RHC rotor blades: ADs and SDRs

[blakmax]

OK, I tried a comment on a thread about someone complaining about the cost issues with the AD and the time in service for his R44 blades and RHC deadlines for discounts. One reply. Thanks hermunculus.

I thought the comments may have been buried in an obscure posting which everyone ignored as an operator whinging about costs (which he has every right to do) but I am more concerned about the implications of reports of short term life bonding issues for a mandated replacement item, so I started a new thread in the hope of raising the issue on an airworthiness basis rather than a cost basis.

Upfront I want to draw people's attention to this link 4 March ? 20 May 2015 | Flight Safety Australia (http://www.flightsafetyaustralia.com/2015/06/24-march-20-may-2015-3/)

Robinson R44 main rotor blades—main rotor blade debonded. SDR 510020934
While carrying out CASA AD/R44/25 Amdt 1, it was decided to remove both tip caps from the blades. Small blister found on the underside of the band line on one blade. After removal of corrosion it was obvious debonding had occurred. On other blade, fretting line on the trailing edge of the weight cap was found. P/No: C0167. TSN: 104 hours.

My understanding is that this part number indicates that the NEW blades as specified by the AD are already exhibiting disbonds after only 104 hours service? Is my assessment correct?

Happy to accept contrary information, but if true the implications are substantial.

Regards

Blakmax

[Self loading bear]

Edited and re-typed from an usable computer instead of tablet:


Blakmax,

A quick Google search on rhc c0167 leads to R44-SL-49. Which confirms that these are the newer blades.

As you have stated recently on another thread:
Bond failures can be prevented.
There are really only two causes of bond failures:
bad production processes or bad design and certification processes.

You have also stated earlier that the Robinsons blades have a (very) short bonding overlap.
I understand that this does not neccessarily makes it a bad design but the design does not leave much buffer for flaws in the production proces?

The FAA should have looked at design fatigue life at type certification.
The FAA should also have examined RHC's production processes for its production certification (to multiply the type certified design)

I do not think that the FAA can be held liable but where would you recommend that the FAA should strenghten its competency?

Regards SLB

[blakmax]

Hi SLB

Firstly, thanks for confirming that these are the -7 blades.

One of the changes that was made for the -7 blades was to extend the overlap length substantially by extending the skins right up to near the leading edge, so that should give a bit more damage tolerance than the short overlap -5 blades. That is a significant improvement.

The down side is that they have opted for forming the skins by bonding three layers of skin as the blade is formed (four in the regions where the balance weight access slots exist). Now while that should also enhance the fracture toughness of the structure, but also dramatically increases the use of adhesive bonds so the design also increases the chance of bond defects because there is now three times the amount of adhesive being used, and adds a further three times as much interface to be reliably treated.

The fundamental issue with management of bonded structures is that currently the regulations require demonstration of static strength, fatigue resistance and damage tolerance, but there is no regulatory requirement to demonstrate bond durability. In other words, show that the bond is strong enough and fatigue resistance, and that it can tolerate bond defects at the time of manufacture, but there is no actual requirement to demonstrate that the bond will maintain its strength for the life of the structure. The other significant deficiency is that the way damage tolerance is applied directly implies that the bond surrounding the defect maintains pristine strength, and it can be demonstrated that this fundamental assumption only applies to large voids which occur in production. For porosity in production or disbonds which occur in service, the assumption that the adjacent bond is pristine is invalid.

See http://www.adhesionassociates.com/papers/59%20Davis%20and%20MacGregor%20THE%20CONDITIONS%20WHERE%20ND I%20MAY%20NOT%20PREVENT%20FAILURE%20IN%20REAL%20BONDED%20STR UCTURES%20final.pdf


I can assure you that as a direct result of the investigation of the crash of DQ-IHE the FAA composites people now considers adhesive bond durability to be its most important issue (reported at an FAA meeting on bonded structures in Salt Lake City July 2014). However, whatever the outcomes of their efforts, they can not apply the findings and changes retrospectively, so the current structures will continue to carry risks.

I have personally been attempting to increase the level of understanding within the European and FAA communities by conducting courses on Adhesive Bond Failure Analysis and Prevention, but it is hard to get past the OEM "we know everything" attitude, a lack of understanding of adhesive bond issues for the on-site Designated Engineering Representatives and a lack of understanding for the failure forensics for adhesive bonds within the crash investigation community. Essentially the deficiency in failure forensics competency means that there is no positive mechanism to close the loop which should correct deficient design and production practices.

There are also a number of mantra trotted out by manufacturers when an event occurs. For example I am prepared to wager a good bottle of scotch that the OEM in the current blade case will state that the disbond was caused by corrosion. I can assure you that it is exactly the opposite. Adhesive bonds depend directly on chemical bonds at the interface. For corrosion to occur, the chemical bonds formed at the time of adhesive cure must dissociate for the surface oxides to hydrate as part of the corrosion process. Therefore, the disbond must occur before the corrosion can commence. The disbond is not caused by the corrosion, the corrosion occurs after the disbond occurs.

Regards

Blakmax

[cockney steve]

Another outstanding post, Sir.:D:ok: Perhaps the way forward, is to contact the relatives of victims and encourage their legal representatives to sue the individuals who currently ignore your proper, scientific analysis.

They know their product leaves something to be desired in manufacturing and QC. The customer, the Helicopter manufacturer, also must now know, from the top of management downwards, that their product does not, in many cases, have the service -life claimed for it.
They can bluster all they like, that "development" or "inspection" failed to notify them......but a couple pf cases holding them personally responsible for wilful neglect of customer safety, misrepresentation and wilful complicity in homicide.....well! that may sharpen up their thinking and morals!

If these marginal products were destined for machines in the "experimental " category and the buyers knew the risk, that would be a fair and reasonable transaction

That is not the case. The Manufacturers are selling a Certified product at an enormous price and the buyer has every right to expect that the Certification by the regulatory authorities is fit for purpose.

It's not, they are endorsing sub-standard products that are killing people.

[blakmax]

Thanks for the support Cockney Steve.

I stress that this is not a QC issue. The QC guys can only check test data they are directed to follow. Adhesive disbonding is TIME dependent and almost all QC check tests are short-term strength tests, and therefore they will not interrogate the conditions that cause longer term bond durability issues.

The legal liability issue is not as clear as you may believe. For a start, I firmly believe that RHC has in all general probabilities complied with the regulatory requirements so I would expect that their legal eagles would direct any defence along those lines. I have actually been approached by one OEM to provide expert advice along those lines but they have never followed through with the offer, and I suspect the offer was an attempt to shut me up rather than to actually address the technical issues at the basis of the problem.

The vexed issue is that if any manufacturer actually knew that even though they demonstrably complied with the regulatory requirements but also were aware that these requirements produced principal structural elements that had a demonstrated history where they failed to maintain continuing airworthiness and that the risk factors were made aware in published scientific papers, and even though they were aware of the deficiencies in ongoing airworthiness of their structures they continued to issue airworthiness directives which ignored the available evidence of the risks to airworthiness and were aware that their ADs failed to address the issues which constituted the risk, is the defence of "we complied with the regulations" sufficient to defend against legal action? I doubt it.

The objectives of my regular postings are to make the end users aware of the deficiencies in airworthiness management of the very structures which support their lives every day, and to also make them aware of the lack of understanding of regulators, crash investigators and manufacturers with regard to the fundamental causes of adhesive bond failures.

For many years I have suggested that adhesive bond failure issues would only be rectified by legal litigation about a smoking hole in the ground with x number of poor b*stards in body bags. I know the FAA is addressing the issues but that may take a considerable time to reach fruition and their outcomes will not address the airworthiness of heritage structures.

I have published a number of papers on the subject of adhesive bond failures, and I have even conducted a number of courses on adhesive bond failure analysis and prevention over a number of years see www.adhesionassociates.com. (http://www.pprune.org/www.adhesionassociates.com)so any competent manufacturer should be aware of these issues. The FAA certainly is.

Within some conditions, I'd welcome the opportunity to support legal action on issues related to failures of bonded structures, but I am essentially retired on an adequate pension so I am not seeking life-supporting income. My only objective is to drive adhesive bonded structures to manufacture reliable structures.

Regards

Blakmax

[cockney steve]

The vexed issue is that if any manufacturer actually knew that even though they demonstrably complied with the regulatory requirements but also were aware that these requirements produced principal structural elements that had a demonstrated history where they failed to maintain continuing airworthiness and that the risk factors were made aware in published scientific papers, and even though they were aware of the deficiencies in ongoing airworthiness of their structures they continued to issue airworthiness directives which ignored the available evidence of the risks to airworthiness and were aware that their ADs failed to address the issues which constituted the risk, is the defence of "we complied with the regulations" sufficient to defend against legal action? I doubt it.

Exactly what I was driving at. They are wilfully ignoring the evidence you have so slearly put in the public domain over the years. The product is not consistently durable. you know that, We, the great unwashed know that, the manufacturers know that, but they and their customers, the Heli- builders, collude to hide behind the worthless extortion -racket that is it's certificate of airworthiness.
The Certification process is unfit for purpose. the end -user does not expect to pay for a Certified product which will only last safely until the guarantee expires.


If these were motorcar brakes....there'd be an enormous outcry and a worldwide recall...For industrial misconduct of this nature, read "unsafe at any speed" by Ralph Nader...he was responsible for uncovering that one manufacturer KNEW their product was unsafe but thought that it would be cheaper to pay out on successful court cases against them.

Time for a class action against the manufacturers/distributors of these unfit components?

[helofixer]

Let me add that the primer Robinson uses is utter crap. Yes its environmentally friendly for California but in real life down on the gulf coast of the United States their aircraft corrode and fast. We've seen an aircraft with 147 hours on the clock and in for its second annual exhibit corrosion on the trailing edge of the blades, around fasteners, etc. While doing the blade service bulletin that lets you file off the edge We were told by Robinson that we could use epoxy polymide primer instead of the stuff they send in the kit. They by law cannot use certain primers for environmental concerns.

[cockney steve]

They by law cannot use certain primers for environmental concerns.

In their position, I would advise the lawmakers that my product would be substandard, if that law were to be enacted/ enforced.

Therefore, I have a choice....hold the lawmakers accountable for losses , or consider it to be constructive destruction of my business....sue for disruption and loss, relocate to a more benign State.

I'm sure a good publicity campaign would make the local electorate aware of job losses and potential damages, because some ill-thought-out local legislation was forcing out a major employer!

That apart, If they had the will, they could paint the components elsewhere , then ship them back in for finishing/assembly.

[blakmax]

Let me add that the primer Robinson uses is utter crap. Yes its environmentally friendly for California but in real life down on the gulf coast of the United States their aircraft corrode and fast. We've seen an aircraft with 147 hours on the clock and in for its second annual exhibit corrosion on the trailing edge of the blades, around fasteners, etc. While doing the blade service bulletin that lets you file off the edge We were told by Robinson that we could use epoxy polymide primer instead of the stuff they send in the kit. They by law cannot use certain primers for environmental concerns.

Now we are talking about the real issue in adhesive bonding, and the same technology applies to corrosion and paint management. As I have posted many times, adhesive bonds rely on chemical reactions at the interface between the adhesive and the substrate, and the basic principles apply to paint adhesion as well. The common perception in adhesives and paint technology is that the surface must be clean. However, California has banned most of the reliable solvents because of VOC regulations. It is possible using low VOC solvents but the risk is that the slow evaporation rates may result in spreading any contamination by deposition of residual contaminants.

The requirements for a clean surface are true but only part of the story. To enable the chemical bonds to occur, the surface must also be chemically active to enable the reactions to occur. SO IT IS NOT SUFFICIENT TO JUST HAVE A CLEAN SURFACE.

For metals, you need some treatment to remove existing oxides so that the surface can be chemically active. This can be performed by etching (but these processes usually involve the nasty chemicals to be avoided in California). But is may also be performed using mechanical means such as abrasion by particles or by hand abrasion with abrasive papers etc., but hand abrasion is known to be the least reliable process. So it is possible to do this process and still meet CA regulations.

Now I stress that if the bond is performed with cleaning and oxide removal ONLY, then the initial strength if tested will convince you that the process gives a good bond strength. This is the crux of the matter, because the regulations require demonstration of static strength, damage tolerance and fatigue resistance and if these tests are conducted soon after the bond is formed. There is no requirement to demonstrate that the strength, damage tolerance and fatigue resistance are sustained throughout the life of the bond.

What is missing is that the primary cause of adhesive bond failures in service is hydration of the oxide surface formed at the time the bond is performed. The chemical bonds at the time of bonding must dissociate to enable the oxides to hydrate, and in the process the adhesive disbonds from the adherend.

The same is true for why paint flakes off surfaces.

Now it is possible to prevent hydration of oxides on metal surfaces by simple treatments with coupling agents which form strong covalent bonds to the fresh oxides, and it takes more chemical energy to dissociate the coupling agent bonds than is required for hydration, so hydration does not occur. The coupling agents are polymers and while one end of the polymer chain reacts with the oxides, the other end must be selected to react with the material at the other side of the bond (adhesive or paint).

Now what does this imply? If I treat a surface to provide a clean, chemically active surface and then treat that surface with an appropriate coupling agent that prevents hydration and is selected to match the adhesive or paint, then hydration will not occur, so disbonding and paint failure will not occur.

Now it is also important to understand that corrosion is nothing more than advanced hydration of the surface of metals, so if a metallic surface is clean, chemically active and treated with an appropriate coupling agent not only will the adhesive stay bonded, paint will also stay bonded and corrosion should be minimised if not prevented. If you understand this, then you will also understand that the idea that corrosion is the cause of disbonds is bovine excrement.

It is also important to understand that the application of a primer on a metal surface unless it is clean and chemically activated, and is compatible with the materials being applied you are wasting your time.

Regards

Blakmax

[cockney steve]

As a layman, self-taught panel-basher and sprayer, I always thought I had investigated the technology thoroughly.

To me, a primer, is just that! it primes (prepares) the surface for further treatment.

seems I'm wrong!...
I usually prepare aluminium panels with a Scotchbrite pad (like the green domestic pot-scourers) wipe off with Acetone based thinner until the paper towel has no black streaks, then coat with 2-pack, high-build etch-primer.....this is activated with a Phosphoric acid -containing compound.

Always good results, the phosphating kills the surface corrosion even on pitted panels.

I use 2-pack, isocyanate colour coats....It sets like epoxy cement. high build high durability , low solvent content, so low shrinkage (but you must wear a respirator! )


So, after mechanically cleaning the surface, what do you recommend to passivate and prepare the surface? i appreciate adhesives and paint are different, but as you said, the bond has to be there!

[500e]

There is so much to learn CS. Max came to see me when he was in the UK some time ago, he was a mine of knowledge & we learnt a lot,(Thanks Max)
& has posted a lot of links to papers he has produced.
I note he asked for donations to Breast Cancer charity if you found his information helpful.
https://www.xiameter.com/EN/Products/Pages/ProductDetail.aspx?pid=01011278&lir=X59#propertiesAnchor

[blakmax]

OK, I have had some further thoughts on this. The time since manufacture is what determines the extent of hydration if that is the cause of the disbond and hydration resitance is driven by the surface preparation at the time of manufacture. In this case, I doubt that this blade has been made long enough for the disbond to be hydration related. I suspect that it may be a localised contamination problem, and therefore would not indicate a deficiency in the process itself.

I'd be surprised if there are further examples of such disbonds again.

[blakmax]

Hi CS

Primers perform several functions. Firstly, it is imperative that they form strong chemical bonds such that when the adhesive (or paint) reacts with it, the interface between the metal and the primer should be as strong as the bonds between the adhesive and the primer. Primers also may contain specific chemicals which assist in minimising corrosion. Primers also enable a prepared surface to be stored for a short time between bonding steps and that helps production scheduling.

Many primers do contain coupling agents and that would improve durability. The secret of success is to apply the primer as soon as possible after the surface has been prepared, because the surface has had the old oxide layer removed (by scotchbrite is one method, but light grit blasting is far more effective) and the surface is chemically active.

Regards

Blakmax

[cockney steve]

Thanks, Blakmax! I recently rebuilt a "BoB " trailer for a pedal cycle....sandblasted, high build 2-pack primer, 2-pack isocyanate top-coat, wafted on several coats until the mixed paint ran out.:)blasting to primer within the hour!

Daughter towed it behind her bike from Lands End to Lohn O' Groats
finish passed the durability test and project was a couple of hundred quid cheaper than a brand new one. (It should also last longer due to my superior paint- system :8


Q- how would one attempt to grit/sand blast the tinfoil Robbit blades?

Please don't say "very, very,very carefully and cautiously

[blakmax]

Q- how would one attempt to grit/sand blast the tinfoil Robbit blades?


Steve

The way a surface is grit blasted depends upon the type of material. When one talks about grit blasting, the common perception is that you blast the **** out of the surface, such as if you are taking rust off a highly corroded steel ship hull. This is not necessary for surface preparation for painting or bonding because all you need to do is to remove the existing oxide layer. You are NOT trying to "roughen" the surface.

Now for relatively soft materials (aluminium for example) you would reduce the pressure in the gas used for delivery, but for harder materials such as stainless steel, you need to use a higher pressure.

The blasting medium is also a consideration. The medium must actually cut the surface to remove the oxide layer, so soft materials such as walnut shells will not be suitable. We have usually relied on aluminium oxide powder about 50 microns. We also did not recycle the powder to prevent cross contamination.

The propellant gas may also be important. Many people use shop compressed air, but that has a severe risk of oils and water from the compressors. We always use dry nitrogen from cylinders used to compress shock struts etc. Dry, clean and inert; that works well. Just be careful if you use this in confined spaces because the user may develop a blue face and fail to return at tea time.

Regards

Blakmax

[cockney steve]

That level of attention to detail is impressive!...Of course, a properly regulated, cooled, dried and filtered compressed -air supply "should" be totally free of contaminants. but inert gas and once-only grit use is really first-class QC.

OK, I was being a bit facetious about the "tinfoil"....I'd probably be happy hanging under ,say carbon/Kevlar composite blades with a foam core, but the thought of tinfol and foam construction, with demonstrated erratic longevity,means I would not , unless you paid me enough to risk terminating my life early, step into a Robinson product.
I know a Forumite who flies Enstrom.... He sold his previous one to buy a 44 which nearly took his life. Admittedly, It wasn't to do with dodgy blades, just, it would appear, the Enstrom is a much better ship.
If a real legend and sky-God, Mr Dennis Kenyon, flies Enstrom, that's a good enough endorsement for me.
The Robinson is very cheap for initial purchase, for a reason.
I'm not that desperate to fly!