Wing Attach Corrosion

[spmg76013]

VariEze - bottom of center-section spar wing attach fitting: does this look like inter-granular corrosion to y'all? or surface schmutz? I have not yet sanded it other than hitting it with scotch-brite.

Any insight appreciated. the wing attach fitting and the upper spar fittings had none of this.

 

Sean Gillen

Arlington, Texas

[Marc Zeitlin]

3 hours ago, spmg76013 said:

VariEze - bottom of center-section spar wing attach fitting: does this look like inter-granular corrosion to y'all? or surface schmutz? I have not yet sanded it other than hitting it with scotch-brite. Any insight appreciated. the wing attach fitting and the upper spar fittings had none of this.

While it doesn't look like advanced intergranular corrosion, it definitely looks like some sort of corrosion (possibly early stage intergranular) and since there's rust on the steel screws, there's obviously been something going on here. It's not just "schmutz". If there's something like this that's visible on a lower surface AL part, I would be extremely suspect of all of the wing attach fitting parts on this aircraft, and would want to completely disassemble the fittings on both the wing and main spar to investigate.

Now, I will say that trying to evaluate material properties via pics on the web is a losing battle, so I could be completely off base here, but  I  wouldn't fly the plane if this information and pictures were all I had to go on.

[spmg76013]

Thank you Marc, good advice. Yes, all 8 of the steel screws had surface rust. At the very least I'm going to remove the 1ply BID/Foam comprising the end caps (holding the tubes straight), and remove all 10 screws (with heat gun or torch) and re-assess. And do same for the other side as well. If I see any hint of corrosion, I'll plan to completely remove all fittings. (something I will have to research thoroughly before digging in...)

[bmckinney10]

Sean,

I would suggest that before you take anything apart, find someone experienced close to you that may be able to take a look in person.  You may permanently damage good parts.  

I put my VariEze on a trailer and took it down to Covington, TN to the Jet Guys.  Robert Harris and his crew went through everything and we made  few modifications.  My VariEze had been sitting for 16 years.  

If I would have been closer to Marc Z., I would have taken it there.  I visited Marc in the summer of 2020 at his hangar in Tehachapi.  I learned A LOT in a short visit with him.  This was a few months prior to me taking it to Covington and getting it back in the air.

Good luck!

 

[spmg76013]

Thank you Brian, that is a great idea. It'd only be 6-7 hour drive from Arlington. I will call them tomorrow and see what they'd suggest. I've been looking at the layup schedule in Ch 8  for the CS spar to see how/where damage might occur during "extraction" of the plates. I think I'll start with heating up/ removing the bolts/screws and the outer plates first and have a look-see, then go from there.

Thanks again,

SPG1

[Kent Ashton]

Here is a big Advisory Circular on Intergranular corrosion   https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43-4a_.pdf

 

[Jon Matcho]

There's a ton of information in that AC. I just learned of "Filiform corrosion", which may be on the flat plates.

The aluminum around the screws appears corroded and needs special attention (is the white stuff around the screws oxidized aluminum?). Until they're removed you won't know the extent of the problem. The holes should be cleaned up as well regardless.

Where the parts appear to be very salvageable (as is the case from the pics IMHO), I would clean and sand down to 400 grit, apply a conversion coating, then reinstall.

I have no idea how hard that is to do for VariEze wing fittings.

[Marc Zeitlin]

33 minutes ago, Jon Matcho said:

Where the parts appear to be very salvageable (as is the case from the pics IMHO), I would clean and sand down to 400 grit, apply a conversion coating, then reinstall.

I have no idea how hard that is to do for VariEze wing fittings.

The problem, as has been discussed many times previously in this and other fora, is that the worst corrosion is always in places that cannot be seen except by a full disassembly of the wing attach fittings from the spars in both the wing and the main spar. I'm sure I've posted this picture before:

but as can easily be seen, one might think that things are reasonably OK when looking at the areas that contain the wing attach hardware (near the hand), but fairly obviously, this is not a safe plane to fly given the extreme corrosion and flaking of the part of the fitting buried in the composite.

So "cleaning up" visible portions of the fittings is putting lipstick on a pig.

If you do not take the whole fitting apart (probably 10 - 30 hours of work for all four areas - main spar and wings), you'll only be guessing at whether the inside of the fittings looks like this.

Hence the disclaimer I put on all VE condition inspection reports that I write:

"Both Wing Attach Fittings (ALL VARIEZES) - Due to the inherent design from RAF, it is not possible to check for internal corrosion of wing attach fittings. I recommend removing wings at alternate CI's and checking externally for corrosion, with the understanding that without ~40 - 100 hours of disassembly/reassembly, a full inspection of the fittings and full confidence in the condition of the fittings is not possible. Plan on wing removal for more extensive examination at the XXXX CI. Obey RAF's +2.5G / -1.5G limits"

[Jon Matcho]

Thanks Marc, disassembly was implied with my "...then reinstall" mention. 

If I pulled the corroded part in your pic just above, at that point I'd just use it as a template to make a brand new part. 

[spmg76013]

Another builder on the Facebook forum noticed a huge error on my build: I missed CP11 note to add 2 plies UNI around the end of the CS spar prior to installing the fuel tanks. I have gone thru all the CP's, years ago, and marked up my plans accordingly. Plain and simple, that was a miss on my part, I did not mark up that CP 11 change. Makes me wonder what ELSE I missed. [I'll be spending this winter going thru all CPs again.] I found my pictures from the day I put the CS spar and fuel tank on, and sure enough, I did not do that layup (55" UNI wrapped twice around). See attached picture. Looks like I'll be cutting into my fuel tanks and cowl flange to install that layup, when I remove my wing attach fittings.

Upon further inspection, I found other screws with rust on them on a lower-side wing fitting and found one small 'indentation' on a wing fitting. Picture attached.

Though this plane hasn't flown yet, I've decided to remove all fittings, both wing and CS spar, and inspect/replace/treat as needed. Too many unknowns/what-if's.

[Kent Ashton]

Quote

I've decided to remove all fittings, both wing and CS spar, and inspect/replace/treat as needed. Too many unknowns/what-if's.

I would guess you are causing yourself a lot more trouble than necessary.  The bit of rust on the screws is nothing.  The surface corrosion seemed to clean up well.  If the depression is on the upper side (in compression), it wouldn't bother me.  Even on the bottom, it doesn't look like much of a problem.  If the mount hole was cracked or notched where a crack could propagate from the bolt hole, it might be worth changing but I doubt that small depression is going to weaken the aluminum appreciably.  Personally I would find those mounts acceptable but I can't speak to the UNI issue.

[Jon Matcho]

On 10/17/2021 at 3:21 PM, spmg76013 said:

Looks like I'll be cutting into my fuel tanks and cowl flange to install that layup, when I remove my wing attach fittings.

I'd be looking for ways to avoid that, but I would weigh against the importance of those 2 plys of UNI which I have no idea what they're for.

Your head is clearly in the right area though, erring on the side of caution, but damn... cutting into your fuel tanks. It may not be that bad after all if the tanks are not yet sealed.

[Jon Matcho]

Quote

(from CP 11 page 7, see attached image)

Add these instructions to the end of Step 8 (on Page 8-7): Before mounting the fuel tanks, round the edge of the wing fitting plates and layup a three-inch strip of UND wrapped twice around the centersection spar as shown. This provides a glass surface for the cowling lip layup (see Section IIA), stiffens the spar end, and safeties the wing fitting screws.

@spmg76013 I now see why you're concerned. Crossing my mind was the following:

1. Remove the fittings, clean-up, and treat with alodine or another coating.
2. Re-install.
3. Layup a modified UNI schedule, still two 3" wide plies, but from the top of the tank, around the spar, to the bottom of the tank (tapering the top layup).

I'd want an opinion on that from someone else though, and regardless I just might do exactly what you're planning to do. You have easy access to get in that area NOW so why not put your mind at ease? Doesn't look like a crazy amount of work, but I feel your pain!

Then again, I doubt anyone who has treated these wing fittings has cut the tanks open after effectively negating the 55" x 3" UNI wrap!

 

[spmg76013]

Hi Again,

I'm still mulling over how many of the  attach fittings I want/need to disassemble for inspection from the wings and CS spar. At the very least I plan to remove the two WA-2-5 (lower plates on CS spar, starboard and port) which showed signs of water exposure, inspect 'non viewable' regions, and go from there.  I tried to begin that today, but my Radio Shack thermometer only went up to 148 deg F  then stopped, so I need to get another so I can get it up to but not over about 100 deg C).

Regarding the missing 2 plies UNI: my strakes are already 'done', but I'll plan to cut into the tank about 1" as shown in the attached picture, to allow the double wrap of the UNI around the whole spar and over the screw heads. (After the UNI wrap, I'll micro in a replacement "PART A" first, with a 45-deg bevel (so it won't "fall" into the tank) and then put a few plies of BID on top. (Similar for the bottom of the tank). I'll then do the same with a replacement "PART B" on the sidewall of the strake.

Thanks,

SPG1