Duralac/JC5A and Cromate confusion.

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Cliffordagius
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Duralac/JC5A and Cromate confusion.

Post by Cliffordagius » Tue Jun 18, 2019 6:27 pm

Hi All,

New to building and have the parts of my shiny soon to be Sling 4 empennage kit. I have spoken with an inspector as well as the UK importer and a couple of friends also building Sling aircraft at the same point as me. We have different inspectors and it turns out we are all getting different ideas and advice from the Importer and our respective inspectors on what is best practice. SO hoping to stir a debate and see if we can find one…

So, I will deburr and dimple the parts as needed that’s simple enough then I plan to spray with AEROWAVE 2001/6005 PRIMER (All parts!) and then it comes to assembly and this is where the 3 of us have different ideas on what is needed. YES, we are all first timers so please be gentle, it's just me that has decided/agreed to ask on here for the group to learn.

So, when it's all primed (If that's the correct stuff!) we come to assembly and where parts are in contact and where the pulled rivets go into the holes, we are split on the need for Duralac (Green or Yellow!) and JC5A. I have read lots and looked at other builders and everyone seems to do something different, so my question without trying to be leading on where I think I need to put the gloop is... What is best practise?

Yes I could rely on the thoughts of my inspector as he does have to sign it off but with different inspectors having different ideas it would be nice if there was some guidance from the LAA on what best practise is so that us wet behind the ears new builders have an idea on what to do. Also with differences of opinion on what to use and where comes the process on how to do it, like leave the Duralac clamped but not riveted overnight so it dry’s and doesn’t bulge the joint.

I just want my pride and joy to be as good as it can be, and as I plane to blog my build I want the process I use to be a good one as other new builders may copy what I do and if it’s wrong they will make the same mistakes.

Thanks and if there are other tips and tricks us 3 new builders need to learn then please let us know, Oh and yes I did the LAA Metal work course but that was before the kit arrived so the questions now are a little different to what they were before.

Cliff. :D
Clifford Agius
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mikehallam
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Re: Duralac/JC5A and Cromate confusion.

Post by mikehallam » Wed Jun 19, 2019 11:48 am

An interesting and early essential technical conundrum !

To add to the inspectors' views - doubtless of more or less equal validity. i.e. One kills the same cat but different nuances along the way - what did you find on the jollop manufacturers' sites/instructions ?
That will surel add info. ?

[My interest is limited to ongoing Ali/steel tube maintenance.]

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Chris Martyr
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Re: Duralac/JC5A and Cromate confusion.

Post by Chris Martyr » Wed Jun 19, 2019 3:50 pm

Hi Cliff,

Duralac and JC-5A both do pretty much the same thing . But their main differences are their consistencies . Duralac will dry like paint , whilst JC-5A will retain its grease-like consistency .

It depends really on the kind of assembly that it is you're using it for . If you apply it to the faying edges of something that you're just about to close off and never expect to look at again , then Duralac will be fine . But if it is for something that you may need to open up again , or things like bolted joints which may possibly need to be removed to facilitate maintenance or repairs then JC-5A would be more suitable .
The other really significant difference is the price . Duralac is only a bit expensive . Whilst JC-5A is bloody expensive ! [ beats having corrosion though ]
So realistically , it could be said that you could use Duralac for some areas and JC-5A for others , so neither Inspector is really wrong here .
The only thing I will say is ; make sure you wear nitrile gloves when working with these potions as they contain some pretty evil constituents . And if you get it on bare skin , wipe it off quickly with a clean cloth otherwise it'll start to sting and swell up .

It's excellent at prolonging the life of your aeroplane , but unfortunately can have the opposite effect on people . :D
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Cliffordagius
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Re: Duralac/JC5A and Cromate confusion.

Post by Cliffordagius » Wed Jun 19, 2019 6:57 pm

Thanks for the comments and yes I thought much the same JC5A for the joints I wish to open up at some point in the future and Duralac elsewhere.

Question is where do I really need to use it, and for an example here is a page for the first part of the empennage and in particular the Front Spar of the Horizontal Stab: Image

So do I need to put say Duralac (Won't ever be taking apart!) between the surfaces or is spraying with AEROWAVE Cromate ok in here?

On the subject of Duralac the Green V Yellow, now the Green is Cromate free and according to the datasheet has better adhesive qualities than the standard version which I guess is the Yellow.

Image

Also the datasheet says:
It is important that the joint should be closed while Duralac Green is still tacky – to ensure that it will flow sufficiently under pressure to close the gaps in the joint
So the inspectors idea to leave clamped overnight seems to go against the datasheet.

If all metal aircraft built under the LAA are supposed to use this stuff then why is there no guidance from LAA engineering or the inspectors team for the best practise?

Again thanks for helping as an ex-engineer (Car Industry!) the build looks very simple until you hit things like this so sorry for the idiot questions.
Clifford Agius
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coxargus
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Re: Duralac/JC5A and Cromate confusion.

Post by coxargus » Wed Jun 19, 2019 9:41 pm

I've heard it said that if JC5A is used where skins overlap there will be a problem with achieving a good paint finish as the 'goo' will creep out and the paint will lift at the skin joints. Apparently some paint shops may reject a job where it has been used - possibly worth thinking about.

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Chris Martyr
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Re: Duralac/JC5A and Cromate confusion.

Post by Chris Martyr » Thu Jun 20, 2019 4:15 pm

Hey Cliff .
Firstly , don't let anything I say override your Inspector . As long as you're happy with him/her , that is the main thing . Also , don't despair if another Inspector's words don't tally exactly with those of your own Inspector .
There is a whole plethora of products out there , made by many different manufacturers , all of which will do a similar job . Luckily , we as PtF operators are not bound to use any specific manufacturers product for our aeroplanes , unlike Boeing/Airbus/Bombardier,,,etc etc who are tied in to using products which have that specific Approval for their type aircraft.

So don't mislead yourself into thinking that your Inspector is 'waffling' , he is probably just reflecting on his experience from products in the past that he is happy with.

Remember also , that a lot of aerospace products are hideously expensive . It's because they come with a whole shed load of Release Notes and other Approval related paperwork . And that doesn't necessarily mean it'll make your aeroplane into a Eurofighter , as all you've done is pay through the nose for a product approved for something that flies at 1,000+mph , at 50,000ft at temps around -70c.

Look after your Inspector - he's your best friend . And don't be shy about asking his advice . That's why they're there . Engineers only SEEM grumpy . They're neither ; 'glass half-full' nor 'glass half-empty' type people . They just think the glass is twice the size it should be though... :D
Cliffordagius wrote: datasheet says:
It is important that the joint should be closed while Duralac Green is still tacky – to ensure that it will flow sufficiently under pressure to close the gaps in the joint
So the inspectors idea to leave clamped overnight seems to go against the datasheet.
Actually , I think what they are advocating is to apply a light pressure to both components , in order for the jointing compound to fill any voids . I think your Inspector is saying a similar thing here Cliff . Just using different words though .

Regarding your sketch . I would say that all of the components for that assembly would require a dusting of Primer on all sides prior to assembling . And then , apply jointing compound to any edges that are interfacing . [i.e. faying edges]

I'm sure your Inspector is familiar with the machinery of the RV community [ they are rather common :D ] and will be able to give you more handy tips than you can shake a stick at .
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Matt Dovey
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Re: Duralac/JC5A and Cromate confusion.

Post by Matt Dovey » Sun Jul 14, 2019 6:16 am

Didn't even know they still did Duralac!! Wasn't is banned. The last time I used Duralac was in 1988 when I was an apprentice working on the B29 at Duxford. Haven't used JC5A in years. Think since I stopped working on BAe 146's. All horrible stuff. If I remember correctly Duralac dry's out after time and breaks down. think that was the reason why it stopped having wide spread commercial use.
Just to put all this corrosion proofing in to perspective. I've worked on Pipers and Cessna's from the 1960's and 70's. None have had any sort of corrosion proofing or primer on their interior surfaces. Still a lot of them flying about!
Not to say that it isn't a good idea, it is. But a good primer may be all that is needed. I've been asked about which primers to on RV builds before and cant get to excited about. They all tend to do the same this. If your build manuals specifically refers you to a process then go with that.
I think the reason why the LAA do not have any guidance material is there are plenty of reference's in publications like CAAIP's and AC43. Which are quoted on the LAA web site as reference material. Also, even though good practice none of it is really compulsory.
I'm a glass half empty type of engineer.
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Mike Freeman
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Re: Duralac/JC5A and Cromate confusion.

Post by Mike Freeman » Wed Jul 17, 2019 8:48 am

For my RV i'm using an automotive primer which i'm really happy with in terms of ease of application and durability. I then use Duralac between joints and dip each rivet in it too. It may seem overkill to some but my aircraft will be based on the south coast so i'm not taking any chances.

If you go down the Duralac route I recommend buying the tubes rather than a tin. You won't use that much and each time you open a tin there will be a thick skin on it. The tubes can have a tendency to separate on its hard to mix it in the tube so what I do is to open the tube by unrolling the bottom end and pour it all into a small jar making sure you get all of it out. I can then mix it easily keeping it sealed between jobs and by adding a bit of thinners if it gets too thick can get quite a lot done before it becomes unusable.

There was a great deal at the LAA show a couple of years ago where some tubes hadleaked at LAS and they were selling all the good tubes that had been packed with them for £1 each as the outsides of the tubes were covered in the stuff.

I'm hoping a similar accident happens at some point this year before the end of August. :wink:
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BobD
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Re: Duralac/JC5A and Cromate confusion.

Post by BobD » Wed Jul 24, 2019 7:01 am

Mike Freeman wrote:For my RV i'm using an automotive primer which i'm really happy with in terms of ease of application and durability. :
Mike, I have sent you a PM.
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Birtyboy
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Re: Duralac/JC5A and Cromate confusion.

Post by Birtyboy » Sun Aug 11, 2019 11:00 pm

I’ve also been reading about these products and I’m unsure what’s best or whether either is really necessary?
I’m leaning towards none of the above and unless my inspector requests it I’ll give it a miss. I can understand it if no priming was to be used and it was being left bare but as I’m priming all parts individually I think this alone will be a sufficient barrier from corrosion.
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