The International Cessna^® 170 Association

Hey guys,

Has anybody seen this?

http://www.rpxtech.com/index.html

Thoughts? Though it's comparing apples to oranges, I balance every propeller on my model airplanes, particularly my competition airframes for many of the reasons stated in their sales pitch. An R/C airplane is a completely different animal when it comes to airworthiness than a full-scale airplane is, so I was a bit taken aback when it was suggested that the preferred method for adding weight to the propeller was to simply put washers under the prop bolts. That seems a little unsafe to me, but then again, I'm no A&P.

That seems like a pretty cool tool to have, but I'm curious if anyone has ever dynamically balanced their propeller, and if there were any substantial benefits noted from doing so. I realize that these are 100 knot airplanes and that the C-145/O-300 is a very smooth engine. Any fine-tuned dynamic balancing is not going to make any quantifiable difference in speed or efficiency, but the reduced stress from vibration surely is worth investigation.

Thanks for the input!

Best regards,

Ryan

Ryan,

Instruments like the DynaVibe balancer have been around for a long long time in the helicopter world. They were expensive, and the mystery of their working was a black art understood by few and only a few got to use them. I've spent hours running up a helicopter and shutting it down so the mechanic could make a move only to shut it down for him to repeat. They took time and it was expensive and once some looked like the understood the system and could do it efficiently, they were dubbed the vibrex king and assigned to do all the balancing.

Over the years as computers have gotten better, faster, more power in a smaller package and more importantly, less expensive, it seems you see a few more machines around and more people have seen the benefit. At the same time helicopters have become more prevalent and there are more mechanics who understand the benefits and have learned the machine. And of course the machines have gotten easier to use through software enhancements and the black art has move to the software rather than the mechanic.

And if you have a machine how can you pay for it, balance airplane propellors on the side. And so you are seeing this practice more and more though I'd bet the vast majority of airplanes flying today have props that have only been statically balanced and then that was thousands of flight hours ago when it was last in a prop shop.

The problem is as you mentioned with a dynamic balance is unlike helicopter that were designed with a known place to install the washers, airplanes for the most part don't have a place for them. If you run a Lycoming you can mount them on the flywheel or more likely the spinner back and not be restricted to the prop bolts. With our Continentals, if you run a bullet spinner you can use the back plate as well though the diameter is more restrictive than many Lycomings. But if you are running a skull cap you only have the propellor bolts and that is pretty restrictive. Unlike a model propellor you can't shave the back of the prop or slightly clip the tip. Well you could I suppose clip the prop tip but only to a point and at the expense of a new prop. I wouldn't do it. Of course you could always add paint to a light blade or remove paint from a heavy blade but now we would be down to splitting hairs only for the extreme.

I've yet to have any of my airplane props balanced dynamically even though I've had the contacts to do so for some time. The charge is usually in the $150 to $300 neighborhood. I do think about it from time to time and a friend helicopter mechanic even owns one on my home airport. It just hasn't happened yet primarily because given the restrictions I have with no place to install weight on either of my aircraft and the doubt we could be able to improve anything. Kind of a $200 roll or the dice.

Units like the one posted have been around quite a while now with the older units costing 4-5 times as much as the unit you reference. I had mine balanced a few years back and it made a huge difference. I'll be putting a new prop on my 170 soon and will definitely get it done again.

Wow, you are a spry bunch of geezers on a Saturday morning.

Thanks for the background Bruce and the testimonial Karl. It sounds like it would be something worth pursuing. I appreciate you guys answering my incessant questions.

Ryan,
I was scheduled to balance the props on a Twin Beach (bomber) this morning at Aurora however the rain and wind have put us off.

I use the Aces balancer http://www.acessystems.com/.

I have had good success using the spinner backing plate to mount balance weight. I have never balanced a 170 with the scull cap however it should work ok using the prop mounting bolts, that is the way we have balanced a wood prop on a Stearman (using either washers and over length bolts or metal plates that span two prop mounting holes.

As Bruce has mentioned the computer controlled balancer is almost funny book simple, after all if Sandra Bullock can figure out how to fly a Russian or Chinese space ship from comic brook drawings I can figure out how to run a prop balancer. I have been able to get the vibration level on my 170 down to fluctuating between 0.00 and 0.01.

I have one and use it about 4 times a year on word of mouth. They work extremely well. I have had it for about 6 years. Worth every penny even on our 6 cylinders. It makes a huge difference in most cases. It also identifies pending trouble in the crank bearing area. Cant say enough good things. My testimonial is on the Dynavibe website. D