Half painted Fw 190 wing undersides - the purpose?

[Kari Lumppio]

Hello!

I'm wondering about the Fw 190 wing undersides where the leading edge was painted with some colour (grey or light blue) when the rest was left unpainted. Period of time latter half of 1944 and on.

The books I have read explain the thing as camouflage against low flying strafers. Can't help myself of the nagging thought that Luftwaffe was at the time abandoning the underside camouflage alltogether. Why there suddenly arose a new need for underside camouflage at that same point of time? Plus one doesn't see the half-painted wing undersides on other LW a/c types (or any other Air Force of any period for that matter).

Related question: what colour is the Warnecke & Böhm filler 119 D? It is somehow related to the unpainted Fw 190 wing undersides.

It is this filler thing which makes me to propose another hypothesis. What if the half-painted area is actually area aerodynamically smoothed with filler? Germans were still in 1944 trying to make the most out of their planes. Why not copy the P-51 Mustang wing surface finish (= wing forward half smoothed with filler)? The smoothing of Fw 190 wing leading edge would make at least some aerodynamic sense as it did not have slats like Bf 109 (disruption at slat trailing edge makes the flow turbulent no matter what). IIRC Hoerner in his aerodynamics book (title escapes my mind now) complained about the uneven finish of German planes (Bf 109) and the resulting drag and drop in performance.

The proof would lie in finding if the Fw 190 wing upperside has the same paint/filler as the leading 50% of the underside of "unpainted" wings.

So there. Antitheses, other hypotheses and especially syntheses welcomed.


Regards to every researcher on this field,
Kari

[Don Neibling]

Hello Kari,
One reason may be that at that late stage of the war it was more important to save time and resources. It was probably thought that it was more importent that the aircraft be better camouflaged on the ground than in the air. Filling and rubbing back imperfections is a very time consuming job and would add greatly to construction time.
Kindest regards,
Don.

[George Hopp]

I would go with your hypothesis that the metal surfaces were becoming so poor that a coat of paint (perhaps with filler, perhaps not) was put over the leading edge of the wing to smooth the airflow over that part of the wing.

The Me 262 also got that treatment, ie. some paint on the leading edge of the wing, but with most of the underwing left unpainted.

Interestingly enough, in a report comparing wing structures on Allied and German a/c, the leading edge slats on the 109 were criticized, as were the larger rivets on German a/c. They needed more effort to insert, and caused surface buckling.

[Eric Larger]

Hello all of you

The purpose of half-painted undersurfaces is twice , save material and save time during the production process . This is clearly explained in our book dedicated to Fw 190Ds camouflages and markings .

On summer 1944 , Focke Wulf did test on 50 production machines (Fw 190A ) to test the efficency of this process at Sorau .

If the purpose is clear the reasons of this process are clear also .

First there was no need at that time to hide aircraft viewed from ground , as for several months the Luftwaffe turned to defensive actions , so underwing painting was not a priority .

Seconds the breakdown of the communications ( this was the major effect of strategic bombing , ie Allied reports in summer 1945 ) make supply in raw material more difficult , so anything that could be save had to be saved . For instance , you can ee several wodden part in the list of pieces of FW 190D-9.

Thirds the lifetime of a fighter at the end of the war was very short , please have a look to J.Y.Lorant & R.Goyat book dedicated to JG300(volume II) , and you will have several examples when pilots bailed out their machines and picked up very soon brand new ones. They were consumables .

I have several pictoral examples of rows of wings of Fw 190D-9 , waiting their assembly at Fiersler Kassel , half painted .

Now the question concerning the leading hedge . It was painted , two purposes , thirst protection of the metal , Seconds(just a guess for Fw 190) is try to limit the reflexion of the light when seen from the air . Do not forget that several Fw 190 at the end of the war had their landing gear covers oversrpayed with camouflage paint (they can be see from the air as they are not hidden with the wing completelly) .

Last point the colour applied on leading hedge , for us it is the colour avaliable , RLm 76 , Blue-Green , RLM 75 . Dont forget that RLM 75 was abandonned early on production batches (Nov 1944) and should be available in quantity .

All the best

Eric Larger

[Sergio Luis dos Santos]

Seconds(just a guess for Fw 190) is try to limit the reflexion of the light when seen from the air .

This purpose is described in Ken Merrick´s book volume one. There is mention that during testing of unpainted wings there was a strong reflexion on the parked aircraft so the area around leading edge and wheel covers were painted to reduce it.

[Kari Lumppio]

Hello all!

I do have the Merrick opus, but didn't have noticed his explanation for the half-painted undersides (found in the photo caption on p. 103 and in text on p. 104).

But quoting the very same Merrick book:

(of the first 50 Fw 190 with unpainted undersides, page 102)
"... only the primer filler has to be applied on the bare sheet metal ... the deletion of camouflage paint has to be particularily noted."

(the first communication letter dated 4.7.44 - "Fw 190 abolition of camouflage paint on the aircraft underside", page 102):
"... For the priming of bare sheet metal we have considered the putty 119 D from the Warnecke & Böhm company, which we ordered on 16.7.44 by telex..."

(the second document on page 103):
"...Therefore it is not necessary to obtain special paints for this large-scale test other than the already quoted putty 119 D from the Warnecke & Böhm company"


I think we can all agree that filler/putty/primer 119 D was indeed used on the mentioned Fw 190 with unpainted undersides. Question is where and why?

If the deletion of camouflage was done because of saving raw material and time it makes no sense to putty the airframe only for cosmetic reasons. My guess is that the filler was used to make the airframes smoother and more aerodynamic.

On single-engined planes with tractor propeller the whole fuselage is in turbulent flow. Would puttying the fuselage seams bring any noticeable effect? I do not know for sure, but my guess is the effect would be neglible.

Making the wing leading edge smoother (especially on the 1/3 - 1/2 chord on upperside) would instead make a noticeable difference if the starting point was far from perfect.

This is my reasoning for suggesting the half-painted wing could be result of using putty surfacer.

Many authors also write about Fw 190 having upperside camouflage of consisting of some light grey primer (sometimes identified as RLM 77) and green/grey paint. Like mr. Hopp already wrote also Me 262 used primer. This type had podded engines (= fuselage in smooth airflow) and the fuselage seams were puttied and taped over to make it more aerodynamic (on NASM "Yellow 7" the primer on fuselage sides has been identified as Munsell 10 Y 7/1 - I don't have any FS for it). Was this finish on Me 262 waste of time and material? Why would it be that on making Fw 190 perform better?


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. I really hope that I am not getting anyone angry and apologize if this is the case.


With Respect,
Kari

[Eric Larger]

Hello

first do not forget that these documents are attached to tests done in summer 1944.

Effectively if putty is used to smooth the under surface , it has also a function of protection . This putty was probably useed to seam the panel lines and to avoid anything (mud, oil, dirt...) to come into the space left between two aluminium panels. I think that first they tried to test if undersurfaces puttied can resist to airflow . This , in anyway, save material as no paint was applied over . And it saved a lot of time .

Now the reality and the use at a large production scale is different . Please look carefully to several pictures of Fw 190D-9 , this is the example I know the best , and look carefully at the state of the surfaces (fuselage , wings , tail) , you can notice that on any of these surfaces , no putty was applied to seam panel lines or to cover rivets . So the request in the test of using putty was abandonned .

At that time , as I said previously , there was no need to do it , due to the very short lifetime of an aircraft . The term of performances should not be taken in account , the purpose was to produce as fast as possible war machines .

Now concidering the used of light paint on upper surfaces . We think that the undersurfaces paint (RLm76, Green-blue, or RLM75 ) was also applied on uppersurfaces , on some pruction batches .This paint could also act as a primer on upper surfaces ( the most important surface to hide the aircraft from the air ) and then a full or partial camouflage scheme (RLM82 , 81 , 83 or rlm75 ) was applied producing examples well identified like RLM 76/83(W.nr 211939) , or RLM 75/83 (210051), or RLM82/83 (210102).

The some paint can be applied at unit level to cover repairs , the best example is W.Nr 211934 ( initial painting scheme W2 undersurfaces (metal + rlm76), RLM83/82 uppersurfaces .One wing has repainted undersurfaces (starboard wing ) with rlm76 (balkenkreuz area) and uppersurfaces (same wing) with RLM75 see pages 160 to 164.

This is just guess as no document so far (known to me ) has been found to confirm this .

On the other hand RLm 76 or RLm75 can be used on the undersurfaces to mask some minor repairs see page 40 (photo in the middle) of our book it is clearly visible .

We do not think that RLm77 was used but more probably a new variant of RLM76 called 'Weissblau" , containing less cobalt blue pigments .

hope that helps

Eric Larger

[Kari Lumppio]

Hello again!

This shall be my concluding post on this topic if nothing new surfaces.

The first thing I don't understand is how much time or raw material could be really saved by painting only half of the underside wing? Ailerons and flaps were painted as was the upperside. The downtime because of paint drying (hardening) is the same and painting the whole wing would have taken some 15 minutes more (my guess based on (little) experience).

Second thing I still don't understand is why no other type had this type of camouflage? For example ground angle of Ju 88 is more or less the same as Fw 190 judged from pictures.

Third thing I don't understand is that camouflage (glare prevention) would take preference over aircraft performance. No colour can prevent shadow etc. revealing the form of aircraft shape. Tarpaulins, camo nets, tree branches etc. would do that. I don't see surface colour as the only option of camouflaging an aircraft.



Smoothing the wing surface can reduce the profile drag coefficient to half*. Even if the wing profile drag is only a portion of total drag in the high-speed end (where induced drag decreases) this can make a real difference. I think any novice LW pilot would find use for extra 20-30 km/h (pure guess, someone with real numbers?) or so for the top-speed of their mounts.

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. This was also the original trigger for thought together with the 119 D filler mentioned in the Fw 190 documents.

Surfacer - if used - would also be beneficial over the rivet lines on the leading edge (upperside). This is where the difference in smoothness would be really felt. The photos I have looked are not of such quality to see if the rivet heads are covered or not. The ones showing undersides clearly are usually crashed wrecks and panel lines on them are not 100% counter proof against surfacer use.

Surfacer (filler) does not have to be some thick stuff spread with spatula. There are very fast drying nitroputties which can (and could) be shot with sprayguns. I've been involved in couple of repainting projects of glassfiber wings (a glider and a motorplane (twice)) and do know what the sanding entails. I also know that with right tools the sanding can be done quickly and efficiently especially as on the metal wing there are no fiber reinforcements ("sand-throughs") to be worried about.



Thanks for the responses and would love to see more of them.

Regards to all,
Kari



* Ref: NACA report 667 "Determination fo the profile drag of an airplane in flight at high Reynolds numers" http://naca.larc.nasa.gov/reports/1939/naca-report-667/
Quote from the abstract: "... the surface irregularities on the original wing increased the profile-drag coefficient 50 percent above that of the smooth wing."

[Eric Larger]

Hello again again,

My point of view is strickly based on Focke Wulf Fw 190D and Ta 152 production , I do not know enough about other machines to pretend to be able to write something concistent about their painting scheme and to wonder about the reasons to apply such or such paints .

The camouflage study cannot be separated from the production of the machine itself , it is a part of the industrial process .

The ratio, between production time , amount of raw material, and lifetime of a machine has to be taken in account too .

German do not build machines to be used for years(or they will be dangerous with so much wooden parts on such basic airfields) , but for at least months , and more often for just hours .

The production situation

Some sentences extracted from an American report done in May 1945 and issued in September 1945 ,about Focke Wulf Bremen ...

" ...By 1945 , conditions became chaotic as a result of plant bombing, non-delivery of components parts and the collapse of the german transportation system. Production fell 66 percent , a denial of 795 aircraft, during the first three months and production virtually ceased by March , when only 30 aircraft were delivered . "

" However , the choice of final assembly and flight hangars as target was not as damaging to production as would have been the jig manufacturing plant at Gassen" .

So the terms are clearly established , the problem the german plant at Bremen had to cope with , are the components for the aircrafts , raw materials and their supply , the term of performance is far far behind .

Production of Fw 190D-9

Now back to Fw 190 . Focke Wulf , since 1943, try to simplify as far as possible the production of this machine , try to save as many raw materials as possible , and try to split the production into many small plants not easy to detect and destroy .

This of course produced a problem , the gathering of all components .

On the other way simplification , enables the production of components to be maintained at a certain level with less skilled workers .(to simplify)

Concerning FW 190D , this can be observed in the Ersartzteilliste istself , where optional parts are mentionned like :

Fuselage access door , 2 main variants one in metal one in wood , the same for radio access hatch, or flaps ....

We can divide the main airframe in 4 major components , all of them composed of several sub-components (I choose the one having an influence on camouflage )

1) engine : including engine cowling not produced by focke wulf and delivered painted
2 ) fuselage : windscreen and blown canoy often delivered perpainted
3) tail unit at least 5 sub components indentified , top of the fin (wood or metal) , rudder, extension part , tail
itself and horizontal stabilizators
4) wings at least 9 sub components , 2 wing tips , 2 flaps (wood or metal) , 2 landing gear doors (wood or
metal) , the wing themselves, and 2 ailerons .

All sub-components were probably delivered at the sub-assembles assembly location ( for exemple the 9 sub components for the wings) , still painted .

Focke Wulf issued also painting directives for Ta 152 A (abandonned) , that may have been used for Fw 190D-9 , where it is clearly mentionned that the undersurfaces should not be painted.

Camouflage is the visible result of all these simplifications and changes in the production process and of the supply problems

first effect

- the general painting process was revised , no putty , no primer , less paint

- on several wrecks recovered the camouflage paint was applied simply on bare alluminium (some produced at Fall 1944)
- No putty can be seen on FW 190D .
- Avoid to paint the surfaces that do not need to be painted ,undersurfaces and interiors (except cockpit)



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 .

Second effect ,

the use of the advantage of having pre_painted components , for instance the engine cowling was often left in his delivery paint , we call it factory painting scheme (RLM83 or RLM71 and Rlm76) , or often the ailerons can be seen in one solid colour .

Third effect

The application of the "official" painting scheme produced by the manufacturer . Unpainted under surfaces , the scheme was revised ( for the reasons exposed in a previous post) , application of more defensive paints as RLM81 /RLM82 and RLM83 . The colour were probalbly not availabe at the same time explaining why some intermedaite painting scheme existed .

Other manufacturers and aircrafts

Why this scheme was not applied on other aircrafts is good question , but Me 262 and Bf 109 G-10 ot bf 109K-4 are known to have unpainted under surfaces . perhaps someone could explain it to us .


So it is clearly visible that the question of the performances and top speed was not to the first purpose , don't forget also that Fw 190D-9 was an intermediate solution , before producing in mass Ta 152. Would it be also important when in March- April 1945 the fighters were often used for ground attack ?

Camouflage do not take the advantage on performances , this took his place , in the industrial process of building a war machine , concidering the war and industrial situation.

German were not producing Formula 1 , they were producing consumable war machines in mass . This is not really the same production and purposes and also not he same workers required.

I may wish that other luftwaffe enthusiasts could discuss about other late war machines , it will be very interesting to read their conclusions or observations .

All the best

Eric Larger

[Dick Powers]

Eric,
I am presently working my way through your 190 book. It's very impressive. Thorough, well produced and a beautiful end product.

Throughout, your assumptions are given, some with sources, and conclusions stated along with qualifications. This book reinforces your statement that the camouflage and markings cannot be separated from the historical context.

One of the best books I've seen in a while. And I'm not even a modeler.