Dynamic Propeller Balancing

How to Safeguard Your Aircraft’s Parts & Components and Elevate Your and Your Passengers' Comfort Level with Dynamic Propeller Balancing.

Vibrations make flying uncomfortable for pilots and passengers, and prolonged vibrations put excess stress on critical components in your aircraft. Engine mounts, magnetos, avionics, control systems, and nearly every part of the aircraft can be affected by excessive vibration. If you find loose rivets and cracks in the aircraft cowling or spinner, dynamic propeller balancing could be beneficial.

Sometimes, what appears to be engine vibration is actually due to an imbalanced propeller. Even if you can’t feel or hear vibration while flying, your aircraft propeller could still be out of balance. Over time, a slight propeller imbalance can lead to vibration problems that gradually grow in magnitude and compromise flight safety. Often, pilots become accustomed to the level of vibration and do not notice the increase in vibration over time.

Proper propeller balancing is key to correcting vibration issues early, helping to prolong the service life of components ranging from the exhaust system, engine mount, and airframe to the cowling, spinner, instruments, and avionics.

Unfortunately, many pilot-owners do not take imbalanced propellers seriously or are even unaware that their propeller installation is out of balance. Similar to engine pre-heating and preservation, dynamic propeller balancing is often neglected. It is striking that pilot-owners spend substantial amounts on their aircraft and various accessories, yet overlook simple, effective maintenance that can keep their aircraft in top shape.

Why Dynamic Propeller Balancing Is Important

All propellers come from the factory or propeller shop statically balanced, which simply ensures that no single blade weighs more than another. However, dynamic balancing measures the vibration experienced by the engine/propeller system as a whole during operation.

Static Propeller Balancing

Static propeller balancing involves ensuring the propeller is balanced within itself, so that no blade is heavier or lighter than the others. High-quality propellers are typically statically balanced right from the factory, and this is also a standard procedure performed by propeller shops after routine repairs or overhauls.

While not a mandatory part of the overhaul process, pilot-owners are advised to opt for dynamic balancing to fine-tune their propeller assembly and safeguard critical aircraft components. This method uses accelerometer sensors to measure vibration magnitudes in inches per second (IPS) that the engine/propeller system experiences while in operation.

This technology enables us to determine the exact angle of imbalance, allowing us to add or remove a small amount of weight to achieve balance. The process is repeated until the assembly is optimally balanced. With its high level of precision, dynamic balancing ensures that the engine and propeller combination is balanced as a whole, significantly smoothing the aircraft’s overall operation.

Although not all vibrations can be completely eliminated — vibrations from engine combustion, gear reductions, and accessories may persist — reducing vibration through dynamic balancing can significantly decrease fatigue and damage to the aircraft.

When and How To Dynamically Balance Your Propeller

It is advisable to perform dynamic propeller balancing when the propeller is initially installed, removed and reinstalled, repaired, or if there has been a change in the engine/propeller installation. This process is conducted using specialised equipment that accurately measures vibration and precisely identifies the location of the imbalance.

Pre-Balance Inspection and Precautions

Dynamic propeller balancing requires several preliminary checks to prevent issues during the process:

- Check for any applicable airworthiness directives or service bulletins for the engine/propeller combination; some combinations may require modified dampers due to increased torque impulses.
- Ensure compliance with manufacturer’s and legal requirements for dynamic propeller balancing.
- Inspect the propeller blades for damage and overall condition.
- Examine the spinner and attachment bulkheads for any mass imbalances caused by foreign material, missing screws, or damage.
- Verify correct blade tracking. Any tracking errors should be thoroughly investigated and corrected, which may require sending the propeller to a repair station.
- Perform any necessary maintenance and/or repairs before dynamic balancing.
- Note and remove any existing dynamic balancing weights, but retain any static balance weights.
- Secure all loose cables and properly tie down the aircraft.

Equipment Installation

Begin by removing the engine cowling(s). Mount an accelerometer on the top of the engine, vertically, perpendicular to piston travel, and as far forward as safety permits to maximise sensitivity. Install the optical tachometer behind the propeller, aimed at a strip of reflective tape on one of the propeller blades. Ensure the tape is placed on a flat, non-rounded surface so that light from the tachometer reflects back to its sensor.

Perform Dynamic Propeller Balancing

Typically, it is possible to enter aircraft details into the balancing equipment’s user interface and print a test report. Follow the manufacturer’s instructions for specific test modes and procedures. Start the engine as per the aircraft/engine manual, setting the predetermined propeller speed after engine warm-up. Collect the data, then shut down the engine after completing the tests and allowing for a cool-down phase.

Based on the collected data, determine the necessary balancing weights, usually added in the form of screws, nuts, washers, or bolts (if on the flywheel). Adjust the weights and repeat the process, refining as needed until achieving a vibration magnitude of 0.07 IPS or lower. Once the target vibration level is met, print or save the report, deinstall the equipment, and reinstall the removed engine cowling(s).

Recommended Equipment for Dynamic Propeller Balancing

Among the most popular systems on the market are the DynaVibe Classic and GX systems from RPX Technologies. These DynaVibe systems include a handheld analyser with accelerometer sensors and tachometer. They provide an automatic “solution” to counterbalance the propeller’s imbalance and reduce vibration. This solution typically involves adding weight either on the prop spinner or on the flywheel (for Lycoming engines) opposite the location of the existing heavy spot. As flywheels and spinners have pre-existing locations for mounting screws or bolts, the system automatically suggests a “Split Solution” that allocates the weight among the existing locations without the need for drilling new holes.

Another widely used system is the MicroVib™ II Aircraft Analyzer from Dynamic Solutions Systems. The MicroVib™ II Aircraft Analyzer offers similar features but is twice as expensive, making it a potential choice for professional users.

Conclusion

Anytime your propeller is removed from the aircraft for service, repair, or overhaul, performing dynamic balancing is a prudent preventative measure. Even if the flight seemed smooth and the propeller had never been removed, many pilots report a noticeable improvement in their flying experience after dynamic propeller balancing. This is likely because the engine/propeller setup had never been dynamically balanced initially. It’s remarkable how much more comfortable flying can be with reduced vibration.

About Quest Aeronautics

Quest Aeronautics is a state-certified engineering office for aviation, dedicated to shaping the future of general aviation by providing innovative and cost-effective solutions to enhance aircraft performance and operations. With a focus on CS/FAR-23 and experimental/amateur-built (E/A-B) aircraft, Quest Aeronautics provides a range of services including flight testing, aircraft operations and maintenance consulting, high-quality aviation products, and tailored support for E/A-B projects. Collaborating with industry-leading partners, Quest Aeronautics is committed to delivering unparalleled support and expertise to individuals and organisations in the general aviation market.

About Author

Sebastian, the founder of Quest Aeronautics, is a driven and enthusiastic individual with a passion for aviation. Before delving into aviation, he gained valuable experience as a chemical process engineer and laboratory technician. Sebastian holds a Master of Science in Engineering and a commercial pilot licence, with several fixed-wing aircraft ratings under his belt. He has also completed an introduction course for fixed-wing performance and flying qualities flight testing at the National Test Pilot School in Mojave, CA and is compliance verification engineer for flight.