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Old 09-22-2017, 12:10 AM   #1
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Default Acroduster 2 Vibration Part 5

Brought forward from part 4 (9-15-2017)



" My friend/IA says to change the mounts. He also said to get TT out of my head as "the" operative factor, "I've seen a bunch of those engines go 3000 hours"....well maybe?

I'm going to change the mounts. Go from there. Hopefully the vibration goes away and I keep on cutting filters every 10 hours unless metal making gets worse.

Another friend has a O320 that must be opened up and my IA friend agreed to let me help. Looking forward to that.

Thanks,

Jack "


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Old 09-22-2017, 12:22 AM   #2
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I changed the Lord mounts today. Barry Mounts to be exact. Their site gives good tips on changing them, loosen them and change one at a time(with engine weight on hoist). Rock the prop, pull spacer at engine out and rest is a snap. Took a couple hours and more to replace cowl.......and it was hot.

Then I took it for a ride frankly not expecting much and I was right.

Anyone interested in what would seem to be a perfectly good set of used Lord Mounts?

That's not the whole story.

I think I have this figured out?

But changing the lord mounts seems to have been a waste of time and $476 + shipping.

More later, like I said I think I have it figured out....... I keep a detailed log of work. I looked at my log and compared with when the vibration started. I missed something when I looked before. Been chasing my tail.

Jack


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Old 09-22-2017, 04:33 AM   #3
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Good news, I hope? Inquiring minds want to know.
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Old 09-22-2017, 12:10 PM   #4
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Ok, I don't know how "good" the news is. I figured out that the actual vibration hasn't changed since my first flight. My perception of it changed due to changes I made when I installed the front cockpit controls, the rudder peddles. I also had to reroute the brake lines.

Two things made the perceived vibration worse. 1st was the re-tensioning of the cable between the rear rudder peddles. 2nd was a separate change I made to straps holding the ends of the exhaust pipes.

I was disappointed to say the least on my first flight after changing the lord mounts. Then I moved my feet off the rudder peddles and noticed that the vibration was not being transmitted to the airframe? I asked myself exactly what the heck was going on? I landed and reviewed my notes and entered into my head scratching mode. The notes revealed the cable re-tensioning and the head scratching recalled the change I made to the exhaust. I had used the stock Piper Comanche straps to hold the exhaust. But of coarse I had made a longer mount copying the Piper mount but longer and the straps have a different fit. Changing them back made a profound change in vibration through the peddles.

Of coarse I do NOT know if the absolute vibration level is a real issue/problem?

At least I've resolved the sudden change in the vibration level that had me wondering, (pardon my language) WTF!


Now I need to decide if dynamic balancing is worth the effort?

Jack
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Old 09-22-2017, 12:28 PM   #5
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On the Lord Mounts. I've discovered that these rather simple rubber mounts are maybe not that simple. Ask yourself why there are so many variations for different engine installations? The engine mount cups are pretty much the same.

In the case of the generic homebuilt lord mounts offered for the RV's or offered by ACS and maybe for some certified aircraft the two half of the rubber mounts are the same. Not so with the piper Comanche mounts. Two different part numbers and they are of different lengths(static). How they are assembled front/back-top and bottom on the engine mount are reversed.

I suspect there is more to the dynamics involved in engine mounts than we(at least I) might think? Each engine/aircraft/mount has different dynamics needing different rubber mounts.....

In my case having made a rather different mount design, who knows if the lord mounts designed specifically for the Piper Comanche still do the job?

Or maybe I'm over thinking again?

The joys of E-AB
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Old 09-22-2017, 01:26 PM   #6
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Depending on being scalped on the money, dynamic balancing is worth it. It will tell you one of three things. It's perfect, it can be made perfect, or you have a problem. How big a problem you want to put up with is up to you. It's not magic. Most tires today are dynamic balanced today. You would not put up with a tire thumping through the steering wheel.
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Old 09-22-2017, 02:32 PM   #7
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Quote:
Originally Posted by TFF1 View Post
Depending on being scalped on the money, dynamic balancing is worth it. It will tell you one of three things. It's perfect, it can be made perfect, or you have a problem. How big a problem you want to put up with is up to you. It's not magic. Most tires today are dynamic balanced today. You would not put up with a tire thumping through the steering wheel.

What exactly can it tell you?
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Old 09-22-2017, 03:45 PM   #8
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Worse vibration I ever had was the first take off in my old Stinson 108-2. We had it down for annual and did the engine and all new firewall forward. We also installed new tires and tubes.

On take off I was already amped up as it was a brand new engine. So I was ultra aware of vibration. Well as soon as I lifted off. Huge vibration. I was to far down the runway to abort. I started looking at engine gauges etc etc. and in trying to "feel" the vibration to see where it was coming from I placed my feet on the rudder pedals farther up...and accidentally pressed the toe brakes. The vibration...stopped! Well it took my brain about a min to figure out hey dummy it's the new tires the guys didn't line the tube dots up with that's causing the vibration. But I did figure it out eventually and after I landed I checked and sure enough the dots on tubes were not inline with the dot on the tires etc. once that was corrected...I didn't even balance them any other way. The vibration stopped.

Now I know you installed the tires and tubes correctly...but is there a change it's just really off balance tire/tube? What happens when you press the brakes on flight? If the vibration gets better you found the problem.
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Old 09-22-2017, 03:57 PM   #9
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I doubt if my tires rotate in flight? Many of our club fleet had less than perfect tire balance. I learned early on to hit the brakes after take off.
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Old 09-22-2017, 04:30 PM   #10
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Dynamic balancing can tell you a lot.
By analysis a good operator can tell you if you're good, how bad it is, and they can even tell you if it is a prop issue or engine issue and even which cylinder (rotating assembly) is the culprit.
Get it done and put your doubts and suspicion to rest.
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Old 09-22-2017, 07:19 PM   #11
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I had the Skywagon dynamic balanced early this summer. Same deal, it was vibrating a little but performing to the book. Now it's glassy smooth in cruise.

Easily the best $250 I've spent on that ship. I say it's worth a shot at least.
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Old 09-23-2017, 04:18 AM   #12
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I'll give the folks at Bedford a call and see if they might be "good" operators. At the least probably good for peace of mind. At best could save my/our lives.


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