Dynamic Balance Dilemma

Geico266

Geico266

Touchdown! Greaser!
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Geico
I dynamically balance places for fun. I have a Dynavibe balancer that up to now has worked flawlessly and I have balanced 30 planes. I recently ran into a situation that is just plain weird. The last two planes have had weird "solutions" IE, large amount of weights to balance the plane.

All of the planes I have balanced took anywhere from 20- 50 grams of weight to balance. Some as rough as .45 IPS.

Plane #1. Never balanced before IO-360, 600 hours, recent tune up and carb overhaul and adjustment. First run .35 IPS. Added 70 grams of weights, now down to .14 IPS. Plane would not start for the last run so we left it at .14 IPS. Could not test fly it as the owners don't want to fly it without insurance. :rolleyes:

Plane #2. Never balanced before IO-360, 20 hours on over haul. First run was .030 IPS, added 70 grams of weight to get it to .07 IPS. Cannot fly because we would need to modify the cowling to accommodate the weights.

I just don't feel comfortable adding this much weight! I called Dynavibe and they had me sent the unit back to them for testing and we will know tomorrow if it is in calibration.

The 70-80 grams of weight for 2 planes in a row cannot be coincidence.... or can it?

We will know tomorrow. :confused:
 
For those numbers you should be able to feel the difference if the vibration was actually decreased. But it certainly sounds fishy - check a known smooooth engine before sending it in.
 
if it comes back with a clean bill of health, use it to re-check an engine you did recently before it went screwey. if you can't repeat the results send it back again
 
I hope no one dropped the accelerometer in your setup. All it takes is to drop it once and permanently damage it.

When I had my Aces 2020 I never permitted anyone to touch the equipment and it remained (when not in use) is a special padded case, locked.

Also, if the cable has been kinked it can throw off the unit.
 
One other consideration: was the prop correctly indexed to the crank when it was installed? It makes a difference on some engines.
 
steingar said:
I knew you were weird, but...
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:rofl: For fun & profit. ;)

Clark1961 said:
For those numbers you should be able to feel the difference if the vibration was actually decreased. But it certainly sounds fishy - check a known smooooth engine before sending it in.
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I sent it in already. Should know this am what they find.

JHW said:
if it comes back with a clean bill of health, use it to re-check an engine you did recently before it went screwey. if you can't repeat the results send it back again
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Good advice.

RotorAndWing said:
I hope no one dropped the accelerometer in your setup. All it takes is to drop it once and permanently damage it.

When I had my Aces 2020 I never permitted anyone to touch the equipment and it remained (when not in use) is a special padded case, locked.

Also, if the cable has been kinked it can throw off the unit.
Click to expand...

Oddly, on the balance right before these last two the cable touched the exhaust and melted the cable covering. It certainly didn't look too bad, but it could be the problem.
 
Kiddo's Driver said:
For those of us not in the know, how much do you typically have to add?
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Generally I have had to add anywhere from 1-30 grams. Usually about 1 AN4-7 (1/4-28 x 1.5") bolt and a washer. The last two planes were 3 AN4 bolts and a bunch of washers. :eek:

The weird part is two at once, and the initial readings were relatively low, .30 .35 IPS (inches per second)
 
Were these props properly statically balanced first.

If you have a brand new prop it is always better to have a prop shop statically balance it before installation.

Prop manufacturers are not allowed to statically balance their own props. Weird, but true.
 
Well my Dynavibe checkout perfect. The sensors were tested and found to be within specifications and working properly. The unit was certified with no calibration needed.

What a strange coincidence to have 2 planes take the same large amount of weight. Weird.

At least I know the planes are balanced correctly and are ready to fly. :happydance:
 
kgruber said:
Were these props properly statically balanced first.

If you have a brand new prop it is always better to have a prop shop statically balance it before installation.

Prop manufacturers are not allowed to statically balance their own props. Weird, but true.
Click to expand...

Both are constant speed props. Usually, they are static balanced at the factory or over haul shop.
 
probably a stupid question, but could the planes not be run up on the ground to get an idea if the balance was correct? or do you need to get them up in the air?
 
BTW, Dynavibe was great to work with. They were just as curious as I was about seeing if the unit was working properly. They sent me text updates about the calibration test, and an email with the calibration results. Very professional IMHO. Testing was all done free including return shipping!

Kudos to Dynavibe!

If you own a plane you need it dynamically balanced! Period! Get a couple of guys togeather or have your EAA Chapter buy one. It will pay for itself. They are inexpensive and work great.

http://www.rpxtech.com/

Balance jobs should not cost over $200 if you just hire someone. :no:
 
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Geico266 said:
BTW, Dynavibe was great to work with. They were just as curious as I was about seeing if the unit was working properly. They sent me text updates about the calibration test, and an email with the calibration results. Very professional IMHO. Testing was all done free including return shipping!

Kudos to Dynavibe!

If you own a plane you need it dynamically balanced! Period! Get a couple of guys togeather or have your EAA Chapter buy one. It will pay for itself. They are inexpensive and work great.

http://www.rpxtech.com/

Balance jobs should not cost over $200 if you just hire someone. :no:
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So was it broken, or were the props just that badly balanced?
 
Geico266 said:
Generally I have had to add anywhere from 1-30 grams. Usually about 1 AN4-7 (1/4-28 x 1.5") bolt and a washer. The last two planes were 3 AN4 bolts and a bunch of washers. :eek:

The weird part is two at once, and the initial readings were relatively low, .30 .35 IPS (inches per second)
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Seems strange to me too.....:confused::confused::confused::confused:.....:dunno:
 
N801BH said:
Seems strange to me too.....:confused::confused::confused::confused:.....:dunno:
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very strange, have you tested it with a known smooooooth engine? That tests the instrument and the operator...
 
rbridges said:
probably a stupid question, but could the planes not be run up on the ground to get an idea if the balance was correct? or do you need to get them up in the air?
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Yes, they could both feel that they were smoother.
 
Clark1961 said:
very strange, have you tested it with a known smooooooth engine? That tests the instrument and the operator...
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I will do that when I get it back. I'm sure it will be fine. It was tested and certified by an independant calibration shop.
 
N801BH said:
Yeah, but.....

70 grams is 3.4 ounces....

That is ALOT of weight...:yikes::yikes::hairraise:..

And,, two planes in a row is REALLY weird...:redface:
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Hence my thread, and why I sent it in for testing. :yes:

Can't wait for the owners to test fly the planes and get a pirep.
 
RotorAndWing said:
Doesn't Dynavibe perform a split solution?
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The Aces unit I use to balance my toy does split weight locations... In fact I prefer it as the final result is a smoother running set up..... But... IIRC, I still need just about the same amount of weight, just not in a single location...
 
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