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Heavy Mod - 1/18 21st Century Toys P-47D Razorback

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Posted (edited)

As I look through wartime photos of P-47's, I see that aircraft were not always equipped with bomb pylons, or "wing tank adapters" which is what Republic called them.  But the one I am making did:




No question.


So the bomb pylon (Dottie Mae):




The model didn't come with them, at least mine didn't.  Not that they would be usable.  So it has to be a scratch build.  I have begun the layout activities:




The lower right drawing is my side view layout 3x size.  You may notice the wing lower contour is far different from what you see on the actual engineering drawings.  The contour is practically flat!  Well it is what it is, but it forces me  to make alterations to account for it.  For instance, my pylon will not have as deep a nose, and that may not look quite right.  Nothing I can do about that. 


These pylons have many many parts, and have fairly complex shapes which are not very well defined on the drawings.  For contours the reader is just directed back to "the loft" which we are not privy to.  But much can be inferred from the various views on the drawings.  I'll get there.


There are three trouble areas that I anticipate (circled in red on the top install drawing 93C78130):






First is the nose.  I am going to try to wrap thin plastic around a couple of former ribs.  And if that doesn't work, I will hog out the shape from a block of plastic.  Maybe too much to call that a "trouble area", but it will be tedious and challenging to say the least.


Second is the area right behind the aft sway brace.  This is a contour transition area that is poorly defined, and even if well defined will be very challenging to create from scratch.  At the moment I don't even have a plan.


Third is the aft end which is occupied by a very complex casting.  The part is meant to be a hinge for a stabilizing post used for one of the larger fuel tanks that were sometimes used.  When not used it hinges forward to a stowed position as shown on the drawing.  That casting is going to be a tiger to represent.  I have no good plan yet.  MOF - that part was so challenging, even the Dottie Mae has only a simple sheet metal replacement for it.  See the photo above.


So I  have my work cut out for me - a project within a project.   Bring it on!

Edited by JayW

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This would make a really nice bank.


Great stuff going on here, Jaybo.  Everything you've done looks the ticket.  Delicate transitions in that housing.  Good luck.




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Posted (edited)

I have an "interim" report on the bomb pylons, or "wing tank adapters".  Here is a repeat photo of this item:




That way you can look at some of the details I am attempting to replicate and compare.


This is difficult work to get right.  My first effort was (is) to create the forward portion of the pylon box.  It involves two side skins, a forward frame, a mid frame, and a bottom "floor" of sorts.  The framework provides the shape the side skins must take, and also provides the mounting surface for the bomb shackle, and later the sway braces.  It also provides the attachment surfaces for the aft end of the pylon which I have not started yet.


Here is the basic forward box (both of them):




The shackles are very similar to the centerline one I showed a couple of posts ago.  You also see the side skins - notice the aft ends where contour transition begins.  A very pesky thin bent-up "bulkhead" holds the local contour and forces it to taper to a sharp edge.  This will be much more evident when I produce the aft portion of the pylon.


A couple more shots:






I have included the Dzus fasteners similar to what was done on the wing and fuselage, only smaller diameter.  Note also the elliptical nose formers I have included in which to attach the nose skin shown here:




Man - that little curved skin part is pressure packed.  It is the most visible part of the pylon and it has to be good.  This includes properly matching up to the wing contour.  I fail on this part, and I have to start over.  The part you see has excess on all four sides and is trimmed to shape after being glued to the nose formers.  Like this:




Here is a test fit:




So far , so good.  It was just a matter of filing and sanding a little at a time til it fit up OK.  There is much to go.  Complicated little suckers these are!



Edited by JayW

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Man there's some work in those Jay! Your styrene-taming is very impressive indeed. Did you try heating the nose piece in a little warm water? It may have relieved the bending stresses on it a little. In any case, it worked for you!


Outstanding as always mate,



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Posted (edited)

"Man there's some work in those Jay!"   True statement Craig!   It is actually a fun project, and they are little models in themselves.  You ain't seen nothin' yet.  Lots and lots of work remaining.  The challenge of course is to make them look crisp and not sloppy.


Did I heat the nose pieces?  No.  The gage is .01 inch which is fairly formable as is.  What I did do is to "pre-form" the pieces over small diameter tubing.  Although there was alot of springback, from there it was fairly easy to wrap around the former ribs.  Contour is not that severe, and the length of the part is nothing like a flap or aileron nose skin.    


BTW - I try to use styrene as my go-to material, because glue, either liquid or tube, is so effective.  Metallic materials rely on epoxies, which do not weld the material together like styrene glue does, but just fill in micro pockets and other irregularities.  So the bond often is not as robust.  And, curing time is longer than a styrene glue bond.   I have been burned before, however, and wished I had used something else!

Edited by JayW

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Posted (edited)

Progress is soooo sloooow.  I have life issues competing for my time, but I jump on the P-47 whenever the coast is clear.  The finish is in sight, so it's frustrating to have to go so slow.


Anyway - continuing on the pylons.  One of the peskiest details so far are the "blocks" on either side of the main body of the pylon above the shackle hooks:





Here is the drawing of the forward details (aft is similar):




What is the purpose of these "blocks"??  They are made of steel sheet, and have heavily formed bumps hammer-died into them.  They also have small free flanges sticking out in the breeze.  Their proximity to the bomb shackle hooks must mean something - perhaps they are bumpers in case a bomb or tank releases poorly?  But why the flanges?


Anyway - if any of you know, please chime in.  Meanwhile I set out to make them in 1/18 scale - the bumps being the challenge.  I tried puddles of 2-part epoxy (fail), and a shaped chunk of plastic rod (fail - too small to deal with).  In the end I started with a rough shaped chunk of plastic, and poured a bit of epoxy over it and it worked fairly well.  The chunk of plastic was first glued to a shaped and bent-up piece of .005 thick plastic sheet:




With the plastic rod (whittled on):




With a modest epoxy pour, and attached to the pylons:




Note also I have completed the sway braces (minus the threaded posts which will be added later).  They were made from .08 x .156 inch rod.  The rear ones were a real adventure as I had to attach them via a complexly shaped chunk of rod shaped to match the local pylon contour in a transition area.


Here is the completed pair of forward pylons (minus decals and final flat top coat):




Now, it is time for the aft fitting, the aft pylon skins, and that odd post used to steady the large drop tank.  All are small scale scratch built challenges.


Take care, hope Easter was good for you all.

Edited by JayW

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Posted (edited)

Another update on the surprisingly difficult and involved bomb pylons.  The aft halves are proving very difficult, as I am having to custom make each skin panel to match up with variations that have made their way into the build-ups.  There are four skins (two per pylon) and so far I have had to scrap two or three each to finally get one I can use.  Also, that aft fitting I mentioned in a previous post was small and difficult.


The aft end of the pylons are dominated by a hinged arm assembly that is normally stowed, but extended and used to further stabilize the Lockheed (quite large) 150 gallon fuel tank when used.  That and the structure to mount it.  A cartoon picture from the combat tanks & bombs drawing (93X10101):






You can see that arm pretty clearly hanging down and making contact with the top of the tank. 


Here is a picture from the pylon installation drawing 93C78130, showing that arm assembly:




The arm assembly is shown stowed, and also extended in phantom lines.  Note the aft fitting that is attached to the wing by three bolts (shown in the top view).  That fitting provides the hinge point for the arm, and also an adjustable overtravel stop bolt and jam nut.  Note also the forward end of the arm is latched in place by a spring loaded mechanism on the bottom of the aft pylon fairing.  I find this all very curious - all just to be able to use the Lockheed aux tank. 


Now that fitting.  It has a very complicated shape and is made from a very complicated casting.  Look at the machined part drawing (93C07202):




The Dottie Mae resto project never even tried to reproduce this part.  They just fashioned some sheet metal equivalent:




Here is my effort on this very pesky part:




 From there, I proceeded to make a framework of sorts for the aft triangle of the pylon:




This provided decent support for the triangular skin panel (this one here is the 4th try after three misfits): 




Note that part has to form the bottom sharp edge of the fairing aft of the aft sway brace, the flat for the arm assembly to be stowed in, an interface with the aft fitting, an interface with the wing lower surface, and an interface with the pylon forward skin.  All that made the part shape very tricky.


The arm assembly itself is defined on drawing 93C78236:





It has a hinge hole on the left, an attach point for a spring in the middle, and a wing of sorts on the left (the "wing" contacts the aft region of the Lockheed tank to provide more stability.  You will see mine below.


Here is the finished LH pylon, painted and with decals:






A close-up of the arm assembly:




And the pylon final installed onto the wing:




Whew!  Now, the RH pylon is a couple days behind.  Then it is on to the pitot mast.  And then all the various wing decals.  At that point, I will post progress and that will be the last I post in this two and a half year long "work in progress" string.  I thank all of you who stuck with this so long!






Edited by JayW

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Jay, is the far aft arm a stabilizer as well, depicted stowed?

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