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  #11  
Old 12-27-2017, 10:07 AM
DHeal DHeal is online now
 
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Location: Windsor, California
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I balanced my RV-12 with the spinner ON (you really have to since the spinner is part of the balance equation and the pitot tube needs to be supported). I added a very small amount of weight under the outer rim of the rear spinner bulkhead -- the weight is held on by one of the spinner's rear screws. This is very easy to do but does mean that you have to remember where the weight goes if you subsequently remove/reinstall the spinner (also the top cowling has to be removed to access the nut holding the weight on). I guess I could figure out some way to attach (glue? Ugh.) the weight/MK nut to the spinner bulkhead but that seems a tad finicky.
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  #12  
Old 12-27-2017, 12:20 PM
alexe alexe is offline
 
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Yes, you balance with the spinner on. Temporary weights should be added on the outside of the spinner (under the aft spinner mounting screws). Once a acceptable balance is achieved, the weights have to be moved and bolted to the rear spinner bulkhead (no glue!!!). The operators manual of the balancer should explain the math required to relocate the temporary weights to the spinner bulkhead.
Alex
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  #13  
Old 12-27-2017, 11:11 PM
waterboy2110 waterboy2110 is offline
 
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Quote:
Originally Posted by jeterjim
I just got a dynavibe and would like to know how you attached the weights to the spinner.?
You will be drilling a hole through the rear spinner bulkhead for the balance weight.

Once you determine the angle where the maximum IPS exist weight will be added 180 degrees from that point.

Make sure the engine is up to operating temp. You will be running the test full throttle to gather the data. I found that adding weight to the spinner screws didn't do anything.

Get some AN hardware before you start. You'll need a couple AN3 bolts and all metal locks. Get some AN 970 washers so you don't get caught up stacking up a half dozen 960’s. To remove 0.68 IPS at 360 degrees I added 29 grams at a 5 inch radius at 180 degrees.

There should be a label placed on the spinner bulkhead that states that the prop / spinner / bulkheads are balanced as a system to notify anyone working on the plane that it must be reassembled the same as it was taken apart and of course a log book entry.
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Last edited by waterboy2110 : 12-28-2017 at 03:03 PM. Reason: typo
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  #14  
Old 12-28-2017, 11:56 AM
rvbuilder2002 rvbuilder2002 is offline
 
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The standard method of doing a propeller balance is to add temporary weights to aft spinner attach screw locations.
I (and others) have been doing it this way for years and the procedures manual for the Asus prop balancers recommends this method.

It usually requires using a longer screw but that doesn't matter because you are calculating the Delta (weight difference) between the original screw and the weight used for a balance run anyway.
Once a good balance result is attained calculations are made to install a slightly higher amount of weight (because of the different polar moment of inertia) further inboard on the spinner pack plate.
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  #15  
Old 12-29-2017, 11:02 AM
waterboy2110 waterboy2110 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
The standard method of doing a propeller balance is to add temporary weights to aft spinner attach screw locations.
I (and others) have been doing it this way for years and the procedures manual for the Asus prop balancers recommends this method.

It usually requires using a longer screw but that doesn't matter because you are calculating the Delta (weight difference) between the original screw and the weight used for a balance run anyway.
Once a good balance result is attained calculations are made to install a slightly higher amount of weight (because of the different polar moment of inertia) further inboard on the spinner pack plate.
Scott is correct in that the manual asks to use the spinner screws to add weight during initial runs. The procedures go on to tell the mechanic to add weight at the 180 degree radial of the measured IPS. Placing weight on the spinner screws is a good ball park place to start to see if you are moving in the right direction but experience has shown that simply moving the weights from the radial of a spinner screw inboard to the backing plate with a simple weight and balance equation would rarely lead to optimum results. Spinner screws are generally 30 degrees apart and in this application do not exist on the propellers radial.

Consider the photo below:


Here we see our balance weights directly under the #2 blade on a typical prop and hub assembly (if you haven't described each blade by SN you will need to do that so the assembly, once balanced, can be returned to the balanced state during any subsequent service).
The placement of the weight at or near a blade would be expected since the blades arm under acceleration generally would exhibit the greatest moment.
In this application the #1 blade was heavy coming in at 0.68 IPS at 360 degrees. As you can see from the photo there are no spinner screws in the vicinity of the angle the instrument is calling out to add weight. The procedure also asks that you make small corrections to the weights and work towards a solution. In this case 10 grams was added at 180 degrees which brought down the IPS into the 0.4's at 170 degrees. Another 10 grams was added there and after a few more runs the total weight came out to 29 grams split between 170 and 180 degrees. This was achieved by using two AN3-4 bolts with all metal locks, two AN 960 washers on the bolt head (each 1 gram) and four AN 970 washers each weighing 4 grams.
At each run four measurements were made using the averaging function on the balance tool. The final test run for this propeller assembly is 0.01 IPS clocking randomly around the prop. Basically noise at this point.

Did it make a difference? You bet it did. Rotax SL-912-010 describes inherent vibrations in the 912 engines that can be excited by external inputs to the power plant. In the SL they describe what appears to be extensive vibration analysis on the power plant and discovered that between 3600 and 4800 rpm harmonics could cause a low frequency vibration to occur. I actually experienced this on the new engine (wasn't present on the first engine) in that when the throttle was retarded through the described RPM the plane would shudder.
After exhausting all listed items in SL -912-010 I determined that the prop needed to be surveyed. The IA that I use to work with who regularly provided propeller balance service (and taught me how to balance props) had moved on so I went ahead and bought the DynaVib since it was affordable and I felt that it was the instrument I needed to hunt down the source of the vibration during deceleration.

Once the propeller system was balanced the engine resonance could no longer be excited and the plane is as smooth as silk now. Flew it 1200 miles the other day and it the engine performed flawlessly.

A word about balancing:
In certificated aircraft, unless balancing is described by the manufacture, dynamic propeller balancing is considered a major alteration. The FAA and those of us licensed by the FAA take this stuff seriously and so should you. Be careful and by all means work within the constraints of your certification or ask for help. There are plenty of folks that can guide you through the process so that you end up happy with the work and safe when all is said and done.
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Last edited by waterboy2110 : 12-29-2017 at 11:04 AM. Reason: typo
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  #16  
Old 12-29-2017, 12:37 PM
rvbuilder2002 rvbuilder2002 is offline
 
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I have never used a Dynavibe balancer so it may not have the capability, but the ASUS balancers do the weight adjustment and repositioning calculations for you.

During the balancing process, if the called for weight location doesn't coincide with a spinner screw it will calculate the amounts to split the weight between two screw locations that you choose.

Once the balancing process has been completed using temp weights on the spinner screws, it will convert that to a location further inboard on the spinner for attaching permanent weights.

There is no guessing or approximating.
I routinely achieve a balance down to only .01 IPS with the temp weights and then still have .01 IPS after the permanent weights are installed.
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  #17  
Old 12-29-2017, 01:05 PM
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jcaplins jcaplins is offline
 
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Quote:
Originally Posted by waterboy2110 View Post
If you're flying a Rotax and just want to know what you're IPS is I'd be happy to come by and set it up any where between say KFAT and KRDD. Five minutes after the cowl is removed and the engine is warm and you'll have the data. Just an opportunity to meet folks and use the tool for me.

Not a Rotax, but a Subaru with a 4 blade electric CS prop.

I have a beat frequency that I'm trying to sort out... so If you would like to play with your new toy, I would like to experiment as well.

(I've done a dynamic balance before, about 15 hours later I noticed the beat frequency.)

I'm at Yolo county, KDWA.
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  #18  
Old 12-29-2017, 05:07 PM
waterboy2110 waterboy2110 is offline
 
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Quote:
Originally Posted by jcaplins View Post
Not a Rotax, but a Subaru with a 4 blade electric CS prop.

I have a beat frequency that I'm trying to sort out... so If you would like to play with your new toy, I would like to experiment as well.

(I've done a dynamic balance before, about 15 hours later I noticed the beat frequency.)

I'm at Yolo county, KDWA.
No problem. PM me and we can set a date to meet
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  #19  
Old 12-29-2017, 05:11 PM
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Walt Walt is offline
 
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Quote:
Originally Posted by waterboy2110 View Post

A word about balancing:
In certificated aircraft, unless balancing is described by the manufacture, dynamic propeller balancing is considered a major alteration. The FAA and those of us licensed by the FAA take this stuff seriously and so should you. Be careful and by all means work within the constraints of your certification or ask for help. There are plenty of folks that can guide you through the process so that you end up happy with the work and safe when all is said and done.
Just to set the record straight, AC 20-37E is clear that prop balancing is not considered a major repair or alteration.

(c) For aircraft or propeller manufacturers that provide procedures for dynamic balancing of the propeller in their maintenance manuals or instructions for continued airworthiness, propeller balancing is not considered a major airframe alteration.

(d) When approved aircraft or propeller manufacturer’s procedures are not available, there are other acceptable dynamic propeller balancing procedures. These include, but are not limited to the Chadwick-Helmuth Publication No. AW-9511-2, entitled “The Smooth Propeller”, and ACES Publication No. 100-OM-01, entitled “ACES Systems Guide to Propeller Balancing”. Dynamic balancing of propellers using FAA-approved or -accepted dynamic propeller balancing procedures is not considered a major propeller repair unless the propeller static balance weights are altered or when using the Chadwick-Helmuth or ACES type documents on propeller installations of 500 horsepower or more.
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  #20  
Old 12-29-2017, 06:17 PM
waterboy2110 waterboy2110 is offline
 
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Quote:
Originally Posted by Walt View Post
Just to set the record straight, AC 20-37E is clear that prop balancing is not considered a major repair or alteration.

(c) For aircraft or propeller manufacturers that provide procedures for dynamic balancing of the propeller in their maintenance manuals or instructions for continued airworthiness, propeller balancing is not considered a major airframe alteration.

(d) When approved aircraft or propeller manufacturer’s procedures are not available, there are other acceptable dynamic propeller balancing procedures. These include, but are not limited to the Chadwick-Helmuth Publication No. AW-9511-2, entitled “The Smooth Propeller”, and ACES Publication No. 100-OM-01, entitled “ACES Systems Guide to Propeller Balancing”. Dynamic balancing of propellers using FAA-approved or -accepted dynamic propeller balancing procedures is not considered a major propeller repair unless the propeller static balance weights are altered or when using the Chadwick-Helmuth or ACES type documents on propeller installations of 500 horsepower or more.
Well - I guess I took this statement from the Aces-Guide-Propeller-Balancing document Revision 2.0 June 1996 1000-OM-01,which is data approved by the administrator, literally...

"Modification of the spinner bulkhead, either by drilling or adding weights in the form of nuts, bolts, washers, or any combination thereof, requires the completion of FAA Form 337 for return to service"

A 337 is a major alteration / repair form for certificated aircraft. I was taught that when in doubt fill it out .. the 337 that is.

Since the AC states less than 500 HP I would agree that statement could override the one made in the ACES doc.

Walt - I see by your signature that you're quite experienced in this arena. I'm not challenging you or the work you do. I'm simply providing the data that led me to my conclusion. Thanks for the pointer Walt. Good data is always welcome.
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Last edited by waterboy2110 : 12-29-2017 at 07:28 PM. Reason: typo
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