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

[JayW]

38 minutes ago, Oldbaldguy said:

I would expect that off-center or less than optimal arrested landings would put some pretty violent torquey side loads on the 288 bulkhead at the tailwheel attach points.  Same with a wonky landing that ends up in a ground loop or something similar.  So the truss would help transfer those loads past the gap in the structure left by the wheel well opening, taking the place of the fuselage structure that isn’t there.  Did I get that right or miss it entirely?

 

Ya missed it entirely big guy!  Any side loads from the tail hook would transfer into the gear itself, which is what the hook attaches directly to, and from there transfer into the Sta 288 bulkhead and forward where the inertia of the aircraft would try to react (not aft).  Any fuselage structure aft of the 288 bulkhead wouldn't see it at all.  BTW - the gear attach fittings have some very stout back-up structure going forward for those big arresting hook loads, off center or no.  If the hook attached to the fuselage itself, aft of the cutout (like the Hellcat), then what you say would be true.

 

It's gotta be fin/rud side loads, and the torque generated by same (since the total load center would be well above the fuselage centerline, imparting a twisting moment).   The Corsair aft fuselage has a long opening on the bottom where the tail gear doors are.  Push hard sideways on the fin (which is directly above the cutout) at its mid span, and an unreinforced fuselage is going to probably we a bit wimpy, and twist a bit if not alot.  That truss would stiffen it up nicely.   However - we are not privy to the stress notes from the Vought analysts back in the 1940's!             

Edited November 16, 2022 by JayW

[Oldbaldguy]

14 minutes ago, JayW said:

 

Ya missed it entirely big guy!  Any side loads from the tail hook would transfer into the gear itself, which is what the hook attaches directly to, and from there transfer into the Sta 288 bulkhead and forward where the inertia of the aircraft would try to react.  Anything fuselage structure aft of the 288 bulkhead wouldn't see it at all.  BTW - the gear attach fittings have some very stout back-up structure going forward for those big arresting hook loads, off center or no.  If the hook attached to the fuselage itself, aft of the cutout (like the Hellcat), then what you say would be true.

 

It's gotta be fin/rud side loads, and the torque generated by same (since the total load center would be well above the fuselage centerline, imparting a twisting moment).   The Corsair aft fuselage has a long opening on the bottom where the tail gear doors are.  Push hard sideways on the fin (which is directly above the cutout) at its mid span, and an unreinforced fuselage is going to probably we a bit wimpy, and twist a bit if not alot.  That truss would stiffen it up nicely.   However - we are not privy to the stress notes from the Vought analysts back in the 1940's!             

Got it!  Now I see it.

[JayW]

3 hours ago, brahman104 said:

You may even want to resort to some pewter sheet for those bits instead of litho.

 

Yikes!!  Wait - haven't you done some tough fillet fairings in annealed alum?  I know Peter has.  

[KiwiZac]

Incredible.

[JayW]

Continuing on with the tail wheel bay, when I looked into this sub-project, it looked to me that the tail wheel door operating mechanism was going to be the toughest challenge, mostly due to its chain drive:

 

 

Here is a picture found in the Erection & Maintenance manual showing the entire mechanism, including the chain and sprockets:

 

 

Recall I tried a "proof of concept" chain, with some limited success:

 

 

This effort convinced me to give it a try.  Earlier today, after many many hours of high-magnification toil, I completed the LH side mechanism, at least the chain drive portion.  Challenging it was.  But a steady hand and few interruptions helped me get through it.

 

A few details sitting on the bench:

 

 

 

And on the airplane:

 

 

 

 

Immediately apparent are the two chain segments, connected to each other by turn barrel links.  Note that part of the installation are the two specially designed bulged frames with bearings that support the "intermediate shaft".  The intermediate shaft has the larger of the two sprockets and a crank arm where the push rod is attached.  That pushrod's upper end attaches to the "upper shaft" already completed along with its support brackets on the Sta 288 bulkhead.  Also already installed were the two little fittings on the lower longeron, which provide the supports for the "lower shaft".  The lower shaft has the smaller of the two sprockets, and a crank arm where another push rod (not shown) connects to the forward tail gear door.  Note the lower shaft has a temp installed pin (0.030 inch diameter plastic rod) - I cannot permanently attach the lower shaft yet, otherwise it will prevent installation of the aforementioned "truss" structure.  It must be able to pivot out of the way for that to happen, further down the road.  It's another one of those sequencing difficulties. 

 

All this stuff was done using various plastic sheet and metallic tube stock; no help from 3D print.  It is a perfect example of a "Rube-Goldberg contraption".  God only knows why the tail gear doors are not actuated merely with gimbal ended pushrods attached directly to the tail gear carriage, as so many other aircraft have.  But I am very happy that I was able to represent it; I know of no other Corsair model where it is (the large scale on my Corsair makes it possible if only barely).  

 

Now, to do it again for the RH side.  It is soooo laborious, and soooo tiny.  I hope however that my viewers don't think this violates the "sometimes less is more" axiom.  I don't think so. 

 

 

Edited November 20, 2022 by JayW

[Jim Barry]

Amazing Jay. The master scratchbuilders are good at replicating a complex part (like a prop blade) using molds and resin to make the rest. I wonder if the other chains are a candidate? I’ve pressed things into polymer clay and then poured clear resin in the mold with some success and expect to do more along these lines ahead in my builds. Just a thought. 

[brahman104]

On 11/17/2022 at 3:36 PM, JayW said:

 

Yikes!!  Wait - haven't you done some tough fillet fairings in annealed alum?  I know Peter has.  

 

I certainly have Jay! And some tighter ones to come yet . They're quite the challenge, especially trying to get some of the smaller creases out..... I have no doubt from what I've seen you do so far that you're more than up for it, but Pewter may be a little more forgiving in certain situations. Whichever way you choose to go, I know it's going to look awesome!

 

Craig

[Thunnus]

More chain magic!  Always incredible watching you do what you do, Jay!

[Gazzas]

That's amazing work, Jay.

[Ironwing]

[scvrobeson]

Fantastic work on the chain drive. I would have thought maybe some scale motorcycle chain would work, but your scratch-work looks even better!  Keep it up!

 

 

 

 

Matt 

[JayW]

14 hours ago, scvrobeson said:

Fantastic work on the chain drive. I would have thought maybe some scale motorcycle chain would work, but your scratch-work looks even better!  Keep it up!

 

Matt - would have loved to do that.  But the smallest scale I could find was 1/12, and it was just too large.  

[JayW]

Soon, I will post some significant progress on the aft fuselage.  I await some long overdue 3D print parts for the tail wheel bay, and I may wait to update until I get those parts and prepare and install them. 

 

In the mean time, I am hand wringing a bit on the antenna masts.  First an abbreviated history of antenna masts for F4U-1A aircraft (not the birdcage versions), as I understand it:

 

All aircraft were manufactured with a tall antenna mast just aft of the engine accessories compartment, about 12 inches right of the aircraft centerline.  It appears to me the sole purpose of the mast was for attachment of the long aerial antenna that extended from the mast to the top of the fin, and then back down to the aft fuselage. This mast was notorious for breaking off, and many versions were designed, apparently none completely fixing the problem.  A picture:

 

 

Late in the -1A production run, another tall mast antenna was added aft of the sliding canopy on or near the aircraft centerline on top of the "turtle deck" (not to replace the forward mast, but in addition to).  This mast is associated with a change in radio equipment, I believe introduction of VHF equipment as opposed to MHF, and unlike the forward mast, appears to be an actual antenna.  And apparently this aft mast had a propensity to break off as well.  A pic:

 

 

Now, I have looked at every picture of VF-17 F4U-1A's I can find, and NONE of those aircraft have the forward mast.  There must have been a field modification kit that removed it and supplied a patch for the remaining hole in the fuselage panel.  So far so good - my #17 will not get the forward mast.  I'd love to know what the patch looks like....

 

What I have found in my VF-17 search is the presence of the aft mast.  Many many, but not all, VF-17 aircraft have the aft mast.  And, most if not all of those aircraft were manufactured BEFORE that mast was incorporated into the production lines at Vought.  So that mast and it's radio equipment were retrofitted by some sort of field modification kit.  Something that created a hole on top of the fuselage aft of the canopy, and added support bracketry to the Sta 218 bulkhead (which comprised the aft wall of the radio compartment behind the pilot seat an seat armor), that in addition to whatever wiring was added for the new radio receivers and transmitters, etc.  Even that picture showing VF-17 and the carrier going through the Panama Canal shows (although not very clearly) at least some of the aircraft with aft masts and not forward masts.  So they were there early on:

 

 

And I found more.   Many VF-17 aircraft have neither the forward nor the aft mast.  The aft mast has been replaced by a "whip" antenna, apparently as a result of those mast breakage issues.  The few pictures I have of Hedrick's #17 appear to show the absence of that aft antenna and in its stead a "whip antenna".  It is this "whip" antenna I am now interested in.  There is no Vought production drawing that shows it, so it must be another field modification.  For the life of me I cannot find any definition of it, except fuzzy pictures from relatively far away.  Look at this picture of Hedrick's plane:   

 

With all the branch debris in the background it is hard to tell, but I think there is a whip antenna there.  Certainly there is no mast.  Here, #29 is shown, clearly with a whip antenna:

 

 

Anybody have any information on a "whip antenna" for the F4U, where I can model something accurate?  If not, I might just have to add the aft mast.  At least I  know what it looks like.       

 

       

Edited December 9, 2022 by JayW

[Oldbaldguy]

As I am sure you already know, an antenna mast from that era and an antenna as we now know it are not the same thing.  An antenna mast is a nonconducting device, usually wood, used as a stand-off for a longish, flexible wire aerial used in certain radio installations.  The drawing you provide labels the aft antenna mast as an antenna mast, not an antenna or an aerial, so it, too, is a wooden thing bolted to a bulkhead.  There is even a small hole depicted at the top of the aft mast to which an insulator and wire aerial would be attached.  Since I see no provision to connect the mast to a radio, I would opine that it is just another mast.  While I certainly don’t know for certain if this applies here, it would be about this time that the FM radio came into its own in the US military.  Designed to be small, portable and efficient without the need for big cumbersome aerials, its initial use was direct verbal communication between armor and infantry units without the need for Sgt Rock to bang on the tank’s hatch to talk to the guys inside.  The Army FM radio school was actually housed at the Armor Center at Fort Knox, Kentucky, and not at the Signal Corps school early in the war.  I know this because my father in law went there for training.  Once demonstrated in Europe, this new technology (scraped together by five or six guys at Motorola, I think) quickly spread throughout the services, allowing just about everyone to talk to everyone else using these small, easily portable and effective voice radios.  I wonder if the whip antenna seen in the photos is part of an FM radio mod - or something similar for both comm and navigation - installed in the airplanes once the equipment became available.  As far as holes in the skin where the masts were, a simple skin patch riveted over it would work just fine if they bothered to cover it at all.

[JayW]

16 hours ago, Oldbaldguy said:

As I am sure you already know, an antenna mast from that era and an antenna as we now know it are not the same thing.  An antenna mast is a nonconducting device, usually wood, used as a stand-off for a longish, flexible wire aerial used in certain radio installations.  The drawing you provide labels the aft antenna mast as an antenna mast, not an antenna or an aerial, so it, too, is a wooden thing bolted to a bulkhead.  There is even a small hole depicted at the top of the aft mast to which an insulator and wire aerial would be attached.  Since I see no provision to connect the mast to a radio, I would opine that it is just another mast.  While I certainly don’t know for certain if this applies here, it would be about this time that the FM radio came into its own in the US military.  Designed to be small, portable and efficient without the need for big cumbersome aerials, its initial use was direct verbal communication between armor and infantry units without the need for Sgt Rock to bang on the tank’s hatch to talk to the guys inside.  The Army FM radio school was actually housed at the Armor Center at Fort Knox, Kentucky, and not at the Signal Corps school early in the war.  I know this because my father in law went there for training.  Once demonstrated in Europe, this new technology (scraped together by five or six guys at Motorola, I think) quickly spread throughout the services, allowing just about everyone to talk to everyone else using these small, easily portable and effective voice radios.  I wonder if the whip antenna seen in the photos is part of an FM radio mod - or something similar for both comm and navigation - installed in the airplanes once the equipment became available.  As far as holes in the skin where the masts were, a simple skin patch riveted over it would work just fine if they bothered to cover it at all.

 

Hi OBG.  First I will say that I am a real dummy when it comes to all things electrical in nature, including radios and antennas.  So I am perfectly willing to hear corrections for what I am about to state. 

 

I do know however that radios that operate at certain frequencies need antennas that correspond to the those frequencies.  Low frequency radio waves have large wave lengths, and high frequency radio waves have small wave lengths - anyone who remembers any basic science will know that.  Antenna size (or length) needs to correspond to wave length.  So long wave length radio waves need long antennas (like the long wire aerials we see on many WW2 aircraft).  And very short wave lengths need shorter antennas (like the whip or those contained in a mast).  As an aside, ETO fighter units used VHF (very high frequency) equipment exclusively (with the AN-104 antenna), and therefore removed the lower freq stuff supplied by the manufacturer (the Detrola's).  Hence, you do not see long wire aerials on ETO fighters even though many modelers model them.

 

Corsairs initially had radio equipment only in the MF range (medium freq, medium wave length).  Apparently, short AN-104 type masts were of insufficient length to work with those receivers and transmitters.  So that is why we see the long wire aerials on Corsairs and any other aircraft with low or medium wave length radio equipment.  Somewhere in the production run, the Navy went with VHF equipment, either in addition to or in place of the MF/HF stuff, and that is when that new antenna popped up.   

 

I did a little research in Aircorp Library and the web.  The aft antenna you see in the picture I provided is a AN-104 series VHF (very high frequency) antenna.   It is the same item as what we see on other US fighter aircraft - P-47, P-51, P-38, F6F to name a few.  That nasty looking spike mast that sticks up (or in the case of the P-38, down).  It has innards hidden inside it that must be the equivalent of the whip antenna.  BTW - cars have whip antennas in one form or another.   Here is a description of this antenna I found on the web:

 

 

This antenna mast has a cable attached to its bottom (not shown in the pic I supplied last post, but it shows up in a different view of the same drawing, and here in the parts catalogue (item #14):

 

 

 

The mast also has a small hole on its tip that allows for the rigging of the aerial wire for the MF/HF equipment; therefore it has a dual function.  In the absence of the forward mast, the aerial can be rigged to the aft mast instead. 

 

The Corsair's forward mast, versions of it which are effective for the entire production run, is simply a tower with a hole in its tip to rig the aerial wire.  As you state, it is not an antenna.  But the aft mast is.

 

Edited December 10, 2022 by JayW