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2 hours ago, Nightinggale said:

In real life, steel and aluminum weights the same when used for construction.

If that were true, fewer than 100 percent of airplanes would be mostly aluminum. The yield strength of aluminum is lower than steel, but the density is much lower than steel. Built to the same strength, especially in the purely elastic domain, aluminum parts are far lighter than steel equivalents.

Adding density to the game would mess up many things though. (110 kg/tile liquid lead would flow though 10kg/tile water pipes. Actually, that sounds awesome.)

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I think the contradictions in this thread are based on simplification. The strength of a metal is more than just one score. Take for instance iron. Say you want to build a building and you want iron pillars. You buy some iron pillars, install them and they work. Now you want to build a railroad. You get the same type of iron and build the rails, but then the rails keep cracking. The reason is the weight goes from the wheel, down through the rail and then sideways to the sleepers. The stress compresses the iron while traveling down, but the point where it turns from vertical to horizontal, it will actually stretch instead of compress and "pillar iron" has horrible stretching abilities and is likely to crack under such load. It's also likely to crack due to vibrations. The solution is to use a different type of iron, one which can handle the stretching and vibrations. This type however isn't well suited for pillars because it has lower compression strength and a pillar of the same size would be able to support less weight. Metal can have hugely different properties even when comparing two types of the same metal.

Another interesting material to look at is concrete. It has great compression strength, but no stretching. Steel is added to handle the stretching and is usually added as a net because a net is cost effective for stretching, but doesn't aid compression. The combo results in a very strong material. Steel is used because it has virtually identical thermal expansion as the concrete. If a temperature increase means the block is 3% longer, it would be beneficial if the metal on the inside will grow around 3% and not just 1%. It helps to prevent cracking from the inside.

Around a hundred years ago, some guy (Mr Bentley I believe) looked at car engines and noticed the pistons were made of steel. Since pistons start and stop all the time, he figured that it lost a lot of energy on braking and accelerating the pistons. He made aluminum pistons to match the same size and now he had reduced mass, but still the same surface area for the fuel to deliver pressure on. The result was a car with an agile engine, which won any race it was in. Granted he also did some other improvements, but the pistons were a major part of it. This means in some cases the shape is more important than the strength even for components under great force.

Now if we go back to planes. First of all I believe they use the "carbon fiber of aluminums". It would be reasonable to assume they pick high grade metal, which has the best strength to weight ratio and as such is lighter than the aluminum we can buy in the hardware store. Secondly they have a huge surface area compared to the weight. Most of the surface area is about shape rather than strength, making aluminum a good choice. Thermal expansion makes it wise to use the same metal on the surface as on the inside. Planes pretty much just hit air meaning the stress of each part can be calculated fairly accurately and they can be designed accordingly.

Surface vehicles live in a different world. Weight is less important (not unimportant, just less important). If you want to buy a 1-3 car train for a rural railroad, you will notice the existing mass produced trains from the big train factories all weight around the same regardless of steel and aluminum use. They have to pass the same crash tests, hence they end up with the same weight when using standard metals (not crazy expensive alloys). It is possible to find exceptions to this rule, but that's not for mass produced open market trains. The special cases are stuff like crazy heavy steel trains ordered by politicians who have to be reelected in iron mining towns or (mainly historical) acceptance of aluminum trains being less safe because low speed and no heavy trains on the line or whatever arguments people can come up with for accepting saving money on safety.

In short, saying aluminum has the same strength as steel when using the same mass is valid, but at the same time due to the complexity of the issue, steel and aluminum aren't interchangeable.

13 hours ago, Xenologist said:

In real life, aluminum is a good, lightweight strong material. Why don't we use 1/2 the amount of aluminum per building (Only the refined metal)

Right now the code assumes all buildings to have the mass set by BuildingDef. Adding conditional mass will make calculations more complex and I'm not a huge fan of making temperature exchange related calculations more complex than they already are.

I'm not against the idea as such for gameplay value. In fact it could be interesting if the user is correctly informed like it's printed -50% mass used for construction just like overheat temperature modifiers. I'm against making temperature calculations slower while people in other threads write about the game being too slow as it is right now. I don't value this idea high enough to risk another slowdown.

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The aluminum chassis of an airplane is very much a highly engineered load bearing device. Hitting wind might sound like it's no big deal. Until you realize the quarter million pounds of thrust provided by the 747 jet engines can launch an entire family of brachiosauruses directly skyward.


Fig. 1

The point I made was simple. No need to dance all around it. When engineers are highly restricted in terms of weight (airplanes, the ultimate example), they choose aluminum over steel.

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58 minutes ago, nakomaru said:

The aluminum chassis of an airplane is very much a highly engineered load bearing device. Hitting wind might sound like it's no big deal. Until you realize the quarter million pounds of thrust provided by the 747 jet engines can launch an entire family of brachiosauruses directly skyward.

1 hour ago, Nightinggale said:

Planes pretty much just hit air meaning the stress of each part can be calculated fairly accurately and they can be designed accordingly.

I didn't say (or at least didn't intend to say. Admittedly I wasn't clear) that air resistance is nothing. The Concorde had a pretty toasty external temperature due to friction against the air. In fact not boiling the fuel in the wings was a design goal.

What I meant is that planes have predictable forces, both in direction and intensity. Sure going max speed pulls wings backwards. Max engine thrust have a significant force forward. My point is that the directions are known. The engine thrust will never be sideways. It will only be reversed when reversing the exhaust, which is another predictable stress to the engine mount and wing attachment. Not only is the wind resistance predictable, it's also uniform. It's not like one part of the wing is moving forward at full speed and the other end of the wing is reversing at the same speed. I could carry on with other parts of the plane, but it won't change the point. Whatever the plane is doing, the forces have non-random directions.

All this combined means it's possible to construct a very strong internal structure, which can handle the expected loads. I imagine the connection between engine mounts and wing attachments would be fairly strong despite from the outside looking like the rest of the wings. This has to be strong. There is no question about that. Another part is controlling the air flow for minimum air resistance and control lift. This can add a lot of surface area, which isn't part of the load bearing system. Such locations wouldn't need strength and just have the needed shape. In fact if a hole is located on a plane, mechanics look up the expected stress of the part in question. If it's purely surface shape and doesn't matter for the forces at work during flight, then a short term repair can be made with tape (unsurprisingly special tape). This means it's possible for passengers to look out the window and see the engine being taped together... or at least that's what it looks like. The tape is purely there for reducing wind resistance.

Aluminum is king when it comes to providing the correct surface shape in locations where strength isn't critical. If strength is very much required, odds are that pure aluminum isn't used, but rather aluminum alloys, which mixed with other metals provides a lot of strength without increasing the weight significantly. Such alloys can be allowed to be crazy expensive because the extra price will be nothing compared to saved fuel costs from the reduced weight.

Compare this to a car. Imagine two cars crash into each other. One of them rolls over and possibly rolls down a hill. A lot of forces are at play where and they are much less predictable. This means unlike planes, cars will not be able to have strong and weak points. Without locations, which can intentionally be made for shape rather than strength, the weight boost from aluminum is less significant. Without the budget for expensive lightweight alloys, aluminum becomes gains a worse strength to weight ratio. The result is that cars doesn't gain the weight bonus from using aluminum that planes do. There are specific locations where shape and low weight is important and aluminum is used because it's "strong enough". I'm thinking pistons, wheels/suspension etc.

I'm not saying there aren't any aluminum cars. You can likely find some on the racetrack. There just aren't that many on the roads. If aluminum would lower the fuel consumption for the family car, the cars would be all aluminum because that would give a better eco rating. Since we still see steel cars and they are fighting to meet environmental requirements (sometimes they even have to cheat to meet requirements), aluminum doesn't seem to be the wonder metal to solve all weight problems.

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