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 hangar 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
