Dynamic Propeller Balance

How does it work?

Adam,

The plane ran great. I’ve never been able to operate in the 2200 to 2300 RPM range. You have a great service. Could you refresh my memory on the additional prop work you thought I needed?

Thanks again.
Kirk

Dear Kirk,

We have recently received and updated our MicroVib computer, so there is a copy of your balance report in the mail.

Your initial powerplant vibration level reported in at 0.938 inches per second. After five engine runs, we were able to bring the vibration level to 0.053 IPS. A large amount of weight was required to meet this "smooth" propeller balance, and are located exactly opposite of the static balance weights installed at a prop shop when the propeller was last worked on (overhaul ?). I would recommend that the propeller assembly be sent to a prop shop for at least a static balance check (or overhaul if it is time). If you have this procedure preformed, you'll want to remove the dynamic balance weights from the spinner assembly prior to the prop shop getting the propeller, and perform a dynamic propeller balance subsequent to the prop shop work. In most cases, less weight will be needed for the dynamic prop balance. This is desirable because less compensation is working against a lesser vibration level. Why didn't I move the static weights, you ask? Has to do with a certification; having the manuals; a legal thing. I do not have the rating (propeller) to remove, balance, and install static weights on the propeller hub. Propeller overhaul shops have this ability.

In the meantime, you have a smooth running powerplant. The next time you have someone remove the spinner from the propeller, they'll just notice that you have a lot of balance weights installed ... and you'll know why.

Good to hear that your bird is running well. Glad we could be of service.

Keep in touch.

Adam Halop
A&P Aviation Services

Adam,

Does it pay to balance a new (600 hour) Cessna 172S? What about rigging?

I have no complaints on either, but I've seen what it can do for an older airplane.

Thanks,
Chick Svoboda

Dear Mr. Svoboda,

Couple of old sayings that apply here:

• "Never hurts to try."
• "You'll never know until you have it looked at by a professional".

[Top]

How does it work?

The prop balance service will use high tech equipment to pick up an imbalance of one thousandth of an inch per second (IPS) in your powerplant installation (engine/propeller combination), and gives the procedures and techniques to install permanent weights onto the propeller spinner assembly which will dynamically balance the propeller assembly.  An accelerometer is place on the engine, preferably on the center line of the crankcase, longitudinally in-line with the crankshaft and as close as possible to the propeller assembly.  A photocell (or laser optic) is placed on the exterior cowling to pick-up the placement of some reflective tape affixed to one of the propeller blades.  The accelerometer senses vibration and the photocell notes the location of the vibration (or highest point of vibration).  Both of these data points are inputted into a computer box through harness connections between the three units.  The computer box gives actual propeller rpm, vibration level, vibration location and what weight to install to gain a perfect 0.000 inch per second of vibration.  This vibration is lateral displacement, the difference of the two spinning masses, the propeller and the engine.

Once the initial engine run is complete to sense the initial vibration level, the first temporary weights are installed, per the computer's recommendation, then a second engine run is performed and the computer will take both first and second engine run data to compute if more weights are to be installed or moved to a better location to obtain a "smooth" propeller.  It is this third engine run that I use the previous steps data to gain the permanent weight location to be installed on the propeller assembly.

As time goes by and hours are incurred on your engine and propeller, normal wear-n-tear will take its toll on the static balances set by the engine and propeller manufacturers. Remember, each of these manufacturers produced their product independent of one another, and the static balance and turning mass of one unit (the engine) will not match the turning mass and static balance of another unit (the propeller). This is where a dynamic balance procedure of the powerplant assembly would verify if the inches per second of vibration is more than 0.1 IPS (inch per second) desired. Note, that the less vibration your powerplant produces and has to incur, the longer it will last, as well as less stress is put on the accessories, airframe and passengers.

To have our powerplant assembly dynamically balance with A&P Aviation Services, the cost includes a 2-3 hour completion of this procedure and an accuracy check of the mechanical engine tachometer is conducted.  All work is performed in accordance with Dynamic Solutions Systems MicroVib II, which meets FAA standards for this minor alteration.

Please contact A&PAS to schedule your dynamic propeller service: