Prop balancing

[13brv3]

Glad to hear you got it balanced. .19 is actually not that bad, but as you can see, it's a lot worse than .03 Nothing good can come from vibration at any level.

There's a chart on page 10 of this document, which is the ACES (balancer manufacturer) guide to prop balancing. It gives the range of imbalance, with comments as to what you would expect from those levels.

http://www.acessystems.com/downloads/gpb/gpb.pdf

Cheers,
Rusty (currently balancing my coffee cup)

[Ironflight]

I've never had this done to one of my airplanes, but am considering givign the RV-8 the royal treatment (after she comes out of the paint shop!). One question I have always had is "how sensitive is the balance job to chnages?" - that is, if I take the spinner off for maintenance, and put it back on with screws in different holes, does that invalidate it? I mean, the adjustments I've seen are just one washer here or there...It almost seems like bugs on the blades coudl change it!

Paul

[13brv3]

Hi Paul,
I wouldn't think the difference in weight between similar type screws on the spinner would be much. At least I've never worried about it, but you could certainly buy a box of screws, and weigh them to find a set that were all the same weight. You'd need a really good scale, and a huge lack of anything better to do

Bugs could easily exceed the difference you'd make by swapping screws around. The farther an object is from the center of the prop, the more effect it has on balance. I'm sure you won't be allowing any bugs on your prop though

I flew my original RV-8 for about a hundred hours before I sold it, and it had a new Lycoming, Sensenich prop and aluminum spinner. I never noticed anything I would have considered rough, but by 100 hours, I was fixing stuff like cracked baffles. Later, I shook lots of stuff loose with a big wooden prop on my RV-3, until I bought a balancer. It was about .5 on the scale when I started, and MAN what a difference! I'm a true believer in balanced props now.

Cheers,
Rusty

[Ironflight]

I had always planned to have the -8's prop dynamically balanced, i just hadn't gotten around to it....with the one-year anniversary of first flight looming, a local itinerant prop balancing gentleman walked up and introduced himself the other day, and I saw no reason not to let him do the job this morning. In all my years of airplane ownership, this is not something I had treated myself to before, so I hadn't actually watched it - I took a couple pictures for folks who might be curious.

The accelerometer is mounted to a forward case bolt, so you run the test with the top cowl off. It took just a minute to attach the sensor and run the cable back and down the wing, taping it on to make sure it stayed put.



A small reflective piece of tape is put on the prop blade to reflect the strobe light. We then tied the tail of the plane to my truck ( as well as chocking the wheels and holding the brakes.),since I wasn't sure everything would hold at 2400 RPM.



The rest of the system is just a spectrum analyzer and a strobe light. The system flashes at the time of the peak acceleration, and that "freezes" the prop so the guy out front can see where the "heavy" point is.



Then it was simple to attach the balance weight and run up again. We only had to run the engine twice, because he guessed right on the weights the first time! I thought that things were pretty smooth as is, but we measured the imbalance at 0.27 ips the first time. Post-balancing, we had it down to 0.02 ips. It was noticeably smoother after balancing, just running on the taxiway. I didn't get a chance to fly it, but I am expecting it to really hum!

Paul

[13brv3]

Originally Posted by Ironflight

I thought that things were pretty smooth as is, but we measured the imbalance at 2.7 ips the first time. Post-balancing, we had it down to 0.02 ips. Paul

Hi Paul,

I sure hope you meant .27 and not 2.7

Rusty (no vibration at all, but then it's not running yet either)

[Ironflight]

Darn decimal points....yup 0.27!

Paul

[Ironflight]

Got a chance to fly with the newly-balanced prop this morning, and even though I thought the airplane was smooth before....it now is noticeably quieter and hums at cruise RPM. Well worth the money!

[dan]

Originally Posted by Ironflight

Well worth the money!

And imho, worth doing very early. I figure as soon as the engine is broken in, it's time. Otherwise you're subjecting everything in your airplane to needless vibration. Just my 2 cents!