RE: What do you think about JETLEGEND L39?

RE: What do you think about JETLEGEND L39?
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RE: What do you think about JETLEGEND L39? - 5/14/2008 10:14:09 PM

Posts: 852
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From: .., BELGIUM
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And last but not least... the most inner tube is a short one, making inserted rods quite useless other than for this 2".

Please take a very close look also to the surface of the tubes, how they were made coarse, where the resin still sticks and where it is obvious it never adhered to the tube around it....

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(in reply to SpiderJets)

RE: What do you think about JETLEGEND L39? - 5/14/2008 10:37:11 PM

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From: .., BELGIUM
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I did also receive an e-mail from Mr Yang from JetLegend, saying that they produced already 110 pcs of L-39's and two (including the one of Christos) had the case of a broken wing tube so far.
(Not all of them have flown yet, of course.)
So, his case is not an isolated one either.

This quality discussion will always stay in the grey zone as long as we do not speak of statistical repeat, I agree. But still, nobody can ignore that a much better and safe solution could have been found for the wing tubes, in particular for a plane of this size and in such thrust class. Hence, so far, I still ask myself the question why did they use this method, for a succesful product on the market. Price compromise, quality CF tube supply compromise, or simply design+manufacturing error ?...

I have become a fan of this JetLegend product, a very nice quality for money, but of course such flaws must be corrected with immediate effect first and should not be ignored !

Nicolas.

(in reply to SpiderJets)

RE: What do you think about JETLEGEND L39? - 5/14/2008 10:50:56 PM

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From: hull, UNITED KINGDOM
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Denny,

I hear what you say but the facts speak for themselves; the design has been used on many JL jets and at no time have I ever heard of a CF tube failure. To really say there is a design flaw you would need repeatability on the same subject. This has not occurred...
Repeatability is the fundamental requirement in structural and other types of testing otherwise the data is useless and just speculative.

Why hasn't there been any other incidences of this failure occurring? Despite the loads on this spar there have been no other reported issues. Perhaps there was a manufacturing fault with this one, who knows?

We can go round the houses on this one forever I suppose; it's a shame that we lost an L39 but to condemn a whole product line without hard, repeatable data is wrong.

Jeff

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Exclusive UK JetLegend Dealer

(in reply to aerialcameraman)

RE: What do you think about JETLEGEND L39? - 5/15/2008 5:41:06 AM

Posts: 739
Joined: 12/6/2001
From: Nicosia, CYPRUS
Status: offline

Jeff,

Yang himself has admitted to two already, broken carbon tube incidences. Is this something to be taken lightly??? Not many of the 110 L39's he produced are flying yet, so, how many more incidences of total destuction does he need before he admits he has a problem there? If it were the airframe loss only that mattered, I wouldn't even consider making a big thing out of it. But the airframe cost contributes only 20% of the total investment. Below is an abstract from Yang's email:

"Let's come back to Mr. Philotheou's issue, I know it's true that the carbon tube was broken in air. But is it definitely our fault? Look backwards, since L-39 was released, we sold about 110 sets, I believe some were flown, some are still in building. In the feedback, there are a lot of compliments on this model. Any complaints? Yes, mainly are no instruction manuals. Any accidence? Yes, mainly are one's own flying problems that require to purchase accessories for replacement. And there are two cases of carbon tube broken including Mr. Philotheou. With all above, I think, basically this model's design is successful. If there is any structural problem, I think I would received a lot of feedback. Then L-39's sales would have been stopped. Mr. Philotheou's L-39 was flown six flights before you sold him, if there is a structural faulty, do you think you have a chance to sell him?"

Chris

_____________________________

IJMC-Cyprus, JET-TRONICS' REP
WREN'S REP in Cyprus

(in reply to jeff sewell)

RE: What do you think about JETLEGEND L39? - 5/15/2008 7:23:01 AM

aerialcameraman

Posts: 58
Joined: 1/19/2007
From: Limassol, CYPRUS
Status: offline

Jeff

I have had more than 100 flights on my L39 and I would not have bothered to repaint it and correct some of the scale defects that are apparent if I didn't think it was a good model. I noticed the tell tale stress fractures after only two flights and did something about it. The more I looked into that part of the design the more horrified I became. There are dozens of reasons why the design is flawed and it is thankfully correctable. Mr.Yang does however have this unfortunate habit of pissing people off which is something that you don't get when dealing with people such as BVM. Four months down the line I can't finish my model off because I can't get a simply replacement canopy pat.

Over the last forty years I have been strapping full size aircraft to my arse and have accumulated around 12,000 hours which includes display flying and working as a test pilot and licenced engineer for the purpose of gaining approvals for major and minor aircraft modifications, writing flight manual supplements etc. and convincing the Civil Aviation Authority that the modifications are safe within the flight parameters set out. I'm still alive today which must mean that I have some idea of what this business is all about.
We have a saying "When facts are few **** abounds". In the model business there is a lot of ****.

Denny

(in reply to jeff sewell)

RE: What do you think about JETLEGEND L39? - 5/15/2008 8:39:45 AM

Posts: 640
Joined: 1/3/2004
From: Irvine, CA, USA
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After reading through this forum, I noticed that many L39 fliers have reinforced, modified the spars to make them stronger and enjoy many safe flights. Ever since the ARF planes show up in the 80s, I'd always reinforced every ARF I purchased because I assumed they were not built to withstand the stress that we are putting on them. To make these ARFs affordable, these factories have to hire cheap labor so they can produce them fast. I like to buy ARFs because it beats to build everything up from kit planes. Adding some strength to the ARFs is simple and cost effective. If we are doing that on prop planes, we have to do that on jets. it's our ultimate responsibility as a pilot to decide whether the plane is air worthy or not. We have to use our experience and knowledge to inspect the product and decide it's good to fly or not. If the spar look too small, then don't fly it until we reinforce it. This will prevent future accidents like this one.

My conclusion is that I will continue buying them because they are aerodynamically safe to fly, but I always assume that they are structurally unfitted for my flying behavior (I land hard,

)so I will over engineeringly reinforce them to increase it's safety margin. Heavier, yes, I don't mind burning more fuel.

I am looking for nav and landing lights for L39 ? Where can I get them/

Mike

(in reply to aerialcameraman)

RE: What do you think about JETLEGEND L39? - 5/15/2008 8:57:31 AM

ceffi

Posts: 87
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From: 34590 WabernEurope, GERMANY
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quote:

I am looking for nav and landing lights for L39 ? Where can I get them/

Hi Mike,
look here,

http://www.flugmodellbau.de/product_info.php/info/p1870_Scaleset-L-39-Albatros-1-5.html

Christian

(in reply to mikedenilin)

RE: What do you think about JETLEGEND L39? - 5/15/2008 9:01:18 AM

Posts: 852
Joined: 12/26/2001
From: .., BELGIUM
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Mike,

Not fully correct. The pilots are reinforcing the wing tubes RIGHT NOW, because of a reported mid-air broken wing lately.

Bear in mind that if forums like this to exchange ideas and experiences would not exist, we would all be left out in the blue and multiple crashes would happen. ARF's would have a very short life span and get the reputation as being unreliable and unsafe.

As for the lights, I still have my set (was never installed), and no longer the plane

. Whoever wants my set (only the two headlights and transparant domes for the wing tiptanks are missing, but can be easily ordered), please PM me.

Best Regards,
Nicolas.

(in reply to mikedenilin)

RE: What do you think about JETLEGEND L39? - 5/15/2008 9:31:08 AM

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From: Irvine, CA, USA
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Hi Nicolas,

Some are doing it now, but some have already done that before this incident. Barry did that before this had happened.

Yes, you are right, this is where we share knowledge, experience and paint. ( I just lost my Fury last week due to cracked TX crystal, they're all gone in smoke.

Mike

(in reply to SpiderJets)

RE: What do you think about JETLEGEND L39? - 5/15/2008 12:10:40 PM

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From: Erie, PA, USA
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Hello Nicolas,
I was just reading through this thread and I am sorry to here about Chris's loss of the air frame you built.

The exchange in this thread about Chinese quality and engineering seems to be strangely familiar as the writings in the Formost 150 thread

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Rich
Jet Central Falcon Owner

(in reply to SpiderJets)

RE: What do you think about JETLEGEND L39? - 5/15/2008 2:52:35 PM

Posts: 852
Joined: 12/26/2001
From: .., BELGIUM
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quote:

ORIGINAL: RCISFUN

Hello Nicolas,
I was just reading through this thread and I am sorry to here about Chris's loss of the air frame you built.

The exchange in this thread about Chinese quality and engineering seems to be strangely familiar as the writings in the Formost 150 thread

To some extent, I agree with you, but let's stay positive and optimistic in the first place !

JetLegend makes good products, nobody is perfect though. Every brand has its' weaknesses. It is a true pitty that a serious manufacturer like JetLegend made a compromise on selecting such bad solutions for a vital part such as the wing joiners. The rest is overall excellent value for money.
As far as we can estimate, there are some 10-20 L-39's flying already. Two had a broken wing tube. That's in the worst calculation a risk of 20%, which is a high risk.

The Formost too, also excellent value for money (I consider I got an almost free of charge jet in case of the Formost, so it is excellent value for money too although I spent so much extra work on making it safe. -pun intended-).

Nicolas.

< Message edited by SpiderJets -- 5/15/2008 3:08:58 PM >

(in reply to RCISFUN)

RE: What do you think about JETLEGEND L39? - 5/15/2008 3:14:26 PM

Posts: 983
Joined: 4/11/2002
From: Erie, PA, USA
Status: offline

Nicolas I am always optimistic

and I fully agree with Mike's intent in his statement below.
it is ultimately up to the builder/flyer of the airframe to ensure airworthiness.

quote:

ORIGINAL: mikedenilin

After reading through this forum, I noticed that many L39 fliers have reinforced, modified the spars to make them stronger and enjoy many safe flights. Ever since the ARF planes show up in the 80s, I'd always reinforced every ARF I purchased because I assumed they were not built to withstand the stress that we are putting on them. To make these ARFs affordable, these factories have to hire cheap labor so they can produce them fast. I like to buy ARFs because it beats to build everything up from kit planes. Adding some strength to the ARFs is simple and cost effective. If we are doing that on prop planes, we have to do that on jets. it's our ultimate responsibility as a pilot to decide whether the plane is air worthy or not. We have to use our experience and knowledge to inspect the product and decide it's good to fly or not. If the spar look too small, then don't fly it until we reinforce it. This will prevent future accidents like this one.

My conclusion is that I will continue buying them because they are aerodynamically safe to fly, but I always assume that they are structurally unfitted for my flying behavior (I land hard, )so I will over engineeringly reinforce them to increase it's safety margin. Heavier, yes, I don't mind burning more fuel.

Mike

_____________________________

Rich
Jet Central Falcon Owner

(in reply to mikedenilin)

RE: What do you think about JETLEGEND L39? - 5/15/2008 3:16:22 PM

Posts: 1747
Joined: 8/23/2004
From: klimmenlimburg, NETHERLANDS
Status: offline

quote:

ORIGINAL: jeff sewell

Denny,

I hear what you say but the facts speak for themselves; the design has been used on many JL jets and at no time have I ever heard of a CF tube failure. To really say there is a design flaw you would need repeatability on the same subject. This has not occurred...
Repeatability is the fundamental requirement in structural and other types of testing otherwise the data is useless and just speculative.

Why hasn't there been any other incidences of this failure occurring? Despite the loads on this spar there have been no other reported issues. Perhaps there was a manufacturing fault with this one, who knows?

We can go round the houses on this one forever I suppose; it's a shame that we lost an L39 but to condemn a whole product line without hard, repeatable data is wrong.

Jeff

Jeff to be sure:

are you getting my emails or PM,s?

_____________________________

Sandor Kruise
Dealers for:JetCat,Graupner,Futaba,Fei-Bao,Pro-Lynx,Airpower,Jets-munt,Xicoy,Jet-1A,Composite-ARF.
"Home of the Pro-Lynx Gears"

(in reply to jeff sewell)

RE: What do you think about JETLEGEND L39? - 5/16/2008 11:32:14 AM

Miquel

Posts: 27
Joined: 11/10/2006
From: spain, SPAIN
Status: offline

Hi all, Im the other L-39 crash, Yang take note of this case and now are studying what happen

Yang is very responsablity person and I know Yang gime me (both) a serios respouse abaut this.

best regards

< Message edited by Miquel -- 5/16/2008 11:38:58 AM >

(in reply to digitech)