Dynamic Propeller Balancing
The most common source of aircraft vibration is the result of imbalance between the propeller
and drive train. The vibration created due to the imbalance can effect a wide range of aircraft
systems, such as:
The dynamic propeller balancing procedure can be done on any aircraft in a flight-ready state. A small vibration sensor (accelerometer) is attached to the engine in a location where vibration due to mass imbalance is at the maximum--at the crankcase spine as close as possible to the propeller flange. A small tachometer pickup (photo-tach) is also mounted to the cowl or engine to produce a propeller tach signal. The engine is operated and the vibration and tach signals are processed by the balancing computer. The balancing computer measures the vibration level (magnitude) produced by the accelerometer which corresponds to the amount of mass imbalance which exists. The balancing computer also provides a "phase angle" which corresponds to the location of the mass imbalance on the propeller disk. The vibration and phase angle are used to compute a balance solution (weight amount and location). Once the prescribed weights are attached to the spinner bulkhead and the engine is run again, the computer "learns" the reaction to the weight and location of the trial weights installed and recomputes on each additional run process until the measured imbalance is found to be at an acceptable level. The entire process usually takes 3-5 runs and an average of 3-5 hours.
FAQs:
My aircraft runs fine. Why should I have my propeller dynamically balanced?
The average aircraft which has not had a dynamic prop balance has a vibration level due to propeller mass imbalance of about .45 inches per second velocity (IN/S). This level is over four times higher than what is considered to be an acceptable vibration level for propellers and represents a significantly higher level of wear and fatigue on engine components, accessories, airframe structure, avionics and electrical components than recommended. This average level can be noticeable to pilots and occupants, however, we often say that vibration is like cholesterol. Its accumulation creeps up on you without your noticing. As it increases gradually, our bodies become accustomed to it and its increase becomes rather unnoticeable. As with cholesterol, it is advisable to have a “check-up” to see what your actual vibration level is at. We recommend having a “check-up” at least every 500 hours of flight.
What level of propeller vibration is acceptable?
In most cases, the vibration level due to mass imbalance can be brought down to a value under .10 inches per second (IPS) very easily. In a Dynamic Solution Systems study, the average level seen post-propeller balance was .039 IPS, however, our average is less than .024 IPS! Propeller mass imbalance dominates the vibration levels in a normally operating combustion engine. We do have the technology, however, to single out the engine combustion rate vibration values by cylinder to help determine the health of your engine.
Won't having my propeller dynamically balanced "mask" other problems?
No. An engine with internal or external problems which result in unusual vibrations will not respond to prop balancing in the same way that an engine which only suffers from mass imbalance will. Evaluating ALL of the vibration data obtained helps us determine whether vibration is due to a propeller/engine mass imbalance or if there are other problems causing excess vibration.
If I have a new or overhauled propeller, is there any reason to have it checked?
When a prop balance is performed by the manufacturer or overhaul shop, it is a static (NOT MOVING) balance, or "bubble balance," on the propeller only. Dynamic balancing is performed on the entire rotating assembly (engine, propeller, spinner, extension, etc.) in its normal operating configuration while the engine is running. Constant speed propeller blades are centrifugally loaded and seated in the hub only under operating conditions. The result is a true balance under all operating conditions. We recommend that at least 5 hours of time are on a new or overhauled propeller before dynamically balancing to allow for grease leveling, seating of bearings, shim wear, etc., to occur.
Since I have a geared engine, is there any reason to have a dynamic balance performed?
Geared engines have a greater need of dynamic propeller balance because the propeller mass is greater compared to the reduction gear box mass. Studies done by the U.S. Navy indicate that dynamic propeller balancing on turboprop aircraft results in 100% increase in TBO of reduction gear boxes.
When should I have the prop rebalanced?
We recommend checking the dynamic balance at the next annual or 100 hour TIS (Time In Service) to indicate the wear/imbalance pattern over time of your prop/engine system. (This would be the optimal solution.) Also, if a large nick is reworked or the prop is removed and reinstalled for any reason, the dynamic balance should be re-checked as the location movement on the crankshaft flange can cause an imbalance level in excess of .3 IPS. We recommend that a dynamic balance check be performed at least every 500 hours maximum TIS.
Question for you:
Would you put tires on your car or truck without having a dynamic balance (spin balance) performed? Well, the propeller on your aircraft weighs as much or more than a car tire and can produce much higher vibration levels and is directly mounted to your engine. Why wouldn't you have the propeller dynamically balanced?
and drive train. The vibration created due to the imbalance can effect a wide range of aircraft
systems, such as:
- avionics, radio and indicator failure
- alternator or generator failure, attachment bracket cracks, thrown drive belts
- vacuum pump failure
- wiring harness failure, chafing, terminal end work hardening failure
- fuel control failure
- leaky oil coolers, cracked weldement areas
- cracked or broken exhaust components, heat muffs
- cracked or broken carburetor air box
- baffle, cowl and sheet metal cracks
- broken or cracked engine/turbocharger mounts
The dynamic propeller balancing procedure can be done on any aircraft in a flight-ready state. A small vibration sensor (accelerometer) is attached to the engine in a location where vibration due to mass imbalance is at the maximum--at the crankcase spine as close as possible to the propeller flange. A small tachometer pickup (photo-tach) is also mounted to the cowl or engine to produce a propeller tach signal. The engine is operated and the vibration and tach signals are processed by the balancing computer. The balancing computer measures the vibration level (magnitude) produced by the accelerometer which corresponds to the amount of mass imbalance which exists. The balancing computer also provides a "phase angle" which corresponds to the location of the mass imbalance on the propeller disk. The vibration and phase angle are used to compute a balance solution (weight amount and location). Once the prescribed weights are attached to the spinner bulkhead and the engine is run again, the computer "learns" the reaction to the weight and location of the trial weights installed and recomputes on each additional run process until the measured imbalance is found to be at an acceptable level. The entire process usually takes 3-5 runs and an average of 3-5 hours.
FAQs:
My aircraft runs fine. Why should I have my propeller dynamically balanced?
The average aircraft which has not had a dynamic prop balance has a vibration level due to propeller mass imbalance of about .45 inches per second velocity (IN/S). This level is over four times higher than what is considered to be an acceptable vibration level for propellers and represents a significantly higher level of wear and fatigue on engine components, accessories, airframe structure, avionics and electrical components than recommended. This average level can be noticeable to pilots and occupants, however, we often say that vibration is like cholesterol. Its accumulation creeps up on you without your noticing. As it increases gradually, our bodies become accustomed to it and its increase becomes rather unnoticeable. As with cholesterol, it is advisable to have a “check-up” to see what your actual vibration level is at. We recommend having a “check-up” at least every 500 hours of flight.
What level of propeller vibration is acceptable?
In most cases, the vibration level due to mass imbalance can be brought down to a value under .10 inches per second (IPS) very easily. In a Dynamic Solution Systems study, the average level seen post-propeller balance was .039 IPS, however, our average is less than .024 IPS! Propeller mass imbalance dominates the vibration levels in a normally operating combustion engine. We do have the technology, however, to single out the engine combustion rate vibration values by cylinder to help determine the health of your engine.
Won't having my propeller dynamically balanced "mask" other problems?
No. An engine with internal or external problems which result in unusual vibrations will not respond to prop balancing in the same way that an engine which only suffers from mass imbalance will. Evaluating ALL of the vibration data obtained helps us determine whether vibration is due to a propeller/engine mass imbalance or if there are other problems causing excess vibration.
If I have a new or overhauled propeller, is there any reason to have it checked?
When a prop balance is performed by the manufacturer or overhaul shop, it is a static (NOT MOVING) balance, or "bubble balance," on the propeller only. Dynamic balancing is performed on the entire rotating assembly (engine, propeller, spinner, extension, etc.) in its normal operating configuration while the engine is running. Constant speed propeller blades are centrifugally loaded and seated in the hub only under operating conditions. The result is a true balance under all operating conditions. We recommend that at least 5 hours of time are on a new or overhauled propeller before dynamically balancing to allow for grease leveling, seating of bearings, shim wear, etc., to occur.
Since I have a geared engine, is there any reason to have a dynamic balance performed?
Geared engines have a greater need of dynamic propeller balance because the propeller mass is greater compared to the reduction gear box mass. Studies done by the U.S. Navy indicate that dynamic propeller balancing on turboprop aircraft results in 100% increase in TBO of reduction gear boxes.
When should I have the prop rebalanced?
We recommend checking the dynamic balance at the next annual or 100 hour TIS (Time In Service) to indicate the wear/imbalance pattern over time of your prop/engine system. (This would be the optimal solution.) Also, if a large nick is reworked or the prop is removed and reinstalled for any reason, the dynamic balance should be re-checked as the location movement on the crankshaft flange can cause an imbalance level in excess of .3 IPS. We recommend that a dynamic balance check be performed at least every 500 hours maximum TIS.
Question for you:
Would you put tires on your car or truck without having a dynamic balance (spin balance) performed? Well, the propeller on your aircraft weighs as much or more than a car tire and can produce much higher vibration levels and is directly mounted to your engine. Why wouldn't you have the propeller dynamically balanced?
