For one thing, despite what the author says, there are masonry bridges with spans longer than 100m.
The record is 146m.[1] Building really large masonry bridges was a thing in China when a huge low-priced workforce was available, and heavy machinery and large steel beams were less available.
Overreliance on simulations creates a need for really accurate simulations, which means considering lots of secondary effects and having enough data to support a simulation. This is hard.
The problem with development by hand is that you can't deal well with multiple constraints. Modern electronic design: It can't cost much. It can't use much power. It can't be big. It can't interfere with other devices. It has to have really good performance.
You have to do a lot of simulation, tweaking different parameters, to meet all those constraints. Or build a lot of prototypes. You usually can't just do a conservative design and get a saleable product.
If you were designing a car today, and were willing to have 25% more weight, you probably could design it with a slide rule. You'd get a 1954 Buick Roadmaster, a sedan with a curb weight of 1983 kg.
"An engineer is someone who can do for fifty cents what any fool can do for a dollar."
The author calls out that they aren't a civil engineer, and the bridge example wasn't meant to necessary reflect reality.
> If you were designing a car today, and were willing to have 25% more weight, you probably could design it with a slide rule. You'd get a 1954 Buick Roadmaster, a sedan with a curb weight of 1983 kg.
Being 25% heavier than necessary is likely far too much. You could definitely design a car using analog tools and calculations to within <5% of the minimum requirements.
This is a great example of where too much precision is a bad thing!
A 1954 Buick Roadmaster had a curb weight of 4,430 lbs. Choosing a random modern car, a 2022 Toyota Camry has a curb weight of 3,310 lbs.
Assuming those as a baseline, each 1% of weight due to "overprovisioning" would be 44.3 and 33.1 lbs respectively. Lowering the load capacity of the vehicle by 5% would mean a 221.5 lb reduction in capacity for the Roadmaster and 165.5 lb for the Camry.
You have to account for not only the precision of your design, but also the precision with which it is used. I seriously doubt I could estimate to within 200 lbs how much the combined weight of all occupants and cargo in my vehicle is at any given time. It's therefore fair to say that the use case for a car is not estimated to within 5% of reality - so the car must be overbuilt by some margin of >5% to account for that.
If the precision of the intended use case is that high, spending additional time to reduce vehicle weight to <5% of the target capacity is wasted. It's better to make it a bit heavier than strictly necessary than it is to spend the resources to know precisely how heavy it needs to be to meet an imprecise requirement.
>Being 25% heavier than necessary is likely far too much. You could definitely design a car using analog tools and calculations to within <5% of the minimum requirements.
Most of the complexity of modern cars goes to crash standards which are much more rigorous than in the 1950s. I doubt you could design a car within 5% that meets crash testing standards without simulations or live testing.
True. Look at crash test videos. The entire front of the vehicle has crumpled and absorbed the crash energy, while windshield and passenger compartment remain intact. Figuring out just where to punch holes in the sheet metal beams to do that requires simulation.
Sometimes the best engineer is the one who knows the fools are going to spend a dollar anyway, so he makes it more than twice as good as he could if he stuck with the 50 cents.
One of my favorite cars from the slide rule era is the 1966 Ford Mustang.
About the same curb weight as the decades newer Nissan 280ZX except the Mustang with the small V8 can reach about twice the horsepower. But when driven conservatively would almost equal the gas mileage of the small Japanese roadster.
Overreliance on simulations creates a need for really accurate simulations, which means considering lots of secondary effects and having enough data to support a simulation. This is hard.
The problem with development by hand is that you can't deal well with multiple constraints. Modern electronic design: It can't cost much. It can't use much power. It can't be big. It can't interfere with other devices. It has to have really good performance. You have to do a lot of simulation, tweaking different parameters, to meet all those constraints. Or build a lot of prototypes. You usually can't just do a conservative design and get a saleable product.
If you were designing a car today, and were willing to have 25% more weight, you probably could design it with a slide rule. You'd get a 1954 Buick Roadmaster, a sedan with a curb weight of 1983 kg.
"An engineer is someone who can do for fifty cents what any fool can do for a dollar."
[1] http://highestbridges.com/wiki/index.php/Danhe_Bridge