tma1
New Member
Posts: 3
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Post by tma1 on Dec 8, 2018 22:19:21 GMT
It seems to me that there is a problem with the calculation of the tanks. Simple example: tank material is aluminum-copper-lithium and holds 100 t of kerosene, then the tank has a dry weight of 3 t at a hight to radius ratio of 20, but a massive 29 t at a hight to radius ratio of 0.05. Where does this extreme difference in dry weight come from, although the volume stays the same?
If I create tanks with larger diameters, for example simulate the LH2 tank of an ET of the Space Shuttle (aluminum-copper-lithium, diameter 8.4 m, length 29.6 m, holds 106 t H2) is formed in CDE a tank with a length of only 18 m, but a hefty 51 t. It is much shorter compared to the original, but incredibly heavy. The entire ET weighed only 26.5 t empty (not just the LH2 tank, but complete with LOX tank, Intertank, isolation and so on).
In general the tanks seem very heavy, but the larger their diameter becomes the worse the ratio becomes.
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Post by bigbombr on Dec 9, 2018 8:39:11 GMT
The game tries to make tanks cylindrical. Shorter tanks mean the flat sides are proportionally larger (convex shapes are stable under pressure, flat shapes have to resist pressure with their yield strength). This means that long tanks have small flat parts and thus don't need to be as thick. For the highest mass ratio's, try to maximize aspect ratio and pick a material with a high yield-strength-to-density ratio (stock: Vanadium Chromium Steel, community materials mod pack: High Grade Epoxy Carbon Fibre Composite, future propulsion pack: some flavor of carbon nanomemes).
I'd like it if we could get cylinders with domes as end caps (rely purely on tensile strength, would mean even lighter tanks), toruses and spheres for propellant tanks.
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Post by AtomHeartDragon on Dec 9, 2018 10:28:27 GMT
I think that by default tanks should be composed of two hemispheres, with optional cylinder in between - so spherical or capsule shaped depending on the aspect ratio.
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tma1
New Member
Posts: 3
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Post by tma1 on Dec 9, 2018 16:10:05 GMT
In reality, propellant tanks always consist of two hemispherical end pieces with a cylinder in between, so it is also displayed graphically in CDE.
Does that mean that the calculation does not correspond to the graphical representation, but is calculated with completely flat end pieces?
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tma1
New Member
Posts: 3
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Post by tma1 on Dec 9, 2018 20:35:36 GMT
The game tries to make tanks cylindrical. Shorter tanks mean the flat sides are proportionally larger (convex shapes are stable under pressure, flat shapes have to resist pressure with their yield strength). This means that long tanks have small flat parts and thus don't need to be as thick. For the highest mass ratio's, try to maximize aspect ratio and pick a material with a high yield-strength-to-density ratio (stock: Vanadium Chromium Steel, community materials mod pack: High Grade Epoxy Carbon Fibre Composite, future propulsion pack: some flavor of carbon nanomemes). I'd like it if we could get cylinders with domes as end caps (rely purely on tensile strength, would mean even lighter tanks), toruses and spheres for propellant tanks. Simply choosing a different material does not solve the problem. Even a tank made of VCS becomes ridiculously heavy with a larger diameter. In addition, in reality, in a steel alloy, you would probably design a balloon tank to get a really lightweight tank (like the old Atlas, or the Centaur upper stage), but the possibility does not exist in CDE. |
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