Prop balancing

I am considering removing the outer rivets from the doubler plate of the spinner backplate and substituting with 6/32 screws and nuts. This will enable me to balance the hartsell constant speed prop . ie it will enable a place to add weights for balancing.
What have others done?

It doesn't take much

rv72004 said:

I am considering removing the outer rivets from the doubler plate of the spinner backplate and substituting with 6/32 screws and nuts. This will enable me to balance the hartsell constant speed prop . ie it will enable a place to add weights for balancing.
What have others done?

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Personally, I wouldn't go to that much trouble. It usually doesn't take that much weight. All I had to do when we balanced mine was to replace one of the spinner mounting screws with a longer screw and a thick washer.

Don't know about your hub, but my C2YK hub has no fewer than 6 built-in provisions for adding weight -- two at each blade root and one on each side of the rear of the hub (maybe more if I missed 'em). When I had my prop balanced, it was an 8 gram weight that needed to be added. We're talking miniscule. Take a look at your prop hub and you'll probably see the "built-in" locations I'm talkin' about.

The guy who dynamically balances props around here (http://www.propbalancing.com/) puts the weights, which are small AN3 bolts, in the holes on the ring gear. What else would those holes be for?

AlexPeterson said:

What else would those holes be for?

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Harmonic dampener? Just a guess. I'll ask the guy I know from SoCal who recently installed one how he mounted it...

Harmonic dampeners (at least the Landoll) are mounted using these holes, but I don't know if that was the intended purpose for them.

AlexPeterson said:

The guy who dynamically balances props around here (http://www.propbalancing.com/) puts the weights, which are small AN3 bolts, in the holes on the ring gear. What else would those holes be for?

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I've seen this done, and have done it myself as well. It sure seems to work well, and it's convenient as can be.

Cheers,
Rusty

They holes are actually to mount a spinner bulkhead on, see also Mooney M20J spinner installation. (You should know that one Dan ).

osxuser said:

They holes are actually to mount a spinner bulkhead on, see also Mooney M20J spinner installation. (You should know that one Dan ).

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I was oblivious when I had my Mooney...I'm probably still oblivious.

Had my prop balanced today

Today I was driving into the airport on my way to convert avgas into noise and saw a Lancair getting a dynamic balance out on the ramp. Wanting to have this done on my airplane for some time now I stopped and asked when he could fit me into his schedule. What a nice surprise to be told that he could fit me in within the hour.

The change in the airplane cannot be overstated. From idle as the power is applied the engine is silky smooth. After settling up with this gent he turned me loose to have a flight and try out the new feel of my baby. Prior to the balance there was a feeling of power when the throttle was push in on the runway as the plane surged forward and the acceleration sits me back into the seat. There was a particular point in the take off roll where the prop felt like it was cavatating for lack of a better description and then it pulled hard again, or at least the sound gave this appearence. When flying the factory 9A with the MT I didn't notice anything like this and just thought that it was a characteristic of the Hartzell. Now as the throttle is advanced the engine feels smooth and the pull sounds and feels steady. If the truth be told the plane feels less powerful with the new smooth feel. On climb the same could be said. The cruise climb was good at around 1100fpm and 130mph indicated and the tower gave a frequency change at mid field on downwind, but the plane just felt less powerful. After leveling off and setting up for cruise I was beginning to like this smoothness as I got used to it, a lot. The feel on the rudder pedals was different and placing my hand on the glare shield showed the vibration that I never truly realized that my plane had was gone. On decent I've had a vibration that shows up as the manifold pressure is reduced below 20 inches or so with the prop set at 2300 or above. I've just been compensating for this by slowing down the prop on decent to 2200 and as this became habit I kind of stopped thinking about it anymore. This was a subject that I talked about to several people running my engine prop combo and almost everybody had the same vibration which made me think it was normal. Well this is gone now too. At this time I'm thrilled with the improvement and embarrassed that it took me almost two years to have the prop balanced. If your wondering about having yours done the results have the potential to be a big improvement. I haven't read the print outs yet, but we started at .19 and ended up at .031 after the balance. With no experience with this it is unkown to me if this is a miracle case or if gains such as this are common. It is also unknown to me how bad .19 actually was. All I know is this was money well spent.

Blue Skies,

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)

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

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

Valkyrie's Prop Balancing

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

Ironflight said:

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

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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)

Darn decimal points....yup 0.27!

Paul

Smooth Like Glass.....

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!

Ironflight said:

Well worth the money!

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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!