is either:
Or some combination of these three things.
Dynamically balancing your prop is a quick and easy fix. We have a page on our website – and numerous blog posts – that all share the testimony of those who have rid their aircraft of vibration by using DynaVibe. If we were to summarize, in the sentence, what we often hear after balancing, it would be “I can’t believe the difference!” or “It feels like a brand-new airplane!” You will feel a difference when you dynamically balance your prop. If it could, your plane would thank you.
RPX also sells the most affordable track-and-balance system for helicopters, that also is very easy to use, and streamlines the track-and-balance process. But again, “Why should I care?” is a fair question.
The track-and-balance process is a bit more complex than the prop balancing process, and historically, the equipment has been more complex to use as well. Since we entered this market with our DynaTrack solution, we found that many shops who had older track-and-balance gear were frustrated with it. It was hard to use, took too long to complete the process, or both. The result in many cases was that tracking on blades on some ships wasn’t done, or done very often, because the process was too difficult.
We’ve found that there are two types of users who really value DynaTrack. One is the user who previously could not afford the $20,000+ price tag of a track-and-balance system. At under $7,000, our system is within reach of almost everyone!
The other type of user that has grown to love DynaTrack is the one who was frustrated with their old system. Ours is really easy to set-up and use, and because it is so affordable, you can replace your old, frustrating equipment with the DynaTrack which is easy to operate. With our patented Blue-Track technology, it is easy to accurately track blades under a wider variety of sky conditions, saving you a lot of time and frustration. Because DynaTrack is so affordable, you can have a couple at the shop so your mechanics can work on multiple ships simultaneously and an additional tracker in the field which would increase productivity and make you more money.
In summary, customers care about DynaTrack because it is less frustrating to use than your existing equipment and it will make you more productive. DynaTrack is also contributing to cleaner air around the shops that use it. Not because of carbon emissions, but because its use is not accompanied by cursing. Track, balance, done! No profanity needed.
Warren Cilliers owns Cilliers Aviation, a maintenance business in Palatka, Florida, where he works primarily on aerobatic airplanes, such as the Extra 330SC. He also travels the world as technician for Michael Goulian and Team 99, as Goulian competes in the Red Bull Air Race World Championship. In both endeavors, Cilliers uses a DynaVibe Classic to perform dynamic propeller balancing. “Definitely used the DynaVibe and it’s really helped us out,” says Cilliers.
In the past year, Cilliers estimates he has used DynaVibe to complete 40 prop balances. “That's without advertising,” says Cilliers. “It's really just my customers that come through my shop and word of mouth in the area. It's been great.”
Cilliers understands the preventative maintenance benefits of keeping propellers balanced: “It's obviously very important on any aircraft, not only aerobatic airplanes, for fatigue and wearing of parts, gears in the engine, magnetos, everything, even going down to fatigue on the airframe, with vibration and cracks on the aluminum and things like that.” Because of the benefits, dynamic balancing with DynaVibe has become a standard procedure Cilliers does for his customers. “It's so easy to work. I've got it down to an art now, where I can just take it out in my ground run, and just balance it for them. They really appreciate it.”
Cilliers is getting great results from balancing with DynaVibe that his customers can feel. “I've never had any negative report back from any customer. Whenever I do a balance, even if it's not as much out-of-balance [to start with] – where I think the customer would not even feel it – they always report back that they notice a difference.”
Customers feel the difference and get the benefits of Cillier’s balancing work. With DynaVibe, the balancing process is easy and the payback on the investment in the balancing equipment has been excellent. “The simplicity of DynaVibe makes it easy. It's been great, and well worth the $1,600 that I've spent. I've probably paid for it about 10 times already, so I’m very, very pleased with it.”
We sometimes refer to our offices here at RPX Technologies HQ as "nerdville" because our work involves lots of "techie" tools like 3D printers, laser cutters, compilers, mathematical simulation software, and an array of gadgets and electronic test equipment that bring out the inner nerd in us. So, when we get questions about the science behind how DynaVibe actually works, there's almost a competition to see who can be first to answer the question!
Last week we got a question that we loved, because it lets us talk about the principles behind how DynaVibe prop balancing equipment works. Here's what came in:
Q: Balance limits are usually specified in IPS (inches per second). But an accelerometer measures acceleration (G-forces) which are measured in inches per second per second (in/sec^2 [IPSS]). Which is actually measured? If it is IPS, how is that determined from the acceleration?
Kudos to Tom, the submitter of this question through our email@example.com email address (where anyone is welcome to correspond with us)! Here's the answer:
A: You are correct. Vibration is often measured using accelerometers, which directly measure acceleration (e.g., IPSS). Acceleration must be converted to velocity (e.g., IPS) by also considering the frequency of interest and doing the math. The DynaVibe is doing this conversion continuously using one of several methods depending on the operating mode.
You may be wondering why IPS (velocity) is reported, and not IPSS (acceleration). The reason is that velocity is more indicative of machine damage from vibrations in the "thousand cycles per minute" range (for example, engine or prop RPM). While not aviation specific, various standards (notably ISO 10816) cover vibration analysis for machinery of various types, sizes, and rotating speeds. Charts like the one below (notice that velocity in IPS is on the left vertical axis) are quite common in the machinery world:
At very high frequencies (i.e., ultrasonics), acceleration is commonly used and is often reported in "g" units. (This is what the DynaVibe GX3 with Turbine Kit, with our high speed accelerometer, measures and reports in VibeSurvey and Williams modes).
With many of the DynaVibe GX3 modes that utilize our standard accelerometer, such as Spectrum mode, we default to velocity, in IPS, with the option to switch views to acceleration, in IPSS.
By the way, as frequencies get very low, displacement is used (i.e., low frequency fatigue/bending). This typically uses different instrumentation than for acceleration and velocity.
How does all of this lead us back to velocity and IPS? Propellers just happen to be in that middle range shown in this graph, where velocity is the best indicator of damage and the preferred U.S. unit of measure for propeller vibration is IPS.
We love getting questions like this, so if you have one you want to ask, please use our "Contact Us" form to let us know what's on your mind.
Your prop was statically balanced at the factory and that's good enough?
A static balance may balance the prop but it does not correct the net imbalance of the rotating assembly.
This is a relatively new, statically balanced prop on a Cessna 210. The first "statically balanced" reading was 0.6 IPS, which is pretty typical. It took 10 large washers (mind the reflection which makes it look like 20) on the spinner to pull it into balance (0.06 IPS).
This may look like a lot of weight, but the rotational forces are now neutral! Before the prop was dynamically balanced, this is the amount of weight was constantly shaking the airplane and stressing every part of the engine and airframe. That's a LOT of stress at 2000+ RPM!!!
The point is that a prop static balance is not enough. The static balance gets the balance in the ball park but you really need to balance the entire assembly. Not just the prop. The latest data that we have been analyzing shows that around 80% of all GA aircraft are flying with imbalanced props even though most were statically balanced.
Running your air cooled engine with the cowl removed is harder on the engine than you may realize. Uncowled, air is blown over the cylinders and not through the cylinder's cooling fins. So the bottom of the engine is left to heat-soak and the top is cooled. This uneven heating results in distorted cylinders which damages the cylinders and the moving parts inside the cylinders.
Continental recommends fabricating a scoop out of sheet metal for use when running up the engine on the ground when the cowl is removed. This provides a safe amount of airflow for runups and can usually be constructed in a way that it is out of the way for most maintenance procedures. (Drawing credit: Continental Motors)
Bob Pastusek is vice-president and a board member of the Lancair Owners & Builders Organization – LOBO – and is their go-to maintenance guy. A few years ago, the LOBO Board became concerned that people were not tuning up their airplanes properly; they were not following all the recommended engine and airplane manufacturer’s guidelines in doing their condition inspections. “Experimental owners are not obliged to follow them,” said Pastusek. “Nonetheless, like putting air in your tires or oil in your engine, some recommendations are more significant than others. We came to the conclusion that some people were not doing some of the important ones, based on accidents and probable cause findings that indicated maintenance wasn’t as good on these airplanes as it could be.”
In December 2014, LOBO put together a kit of materials for testing and inspecting the engines, specifically Continental aircraft engines. “This worked out really well for us,” Pastusek continued. “So at the fall LOBO fly-in, we asked what people (members) thought about it, and the feedback expressed a desire to include some additional equipment in the kit. One of the principal requested pieces of equipment was a prop balancer.”
Pastusek first learned about the DynaVibe aircraft propeller balancing system at Oshkosh four or five years ago. He bought one for his local EAA chapter and has used it several times to help chapter members balance their props. “Having personal experience with DynaVibe, knowing that it works and that it is a reasonably priced piece of gear that our average homebuilder could figure out how to use, we bought new DynaVibe systems to include in our three engine inspection and tune-up kits.”
Pastusek recognizes the importance of keeping the prop in balance. “It makes the airplane engine run smoother, with less wear-and-tear on the engine. The aircraft is much more pleasant to fly.” In general, Lancairs use factory-balanced, high-end adjustable pitch props. “They come pretty well balanced; we generally don’t have an issue with props significantly out-of-balance. However, there are a couple of things that homebuilders can do, particularly in mounting the spinners and things like that, that can cause them to be out of balance. It’s a very easy thing to check and improve. If you find the prop out of balance and fix it, it really makes the airplane run a lot smoother. These are very large engines in relatively small and lightweight aircraft, so a prop imbalance will shake the airplane around pretty well.”
The LOBO engine test kit with the DynaVibe prop balancing system is expected to be available to members in April 2016. “We think the DynaVibe is a relatively sophisticated but easy tool to use in the field,” Pastusek concluded. “It works like a champ.”
The affordable DynaVibe Classic propeller balancing system is just $1,495 shop for it the DynaVibe online store. If you'd like to know more about DynaVibe, please contact us at 405.896.0026, firstname.lastname@example.org, or click on "Contact Us" tab near the bottom of this page to enter your email address or phone number and we’ll contact you!
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 email@example.com or click on the "Contact Us" tab.
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!”
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 click on the yellow "Contact Us" tab near the bottom of this page and we’ll contact you. To get pricing or buy a DynaVibe system, visit our online store.
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. Fill out the form on our Contact Us page and we’ll respond to you. Visit the online store to buy your own DynaVibe unit, email us with your questions at email@example.com or just call us if you have questions about the process: 405.714.2516.