R22 & R44 blade delamination

[blakmax]

The NTSB comments on humidty, temperature are correct

Despite the derision shown on the pprune pages directed at the NTSB for Recommendations A08-25-29, the main cause of Robinson’s (and other manufacturer’s) bond failures actually is a combination of the manufacturing processes, high service temperatures and humidity. The problem is not related to degradation or brittleness of the adhesive itself. If weakening of the adhesive material or fatigue occurred, the failure would occur through the carrier cloth which is incorporated into the adhesive film by the adhesive manufacturer to enable the material to be handled without splitting. In a properly manufactured bond, this is the weakest plane in the bond, and if stress caused a failure, it should propagate thorough that plane. In many cases, bond failures have occurred at the interface between the adhesive and the metal. This means that the interface between the metal and the adhesive has degraded to a level where it is weaker than the plane of the carrier cloth.

Adhesive bonding relies on the formation of chemical bonds at the interface at the time of manufacture, between the adhesive and (usually) oxides and hydroxides on the metal surface. With even moderate levels of processing, it is possible to develop bonds which are sufficiently strong in the short term to pass testing. However the performance of those bonds over time depends on the resistance of those chemical bonds to degradation in service, and the most common form of degradation occurs when the oxides hydrate. For the metal to form a hydrated oxide the chemical bonds between the adhesive and the metal dissociate, leading to degradation of the interface. Chemical treatment is required at the time of manufacture of the bond to prevent hydration in service. This type of failure is characterised by an absence of adhesive on one of the bonding surfaces.

Now in some cases, there is what is termed a mixed-mode failure, where some of the adhesive fractures and some of the interface fails. This is typical of a bond that has gone part of the way down the path of degradation and the blade experiences some stress that exceeds the strength of the remaining bond. The longer the time since manufacture, the more that hydration occurs and the weaker the bond becomes.

Moisture is absorbed by ALL epoxy materials by diffusion, and paint simply slows down that diffusion process. It is that absorbed moisture which attacks the interface, causing hydration. High temperatures and high humidity accelerate the absorption process, and so they accelerate the degradation process. Hence, the NTSB findings are correct. The real solution to the problem is contained in the other NTSB recommendations where they suggest amendment of the Advisory Circulars to require all manufacturers (not just RHC) to demonstrate bond durability as part of the certification basis for the aircraft.

To satisfy Topendtorque's stated criteria, I am a scientist, this material has been published and has been subject to peer review.

[RotorSwede]

?

I'm worried.

So the R44 has blades with sub-standard quality and no certain method of detecting the faults ?

Shouldn't the entire fleet be grounded until a method of discovering the faults has been implemented ?

It's just a question, looking forward to the inputs from more experienced pilots and mechanics.

RS

[topendtorque]

Thanks Blakmax for that illuminating info.
I had thought that an ultra sound test might be developed as it had been for other serious issues at short notice, such as the '47 M/R grip for example.

Then I read "rotor swedes" post and thought, hey, if the common acoustic based tap test doesn't work, then how would any sort of sound frequency work?

It is amazing what can be seen inside one's stomach for sure but when you try the same stunt on a cow and encounter surface hair, even lacquered well down with gel, or inside open spaces then it is very difficult.

Maybe that would be the case with all of the little space pockets inside the bonded area?

It is still a tough call to suggest that an approval on a blade structure for a certain life is suggested now to be suss, perhaps well before its time.
Are you absolutely positive that such blade failures, or suggestions of impending ones, are not prone to a faulty manufacturing creep.

one thing I have noticed and that is the original issue paint on many Robinsons seems to be much more durable than any alternative. why is this so? it seems a bit like the factory fitted tyres on your new motor-car that always last heaps longer than any replacement.

I guess that you are saying that the hydration only occurs after the moisture penetrates in a plasma like fashion at the fluctuating and perhaps quite high hydraulic pressures that must occur out toward the fast tips. albeit on the higher pressure underside of the blade.

I would have thought that there would be a permanent gas insulation within the blade caused by diffusion which might have worked as a preservative and a barrier to the hydration, had the water been kept out, so to speak.

I always think of diffusion that causes that grey fog, just before daylight that seems to preclude ones ability to easily find the master switch. although it seems to be dissipating with age, maybe there is less grey matter for the alcohol molecules to randomly collide with or maybe the habits are more entrenched.?
tet

[cockney steve]

Slightly off-topic and in reply to the last poster (E.T. ,-#185)

eVEN MORE DISTURBING WAS THE SAGA OF THE "MINI 500" Fortunately for UK pilots, this was never approved, but in the US, it was allowed to be sold with reckless impunity into a totally unmonitored and unregulated environment

Darwin had a field-day with that thing! (It has to be said, that with development, it could possibly have become acceptably reliable and safe.-an unused kit recently appeared on Fleabay-listed as being in Germany.

Rotorway has also had it's problems,but i'm still baffled by the huge wedges of cash that people are prepared to pay to be test-pilots in marginal machines.

That said, the Robinsons would appear to offer the optimum "bang for the buck" in rotary-wing flying. Each pilot assesses his own risk-acceptability-level.

Would I take a ride in a Robbie?- probably!
Would I ride REGULARLY in one?- NO!...the odds would shorten to much for me!

[Runway101]

Would I take a ride in a Robbie?- probably!
Would I ride REGULARLY in one?- NO!...the odds would shorten to much for me!

What would you say if being in a Robbie would be the only way to be in the air for you? Say all your money is only enough for a Robbie or a Rotorway or something like this?

[deeper]

r44 main rotor delamination

this machine is privately owned and has done only 400+ hours in two years.

[Hughesy]

After a recent fatal R22 accident here in NZ, one of the theorys is blade failure at the hub. Been a few of these world wide. Now being NZ it will take at least 8 months or more for the report to come out, so it is just a theory, but a sound one.

Whats an easy way of getting a R22? Buy a peice of land and one will eventually turn up.

[topendtorque]

A revealing photograph, in more ways than one. Going for warranty is it?

[500e]

Looks like the paint was lifting along the whole end of the lower surface, how far has the paint erosion gone is it just the colour or the primer, looks like colour only.
Was it a tap test or did the Paint lifting give it away? would have thought the lifting paint should have been noticed before it got so far???.
But still with only 400 hours not good would be real if it was mine

[generalspecific]

Ok now we are starting to get a bit sick of this... We have just had our 4th blade delam!

2 R44's one with about 1,600 hours, now one with about 300 hours and 2 R22's one with around 1,200 hours and one with only 320 hours.

Anyone got any thoughts on how to get Robbo to start dealing with this. Hot and humid is clearly killing the baldes. One was a training macine and one was imported from the US so you could make the hard life argument possibly. But one of the low hours 22 and 44 were private machines flown by a limited number of cautious pilots ans the paint was well within the bond line limits with no refinishing ever done etc...

Any one with any posiitive experience from Robinson over warranty?

[Ian Corrigible]

Stark conclusion from the investigation into last November's R44 crash in Israel.

Main rotor blade failure caused R44 crash
Flight International 11/08/10

The fatal crash of a Robinson R44 helicopter (4X-BDM) in Israel in November 2009 was the result of the failure of one of the main rotor blades, according to the report of the Israeli air accident investigator.

Yitzhak Raz, the chief accidents investigator in the Israeli ministry of transport, says the failure was caused by a combination of erosion where the outer skin of the blade is connected to the blade's main spar, and separation of the skin from the "honeycomb" filling.

Raz says: "This combination caused the sudden separation of most of the blade's skin from its spar." The loose blade then cut through the tail assembly of the R44, separating it from the fuselage.

The report suggests: "There is real probability that some of the similar accidents in recent years that involved that type of helicopter were caused by a similar failure process."

The R22 and R44 have suffered multiple accidents, especially in their early days, involving the main rotor damaging the tail boom, but this was often attributed to the intolerance of the design to rapid movement of the cyclical control, which tended to destabilise the rotor blades of these very lightweight types.

Such events were often linked to the use of the types for training, or by entry-level owner/pilots who did not make allowances for this vulnerability.

All on board the helicopter were killed when it crashed into the Mediterranean.

I/C

[delta3]

R44 blades

Talked to a "pitting corrosion" expert recently and without knowing the specifics of the R44 inox blades his first gut reactions were:

-> bonding agents + moisture = turns acid

-> acid for many forms of inox = etches the iron away and creates pitting corrosion

-> pitting corrosion compromises the bond

So he needed no big research study to conclude that the inox choice was perhaps not the best choice...

At least I conclude that we have to keep water away from the bonds, which is off course easier said then done in some regions/seasons.


d3

[delta3]

Memories to good old "Lu"

I/C (some thread creep..)

Why does the "expert" has to bring up "populist messages" like

"The R22 and R44 have suffered multiple accidents, especially in their early days, involving the main rotor damaging the tail boom, but this was often attributed to the intolerance of the design to rapid movement of the cyclical control, which tended to destabilise the rotor blades of these very lightweight types."

I thought people finally understood what theethering rotor and low center of gravity meant. The R22/R44 are not the only theethering ones, cfr the passionate discussions with Lu. Rotor blades are as I extensively showed not destabilized at all, it is just the dynamic interaction between a very stable rotor disk, and less stable trailing body that has to be understood.

d3

[helisphere]

So I read through most of the posts on this thread but I didn't see a clear answer to this question: Is this delam/debond problem only a problem on the steel skin blades? Did the older aluminum skin blades have this problem??

[topendtorque]

Did the older aluminum skin blades have this problem??

not that i recall.

[Keepitup]

You could always try the new -7 blades for the R44 and see how that works, I know it doesn't help with the expense of the other blades, but they might help?

http://www.robinsonheli.com/srvclib/r44sl37.pdf

Keepitup

[Shawn Coyle]

I've heard a rumour (since this is a rumour forum...) of a solution using specially shaped tape that eliminates the performance penalty normally associated with blade tape.
When I know more, I'll post something.

[61 Lafite]

I've heard a rumour (since this is a rumour forum...) of a solution using specially shaped tape that eliminates the performance penalty normally associated with blade tape.
When I know more, I'll post something.

There are many solutions to different problems or perceived deficiencies on Robinsons, and after understanding Frank's philosophy with the aircraft, and his focus on simplicity, I keep coming back to the same thought:

...if it was straightforward to fix, or necessary to change the aircraft so it will safely operate within the published envelope, wouldn't Robinson have done something already? They seem to have done where it matters, with ADs - fuel pipes, fixes to things that might breaklike collectives etc wherever a fundamental flaw is found. The blade solution is there: paint them if they erode, replace them if they go too far or fail a tap test.

But we also get solutions not authorised by the manufacturer, potentially authorised by aviation authorities, which sell in relatively small numbers, and where the risk cannot have been as well assessed as if they were sold by the factory.

It seems to me that the risks of putting these unauthorised (by the manufacturer) modifications on to the aircraft far outweighs any benefit. Yes, even though it's $50k for a set of blades! Helicopters cost a bundle, and as soon as you start looking for where to cut corners on parts, safety is compromised: nothing compares with all new parts purchased direct from a Robinson source, fully QA'd coming out of the factory. Use it till it wears out or needs replacement and buy another new one from the factory.

If the factory tells you what to buy (e.g. oil type, 100LL) then buy exactly that. If the factory doesn't say to stick it on their helicopter, then don't!

Why do so may people - many of whom will never use the aircraft for anything remotely challenging like utility work, long line etc which might require specialist configuration - think they know better than the factory what should and shouldn't be on the aircraft?

... heading for the bunker now....it's radical (and expensive!) to think this way....

Lafite

[blakmax]

blade disbonds

Helisphere

I have examined a number of blades and at least one steel blade exhibited interfacial failure (separation of the bond at the surface of the metal, rather than a fracture through the adhesive layer) with separation at the surface of the spar, as well as the skin. Hence, it would not matter what the skin was made of if the failure is occuring at the opposite side of the adhesive layer to the skin material.

I am greatly concerned by the use of tapes to address this issue. While I have observed some limited evidence of undercutting at the blade tip due to erosion, I disagree that this is the cause of the bond failures. The erosion may exacerbate the problem and accelerate the process, it is highly improbable that such failures would occur at the interface unless the interface was already degraded and the bond was weaker than the strength at original manufacture. Placing a tape over the area will not prevent interfacial degradation and worse yet, will prevent visual inspection of the blade for disbonds. It is a bit like applying another layer of paint without first removing the corrosion.

The interfacial separation I have observed also occurred at a number of sites well away from the blade tip, so covering that area with tape would not influence erosion greatly but would severely inhibit visual inspection.

There is more information on this type of bond degradation issue at Publications - Max Davis - Adhesion Associates The paper is Assessing Adhesive Bond Failures: Mixed-Mode Bond Failures Explained

Regards

Blakmax

[lelebebbel]

The blade solution is there: paint them if they erode, replace them if they go too far or fail a tap test.

Surely you can't be serious. Have you had a look at the pictures a few posts above yours? 400hrs, paint well within limits - unservicable. How can that possibly be called a solution?