Dynamic Prop Balancing

[Bruce]

Can anyone tell me who does this in the Dallas area.

Thanks,
Boomer

[Wallbangar]

Anyone know of a good guy near Austin, Tx. with a balancer ???????

[rcfaubion]

Originally Posted by Captain Avgas

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.

Just had my -4 done yesterday, left the spinner on and used the holes in the flywheel to attach weights (holes are spaced every 30 degrees). This worked great and now is very smooth!

[rcfaubion]

D-B my prop at 2150 (max static rpm), what can I expect the balance to be when turning 2500=2600 in cruise? And how would you account for this if there is a noticeable change? Any thoughts would be appreciated.

[mikegraycmg]

Byam Propeller at Meacham in Fort Worth is the main prop service in this part of the world. My recollection is that their balancing services are reasonably priced.

[cguarino]

I have a brand new Dyna Vibe balancer that I'll rent out (DFW) for $100 DIY. PM me.

[Geico266]

Anyone in the Lincoln, NE area I do balancing for $150.

Have RV, will travel to your place.

[rvmills]

Originally Posted by 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

Originally Posted by rvmills

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

Cheers,
Bob

Bob,

Sorry this took so long, but I finally talked with both Eric at Golden State Propellor, and John at American Air Racing. Both concurred that balancing at max RPM will not make you faster. In fact, given that you are running pretty smooth to start, a DB will probably have no perceptable impact on speed. Not sure if it would if you were running rough...unless you were a dern rattle-trap due to the prop...which of course you are not.

John explained that they do the DB at a mid-range RPM, one that "loads" the propellor (it's on the low-pitch stop, and creating thrust...thus bending forward a bit). He said if you went to a higher RPM, the prop would still be on the low pitch stop, and the increased thrust (bending moment) and speed/centifugal force would not make a significant difference in the dynamic balance...especially if the blades are well matched (they should be) and the prop was in good static balance. They both felt that the difference between 2300 RPM (for instance) and 2700 RPM would not be measurable. They both also chuckled when they said "and if you could keep the airplane on the ground...and find someone that was willing to stand in front of it!"

However, they both agreed that doing the DB will have a positive impact on the overall smoothness (albeit somewhat subjective). John added that even if your prop feels good now, a DB is well worth it, as there are vibes at frequencies you can't readily feel that may negatively impact the wear on the entire engine, engine mount, propellor system.

All FWIW of course...I personally think you'll get a knot or two out of it! And I wasn't paid to say that

Cheers,
Bob

[Bob Axsom]

Thanks for the information Bob I really appreciate your time and effort to get it and pass it along. I may do it at Hartzell some time in the future but not before the first race at Taylor, TX on 4-10-10. I fitted the second semi-flat wing tip yesterday and drilled the pilot mounting holes (#30). Some time today I will continue on with that effort. In the process I have been thinking of a way to cover the outboard aileron mounting brackets and associated openings. I still have to do the annual condition inspection so time is getting squeezed.

Bob Axsom

[jlk]

I have watched all the interest in dynamic balancing and I have had my Grumman Tiger balanced years ago, I am sure the equipment today is far superior to then.

What I bring up is the small weight differences in the balance process vs. the constant changes in the power systems of our planes. We use our planes. All props that are flown from pavement get stone dings. Metal props the dings are filed out and the prop touched up or repainted. We replace accessories, adjust timing and you get the idea do maintenance.

All these things change the balance of the rotating mass we call our engine and propeller. Constant speed props, the differential of the angle between blades while moving can cause changes in the vibration patterns; do we think our props move with absolute precision when changing pitch? Add to that, all this changes with RPM.

All this being said, I cannot see how balancing our power systems can have any long term affect, in the moment, at the rpm it was balanced, it is balanced. For how long and what about at other RPM. I propose that this is more placebo affect than actual science. You paid to have something done so you are invested in it, someone shows you a positive statistical result and you feel better about your plane.

I am not an engineer, I only try to present a logical arguement. I would like the engineering types to please put some more science in the discussion, one way or the other.