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Missouri Armada P-51D Mustang: documents and partial scratch from the Tamiya 1/48 kit


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This is all great stuff, it'll be most useful for my Revell P-51D-5.

 

I suppose one thing here is that the wing, even unfilled, is pretty smooth, so the transition isn't all that obvious (especially as the full chord seems to get the aluminium paint.

 

Matt

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Yeah, she's my favorite warbird flying today. No expense was spared to ensure that it was accurate, down to the last detail, to the way it was in early April 1945, around the time it received its nose art and began flying combat missions. It is an early P-51D-20-NA, restored as the early P-51D-20-NA it is/was, with all of the factory details exact to the early P-51D-20-NA production block, with post-factory mods and Technical Orders followed up to April 1945 (such as the metal elevators and ammo bay door modifications). It is a 402nd FS, 370th FG, 9th AF combat-vet, which flew ground-support missions, hence the two 500-lbs bombs it carries. It never had the APS-13 tail warning radar installed, and photos of the aircraft from April 1945 show it still with the N-9 reflector gun sight (it has a working N-9 gun sight, but typically left off when flying).

Here are some details I've written up in the past to describe the "Sierra Sue II" restoration:

 

- The skins on "Sierra Sue II", which are a combination of original and new, represent the unpolished finish that the skins on these aircraft had when new in 1944. Where new skins were used in the restoration, the period-correct dull and shiny mil-clad finishes were reproduced and left unpolished. On original 1944 skins, the surfaces were buffed/polished only to the level of closely matching the unpolished new skins. As some of the curved skins, fairings and fillets were formed into shape on presses and rollers, the more times they had to pass through those machines the more marred/dull the surfaces would become - something which can clearly be seen in original wartime photos, on these same panels, and you can see in the restoration.

- The companies Alcoa and Reynolds provided the aluminum in original WWII production, and their factory-applied watermarks, containing the company name and aluminum sheet specifications, were always printed, in rows, on at least one side. This practice is still done today, but the modern watermarks aren't the same as the period/1940's era watermarks. The modern watermarks were stripped from all of the new skins and the period-correct watermarks were applied to the new skins and reapplied to the reused original skins. Per original, most of the skins were cut so that the watermarks would always be on the interior-facing surface, but that didn't always hold true all the time. For instance, when "Sierra Sue II" was disassembled, it was noted for each skin/panel if the Alcoa or Reynolds company watermarks were present on the interior-facing surfaces. If they weren't, AirCorps Aviation could then conclude that the watermarks had been on the exterior-facing surface and recreated as such in the restoration. On "Sierra Sue II", you can see various panels/skins all across the airframe where the period-correct Alcoa or Reynolds watermarks ended up on the exterior surfaces, as per original to the airframe and what factory photos show.

- During original NAA factory production, wherever spot-welding took place, an acid gel was brushed onto the surfaces of the skins in these areas, which would etch and purify the surface, making for a good bond when spot-welded. These areas of acid wash can be seen in many (most all) factory photos. Skins weren't required to be coated with primer, since the Alclad finish was considered a good enough barrier against corrosion. As a result, in the restoration, as per original, when you look into the gear wells and other confines of the aircraft, the skins remain bare on the inside too, often showing the period-correct manufacturer's watermarks, attached to frames and extrusions that had to be primered.

- On "Sierra Sue II", the primers and paints used are as exact to what was used originally in 1944 as can be achieved today, and applied in the same manner. Most all restorations today use modern paints that are colored to look like various shades of yellow and green zinc chromate, but as such, never perfectly match the original 1940's primer finishes, being too smooth, lacking the original period-correct texture and finish and lacking in authentic imperfections. In the restoration of "Sierra Sue II", original zinc chromate, accurate down to the original 1940's chemical composition, was used. Raw zinc chromate has a natural yellow color, and during WWII, NAA tinted raw zinc chromate with a bit of black paint to create a green/olive drab colored zinc chromate - AirCorps Aviation did the same to match the same green tint/shade. On all surfaces requiring primer, a coat of raw (yellow) zinc chromate was applied, and on surfaces requiring two coats of primer, NAA used their green zinc chromate for the second coat, so as to provide clear indication that a second coat had been applied and fully covering the first coating. AirCorps also found that there was a third color developed/used by NAA on some parts, which mixed raw zinc chromate with a bit of black paint and a bit of blue paint, and was reproduced on those same parts by AirCorps. During original production, many parts, such as ribs and brackets, were dipped in primer, rather than sprayed, and those parts in the restoration process were treated the same way - the result being that all of these parts have the same streaks/runs in the finishes as per original. Where parts where sprayed with primer, no real care was taken for a smooth uniform finish, and the coatings were often uneven - to be fully authentic, this was duplicated in the restoration. The primer and paint applications were also done during the restoration at the specific points in time during the assembly process as was performed at the factory - this results in factory-authentic paint overspray in areas and ensures that some parts received primer/paint and other parts didn't, per original (such as the nut plates for the wing-fuselage fillets being installed after the cockpit sections were sprayed interior green, meaning that those items remained bare - or the fact that, as per original, since so much of the fuselage structure is assembled before the cockpit section is finally painted interior green, there are areas around ribs and behind brackets where the interior green primer would not reach, creating a ghosted image/impression where the bare metal of a skin and/or the yellow zinc chromate of a rib/frame can still show through). On the interior, the instrument and switch panels were painted in semi-gloss black lacquer, as per original, and most of the exterior markings were applied using alkyd enamel paint, as per original. All of these original primers and paints aren't as durable as modern paints, and will wear with chips and scuff marks just as easily as they did in the 40's. AirCorps also found that at times there were parts finished in green zinc chromate (the two-coat color) that didn't have yellow zinc chromate below and wouldn't have needed two coats. What would happen, therefore, is if a batch of yellow zinc chromate ran out during original production, to prevent the slowing of the production pace, they would just simply use the green zinc chromate, already there and available, until a new batch of yellow zinc chromate was ready. During disassembly of "Sierra Sue II", prior to restoration, each part was noted for which primer coating(s) it had, and so that part, following cleaning and inspection (or replacement) was then refinished with the same primer(s) before it went back into the aircraft.

- On Mustang production, the stainless steel rub plates on the landing gear clamshell doors always were coated in (yellow) zinc chromate. This was done because you had to have a protective layer between the steel of the rub plates and the stamped aluminum gear doors so as to prevent dissimilar metal corrosion. Sometimes, such as on really late production, only the side of the steel in contact with the aluminum gear door was coated, but for most Mustang production both sides of the rub plates were treated with zinc chromate (as can be seen in many original wartime photos). "Sierra Sue II" and AirCorps Aviation's most recent restoration, "Lope's Hope 3rd", are the only Mustangs restored to-date with this authentic detail of having yellow zinc chromate rub plates showing on the clamshell doors. Furthermore, you can also see authentic traces of zinc chromate (overspread) around the edges of the stainless exhaust shroud panels, where they are attached to the aluminum cowl panels, and where the stainless panels at the root of the flaps are attached to the aluminum structure.

- The rivets used in the "Sierra Sue II" restoration come from specially-ordered new batches made to original wartime spec/appearance. All current manufactured rivets, following the MS standard, are required to have the manufacturer's logo/mark stamped on the rivet head, but during WWII, the AN rivets had no stamps. During original wartime production, NAA sourced the rivets from a number of different suppliers, and the rivets came in three different variations of anodized colors - clear (silver in appearance), iridite (yellow in appearance), as well as blue (which is thought to have originated from a Navy spec). AirCorps Aviation contracted with the National Rivet and Manufacturing company to produce whole new production runs of period-correct rivets, without the manufacturer's stamp, and coated in the three different original anodized colors. At the NAA factory, these different batches of rivets were poured into bins and the colors would end up mixing together - as a factory worker pulled a rivet from the bin, it didn't matter what color it was, as long as the bins remained replenished, and the result was a random patchwork of silver and yellow, and sometimes even leftover Navy blue rivets, across the airframes (as can be seen in the restoration).

- During original wartime production, NAA had a process where they would smooth out the first 33-40% of the wing, from the leading edge back, and then paint the main wing assembly silver. Acme Red Vellutine Glazing putty was used to cover skin butt joints and Acme Gray Surfacer No.53N5 was used to cover any irregularities, in this region of the wing. The entire area was then sanded smooth before a coating of silver lacquer was applied. This process was accurately duplicated in the restoration (though a modern, more durable putty was substituted for the Acme Red Vellutine putty).

- All of the hardware/fittings on the restored "Sierra Sue II" are the correct AC and AN types to what was used during WWII - in fact every piece of hardware used is precisely as it was when the aircraft left the factory during WWII, including the spline nuts, electrical terminals, Dzus fasteners, Hi-shears, electrical clips, switches and breakers, etc.

- On "Sierra Sue II", the bolts, which total nearly 2,500 per aircraft, of 178 different sizes, are each individually authentic to what was used during original production, rather than just being modern MS bolts off the shelf. As many of the bolts on the aircraft are original to the airframe as was possible to keep/reuse, but all of the newly-made bolts on the aircraft were re-manufactured to the original wartime-manufacturer's specs and with the original 1940's manufacturer logos/letters on each bolt head. Across the aircraft, you will find bolts with the embossed markings of the original 1944 suppliers, including Air Supply, Air Associates, Cooper, American Screw, Rockford, and a few others. On "SSII", each bolt, where/if replaced, matches the same original period manufacturer-marked bolt as was removed during the restoration. Furthermore, the bolts in the restoration are stained in dyes of a variety of authentic colors (red, orange and blue) - during original production, the dye meant that the bolts had been magnetically inspected.

- The wiring on these aircraft, originally, was insulated with black rubber and wound with cotton string, which is no longer available today and wouldn't be able to be allowed by the FAA in a flying aircraft. In the restoration of "Sierra Sue II", the wiring was specially made with black silicon insulation and then wrapped in cotton string, per original. The logos and writing that were stamped on the original wires was researched, down to the specific font and various font sizes, and accurately reproduced on the new wiring using a period Kingsley wire stamping machine.

- All of the markings were applied in the various manners they would have been during WWII, whether it be masked and sprayed on or painted on with a brush, freehand. The vast majority of the "decalcomania" (to describe all of the text/labels applied all over the aircraft) on the exterior of Mustangs was applied originally using rubber stamps. AirCorps Aviation had these stamps reproduced so that all of these markings applied using rubber stamps originally were applied on the restoration just the same way (and with the authentic imperfections you get using stamps). Other markings were applied using stencils or water transfers - all of these processes were used in the restoration wherever/whenever the same was done originally. Of course in all of these manners of form, the original fonts were reproduced.

- If you look throughout "Sierra Sue II", you'll find reproduced factory worker grease pencil marks, period-correct inspection stamps and stickers, etc., all reproduced where they had been found and documented when the aircraft was disassembled prior to restoration. The cockpit/interior is as stock and fully equipped as any Mustang restoration to-date, down to having the flare pistol, drop message bag, factory-supplied checklists and diagrams, and more, all stowed where you'd find the items when climbing in the aircraft in '44. The modern avionics are extremely minimal and are installed using an easily removable bracket and in a manner that does not remove any authentic details from the cockpit. The gauges were all restored using fluorescent paint to glow under UV light as per original. "Sierra Sue II" is complete with the fuselage fuel tank, working wartime SCR-522 radio, full armor plating throughout, reproduction armament that is wired to the trigger with working solenoids, fully loaded with ammunition that is correctly marked for the types and patterns of bullets used originally by the the 370th FG, functioning bomb/drop tank release system, working N-9 gun sight, working gun camera (loaded with film), and more...
 

Edited by John Terrell
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Dear chaps,

first of all, thank you very much for these new infos, videos (that I yet had not time to all view) and great links, especially of the « Sierra Sue II ».

Unfortunately , my English is not good enough to be sure of some conclusions, that is why I will ask you to confirm what I seem to have understood, but before, an important remark must be done imho: we have focused on the rivets question, indisputably important, but the docs we have show that not only rivets were filled but also most of the panels separations (except the removable ones). From this point of view, my actual wings are not right. I wonder if many modelers have ever represented this and I worry a bit about the aesthetic conséquences of representing such a reality on a 1/48 scale model, but if we want to be as close as possible from truth, it seems to me obvious that this major observation must be taken in account.

John (Terrell), could you, on a simple drawing, represent what had to be the filled areas on the Missouri up and bottom wings please? it would be a great contribution to the thread and a great help for me.

Antonio, you are probably right about the rivets that were not holes, but how to represent them on a 1/48 scale model?

Notice that, on the JMV model, they don't look as holes but just as little spots, very natural. This because of the technique used, that I showed above (in particular because of the rivets sanding). The reality at 1:1 is something, the 1/48 scale another, and I don't worry too much about the rivets look.

Well, anyway, I think we do our best here to offer to ourselves and to the reader accurate infos about this aircraft.

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Thanks ( again ) to Antonio for the splendid video which I will watch fully on my large computer screen this afternoon, and to John ( Terrell ) for the fascinating insight into the restoration of" Sierra Sue II ". Also thanks again to you Olivier for starting this thread which has brought us so much more information on the Mustang.

 

Cheers

 

John

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First of all, I apologize for the error I made above speaking of treatment about the Alclad.

Now I looked at the O'Leary book again and noticed this pic on page 145:

 

PkjgKa.jpg

 

You will notice that these are clearly P-51D wings, and however, the wingtips rivets were not filled. So, it remains impossible for me today to know if, on the Missouri, the wingtips were puttied or not. In the lack of certainty, I will leave my wingtips rivets, unless a new element comes on the thread.

 

P.S: John (Terrell), would you say there were 3 different areas following the treatment applied on the wings, or only 2? the diagram 154, partially wrong as you mentioned above, suggests 3 areas. Do you agree? I think somewhere in the O'Leary book, these 3 areas are mentioned but I don't remember where...

A new accurate diagram, replacing the 154, would be necessary. I would not mind doing it, but too many points remain unclear for me now...

 

 

 

 

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18 minutes ago, Olivier de St Raph said:

First of all, I apologize for the error I made above speaking of treatment about the Alclad.

Now I looked at the O'Leary book again and noticed this pic on page 145:

 

You will notice that these are clearly P-51D wings, and however, the wingtips rivets were not filled.

Hi Olivier,

 

It's a mistake, on the picture you show those are P-51B wings, shorter ammo doors, cut out for the landing light on the left leading edge, and the light on the top (and the bottom) of the wing tip, instead of being at he tip.

 

Laurent

Edited by silberpferd
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I am currently working on a diagram to illustrate the most common D-model wing filler application and will post soon when completed. This diagram I am working on follows the research of a good number of actual P-51D factory production run photos, not earlier examples and not publicity/staged photos - as well as following the guidelines written by North American Aviation.

 

Before I post the diagram I am working on - the process at the factory, both backed-up by NAA documentation and factory photos, was that the first 40% or so of the wing was sprayed with Grey Surfacer first. According to NAA, six coats of this Grey Surfacer was typically used to smooth over/cover up all irregularities, such as sunken or raised rivets, skin butt joints (panel lines), Phillips head screws, etc. The Grey Surfacer shows up in factory photos as the very dark colored application (appearing like paint). Once this was finished, if any skin butt joints (panel lines) had not been completely covered over with the application of Surfacer, then Red Glazing Putty was applied over all of these skin butt joints (panel lines) in this region, and then sanded smooth (this appearing as the brighter/lighter areas focused on primarily just the panel lines over the top of the dark grey surfacer).

Edited by John Terrell
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10 minutes ago, silberpferd said:

It's a mistake, those are P-51B wings, shorter ammo doors, cut out for the landing light on the left leading edge, and the light on the top (and the bottom) of the wing tip, instead of being at he tip.

Thank you Laurent. I understand that Michael O'Leary made a mistake and that the ammo doors were shorter on a P-51B wing, but the rest is not very clear for me. Could you explain this story of light (that Antonio ever mentioned above if I am right) and if possible with a simple drawing (sorry for my ignorance)?

If you prefer, you can do that on PM, as you prefer...

Cheers

8 minutes ago, John Terrell said:

I am currently working on a diagram to illustrate the most common D-model wing filler application and will post soon when completed. This diagram I am working on follows the research of a good number of actual P-51D factory production run photos

Great John, thank you so much! your diagram will replace advantageously the doc 154... I will wait it to go on with my wings...

Cheers

 

Olivier

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Antonio, thanks a lot for this link to the "Sierra Sue II" restoration video, it is really amazing, considering that J.T said that it is one of the most accurate restoration. Here are several screen captures I made from it. The only regret is that it is a 20-NA if I remember well, and I am not sure we can refer on every aspect for the Missouri.  

LbMQre.jpg

w9r1Nh.jpg

z2Ess9.jpg

wGTq9Q.jpg

sfCG4G.jpg

4b1rbV.jpg

dEVNQy.jpghIZqJR.jpg

5GaZ1D.jpg

yYrGYp.jpg26VXox.jpg

 

P.S: I renonce to number the docs, it was not a good idea, it is not a problem to refer to the post in which they are. And it is unfair to decide that such a doc is more important. And sometimes (quite frequently...), a doc considered as important is finally not so (as the diagram 154, fe). More, this will earn me a bit of this precious time I miss so much!

On the other hand, I will go on numbering the build progress...

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I said above that I would fill the separations between panels (post#654), after having seen JT pics of the "Sierra Sue II" (his post#647). I think now this would be an excessive attitude. Looking again at the many docs (like the one below), if it is necessary to get very thin separation lines too thick (as for the fuselage, see above the work I did), we can however see them:

LT1bRs.png

 

My problem now is that imho, this should be done not only on the filled areas, but on all the wings, as for the fuselage, that was not filled at all. And if it is quite simple to do it on areas where I have removed the rivets (filled areas), doing the same everywhere else would mean for me to have to redo the riveting job...

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Hi Olivier,

that last picture is a post war  (ww2) picture, look at the national insignia , it has the red bar in the middle,  looks like from  the korean war era Mustangs,  where the filler/ putty finish and polishing  maintennace was not  important and used anymore, it can be seen in many pictures of this time, Mustangs were outdated at this timeand  used as secondary ground attack missions so that extra speed was not that vital then, jets took over, sorry Olivier but I guess this picture should not count for Missouri or ww2 standard as reference

cheers

Edited by antonio argudo
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Based on all of the P-51D factory production photos I have seen, these couple of images I've put together illustrate the general way in which the two different coats of surfacer/filler were applied. The Gray Surfacer was sprayed on first (usually six coats, according to North American Aviation) to cover all rivets, skin butt joints, screws and any other irregularities within the first 40% of the chord of the wing. After this was completed, any skin butt joints (panel lines) and other irregularities (such as Phillips head screws or too much depressions in areas of rivets)  which weren't completely covered over with the Surfacer were covered with Red Glazing Putty and sanded smooth.

 

26749828888_b1500fa649_h.jpg

 

26749829318_2bf4195122_h.jpg

 

39724004805_bc9afd3b7e_o.jpg

 

39724004765_354c0dfbfc_o.jpg

 

25748945097_4b01b565da_o.jpg

 

39724004845_53e5c236ea_o.jpg

 

Note in the very last picture, which I believe is from the Dallas factory, the whole wing appears to be coated in the Acme Gray Surfacer.

This original unrestored wing, from a P-51D-5-NT, shows an ample amount of the Red Glazing Putty (which had a pink hue) and Gray Surfacer peaking through the silver paint within this first 40% region of the wing. Note that a good amount of the Red Glazing Putty can be seen in areas outside of the panel lines as well, indicating that it was used to cover areas of deformation in the skins around rivets as well (used over the top of the Surfacer wherever it was deemed required for a smooth finish).

 

26747858738_78d639c15f_o.jpg

 

25748945167_737fab4832_o.jpg

 

39724004995_e9a65cc078_o.jpg

 

25748945377_b66ed2e4db_o.jpg

 

Edited by John Terrell
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With Missouri Armada, you're dealing with a wing which would have had the filler, the factory-applied silver paint, and the RAF paint applied over all of that by the 357th FG.

 

Here are a couple photos of a P-51D in Theatre/combat service. Note that some of the finish has been worn down, revealing just a bit of the panel lines and screws. Overall, the finish looks pretty good though. Photos via Martin Kyburz.

 

40619929751_5aa3872a61_o.jpg

 

39724659345_4223620c31_o.jpg

 

Edited by John Terrell
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very nice John!!

maybe just to add a small thing to make it more complete, you didnt mention about the Yellow Zinc Chromate coat on your diagram, do you know how many layers were used, was it a thick application?

factory_wings_putty_Buscar_con_Google_2.

qw3.jpg

cheers

 

Edited by antonio argudo
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1 hour ago, John Terrell said:

This original unrestored wing, from a P-51D-10-NA through early P-51D-20-NA production/generation 8th or 9th AF Mustang, shows an ample amount of the Red Glazing Putty (which had a pink hue) and Gray Surfacer peaking through the silver paint within this first 40% region of the wing. Note that a good amount of the Red Glazing Putty can be seen in areas outside of the panel lines as well, indicating that it was used to cover areas of deformation in the skins around rivets as well (used over the top of the Surfacer wherever it was deemed required for a smooth finish). This wing is displayed in Germany and is likely a leftover of the mass scrappngs that took place in Europe/Germany after the end of the war - the wing was torched off, rather than damaged/ripped off in crash.

This wing comes from P-51D-5-NT 44-11326, MIA on 05 December 1944, recovered from a lake in 1969.

 

https://www.mhmbw.de/das-besondere-exponat/fluegel-einer-abgeschossenen-p-51-mustang

 

Laurent

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3 hours ago, Olivier de St Raph said:

Thank you Laurent. I understand that Michael O'Leary made a mistake and that the ammo doors were shorter on a P-51B wing, but the rest is not very clear for me. Could you explain this story of light (that Antonio ever mentioned above if I am right) and if possible with a simple drawing (sorry for my ignorance)?

I meant those

 

zoSTPjz.jpg

 

there are 2 lights on each wing tip of a P-51B, one on top, the other on the bottom, while there is only one for the P-51D, on the side of the wing tip.

 

Laurent

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John, this post#663 is a must! (the 664 is very interesting too...)

Your diagram is great. It not only shows the different treatments applied and the areas concerned, it also shows precisely (much more than the previous docs I had used to do  them) the rivets lines. I will take advantage of working on the panels limits (decreasing them a lot up to getting fine lines) to redo (at least partially)  the riveting job. A patient work for a much more accurate design of the whole aircraft...

Thank you so much for your great contribution to the thread.

Thanks too Laurent and Antonio, we have a Champions League team here, and I will do my best to deserve my presence in such a team! ;)

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Hi Olivier,

 

Earlier in this thread, you were looking for some discussion, advice and photos about how to depict the wheel wells, so here is a bit of a start...

 

In order to wrap one's mind around why the wheel wells and other interior sections of the P-51D looked the way they did, it helps to understand the production requirements and methods that led to the random patchwork/mix of finishes you see throughout the airframe:

 

1. On all early to mid production P-51D's, the aluminum skins didn't typically require any coatings of zinc chromate on the interior-facing surfaces, and mostly were always left bare aluminum. It was felt that the Alclad coating of the aluminum was enough protection from corrosion as long as the Alclad finish was not compromised. It wasn't until very late production that it was mandated to treat all interior surfaces with zinc chromate - if I recall correctly, this being true of the P-51D-20-NT and later Dallas production, and not until the P-51D-30-NA in Inglewood production.

 

2. The general rule was that all aluminum extrusions, castings and forgings were required to be treated with a single coat of (raw) zinc chromate. Zinc chromate, in its natural raw state, has a yellow color. This meant that for the majority of parts, including the spars, ribs, stringers, longerons and any aluminum-cast brackets were all "yellow" zinc chromate. Any stainless steel parts that had to come into contact with bare aluminum also had to be treated with a coating of (raw) "yellow" zinc chromate - sometimes on all sides (as if when dipped in primer), and at other times only on the side in contact with the bare aluminum parts (as when sprayed with primer).

 

3. The general rule was that all magnesium-based castings and forgings (mostly in the form of brackets) were required to be treated with two coats of zinc chromate for extra added protection. This process was handled by applying a first coat of (raw) "yellow" zinc chromate, followed by a second coat of "green" zinc chromate, which was made by mixing a bit of black pigment with raw zinc chromate. This second coating was purposely pigmented in this manner so that the part could clearly be seen to be covered by two coats of primer.

 

4. To complicate matters, as has been found on all unrestored Mustangs, prior to restoration or currently preserved, what also tended to happen a lot on the shop floor was that aluminum parts ended up being finished with green zinc chromate as well, in lieu of the availability of yellow zinc chromate. There were two key reasons for this...

 

- a. If a batch of yellow zinc chromate ran out, they weren't going to wait until the next batch came in to spray the parts, they just used the green zinc chromate already available.

 

- b. Many parts (such as ribs and brackets) were coated with zinc chromate by dipping them into massive tubs/containers of zinc chromate. If a batch of aluminum parts were to be dipped in the containers of zinc chromate, and a container of green zinc chromate was available while all of the yellow zinc chromate was being used at the time, well those parts would go into the green instead - any opportunity to at least maintain the required pace of wartime production or speed it up if at all possible.

 

5. To further complicate matters, on all parts that were spot-welded together, such as the landing gear doors, gun bay and ammunition bay doors, cowl panels, etc., none of those parts could be primered prior to assembly, otherwise the spot-welding process would not work well. This is the reason why throughout most all P-51 production, the gear doors were always left bare metal. Also, as a result, while on some Mustangs the gun bay and ammunition bay doors were treated with zinc chromate following assembly, others left the factory with gun bay/ammunition bay doors where the interior surfaces were still bare. There was also a lot of spot welding in other areas around the fuselage and tail cone that had to take place using only non-primered skins, and then assembled without any spraying of zinc chromate afterward.

 

Where as one bracket in one wheel well may have been made of aluminum and finished in yellow zinc chromate, the exact same bracket in the other wheel well could be made of magnesium and finished in green zinc chromate. At the same time, both brackets could be made of aluminum and be finished either yellow or green, etc., depending on what was done with what was available at any given time on the production line to keep up with the pace of production and not slow things down. There is often no rhyme or reason, it was just what was available to use at that moment when the wing was manufactured - and, as I recall, the two separate wing halves were built/assembled on different sides of the factory before they were brought together as a single unit.


Here are a selection of photos to illustrate these points...


This first selection of photos is from the restoration of the P-51D-20-NA "Sierra Sue II". When this aircraft was disassembled prior to restoration, a detailed analysis was performed on each part as it came off the airframe as to which finish it had originally. Each part was documented as to whether it had been finished in (raw) yellow zinc chromate, green zinc chromate, or simply left bare. This was documented for each part so that when it went back into the aircraft it had the same correct finish it had when it originally left the North American Aviation factory in November 1944. In the case of this particular airframe, it was found that the metal skins on both wings had been left bare on the interior-facing surfaces from the factory.

 

The zinc chromate used on the restoration of "Sierra Sue II" is the original stuff, via a company in California which is the last that still makes it just like it was in WWII. Parts that were dipped in zinc chromate originally, rather than sprayed, were treated the same way in the restoration, so they have all of the same streaks/runs in the finishes as they did originally from the factory. Although the bare metal skins at the roofs of the wheel wells appear quite shiny, they are not polished and have the same Alclad finish they would have had when new in 1944 (and would dull over time). Here is a walkaround of "Sierra Sue II" while it was nearing the completion of restoration, which provides some more great views of the wheel wells (all finished just as they were found to have been originally in 1944): https://www.youtube.com/watch?v=a6pylSQlINs


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Now here are a selection of photos from the unrestored/preserved wheel wells on the later variant, museum-displayed, P-51D-25-NA 44-73349, showing all original and worn factory finishes. Note how on this particular, later aircraft, the skin forming the roof of one of the wheel wells is bare, while the skin on the other wing was coated in zinc chromate. Note that some other photos of this aircraft (namely the interior) were posted earlier in this thread too, and how many of the original American/English placards & decals were replaced with versions written in German - this is because those were applied while the aircraft was in the service of the Swiss Air Force, following WWII. Photos by Martin Kyburz.

 

(Note the curved rib at the top left area of this first photo is green zinc chromate, just like what was found on and reproduced on "Sierra Sue II" - the very same rib, while all the others were yellow zinc chromate.)

 

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Here are some photos from the restoration of "Happy Jack's Go Buggy". This airframe is believed to be a P-51D-30-NA. On this restoration too, when it was disassembled prior to restoration, each part was documented as to which primer finish it had, having still survived mostly untouched since original manufacture. It is interesting to note how, just like the preserved P-51D-25-NA above, this one too had the same left side wheel well roof skin finished in yellow zince chromate and the one on the right wing was left bare. On this restoration, like most, the primer finishes are all modern paints colored to look like the original primer colors found when the aircraft was disassembled prior to restoration, and it is interesting to note the differences in appearance as compared to the "Sierra Sue II" restoration which actually used the real, original primers (the skins on the "Happy Jack's Go Buggy" were also purposely worked on to achieve a "faux patina" to mimic an aged/oxidized appearance). Photos by Mike Vadeboncoeur.

 

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Edited by John Terrell
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Interesting stuff John. Does the hook that hangs down from the small opening in the top hold the wheel up when retracted? And it looks like all the inboard-outboard stringers on the 'ceiling' were always primered, usually in yellow but you might get the odd green one if the paint had run out. I'm trying to convince myself (for my own 1/72 purposes) that the centre partition between the two wheel wells could be painted either yellow or green, depending on paint availability. The photos of the unrestored swiss aircraft seem to suggest green (perhaps over a coat of yellow), though it's worn off quite a bit.

 

Justin

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15 hours ago, John Terrell said:

On all early to mid production P-51D's, the aluminum skins didn't typically require any coatings of zinc chromate on the interior-facing surfaces, and mostly were always left bare aluminum. It was felt that the Alclad coating of the aluminum was enough protection from corrosion as long as the Alclad finish was not compromised. It wasn't until very late production that it was mandated to treat all interior surfaces with zinc chromate

Thank you very much, John, this is the very important info I was expecting! Do you have pics of these early and mid production wells? the ones, great and very useful anyway, you just posted, are for later versions than the Missouri.

But the more I would need for now to go on with my wings would be pics showing the top and bottom surfaces, completing the ones you ever brought in the post 664, to appreciate what panels separation were a bit more visible, and which ones were nearly invisible on an in service aircraft. I know I ask a lot...

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Hello John,

I have small doubts about some aspects of your great diagram, if I refer to the "Sierra Sue II" restoration, that you yourself mentioned as very accurate.

1) the limit of the Acme surfacer, that should be a bit more frontal, especially on the up side (bottom side OK or nearly so)

2) Are you sure that, on the inside part of the wing, the Acme was applied like you show, with a quite large strip? It is difficult to see on the doc 152, but enlarging this area, it doesn't seem to me that it was so.

3) On the wingtip, on the other hand, the Acme seems to cover more than your diagram.

Could you modify the diagram consequently or give us your arguments on these points, please?

 

All the best

 

Olivier

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P.S: that said, I hope the Missouri, that was an earlier D version than the "Sierra", had the same Acme and Red Vellutine areas treated... Indeed, we could see above that the P-51B had less surfaces covered...

 

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In fact, we could see through the many examples more or less of the wings surface covered, with even sometimes the whole wing covered (J.T post#663 last pic). I will personally base myself on the below version (that matches quite well imho with the "Sierra" restoration pics), but it is up to every modeler to decide what version was the right one on a P-51D-10-NA like the Missouri, with an impossible way to be sure what was right. 

 

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