Walt

Walt

Well Known Member
Did my first RV12 prop balance today on Petes very nice RV12. One thing I wasn't prepared for was I needed some metric hardware to attach my vibration pick-up to the engine so we had to go on a hardware hunt before we could even get started. But other than that the process went very well and we were able to reduce Pete's vibration from an intial of .563 IPS to a final of .039 IPS, a SIGNIFICANT reduction.

Keep in mind .2 IPS is considered the upper limit (the red circle in the polar plot below) so our intial reading of .563 IPS was almost 3 TIMES the upper limit. The final number of .039 IPS is less than half the "after balance" limit of .1 IPS and I was very pleased with how it went. We attached the weights (18 grams) to the spinner bulkhead as we usually do with certified aircraft at a single bolt location.

Thanks Pete for giving me an opportunity to work on your aircraft and I hope you enjoy the smoother ride:D

vibs.png


We also did an engine vibration survey (and all looks good there)...

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Thanks Walt

Yes indeed, Walt did a great job and the difference is noticeable as you would expect from reading Walt's documentation. Prior to the 12, I have always flown high performance aircraft with constant speed props. Both Hartzell and MacCauley encouraged flying with a balanced propeller for ride enhancement yes but as well for engine and propellor longevity. Both state in their operating manuals that dynamic balancing will prolong the life of the propeller, engine, airframe and avionics. To my knowledge, no such recommendation has been discussed concerning the RV12 yet the same reasoning should apply in spite of the gearbox.

Rotax with its extensive, well-written manuals makes repeated requests of owners to reduce anything that involves vibration. All engine specific maintenance isssues that influence vibration are highlighted repeatedly. Rotax doesn't sell propellers but propellers certainly influence vibration and are attached to the engine.

I now have a much smoother ride and hopefully have extended the life of my engine as well as everything else that doesn't like to vibrate, including my brain.

I do know that the balancing business can be much like the septic business...those who know what they're doing and those who just take your money. Make your selection carefully if you decide to go this route.

I think the decision to balance or not balance is a no-brainer. Walt made me a believer. He's also a very nice guy and very knowledgable concerning this topic. I couldn't be happier...thanks Walt.

Pete
 
Great job Walt. The Rotax 912 is no difference when it comes to balancing. Sure makes a difference. I balanced my -12 and the results were similar to what you achieved. Much smoother now.


I highly recommend dynamically balancing any aircraft.
 
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My prop just came back from Sensenich with the new hub design. As soon as weather permits I will reinstall it and set the pitch, then test fly. Hoping for much less vibration than before, but the above posts suggest I wil probably want a dynamic balance as well. I'll report back.

John
 
Weights are added to balance when doing a dynamic propeller balance. For those who have completed a dynamic balance on the RV-12, where are you placing the weights?
 
rejnovca said:
Weights are added to balance when doing a dynamic propeller balance. For those who have completed a dynamic balance on the RV-12, where are you placing the weights?
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We attached the weights to the RV12 spinner bulkhead the same way we do with many certified aircraft. We drilled a single hole for a 3/16 bolt and added washers for the exact amount of weight required.

On Lycoming powered aircraft we are able to use the flywheel holes for balance weights but there is no provision like that on the Rotax or Continental powered aircraft.
 
BigJohn said:
My prop just came back from Sensenich with the new hub design. As soon as weather permits I will reinstall it and set the pitch, then test fly. Hoping for much less vibration than before, but the above posts suggest I wil probably want a dynamic balance as well. I'll report back.

John
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John,

If you're not amazed, please call Larry and I immediately! By the way, I neglected to say that Larry did tell me to do it some time ago but you know how it takes awhile to get around to everything you want to do. Anyway, I do everything Larry tells me to do except cheer for Nebraska.

Pete
 
I have been advised by a couple of professional prop balancers that one should wait awhile (@ 50 engine hours?) before balancing a prop. Supposedly this gives the engine a chance to "break-in" and get internally settled before you do the prop balance. Just a thought....
 
Peterk said:
John,

If you're not amazed, please call Larry and I immediately! By the way, I neglected to say that Larry did tell me to do it some time ago but you know how it takes awhile to get around to everything you want to do. Anyway, I do everything Larry tells me to do except cheer for Nebraska.

Pete
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Now that Nebraska is not in the Big 12 I am a Texas fan big time. ;) Go Horns! Hook em!
 
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DHeal said:
I have been advised by a couple of professional prop balancers that one should wait awhile (@ 50 engine hours?) before balancing a prop. Supposedly this gives the engine a chance to "break-in" and get internally settled before you do the prop balance. Just a thought....
Click to expand...

I had a freshly rebuilt engine and used prop balanced before the first flight. They did an excellent job. It lasted until the after-market camshaft pitted at about 350 hours, and we had to tear down the engine again.

From this, I'd say that there's no need to wait.

Dave
 
DHeal said:
I have been advised by a couple of professional prop balancers that one should wait awhile (@ 50 engine hours?) before balancing a prop. Supposedly this gives the engine a chance to "break-in" and get internally settled before you do the prop balance. Just a thought....
Click to expand...

Some engine manufacturers claim that their engines "arrive" balanced. Of course Walt insists that you don't have a balanced "system" until the prop which attaches to the shaft is balanced with the engine running. Makes sense to me. As to a "settling" engine, I defer to the experts.
 
DHeal said:
I have been advised by a couple of professional prop balancers that one should wait awhile (@ 50 engine hours?) before balancing a prop. Supposedly this gives the engine a chance to "break-in" and get internally settled before you do the prop balance. Just a thought....
Click to expand...

In my humble opinion, once the rings are seated and you're comfortable doing some ground runs you're good to go. After 20 hours (probably more like 10 in most cases) the rings are set and there is nothing else that will "break in" that will effect prop or engine balance.
 
Finally got good weather yesterday to test my prop balance. See photos in my blog entries 5/8 - 5/11. Observed a huge difference in vibration levels. Now the Rotax/Sensenich combo is smoooooooth......

I am now a member of the prop balancers fan club!
 
BigJohn said:
Finally got good weather yesterday to test my prop balance. See photos in my blog entries 5/8 - 5/11. Observed a huge difference in vibration levels. Now the Rotax/Sensenich combo is smoooooooth......

I am now a member of the prop balancers fan club!
Click to expand...

Now the question is: will the new hub (SB) mess up an existing balance. Walt says not necessarily so here's hopin'.

Pete
 
For the price we pay for the components, this uninformed view is thinking why don't they balance it before selling it (engine AND prop)?
 
You can't dynamically balance an "assembly" until you have all the rotating parts in place (spinner and spinner bulkhead, prop, bolts, screws, engine etc).
 
Yeah, forgot about the spinner. Still does ROTAX or Sensenich make any attempt at all to balance their components? Years ago I became a proponent of balancing auto engines, wow what a difference. We balance the crank, with rods and pistons, and then bolt on a flywheel, torque converter, etc that are balanced, and it all comes together in the end.
 
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Prop manufacturers do a static balance only.

Tires and wheels are "balanced" individually but until you put them together and dynamically balance them as an assembly there will be some imbalance due to tolerances. Same thing with props and engines.
 
The fellow who balanced my prop rode with me yesterday, and agrees with my assessment that the vibration level is way down. However, since we balanced with the spinner off, and I adjusted the pitch a bit after the balance, he wants to double check the final balance with everything in place. We'll probably do that this week. I'll post results.
 
Bottom Line?

May be a bit early given the number of RV-12 flying but should not the bottom line be: Do the dynamic balancing no matter what?
I have suspected since the beginning that the LOOSE ENGINE MOUNTING BOLTS were related to excessive vibration.
 
It is hard to justify NOT getting it balanced, and with Walts very reasonable prices, a real no-brainer I think.
 
BigJohn said:
However, since we balanced with the spinner off, and I adjusted the pitch a bit after the balance, he wants to double check the final balance with everything in place.
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The spinner can make a huge difference so you do need to recheck with the spinner installed. And don't forget to mark the spinner so it always goes back on the same way it came off (most RV's it will only fit one way).

Doing a Cessna one day I forgot to mark the spinner when taking it off to add the final balance weights and of course I got it on 180 deg out. As soon as I started it up I knew it was on wrong as the balance had gone way off, didn't even have to get above idle to see it was wrong it was so far out!

You would think with a symetrical factory aluminum spinner that there would not be much difference right.... wrong!
 
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