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  #11  
Old 06-26-2007, 10:44 PM
AcVibes AcVibes is offline
 
Join Date: Jun 2007
Location: Cumberland, WI
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Quote:
Originally Posted by Indigo
The Chadwick manual " The Smooth Propeller " calls out for a balance to be at .2 or better to be considered balanced, if the propeller started at 1.7 that is really high, when i do balances on reciprocating engine they normally start at the .5 to .8 range and i can always acheive at least a .2 and most times i can get .1. The good thing about balancing is that even if you do not feel it the rest of the airplane can, baffling and other items that crack due to wear from vibrations have a longer life after balancing.

The reason Chadwick came up with the .2 Inches per second "Good" is becuase this was the "noise floor" of the equipment....they could not tell if the vibration level was much lower.

Modern digital equipment can go much lower... repeatably.

.1 is over 5 times higher than my post balance average. I have taken even some .04 IPS under .005 IPS the results are like comparing 80 grit sandpaper to 1200 Wet & Dry.
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  #12  
Old 06-26-2007, 10:59 PM
AcVibes AcVibes is offline
 
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Location: Cumberland, WI
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Smooth is an adjective that describes words...

A analogy...

What is your cholesterol level? What is your blood pressure? Just because you feel ok does not mean you have a great chance of keeling over tomorrow...

How about having someone hook up some calibrated test equipment and showing real numbers what the vibration health of your engine/prop/airframe....you will even get an idea if an how it can be improved....

Vibration damage to an airframe, wiring, electrical circuit is CUMULATIVE...you can never remove the workhardening effects of vibration without a serious amount of cash and time.

Best regards,

Jim
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  #13  
Old 06-26-2007, 11:16 PM
AcVibes AcVibes is offline
 
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Location: Cumberland, WI
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If you know the rotational frequency and have an accelerometer mounted at the correct position you can see the vibration amplitude of the item in question...Raddatz uses the DSS MicroVib II equipment and the MicroBase Pro software. The complete history of the balance procedure, spectrum and waveform plots are downloaded to a computer and processed the MicroBase Pro software. Machine rotational speed identification files are attached to the specific spectrum plots...peaks are ID'd with the rotational speed of the component....simple equipment with few separate items speeds can plotted as well as much more complex items like PT6 engines (and special reports generated for the MORE program for one example)

I have samples of these reports on my website www.aviationvibes.com from a 6 cylinder Continental ....note these forms make great "health records" for future and fleet type comparisons...and great logbook entries!

Best regards,

Jim
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  #14  
Old 06-27-2007, 06:54 AM
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pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,885
Default No feel

I fly both an Air Tractor with a 110" Hartzell and my RV with a three-bladed Catto. An A@P friend balanced both airplanes and I can assure you, Bob, that you cannot feel high frequency vibrations that are cumulatively destructive. My PT-6 in the 'Tractor always "felt" smooth until I saw the IPS during balancing.....big improvement and this engine has almost 8000 hours on it and is still strong and smooth. The RV picked up a noticeable, albeit small, increase in max cruise RPM's. I'm definitely a believer......it started with a Ford 427 balanced in my kit Cobra-long time ago

Regards,
Pierre
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  #15  
Old 11-15-2007, 04:13 PM
Chris Santschi Chris Santschi is offline
 
Join Date: Jan 2005
Location: Festus, Missouri
Posts: 72
Default Prop Balancing

Does any body know who offers this service to balance props in the Missouri area. Im based at 8WC

Chris RV 8 N627CS
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  #16  
Old 11-18-2007, 06:43 PM
Guenthfa Guenthfa is offline
 
Join Date: Sep 2007
Location: Chehalis, WA
Posts: 28
Default Prop Balancing

There are basically 3 units of measure in vibration: acceleration (G's) Velocity (IPS) and displacement (Mils PP).

Typical displacement readings are found on large rotating equipment and recorded with a non contacting proximity (eddy current) probe. As the target material moves closer to or farther away from the probe, the output voltage changes. Readings are in distance of movement and usually mils (.001") from peak to peak of the sine wave.

Velocity is measured with a velocity transducer which is nothing more than a magnet suspended inside a coil by a spring. As the mounting base vibrates the magnet moves up and down generating a voltage. This is read as a distance of movement over a given period of time hence inches per second (IPS) and usually read in IPS peak which is from the center of the sine wave to either the upper or lower peak of the sine wave. Anything over .5 inches per second is considered to be rough. Velocity transducers are prone to mounting error, resonance, fatigue and are typically found in the low to mid frequency applications.

Acceleration is typically measured with an accelerometer which is a peizio electric crystal system that measures rate of change or "G's" and is usually used for high frequency applications. Industry standards for acceleration readings are usually in RMS or .707 x peak. Accelerometers are very tough, able to withstand high temperatures, have a very high mounting resonance and are relatively inexpensive compared to the other tranducers. Most of the data collectors will integrate the output of the accel to IPS for balancing applications.

The first step in dynamic balancing is to make sure that imbalance is causing the vibration problem and not something else. There are several things to look for if imbalance is in fact all or most of your vibration: 1) It should increase (or decrease) as a function of speed. 2) If you have a 2 channel system and mount the accelerometers 90 degrees of rotation apart the the vibration peaks should be 90 degrees, +-15 degrees out of phase.....or 270 degrees out of phase depending on direction of rotation. 3) 80% of the vibration energy is at 1 times rotation speed (1x).

Once you have the voltage signal (amplitude vs time) most data collectors will run a FFT to convert to an amplitude vs frequency spectrum which is where you can diagnose most vibration problems. Imbalance, assembly error, alignment, gear problems will all be syncronous, i.e. at multiples of running speed, 1x, 2x, et. Rolling element bearing problems are always non-syncronous for example .564x, 2.456x

Anytime you can reduce vibration you are making everything work better, last longer AND creating less pilot fatigue. If some of you guys are getting down below .1 IPS that is great. Most balance techs will keep making runs until they reach the resolution of their gear or they are chasing the remaining imbalance around with no reduction in amplitude which most likely means the remaining vibration is not a result of imbalance.

Last edited by Guenthfa : 11-18-2007 at 06:48 PM.
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  #17  
Old 11-18-2007, 07:18 PM
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gmcjetpilot gmcjetpilot is offline
 
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Default It's part science and part ART

Not all equip is the same and more over not all technicians and techniques are the same. The test should be done under power with the blades off the stop (constant speed prop) with the cowl installed. This is hard to do on the ground. Still there is judgment in how you do the test, where you put the accelerometers, interpret the data and apply the weights.

You will notice a dynamic balance if its done properly and you had dynamic imbalance prior. I found it took three iterations and two technicians to get it right. When the sweet spot was found it was noticeable.

As far as vibration don't forget the engine mounts and things that hang off the engine and touch the airframe, baffles, control cables, houses all can transfer some buzz to the cockpit. We are almost sitting on the engine with just a piece of sheet metal between us. The engine mount is hanging off brackets mounted to structure that is right at our feet and elbow. The engine has its own vibs, and the prop has its own vibes as well. Its the total system that you try to optimize, but if the engine is out of balance dynamically or power produced by the cylinders are not even, than all the balance in the world on the prop can not totally cancel that out. Like wise if the prop blades are not tracking or at the same pitch, balance wts. can do only so much. VALUE? Look its a tune-up not a miracle. If you have severe vibs than start looking around for other issues. I highly recommend LORD CORP engine isolation mounts verses other brands. I found just witching to the LORD Corp solved most of my vib issues and the dynamic balance was the cherry on top.
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Last edited by gmcjetpilot : 11-18-2007 at 07:26 PM.
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  #18  
Old 11-18-2007, 07:29 PM
David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Chesterfield, Missouri
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Quote:
Originally Posted by MSFT-1 View Post
When I wrote the original post, I was quoting my numbers from memory (obviously a flawed memory). I pulled out my paperwork from Hartzell and here are the numbers they recorded:

Pre balancing: 0.173
First run: 0.084
Second run: 0.045

These numbers seem much more inline with what other people have reported here.

Bruce
N297NW
RV-8
And most of the .045 is probably engine vibration, which they can't do much about.
I had mine balanced recently and it came in at .016 at 2100 rpm. That's with a 3 blade MT which is little smoother than 2 blade props. The .045 your guy achieved with a Lycoming is excellent.
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  #19  
Old 11-18-2007, 07:49 PM
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Geico266 Geico266 is offline
 
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Location: Huskerland, USA
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Quote:
Originally Posted by Chris Santschi View Post
Does any body know who offers this service to balance props in the Missouri area. Im based at 8WC

Chris RV 8 N627CS
Call the local FBO and they will have a few leads for you. Most all bigger FBO's have access to a balancer. If not we have a guy here in Crete, NE KCEK that does them for $150.

$250 was a rip off.
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  #20  
Old 03-30-2017, 01:14 PM
AirAce AirAce is offline
 
Join Date: Jan 2009
Location: Fallon, NV
Posts: 7
Default Prop Balancing

1. Static balance is a valid balance.
2. Static balance can be virtually perfect.
3. After static balance If vibration occurs, the engine is the problem.***
4. Sometimes engine mounts are the problem. This is mostly noticeable during rpm acceleration or deceleration.
5. Do not unbalance the propeller to balance the engine.

*** Propeller clocking on the crankshaft is IMPORTANT. Wrong clocking can be the cause of bad vibration.

Hartzell and McCaully make sure your prop can be install I only one clocking. Follow their lead.
Kent
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