What’s Shakin, Part Two

By Ray McNaught, EAA chapter 1541 Board member

Now that you know how an out of balance propeller/rotating assembly causes wear and tear on every system in your airplane I wanted to let you know EAA Chapter 1541 members have a solution for a smoother running engine. We now have access to a DynaVibe GX3 state of the art, top of the line balancer made by RPX technologies.

Whether you take advantage of this balancer or go to your favorite mechanic and pay him $250 to balance your prop you should get it done for the long term health of your airplane and your enhanced personal comfort while flying.

First, if you own an experimental aircraft you can balance your prop yourself and make your own logbook entry with my help running the balancer and showing you where and how to add the correct amount of weight. We will dynamically balance your propeller following guidelines found in the ACES Systems Guide to Propeller Balancing as spelled out in FAA ADVISORY CIRCULAR, AIRCRAFT PROPELLER MAINTENANCE- AC 20-37E.

Second, If you own a certified aircraft we can still get it balanced with the supervision of a local A&P.

What does it cost? You ask. For your experimental I’m asking for a $150.00 donation. Of which $100.00 will go toward the cost of the balancer and it’s annual “NIST” traceable calibration certification and $50.00 will go into the EAA chapter 1541 “Permanent Home” Hangar Fund. Should your aircraft be Certified I am trying to get one of our local AP/IA’s to supervise the process for an additional $50.00 ($200.00 total).

I anticipate that on a rare occasion there will be an aircraft that will already be in balance and in that case I would ask for a minimum of the Hangar fund donation of $50.00.

I recently balanced an RV-9A and the owner asked that I check the balance first because it had previously been dynamically balanced a few years before. The result was a .35 ips vibration (ips= inches per second, the value used for vibration amplitude). .25 ips – 1.0 ips is considered a rough vibration (or in the red zone!) After removing the previous balance weights the balance had improved to .20 ips and the analyzer had a solution to reduce the prop vibration. The balance weight asked for was added and another run revealed another solution for further vibration reduction. The next and last run showed we had reduced vibration to .04ips which is in the excellent to perfect range!

After accepting the final balance the analyzer generates a report along with a spectral analysis of all vibrations that it senses. The spectral analysis revealed that there was a vibration that occurred between one fourth to one half the frequency of the rotating mass of the propeller/engine assembly. This typically indicates something loose like motor mounts being loose or worn. Since the owner of the aircraft was already aware that the spinner of his RV was sagging about a half inch below the cowling he decided he would put in new lord motor mounts. After the new mounts were installed we performed another balance run (just to see!) This time the prop came in at .02 ips at 2,100 rpm, and the lower frequency vibration from the worn mounts was reduced way down into the normal range.

If you would like to have a smoother running airplane or even just verify your propellers dynamic balance is in an acceptable range or just get more information please send a text message to Ray McNaught at 916-768-5630 or send an email.