Blades questions
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Joined: Jun 2006
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From: In the air with luck
Blades questions
As a real dim person I wonder if some one can enlighten me,
Blade weight.
Should all blades on a head weigh the same ( gross weight) not dynamic?
Why if a blade is built to a close tolerance does it vary appreciably in weight from another? forget paint erosion.
Tip weight is important, it appears to be more important than GW ?
I understand that some segmented blades are weighed at points along their length and segments are changed to get even weight distribution, ( I am told to within 1Gram or less, is this correct?
I would have thought out of balance along length would cause track to fluctuate with speed\load? + if the blade weighs the same as the other 2\3\4\5\6 on the head there should be less time spent BY AP to balance assembly? less stress\wear on the head & flight controls in general, leading to smother ride, in a word less cost to owners.
I am sure there is some one who can explain why my thinking is incorrect, or is it easier for the user to pick up the bill for poor manufacture?
Blade weight.
Should all blades on a head weigh the same ( gross weight) not dynamic?
Why if a blade is built to a close tolerance does it vary appreciably in weight from another? forget paint erosion.
Tip weight is important, it appears to be more important than GW ?
I understand that some segmented blades are weighed at points along their length and segments are changed to get even weight distribution, ( I am told to within 1Gram or less, is this correct?
I would have thought out of balance along length would cause track to fluctuate with speed\load? + if the blade weighs the same as the other 2\3\4\5\6 on the head there should be less time spent BY AP to balance assembly? less stress\wear on the head & flight controls in general, leading to smother ride, in a word less cost to owners.
I am sure there is some one who can explain why my thinking is incorrect, or is it easier for the user to pick up the bill for poor manufacture?
Joined: Sep 2007
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From: Queen of The Moorlands
Crikey 500e, Sven is right, opinions vary about the subject of blade balance about as much as the JFK theories. Lets just say that the science and art (For it is surely both of these) of blade / rotor balancing starts in the blade manufacture and becomes a process rather similar to painting the Forth Bridge.. i.e. endless.
I would say that there is no one parameter more important than the other, however the sequence and manner in which each adjustment point is dealt with is crucial to the whole equation.. and that old boy is where each man has his own take on it.
I would say that there is no one parameter more important than the other, however the sequence and manner in which each adjustment point is dealt with is crucial to the whole equation.. and that old boy is where each man has his own take on it.
Joined: Mar 2007
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From: UK
A little light reading for you, that may answer most of your questions....
http://www.rwas.com.au/blade-balancing.html
http://www.rwas.com.au/blade-balancing.html
Joined: Oct 2003
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From: Over here
Mostly, blades don't weigh the same because of heads, and a few other things. When changing the head on a 206, you balance it to grams, with the blades attached, by adding weight to one blade or the other. Even having the door open while balancing will throw it off. That's just the start, though, because dynamic balance isn't the same as static balance. If it isn't balanced statically, though, you'll have a very hard time getting a dynamic balance. Trying to balance mismatched blades, which have different ages, and different stiffnesses, can be an exercise in futility. There are lots of factors in getting dynamic balance, but it starts with static balance.
Joined: Feb 2003
Posts: 373
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From: ON A HILL
Blades Question.
R22 blades that have done a fair few hours eventually develope a gentle curve to the leading edge. This is easily checked by putting the blades leading edges together. This would suggest to me that a stress is raised tending to want to bulge the blade skin where it attatches to the leading edge. Could this contribute towards delamination?. The curviature must also alter the chordwise balance placing the chordwise c of g aft of its original position giving a tendency for the blade to climb. Anyone else noticed this? Little wonder they are sometimes a bugger to balance Bug.
Joined: Feb 2005
Posts: 7
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From: Australia
Common Misconceptions - Blade Balancing
500e,
Nodrama has hit the nail on the head. If you can read through the site, it will explain your questions.
As is also mentioned on that site, for too long the rotary wing industry has had a very poor understanding of arguably the most important thing which we all depend - the rotor and how it works, balance wise.
This is typified by the common misconceptions as amply demonstrated by Gomer Pylot. His ideas about depending upon the blades age, stiffness (blades are designed to flap - if they didn't we would not have a job) and mismatched blades is a classic statement which proves the widespread lack of understanding of rotor blades. When you hear these statements uttered the first thing that should cross your mind is - "this person does not understand the problem and is simply guessing". It is not their fault, it is simply an indication of how ignorant we have become and that we have not passed on corporate knowledge of such things.
It is how the wider industry still tries to explain away the simple phenomina of migrating span moment arm. (See ). When the greater industry begins to understand this basic phenomina and accept that it begins to happen as soon as you put a new set of blades on a rotating head, it must then accept what to do about managing this age old problem. See http://www.rwas.com.au/blade-management.html
Trying to match rotor blade hours, mass etc were early crude ways in trying to handle this problem - but rather unsuccessfully.
While we have theorised till infinitim over the aerodynamics involved (and still can't agree on the finer points), we have largely ignored the balancing of the rotor system. We appear to have been happy to leave it to the Noel Triggs (Helitune), Chadwicks or Stewart Hughes to come up with "Black Magic" solutions. THey have done wonderful jobs of solving the Dynamic Balance problems.
We now have to understand the interaction of the Static and the Dynamic imblance and how to correct for each....
The rwas web site will hopefully shed some light on the not-so-black-magic "art" of rotor track and balancing. In particular the blade adjustments and how they work and when they should be used. The interaciton of Static and Dynamic balance.
How we should have easy access to the Span Adjustment weights at operator level and be adjusting these weights to get the static balance within close OEM tolerances, then use the Dynamic adjustment packages to correct for purely dynamic problems (aerodymanic variatiopns, engineering tolerances in assembly, worn bearings, alignment variations etc) which they are designed to compensate for.......not chew up these dynamic adjustments by tryng to compensate for a Static problem (migrating or shifting Span Moment Arm).
These Span weight adjustments and balances should only be done with appropraite tooling. Tooling which enables simple, accurate measurment and comparison to OEM design ideal specs. That tooling is available....just needs OEMs to accept and approve its use.......
After the industry grasps how important the control and adjustment of Span moment arm is to the almost guaranteed success of the Dynamic Balance, they will hopefully begin to apply pressure to aircraft manufacturers in order to force them to change the design of their blades away from sealing the Span adjustment weight packages in the tips pf rotors (eg B412, AW139 ect)but instead design them with easy access to enable easy adjustment such as B205, 206 UH60 CH47 etc. (While these are still not what you would call "easy access", it is better than B412 or AW139 which require blades to be sent back to overhaul for tips to be debonded at much cost to the operator and revenue to the OEM/blade overhauler).
Hopefully industry design engineers will get the message and redesign their blades to make them more user friendly and lower operating costs.
One major Helicopter company is about to release a revolutionary design with the Span Adjustment weight packages totally exposed for easy access and designed for easy adjustment at operator level (onya Boeing). If other OEMS have any brains, they will ultimately follow suit.
Hopefully Nick Lappos may take a new broom through Bell and change their design philosophies to incorporate similar design features to make rotor track and balance far more straight forward and less time consuming than traditionally has been the case.
Sorry this has ended up much longer then intended. But hopefully this will provide food for thought, help answer some widespread misconceptions and promote discussion........
Nodrama has hit the nail on the head. If you can read through the site, it will explain your questions.
As is also mentioned on that site, for too long the rotary wing industry has had a very poor understanding of arguably the most important thing which we all depend - the rotor and how it works, balance wise.
This is typified by the common misconceptions as amply demonstrated by Gomer Pylot. His ideas about depending upon the blades age, stiffness (blades are designed to flap - if they didn't we would not have a job) and mismatched blades is a classic statement which proves the widespread lack of understanding of rotor blades. When you hear these statements uttered the first thing that should cross your mind is - "this person does not understand the problem and is simply guessing". It is not their fault, it is simply an indication of how ignorant we have become and that we have not passed on corporate knowledge of such things.
It is how the wider industry still tries to explain away the simple phenomina of migrating span moment arm. (See ). When the greater industry begins to understand this basic phenomina and accept that it begins to happen as soon as you put a new set of blades on a rotating head, it must then accept what to do about managing this age old problem. See http://www.rwas.com.au/blade-management.html
Trying to match rotor blade hours, mass etc were early crude ways in trying to handle this problem - but rather unsuccessfully.
While we have theorised till infinitim over the aerodynamics involved (and still can't agree on the finer points), we have largely ignored the balancing of the rotor system. We appear to have been happy to leave it to the Noel Triggs (Helitune), Chadwicks or Stewart Hughes to come up with "Black Magic" solutions. THey have done wonderful jobs of solving the Dynamic Balance problems.
We now have to understand the interaction of the Static and the Dynamic imblance and how to correct for each....
The rwas web site will hopefully shed some light on the not-so-black-magic "art" of rotor track and balancing. In particular the blade adjustments and how they work and when they should be used. The interaciton of Static and Dynamic balance.
How we should have easy access to the Span Adjustment weights at operator level and be adjusting these weights to get the static balance within close OEM tolerances, then use the Dynamic adjustment packages to correct for purely dynamic problems (aerodymanic variatiopns, engineering tolerances in assembly, worn bearings, alignment variations etc) which they are designed to compensate for.......not chew up these dynamic adjustments by tryng to compensate for a Static problem (migrating or shifting Span Moment Arm).
These Span weight adjustments and balances should only be done with appropraite tooling. Tooling which enables simple, accurate measurment and comparison to OEM design ideal specs. That tooling is available....just needs OEMs to accept and approve its use.......
After the industry grasps how important the control and adjustment of Span moment arm is to the almost guaranteed success of the Dynamic Balance, they will hopefully begin to apply pressure to aircraft manufacturers in order to force them to change the design of their blades away from sealing the Span adjustment weight packages in the tips pf rotors (eg B412, AW139 ect)but instead design them with easy access to enable easy adjustment such as B205, 206 UH60 CH47 etc. (While these are still not what you would call "easy access", it is better than B412 or AW139 which require blades to be sent back to overhaul for tips to be debonded at much cost to the operator and revenue to the OEM/blade overhauler).
Hopefully industry design engineers will get the message and redesign their blades to make them more user friendly and lower operating costs.
One major Helicopter company is about to release a revolutionary design with the Span Adjustment weight packages totally exposed for easy access and designed for easy adjustment at operator level (onya Boeing). If other OEMS have any brains, they will ultimately follow suit.
Hopefully Nick Lappos may take a new broom through Bell and change their design philosophies to incorporate similar design features to make rotor track and balance far more straight forward and less time consuming than traditionally has been the case.
Sorry this has ended up much longer then intended. But hopefully this will provide food for thought, help answer some widespread misconceptions and promote discussion........
Thread Starter
Joined: Jun 2006
Posts: 1,022
Likes: 2
From: In the air with luck
The AU site is a interesting read and there is a lot of information to sift through.
I can understand the migration of the span weight moving the center of lift over the blade surface, but still find the almost total disregard for static weights baffling.
Surely if you start with a blade that weighs say 15 grams more than the other 3 on say a 500 you are on a hiding to nothing as Max. balance is 150grams at head, there fore the blades overall weight is very important.
( on the 500E you balance the head without blades to start I understand,so GPs remark should not count)
Also where the excess weight or lack of is relative to the blade length, will effect the flap characteristics of the blade, again causing balance or & track problems.
The paint scenario is rather interesting, as if you run 22\44 and are painting blades to comply with POH you will be either sending blades back for stripping and re paint on a monthly basis or trying to blend in the leading edge daily, with a build up on the leading edge.
O happy days
I can understand the migration of the span weight moving the center of lift over the blade surface, but still find the almost total disregard for static weights baffling.
Surely if you start with a blade that weighs say 15 grams more than the other 3 on say a 500 you are on a hiding to nothing as Max. balance is 150grams at head, there fore the blades overall weight is very important.
( on the 500E you balance the head without blades to start I understand,so GPs remark should not count)
Also where the excess weight or lack of is relative to the blade length, will effect the flap characteristics of the blade, again causing balance or & track problems.
The paint scenario is rather interesting, as if you run 22\44 and are painting blades to comply with POH you will be either sending blades back for stripping and re paint on a monthly basis or trying to blend in the leading edge daily, with a build up on the leading edge.
O happy days
Joined: Sep 2007
Posts: 97
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From: Queen of The Moorlands
500e
I don't think SHAK'N and the others are disregarding anything, but hark to my earlier statement about so many parameters and blade construction / overhaul. In the Royal Navy we always placed greater emphasis on matching blades by 1st moment, rather than by weight. sure we matched them by weight to a degree, but the 1st moment matching allowed us to achieve better results in the air. Unfortunately, as I found when I left the Navy some years ago, when you speak of such terms to a maintenance organisation, you are usually greeted with a parisian shrug.
Incidentally SHAK'N, as you know, black magic boxes were originally designed to operate on a basis of a logical progression of adjustments, which themselves relied to a fair degree on the type of set up to which you refer.. sadly through the passage of time and the reliance on such kits like the Rotortuner or the Chaddy 8500's, this base philosophy is being lost, and largely, instead of smoothing a rotor, operatives are simply altering the way vibration is percieved in order to achieve a figure on a display. As Noel himself used to say "We've become bloody button pushers instead of engineers!".
Incidentally 500e, your second post is now moving into cross coupling effects.. i.e. the effect of blade pitch on mass balance for example, which serves to demonstrate that 1st moment, and pitching moment position or adjustment can almost make blade weight matching irrelevant.
This could go on all day...
I don't think SHAK'N and the others are disregarding anything, but hark to my earlier statement about so many parameters and blade construction / overhaul. In the Royal Navy we always placed greater emphasis on matching blades by 1st moment, rather than by weight. sure we matched them by weight to a degree, but the 1st moment matching allowed us to achieve better results in the air. Unfortunately, as I found when I left the Navy some years ago, when you speak of such terms to a maintenance organisation, you are usually greeted with a parisian shrug.
Incidentally SHAK'N, as you know, black magic boxes were originally designed to operate on a basis of a logical progression of adjustments, which themselves relied to a fair degree on the type of set up to which you refer.. sadly through the passage of time and the reliance on such kits like the Rotortuner or the Chaddy 8500's, this base philosophy is being lost, and largely, instead of smoothing a rotor, operatives are simply altering the way vibration is percieved in order to achieve a figure on a display. As Noel himself used to say "We've become bloody button pushers instead of engineers!".
Incidentally 500e, your second post is now moving into cross coupling effects.. i.e. the effect of blade pitch on mass balance for example, which serves to demonstrate that 1st moment, and pitching moment position or adjustment can almost make blade weight matching irrelevant.
This could go on all day...
Last edited by Alloa Akbar; 26th March 2008 at 15:26. Reason: Afterthought...
Thread Starter
Joined: Jun 2006
Posts: 1,022
Likes: 2
From: In the air with luck
So we are agreed that the closer the weight is from one blade to another, spread along length and chord the easier it is to arrive at the best result.
If this is the case we as users should be putting pressure on blade manufacturers, to make life easier for the AP, which in turn means cost saving in time, ware. & fatigue,
I appreciate even if I do not fully understand the other forces operating on the blade BUT you have to start somewhere so even = weight for all blades seems a simple start point.
PS
I have a theory about JFK.
If this is the case we as users should be putting pressure on blade manufacturers, to make life easier for the AP, which in turn means cost saving in time, ware. & fatigue,
I appreciate even if I do not fully understand the other forces operating on the blade BUT you have to start somewhere so even = weight for all blades seems a simple start point.
PS
I have a theory about JFK.
