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In a project I'm currently working on, the primary species stands at roughly 19 feet tall on average. While there are advantages and disadvantages to such a size, this scaling would present a number of logistical issues and whatnot.

On this species' home planet, the native organisms are likewise megaflora and fauna, for better and worse. What I am mainly concerned with today, though, is how the size of this species would present technological impairments in the field of engineering. Considering the square-cube law and many other laws of physics, how might more complex, modern devices such as cars, tanks, aeroplanes, or ships be affected by the weight and space occupied by their creators? Would some of these inventions even be able to function?

Edit: Based on my crude math, an adult of this species would likely weigh around six thousand pounds or so. I'm not sure how accurate this would be, however. The planet itself is slightly smaller than Earth, but the gravity isn't substantially lower. Additionally, this question is primarily focused on vehicles in specific.

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    $\begingroup$ You should highlight you are asking specifically about vehicles, otherwise this is going to get closed as too broad by people who miss that. $\endgroup$
    – John
    Mar 26, 2023 at 14:10
  • $\begingroup$ A 19 foot tall human is going to need help losing heat at normal room temperatures that 5-to-6 foot tall humans find comfortable. So the A/C in the car is going to need to be very robust. $\endgroup$
    – Boba Fit
    Mar 26, 2023 at 15:35
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    $\begingroup$ How heavy are they, a 19ft elephant has very different mass than a 19ft hominid. $\endgroup$
    – John
    Mar 26, 2023 at 21:39
  • $\begingroup$ Added weight, not sure how accurate it is but it should give a general idea. $\endgroup$
    – gumbo
    Mar 26, 2023 at 23:21
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    $\begingroup$ I feel like drones or any other RC vehicles would get an appearance a lot sooner; they would be an order of magnitude smaller and more efficient $\endgroup$ Mar 27, 2023 at 0:26

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There would be NO engineering limitations or difficulties. In fact, from one point of view, we've already solved this problem.

Assumption: I'm going to take your weight assessment at your word — but I don't believe it. Are we talking about elephants? I'm 5'10" and weight about 250#. Quadruple my height and linearly my weight would be 1,000#. Let's freak out and say that I'd have to be 2,000# to handle the size. That's still a long way away from three tons — and I'm not convinced one ton makes sense. I'm going to assume that we're talking about a humanoid species and not an elephant, dinosaur, or any other species that might stand 19' tall but also span about 20' in length, which humanoids likely wouldn't. Maybe I'm wrong due to the square-cube law... but you'd need to show me your mathematics.

Allow me to introduce the Canter Pickup Truck

enter image description here
Image courtesy Fuso Trucks. Click to enlarge.

Models range from 3.0 metric tonne (3.31 tons) carrying capacity to 6.0 metric tonne (6.61 ton). You state you only need three tons. All you need is to create a larger cab, pushed further back on the chassis, with a bigger seat, steering wheel, and controls.

Need something bigger?

Done deal.

How about the BelAZ 75710 haul truck? 450 tonne (496 ton) carrying capacity. Once again, just build a bigger cab.

enter image description here

Conclusion

I can't think of any particular engineering limitations your species would encounter, assuming they're humanoid. We use tweezers, they'd use tweezers. We use pulleys, they'd use pulleys. The fact that we don't need to design vehicles that can accommodate a 19-foot 6,000-pound creature doesn't mean we can't. Quite frankly, we can. Today. Right now.

Note that there's a difference between an engineering limitation and a change in engineering specifications. Road base would need to be deeper and asphalt and/or concrete deeper to handle the heavier load — but there's nothing stopping anybody. So you'd need higher underpasses to handle the taller vehicles and stronger materials, stronger frames, and thicker roads to handle the weight.

But humanity has even solved one of those problems. U.S. freeways are designed to handle a maximum-weighted semitrailer weighing 80,000# (40 tons or 36.29 tonne).

There isn't a problem here. I can't think of a single vehicle, from canoes to space ships, that can't be built to handle your creatures.

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    $\begingroup$ On Your assumption: increasing just height and mass linearly would lead to a non-survivable creature as the weight would crush the bones just by standing up. Even scaling up according to the cubic growth (4 times size leads to 64 times mass) would still not be survivable. A functioning giant would have (in comparsion) much thicker bones, especially in the legs, and way more muscels and thicker senews. Edit: I watched a documentary a while ago and if I recall correctly the size to weight ratio to scale things like humans up would be somewhere between the power of 3 and 4. $\endgroup$
    – datacube
    Mar 27, 2023 at 13:49
  • $\begingroup$ @datacube addendum: so scaling you up at least close to properly (cubic) would lead to a weight of 16.000 lbs $\endgroup$
    – datacube
    Mar 27, 2023 at 13:55
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    $\begingroup$ @datacube I took the OP at his/her word because despite the science-based tag, the established requirements for the question were 19' and 6,000#. But to underscore my contempt for the blind use of the square-cube rule: a Carnautaurus coaxed to stand up strait would be about 40' tall, and it's estimated weight was only 3,000#-4,600# - and that's with a leg structure that a humanoid wouldn't use. Me thinks everyone's forgetting to use actual data. $\endgroup$
    – JBH
    Mar 27, 2023 at 16:00
  • $\begingroup$ @datacube That was my first reaction, too. May be these giants live on a planet with lower gravity? Actually that would naturally let them evolve to become larger (assuming it is evolutionary beneficial). $\endgroup$ Mar 28, 2023 at 18:29
  • $\begingroup$ @JyrkiLahtonen OP specifically mentions: "the gravity isn't substantially lower" $\endgroup$
    – datacube
    Mar 29, 2023 at 7:27
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The vehicles for the 19 foot-tall people would have to be designed and operated differently than vehicles for humans, of course. But it is probable that your alien planet would probably have lower surface gravity than Earth, and so their vehicles would probably be designed and driven differently on that planet than they would be on Earth.

A 19 foot tall intelligent species would be possible on a planet with Earth like surface gravity.

The tallest recorded giraffe, George, stood 20 feet tall.

https://a-z-animals.com/blog/the-tallest-giraffe-ever-recorded/

The extinct giant ground sloth Megatherium americanum was huge.

Megatherium americanum was one of the largest animals in its habitat, weighing up to 4 t (8,800 lb),5 with a shoulder height of 2.1 m (6 ft 11 in) and length of 6 m (20 ft) from head to tail.[7][8][9] It was one of the largest ground sloths, about as big as modern Asian elephants.

Megatherium had a robust skeleton with a large pelvic girdle and a broad muscular tail. Its large size enabled it to feed at heights unreachable by other contemporary herbivores. Rising on its powerful hind legs and using its tail to form a tripod, Megatherium could support its massive body weight while using the curved claws on its long forelegs to pull down branches with the choicest leaves. This sloth, like a modern anteater, walked on the sides of its feet because its claws prevented it from putting them flat on the ground. Although it was primarily a quadruped, its trackways show that it was capable of bipedal locomotion. Biomechanical analysis also suggests it had adaptations to bipedalism.[10]

https://en.wikipedia.org/wiki/Megatherium

So that is an example of a sometimes bipedal mammal the size of an elephant that might have reached close to 19 feet tall on its hind legs.

I have seen a photo of a big male Asian elephant walking on his hind legs with a woman standing on his tusks. He would walk on his hind legs for a considerable distance in his performances.

In the wild, big male African elephants often rear up on their hind legs to grab high tree branches with their trunks. A big bull that is about ten feet tall at the shoulder would easily rear up to 15 or 16 feet tall at the top of the head, and could reach over 19 feet high with their trunk.

Since the largest African elephant ever measured was more than 13 feet tall at the shoulder, I assume that if he was able to stand on his hind legs the top of his head would be about 19 feet above the ground.

Of course African elephants don't stand on their hind legs much, nor walk far on their hind legs. But a being somewhat similar to an African elephant but thinner and weighing less might become bipedal.

I note that elephants do make and use tools, though not as much as humans, and their intelligence range might have a considerable overlap with that humans, and they might be classified as intelligent beings and persons instead of mere animals.

Some extinct proboscidean species were larger than modern elephants.

The largest land mammal of all time may have been a proboscidean; Palaeoloxodon namadicus was up to 5.2 m (17.1 ft) at the shoulder and may have weighed up to 22 t (24.3 short tons), almost double the weight of some sauropods like Diplodocus carnegii.4

https://en.wikipedia.org/wiki/Proboscidea#:~:text=The%20largest%20land%20mammal%20of,some%20sauropods%20like%20Diplodocus%20carnegii.

One partial skeleton found in India in 1905 had thigh bones that likely measured 165 centimetres (5.41 ft) when complete, suggesting a total shoulder height of 4.5 metres (14.8 ft) for this individual elephant.

Two partial thigh bones were found in the 19th century and would have measured 160 cm (5.2 ft) when complete. A fragment (currently unlocated) from the same locality was said to be almost a quarter larger; volumetric analysis then yields a very speculative size estimate of 5.2 metres (17.1 ft) tall at the shoulder and 22 tonnes (24.3 short tons) in body mass, which if correct would make P. namadicus possibly the largest land mammal ever, exceeding even paraceratheres in size. However this estimate based on the "distal femur portion" requires reexamination, as the author himself could only suspect that "fossils are likely stored in the Indian Museum of Kolkata; until such a collection can be revised, this size estimate will remain speculative."[8]

https://en.wikipedia.org/wiki/Palaeoloxodon_namadicus#Size

So if the largest size estimate is correct, and if individuals of Palaeoloxodon namadicus were intelligent enough to be considered people, they would examples of people who once lived on Earth who were almost as tall as your 19 feet when walking on all fours.

And it is easy to imagine a proboscidean species which was thinner and taller than Palaeoloxodon namadicus or any other known proboscidean species and reaching a height of 19 feet while on all fours, while not weighing more than about ten tons.

So it is theoretically possible for a bipedal species of intelligent beings to be about 19 feet tall on a planet with the same surface gravity as Earth.

On a planet with a lower surface gravity than Earth, animals and people would have lower weights relative to their body mass. And though 19-foot-tall people should be possible on planets with Earth's surface gravity, I suspect that they would be many times more common on planets which have a much lower surface gravity.

I note that the ability of a planet to retain atmospheric gases, including the oxygen necessary for large land animals and for intelligent beings, depends on the ratio of the planet's escape velocity divided by the speed of gas molecules in the exosphere of the planet.

It is the escape velocity, and not the surface gravity, of a planet which is important to that planet's ability to retain a dense atmosphere for geological eras of time, time enough for intelligent life to develop on it. And the surface gravity and escape velocity of worlds are calculated according to different formulas and don't vary the same way with different planetary properties.

Here are links to online surface gravity and escape velocity calculators that I sometimes use.

https://philip-p-ide.uk/doku.php/blog/articles/software/surface_gravity_calc

https://www.omnicalculator.com/physics/escape-velocity

According to a calculation on page 54 of Habitable Planets for Man, Stephen H. Dole, 1964, the least massive planet capable of retaining an oxygen rich atmosphere for long would have an escape velocity of 6.25 kilometers per second.

https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf

An escape velocity of 6.25 kilometers per second is 0.55873 of Earth's escape velocity of 11.186 kilometers per second.

According to Dole, a planet with an escape velocity of 6.25 kilometers per second would have 0.195 Earth mass, 0.63 Earth radius, and 0.49 of Earth's Surface gravity. Note that the surface gravity and escape velocity don't have the same ratio compared to Earth's surface gravity and escape velocity.

However, Dole's formula for the relationship between the mass of rocky planet and its radius, average density, surface gravity, and escape velocity is probably obsolete due to our greater present astronomical knowledge. There is considerable possible variation in the average density of terrestrial type planets. Thus you might be able to design a planet with a surface gravity lower than 0.49 g and an escape velocity higher than 6.25 kilometers per second.

But there are limits to the density of a terrestrial type planet. Iron is the densest common material in the universe, so no terrestrial type planet should have a higher average density than that of iron. And if a planet has too low a density, its entire surface will be covered with a liquid ocean many miles deep, and there won't be any dry land. Also, the lower the average density of the planet, the rarer metals will be, and the people will need metals for many machines and vehicles.

I assume that the animals and people on your planet will have an average density similar to water, like animals on our planet. Thus your 19 foot tall people will have the same mass they would have on Earth. So their inertia when they stop or start moving would be the same as on Earth.

But their weight would be much less on a low gravity planet than on Earth.

Astronauts in microgravity have to remember when moving large objects than their mass and inertia is the same on Earth, while the weight of the objects is zero.

If there are any characters from Earth in your story, they will find they have to remember that the mass of objects is the same while the weight is lower on your planet.

I note that the materials the machines and vehicles are made out of should be the same as Earth materials, and so should have the same mass and inertia as those objects have on Earth, while being much lighter on that planet.

So the vehicles for the 19 foot-tall people on your planet, if it has a lower surface gravity, should be engineered and driven somewhat differently than they would be on Earth.

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19 foot humanoids would in all likelihood be of different proportions to Homo Sapiens. Their bones would have to be bigger to cope with the extra weight. They would need a way to reject additional heat and some means not to die or seriously injure themselves during a fall (padding, rapid reactions?).

Beings of such a size would find transportation more of a challenge as everything would need to be on a larger scale. This probably means that mechanised transportation would be delayed in development terms until later and possibly occur in a different order. Cars would be possible but would need to be much larger and be a little more complex.

Ships would be less of a problem as they tend to be large anyway. Tanks might not be practical as they might present too large a target and be too slow. A rocket carrying a crew into orbit would be very difficult and might have to wait until uncrewed rockets had been developed to Starship like proportions.

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