Dynamic Prop Balancing

[Pat Hatch]

Originally Posted by ronschreck

When I had my Whirlwind 200RV inspected at 650 hours I asked if it needed to be re-balanced. According to them, NO.

Ron, I'm not so sure that what you are really doing is unbalancing the prop to balance the engine! At least that's the way the guy that did mine explained it to me. That you are really balancing the entire package of prop and engine combined. So that any unbalance inside your engine is compensated for by the weights added to the prop spinner. Of course, any unbalance in the prop is also being compensated. He was telling me that any prop work or major engine work (a cylinder change, for example) would be reason to re-balance.

Part of his sales pitch was extended avionics life, engine and airframe life, even the light bulbs will last longer. Made a big difference for me. I was amazed by the improvement in vibration level--very noticeable.

[Bill Phillips]

Webb, bit confused from the thread. Does he balance the prop on the plane or is the prop detached and balanced on a machine? How can we contact the fellow in MS that does the work so we can hire his services? Best regards, Bill

[Pat Hatch]

Originally Posted by Bill Phillips

Webb, bit confused from the thread. Does he balance the prop on the plane or is the prop detached and balanced on a machine? How can we contact the fellow in MS that does the work so we can hire his services? Best regards, Bill

I'm not Webb but I'll try to answer your question. It's called "dynamic balancing" because it is done on the plane with the prop in motion. In my case, they take off the top cowl and mount a vibration sensor on the top forward most case bolt on the engine. Next, a strobe sensor is mounted (taped) on the side of the bottom cowl pointed at the prop, about mid-blade. A reflective tape is placed on the back side of the prop blade aligned with the strobe/sensor. These two inputs are connected to a processor and the technician gives the thumbs up to start the engine. In my case, he wanted 2150 rpm and then he wanted me to dial the prop back to 2100 rpm so that the governor was controlling the prop and not the low-pitch stop. He then reads the vibration level and gets an approximate weight and coordinates for a correction. The correction is just a few grams of AN washers that are bolted to the back plate of the spinner at a certain angle and distance from the center of the crank. There is a bit of trial and error involved and he may want you to repeat the run and adjusts the weight until he gets most of the vibration out. The resulting AN washers are then permanently bolted to the spinner back plate. Put the spinner and top cowl back on and you are done. I think you can plan on spending anywhere from $150 to $300 or so. There are plenty of folks around who do the work and you should be able to find someone in your local area or nearby. It might help to get a group together if you need to bring someone in to do it.

[Bill Phillips]

Thanks for the info. I plan to have this done to my RV. Bill

[Radomir]

Bill, if you come to the Charlotte area let me know.. I have the instrument and I can do it for you... I charge $150..

[bhester]

I am now offering DynaVibe - Dynamic Prop Balancing Service! I just did my aircraft last week. Went from .48 ips to .06 ips with just a couple adjustments. I may fiddle with it later to get it even better but that made a big differance with the vibrations.

You can read about it on my web site:
http://home.newwavecomm.net/bobbyhes...gDecFlying.htm

[Bob Axsom]

As hard as it is to believe perhaps I have never had a prop dynamically balanced. Recently I replaced a Hartzell C/S with 7666 blades with one with F7496 blades. It is faster by 3 kts as advertized but it is noticeably roughter in vibration. After a few flights it seems fine and I'm interested in speed mainly but I'm thinking I may be able to get a fraction of a knot by getting the dynamic balance done at 2700+ rpm. Any experience in this in this frame of reference?

Bob Axsom

[rvmills]

Bob,

We balanced my Hartzell 80" D-twist 2-bladed prop at 2300 RPM, and brought it down from about .5 to about .03 IPS. Felt to me like a noticible difference...not super-dramatic, but noticible.

The most interesting result was that after the balance, 2750 (max) RPM feels to me like the smoothest RPM, and the vibes increase as I slow the prop, peaking at 2300 (go figure, that's where we balanced it!), and then smoothing a little as I back it off further.

That doesn't really answer your question about balancing it at max RPM, but I thought you might find it interesting. The prop guy (Golden State Propellor) is a friend, so I'll ask him what he thinks about your question.

On another note, I have had the prop off once since the DB (crank sensor install on the Electroair EI), and have wondered if doing so marginalized the previous balance. Interesting to revisit this thread to see what others have said (little of both, yea and nay). I'm pondering a Hartzell BA as well, so a new DB may have to wait till that decision is made.

Will let ya know what I hear from Eric at GSP.

Cheers,
Bob

[Bob Axsom]

Originally Posted by rvmills

Bob,

...

Will let ya know what I hear from Eric at GSP.

Cheers,
Bob

Looking forward to that information. It may be that there is no experience out there but if there is a benefit I find that hard to believe with all of the racers out there.

Bob Axsom

[Captain Avgas]

Originally Posted by Pat Hatch

Put the spinner and top cowl back on and you are done. I think you can plan on spending anywhere from $150 to $300 or so. There are plenty of folks around who do the work and you should be able to find someone in your local area or nearby. It might help to get a group together if you need to bring someone in to do it.

Pat, are you saying that the balance was done with the spinner off. I would imagine that a spinner itself (and particularly a Vans spinner) could be considerably out of balance.

I think I'd want the balancing done with the spinner installed.