What is a Dynamic Propeller Balance?

This is the process where an electronic balancer is attached to the aircraft engine and the rotational imbalance is measured and corrected. This is the same principle as balancing the tires on your automobile. The unit of measure for  propeller vibrations is IPS. IPS is just an acronym for "inches per second"  (velocity). When measuring a vibration, the velocity is the speed the object reaches as it passes through the center of the range of displacement. Similar to the highest speed a pendulum reaches at the center of its swing. It has been found through experience that velocity is a better unit of measurement to use if you want the numbers to track with how severe a vibration is independent of RPM. In other words, a 1 IPS vibration is pretty severe no matter if the object is turning at 200 RPM or 200,000 RPM.  

What do I get out of a dynamic balance?

• Better quality ride
• Minimize vibration
• Minimize cabin noise
• Minimize structural stresses
• Minimize pilot fatigue
• Minimize power loss
• Increase bearing life

The above items are things that can happen because of a propeller balance. The worse the vibration, the more return you get on your preventive maintenance when the propeller is balanced. The less the vibration, the less the wear and tear on components.

When should I have my propeller balanced?

• If it has never been balanced before
• Engine overhaul
• Propeller overhaul
• After any major maintenance performed on the engine
• Installation of NEW propeller or engine
• At each 100 hours time in service
• At each annual inspection
• Any time the propeller is removed and reinstalled

The above items are suggestions, the optimal solutions to keep propeller vibrations low. The dynamic balance, balances the entire rotating powertrain. A .001 of an inch change on the engine shaft during a propeller removal and reinstallation can cause upwards of a .3 ips of vibration.

Signs that your propeller needs balancing

• Repeated cracking of engine baffles
• Generator/Alternator mounts breaking
• Repeated exhaust cracks
• Spinner bulkhead cracking
• Spinners cracking
• Compass fluid "foaming"
• Feet "falling asleep" during flights
• Instrument panel shaking
• Repeated instrument failures
• Repeated carburetor air box cracking
• Cowling and sheet metal cracking
• Cracked or broken engine mounts

I know what a Dynamic balance is, why should I have it done to my aircraft, it feels fine?

The average vibration level on most aircraft that has not had a dynamic balance completed on its rotating powertrain is above .4 ips.  This level is 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. The original accepted level of vibration in aviation is .2 ips (only because the first balancers used started to give questionable solutions below .2 ips. One started chasing their tail). Most technicians still use this as their limit. With the newer systems on the market, the ips levels can be constantly lowered to well below .2 ips. If you have been flying the same aircraft for a period of time, you will get accustomed to the vibration that is being produced (feels fine). After the propeller is balanced is when it is realized just how much vibration was present. The aircraft manufacturer subjects their products to vibration and shock testing to determine possible times before failure. The less vibration an aircraft or product is subject to, the longer the lifespan between failures. Vibration redirects energy from the intended purpose into bearing area friction; friction will rob your horsepower! The smoother the rotating power unit is, there could be more available horsepower produced to the propeller and which could produce more thrust. Your vibration level may be significantly higher or lower than the average, but only a trained technician with a vibration analyzer can tell for sure.

What level of propeller vibration is acceptable?

Here are some vibration levels that are possible, and what to expect at the different levels.

DANGER------------------1.25 Inches per second. This is very rough and dangerous to
		the aircraft and components. The propeller should be removed
		and a static balance performed.
VERY ROUGH----------1.00 Inches per second. Propeller can be dynamically balanced;
		a large amount of weight will be required, not the best solution.
		Ideally, the propeller should be removed and a static balance
		performed. For any level above a .8 ips you should consider a static balance.
ROUGH--------------------.5 Inches per second. Propeller balancing will greatly enhance the ride comfort.
		Long term operation at this level could cause premature wear.
SLIGHTLY ROUGH----.25 inches per second. Again, a balance will enhance ride comfort and reduce
		possible premature wear.
FAIR-------------------------.15 Inches per second. The maximum vibration level after a dynamic balance.
GOOD----------------------.07 Inches per second. Vibrations at this level and below is considered to be
		the area where the pilot and passengers will not feel any rotational imbalance.
		This level and below should be the balancing goal.