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13m Wings Help! 15 Jun 2015 10:48 #900

Hello All!

The aircraft is currently passing the inspection of obtaining the certificate of airworthiness and I hope this week are ready if I find some information.

Unfortunately , I have no plane construction of the junction of the wings to the fuselage at 13m, I have only 12m plans model .

The question is, civil aviation inspector needs to know if the metal material used in the binding of 13m wings is the same thickness and quality in the 12m wing model.

Somebody can send to me with unswer with details about?, my email is This email address is being protected from spambots. You need JavaScript enabled to view it., also if you have some picture about this page of 13m plans, or the metalic material list...

Waiting for your news and help, Thank you very much.

My Best Regards.

Cristobal Aranda

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13m Wings Help! 18 Jun 2015 10:40 #902

Hi Cristobal

Apologies for the delay in replying - I've been away for the last week and am just catching up now.

The length of the wings shouldn't make any difference to the metal wing junction fittings - longer wings just give you different flight characteristics (efficiency, glide ratio, wing-loading, sink rate, etc). The load on the fittings should (I think) remain the same... though I'm open to correction here!

I see from the set of plans (page 3 / Sheet 2 of the pdf file) on this website that the original wing junction fittings were made out of 0.125" thick 4130 steel with a load bearing strength of 125,000 psi. 4130N steel actually has a bearing strength of 140,000psi - so you need to know the precise material your fittings are fabricated from.


If you know the all-up weight of the glider (glider + pilot + everything else you take with you) then you can work out the required strength and dimensions of the metal fittings yourself and compare your figures to the actual fittings you have. You can see how I calculated the requirements for my wing fittings here (using Jim Marske's method) here:

carbon-dragon.ihpa.ie/index.php/cd-builders/phil-lardner-s-cd#modifications - 3-Part Wing - Analysis.

If that's beyond you, or it takes you out of your comfort zone then I can do the calculations for you... if I find a spare evening... but that could be some time!

If you're doing the calculations yourself then you need to take your all-up weight and multiply it by 1.5 to give you the standard safety factor at 1g. You then need to multiply that number by 5 to get your maximum design load (or x8 to get your ultimate load limit - where the fittings are expected to fail.) Use the all-up weight x 1.5 x 5 number in your calculations.

Strictly speaking you do not need to include the weight of the wings themselves as they are considered to lift their own weight and do not react it through the wing junction fittings.

You'll find a full description of how to design and calculate wing junction fittings in Jim Marske's excellent Composite Design Manual, available here: www.marskeaircraft.com/

Hope this helps,


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Last edit: by Phil Lardner. Reason: Wing loading tests need to be done to +5g (not +4g as earlier stated!)

13m Wings Help! 19 Jun 2015 08:45 #903

Hello Phil . Thank you very much for the information.

This weekend will work at the junction of the wings and take some photographs . The problem is that the plates originally used by the old owner to connect the glider's wings , are made ​​of stainless steel and need to be replaced by steel 4130. The second problem is abouth the design of the form of the plates corresponds to model between wingspan 12m and 13,1m , having doubts about the shape and thickness they should have. Now, any doubts disappears, Thank´s a lot.

In the old aircraft documentation , the owner requested the modification of building long wings , and was approved of by the civil aviation inspection of the time. I detected this error on the material used , and communicated to the inspector of the aircraft, and is the last detail that requires the aircraft to begin test flights.

Okay Phil . Thank you very much again and hope to have very good news soon

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13m Wings Help! 19 Jun 2015 08:48 #904

Forget say that in Spain is compulsory test negative charge. It will be held next weekend and I'll make photographs and videos of the whole process

My Best Regards.

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Last edit: by Cristobal Aranda.

13m Wings Help! 27 Jun 2015 15:26 #905

Hello All!!! Very good News... Mr. Jerry Gross contact me and I´m very happy because he have another woodstock in final construction task (paint wings and fuselage), and I receibed by email details about the design and specific material to use in the 13m bonding structure Wings and at this moment, just I am waiting to receive a copy of the plans about the area in question to proceed with the manufacture of metal parts and adapting to my model .

I am grateful to Phil and Jerry , without their invaluable help, the process of legalization of my aircraft would have extended in time almost indefinitely , due to the limited information available on internet about the Woodstock with 13m wings.

Thank you so much , and continue updating the other thread with photographs and videos about the job and test flights (when I have the civil aviation test flights autorization).

Greetings All

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Last edit: by Cristobal Aranda.

13m Wings Help! 27 Jun 2015 16:21 #906

That's great news Cristobal!

I hope the certification process goes smoothly... and I hope you can persuade Jerry to share some photos of his Woodstock construction project - I'd be really interested to see them!

All the best,


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