Fat Man (F31) at 1/24

[johnbergstromslc]

I see you are using Google Sketch Up as your design program. What are the best design programs to use for papermodeling?

[nando]

Originally Posted by johnbergstromslc

I see you are using Google Sketch Up as your design program. What are the best design programs to use for papermodeling?

As you can see in my signature in the "Sopwith SwalloW" thread, everything began from the need to use software free or cheap and my research had this main target. I tried Rhino (the trial version) and it's a professional software used by many professional designers also in this forum, but it's very expensive, at least for me. I tried Blender: it's free, very complete, with embedded the unfolding functions. I tried Metasequoia: it's free, complete and well integrated with Pepakura. But I haven't a good feeling with both, Blender and Metasequoia. The first is very complex and oriented at the animation and organic subjects. The second isn't friendly when you manage the threedimensional object.
With SU, despite it isn't so easy to pass from the project at the paper model, also using Pepakura for unfolding the parts, I have a good feeling. But You have to consider that when You reach some result with some tool, this tool tends to become the favorite and the most useful, more and more you accumulate practice and knowledge.
I think you have to decide which sort of design you want to realize (simple, complex, professional), then You have to try the software you think is better for the purpose and finally choice and practice, practice, practice ....
I hope this was useful for you, but everyone has his preference and his target, so the final choice is yours.

Best, Nando

[johnbergstromslc]

Originally Posted by nando

As you can see in my signature in the "Sopwith SwalloW" thread, everything began from the need to use software free or cheap and my research had this main target. I tried Rhino (the trial version) and it's a professional software used by many professional designers also in this forum, but it's very expensive, at least for me. I tried Blender: it's free, very complete, with embedded the unfolding functions. I tried Metasequoia: it's free, complete and well integrated with Pepakura. But I haven't a good feeling with both, Blender and Metasequoia. The first is very complex and oriented at the animation and organic subjects. The second isn't friendly when you manage the threedimensional object.
With SU, despite it isn't so easy to pass from the project at the paper model, also using Pepakura for unfolding the parts, I have a good feeling. But You have to consider that when You reach some result with some tool, this tool tends to become the favorite and the most useful, more and more you accumulate practice and knowledge.
I think you have to decide which sort of design you want to realize (simple, complex, professional), then You have to try the software you think is better for the purpose and finally choice and practice, practice, practice ....
I hope this was useful for you, but everyone has his preference and his target, so the final choice is yours.

Best, Nando

I actually like to work in chipboard (that 'cardboardy' stuff at the back of a legal pad) at 22 mils thick. I would like to find a program flexible enough to make allowances for the thicker material I like to use.

Any programs better than the others in this respect?

[nando]

I'm not sure to well understand which kind of material you are talking about and how thick is it (22 millimeters?!), but at the end it is a matter of thickness.
In SU i solved the problem in the way that i described in this post, so, you have to define the scale of the model and the thickness of the material you'll use and then calculate how width the gap between the parts of your model. You must keep in mind that in SU I'm designing the model at the dimension of the real thing.
In the other softwares I don't know how we can solve the issue.

In the mean time i'm working on the textures and I did and re-did them many times, because i'm still not satisfied of the result. For well understand how the the colors are distributed, i used the fethure of SU that allows to match a photo with the model, and here a short screen-capture shows the result.



It seems to me that the model is good enough and now i have the information i need about the paint schema.

Best, Nando

[cdavenport]

That is so cool! I see you have to erase the tire. Ain't technology grand?

[johnbergstromslc]

Originally Posted by nando

I'm not sure to well understand which kind of material you are talking about and how thick is it (22 millimeters?!), but at the end it is a matter of thickness.
In SU i solved the problem in the way that i described in this post, so, you have to define the scale of the model and the thickness of the material you'll use and then calculate how width the gap between the parts of your model. You must keep in mind that in SU I'm designing the model at the dimension of the real thing.
In the other softwares I don't know how we can solve the issue.
Best, Nando

It's the stuff at the back of a legal notepad. 22 mils (1 mil =.001"=.0254mm) is equivalent to 5 sheets of regular paper, or 3 sheets of cardstock. Probably a lot thicker material than most people on this forum work with....

[cdavenport]

You have to be careful with measurement units. No one on the forum uses mils. I, too, was confused. I missed important notation and saw only "mm." Funny how the mind works.

[alfadoc]

Very nicely done. Nice smooth egg shape; did you burnish the rings at all to smooth the curve?

[nando]

No more to show at this moment, but the work is still on the way, despite some healt problem i had yesterday that stopped me.
Meanwhile i'm looking around for more information.
About the function of the hopper on the tail of Fat Man i found this note in the book ""Nuclear Weapons of the United States":

"[...] Although the basic Fat Man model "1561" worked properly, it was not a very well designed weapon. Both it and the Mk-III stockpile model (stockpiled in 1945) were
aerodynamically unstable at high speeds, causing the weapon to wobble (a combined yaw and rapid rotation) during its drop-terminal velocity of the weapon was .9 to .95 Mach.
To keep this at a minimum, during the war, drag plates were installed in the tail box to slow the weapon down. These plates were not always reliable, however, an example
being the post-war Crossroads Able nuclear test. In this test it is believed one of the plates either collapsed or was lost in the drop. The resulting wobble caused the bomb
to miss the target battleship by over 1,000 feet.
Following the war a major effort was made to rectify this problem. This effort involved extensive wind tunnel tests conducted by John Northrop of Flying Wing fame.
[...]
The Aerodynamic instability was just one problem with the earlier Fat Man models. Because they were hand made at Los Alamos, it took an average of two days for a 39 man team to assemble one Mk-III. In addition, following assembly the bomb could only remain combat ready for 48 hours. After this, it had to be partially disassembled to replace or recharge the batteries that powered the bomb's fuses. It was because of these problems, and a shortage of nuclear material in 1947, that development began on an improved bomb called the Mk-IV. "

It confirms my suspects about the instability issue of Fat Man model.

There's another interesting note about the relationship between the first atomic bombs models (Thin Man, Little Boy and Fat Man) and the Grand Slam/Tallboy english bombs.
In the Wikipedia chapter about "Silverplate" (code name for the aircraft modification project for the B-29 Superfortress to enable it to drop an atomic weapon) we can read:

"the Fat Man shapes exhibited significant wobble characteristics, apparently due to poor workmanship and misalignment of the tail fins. All three bombs had also failed to release immediately, frustrating calibration tests. A fourth testing flight resulted in the premature release of a Thin Man shape while the B-29 was still en route to the test range and severely damaged the aircraft. The modified glider mechanisms had apparently caused all four malfunctions, because of the weight of the bombs, and were replaced with British Type G single-point attachments and Type F releases as used on the Lancaster to carry the 12,000 lb Tallboy bomb."

I will answer to your questions as soon as I'll solve my "instability" issues.

Best, Nando

[cdavenport]

Get well, Nando!