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TURBINE HELICOPTER MAIN ROTOR DYNAMIC BALANCING


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#1 thanosk

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Posted 13 June 2017 - 04:46

If you are to replace one or more blades on a three bladed rotor using blades with different history and mass distribution i.e hours, repairs, paint coatings etc, how can you make a matched set?

Is it adviseable to use one blade as a reference to match the others?

If this is the case under what criteria you choose th reference blade?


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#2 pokey

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Posted 13 June 2017 - 12:37

do what the factory does: try another blade till ya get 3 to fly happily together :D  most of us do not have that option tho. That is where the  expression SOL comes from.  All BS aside? ya make it fly to an acceptable level of of of of of of of.

 

send them off to a blade shop, that is no guarantee either. couple thousand shipping too---make sure you insure them !.. oh wait. they will say it wasn't "packaged properly"..... you got the $$ to sue UPS?


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#3 pokey

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Posted 14 June 2017 - 08:19

getting 3 blades matched in all categories is pretty much impossible. Weight, moment, center of gravity, center of pessure, & prolly some more that only Merlin the magician knows of.  The factory matches them as close as they can to a "master blade", so do reputable blade shops--altho? the standards that each have vary from source to source. Its pretty much a shootin' match trying to find and make a strange blade fly with the bunch, its not rocket science & it can be done.  Whenever i need blades? i try to find a set that has flown together their whole lives.  I'v tried to 'make' a mis matched blade fly along with others---sometimes futile, sometimes successful. Blades are very expensive too-even on the used market & a blade shop will easily charge you over a thousand per blade just to inspect/paint/balance to THEIR master blade,,,,,,,,still no guarantee.



#4 pokey

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Posted 14 June 2017 - 09:49

as far as dynamic balance, all said & done? i still like the old chadwick, not many users understand it's principle, that is why all these new fangled balancers have come about. Vibration is really quite simple, and then again is very complicated once one tries to analyze  it.



#5 500E

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Posted 15 June 2017 - 15:42

as far as dynamic balance, all said & done? i still like the old chadwick, not many users understand it's principle, that is why all these new fangled balancers have come about. Vibration is really quite simple, and then again is very complicated once one tries to analyze  it.

Totally agree regarding Chadwick Pokey you can only make one adjustment at a time or you will chase your tail for days.

Regarding getting blades to fly together there are ways i wonder how meany people have just weighed their blades overall weight let alone  root ,tip & chord.

We rang 3 blade shops for weight of master & had 3 different weights !! & not just a couple of grams either.

Paint  makes a huge difference to both overall weight & distribution of weight.

Dampers also make a big differance


Fly the dream fly 500

#6 Rupert

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Posted 20 June 2017 - 14:57

Balancing weights and trim tabs. If your mechanics have good software, hardware and experience, they can match two, three or more unrelated blades. Not a problem.



#7 pokey

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Posted 20 June 2017 - 15:26

Balancing weights and trim tabs. If your mechanics have good software, hardware and experience, they can match two, three or more unrelated blades. Not a problem.

 

You forgot to mention sweeping, & some blades have more than one fore/aft position for the tip weights (thereby effecting the cordwise balance). Many have inboard and outboard trim tabs too. Yes, as stated above, the 'new fangled' balancing equipment is "supposed" to make it so a monkey can track & balance a ship in just a couple of hours. That is not always the case & a thorough understanding of the blade/blades you are dealing with is not only essential, but may save you days, or even weeks of chasing your tail.

 

There are many things also to consider than just getting the ship to fly smooth on the ground, in a hover, high speed flight. How about what happens when you let go of the collective? what does it want to do? rise? fall??,,,,,,,,,,,do these new computerized balancers tell the mechanic that?.  Just because you own the latest & greatest balancer, does not guarantee adequate results.

 

Like 500 said above?, how many have actually weighed a blade B4 trying to match it with the others? not only the overall weight of the blade, but the tip, the root & the chordwise? Do many even know HOW to check the chordwise balance? What will it effect if not the same as the others? Aerodynamic and mechanical twisting moments?

 

I don't claim to be an expert, but i have had enuf balancing problems to know that there is more to it than just a pitch link adjustment, trim tab, balance weight, sweep, to make it fly acceptable in all regimes. And YES, you will come across a stubborn blade that no matter what, will refuse to fly nicely with the others, what do ya do then?

 

Not sure what the OP had in mind with his question, but? i am assuming that he wanted to know "how ya know", B4 ya waste to much time on the project.



#8 pokey

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Posted 20 June 2017 - 16:05

Balancing weights and trim tabs. If your mechanics have good software, hardware and experience, they can match two, three or more unrelated blades. Not a problem.

 

Software, yes. Now that is where i call them "new fangled" balancers. I have never used one myself, but have heard how easy they are to use, & that is why the balancer has evolved from the old chadwick. It was a 'seat of the pants' balancer. very simple & effective to use. once you understood it & it's limitations. It basically is a piazo-electric accelerometer that is uni-directional---which means? You shake it & it only notices ONE direction (hence it "fires" the strobex at the 'heavy' side) now then? the more you shake it? the more voltage it puts out, so? now your IPS scale comes into play, shake it a little?--little ips.. shake it really hard? more vibration registers on the IPS scale. SO? no we have direction and intensity of our vibration. & here is where the operator experience comes in (and lack of computerization) comes into play. One move at a time!  now? if we completely completely computerized the future of ALL possible moves? well you see how that is 'supposed' to save us time/money/operator experience levels.  Ever try to win a chess game on the internet with a computer? ya really can't. Can a monkey win? Nope, has about as much of a chance of winning as you or i.

 

Now then? i buy blade B from Joe & want it to fly with my blades A & C.  (ya get where this is going?)



#9 MLH

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Posted 29 June 2017 - 09:50

 Do many even know HOW to check the chordwise balance?

 

http://www.vectorav....ade_balance.htm

 

 

Mike



#10 500E

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Posted 02 July 2017 - 05:48

Real interesting read Mike thanks

Build interesting as well


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#11 MLH

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Posted 03 July 2017 - 21:41

Building the Helicycle has been a labor of love, but after several years and way to many rabbit trails I'm looking forward to flying, hopefully by this fall.

 

Mike






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