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

[Woody V]

8 hours ago, JayW said:

annealed material is soft and without any real strength.  That is probably the basic condition of any aluminum alloy.  It must be heat treated to give it the kind of strength required for aircraft structure. 

Depends on the alloy. The most common alloy used on the aircraft I worked on in the 60s was 2024 which is alloyed with copper and was available annealed if you needed to make something like a leading edge rib. Heat treating it is relatively simple, just heat it to a certain temperature for a certain amount of time. 2024-0 is annealed and 2024-T3 is heat treated. There is also pure aluminum 1100 that is dead soft that can't be heat treated. The 1100 I ever saw was used to make a certain kind of rivet. 

[patricksparks]

11 hours ago, JayW said:

Yes, and yes.  I have a couple things I am going to try before I resort to annealed sheet.  This particular panel has so little amount of double curvature, I thought I'd get away with it.  Next post I'll describe.  

 

 

 

 

Kevin - annealed material is soft and without any real strength.  That is probably the basic condition of any aluminum alloy.  It must be heat treated to give it the kind of strength required for aircraft structure.  I do not know of a way to take annealed material and heat treat it to a stronger condition in a home environment.  I believe it is a complicated process and done at foundries or metallurgical facilities of some kind or another.  However, heat treated aluminum can be annealed by simply heating it, believe it or not.  Don't ask me how.  Peter C does it all the time with his heat treated litho, just by putting it to a gas stove flame.  Maybe that is what you are thinking of?

 

I have a big roll of annealed aluminum sheet .005 inch thick.  I also have two kinds of strong heat treated aluminum sheet.  One is the same litho Peter uses (he sent me a batch a while ago); the other similar.   The heat treated stuff cannot be used for complex curved stuff like wing tips or fillet fairings - that is for the annealed stuff.  But annealed material picks up every little blemish when worked - a dust mote, a hair, a small sliver, etc.  It also show the adhesive used to bond it, if the adhesive is thick at all.  And punching fastener head marks in it often results in holes, or at least the marks being too deep.  So it's best used only if you must.

 

I know from my past profession that all aluminum has basically the same stiffness.  Heat treated, or annealed - same stiffness.  The reason why annealed material bends and conforms is not stiffness related, but strength related.  To bend or deform either one - you just take the material beyond its ability to react a load until it begins to deform and not spring back.  That load is much higher for a heat treated material.  Plus, heat treated material is more brittle, and will fracture if deformed too much.  Annealed material - much more pliable, less prone to fracturing. 

 

So - these slightly compound curvature sheets - the heat treated stuff is about as pliable as paper (like not at all).  So it wants to wrinkle or buckle or pooch.  But so does the annealed stuff, if you are not taking it beyond its yield strength.  And trying to stretch it over a slightly compound curved surface doesn't take it beyond that stress.  So the problem  persists.  I am still going to get wrinkles or pooches.  But with annealed material, it locally responds better to burnishing and bashing.  So the wrinkles can hopefully be more effectively burnished out.  The penalty is a more messy looking panel with more blemishes. 

 

I don't know what I'm going to do yet.            

Looking great Jay !!!, when I was putting aluminum on my P-51 I ran into the same issues with buckling on the upper cowling, I made my masking tape templates , cut out my panels riveted them and the annealed only the portion where the buckling problem was occurring based on the failed parts previously attempted. I anneal the parts with a quick pass over the kitchen stove top burner(gas stove) doesn't take alot of heat to anneal the thin sheet stock !!!

Hope it might help.

Pat

[Oldbaldguy]

Hmmmm.  I think the problems you are having come from these parts on the 1:1 airplanes being stretched and/or molded to a permanent shape in dies and then trimmed to their final dimensions in a fixture.  The trimming to final dimension part is where your troubles come from.  You can’t replicate this by simply bending flat stock that has been cut to fit because, as you well know, it will stretch or crimp as you work it, throwing off your edge dimensions.  You then must remove material to relieve the kinks and ripples to make it fit properly.  Since we’re finding that a Corsair is one giant mass of compound curves with nary a straight line anywhere, yours is no easy task.  The good news is that you are dang near done with the really hard parts; the wings and such will be easy after this.  For your next project you might want to forego scratch building a Mustang, which is slab-sided enough but still has a fair share of compound curves, for something less curvy.  F-117 maybe?

[JayW]

5 hours ago, Woody V said:

Depends on the alloy. The most common alloy used on the aircraft I worked on in the 60s was 2024 which is alloyed with copper and was available annealed if you needed to make something like a leading edge rib. Heat treating it is relatively simple, just heat it to a certain temperature for a certain amount of time. 2024-0 is annealed and 2024-T3 is heat treated. There is also pure aluminum 1100 that is dead soft that can't be heat treated. The 1100 I ever saw was used to make a certain kind of rivet. 

 

All correct Woody.  Of course the 7000 series alloys became more common due to superior strength/weight.  However, more prone to fatigue cracking....

 

What has always bewildered me, and perhaps a source of Kevin's confusion as well - To get a high strength temper, annealed alloy must be "heat treated".  Yet, to convert a heat treated piece of aluminum back to annealed, it must be heated as well.  WTF!!  Any metallurgist worth his salt can explain this, but I am not one.  Could google it I suppose.  Do you know?

[JayW]

1 hour ago, Oldbaldguy said:

For your next project you might want to forego scratch building a Mustang, which is slab-sided enough but still has a fair share of compound curves, for something less curvy.  F-117 maybe?

 

Ha!  Nope, gonna be a Mustang.  Airscale Peter managed to do a near flawless skinned 1/18 P-51C (Lope's Hope), as most of us know.  So it can be done!  I'm gonna get over this one way or another....

[Maybach_man]

You would need a miniature shrinker/stretcher to form the edges correctly...... 

[airscale]

On 2/27/2023 at 6:11 PM, JayW said:

 

Sure was!  And it did go better than feared.  The aft crown panel on the turtledeck was a disappointment though.  Was wondering what you thought of that (excessive compound curvature).  How do you think you would have tackled it?    

 

 

more amazing skinning work Jay - hats off to you

 

you ask how I would have done that panel (&it looks fine, don't beat yourself up about it..) so let me chime in. It's the same approach for all compound curve panels - and as you found out, that is not just super curvy fairings, but ANYTHING that is not truly linear. I would use the litho I sent (I don't know what you call it annelaed or not) and if possible made a tape template and all that good stuff, but when it came to laying it down I would have annealed it over a stove - as Patrick says, this can be sort of localised to where the compound bit is if possible. Now the bit I think that is the difference is I am not scared of it rippling, wrinkling or the undulations from the glue beneath as all of that can be either beaten or sanded away. It is hard to take really coarse paper to it and it takes cleaning up with ever smoother grades, but all of those blemishes can be sanded, then polished away. Any rivet work done beforehand can be redone as they leave winess marks however feint and adjacent panels can be protected with tape. A wire wool at the end and it will look the same as the panel next to it. My advice is sometimes you have to take the hit and just use heated litho - it needs working, but you will find you won't have the same problems (maybe a new set though )

 

Peter

[Woody V]

18 hours ago, JayW said:

Yet, to convert a heat treated piece of aluminum back to annealed, it must be heated as well.  WTF!!  Any metallurgist worth his salt can explain this, but I am not one.  Could google it I suppose.  Do you know?

 

Other than applying heat, it's what happens after that makes the difference. My memory is a bit sketchy after almost 60 years, but as part of my training during USAF tech school we had to make a reading edge rib with -0 and heat treated and I still have the one I made.

Annealing: Annealing is done at 750°-800°F for at least 2 hours at temperature, followed by slow cooling in furnace.
 

Heat Treating is a bit more complicated: 2024 is an age-hardening aluminum alloy and responds to heat treatment to accomplish the strengthening (aging). The T4 condition is attained by a 920°F heating followed by a cold water quench and aging at room temperature. T6 is attained by the same 920°F and quenched followed by a 375°F for 10 hours and air cooling.

[Derek B]

22 hours ago, airscale said:

 

 

more amazing skinning work Jay - hats off to you

 

you ask how I would have done that panel (&it looks fine, don't beat yourself up about it..) so let me chime in. It's the same approach for all compound curve panels - and as you found out, that is not just super curvy fairings, but ANYTHING that is not truly linear. I would use the litho I sent (I don't know what you call it annelaed or not) and if possible made a tape template and all that good stuff, but when it came to laying it down I would have annealed it over a stove - as Patrick says, this can be sort of localised to where the compound bit is if possible. Now the bit I think that is the difference is I am not scared of it rippling, wrinkling or the undulations from the glue beneath as all of that can be either beaten or sanded away. It is hard to take really coarse paper to it and it takes cleaning up with ever smoother grades, but all of those blemishes can be sanded, then polished away. Any rivet work done beforehand can be redone as they leave winess marks however feint and adjacent panels can be protected with tape. A wire wool at the end and it will look the same as the panel next to it. My advice is sometimes you have to take the hit and just use heated litho - it needs working, but you will find you won't have the same problems (maybe a new set though )

 

Peter

 

Good advice Peter. I basically use the same technique (minus the annealing) to apply normal aluminium kitchen cooking foil to my models, so it works equally well with litho plate or foil! Looks like you have definitely got the hang of this technique Jay, well done.

 

Derek

[daHeld]

Don't worry Jay, you did a great job with this panel. It looks good.

When I use aluminium over compound curves, I often use it over-scale, so that the panel is bigger than it needs to be. I then stretch it over the template until it adheres to the curvature without gluing it on. When possible, I use some clamps to hold the panel in place. That way all the wrinkles will be cut away at the last stage. 
I then apply the masking-tape-pattern and cut the panel to the right dimensions.
I mostly use annealed aluminium, the other stuff is too stiff for my liking.

[JayW]

Thanks for the encouraging comments!  The opposite panel was next.  I decided to just try again with the same litho material (not annealed material), but attempt to roll a bit of double curvature into the part, merely by rolling it one way, turning it 90 deg, and rolling it that way.  Several times.  Was hoping that would give it a touch of "bulge".  Also I re-sequenced the order in which I CA'd down the edges. 

 

The detail panel waiting for the installation wrestling match, on the saw horses of course:

 

   

 

It actually laid down a bit better than the LH side panel I was grousing about last post, for reasons I will never know for sure.  Although the fight was just as intense.  BTW - the saw horses are scaled accurately for a typical saw horse.  Gives you an idea of the size of this panel.  

 

Here I show it glued down, after about a half hour of knock down drag out fighting.  That was last evening.  This morning I found an edge that popped back up sometime during the night.  "Ping!"  So I CA'd it back down.  Lotsa stresses in that panel; hope it stays put now.  You also see a couple of belly panels, which were alot easier:

 

 

 

Pan back some to see the belly and the tail gear bay:

 

 

Next up - the turtledeck crown panel just aft of the cockpit.  This:

 

 

On the model, this:

 

 

Note this panel has the aft track slot for the sliding canopy.   I am actually going to use that as is; it works just fine and is in the right place.  Note also it has an indentation for the aft end of the canopy to fit into.  That is not really accurate, but I think I am going to use it anyway.  The challenge is skinning it - I cannot skin the indented area; otherwise the canopy will not fit properly when closed.  Guess I will just feather the edges of the aluminum at the edge of the indentation and hope for the best.  I think it will be OK.

 

Along with this, it is time to lay out the aft end of the canopy - the upper armor plate, the head rest, and the pilot's seat installation.  I have started the Rhino layout:

 

  

 

Once done, with parts fabricated and installed, the way is paved for joining the mid/aft fuselage with the long-dormant forward fuselage.  Huge milestone, not that far off!  

 

For those of you wondering when I will skin the fin, I am wondering too.  That fin tip extension I have to add is going to be uber-fragile so I want to delay it as long as I can.  It will be done prior to the fuselage join though, as will the h/stab tips.    

 

Edited March 4, 2023 by JayW

[LSP_Kevin]

An awesome battle to witness, Jay, but you appear to be prevailing.

 

Kev

[daHeld]

If you put in a few scale clecos, no one will believe you that this is a model panel... 

[JayW]

21 hours ago, daHeld said:

If you put in a few scale clecos, no one will believe you that this is a model panel... 

 

It's the saw horses!  I am going to have to gussie them up to look more realistic.   Yeah - there is a certain similarity making individual skin panels that makes them look real in aluminum.  But true skin panels were assemblies that had frame segments and stringers as well as the skin detail - rivetted and/or spot welded.    

[JayW]

Let's see where were we....fuselage skinning!  It's done!  

 

First, a new mounting fixture for the Corsair fuselage:  

 

 

Out with the old, in with the new.  This simple platform allows me to orient the fuselage in a vertical direction, in a fairly stable way.  It plugs into the engine aft section:

 

 

It's near term purpose is to help with the forward-most skin panels on the mid-fuselage, which must match very closely the aft end of the already completed forward fuselage.  Like so:

 

 

 

Just cannot get over how large this model is - it dwarfs the 1/32 scale Corsair to the left.  

 

So on to the large side panels.  This time I chose to make them out of soft annealed sheet in the hopes that they would behave better with the compound curvature.  And they did for the most part:

 

 

 

Great care had to be taken to keep working surfaces free of any debris of any kind.  

 

Installed and final trimmed to the forward fuselage:

 

 

If you sense that is a big victory, you would be correct!  I had been handwringing over this join for months and months.  The other side:

 

 

Two reasons for concern on this join at the Sta 186 manufacturing splice - skin edge matchup (little to no gaps) and painting.  The first concern is no longer a concern - the edge match up is good.  Painting - gonna be a giant challenge made bigger because of paint lifting issues in this area. 

 

Note the crown panel with the aft canopy track slot is there too.  That panel behaved well - a pleasant surprise:

 

 

 

Another view:

 

 

The canopy work is going to be a real hoot - it's on the radar.

 

To finish off the mid/aft fuselage skinning, the last belly panel had to be made and installed:

 

First step is to get the periphery from tape and pencil marks:

 

 

The new platform helps alot here....

 

And glued down and trimmed:

 

 

Being a smaller panel, I used the preferred heat treated litho - probably not the right choice because it fought me all the way trying to get it to lay down.  It's down though.  Another:

 

 

You can hopefully see that the entire fuselage is now skinned.  What a journey.  Still gotta do the fin and the stab tips - but no problem.  Another thing though needs to get done first - the aft end of the cockpit.  The seat support, seat, seat belts, armor plate, and head rest.  Tricky stuff especially the seat support, so I am modelling it in Rhino first.  It's progressing:

 

 

 

I believe next post is going to show some of that aft cockpit stuff.  Take care LSP'ers.

 

 

Edited March 9, 2023 by JayW