Answers to several of yesterday's comments on hull thickness.
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Mark Cook Writes:
> Subject: (1927) Pigs,...er...Windshields in Space!!
> In subject (1922) Rob Dean [email removed] writes:
>> (Windshield analogy deleted)
> On the other hand, everybody MIGHT have bulletproof glass in their windows
> if they ran the risk of breaking one and SUFFOCATING before they got to
> the next body shop. :-)
Well, maybe so. Of course, if your car was properly compartmentalized and
your windshield was self sealing...
> Sorry, Rob. I couldn't resist.
Feel free. I'll do the scut work as soon as we're finished hashing out
the rationalizations.
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"T. L. Hayes" [email removed] writes:
> Subject: (1932) Re: Rob Dean's Posts
> From: "Robert S. Dean" [email removed]
>> As two sample calculations, I considered a cylindrical pressure vessel
>> capable of containing one standard atmosphere of pressure (14.7psi) <Sorry
>> about the English units--I'm an engineer>. I considered it to be made of
>> mild steel, with no special alloys, etc, giving a yield strength of
>> approximately 50,000psi. I also ignored end cap effects. I decided that a
>> safety factor of 2.5 was sufficient, so I put in a value of 20,000psi as
>> the maximum allowable stress in the skin. At those conditions, a cylinder
>> 10ft in diameter would need a wall thickness of less than 0.05 inches, which
>> is less than Traveller armor value 1. A 100ft diameter cylinder (ship
>> sized) would require a wall thickness of 0.44 inches, between Traveller
>> armor values 3 and 4. 50,000psi mild steel would be the equivalent of
>> armor type A (soft steel).
> I have not designed many ships but I don't see how you go from thickness to
> armor value (or vice versa). Again, I have not designed but maybe half a
> dozen ships but if I understand things correctly a 100 ton ship occupies a
> volume of 1350 cubic meters and has a mass of 40 tons. Multiply by 33 for
> an armor factor of 40 and by 1.25 for soft steel and you get 1650 tons for
> weight (mass). I believe a minimum surface polygon enclosing the volume
> listed would be a sphere 685.6172 cm in radius. I don't know the density
> of steel but the specific gravity of iron is about 8 gm/cc (which means
> the density of steel is about the same?). If you assume a mass of
> 1,650,000 gms and calculate the thickness of the skin of the sphere you
> find it to be 0.0349 cm or about 0.0137 in. If the density is greater
> than 8 gm/cc then the thickness will be even less. Somebody check these
> numbers, you know how bad I am with numbers!
> Assuming no miscalculations, wouldn't this coupled with your calculations
> mean that the hulls should have a higher armor rating?
I will have to admit that I didn't do the calculations that way, although I
probably should have to be valid. Like any good engineer, I merely looked
the answer up in my handbook, which in this case is the design system from
Striker, where each armor value was equated to a certain thickness of hard
steel. To get an armor value, you took the thickness, multiplied it by a
fudge factor for the material, and then compared it to the table. So that's
where those numbers came from. If somebody would like to do a surface area
to weight correlation for each of the basic configurations, it might be
handy. In Striker, everything was a rectangular block, so when you mult-
iplied the face dimensions by the armor thickness, you always got a valid
weight.