Copper paint/coating on RAF radial engined bomber engine nacells

[Spitfires Forever]

Just had a question. I am finishing up my Tamiya Beaufighter and just painted the copper coating on the leading edge of the engine nacelles. I have noticed over the years that this copper effect was used widely on most of the radial engined bombers like the Stirling, Blenheim, Beaufighter etc. Simply, what is the reason for this? 

Cheers

 

 

 

[Werdna]

It's not copper, or copper effect - I think that's a bit of a myth.  It's just what happens to exhaust collector rings when they get hot, much the same as the exhaust stacks themselves.  The 'colour' of the collector ring will vary depending on whether the engine is running, stationary and/or whatever the power setting is.  

[Orso]

Isn't that part an exhaust collector that get heat stained, not a copper coat?  The heat discolour the metal differently.

[Ray_W]

A regular question and I am sure some will join with possibly links to prior discussion. The metal leading edge typically seen on the nacelle of some Bristol radial engines, like your Beaufighter, was a steel collector ring (manifold) for exhaust gases. They would start off as shiny steel and then change colours to blues and copper bronze colours typical of exhaust manifolds sitting in an airstream as dependent on age and operating conditions. There are some nice colour images of restored aircraft that show the effect well.  For example if you do a search on "restored bristol blenheim" and look at images. I have also read that some collector rings were painted with a black heat proof paint (nightfighters?) but have never done the research to prove this.

 

Ray

[spitfire]

A quick search turned this up.

Cheers

 

Dennis

[Ray_W]

@dogsbody posted a nice image of a manifold cross-section in this build here:

 

Ray

[stever219]

British radial engine collector rings were as copper coated as the rear fuselage skins of, for example, F-100s.  If you've ever done metalwork at school you get the same effect by hardening and (partcilarly) tempering metal.

[Pete in Lincs]

Yep, pretty much the same effect as you get on old motorcycle exhausts. 

And yes, on Aircraft like the Halifax and radial engined Lancaster (B II) they could be painted black.

[Graham Boak]

They could also be painted white on Coastal Command aircraft.  The last Bristol engine to have this collector ring was the early Centaurus, but when the captured Fw.190 showed the UK industry how to combine radial engines and low drag, the Centaurus was redesigned which made it too late for the war.

[alt-92]

Blenheims, but still: collector rings as used on Bristol engines.

Factory fresh: 

 

Reasonably new:

 

Heat stained:

 

On a Beaufort:

 

 

 

Bonus: As referred to earlier, heat staining on an F-100 tail.

 

 

[Spitfires Forever]

Looks like the phenomena has been well explained and documented. It didn't quite make sense as to why any special coating would be applied thusly my query. The model companies for the most part try to get the color call outs correct so most of us go with the information at hand. I figure that maybe a very light dry brushing of aluminium over the copper may best give the effect I am looking for or at least get me close. Time to experiment a bit. Thanks to all for the help.

Cheers

[Doolie]

Cue @dogsbody

[dogsbody]

Okay. The collectors started out as a not to shiny steel colour. Somewhere I have read of what type of steel alloy it was, but I can't find it now nor do I remember exactly what it was. It was perhaps a type of stainless steel, but it wasn't polished and shiny.

Once installed and the engine was running, the heat would gradually stain it to a brownish, coppery tone. A lot would depend on how long the collector was used and how the engine was run. Different engines may have made a difference in the colour. Would the collector on a 9 cylinder poppet-valve Bristol Mercury with less the 100 hours on it, look the same as the collector on 14 cylinder sleeve-valve Hercules engine with 300 hours on it, I don't know. 

Here are some colour photos of restored aircraft that are or were recently flying. Observe the collector colour.

 

 

 

 

 

 

Here's a WW2 era B&W photo of new collector rings:

 

 

This is an early WW2 photo showing a newly built Blenheim with just a small amount of engine running time:

 

 

 

 

Take from this what you will.

 

 

 

Chris

[Don149]

I use a mix of Humbrol 12 and 53 , buffed up when dry . If that is of any help .

                                                                                                                            Don .

[Chuck1945]

4 hours ago, Spitfires Forever said:

Looks like the phenomena has been well explained and documented. It didn't quite make sense as to why any special coating would be applied thusly my query. The model companies for the most part try to get the color call outs correct so most of us go with the information at hand. I figure that maybe a very light dry brushing of aluminium over the copper may best give the effect I am looking for or at least get me close. Time to experiment a bit. Thanks to all for the help.

Cheers

Skip the copper completely. Paint the ring steel or aluminum (burnt metal is even better if your favorite paints have that) first then use layers of clear orange, red, blue or even yellow to get the end result.

[JohnT]

9 hours ago, alt-92 said:

 

Bonus: As referred to earlier, heat staining on an F-100 tail.

 

 

The reason my 1/32 F-100 stays in the box. 

[Seawinder]

6 hours ago, Spitfires Forever said:

Looks like the phenomena has been well explained and documented. It didn't quite make sense as to why any special coating would be applied thusly my query. The model companies for the most part try to get the color call outs correct so most of us go with the information at hand. I figure that maybe a very light dry brushing of aluminium over the copper may best give the effect I am looking for or at least get me close. Time to experiment a bit. Thanks to all for the help.

Cheers

The best product I've found to replicate the effect is Alclad II Hot Metal Sepia. I start with a base coat of Alclad Stainless Steel. Then I apply the Hot Metal Sepia in light misted coats. The color builds up gradually, so I stop when I like the look. The darkness varied with the age of the plane, so there's definitely leeway. Here's a Blenheim I did last year. At least some photos show a narrow ring of unstained metal around the opening, so I masked that off to leave it stainless steel color:

 

[alt-92]

On 8/19/2022 at 4:39 PM, Spitfires Forever said:

The model companies for the most part try to get the color call outs correct so most of us go with the information at hand.

Mostly, but they also try and keep it simple. How many times have you seen instructions call out silver landing gear? 
Using copper in the painting guide could be seen as the 'closest thing' to reality while not complicating things for the average modeller - even if it is a bit of a cop(per)-out.

[Graham Boak]

It has to be a colour in their favourite paint range.  Much more important than getting it right.

[Spitfires Forever]

22 hours ago, Seawinder said:

The best product I've found to replicate the effect is Alclad II Hot Metal Sepia. I start with a base coat of Alclad Stainless Steel. Then I apply the Hot Metal Sepia in light misted coats. The color builds up gradually, so I stop when I like the look. The darkness varied with the age of the plane, so there's definitely leeway. Here's a Blenheim I did last year. At least some photos show a narrow ring of unstained metal around the opening, so I masked that off to leave it stainless steel color:

 

Nice job! I'm not really satisfied with the copper application so thanks for the tips.

Cheers

[alt-92]

Alternatively, AK Xtreme Metals - Steel, Gun Metal and (pale) Burnt Metal can bring you something similar.

[Phoenix673]

This was produced by using a metal base coat followed by several numerous coats of bronze, gold and silver (with touch of rust)

[Tail-Dragon]

This was done by painting the collector Tamiya titanium silver, masking the forward ring, and fogging on thinned Tamiya dark earth. Finally, fogging on thinned Tamiya dark iron to the rear.

For a more burnt appearance, thin blotches of blue and purple could have been added (next time)!

 

borrowing one of Dogsbody's photos ...

 

apologies, previously shown build ...

 

 

Edited September 3, 2022 by Tail-Dragon