About airplanes...

Dynamic propeller balance is probably one of the most cost effective ways to decrease your operating costs. Let's face it, vibration causes fatique, and fatique causes failures. Sometimes they are annoying failures, a sheet metal crack here, a lost fastener there, and sometimes they are failures that really get your attention, like a cracked oil cooler or exhaust manifold. Ddynamic propeller balance equalizes the weight of the propeller and all it's attendant parts about the center of rotation. In effect, the propeller that is out of balance orbits about the physical center of rotation creating vibration at the speed of the propeller. It is typically measured using an accelerometer mounted on  the engine close to the propeller. The accelerometer measures all the vibration at that point and so the signal must be filtered to block frequencies other than the propeller. The other key to finding the imbalance point is a phase sensor. This is usually a photocell device of some sort triggered by a reflective strip. Earlier analog balancers fed this signal to a Strobe light used to observe a reflective strip on the propeller. The "angle" and the "amount" of vibration produced by the prop was then displayed on a meter, graph or display screen. Calculating the weight and location was up to the user.

  

Modern balancers are really BDLs (Balancer/Data Loggers) They still give the same readings, but perform balance calculations based on static or adaptive computer scripts to calculate balance solutions. The  higher end models now perform Fast Fourier Transforms, which parse the accelerometer signal into an X/Y plot of frequency and amplitude.The resulting "signature" can be used to diagnose a host of problems (not limited to the engine or prop). Spectrum analysis is used for everything from detecting individual submarines (acoustic) to identifying trace elements in your engine oil (light spectra) to scheduling downtime in a nuclear powerplant (vibration). The propeller is only one of the sources of vibration in an airplane engine. Getting the prop in balance is one thing, but to determine if everything else is running normally takes someone with  experience and a database. JFDynamics has both.

 

By observing these peaks and valleys of amplitude across the frequency band and by comparing to other engines with known good histories, a considerable amount of troubleshooting can be done with no dissassembly of the engine.  This is especially true of turbine powered aircraft. Vibration signature analysis is used for machine health, where it has proven to be an effective way to identify and predict failures before they are catastophic or result in an unscheduled shut down.  In most cases, a visual inspection or other measurement will confirm a problem. In some cases vibe analysis is the only way to identify pending failure. 

 

What can you expect after a dynamic balance?  A reasonable price, a tach check, a hard copy record of the engine vibration,  a log book entry, a quality weight installation that is safe, and a much smoother engine. Many pilots comment on the smoother low speed operation at idle. What is noticeable is the smoothness as the engine is accelerated to takeoff power. There is normally an overall smoothness at cruise, with many of the squeaks and rattles gone. What cannot be felt, but is also a byproduct of a fine balance is the lessened wear and tear on the engine and airframe.

 

 If you don't think your airplane can be improved via a dynamic balance, how do you know? Time and again "I think it is smooth" turns into "I thought it was smooth".  If your baffles look like Swiss cheese they have so many stop drills in them, or you don't have to stir your coffee while the airplane is running, or if you just want the assurance that things are up to snuff, drop an email or call.