Half painted Fw 190 wing undersides - the purpose?

[Franek Grabowski]

Originally Posted by Crumpp

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.

Well, this couple means some months, depending on groundcrew of course, and it was longer than an ordinary period of service in a combat unit.

Remember too, using the Oberflächenschutzliste 8 Os 155:
It is very doubtful bare metal would have just been left in a rough surface.

This was because of specifics of new camouflage coat, extremally thin. Puttied, painted and polished aircraft will always have better aerodynamics rather than the bare metal one.

[O.Menu]

But didn't the U.S. stop painting their planes because they got better range and better max speed than the previously painted ones?

Imho Germans simply lack of paint in the last months of the war (dont forget that you need petrol derivatives to thin the paint) but contrary to the U.S. they absolutely need to keep their camo not to be destroyed in the minutes with all those ennemy airplanes over their heads...

[John Beaman]

Hi Oliver:

IIRC, the US decision to drop painting was based on a significant manpower savings during production combined with the fact they no longer needed the camouflage when on the ground. Also, the P-51 did have painted wings. Most NM aircraft had clear protective coating, so there was some smoothness there. I do not recall the exact amount but the paint on a B-17 weighed in the 300 pound range, so that helped as well. Lastly, some units made the decision to paint their NM machines, notably the 55th, 56th, and 357th Fighter Groups. Some 9th AF units did, but strangely, in view of their nearness to German lines, most kept their NM finishes.

[Franek Grabowski]

Originally Posted by O.Menu

But didn't the U.S. stop painting their planes because they got better range and better max speed than the previously painted ones?

No, it was only to speed up production.

[Crumpp]

No, it was only to speed up production.

Actually according to sources at the USAF Museum at Wright Patterson it was due to performance. This is also backed up by the experience we have in using original finishes.

The paints used by the USAAF in WWII were all contracted from the same company out of California. Proper application took at least one coat of primer, 2-3 coats of paint, and clear coat. This adds almost 200 lbs to the weight of a P51D fighter. Using the original paints, in just 2 hours in the air, the paint begins to crack and chip. Faster if the aircraft is maneuvered hard. This adds drag and degrades performance. Both shedding weight and reducing drag improve an aircraft.

These T6 Texans are painted with WWII USAAF paints and the B17 had the late war USAAF finish:

http://theotherorlando.com/contents/...ingtigers.html

http://www.warbirdmuseum.com/

Now the RLM finishes are slightly different. The granulation is much smaller than what was produced in the US. In fact, the finishes seen on modern USAF fighters are a direct descendant of the RLM paints according to the USAF Museum at Wright Patterson, AFB Ohio.

This can be seen immediately on any actual RLM finish.

These drop tanks and many of our skins still have original RLM paints applied:

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

Here is a close up of an original leading edge:

http://www.white1foundation.org/parts/leadingedge2.jpg

Our pilots chair has a new coat of original RLM paint:

http://www.white1foundation.org/parts/pilotseat2.jpg

If you look closely you will see paint is not "chipped" but rather worn. This is typical of the RLM finishes we find. The paint is chalky and while it does wear the edges tend to feather or smooth as opposed to being as thick and sharp as the US paints. The RLM finishes cover in one coat as well. When mixed correctly there is no tendency to fisheye, orange peel, or run. One coat of primer, one coat of paint, and one of sealer is all that is normally required. This means the finish is lighter. About 60 lbs for a Bf-109 on average. Much less surface area and paint which weighs less than what goes onto a P51.

I tend to think the Germans did not go to bare metal completely because with their finish technology it was not the problem it was for the allies.

Not painting the leading edge would improve performance, save production materials, and time.

So this is correct for the RLM finishes:

This was because of specifics of new camouflage coat, extremally thin. Puttied, painted and polished aircraft will always have better aerodynamics rather than the bare metal one.

But I do not think it is applicable for all aircraft finishes for all combatants during WWII.

All the best,

Crumpp

[Graham Boak]

This is very interesting information: do your sources cover British paints? My understanding is that the 1940 switch to the S or smooth paints with finer pigmentation meant that the British paints were equivalent to the smooth German ones: it is a bit of a surprise to find that the US lagged behind in this matter. This perhaps casts new light on the habit of some US fighter groups to use British paints.

Certainly the difference between a rough and a smooth paint finish could give a significant performance penalty: however I'm very surprised to see you discount the production story. Other steps taken at the same time, such as not painting the interiors with anti-corrosion paint, were certainly made in the direction of cutting production time and costs.

[Franek Grabowski]

Well, British findings following investigation that started when first such US aircraft appeared stated that there were no performance gains, and although finish was much easier to maintain, there were several drawbacks. There was a pressure from US industry to drop the camouflage, but decision was not taken until late 1944. This is discussed in Paul Lucas book on RAF markings 1945-50.
Another point is that Mustangs had their wings puttied and painted even in NM finish - certainly not without reason. Puttying was quite common, at least at some point during WWII, eg. Spitfire was puttied, although it is not often visible.
Certainly there were differencies between US (Du Pont?) finishes, British ones and German ones but I think you overestimate the effect. The bits in original paint I have sen or I owe are not representative but judging by photos, if RAF aircraft were properly maintained, there were no dents but some on walkways and movable panel edges plus a lot of discoloration, this after months of flying.
Regards

[Crumpp]

Well, British findings following investigation that started when first such US aircraft appeared stated that there were no performance gains, and although finish was much easier to maintain, there were several drawbacks.

I don't know much about the British paints. It sounds very interesting. From what Graham relates and the findings of the RAF I would say they did not have the problems the USAAF experienced. They sound very similar to the RLM finishes and probably did not have the need to change their finishes.

Other steps taken at the same time, such as not painting the interiors with anti-corrosion paint, were certainly made in the direction of cutting production time and costs.

To me those kind of cutbacks make perfect sense. Most of these airframes were not lasting long enough to risk corrosion. However as someone stated earlier, when at their best the Luftwaffe designs were equal to the allied fighters in performance. A force made up largely of inexperienced poorly trained pilots was also flying them. The only hope the Jadgwaffe had was to have these new pilots gain enough experience to be effective. To do that they needed every once of performance they could muster. As the RAF found out in 1940 the airframe is replaceable, the pilot is not.

Not saying every airframe was a pampered formula one racer, I just think they did the most practical things they could to improve performance AND improve the logistics.

All the best,

Crumpp

[O.Menu]

From "The Mighty Eight Warpaint & Heraldy" by R.A.Freeman, p14:

"The main benefit derived from discontinuing camouflage painting was the saving in production cost and time. Comparison test had shown a gain of between 4 and 7 mph, with weight saving dependent on the aircraft size and model"..."between 70 and 80 lb on heavy bombers and 15-20 lb on fighters"..."in combat service, there was no appreciable difference in performance"..."some fighters pilots claimed that polished and beeswaxed camouflage finishes gave greater speed than bare metal finish."

[Franek Grabowski]

Well, judging by samples of US paint coming from P-39Q that crashed some 62 years ago, the finish still looks fine and is quite smooth. Naval aircraft continued their finishes, so perhaps there is still something to dig out in this regard?
The German problem started elsewhere, I think discussing camouflage leads to a wrong track.