Half painted Fw 190 wing undersides - the purpose?

[CharlesMetz]

Originally Posted by Kari Lumppio

--snip--
Where my hypothesis in on weak ground is that on the underside there would be no need to smooth the surface further than some 10% from leading edge. The only other wing I know which also has this half-chord treatment is the P-51 Mustang.
--snip--

Kari,

One potentially relevant factor here is that the Mustang's wing was unusual in having a laminar-flow airfoil, the benefits of which were substantially reduced by any suface imperfections.

[Graham Boak]

Charles: the use of the term "laminar flow" for the Mustang wing has always been somewhat misleading. It did not create true laminarity - which would indeed be spoiled by the slightest imperfection. The term was applied to a family of aerofoils where the maximum thickness was moved from about 25% chord to about 40% chord. Even North American's high production standards and this section did not give laminarity beyond the 10% of chord quoted by Kari.

Eric: I think Kari's point is not why undersides and other parts were not painted. It is why the leading edges were. The only suggestion that makes sense to me is the aerodynamic one. I agree that the pressing need for aircraft- any aircraft - would eventually overrule even the most important aerodynamic principles, and that top speed was less important to a fighter-bomber. However, this makes the production line just one more enemy of the much-harried fighter pilot. The German aircraft at their best were equivalent to their Allied equivalents - a second-rate version was a death sentence. As we see in the casualty lists.

[Eric Larger]

Yes I undertand very well what do you mean , but again I am not sure that reaching the best performance was the highest priority.

Several machines , as you can see when reading for example J.Y Lorant 's book on JG300 , were produced but were not efficient war machines , tabs not tuned , undercarriages misfunctionning , engines overheating ....

The report written by Barhorn , when commanding JG6 , issued on 23 march 1945 , is very instructive on these points (from memory, problems with wooden landing gear covers , engines ...) .

So to conclude , of course this production and finition processes could have influence on the machine performances . And of course the fact of painting the leading hedge could have also an influence on airflow , but according to me the aerodynamic aspect is far from being the sole one to take in account .

Nice to read your point of view in anyway.

Eric Larger

[pstrany]

Keep in mind that a large percentage of the laborers that built these aircraft were slave labor. They were not inspired by patriotic ferver, but rather by the idea that if an aircraft did not roll out the door on a specific schedule, they could well be pulled out of the line and shot. Add to this that a lot of the laborers were foreign nationals who did shoddy work on purpose as a form of revolt against their taskmasters, and the poor quality of late-war German aircraft is hardly surprising.It is interesting that in the Fw 190, the front half of the underside of the wing was painted. in the Me 262, the entire underwing surface was left unpainted - which makes more sense. Certainly paint would have been at a premium in the closing days of the war, remembering that petroleum products go into paint manufacture. The quality of the paint used on the Me 262 was terrible. If you look at pictures of Wnr 500200, Black "X" of KG 51 after the war, where excess fuel had spilled down the fuselage it almost completely washed away all traces of paint (Classic Pub Me 262 Part 4, Pg 793 is clearest.) This was a not unusal pattern to see on Me 262 aircraft.The only suggestion I would have would either be a perceived aerodynamic advantage (helping to smooth the leading edge of the wing) or to make the absence of paint on undersurfaces less visible. To be added here is the fact that not just undersurfaces of the wings received this treatment, but also the undersurfaces of the fuselage in many cases as well. Going back to Black "X", the undersurfaces of the nose were painted (it was manufactured as a separate part) but the rest of the fuselage was not (per Green/Evans in Eagle Publications' "Stormbird Colors".)Paul

[cproyston]

I keep looking at the points raised in this discussion and can't help returning to the thought presented by the proposed OS-liste scheme (issued in Sept 1944) for the Bv 155 which states:

"...The fuselage sides, side of the vertical tail and leading edge of the wing and horizontal stabilizer should be painted in colour 76. Hereafter, except for the wing and horizontal stabilizer’s leading edge, the aircraft should be then in a cloudy overspray with colour tones 81 and 82. Also, we look ahead to simplify the paint schemes which we should know shortly and will publish. Afterwards, the above mentioned aircraft which will be used for day service, camouflage on the undersurfaces should be deleted..."

(Quoted from David E. Browns Excellent article, http://www.clubhyper.com/reference/luftcamdb_3.htm, published on Hyperscale.com)

The bold highlights are mine to emphasise my point - perhaps a similar order was issued for the Fw 190D?

Just my thoughts on the matter,

Chris

[Micke D]

I have found two photos, possibly three, that show that the upper wing was painted the same way, front part RLM76 or 75, and covered with a thin layer of camouflage paint on top of the wing.

It's shown in a photo, taken by Jerry Crandall? in the 60's, of the wing from Fw 190D-9, W.Nr. 601088, Black <1 + ~, Stab IV. /JG 51, in Eagle Editions about Fw 190D-13 Yellow 10. Most of the camouflage paint seems to have weathered away by then, leaving the RLM 76 that covers the front of the wing.

It's also shown on Fw 190D-9, W.Nr. 211939, Black 4 + -, 6. /JG 6, in "Focke-Wulf Fw 190D camouflage & markings Part 1" from JaPo. It's the photo that shows the repair/repaint of the left wingtip. The camouflage paint seems very thin and the RLM76 shows trough.

The third one is possibly Fw 190D-9, W.Nr. 400xxx, Yellow 11 + -, II. /JG 2 in Carl Hildebrandt's booklet Broken Eagles 1. This plane seems to have a broad dark coloured band under the camouflge paint, on top of the wing spar. But this could of course be paint, or putty, to cover the rivets on a repaired wing spar.

At the moment I can't say on which sides these photos are, as I'm at work.

/Micke D

[Crumpp]

For me this is all about getting an explanation which makes sense. I can't help myself thinking that the current explanations for the half-painted wing undersides (=special camouflage on wing undersides which are supposed to be uncamouflaged) are a bit exotic.

Interesting discussion!

I say I have to agree with the aerodynamic reasons for the leaving the leading edge bare.

As you said you need a certain skill to apply correctly and quickly fast putty on a wing, but on the other hand you do not need to have any skill to handle a spray-gun .

Painting an aircraft is essentially a bad thing aerodynamically. It adds significant weight and additional surface imperfections that can rob performance.

In our restoration of White 1, we are using actual RLM paints. It takes just as much skill to paint an aircraft as it does to paint a car. The RLM paints are very sensitive to reducer ratios. Little too much or too little and the paint does not apply. It takes skill to prepare the aircraft, operate the equipment, and apply the paint. Granted these factories were not trying to turn our show quality finishes. Nevertheless it takes training to apply the paint.

"Surfacing" or "filled and polished" on the other hand can range from simple laborer work to being just as complicated as applying the paint. Depending on the method used of course.

So I would think it is rather a mute issue on the skilled labor.

By not painting these surfaces several things appear to be accomplished:

1. Aerodynamics is improved
2. Production times and cost is reduced

You guys should come check out the Museum and the Restoration.

http://www.white1foundation.org/parts/shop1.jpg

http://www.white1foundation.org/index.htm

All the best,

Crumpp

[Franek Grabowski]

Actually, when properly done, painting improves aerodynamics, as all the imperfections are covered by a layer of paint. Painted and polished aircraft will have a better aerodynamics than a bare metal one.

[Crumpp]

Actually, when properly done, painting improves aerodynamics, as all the imperfections are covered by a layer of paint. Painted and polished aircraft will have a better aerodynamics than a bare metal one.

Sure I will buy that for the first couple of hours of flight.

When the paint cracks, scratches or chips from aeroelasticity though you will lose performance.

Remember too, using the Oberflächenschutzliste 8 Os 155:

In case of needed puttying, (aircraft putty 7270.99) it should be applied on bare metal beyond the border lines of the paint scheme and the bare metal should be polished in the usual way but no camouflage on top of the putty.

It is very doubtful bare metal would have just been left in a rough surface.

[Graham Boak]

If I may drop back to an earlier point that wasn't addressed.

It is important to add filler to gaps along the fuselage. Every gap and step will add drag, regardless of whether the flow is laminar or turbulent. The thicker the boundary layer, the smaller the penalty, but penalty remains.