Old Blanik L 13 Glider

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Martti Mattila

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I have Blanik L-13 Glider in my posession it is those old ones that has issues with their wings and main wing carry tru. Has been flying with VW engine and two people on board. But now after that mishap in Austria where two on board and full waterballast one broke appart during a aerobatic manouver no flying is permitted. From max weight to zero in one night very frustrating. You have those in U.S.A. too. I know some could be modified expensively by authorised shop but these wings are not eligible for that. Bitty to melt down a glider to make beer cans so I have this idea to make a wing struts and that way restore a air worthy in legal aspects.
It is on Experimental category already anyway.
So what people think is it possible modified a cantilever wing to be supported with wing struts. How do you strut already rigid construction where main pins are vertical like a Kitfox and clones.
I know there is a money to be made with this one from frustrated Blanik owners from all over the world. Let me hear it.
 

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TFF

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I don’t think the engineering is the real issue. The issue is going to be regulatory. Even with the freedoms in the USA, there would be a lot of concern of really fixing the issue, because of type of history. Somewhere else in the world, I bet no way.
I don’t think they would be happy without new wings. If adding struts would pass muster, you would model present wings and then add struts to the model. Strut outward would probably become the new focus of strength.
What makes some wings repairable and some not?
 

stanislavz

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What makes some wings repairable and some not?
Different version with thicker longeron. Which was designed after long-term "live" testing.

As far as i know - it was used very intensively for training, and not all overloads were logged, biggest issue here is "grey area" - of that you do not know. And it have strict life limits after severe overloads.
 

Victor Bravo

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If your Blanik was engineered for carrying the load of a VW engine and water ballast IN ADDITION to the two people, I would certainly assume that this particular Blanik would have been equipped with much larger wing spars (than the original L-13), no?

So... if this is in fact the case, then removing the 160 lb. VW engine and water ballast tanks, and then flying it as if it were one of the original L-13 sailplanes... one would assume you have a larger safety margin than an original Blanik.

Then, if you further limit the aircraft to non-aerobatic flight, one would assume you are providing an even larger safety margin.

If you can verify all of these things with an engineer, you should be able to make a very strong case for the government allowing you to inspect the wing structure and continue flying it as if it were an original L-13 glider.
 

stanislavz

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Then, if you further limit the aircraft to non-aerobatic flight, one would assume you are providing an even larger safety margin.
It is not. Problem is - how much damage was done before.. We have many grounded scrapped Blanik on this part of globe due to unability to prove that its resourse was not used to the end. If gone betond that- small cracks may occur and will destroy spar in mid flight with 1 pilot without vw..
 

TFF

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Because it’s an AD, it’s not just any ole fix. That’s where it gets hard. If it was a straight homebuilt, the engineering is up to the owner, at least in the US. This being production based, even if flying under an experimental certificate, would have to abide by the AD. If you have the engineering ability, you can submit alternate compliance, at least in the US you can. If your engineering is sound, they might accept it. If I bought a set of wings to put on something else, I would have to prove the AD had been complied with or changed where it’s a non issue. It’s not simple even if you got a good idea.
 

AeroER

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Cut the wings off. Add two jet engines. Put fuel in the aft cockpit.

Call it the Jetnik.

Or, Blajet if you cut the wings too short.

Paint it red, too.
 

Martti Mattila

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I comply all above and VW is already in a another aircraft and it newer had w.ballast tanks. So making entirely new wings from wood alá Heinkel 162 Salamander and ad jet or fan on top. I think that construction is safer than some Exp. planes but what can you do with authorities.
Czechoslovakia cave 600 Blaniks to Soviets among many other items to pay the cost from 1968 Spring in Prague aftermath. Freedom costs un freedom cost more.
 

raytol

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Gliding Federation of Australia had a fatigue expert calculate the fatigue life of the Blanik L-13. He estimated 12,000 hours! Two Blaniks here already had over 20,000 hours of safe flight. All L-13's over 12,000 hours were grounded and decimated the training fleet for many years. An engineer named Daffydd Llewellen designed a main spar strap and horizontal stabilizer modification that increased the fatigue life to 20,000 hours ( from memory).
I know of one that was set up with a detachable motor with the fuel tank in the rear sear, one pilot only though to stay under the Gross weight.
 

Martti Mattila

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No they are stronger Super Blanik-L23 wings. Designed for aerobatics. Interesting information from Australia. Thank You.
 

AeroER

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Gliding Federation of Australia had a fatigue expert calculate the fatigue life of the Blanik L-13. He estimated 12,000 hours! Two Blaniks here already had over 20,000 hours of safe flight. All L-13's over 12,000 hours were grounded and decimated the training fleet for many years. An engineer named Daffydd Llewellen designed a main spar strap and horizontal stabilizer modification that increased the fatigue life to 20,000 hours ( from memory).
I know of one that was set up with a detachable motor with the fuel tank in the rear sear, one pilot only though to stay under the Gross weight.

Calculating fatigue life is folly without at minimum two bits of information - a plausible load spectrum and a full scale long term test.

Without a test following that spectrum a scatter factor on life is required, something between 2 and 4 times the guaranteed life. Besides that the life should be divided into crack initiation and crack growth to critical length.

None of that is trivial, and it's the only way to get to numbers that should be believed. Besides the detailed analysis required.

Going into new (or modifying old) design, don't analyze and size bad details for fatigue life, design them out. That idea ranges from a naive idealistic goal to impractical in light aircraft due to weight, cost, and the designer's ignorance of just what features are likely to cause a crack.

Adding struts to a Blanik wing is possible, the resulting indeterminate assembly is no particular obstacle. The possible strut geometry, and then incorporating changes that don't aggravate the problem might be. I would take a hard look at feasibility of splicing in a new center section or installing L-23 wings. There is a possibility the gliders are simply junk fit to hang from the roof to remember the old days.
 
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bhooper360

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Good luck. uhm... I have a shapoko router you could borrow?
20170221_094100_1200x900.jpg

fuselage_Ydeformation.gif


After browsing this forum so long, the VW engine did not seem strange. however, I had no idea the blanik could carry water ballast.
 

JimCrawford

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From original post:

"But now after that mishap in Austria where two on board and full waterballast one broke appart during a aerobatic manouver"

I don't know of any glider which permits aerobatics with waterballast, the sloshing loads would be huge and indeterminate. I'm also not sure that the Blanik was equipped to carry water ballast.

Jim
 

Martti Mattila

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Somebody might find that accident report from that precise accident, some Blanik person might have it on hand. Previous owner told me that water ballast thing, it might be just dramatised talk. I don`t like to be told liar. School shootings are not permitted, still happening.
 

bhooper360

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So we agree, clearly, increasing your aircraft wing loading in order to achieve higher cruise performance can facilitate the positive outlet for a stressful environment, unhealthy habits, brain chemistry imbalance etc.
 

Victor Bravo

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Actually, yes it can. For those of you into scholarly research data, look up Mihaly Csikszentmihaly and his work on "Eustress".

Certain kinds of stressful activities, like flying competitively in sailplanes (which includes going after high cruise performance) greatly reduces the types of internal psychological/emotional turmoil and stress in people that (unchecked and unresolved) result in tragedies like we see on the news.

I'd love to say soaring is the only one of these activities, but other high-energy sports, free climbing, mountain biking, and several others will actually do this as well. For me it was flying and soaring competitively, for others maybe it's baseball or horseback. I was thankfully never at high risk for the kind of heartbreaking tragedy we're seeing today, but the flying and soaring at those ages gave me something that made my self-worth and self-respect far higher, putting me further away from whatever breaking point there might have been.
 

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