1/18 Scale Blue Box F4U-1A Corsair Modification

[Oldbaldguy]

Hmmm.  Beginning to wonder if it needs to be painted at all…

[JayW]

13 hours ago, Oldbaldguy said:

Hmmm.  Beginning to wonder if it needs to be painted at all…

Honestly!  How do you not paint a Corsair?  You and Peter C.  Well I know these are compliments of a high order.  Thank you.  More skinning to come on this big project.    

[JayW]

Back around the first of the year was when I gave in and decided to skin the beast.  If you have been following this build, you will recall there was all kinds of discussion about adhesives for the aluminum sheet to be used for skins, and thinners, and availability of these solvents here in the states.  There was also experimentation by myself with some different adhesives and thinners, more often with some poor results like failure to properly mix or loss of adhesive qualities with thinning.

 

Because of availability, and also good results, I have been using Weldwood contact adhesive, available in any hardware store.  It is not overly thick, and has also stayed that way for quite a while.  But not forever - my can of Weldwood, with time, is getting thicker, and that is not good.  Somewhere in this thread my old friend Ironwing emphatically insisted on Xylene for thinning Weldwood (I seem to recall Easixpedro seconded that?).  That stuff ("Xylol Xylene") is also commonly available in hardware stores here.  Today I tried it, and he was right.  It thinned out just fine, and still sticks with authority.  Yay!  With still lots more acreage to skin on this very large Corsair, that is a very welcome piece of news, and represents another improvement in my future results.

 

I just thought some of you would like to hear of that news.  Thanks Ironwing.  

[JayW]

All right - the cowl flap ring is complete as much as I can for now.  This next project (or sub-project) is the nose cowl installation.  This is something I CANNOT screw up.  Outside of the gull wings, one of the most noticeable things about a Corsair is the nose cowl with the big engine inside it, and a big 3-blade prop just in front of it.  It has to be spot on.  

 

The nose cowl in real life, similar to the cowl flap ring, is attached to the engine in 18 places - one for each cylinder head, this time to the front row cylinders of the engine:

 

  

 

There are 18 heavily rivetted nose cowl ribs, each one attached at its aft end to a link and a triangular shaped pair of plates - the plates bolt to a dedicated flange on the cylinder head. I have simplified my installation to not include the link - my ribs attach directly to the triangular plates.  I just could not hope to duplicate that many little parts. You will see these plates next post (not this one).

 

Recall I have had in the queue the 3D printed nose cowl and its ribs, which I showed in a previous post.  The first thing I had to do was to add the better part of 1000 rivet indentations using a #3 punch (scales well for a countersunk head 5/32 rivet) to that nose cowl:

 

 

I could not put too much pressure on the awl lest I crack the somewhat fragile cowl detail.  I hope they show up after paint. 

 

Here are a few of the 3D printed cowl ribs, freed from their stalks, and painted up and ready for installation:

 

   

 

Actually, many are having to be trimmed and whittled on - the cylinder head flanges are all over the place.  Sometimes too far forward, or too far aft.  If too far forward, the cylinder head flange will clash with the aft end of the rib.  When I made the engine, I did not control the location of the cylinders all that well.

 

This post is all about accurate installation of those ribs so they line up with the cylinder head flanges - step number 1 for the nose cowl installation (step two being attaching the ribs to the cylinder heads).  Recall that I made a nose cowl location jig for centering the cowl and controlling its fore/aft location relative to the engine:

 

 

 

Vital that the engine and nose cowl are properly located relative to one another before this work begins.  So I was ready to rumble.  Let me take you through my process - it was revised a bit from what I first envisioned and became more refined as I got into it:

 

1.  Bond (weakly) engine to the nose cowl jig, so it doesn't wiggle around, and so that later I can break it free from the jig:

 

 

2.  Place the nose cowl in the jig, over the engine, clock it perfectly to my handy-dandy vertical scribe line on the jig, and make a pencil mark inside the cowl, exactly where a cylinder head flange is:

 

 

 

3.  Remove the cowl, and using 2-part epoxy (5-minute dry), locate and bond a rib to the inside of the cowl at the pencil mark.  Wait a couple minutes for the epoxy to start to set up, again place the cowl in the jig, reclock, and make any location adjustments to the rib before the epoxy dries:

 

 

The rib must line up exactly to the cylinder head flange, so that the triangular plates can be installed during step two.

 

4.  After the epoxy sets up, remove the cowl from the jig, and apply some thin CA to the rib.  That rib ain't going nowhere.

 

5.  Repeat 17 times.

 

So, I have 10 ribs so far, 8 to go:

 

 

I had hoped to install ribs plus triangular plates right on the jig without needing to remove and replace the nose cowl umpteen times.  But clearances just didn't allow.  I really had to butcher the aft end of some of those ribs due to my poorly located cylinder heads.  Perhaps you can see that.  But that will be very hard to see once the triangular shaped attach plates go in.  There will be 36 of them (two per cylinder head), with Meng nut hardware.  Yikes.  

 

I love this kind of work.  Very challenging.  If successful, I will have a very stout nose cowl attachment to the front row cylinders, properly centered about the thrust line, and convincing looking.  That is in addition to the cowl flap ring, also firmly attached to the aft row of cylinders and properly centered about the thrust line.  And once that is done, I can get to work on the cowl panels directly behind the nose cowl, which will be removable (with magnets).  What a huge ask!  Very excited to try to make it happen.

 

Stay tuned for step two - which is to attach the nose cowl to the engine cylinders via the ribs, 18 places.  Ta-ta!     

 

 

 

 

 

 

Edited July 18, 2022 by JayW

[airscale]

I have a brain that needs surgery Jay - as soon as you are done here would you mind giving it a go?

 

Seriously, what a precise approach and execution - it is one of those (to me) little known thrills when you make something and later down the line it lines up precisely with something else

 

I am enjoying your sideline in jigs and tools as much as I am enjoying the build:)

 

Peter

[Citadelgrad]

Maybe it's just the way my brain works, but I am as fascinated by the extremely neatly executed jigs as I am with the amazing results you are getting on this build.  
 

Keep going! 

[brahman104]

1 hour ago, JayW said:

my poorly located cylinder heads

 

Says no-one in the universe except you Jay.... . This whole project is a case study in precision engineering! Exceptional work on the cowl. Even if I'd made a pencil mark most of mine would have still ended up at a 45 degree angle or something.

 

So good, and waiting for more! 

 

Craig

[LSP_Kevin]

47 minutes ago, Citadelgrad said:

Maybe it's just the way my brain works, but I am as fascinated by the extremely neatly executed jigs as I am with the amazing results you are getting on this build.  
 

Keep going! 

 

Jay's jigs are better than my models!

 

Kev

[Citadelgrad]

11 minutes ago, LSP_Kevin said:

 

Jay's jigs are better than my models!

 

Kev

That's exactly what I was getting at.  He works up a part to help him do something that will never be used after it's purpose, and it looks better than my finished product.  

[Oldbaldguy]

Anybody ever wonder if the guys at 21st Century were to read this thread, if they would be embarrassed at what they could have done with their Corsair but didn’t?  Well, actually, we know they couldn’t have even if they had wanted to, so the whole question is moot.

[JayW]

   "3 hours ago, JayW said:

my poorly located cylinder heads

 

Says no-one in the universe except you Jay.... . This whole project is a case study in precision engineering! Exceptional work on the cowl. Even if I'd made a pencil mark most of mine would have still ended up at a 45 degree angle or something."

 

Well thanks Craig, but there are hidden secrets to that engine build.  Here is a result of the "poorly located" cylinder heads.  Not only did it require me to trim back many of the nose cowl ribs, but the triangular shaped attach plates which will mate the cowl ribs to the engine must have all sorts of shapes, each individually tailored to whatever variation shows up at any particular cylinder head flange.  Here are examples:

 

 

The one on the left is the nominal plate, and that shape is supposed to be used all 18 places.  The other three are examples of the shapes required to mate the rib and flange together based on variations I have measured.  None of mine are nominal!  16 of 18 locations require a special odd shape like the examples you see.  All due to a cylinder head that isn't in the right place.   For context the nominal plate is 0.093 inch vertically between centers, and 0.063 inch horizontally between the left hand center and a vertical line joining the other two centers.  So max variations around +/- .04 inch.  Scale to 1/18 and that is +/- .75 inch!  Too much. 

 

How did a cylinder head get .04 inch off?  Tons of reasons.  They were mounted on top of cylinders made up of hundreds of thin little wafers, and glue between them, which were mounted on a machined engine block with flats that might have been too deep or too shallow.  Those cylinders had little rods through their centers, which slipped inside of sloppy holes in the block, so one might be a couple hundredths forward or aft from an adjacent cylinder.   A cylinder might be leaning a bit.  It might be slightly rotated so its LH cylinder head lobe is aft and the RH one forward.  The cylinder heads themselves were made from dozens of little parts all made by hand, with tolerances of their own.  I mean it goes on and on.

 

Had I had my head screwed on straight when I did the engine, I would have attempted to control the cylinder head fins more closely than just eyeballing them.  But that's all I did!  Fear not though.  This variation is going to be hiding deep inside the shadows of the nose cowl.  You'd have to really look for it.        

 

 

 

  

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Edited July 18, 2022 by JayW

[JayW]

14 hours ago, Oldbaldguy said:

Anybody ever wonder if the guys at 21st Century were to read this thread, if they would be embarrassed at what they could have done with their Corsair but didn’t?  Well, actually, we know they couldn’t have even if they had wanted to, so the whole question is moot.

 

You know - some of their efforts are better than others. Their better ones are pretty nice in many respects - that is why I chose to work with them in the first place.   Given heavy skin gages, a desire to have retractable gear, etc, and a requirement to be somewhat sturdy, much compromising had to be done.  Wings with too fat a cross-section for example.  Skinny tires.  BTW - no way could 21CT duplicate the marvelous mechanism that is the Corsair main landing gear!  Still there are some things that could have been alot better without compromising.  I have no idea why they cannot get the slope right on windshields, and why those windshields and canopies have to be oversized.   And there are other shape boo-boo's that were just a result of poor research or poor measuring - however they come up with shapes....like the Mustang's mid-fuselage lower radiator intake area (and exit) - they just janked up that shape for no reason at all other than erroneous measuring far as I can tell.  Same with the Corsair's mis-shapened forward cowl and oversized canopy.  Why?  

Edited July 19, 2022 by JayW

[adameliclem]

Jay, there are always penny-drop moments in your builds, and the brilliant cowl jig is one of them. I’ve been thinking about how I’ll tackle the, uh, challenging engine and cowl assembly in Kitty Hawk’s OS2U Kingfisher, and your approach might crack it. Lessons learned, confidence boosted. Great work, man.

 

Adam

[JayW]

This is a little premature, but I just cannot help myself - I have to show you all this.  Recall last post I was in the middle of "step 1" of the nose cowl installation, which was installing 18 ribs inside the cowl.   This was being accomplished with a jig of my own making.  That's done.  Step 2, using that same jig, the nose cowl is attached to the engine cylinder heads via alot of triangular plates like this:

 

  

 

As I mentioned before, I skipped the little link you see in that picture, and only used the attach plates.  Here is a pair of those details:

 

 

Very small, easy to lose.  All 18 nose cowl ribs get those little parts, which are differently shaped at almost every location based on variability of my engine. 

 

Here I show that work on the jig:

 

 

 

The blue dots signify location that are done.  Note that there are some inaccessible locations behind the towers on each side of the jig.   That's OK - I can get to those after the assembly is removed from the jig.

 

So I removed it:

 

 

 

That is a large milestone.  Note I had to slice the large circular resting plate in two, and bust it off the towers, to get the engine out of the jig.  The way the jig was designed, the engine was trapped in the jig - couldn't help it.  No prob' - I don't need it anymore!

 

OK - it is now time to take care of the 5 remaining locations.  Even with them not complete, the nose cowl feels very robust.  No flexing whatsoever.  I am so stoked.  Then, paint touch up, some other little stuff, and then on to the cowl panels.

 

Here is a shot of the Corsair with the engine and nose cowl fitted to it:

 

 

 

Now that's what I'm talking about.  I am soooo glad I chose to 3D print that nose cowl instead of using the kit one that I modified on the lathe a few years back (see page 1 of this 60+ page thread).  It's night and day.  Next post I will show you, among other things, the nose cowl attachments in more detail (after I clean them up some).

 

Stay tuned - lots more adventure to come.

Edited July 21, 2022 by JayW

[TAG]

Just... WOW!

 

I can only imagine how stoked you must be on reaching this milestone, Jay. Big up yourself, buddy, you deserve all the accolades.

 

And you know what, now it actually looks like a Corsair!

 

Congrats again, can't wait for the adventures to come.

 

-Thomaz