18

Forget it. To make a helicopter fly, you need a relatively high power-to-weight ratio. Early helicopters used piston engines, but most modern designs use gas turbines. Still, they have problems getting their payload airborne, especially in hot and high conditions. With anything remotely like the renaissance, your power plants will have insufficient power-...


11

Confederate Maryland You don't need the Confederacy to win the Civil War. Just switch around some of the states. In particular, if Maryland joined the Confederacy, it would have been difficult to keep the capital in Washington, DC, as the portion of the District of Columbia containing the White House and other government buildings was ceded from Maryland. ...


10

Tweak the Civil War The Confederacy was unlikely to succeed in the Civil War due to the North's advantages and world opinion being against them, but they could have likely stretched the war out longer. Perhaps have Lee's confidence be reduced after Antietam such that he fights more conservatively in his Gettysburg Campaign turning it into a protracted ...


8

Americans do not like powerful big cities as their capitals. Here is an American idiosyncrasy I have never seen discussed. Americans like their capital cities to be little cities, with no particular power or claim to fame except that city is the capital. In England the capital city is London, the biggest. Same for France, same for Italy. In the US it is ...


6

As noted, steam engines are fare too heavy (or have a low power to weight ratio), particularly if you are trying to "invent" one in the 1500's. Alternatives like Stirling engines would be somewhat better (since they don't have the mass of the water and boiler to go with them), but not by enough. Relatively high power to weight ratio Stirling engines had to ...


4

The Bessemer Process. In principle, the engineering was within range of Roman technology, and it would represent a monumental change in, well, everything. Not just producing steel, but producing steel in mass quantities. Not just weapons but bridges and tools and armour. Then of course, the old favourite, black powder. The Romans would have taken to making ...


3

The Romans could cast bronze with great skill. Cannons and early primitive guns were often made from bronze. Showing the Romans how to make gunpowder and bronze cannons would have been entirely possible. Blackpowder is just sulfur, saltpeter, and charcoal. A cannon is just a metal (bronze) tube with one end closed, a tiny hole to touch a red hot poker to, ...


3

In order to make the most rapid progress, Your guy would have to start with weapons. The reasoning behind this is that while you could help with a great many things, The Gaulles, the Teutons, and the Huns are out there RIGHT NOW. Superior weapons are both symbolic and practical. A legion armed with swords and spearheads that don't readily break when going ...


3

Propeller speed Leonardo da Vince, rather famously, sketched out the design for a mock helicopter. I'm not saying this specific design would work, I'm saying that the Renaissance definitely had people with the knowledge and the drive to make such helicopter if they felt like it. The math required isn't complex The main problem is that you specified ...


2

Consider Japan during the Age of Exploration. This example suggests that the key was not geographic isolation but a strong government that could and did reject contact. In Medieval times, there were even more countries which managed to resist colonization. An interesting question here is if the spread of Christianity and Islam would be colonization. ...


2

It depends If time can be changed, there is nothing you can do to stop it from getting changed. Just by travelling back in time will change time. You breath out modern bacteria and viruses for starters. If you talking to anyone, you delay them so they are not where they were supposed to be thus different people could die in car accidents and others live. ...


2

Your problem is protecting history between 1822 and 1940 There are three events that are critical to the development of AI that cannot be altered and which (if they occur earlier) will cause you problems. But, the first two are theoretical in nature meaning that they are unlikely to be formulated beforehand... 1) Charles Babbage designs the Difference ...


2

As mentioned in other answers, it'd be very hard to bypass the required mass-to-thrust ratio. But do you really need the helicopter to take off on its own power? Autogire Basically, an autogire (or a gyrocopter) is an unpowered rotor in autorotation. In other words, moving around generates the rotation of the rotor (duh) which creates again some lift. It ...


1

You don't start with weapons, if you want to improve military power you start with medicine, logistics, and infrastructure. sulfonamide, the first antibiotics, producible with basic chemistry. The romans had mobile hospitals to support troops, now most of your casualties live, suddenly you are the immortal army. Germ theory will help make this even more ...


1

Pulsejet-powered tipjet monocopter! I have recently asked how early could pulsejets been built, assuming the knowledge of their existence and designs were to be magically known. Turns out that while inventing and designing them is hard and requires modern science, they can be surprisingly easy to build from plans! The consensus seems to be that Renaissance ...


1

Why create Washington in the first place? Compromise of 1790 resulted in setting the capital in Washington D.C. as a bargaining chip for Hamilton's idea of national debt assumption. As the Congress was in the deadlock, it is not hard to imagine a different scenario where South doesn't get the capital and Hamilton's plan fails. This could lead to major ...


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