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

[JayW]

Installation of the nose cowl is now complete:

 

 

 That son-of-a-gun is going to occupy me for a while - cowl panels and cowl flaps. 

 

A few pics to show how the cowl ribs attach to the engine cylinder heads:

 

 

 

The way was then clear to finish off the prop governor controls (the ZC green stuff plus the cable):

 

 

After the euphoria wore off, I began to do some analysis on the engine/cowl combo.  Did some measurements, some clearance checks.  And I found a couple of not-so-cool things.   Was hesitant to report out on this, but hey - full disclosure on this build.  I want to report the good and the bad.

 

First, having to trim so much off the aft ends of those cowl ribs bugged me.  A couple here and there, sure, but almost all of them?  Shouldn't have been that way.  At the same time, the engine's nose (the reduction gearbox) seemed to be sticking out forward of the nose cowl lip a tad too much.  So I took some measurements, and sure enough, it is forward by about 0.02 inch.   Everything else measured right, and a recheck of the jig showed it was right too.  If the engine were indeed too far forward, that would explain why I had to trim the cowl ribs.

 

Well - back three years ago when I was building the engine (and some of you might recall this), when I joined the front row of cylinders to the back row of cylinders (each with their engine block halves), I accidentally allowed a stray spark plug wire to find its way between the two engine block halves at the time I was joining them.  There were .02 inch diameter solder spark plug wires flying all over the place at the time, terminated on one end but not the other.  I didn't discover this until the epoxy I used to make the join was already set up pretty good.  This created a 0.02 inch gap between the front and aft row blocks (the gage of the solder I used for the spark plug wires).  I attempted to close that gap by yanking out the wire, only to break it leaving the broken off portion in the gap.  I put the assembly in a vice to try and close down the gap by smashing the solder, and was hesitant to clamp down too much.  And just hoped for the best.   

 

So that clamping was not very successful, and the error has come home to roost.  The front half of the engine is too far forward, and the aft half is spot on, and the nose cowl is spot on!  What am I going to do about it?  Nothing - there isn't anything I can do.  I am going to hope it is not very noticeable.  .02 inch?  Doesn't sound like much, but scale it up to full size and it is .02 x 18 = .36 inch. 

 

And second - when I first began this build (again some of you might recall this), I was unhappy with the shape of the nose of the model:

 

      

 

There was supposed to be a slight taper to the engine cowlings, and instead the toy had a constant diameter cowl which made the nose look wrong.  So I separated the engine cowl from the airplane and put it on the lathe to turn it down as much as I dared:  

 

 

And called it good.   In the mean time, I built an engine that is too scale.  It doesn't have a reduced diameter to accommodate thick gages on the model.  At the time, I felt I could do this if I kept my engine panel gage to no more than 0.02 inch (versus .08 inch on the original toy cowl).  Since then I have replaced it with the 3D printed cowl which is much better and does a better job of giving that slight tapered look I need.  But the new nose cowl diameter is as small as I thought I could get away with and still clear the engine (it's still a tad too large).  So i needed the engine to be accurate.

 

Enter build tolerances.  I just made a sort of "go - no go" gage, to see how well my cylinder heads will clear the panels.  Good clearance, except for two.  And one of them isn't bad; one of them is:

 

   

 

Yup - that rocker arm cover will hit the inside of the panel.  Arg!! 

 

 

How?  I don't know.  For some reason that cylinder head lobe is just too tall.  So I had to grind it down.  It's really scalped:

 

 

 

Imgur "huge thumbnail" for effect.  Man do I hate that.  I'll dress it up as much as I can, but that rocker arm cover looks pretty bad.  It's on top too, quite visible.  Also I am also going to have to reduce the gage of the engine cowl panels from .02 to .01 or .015 inch.  That makes them less robust.  

 

I'll get over it.  In the grand scheme of things it isn't that bad.  Next post I will show you some Rhino modeling for 3D print parts I need to order about now, and some work on what will turn out to be very difficult engine cowl panels (that are supposed to be removable).  My goal is still to show the engine and not hide it. 

 

Take care, and stay cool. 

 

 

Edited July 22, 2022 by JayW

[Out2gtcha]

WOW, what a slug fest!  All that extra work and adjustment will all pay off in the end guaranteed. 

[brahman104]

Not that I can compare my build to yours at all Jay, but almost every time I work on it, there's always something that I did years ago which now changes or impacts what I'm doing now. Some things I can change, others I have to accept. I know your quest is for perfection as far as humanly possible and you've done everything humanly possible to achieve that in scale, so I know it sucks when you get little things like this that only show up when it's way too late to correct them.

 

Regardless of the real world outcomes, I've just been looking at that close up shot. I'm not seeing a ground down rocker cover; I'm staring in absolute amazement that this is a SCRATCH BUILT 18 cylinder engine! 

 

You've come all this way and you've only had to grind back a rocker cover slightly? You Sir, have absolutely nailed modelling perfection!

 

Craig

[Pete Fleischmann]

That’s pretty effin’ outstanding.

man that’s cool!

 

cheers

P

[Thunnus]

Incredible work, Jay!  The sleuth work to figure out where the extra 0.02 inch came from... unbelievable!!!

[Paulpk]

Jay, I just spent the last few days going through the pages of your incredible build. Fantastic work!!

I am so glad you decided to skin this bird!

 

Your issue with the rocker arm is unfortunate but all part of the compromises we must make working with thicker materials then originally used.

 

Regarding the use of etching primer; I did some tests on brass for a model I am building and Rust-oleum failed the scratch test after being top coated. A number of other box store brands also failed. I had excellent results with an automotive brand by Eastwood. Only downside is the need to top coat within so many hours. It is in their instructions but I am not sure yet what the results would be for a model if I waited longer.

[JayW]

On 6/28/2020 at 3:04 PM, JayW said:

I have progress to show you, actually quite a bit.  The spark plug wire harness is finished with all 36 wires routed, painted, ready to go.  With that, the forward row inter ear deflectors were installed.  And, this was the time when the forward and back row cylinders and crank case halves were bonded together, and the front reduction gear housing was bonded in place as well.  I managed to make every mistake in the book along the way, perhaps the worst of which was to paint a 5 foot length of .025 inch silver solder (for the spark plug wires) primer plus gold before hand.  I thought I'd be sly and pre-paint so I would not have to reach into inaccessible places to paint wires after installation.  Well - as I should have known, the paint flaked off after making bends and curves, or sliding on clamps.  So not only did it make a mess of flakes, but I had to go in and paint inside those inaccessible places anyway.  In the process, I managed to break off a cylinder, requiring a delicate re-attachment in place with lots of stuff already attached to said cylinder.  While joining the two cylinder rows, I accidentally allowed a free end of spark plug wire from the back row to get into the joint.  I discovered this after the epoxy was already dry (or nearly), so I had to extricate the solder wire, breaking the wire about mid-length, and applying about a half hour of careful pressure to get the two crank case halves to seat properly.  They are almost seated; not quite.  That spark plug wire repair was also exceedingly delicate.  There were other mis-steps and gaffs I will not bore you with - but suffice it to say that prior to this work, I was hand wringing about it, and was not sure why.  Now I know.

 

So here is the result of my pressure packed work:

 

 

 

For those interested, here is what I meant about the .02 inch anomaly.  This work was done two years ago.

 

"While joining the two cylinder rows, I accidentally allowed a free end of spark plug wire from the back row to get into the joint.  I discovered this after the epoxy was already dry (or nearly), so I had to extricate the solder wire, breaking the wire about mid-length, and applying about a half hour of careful pressure to get the two crank case halves to seat properly.  They are almost seated; not quite."

Edited July 23, 2022 by JayW

[JayW]

13 hours ago, Paulpk said:

Regarding the use of etching primer; I did some tests on brass for a model I am building and Rust-oleum failed the scratch test after being top coated. A number of other box store brands also failed.

 

Thanks for that Paul.  You went through this entire build so far?  Thanks for that too.  Stay tuned because more adventures await.  As for the Rustoleum, I just rechecked my mule, where I tested it out on an aluminum panel a few weeks ago.  Man - it is just sticking like a pro.  Couldn't ask for better.  I wonder if it works better on alum than brass.   

[JayW]

When I was building the engine nearly three years ago, some of you expressed concern that it would be hidden inside the airframe, forever unseen.  And when I began this build, it was always my intention to have removable cowl panels so that the engine would indeed be visible.   I knew however that would probably be a tall order.  Failure would mean I either do not have panels, and expose the engine, or I have panels, and the engine is largely hidden.

 

Fast forward to today.  Already the engine accessories compartment panels are removable, and look pretty good.  That was a big deal.  Perhaps a bigger deal though are the cowls over the engine cylinders.  And it is time to tackle these items. 

 

The drawing, from Aircorps Library: 

 

 

There are four, with joints on the vertical centerline upper and lower, and 10 degrees below the thrust line both sides.   Those joints are covered by thin external straps:

 

 

Corsair fans will recognize those straps; mine will of course have them.  Each panel In real life is thin sheet metal, stiffened with three circumferential frames, and many little ribs.  The panels, of course, are attached to the airframe with Dzus fasteners.

 

I have options how to make these panels, and what to make them from.  They can be all plastic, all aluminum, or a combination.  I have chosen, for now, a combination - aluminum skins and plastic frames and ribs.  I report to you today on a "proof of concept" effort, intended to learn on, and make my mistakes on, and help me decide if that's a good way to build them.  It represents about a day and a half's work:

 

 

 

The panel you see is the upper LH side one - it has a .004 inch thick skin (similar to what I have been using to skin the rest of the airplane), a .01 inch thick inner plastic skin, and plastic frames and ribs.  Note that skin is very thin - it needs to be because of the tighter than expected clearances to the engine I reported on last post.  It is held in place by back-to-back magnets on its forward edge (common to the nose cowl), and magnets and thin steel strip on the other edges.

 

I have learned much.  First, the forward edge trim is very difficult to get right.  Because the cowl has a slight taper, the diameter at the forward edge is a bit smaller than the diameter at the aft edge.  Which gives a curved edge in a flat pattern.  What you see isn't quite right, but close.  I will do better when I do the real set of panels.  Fair is very good with the nose cowl.  The panel has Dzus fastener marks, which I had to make after (not before) the panel was formed.  That is hard to do.  Because the trim had to be finalized before punching the marks, and that has to be done on a formed panel.   Also note the exterior has self-etching primer on it.  I did not let it dry sufficiently before handling it, so it looks pretty rough.  And surprise - I got some paint lifting when I gave it a tape test.  That is a surprise because I tested that primer out on my mule, and it worked fine.  I need to get to the bottom of that.  And very importantly - the magnets and strips are holding the panel in place fairly well.  I was worried about that.

 

The inside:

 

 

 

It isn't complete, but it's a proof of concept.  I need that stiffening because the skin is so thin.  And the interior detail is also somewhat visible through the nose.  The members have to be carefully configured, and carefully located, to dodge the cylinder head lobes and other clap trap on the engine.  It isn't exactly like the real thing, but quite similar.  You can see the magnets on the forward edge, and stainless steel strip on the aft edge.   Note the wrinkled inner skin.  Glad that doesn't show up on the exterior!  So the contact cement I am using to bond the plastic inner skin to the aluminum outer skin apparently attacks polystyrene.  For my next try, I am going to further thin down my cement, apply a thinner coat.  Even if I do get some wrinkling it's just not that big a deal - it's invisible.

 

Here is the RH upper panel along with the LH panel:

 

    

 

The splice strap is in evidence.  It is made of .004 inch aluminum, and CA'd to the panel skin (one of them only).  It remains to be seen if that CA is good enough.  If not, I will try contact cement.  It needs to be on there good, as I will be putting a fingernail under it to lift the panel off.

 

The inner structure is more complete on the RH panel:

 

 

More wrinkling....

 

I have a whole list of things I want to do a bit differently for the "production" panels, but I think I will stick with this hybrid concept.  All in hopes for perfection or something approaching it.  I am accepting suggestions BTW!  But be quick - production panel work will commence very soon.

 

This is a big victory folks - I can say now that the removable panel plan I had three years ago is going to be a reality.  Next post I will show you the completed panels.  Thanks for looking in! 

Edited July 25, 2022 by JayW

[brahman104]

I wish there was a standing ovation emoji!

 

Those panels are just spectacular! Could you sand/fill the wrinkles once everything is dry, or is there too much risk of deforming the panel? In any case, brilliant work!

 

Do you want to come and make my bomb bay doors fit better? 

 

Craig

[LSP_Kevin]

Just amazing, Jay!

 

Kev

[JayW]

3 hours ago, brahman104 said:

Could you sand/fill the wrinkles once everything is dry, or is there too much risk of deforming the panel?

 

Craig - those panels are proto-types.  I am working on the second set now and they will not have wrinkles, I don't think.  

[JayW]

On 7/22/2022 at 4:39 PM, Pete Fleischmann said:

That’s pretty effin’ outstanding.

man that’s cool!

 

Pete - Speaking of pretty effin' outstanding, I am going through your T38 scratch build.  Damnation!  I believe that I am going to scratch build a P-51D after I finish this (giant) Corsair project.  I paid the big bucks for a 21st Century Toys P-51 a couple months ago, but I no longer want to be living with inaccuracies that are beyond my ability to fix.  Your work plus what Airscale is doing are great guides for me.  It'll be a first for me.  BTW - I have around a thousand questions for you WRT F-16's (did you mention you flew them?).    

Edited July 29, 2022 by JayW

[Pete Fleischmann]

57 minutes ago, JayW said:

 

Pete - Speaking of pretty effin' outstanding, I am going through your T38 scratch build.  Damnation!  I believe that I am going to scratch build a P-51D after I finish this (giant) Corsair project.  I paid the big bucks for a 21st Century Toys P-51 a couple months ago, but I no longer want to be living with inaccuracies that are beyond my ability to fix.  Your work plus what Airscale is doing are great guides for me.  It'll be a first for me.  BTW - I have around a thousand questions for you WRT F-16's (did you mention you flew them?).    

Awesome Jay!

Timmy! just gave me a copy of Mustang in my Workshop- Man I’d recommend taking a look at that!
most of what I know about this scratch building thing I’ve learned from Timmy! He is probably overall, considering all of the modeling skill sets, the most talented modeler in the world..and I mean that with all sincerity.

Timmy’s Tech

The two Scratchbuilt books by John Alcorn are a must as well.. and if you are hanging out with Peter from Airscale, you are on the right path!
 

and yes, I flew the F-16 with the USAF for about 12 years. I miss it every day.

 

Your Corsair is also an inspiration, and I hawk your thread every time I sign on to LSP. VERY precise and beautiful work you are doing! I am enjoying it, and will be sad when it’s finished because no more updates!

 

cheers

Pete

[JayW]

I am glad that I took the trouble to fab up a couple of "proof of concept" panels.  It paid off.  Lessons learned from that, plus verification that the concept was viable (hybrid panel with magnets), allowed me to produce four virtually error-free engine cowl panels:

 

 

 

 

Note also the dog-bone shaped splice plates at the joints.

 

The all important view from the front:

 

 

A rear view showing how well (or poorly) the panels lay down on the cowl flap ring:

 

 

It'll do!  I tell you - back to back magnets (as I used at the nose cowl) works great.  The panels just snap into place.  Magnets and stainless steel sheet, where the magnets are underneath a thin layer of plastic (I used this at the cowl flap ring), doesn't work nearly as well.  The attraction is a little weak.  I had to do that way.  So I had to fiddle around a whole lot with the panel contours to get them to lay down decently.  

 

The insides - supposed to be painted either gray or white - I chose gray, and then got them nice and dirty:

 

 

You might wonder how I am to properly clock four cowl panels, where there is nothing for any of them to butt up against.  This is how I did it:

 

First I installed a small "alignment pin" on the bottom of the nose cowl:

 

 

That pin engages a slot on the inside of either bottom panel:

 

 

Installed it looks like this:

 

 

Once one panel is located, then the other three are easily located.

 

This shot shows that without a doubt, a panel (or all of them) can be removed to show the engine - a goal of mine since I started this build:

 

 

Lastly, for the "it's beginning to look like a Corsair" file, this shot:

 

 

 

I have sent off a 3D print order, and the parts will be in my hot hands in a week or two.  Included in that order are corrected cowl flap details, and once I have them I can proceed on the very difficult cowl flaps.   In the mean time - I dunno, I suppose I will finish skinning the wing upper surfaces.....  

 

Thanks for looking in folks.

 

 

 

Edited July 30, 2022 by JayW