The Expert's Voice

Rotor Blade Quality Surveillance requested

2011-12-24T08:21:00.002+01:00

Blade quality surveillance (BQS) is one of strongly requested support issues. BQS concept of an Offshore wind farm comprises a complete third party assessment of each key procedure to obtain Type and Project Certificate. It covers design assessment (second phase), blade testing and surveillance of important steps in project (IPE). In order to obtain and retain blade airworthiness periodic monitoring of blade production, witnessing of quality assurance inspections, testing and supervision of whole life cycle operation is mandatory as well as supervision of maintenance and repair acceptance procedures.

HMS Technical Advisers strengthened

2011-11-29T22:14:00.000+01:00

We prouly present MATTHIAS VYSHNEVSKYY joining the team. Welcome on board! Matthias has years of experience in flight physics as well as design approval and he is reinforcing the AVIATION wing of the HMS consultancy portfolio.

Lightning strike event scale

2011-08-10T17:47:00.000+02:00

We talk about MINOR COSMETIC findings due to LS when only receptors and blade surface in some way swept over by lightning current. In those cases even receptors do not have to be substituted.
A bit more impact is performing the category WEAR OF COMPONENT, where receptors, connections and sparc gap are affected.
If you might find DAMAGE TO COMPONENTS, you have to admit that not only wear of structural integrity had happend, but also overload in critical sectors. You can have reasonable suspicion that lightning protection system is somehow a wrong design.
Incident with BREAK DOWN OF SYSTEM: in this category the component, i.e. blade is desintegrated and has to be replaced or repaired comprehensively.
And if there had been DAMAGE TO OTHER SYSTEMS you might talk about an accident with wider consequences.
(Event scale stated by Thomas H. Krogh, Electricon, Herning, DK)

It is not all about blades

2011-06-12T14:18:00.001+02:00

when Blade Experts talk ...
I learned a lot about fly-fishing: Fly fishing is an angling method in which an artificial 'fly' is used to catch fish, Torben Schmidt says. He is one of this great sport enthusiasts

Hijacking a single engined aircraft

2011-04-25T11:12:00.000+02:00

I could not believe it's true when I first heard of this incredible story my client presented the other day. But after his explanations on the phone I felt he is apparently in big trouble to verify an insured loss and I promised to try my best to help. Here is the original report of an enthusiast and member of PlanePictures.net André Garcez:

(LPCS Cascais, Portugal) 12-February-2010: Private Pacific Aerospace PAC-750XL André Garcez D-FGOJ c/n 139. ex ZK-JDQ. Straight from a Hollywood movie. A ex-military hijacked the aircraft, after pretending to be a photographer shooting parachute jumps from inside the airplane. The aircraft took off from LPEV (Évora) to LPCS (Tires) with 2 parachuters, and right after, the hijacker diverted the aircraft using a pistol. When the aircraft was landing at Tires, the pilot managed to take the weapon from the terrorist, but he went for the controls and tried to crash the airplane. The parachuters jumped at very low altitude and the aircraft landed with the engine shut down, with a strugle between the pilot and the hijacker, skidded into a ditch breaking the left wing and left again to the grass breaking the landing gear. The pilot jumped from the aircraft as soon as it hit the ground and the hijacker committed suicide (you can see him underneath the left wing). It also seems that the hijacker's car exploded in Évora. Handheld, raining a lot, and almost dark.

Incredible story, isn't it? What brave reaction this pilot had shown! I would have been scared to death...

Ironic Australian decision

2011-01-28T03:18:00.000+01:00

Australian government decided to cancel photovoltaic funding in order to take care about flooding wrap-ups.
Australian thinking not always comprehensible for me.

My comment on Vestas blade incident announcement

2010-09-17T12:51:00.005+02:00

Blade incident on V112-3.0 MW prototype in Lem, Denmark
(Ref: Vestas announcement No. 35/2010)

Randers, 10 September 2010: On Wednesday 8 September 2010, a blade piece detached from Vestas’ V112-3.0 MW prototype wind turbine located in Lem, Denmark.
Vestas confirms that this manually produced prototype blade – one of the first three blades manufactured for the V112-3.0 MW prototype programme – according to general procedure has not been subjected to Vestas’ normal verification and reliability testing program. Based on this incident, in the future, Vestas will, however, ensure that prototype quality meets higher demands than those applied for this prototype production. Manually produced prototypes will, however, always involve a significant higher risk of failure than by automated production processes. Vestas’ specialists and forensic experts have analysed the root cause and their preliminary and unambiguous conclusion is that this is a stand-alone manufacturing mistake caused by a human error during the manual production process of the blade. Among other things, this is clearly seen from the way the blade has broken. To make sure there is no doubt about the root cause, the management of Vestas Technology R&D has decided that Vestas’ internal investigation will be followed up by a third party, external, expert investigation. Furthermore, the result of this investigation will also be communicated to the stock exchange as soon as it is concluded.

This message came on my screen. In forty years of my professional life dealing with design, production and root cause analysis of aircraft wing and wind turbine blade failures, bewildering procedures within the blade production business have seemed to occur.

I do not understand the fuss expressed in the above announcement.

Before series production of blades can be started, the airworthiness of the prototype must be certified. This is the basic idea of a prototype. Prototypes are built to pass static and dynamic design loading in a test bed. This is to verify the documented evidence of conformity with theoretical calculations. Manually produced prototypes are different from samples produced by automated production processes. This raises the question of how you can prove a manually produced prototype to have the same properties as the series units.

Prototypes can not, by definition, be produced in a different production technology to series samples.

A manually produced prototype cannot achieve certification status of an automated production. Instead we must talk about pre-series blades, as real series production must be based on positively passed certification tests. Series production process, as I stated, must be identical to prototype production process to guarantee identical properties. Later on routine tests have to prove each series blade to comply with its archetype (prototype). That sounds formal but it is essential for ensuring the quality system.

But let us focus on the crux of the matter not mentioned in Vestas’ announcement. Principally blade production has been managed in a manually orientated fabrication process for validated reasons. The fibre fabric material used to build blades is somewhat unsuitable for total robotic handling processes. Filament winding, tape laying and pick-and-place handling techniques with pre-impregnated material collect dust in laboratory playgrounds and never had real series merit.

So I read between the lines. The intended automatic blade production process is fundamentally not in place. Development of automatic production system has not yet reached a satisfactory performance, thus unable to have its status frozen. This status is necessary in order for real prototype production to proceed. This is the gist of the matter.

Rotor blade damage classes

2010-09-14T12:00:00.005+02:00

1. Preliminary Note

The aim of this posting is to describe classes of findings within damage assessment and its requirements and responsibilities of servicing.
The classification is derived from well-established standards in astronautics and aeronautics industries where those issues are frozen into laws and provisions in that industrial sector. In wind industries we do not see any approved agreement of this type.

2. Definition of claim class

2.1. Damage class 1

Large scale demolition causing to rebuild sections of a blade or extensive repair. In this class of damage it is typically that main elements for distribution of forces are interrupted: Primary structure broken, i.e. unidirectional belts, Root-inserts.

2.2. Damage class 2

Primary structure damage and secondary structure (sandwich) damage affected to an extension as findings can state holes and/or cracks are penetrating through the sandwich within a limited section not greater than 10% of wing depth at that location.

2.3. Damage class 3

Primary structure damage and secondary structure (sandwich) damage affected to an extension as findings can state small holes and/or cracks in neither covering/outer layer if there is no injury of sandwich core material nor opposite/inner layers.

2.4. Damage class 4 (cosmetic damage)

Erosion, scratches, notches, not affiliated with disruption of covering layers. Damage class 4 for that matter includes also Vortex Generators, Gurney flaps, stall stripes, rain skirts and other secondary covering and cowling.

3. Responsibilities

Repair of class 1 damage is classified “very critical” and has to be authorized by blade manufacturer. Repair is to be done in certified shop (no in-situ repair) and with specially trained and skilled expert staff. Living quality management system is mandatory.

Repair of class 2 and 3 damage are classified “critical” and has to be escorted by an independent blade expert or at least kept by full-fledged repair documentation. Repair plan has to be signed off by expert or manufacturer and rework instructions (field conditions or shop-repair conditions) have to pass its acceptance.

Repair of class 4 damage can be carried into execution by versed workman but also has to be documented in a brief repair report.

4. Requirements

Requirements for blade service staff training, facility provisions and infrastructure of service providers, acceptance of independent expert’s knowledge and approval by customer are not uniformly given and topical matter in German wind association BWE. Cooperation in that issue is welcome.

5. Summary

Very roughly there are two measures of repair methods:
• Tower mounted (minor damages) and
• On the ground (severe damages) in unloaded (shop) conditions.

This definition of blade damage classes is claimed from the author (©HMS 2010) and designed to be the first input in 'AK Rotorblatt' - work group section of German WindEnergy Association (BWE)

Blade production evaluation through damage assessment experience

2010-05-09T07:24:00.002+02:00

Request for partnership with Benchmarking Center (ICB) at Fraunhofer IPK Berlin was wrapped up in order to define strategies for best practices on a management level of this sector. Dr. Holstein explained the core structural blade characteristics of turbine market leaders, common production technologies and its history and name the most frequently identified production related blade failures. His contribution was peppered with numerous updated inspection findings. Main difficulty in walking through the 5 step benchmarking model is the acquisition of the right industrial partners to join an open minded process to learn. I hear you say: This is impossible in wind business! But what the hell, I like this basic approach option.

"Siemens blade falls off at Europe's largest wind farm" - a so called top story in WINDPOWER MONTHLY

2010-04-05T12:22:00.001+02:00

Articles from Windpower Monthly, formerly known as WindAlert, claim to present breaking top news from windy business. So does James Quilter in his article released on 23 March 2010. "This type of incident is exceptionally rare and highly unusual" the head of the operating company stated.
This might be his experience and right for him and his view of the picture.
My perception differs from this. As far as I know 2.3 MW Bonus or Siemens blades are built in a "closed-mold-shot" - a rare production technique, where dry textile and core material is loaded into the mold first and in a second step the two semi-shells are closed. After this is done in a third step infusion of resin is executed. So practically you have the choice of interleaved stacking and wrinkling textile material over a well sized PE core and then close under-shells and over-shell with the risk of clamped and jammed fibers. The other choice is to manage a somehow complicated "blow-up" effect (vac.-suction) after mold segments are closed and interlocked. How often do you open molds again because of leaks?
Now here I spread my wisdom of a 35 years of experience of blow-up production processes not only in wind industry. "You face a lot of technological problems and the risk of fiber-disorientation in terms of wrinkles gives repeatability not really a big chance".
So I do not believe in exceptionally rare incidents in this case, sorry. I am not saying that Murphy's law is a dictum (Anything that can go wrong will go wrong) but I claim: given a sufficiently long time, an event which is possible (non-zero probability) will almost surely take place.

Non destructive testing of blades before installation

2010-03-04T22:03:00.001+01:00

Again questions arise if there is a way to test blades before installation or even after mounting with ultrasonics and/or infrared technology in order to quantify quality level or invisible or masked failures.

NDT techniques like the mentioned (US and IR) today (and I think for a long time in future) are not made to be used as a method for inspection of blades before installation in farms under construction. Both techniques have to be selected and adapted for the case of inspection one intends to do. IR has good features if you search for defects close to the surface. US have better potential if you want to look into the deep layers of structure. But non of these techniques can be used from root section to tip without dramatic change of parameters and system devices and measuring methods like frequencies, coupling heads, calibration and software setup. In other words: if you already know what kind of local fixed defect you are searching for and you already have tested and evaluated all these parameters for this case of testing, you have a slightly chance to be successful to find what you search for.

NDT like US and IR is not an all-purpose inspection feature and are to be chosen for very special assessment of blade defects. A day to day holistic blade quality inspection (inside and outside) like we do in many cases before installation is based on knowledge of the specific production process of the series production, the experience of noticed problems with this type of blade and the intuition of an old fox in the field of polymer chemistry, structural principles of blade design, aerodynamics, mass-dynamics of lightweight structures and last but not least independent standing of experts reference.

If you believe NDT blade testing is ready and in place for an universal monitoring of blade quality you may have been trapped by pseudo-scientific stories about fantastic new imaging techniques which is fiction for sure.

You ask for more information about the book project: tell the story of a case

2010-02-03T05:13:00.001+01:00

First of all I would like to thank you all for your openness to contribute in one or the other way. I would very much appreciate if you could manage to describe a case where your technique or the concept you promoted was successful. This might be, for example, NDT in detecting rotor blade defects. There is some fascinating experience I know of, where ultrasound specialists have scanned sandwich sections with balsa core material where glass fibre layers were partially cut in some inexpressible stupid production process steps. If you don’t mind and if you are able to tell this story without embarrassing the involved parties, this way of illumination of the manuscript has my preference. That long winding canticle your competitors offer talking of putative ingenious equipment is boring to me. My intention is to act on fact boiling down the stories of this book.

I have some other "stories", or let us say "cases" in mind:
-> the peril of what we call greased lightning or
-> the putative efficiency of the 24 hours production cycle or
-> total blade quality through cascading qualified subsystem elements like embedded inserts, pultruded or prelaminated and consolidated structural sections and others.

What about your "story"? No wrinkles, collapsed flanges, tumbling webs ...
How do you feel about active load controlled single pitched blades?
What is the first thing you blade-brained guys have in mind if you go for 10 Megawatt machines?

Anyway - deadline of this call for contribution is coming up soon and I will get back to you offering a conference call for authors of the short list.

Take care - we do.

airborne inspections available

2009-09-12T05:11:00.003+02:00

Encounter of my debut flight apparatus and its derelict

2009-05-06T18:17:00.004+02:00

My personal flight career started on the rear seat of a C 172 with tail index D ELSE. This aircraft was owned by the Technical University of Berlin, astronautics and aeronautics branch, institute guidance and control and me at that time in the main study period to graduate for my engineer degree.
Its last mission was to deliver sky divers at my club at EDVH, the place out of which I operate my Airborne Blade Inspections.
Ashes to ashes and dust to dust.

About Oysters and Blades

2009-04-15T13:33:00.004+02:00

If you want to check (without risk of poisoning yourself) the quality of an oyster, go for a cat and let her taste it –

– if she eats the oyster, it was good.

If you want to check (without any risk of observation faults) the quality of a rotor blade, go for an overload case –

– if the blade fails above the safe load value, then and only then you are sure, it was a good blade.

(old man’ saying with long beard, probably Professor emeritus)

I had a dream last night

2009-04-15T13:16:00.003+02:00

And it does not seem that everything is all right. Long and winding roads were leading to this land of change where the wind was driving huge blades onshore and even more gigantic ones way out on sea providing turbines at its best. One can believe it is well done for our children and we always knew we should do it in the right way and this means to invest as much as we can to get off this oil and gas consuming way of life. Our personal capacity to invest is restricted. We invested our heart and brain and the wisdom grown was swallowed by affiliated groups of global players. So my dream ended with an apparent suicidal drop off the nacelle of a wind turbine. What I found this morning is that b.a.s.e. jumping is more naive and narcissistic than suicidal. Watch them jump, click here

What is essential to improve blade lifetime?

2009-04-10T07:56:00.000+02:00

What is your opinion? How can we have best influence to improve blade lifetime?

:1: improve design?

:2: improve production technologies/quality management?

:3: improve maintenance and overhaul?

:4: improve terms of storage and transportation?

:5: improve inspection and blade accessment/on-site NDT method?

:6: improve meteorological prognosis?

:7: improve or develop realtime load measuring/managing and condition monitoring systems?

How do you feel we can improve - what is your experience? Do not hesitate to comment.

Frequently asked question about automatic blade inspections

2009-04-10T07:54:00.000+02:00

These days I receive numerous mails and phone calls pointing out there is a new automatic blade inspection device available.

“Do you know this robotic system?” they ask. Yes, but …

From time to time you may find breaking news about putative brilliant inventions to solve the necessary blade inspections without the needs of a human inspector. Fantastic ideas are presented and spread out full-bodied across mainstream media. I don’t mind if this information is precise and do not keep quiet about the fact that this is based on academic style pipe dreams, chimeras to win project sponoring and not worth to deal with it. I even don’t mind the fact originators have to suffer in their upcoming insomnia which may develop to a full-grown nightmare when the truth was made public. It is for sure that top-ranking scientific institutes may suffer the loss of their reputation playing around like this.

Sorry, I don’t care.