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

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Hello folks.  Some of you have seen my work on a 21st Century Toys (21CT) P-51D (Miss Velma) a few years ago, and more recently a P-38J (Lucky Lady), both multi-year mod projects.  If you will indulge me, I intend to finish off the big three with a P-47 Thunderbolt.  A nice winter project to get started.  It will probably take a couple of years like the others.  Then some day I will get going on the F4U Corsair, and then I will not have any 1/18 scale models left to modify.  


As is customary, I must show you the unmodified P-47 toy first, and then let you know my plan of attack (if there is one yet).  Here are some shots of P-47D "Jabo":














Unlike my last two efforts, I see no real challenges that risk not being able to be overcome, save one (the engine).  If the engine doesn't pan out, I will just hold my nose and use the existing one.  Although the toy looks as toyish as the others, I believe it has more potential for realism than either the P-38 or the P-51, where I had to live with some inaccuracies that were beyond my skills to fix.


The biggest projects are going to be the landing gear, wheels/tires, wheel well, control surfaces, cockpit, and canopy glass.  My previous two efforts had equivalent projects.  But the big project they didn't have, that this one does, is an engine which can be seen.  And that is the project I intend to work first.


To see the engine up close, of course I disassembled the fuselage:




As you can see, and not surprisingly, this is a BIG model.  But you have to understand that the P-38 build redefined my notion of size.  So I am not intimidated.  The engine (unmodified) looks like this:




That, my friends, is a somewhat plausible effort by 21CT at a Pratt & Whitney R-2800 Double Wasp.  Note the cylinders only have the front half (the rear half being invisible).  Anyway, I have decided that I will salvage none of it save perhaps the bulkhead it mounts to.  Instead I will scratch build the R-2800, at least what can be seen looking into the cowling from the front.  I will not attempt to include the exhaust or intake pipes, or the aft portion of the engine block.  I thought about it, but no - it would be too much.  I will include all 18 cylinders, their push rods, rocker arm covers, spark plugs with wiring, engine block, and all the clap trap in front of the cylinders.  That alone will require hundreds upon hundreds of little parts, and will take me a few months I suspect.  


I found alot of pictures of the R-2800 (early versions), and wish I could get drawings but cannot find.  Also I purchased a Vector resin 1/32 scale R-2800 shown here:




It is a good representation, and will be useful for scaling and copying.  


First order was to determine the size of the engine - one has to consider the thickness of the toy's cowling (.07 inch) which scales to 1.26 inch full size.  That means the engine has to be slightly undersized to fit.  So I did all that layout work and out popped a cylinder size.  Also I decided to construct the cylinders using 0.01 thick plastic for the cooling fins, and 0.01 inch plastic for the spacers between the cooling fins.  Actually this is a little too thick and results in fewer cooling fins than the real engine has.  But it is more than you typically see on R-2800 models I think. 


What you see here are flat patterns of cooling fins and spacers for the cylinder heads of the front row of cylinders (9 cylinders):




Whaaaaaa?   Patience.  Here is the prototype cylinder I made a couple weeks ago:






What do you think?  I thought I would have to trash it, but it actually is good enough to use.  Here it is next to the 1/32 Vector cylinder, and a photo of a real R-2800:




Note the pieces that make up the cylinder head have a 90 deg bend, and a little port for the spark plug.  The pieces of the cylinder itself are much easier - simply round, scribed with a circle template.


That is all for now.  I hope this generates some interest.  Next post will show some results of some real drudgery - making cylinder after cylinder - nine of them.  And perhaps the engine block which will be turned on the mini-lathe.  Then one day the aft row of cylinders.  Many challenges, and an unreal part count.  Stay tuned.









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  • 2 weeks later...

Small update (how does one do much modeling with holidays and family, etc):


In addition to the mind numbing task of scribing flat patterns for cooling fins, something I will be doing for the next couple of months, I decided to try making the engine block.  This would be done on the mini-lathe with round acrylic stock.  To give you an idea of what this will look like, I found this picture on the web somewhere:




Of interest here are the two cylinder banks (the portion aft of the banks will not be included in my model, and the portion forward - the reduction gear crankcase - will come later).  Each bank contains 9 cylinders equal spaced.  And the aft bank is staggered from the forward bank, as the picture shows very clearly.  Also note that each cylinder mount has studs that protrude from the block which allow attachment of the cylinders.  The nuts on those studs are visible on a completed engine, so I need to model them.  Finally note the valve rocker arm pushrod holes, two per cylinder.  They are staggered a bit - one forward and one aft for each cylinder.  I can only assume that there is an intake cam and an exhaust cam inside the block, one in front of the other spinning in a journal.  That means for each cylinder the pushrods will be at different angles.  


My plan calls for turning the basic block on the lathe, converting the machine to an end mill so as to machine flats for each cylinder, and then drill holes perpendicular to those flats for the post that each cylinder will have (.055 wire).  Each step is difficult, and requires a high degree of accuracy.  In order to make it even possible, I had to separate the forward bank from the aft bank, as you will see.


Here is a shot of one of the cylinder banks on the lathe:




As some of you already know, all those fluffy shavings are what clear acrylic looks like when machined off in tiny layers.  It accumulates fast and must be swept away periodically in order to see what one is doing!  What a mess.


And two finished machinings (awaiting the end mill): 




I managed to ruin each piece at least once, for various reasons.  So quite a few hours were involved.


From there it was on to the end mill.  For those of you unfamiliar with the Unimat mini-lathe, it can be dis-assembled and converted into an end mill or drill press, fixing the electric motor onto a stiff post, and using a drill chuck and various cutters or drill bits.  Here is a shot of the flats being end-mill machined on the round section lathe-turned part:




The part is clamped in a vice which is in turn attached to a rotating table, which is in turn attached to the basic machining table that comes stock with the machine.  The rotating table has angle detents (see the red marks).  So I could quite accurately machine each flat at 40 degrees from an adjacent flat.  That gives 9 flats equally spaced.  After properly positioning the piece, I could make passes of the cutter taking a little bit of material with each pass, until I had a completed flat.  Much care must be taken to machine off just the right amount. This was done to both pieces.


From there, holes were drilled in the middle of each flat to accept .055 wire "posts" that each cylinder will have.  It was imperative that the holes be exactly perpendicular to the flats.  To help with this, I made a jig of sorts to properly orient the piece when drilling:




It can be seen that this jig is clamped down to the machining table.  A freshly machined piece is to the right, ready to be mounted in the jig for hole drilling (it already has drill starts on each flat).  Like this:




Here are the two parts with finished flats and holes, stacked together.  Now you should see the method to the madness:




From there, round mounting rings with stud nuts were added.  The rings are scribed and cut from simple plastic sheet (.020 inch thick).  The nuts are plastic hex stock (.030 wide at the flats).  Very laborious work with great magnification required.  Here:




I include the one lonely cylinder I showed last post, along with some push rod tubes (.047 inch diameter plastic rod).  It's a little rough looking but a good start.  This engine is going to be really really busy once done.


Next up is to fabricate a whole bunch more cylinders.  Take care and have a Happy New Year! 

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