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Old 15th Mar 2017, 21:43   #1 (permalink)
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Track and Balance Troubles

I am looking for some track and balance data for the following aircraft:

Bell:
206L
212
407
412

Airbus AS350

If anyone con help me out please contact me. Would love to talked to you! Also what problems you are experiencing with RADS or Chadwick in balancing these aircraft.

Thanks!
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Old 16th Mar 2017, 10:33   #2 (permalink)
 
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I would check the weights of the blade before you try anything. Have discovered on MD blades they can be as much as 250 grams different in weight. Which makes interesting to balance !!! This despite the blades shops having done static balance .....bollocks
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Old 16th Mar 2017, 21:32   #3 (permalink)
 
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Hughes500.....

Not meaning ot be disrespectful in any way but simply to highlight a very, very common problem in this industry which you have just demonstrated brilliantly.....the basic mis-understanding of rotor tack and balance....

It has nothing to do do with the MASS of the blades....but the distribution of mass across the blade particularly span wise. i.e. the Span moment arm of ANY individual blade ...that is what blade shops and OEMs set via the adjustment of the tip weights...not the mass.

Do yourself a favour and have a look at Rotor Blade Balancing - Rotor & Wing Aviation Services - Dynamic rotor track and balance - Australia and educate yourself a little in RTB and its fundamentals which many many people in this industry fail to understand.

Cheers
RG
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Old 16th Mar 2017, 21:48   #4 (permalink)
 
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One of the biggest problems I found with the new computer programs was folks looking at the suggested adjustments but not agreeing with them ..doing some but not all but not entering the actual changes. This completely screws the software and it all goes pearshaped from that point. The software assumes you did all the suggested moves of trim tabs and weights. Then makes another recommendation which just makes it all worse. Not fun.
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Old 16th Mar 2017, 22:17   #5 (permalink)
 
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RG

Sorry mate you are are so so wrong, come over here to the UK and I will show you how a friend does it by painting the blades on a set of scales to make sure they weigh the same. The proof mate is in the pudding. I will guarantee you that balance the head ( in this case a 500 ) with a chadwick with no blades on. Put the blades on having painted them on the scales so they all weigh the same and guess what the balance doesn't even show up on the Chadwick, don't need to add any weights or **** up the dampers by sweeping the blades. Done it on 206 blades, Enstrom blades etc etc. Have sorted blades out that have come back from the so called blade overhaul shops with blades in some cases weighing 250 g and allegedely have been statically balanced. Put them on the aircraft and do they fly like f... Give them to a maintenance company and they will add weight to the head or sweep the blades to try and balance when the fundamental problem is the blades don't weigh the same !!!! The answer really is that simple
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Old 16th Mar 2017, 23:00   #6 (permalink)
 
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Mass however has little to do with tracking. And correct track has everything to do with balance as the effective diameter of the rotor changes with track. Make a blade fly higher or lower than nominal and the effective diameter reduces.

Of course, if you have a heavy blade, you can put it out of track a bit to bring it's effective balance point closer to the head center point. But then you might get into vertical issues.

There is no dark art to RTB. Just experience and observation. Remember your adjustments and remember the effect they had on the RTB. If it isn't going where it should be, back track (no pun intended!) and see if you need to adjust your clock angle. You might be getting the movement you need with your adjustments, just not in the right direction!

Good luck with the 412. They're a prick to RTB to begin with. Talk to Abu Dhabi Aviation, they have (or did have) the best 412 balancing notes around. Oh and don't forget your clock angle corrector. You'll need it on lots of 412's! And re-torque the head after EVERY RTB flight if the head was just put on. The hub has a habit of shifting and ruining your RTB. And pair opposite blades with similar hours as the blades get more flexible as they age.

Fricking 412 RTB. Yeesh.
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Old 16th Mar 2017, 23:19   #7 (permalink)


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Painting blades? On scales? I do not understand.
I find your explanation pretty scary to be honest.
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Old 17th Mar 2017, 07:54   #8 (permalink)
 
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wooden

Not half as scary as a blade manufacturer telling you when asked why the tip weights all weigh the same, to be told that they put the weights in as all the blades weigh the same and you then find the blades weigh up to 250 grams different despite having a standard 150 gram weight just stuck in the end

shouldn't really need to tell you why it makes a big difference if the blades all weigh the same on track and balance !
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Old 17th Mar 2017, 19:27   #9 (permalink)
 
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Steve I have extensive experience using RADS on 206B,L, and 407. I can try to help.
email brassrl at yahoo dot com
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Old 17th Mar 2017, 21:41   #10 (permalink)
 
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No Dark Art?

Never tracked and balanced a Chinook it sounds like!
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Old 18th Mar 2017, 07:06   #11 (permalink)
 
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oh dear oh dear oh dear, how scary it is to hear/see such ignorance in the helicopter industry......

As I said in my previous post, do yourself a favour visit Rotor Blade Balancing - Rotor & Wing Aviation Services - Dynamic rotor track and balance - Australia and www.avionatask to see the REAL problem in balancing rotor blades and why such things as "rogue" rotor blades exist....they exist through the industry ignorance of the importance of Span Moment arm and the accurate control of such an animal.... By believing that it is ALL about the straight Mass or about the Track......codswallop.

Straight Track is not the answer contrary to many misguided people (Nooby???). Certainly, large track displacements are not desirable...But track difference is nearly always essential in order to obtain descent control of the Vertical vibration level....it is a dynamic system and bladed simply must flap...if they didn't ...we would be in big trouble.

Straight mass is not the answer. the extreme case, look at a centrifuge used for "g' tolerance and testing. The manned gondola is way out on the longest moment arm while a stubby counterbalance is on the opposite side of the "hub". I'm sure the Mass of the counterbalance is not identical to the mass of person and structure opposite! And I'm sure those devices are kept in balance....relatively What about your crankshaft in your car?? It is about the DISTRIBUTION of mass - to obtain the same span moment arm on one side compared to the opposite side....not straight Mass.

MD500, you need to understand the difference effect of Mass and Mass distribution, in particaylr the effect of Span mass distribution. Chord mass distribution matters as well but has less effect because of the relatively small moment arm over which it operates. But ask any B412 engineer above Chord Moment arm....that is what you are adjusting when you adjust the Product weights when taking the track change from Flat Pitch Ground -> Hover measurements. ie...dynamic Chord adjust to ensure a relatively constant track of blades from Flat pitch ground to when you physically load the disc to the loaded condition.

I don't wish to get into a long and protracted discussion countering of most of the "solutions" offered by many of the previous posters......Just go and read the references above...do yourself and the industry a favour. Save yourself a heap of money in needless blade changes due "blades which can't be dynamically balanced" and make your fleet of helicopter blades totally inter changeable...its very, very simple and span moment arm and its understanding it is the simple solution.

Span moment arm goes "out" due to exactly the reason that MD500 says that he "cures' the problem. By painting the blade, without checking its span moment arm, paint builds up on some areas that have accumulated layers, while other areas (typically toward the tips and leading edges) only ever have 1 layer due to continual blade erosion. Even though the mass may crudely be kept similar, the distribution ultimately will go way out.....This won't happen immediately but WILL most definitely happen over time and with the accumulated layers of paint.

This is not the only reason for Span Moment arm migration. Trapped fluids such as water or oil in pocket within the blade structure such as in the nomex honeycomb cells for example. The CH 47 is particularly notorious for this as is the UH60 blades. Even the AW139 is common to have water easily trapped in the upper weight pockets on the blade due leakage. Probably the B412 as well if the seal is not done properly...these can have serious effects on the Dynamic balance.

Bird pooh on top of the blades if it has been kept in a hanger where birds roost overnight is another example...throughs out the span moment arm and take an IPS level from 0.05IPS to more than 0.4IPS in a heart beat....personally seen and witnessed this phenomena....4IPS Lateral

The ONLY way to ultimately fix this is to ideally digitally weigh the blades to determine the span distribution and adjust the TIP weights to bring the DISTRIBUTION back to within ideal engineering specs.....then that blade will fly with any other blade within the same design criteria.ie true fleet interchangeability hallelujah the golden grail...

You think I jest?....ask most units in the US Army now, Columbia helicopters (how do they keep there CH47/CH46 blades under control, I wonder), why does the CV22, the RAF on its Super Puma fleet, the Singaporean Defence Force and many other militaries around the world use the same digital tool to balance its prop rotor blades, why do Carson helicopters use it to do their fibreglass S61 blades....

..I could go on but I think you get my drift.

Unfortunately Old school and most OEMs insists on using archaic methods such as physical Master Blades and comparing that blade with your blade on primitive analogue devices similar to your Grandma's kitchen scales in a dedicated aircon'd room etc. Unfortunately, there is a large variance between the population of Master Blades as well, as I am sure most OEM's will concede, afer extensive studies carried out on behalf of the US Army by Avion Inc (see web site referred earlier) which proved this large divergence. Hence a digital, easy to use, Static balance tool was created.

I could go on and on about this topic countering the so-called "fixes offered here by the previous replies but I fear I could bore you to death.


MD500 and the others who have offered replies, and many more who believe that these replies are valid.....do yourself a favour and visit Rotor Blade Balancing - Rotor & Wing Aviation Services - Dynamic rotor track and balance - Australia and Avion/Avtask - Home and start reducing your maintenance costs on RTB and rotor blades....its really not hard.

Start to put pressure on OEMs to allow civil maintenance to access and use the same digital Static balance tool that the US Army, Coast Guard, RAF, Singaporean defence Force, some Sikorsky overhaul shops, and many more organisations world wide have been using for the last 10-15 years.....EVERY maintenance facility should be using such tools on ALL civil helicopters....not just military...

Sorry to carry on so long...I meant to be brief....but if just one person in this industry learns and understands the simple solution from this, I'll be happy.....

Go and visit the 2 x web sites....do yourself a favour, read them both and then tell me I am wrong MD500...

RG
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Old 18th Mar 2017, 07:23   #12 (permalink)
 
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Ring

What you have put out sounds like a very advanced method of what I have described. Just done it on a set of 500 blades by weighing tip and root weights while repainting blades. Blades went on D model 5 runs to track blades up to 135 kts straight and level. At no point did we need to balance the blades as The Chadwick was going round in circles. So we must be doing something right.
Had the same result with loads of blades.
Agree with OEM's and blade overhaul shops. Have discovered so called master blades weigh differing amounts
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Old 18th Mar 2017, 09:26   #13 (permalink)
 
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As a non-technical outside observer I also had the impression from the onset of this discussion between ring and Hughes500 that they are saying, and effectively doing, the same.

Certainly, the condescending remarks of one of the two in this thread seemed out of place to me.
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Old 18th Mar 2017, 12:09   #14 (permalink)

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I hate to think of how many track and balance sorties I've flown in my time; it's certainly hundreds.

It seems perfectly obvious to me that if the lengthwise balance points / C's. of G. of individual blades are not the same, as well as their overall masses, once they are spun on a rotor head there will be imbalanced forces and vibration.

Some obviously haven't quite grasped the complexities. But I don't see it as a reason for insults to be "whirled around". It's a shame that some seem so keen to grasp their chance to belittle others because it spoils what could be a meaningful discussion.
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Old 18th Mar 2017, 20:39   #15 (permalink)
 
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Shy

What makes it worse engineers and OEM's sweep blades by lengthening or shortening dampers ( obviously in a fully articulated heads ) For a while you will get away with this. However after a period you will find as one of the dampers is working harder than the others to keep a heavy or light blade in position and therefore keep everything in balance it will become weaker than its neighbours . Guess what, not only do you then get the imbalance back but you then find you have to buy a new set of dampers !!
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Old 19th Mar 2017, 00:42   #16 (permalink)
 
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I would agree with all the logical explanations and procedures described by the respondents here, except;

with a 500...

Throw all logic, systems, processes and sensibility out the window. They are the most impossible, frustrating little POS to track and balance. After a lifetime of tracking and balancing everything, these things were impossible and I had some really experienced 500 guys working for me. I'll show them how it's done, I thought, after they had fruitlessly spent 3 days farting around with one, including balancing the bare head, changing multiple blades, then changing the entire set out, followed by 2 sets of dampers. Two days later I was no further ahead and we started from scratch yet again. Throw away the logic and record of adjustments and just go for it. We had our best success with a microvibe, but they were never fast. Didn't matter what type of blades or set-up - and some of them were just impossible to do anything with. I have never operated a 500 since then (and I had a bunch of them), and will never, ever operate one again.

Apologies to the original poster who didn't ask for any information on a 500.
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Old 19th Mar 2017, 00:57   #17 (permalink)
 
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ring gear, you didn't read my post. I never said don't balance, just that track affects balance.

Your link seems to take me to a place that wants my money for a "revolutionary tool in rotor track and balance". Are you in sales?????

Every machine is different and different RTB tools ahve different methods of achieving a good result. RADS works well in a 212, but only reasonably good on a 412 (well, when I was working on them anyway. Hopefully RADS is better on a 412 now!).

HUMS on the AW139 works great and I don't agree with your comment about OEM's and master blades.

Many times I've replaced a main rotor blade on a 139 and have had to do NO adjustments. Vertical and Lateral have remained below 0.06 IPS (normal for a 139), which is well below the 0.2 IPS limit. Yes that is correct. I have replaced main rotor blades on the 139 and have not had to do any adjustments.

Try that on a 412!

I'm going to put that down to their blade people being very good at making their blades nearly identical.

Steve, as far as the 412 and RADS goes, when I was working on it, you needed a phase angle corrector in case your adjustments went off on a tangent.

You also needed to keep an eye on what IPS reduction you got for a certain move, compared to what RADS said you would get. Different aircraft had a different sensitivity.

From memory (foggy memory!) we used a 1:1 ratio for mass on the main rotor for what RADS was saying. For the tail rotor we would put 1/2 the mass as the tail rotor seemed to be more sensitive than what RADS thought. For the main rotor driveshaft we did 2/3 the mass. Adjust clock angles as needed.

Some 412's would be good after a few runs. Some would take a week.

I know of one 412 in Alaska (very experienced crew) that had the main rotor blades replaced and the replacement blades were all vastly different hours. Everything reset to nominal and they still had trouble getting good results on the ground (best to get the 412 as good as possible on the ground before flying). 3 weeks later they were still working at it. Bell rep came up to Alaska for a week to show them how to do it and left without improving things.

They finally got it acceptable in most regimes, but not all.

Some people may say that all blades can be made to fly with any other blade, but that just isn't necessarily true. Some people just make crap blades to begin with!!!

Good luck
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Old 19th Mar 2017, 02:23   #18 (permalink)
 
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I apologise if my previous posts appear condescending...was certainly not intended ....simply frustrated with the erroneous myths that have circulated the industry for so many years....and couched as fact.

500... I agree now that you describe your process by weighing the tip/root ends and using that as your yardstick...it is a crude way of assessing the mass distribution....but there are other, much better ways is all I am saying...and it is the distribution rather than the straight overall mass which is the kicker. You can have blades 250gms different in mass fly quite successfully together on the same head....providing the tip weights have been adjusted to compensate and ensure the Span CofG is within the design specs.

Mass is not critical for the balance ....distribution of the mass is far more critical. This is adjusted via span/chord static weights. If the distribution of mass is migrates outside the original design engineering tolerances for what ever reason, (Trapped water, in-field painting, small blade repairs/bogg, blade erosion etc) this will create your dynamic balance problems and you will begin to notice you will have to fly "sets" of blades rather than having interchangeability across the fleet.

Track has its place most certainly. But simply because a blade appears to be flying out of track does not condemn the rotor system to be out of balance....as is often the belief. It is most common actually, to fly the tracks apart in order to achieve a smooth vertical ride....particularly with variations in verticals with IAS.

Nooby....don't look at the tooling ....look at the research behind the tooling. In particular......look at the RWAS site and review the back ground and explanations offered to improve your rotor blade management. Look at the difference in importance between the Static Balance and Dynamic balance.

Look at the means of measuring and adjustment between the two.

How you achieve the static balance in isolation from the Dynamic balance is up to you. Read the sections pertaining to the static balance and why static balance is so important for rotor craft versus the tyre industry. But if you try to compensate the static balance (ie Span moment arm adjustment) with the dynamic balance, all you do is chew up Dynamic Lateral adjustment capability while correcting a static problem...then when it comes to correcting the Dynamic problem (wear in bearing, engineering tolerances/play within the hub/Tx components, small variations between blades etc)....you find there is no more adjustment capabiltiy left....or very little

How many people have run out of room (capacity) to correct a lateral balance problem with their Dynamic Tool (whether RADS/Chadwick./Helitune/ACES or whatever - doesn't matter). This manifests itself as when the move line on correction chart starts to run tangentially past the origin but fails to track inwards towards the origin (we've all seen that right)....and most people are forced to accept an uncomfortable ride because the Dynamic balance chart takes the vibration out the opposite side of the chart without getting down to an acceptable level. The move line passes tangentially past the origin at 0.2ips or greater. This is a classic indication that you have a span moment problem......its tip weight time most likely.

This is particularly true for the teetering systems eg B204/205/206/212. How many Huey drivers (ALL helicopter pilots for that matter) have spent HOURS flying round the flag pole trying to get a pair of blades to fly together. Remember the old Chadwick "Clock Angle" corrector in the older Dynamic Balancers. When the old "static" Balance technique for teetering heads was to suspend the entire rotor head including hub in a box on the hanger floor and add weight to correct the see-saw balance methodology. Where was this weight added? To the Hub bolts ie the DYNAMIC adjustment point.......not the Static adjustment point - (the tip weights where you gain maximum effect for the minimal mass change)..

I'm sure this will sound awfully familiar to a lot of the old & bolds out there.....the same is true for all blades.

I could go on but this is really not the right place..I do not wish to offend anybody on this site...I simply would like to shine some light on an areas which I'm sure you would mostly agree has been treated as a Black Art for far too long ...

Anyway.....once again, please go and read the research and the descriptions on these 2 web sites of why it is so important to treat static and dynamic adjustments as separate things. Because one will definitely affect the other as all of us who have been in this game for longer than we would all like admit.

By way of validation of the bona fides of the RWAS web site in case you were wondering, AgustaWestland (read Leonardo) in Chapter 18 of AW139 Airframe Type Training Course plagiarised the content of this site and published it in their earlier tech training manuals under Vibration Analysis Rotor Track & Balance as their own proprietary knowledge. For those with the earlier digital Agusta tech manuals feel free to look it up and compare.

I apologise to Steve B for diverting his original thread...but maybe content we have discussed will help him sometime in the future when it comes to RTB on any helicopter.

Make your own mind up whether what I have been trying to describe is fact or fiction......

cheers
RG
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Old 19th Mar 2017, 07:08   #19 (permalink)
 
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Cylic

You obviously don't have the dark art ! WE have found that the assumption that all the blades weigh the same was the start of the trouble. Once we got that sorted the rest was actually very easy. As said we then found problems with dampers with them. Discovered that it is not a stretch test that decides if it is ok it is measuring the damper after machine has been flying. If the damper doesn't recover to certain point we throw them away otherwise you get what you have described .
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Old 19th Mar 2017, 21:52   #20 (permalink)
 
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Rotor Blade Balancing - Rotor & Wing Aviation Services - Dynamic rotor track and balance - Australia
Suggested people read that site 2\3 years ago ring gear, most do not want to hear
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