WEATHERING BARE METAL AIRCRAFT SURFACES

[David Rapasi]

The bare aluminum skin of a WWII aircraft would oxidize after a period of time in a dry climate.

This aluminum oxide creates a protective, almost clear coating, and the surface will keep it’s apparent shine.

In a humid environment the oxidization will add a whitish appearance to the surface.

The model was painted with a custom made aluminum lacquer for the bare metal finish.

The weathering was done by applying random light coats of Dullcote tinted with a few drops of flat white.

The darker stains in the aluminum surface are a very thin wash of dark gray sprayed where needed.

After the Dullcote is completely dry, the entire surface is polished with a damp cotton ball and Pepsodent Toothpaste.

The model aircraft is a 1/48 Academy P 47D-30 from the 362nd Fighter Group / 378th Fighter Squadron, AAF Station Straubing, Germany, May 1945.

Dave

[Juergen Klueser]

Looks very realistic!

Regards Juergen

[timc]

Alclad.... that's what it's intended to do to protect the aluminum alloy, usually 2024T4, T6 or some other heat treat. For those that don't already know, Alclad aluminum is an aluminum alloy such as I just mentioned coated with very thin layer (0.002" or thereabouts) of pure aluminum. This is usually done to sheet aluminum that's used for aircraft skins. Structural shapes made of aluminum may also be alclad if they're stamped out of sheet but if they're cast, they're probably made from a block of pure aluminum and machined to final shape then heat treated (makes machining much easier). When the Alclad sheet oxidizes, the pure aluminum corrodes (oxidizes) and forms the protective barrier for the alloy. This would be an entirely normal appearance of clad surfaces after repeated exposure to the elements. The shiny aluminum skins we see on the B-29's for example are because they've not yet succumbed (sp?) to the corrosion, or their entire surfaces were regularly polished and waxed. Take a piece of aluminum foil, throw it outside for a month or so and then have a look at it. Compare it to the appearance of a brand new section just off the roll. You'll see a big difference between the two.

Now don't go thinking that every dull surface aluminum finish is automatically alclad because in a few instances you'd be mistaken. There are also anodized skins that will appear grey and have a distinctly different appearance than the alclad aluminum. For example, the portion of the skins that run across the upper wings of the B-29 between the forward and aft spars and over the fuselage are anodized skins. I forgotten where I read that but if I find it, I'll post the reference. Oh, and while I'm talking of the B-29,s the front of each engine cowl is stainless steel. Why? Because the exhaust collector is right behind the leading edge of the cowl. Same is true of the cowl panels below the exhaust on the P-51 mustangs and behind the exhausts of the P-47's.

Almost nothing in an aircraft is made of pure aluminum (O) and not heat treated. Pure aluminum is way too soft to have any use for any structure whatsoever. However when we heat treat it, it becomes much stronger and can used for all kinds of different things.

There are all kinds of different procedures for protecting and strengthening aluminum and other metals. I've only touched on one method I'm familiar with and even so, not completely.

See what you learn working for an aerospace manufacturer....

[Liberator24]

It is like listening to the great PLATO!!

Thank you for the insight, sir!!!

-Jim

[Prop Duster]

It is like listening to the great PLATO!!

Thank you for the insight, sir!!!

-Jim

Being from Greece, I thought he worked for Airbus

**************************************

timc

Well stated explanation of a complex procedure. It's always good for us to learn about the "reason behind" things, so that our ability's to model are able to improve.

Now you can understand why, the model lacquer is called Alclad II

[Jennings]

Alclad.... that's what it's intended to do to protect the aluminum alloy, usually 2024T4, T6 or some other heat treat. For those that don't already know, Alclad aluminum is an aluminum alloy such as I just mentioned coated with very thin layer (0.002" or thereabouts) of pure aluminum. This is usually done to sheet aluminum that's used for aircraft skins. Structural shapes made of aluminum may also be alclad if they're stamped out of sheet but if they're cast, they're probably made from a block of pure aluminum and machined to final shape then heat treated (makes machining much easier). When the Alclad sheet oxidizes, the pure aluminum corrodes (oxidizes) and forms the protective barrier for the alloy. This would be an entirely normal appearance of clad surfaces after repeated exposure to the elements. The shiny aluminum skins we see on the B-29's for example are because they've not yet succumbed (sp?) to the corrosion, or their entire surfaces were regularly polished and waxed. Take a piece of aluminum foil, throw it outside for a month or so and then have a look at it. Compare it to the appearance of a brand new section just off the roll. You'll see a big difference between the two.

Now don't go thinking that every dull surface aluminum finish is automatically alclad because in a few instances you'd be mistaken. There are also anodized skins that will appear grey and have a distinctly different appearance than the alclad aluminum. For example, the portion of the skins that run across the upper wings of the B-29 between the forward and aft spars and over the fuselage are anodized skins. I forgotten where I read that but if I find it, I'll post the reference. Oh, and while I'm talking of the B-29,s the front of each engine cowl is stainless steel. Why? Because the exhaust collector is right behind the leading edge of the cowl. Same is true of the cowl panels below the exhaust on the P-51 mustangs and behind the exhausts of the P-47's.

Almost nothing in an aircraft is made of pure aluminum (O) and not heat treated. Pure aluminum is way too soft to have any use for any structure whatsoever. However when we heat treat it, it becomes much stronger and can used for all kinds of different things.

There are all kinds of different procedures for protecting and strengthening aluminum and other metals. I've only touched on one method I'm familiar with and even so, not completely.

See what you learn working for an aerospace manufacturer....

Excellent summary!! Terms like "Alclad" and "anodized" get tossed around by modelers with no clue what their meanings are.