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Crezzi

EV97 - Main spar structural failure

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Not sure how relevant it is the Sportstars in Aus but the Swiss investigation into a fatal Eurostar accident raised a few issues owners might want to know about

 

Full accident report - http://www.bfu.admin.ch/common/pdf/u2053_e.pdf

 

A response from the Czech authorities - http://www.evektor.cz/pdf/12162009_LAA_CR_Statement.pdf

 

John

 

 

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It is an interesting read. It is a bit of a worry that the investigators are saying there is an up to 29% difference in the actual versus calculated strengths but the other guys are saying that there isn't!

 

 

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Interesting indeed. Doesn't put me off flying them - within the new limitations.

 

  • static test until rupture was done so the independent structural analysis is of limited interest however
     
  • manufacturer used Weissenger's method to calculate the spanwise lift distribution and get the bending moment so I guess they included some lift across the fuselage. The independent verification used Schrenk's method and I can only guess that they assumed nil lift over the fuselage, very conservative all round - that would account for their higher bending moment. Not enough detail in the report to know for sure. Regardless of how much lift is taken to apply over the fusleage, Schrenk will always give higher bending moments than Weissenger's method, sorry can't remember what percentage. I'd go along with the manufacturer based on what I have read.
     
  • the manufacturer then had an independent review by Prof. Píštěk (I met him when he was in Australia some years ago, seemed very capable) who said the design and testing was OK - consistent with the above


     
  • quality of the spar material is an issue with a section of spar used having a weld extrusion


     
  • as noted in that report "The specifications of the ultralight or Ecolight Eurostar EV-97 aircraft are presented in the manufacturer’s brochures and on its web pages. Among other things, the load factor is mentioned. The value of +6g/-3g g is mentioned under terms such as load factor (design) or facteur de charge. From the details it is not apparent that this figure represents the load at rupture and not the safe load, or rather the permissible operating limits of the aircraft." I've seen other websites where the same thing is done and you're led to believe that the aircraft is stronger than it actually is.


     

".... there was only one accident concerning a wing failure – it was a case of a blatant violation of rules – the owner in his ultralight EV-97 flew aerobatics, expressly forbidden both by the UL regulations and by the operating manual, damaging his aircraft’s airframe in the process. Despite a written warning (!) by the dealer and the manufacturer that his wings are already damaged (permanent overstressing wrinkles on the upper wing skin at the main spar), the owner continued to fly the machine and then, during an aerobatic figure, the wing finally failed."

 

Say no more.

 

 

 

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Guest Andys@coffs

I think the 2nd document of the 2 is the more important (with the exception that the first led to the 2nd :<)

 

So, the manufacturer now has an NDI method of determining the spar cap strength, however, how that will work with the machines in the field is not discussed. That would have to concern me if I had one of these aircraft flying in Australia.

 

The manufacturer identified that they had all of the appropriate Certificates of Compliance for the spar cap material and that the COC and the material manufacturers QA testing showed no defects for the batch that was used, in the failed wing and apparently in the other even lower strength example, would suggest to me that there is no way that you could conclude that the problems are tied to a single batch. They may be, but then again..... That to me means that if I had one of these then until I could arrange for the NDI testing the flight restrictions identified in the 2nd document would need to apply.

 

I suspect we will hear more about this

 

I personally have never been a huge believer in ballistic chutes, always believing that the pain in having one (regular manufacturers inspections and repacks and the associated transportation issues because of the dangerous cargo aspects) never balanced against the benefits.....In this case I could see that I was wrong.

 

Heres hoping that the advanced lifecycle ageing that the swiss investigators alluded to isn't something that we see much of...in the air....

 

Andy

 

 

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As far as I know, the Australian aviation masses still await release of an investigation report following the double fatality in WA two years ago when an Evektor fell out of the sky. It will be very interesting to compare and cross reference all three of the reports once to hand.

 

 

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Guest basscheffers

Are there any EuroStars in Oz? I can only find SportStars on the register.

 

Considering the new limits are only for the EuroStar, I would assume the SportStar has a different spar design.

 

One of the issues with the +6/-3 specification (and people thinking the aircraft is stronger than it is) is that it doesn't specify how often you can stress them like that. Even many Aerobatic aircraft have a different airframe life depending on how many hours were aerobatic and how many normal. So an emergency evasive manouvre which takes you very to 6G momentarily once is unlikely to damage most aircraft. But thinking you can do +4 G aeros in it regularly is going to kill you.

 

 

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Guest basscheffers
As far as I know, the Australian aviation masses still await release of an investigation report following the double fatality in WA two years ago when an Evektor fell out of the sky. It will be very interesting to compare and cross reference all three of the reports once to hand.

Yeah, still waiting. Have it on good authority that it was way over gross and GPS track logs show aeros being done. (the thing had a G meter installed!)

 

Frustrating it hasn't been released yet, but I guess that likely means they haven't found anything clearly wrong with the design.

 

 

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Are there any EuroStars in Oz? I can only find SportStars on the register.

Considering the new limits are only for the EuroStar, I would assume the SportStar has a different spar design.

The manufacturer's bulletin mandates the lower speed limits for "all EV-97 Eurostar aeroplanes manufactured till 01.12.2009 (incl.), except SLW model".

 

I don't know how different the SportStar is - it could be the different name here was just marketing (& a higher MTOW than 450kg). Personally I WOULDN'T assume that it has a different spar design until I'd confirmed with RAAus and / or the importer.

 

John

 

 

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As far as I know, the Australian aviation masses still await release of an investigation report following the double fatality in WA two years ago when an Evektor fell out of the sky. It will be very interesting to compare and cross reference all three of the reports once to hand.

The most recent report on the RAAus site is from Feb 2005 so Iwouldn't hold my breath if I were you !

 

John

 

 

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Even if our local investigators do have a look at the WA crash, I doubt they would have any idea what they are seeing anyway....but we can wait and hope!! Surely by now they should have indicated if it appeared to have been a wing failure, or not. Especially when there have been others. Having looked at the topographic map where the euro crash occured, I can certainly see where unexpected turbulance could have been a factor, however he was a current and experienced pilot, and should have been capable of handling it. I am not real fond of aircraft that throw wings, which is why I fly a Lightwing.

 

 

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Hi crezzi, dont quote me on this but from what i have read, the eurostar, was built slightly different to fit into their 450kg (i think ) european weight limit. The sportstars are built heavier, stronger. Even though they look the same on the outside, they do differ internaly/strucually wise. PS- the sportstar has been built with a airframe life of around 14000 hours (sourced also from reading about them on the manufactures web sight.) But that isnt a guaranteed or anything . PS- the distributor is i think a member of this site. He maybe able to shed some light on the subject. Cheers

 

 

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One of the issues with the +6/-3 specification (and people thinking the aircraft is stronger than it is) is that it doesn't specify how often you can stress them like that. Even many Aerobatic aircraft have a different airframe life depending on how many hours were aerobatic and how many normal. So an emergency evasive manouvre which takes you very to 6G momentarily once is unlikely to damage most aircraft. But thinking you can do +4 G aeros in it regularly is going to kill you.

IIRC the UK design standard (for ultralights) is that there must be no failure at ultimate design load for 3 seconds (and no permanent deformation at the limit load). +4/-2 is the minimum acceptable limit load and safety factor of 1.5 makes minimum ultimate load +6/-3

 

John

 

 

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Hi crezzi, dont quote me on this but from what i have read, the eurostar, was built slightly different to fit into their 450kg (i think ) european weight limit. The sportstars are built heavier, stronger. Even though the look the same on the outside, they do differ internalystrucually wise. PS- they sportstar has been built with a airframe life of around 14000 hours (sourced also from reading about them on the manufactures web sight.) But that isnt guaranteed of anything . PS- the distributor is i think a member of this site. He maybe able to shed some light on the subject. Cheers

You may well be right. I don't know what differences there are but hopefully Peter (or somebody who speaks to him) can confirm if there is any relevance to the Aussi Sportstar's.

 

 

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Just got off the blower after speaking with Peter (Aust Distributor)

 

NONE of the SportStar variants are affected. 016_ecstatic.gif.156a811a440b493b0c2bea54e43be5cc.gif

 

Different wing construction to the EV-97

 

 

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Guest basscheffers
I had wondered for some time if they original Australian SportStars were different. They look so similar.

Their empty weight is also about 30KGs more, some of that probably went into the spar!

 

 

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TH,

 

I edited out the "in Australia" as the same applies to all SportStars. The USA ones are the same airframe, but the yanks have to toe a few different rules with regard to stall speed to fit into their LSA category.

 

Cheers!

 

 

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Guest Andys@coffs
Just got off the blower after speaking with Peter (Aust Distributor)NONE of the SportStar variants are affected. 016_ecstatic.gif.156a811a440b493b0c2bea54e43be5cc.gif

 

Different wing construction to the EV-97

So to me that is good news but there still remains some questions.

 

While the aircraft in question and the sportstar may well be different, are the wings still of the same type of manufacture (yes I know you've written "Different wing construction", but what does that really mean?)and more problematic, using the same type of materials from the same supplier?

 

If the answer is yes then given that the Evektors QA around the suppliers raw material in addition to the suppliers own quality control, would appear to be at the root of the problem, if the documents presented can be taken at face value, then I would want to understand if the problem has relevance to the sportstar, that is, do Australian Sportstars have metal in them, perhaps in critical locations, that came from the same ultimate supplier as the below spec examples identified in the documents?

 

If on a sample size of 2 (that we know of) they found a 29% deficiency of actual to stated then we aren't talking small discrepancies are we?

 

Or do others see it differently to me?

 

Andy

 

 

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EV97 Wing failure

 

As the Australian distributor for the SportStar, it's interesting to read the often speculative comments on this thread.

 

I would like to re-assure Australian (and other) SportStar owners about the safety of their aircraft in regard to this issue and refer owners and others to the Evektor factory website on Welcome to Evektor - Aircraft Producer and Design & Engineering Company.

 

Evektor have made it quite clear that the latest Eurostar model (the SLW) and the SportStar are NOT affected by this issue.

 

Lest you are thinking: "Well he would say that, wouldn't he?" here are some facts.

 

The SportStar is not just a 'name-change' marketing exercise, it is a different aircraft from the Eurostar, developed specifically for the (then) expected Light Sport Aircraft market proposed in 2001/2002. The SportStar was the first LSA of any type to be registered (a) by FAA in the USA (April 2005)and (b) by CASA in Australia (May 2006).

 

3 different versions of the SportStar are flying in the world, including Australia:

 

- the original 'fuselage tank' version, certified to 550 kgs MTOW

 

- the SportStar Plus, with wing tanks, certified at 575 kgs MTOW (which can be increased to 600 kgs without airframe modification, under a service bulletin issued by the factory)

 

- the SportStar SL/MAX also with wing tanks, certified at 600 kgs MTOW

 

The aircraft involved in the WA accident was one of the 'fuselage tank' aircraft. I cannot comment on that accident as the report has not yet been published. However, the manufacturer was involved and co-operated fully in the investigation and it is my understanding that no fault was found with either the design or construction of the airframe.

 

Here are the main differences between the SportStar and the Eurostar:

 

- the SportStar is all round a bigger aircraft

 

- MTOWs on SportStars are between 100 and 150 kgs higher than on the Eurostar

 

- empty weights are also higher, as much as 50 kgs in the latest versions (and yes, some of that has gone into the wing main spar)

 

- the spar design on the SportStar (all versions), particularly at the wing root, is different from the Eurostar. Apart from the higher MTOWs, other practical evidence of this is that the optional wing-fold mechanism available on the Eurostar cannot be fitted to the SportStar.

 

In Australia, we have some of the highest flight-time SportStars in the world - including a fuselage tank aircraft with over 3,500 hours of training and hire, and several SportStar Pluses with over 3,000 hours.

 

LSA aircraft like the SportStar have much higher 'G' ratings than typical GA aircraft - however, this does not mean they can be flown without consideration for load and turbulence. As one contributor mentioned, aerobatics and manouvres like high-G steep turns etc will substantially reduce the life and strength of any airframe (in the case of one well-known military trainer a reduction from 15,000 hours to 4,500 hours for frequent aeros).

 

I firmly believe the SportStar is as safe an aircraft as any on the market - provided you fly it within the manufacturer's limitations and do not abuse it with high-G activities.

 

 

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Just like i said peter, i love the aircraft. (although you have given a bit more information, thank you) i would have no problem flying the a/c. Cheers IMO- they are built fine.

 

 

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Guest Andys@coffs

Peter

 

Thanks for the informative post, there is much info in the post, however the questions I asked are to my way of thinking still unanswered. These being:-

 

1) Is the wing design of the sportstar substantially the same as the Eurostar, that is, while the Sportstar has a higher MTOW and the wing therefore must be designed for the extra weight, is it basically the same design with upgraded sizes etc to cope with the extra MTOW requirements

 

2) Is the supplier of metals to Evektor that is used in the Eurostar, specifically the spar cap material, the same supplier that is used for materials used in the sportstar.

 

3) If yes then how confident are evektor that the metal used in the sportstar doesnt have the same below spec issues that the eurostar spar caps have

 

4) If they are confident then on what engineering basis are they confident.

 

If I owned an Evektor Aircraft these are questions that I would want to have answered.

 

I understand that there is nothing to suggest that there is a problem, however we all know that for a pattern to become obvious there must be the first couple of incidents. If there was a batch of substandard material what is to say that the material was only used in the Eurostar?

 

Andy

 

 

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OK then, here are the detailed answers:

 

1. Although the wing design of the SportStar is similar, the SportStar has a different spar and cap design derived from the Harmony with more focus on fatigue life. As one example, the Eurostar has just a rectangular section of spar cap in comparison with SportStar's L-profile. The SportStar wing design is most definitely not just a beefed up Eurostar wing.

 

2. Raw materials for all Evektor aircraft are supplied from the same certified source. However the some of the rectangular section used for Eurostar caps had the wrong heat treatment. Evektor found on some un-machined rods that up to one meter on a four meter long rod was affected by higher temperature during final annealing treatment. The problem of strength arises when the wrongly annealed one metre length falls close to the inboard wing mount point where the stress is highest. Irrespective, all material had been delivered with proper certificates and Evektor did not find any discrepancies during normal receiving inspections.

 

3. Immediately after the accident (in 2006) Evektor checked all stocked raw material for hardness and conductivity) and they found lower figures in the rectangular section used for Eurostar caps ONLY. All other profiles were OK and met declared figures, including those for the SportStar, and including material used in other parts of the aircraft.

 

4. I'm not sure what you mean by 'on what engineering basis are they confident' other than to refer you to points 1-3 above. All received material is now checked to ensure it meets the certified standards. The entire design of the aircraft was tested very thoroughly before, during and after manufacture - LSA standards are in fact considerably more stringent in many areas compared with the sometimes basic ultralight certification in some countries.

 

I hope this completely answers the concerns of SportStar owners and customers. I hope from this that it can be clearly seen that although there was some substandard material, none of it was used on the SportStar and processes were put in place 4 years ago to ensure that any further substandard material would be excluded from use on any aircraft.

 

 

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