Warbird Information Exchange

Hello all,

Was hoping to get some insight on restoring the tubular for a T-6, well in my case the NA-64. I have been told there are a couple of different ways to do this. Here are the options I have come up with but have questions on, if anyone has any better ideas please advise.

First off is getting the frame cleaned by media blasting. What would be the better media to use, Aluminum Oxide or Soda?

Once I have the frame cleaned what is the best way to protect it while it is being inspected, do I just coat it in a light coat of LPS 3 and then wash it down with mineral spirits to remove the oil before the two-part epoxy paint?

What’s the best way of inspecting the tubular? Is using a 2oz tap hammer and tap testing good enough or should it be sent out for NDT?

Once the frame has been inspected, repaired and primed how do you go about putting hot linseed oil in the frame and how much do you put in? Do you go through the set screw holes for the U-bolt clamps?

Thank You

Patrick

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"Preserving history one rivet at a time"

Warbirds of Glory Museum
North American B-25J 44-30733
North American B-25J 44-28898

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Legend Of Aces Aviation
North American NA-64 3456
North American NA-64 3434
North American NA-64 3448

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I would definitely NDT it!

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Magister Aviation
It's all in my book

I would take it to a commercial blasting booth and let them do it, it's not that expensive and they can do it quick. They will want to use Aluminum Oxide but that's pretty aggressive, I would have them use glass bead or walnut shell at a medium/low air setting. Soda has the opposite problem IMHO, it could take forever using soda.
When you are done with the tap test, examine the welds with a magnifying glass and pay particular attention to the rear aft tubes, which would collect any water as it drained in the airplane. The tap test should be fine, NDT would be a large rather unneccessary expense I think. Your time will be better spent with a straight edge making sure your tubing is straight with no bends. I would then try and have it dipped in a heated trichelorethane tank, many larger auto body parts places have them. That will completely remove the oil. Then paint immediately. Or, if you degrease yourself use Wax/grease remover from the auto paint store or MEK. Use chemical proof gloves and have good ventilation using these chemicals. Don't be stingy with the solvent either, dripping wet will help lift and carry away the oil. Linseed oil the tubes after painting. Any holes in the tube can be used for linseed oil, you may even have to drill some. The idea is to have enough oil inside to slosh it around, you will have to tilt and roll the frame to get good coverage. ACF-50 is actually better than linseed oil but is more expensive. ACF-50 will creep inside the tube and provide better protection as it is a water displacer.
You've got my email if I can be of any help. -Robert

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All I did was press this red button here...

Hi Patrick,

My experience with Wirraway frames, I would go as follows:

Get rid of any loose paint and dirt on the frame and take it to an NDT shop for xrays and at least have the engine mount attachments, wing attach and rear fuselage attach points. Obviously, the low points in the frame will be a good place to look for internal rust. The Wirraway frames I have seen xrayed (including my own) have come out pretty well, even though the frames have been sitting in paddocks minus wings, etc. Do any repairs before blasting.
Before you blast it with any sort of media, I would recommend getting a box of sacrificial pk type screws and block every hole you can find in the frame. Being a North American design,(I'm sure Patrick already knows this, but for all the other boys and girls out there) all the tube clamps have a sheet metal (pk) type screw through them to prevent the clamps from rotating on the tubes. If you can, enlist a buddy to go over the frame to find any holes missed. You do not want any blast media entering the tubes - you won't be able to get it all out. I also wouldn't use soda on these steel frames, as I understand you should wash it off with water - not a good idea in a steel frame that has a bunch of little holes drilled in it! Once blasted and inspected again for cracks, etc, I would then paint the frame. Once the paint is dry and you are happy with it, then fill it up with oil. Believe me, if you oil it before painting, you will never be able to stop the oil leaking out of the screw holes -screws or no screws fitted! On the Wirraways and I am sure the Yale and T-6 should be the same, there should be a screw going onto the rear flat face of the upper rear fuselage attachment. This is the best place to inject the oil. I will try to take a photo tomorrow and post here. Wirraways and T-6's originally used Linseed oil and it was generally heated up before injecting. This has two functions. First, it makes it more runny and secondly, you can feel the tubes warm up as the oil trickles through. This is a good way of ensuring that all the tubes get treated.
Have fun! It's a great looking project - I wish mine was that complete - and it should come up looking a treat!

Thank you guys for all the great information, that helped out a lot.

Patrick

_________________
"Preserving history one rivet at a time"

Warbirds of Glory Museum
North American B-25J 44-30733
North American B-25J 44-28898

http://www.Sandbarmitchell.org
http://www.facebook.com/Sandbarmitchell

Legend Of Aces Aviation
North American NA-64 3456
North American NA-64 3434
North American NA-64 3448

http://www.Legendofaces.com
http://www.facebook.com/Legendofacesaviation

What we generally do is after the fuselage frame has been completely stripped apart is visually inspect it for any obvious damage, repair any obvious damage per the SRM and AC43-13, and then plug all the holes with PK screws and have it professionally bead blasted with glass bead. Have a word with the guy who's actually going to be doing the blasting though and impress upon him that the structure is very thin walled steel (you don't want him going at it like it was a truck frame or something similar) and that it is essentially irreplaceable. Even when that's not actually true I still always tell them that. After it's completely cleaned (especially in the crotches of the tubing clusters which you may have to finish up yourself) have it professionally NDT'd. You want to ultrasound the tubing to check the wall thickness (have the SRM handy so you can see what the tubing is supposed to be) and check in all the traditionally bad spots like the lower longerons at the rear end, etc. We get a die penetrant inspection done of all the welds as well. Since your airplane was never restored before it probably never flew around much with any loose clamps "jangling" around on the tubing and chafing them but look for chafe marks just the same and if they're bad they have to be fixed. If she gets a clean bill of health after the NDT inspection then remove and discard all the pk screws, wipe it down completely with MEK (be careful because it's bad stuff) and good, lint free type rags, and then prime and paint it with a two part epoxy paint. DO NOT POWDER COAT IT! If you powder coat it the size of the tubing increases and the clamps won't fit anymore. You can also develop a crack in the structure underneath the powdercoat that won't necessarily crack the finish. Prime it with the recommended primer for the paint and then finish it in a two-part epoxy paint. An epoxy paint will be impervious to most chemicals and fluids it'll come in contact with like hydraulic fluid, fabric cement, etc) After you're done with that and are happy with the results install new PK screws and rubber o rings in all the holes and re oil the tubing. Hot linseed oil worked well in 1940 but remember that all the tubing was new then. I like ACF-50 as it not only protects the steel but chemically interrupts corrosion that's already in progress, and there's bound to be some somewhere. Fill the fuselage frame until it's full (have spare PK screws and o rings on hand and ready to install because you'll need them) and then roll the fuselage around a few times. Drain the fluid and put it away for next time, re install the plugs, wipe it down with some cleaner (I use "the blue solvent" myself but be very, very careful - especially of static electricity) and enjoy. I would guess your frame would probably need about three or four gallons or so to fill it completely. A Stearman fuselage takes about seven and a half.

Good luck, and enjoy listening to everyone tell you that "It'll never fly" because it's always so much fun to make them eat their words later!

Dan

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Defending Stearmans on WIX since Jeff started badmouthing them back in 2005.

One thing to remember about linseed oil is that once it's out of the can and on rags/ floors ect. it has an affinity for auto-ignition.....any soaked rags should but put in a CLEAN metal trash can outside, lid left loose and out of the sun, and allowed to dry completely before bagging up just prior to the trash guys picking up your cans. Spills should be cleaned up and rags disposed of as above fairly quickly. Cans of linseed oil need to stay tightly capped as much as possible too and should be stored in a fire cabinet if they have been opened, as well as partial cans should be too.

3M makes several attachments that screw onto a standard sanding mandrel that look kind of like old timey vegetable scrubbers with hundreds of rubberlike 'fingers'. They come in different colors (white, green, yellow, etc) and do different things to remove finishes in tough to get to spots, I believe the yellow ones will remove 2 part epoxy aircraft finishes without disturbing the clad surface of the metal. Check with a good sized auto paint store and ask about them.

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Don't make me go get my flying monkeys-