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In a world without fossil fuels, would air travel ever really be developed?

Without fossil fuels, the most likely path that could lead to the development of a proper industrial revolution would eventually be nuclear power and renewables. This world would probably start with hydro-electric power, in which they then move on to nuclear as scientists living in the cities that build up around dams are able to discover more about nuclear physics that would allow this to be harnessed as a fuel source.

While there are other questions that could be raised, how would air travel be developed in this sort of world? Could airships remain viable in the face of electrified railroads and nuclear transport across oceans?

Would fixed wing aircraft or helicopters eventually be developed? What fuel sources might they use?

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    $\begingroup$ Airships. Dirigibles. $\endgroup$
    – elemtilas
    Sep 6 '20 at 2:56
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    $\begingroup$ I am pretty sure sugarcane ethanol can power a heavier than air aircraft. $\endgroup$
    – lvella
    Sep 6 '20 at 12:51
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    $\begingroup$ Agreed - I think that the internal combustion engines would still exist, just using different types. A jet engine will run perfectly well on most flammable liquids including ethanol and vegetable oils, and a petrol engine will run on ethanol as you say - indeed given the octane rating of ethanol it would probably work better. $\endgroup$ Sep 6 '20 at 17:01
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    $\begingroup$ Although they lost out to avgas models a century ago, diesel engine aircraft did fly early in aviation history; and diesel engines will run on vegetable oil. $\endgroup$ Sep 6 '20 at 17:39
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    $\begingroup$ A big problem with no fossil fuels is that a serious metallurgy is pretty much ruled out. $\endgroup$
    – user58697
    Sep 8 '20 at 0:08
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Lighter than air craft:

While the modern combustion-powered aircraft would be a hard sell, there were steam-powered airships built long before the Wright brothers, and hand-cranked designs existed before that. After that, electrically-powered airships were constructed like the La France.

A steam powered model could certainly have been operational, utilizing charcoal or distilled volatiles, and in fact such designs predated ones using fossil fuels. Only the relative efficiency of fossil fuels caused them to predominate. In fact, the diesel engines invented by Rudolf Diesel initially ran on coal dust (easily a sub with charcoal) or vegetable oil, demonstrating that biofuels were already viable early in the history of aircraft. Diesel aircraft engines were viable at the beginning of the aviation industry and are currently enjoying a resurgence.

Once the value and efficacy of aircraft were established, I doubt they would have simply disappeared. It is speculation to say if fixed-wing aircraft and helicopters would have been invented, but I'm guessing that as the manufacture of biofuels for various powered vehicles became more common, they probably would have been at LEAST invented, even if they didn't end up being practical. The versatility of these vehicles would probably still have led to at least specialized functions for them.

But I'm confident there still would have been blimps and dirigibles, and likely better ones than we have today due to lack of competition from gas-guzzling fixed-wing craft. Land and sea transportation also benefited from fossil fuels, so weaker competition in these arenas means the airship would have been quite reasonably competitive as a passenger and even cargo transport.

You may find this question relevant to your question.

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  • $\begingroup$ I was immediately thinking bio-fuels, but wasn't sure whether they would have sufficient output; glad to see history proves they are at least semi-viable. $\endgroup$ Sep 6 '20 at 10:23
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    $\begingroup$ Blimps and dirigibles still need fuel to get from A to B. They save fuel on lift, true, but the downside is that their volume causes a lot of drag. Modern planes have well-optimized wing designs that generate a lot of lift for very little drag, so dirigibles in many conditions are less fuel efficient. $\endgroup$
    – MSalters
    Sep 7 '20 at 8:49
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    $\begingroup$ Here's an interesting question. Given that helium mostly comes from natural gas production, without fossil fuels, where can it be found? Hydrogen could still be synthesized reasonably well, but this would require that the flammable gas bag is never able to be phased out. It certainly wouldn't work for a military for long. $\endgroup$ Sep 7 '20 at 9:04
  • $\begingroup$ @Adam Reynolds If we take out every reference to the effects of at least limited petroleum production, this starts becoming hard to parse out. Still, I get a vision of WW1-type balloons filled with ammonia dropping excess gas canisters on London. en.wikipedia.org/wiki/Lifting_gas It's possible helium could be trapped underground in the same deposits that normally would be filled with natural gas. Hard to say, because of the ease and abundance of getting it from natural gas. Without methane, it might not even need distillation... $\endgroup$
    – DWKraus
    Sep 7 '20 at 13:38
  • $\begingroup$ Concerning the invention of fixed winged planes. I suspect it would have happened and if no where else would have been used by the military. Concerning Helium, Helium on Earth originates from radioactive minerals. alpha particles capture electrons to form helium atoms which accumulate in any gas tight subsurface structure, natural gas is not a requirement although is usually found at similar locations. $\endgroup$
    – Slarty
    Dec 7 '20 at 13:19
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We were flying for hundreds of years before putting an engine on planes:

  • We had man-carrying kites going back to possibly the 7th century.
  • 1783 we had manned hydrogen balloon flight.
  • First heavier than air craft (no human on board) was 1655 apparently (spring powered ormithopter).
  • In 1853, British engineer George Cayley built the world's first real glider.

With no petrol, the wright brothers plane as built couldn't exist (they used gasoline), but we had batteries and electric motors at this point in history, they have a lower power to weight ratio, but that first flight could've occurred electrically in the same period.

Long distance air travel would be harder, batteries are heavier than the same amount of fuel, but lacking fossil fuels, we can still refine ethanol from biomass. There are ethanol powered aircraft, which are actually cheaper to run than gasoline ones. That linked one is commonly used for crop dusting, and can be powered by ethanol generated free from waste parts of crops. There's no reason that can't scale up to a small airliner-sized aircraft.

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    $\begingroup$ "batteries are heavier than the same amount of fuel" – That's only part of the problem. The problem is compounded by the fact that, unlike fuel, they stay heavy as they are depleted. That's why, for example, Rocket Labs mounts the batteries on the outside of the Electron rocket and drops them to burn up in the atmosphere as soon as they are empty. $\endgroup$ Sep 6 '20 at 14:23
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In Brazil "pure" ethanol (94% ethanol, 6% water) is sold at every gas station, and pretty much every new car sold can run with any proportion gasoline-ethanol mixture (they call it "flex" engines).

So, the infrastructure for a fuel that can power a combustion engine for a heavier than air aircraft does exists independently from oil since the 1970's.

The history would certainly be different, and possibly there would not be the political-economical incentives for airplanes to be what they are today, but it is quite possible they would be invented and be used for local travel in places where sugarcane is viable.

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    $\begingroup$ Spot on. But you don't need sugarcane. You only need cheap alcohol. Any high-starch crop will do. $\endgroup$ Sep 6 '20 at 21:33
  • $\begingroup$ @cmaster-reinstatemonica the efficiency of sugarcane per planted area is unmatched, and I doubt any other crop would have been economically viable. For instance, maize produces half the amount of ethanol per planted area, and takes much more energy in the processing into ethanol (so much that its subsidy is highly controversial in USA). I am not sure about sugar beet, though. $\endgroup$
    – lvella
    Dec 24 '20 at 16:37
  • $\begingroup$ My point was that there are other crops than can be used to produce ethanol, it is not a requirement that you are "in places where sugarcane is viable". Actually, I was neither thinking of corn or sugar beet, I was thinking about plain old potatoes. As far as I know, the ethanol that we buy around here as a cleansing agent / cooking fuel is made from potatoes. You can grow high-starch crops in any region that supports agriculture, allowing you to produce ethanol virtually everywhere. $\endgroup$ Dec 24 '20 at 19:25
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River-side mill towns existed before electricity could be used to export energy.

Would fixed wing aircraft or helicopters eventually be developed? What fuel sources might they use?

sailplanes, definately.

Oowered craft, maybe for military applications, and use by the very rich. They would probably be ethanol fueled, it's hard to speculate on which type of engine they would use.

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solar wings

Today there are experiments with solar- and battery powered electrical aircrafts. They work well enough! Though, to save energy, they fly slow. Get used to have a cruise speed of 300km per hour maxi.

catapult start

If you have to use less power, you can still fly. Most power is needed during take-off. Would it be a strong requirement that no fossil fuels are used, airports could have an aircraft-carrier-like catapult to help supplying a part of the energy.

sailing

In-flight you can be totally powerless with today's normal aircraft ( like Boeing 737, A350, Dreamliner, Comac and the like) and fly hundreds of kilometres without problem. That said, you will be even slower than the solar aircraft above, probably in the range of 100 - 200 km per hour, also you need some means to get them up there in the first place. If you build sailing aircraft specifically for this speed and purpose, it will get better. If you are ready to spend part of the flight time using convections to gain height, you can fly very very long without power, but your average speed gets even lower. Trains are better and faster then.

hydrogen engine

Today's turbines can be powered by hydrogen, too. On first glance this is even attractive because hydrogen has a 4 times higher power-to-weight ratio than kerosene. However the storage of hydrogen is so complicated that it will eat up much of that weight-advantage or even more. So imagine today's aircraft with a different kind of fuel storage, probably in the belly and not in the wing, so the wing can be slightly slimmer but longer, and you have that just-subsonic aircraft from today, but without fossil fuels.

I don't know if we would have taken the same development path towards this fossil-free aircraft like here, on a world entirely without fossil fuels.

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Not directly related to the fuel used in the aircraft, coal is also used to create coke which is used in the creation of metal products

In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron. Coke's superior crushing strength allowed blast furnaces to become taller and larger. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Before this time, iron-making used large quantities of charcoal, produced by burning wood.

As other answers show fossil fuels can be replaced with other fuels. However the lack of easily and cheaply available fossil fuels would impact the course of the Industrial Revolution in your world impacting the availability of many technologies.

Additionally the lack of fossil fuels means that the use of wood as a fuel remains high leading to higher levels of deforestation which can deeply impact a region's ecosystem. Japan managed to prevent deforestation by changing their use of forests (source: https://www.appropedia.org/Japan_Forestry). Easter Island, however, did not.

With the loss of their forest, the quality of life for Islanders plummeted. Streams and drinking water supplies dried up. Crop yields declined as wind, rain, and sunlight eroded topsoils. Fires became a luxury since no wood could be found on the island https://rainforests.mongabay.com/09easter_island.htm

Would Britain have avoided Easter Island's fate without fossil fuels to burn for simple things such as heat and cooking? A different approach to the use of wood and forest management would be required. Further impacting the course of industrialisation. Farming is also impacted by industrialisation, think of all the tools and machines. Further farming depends on fossil fuels for synthetic fertilizers (https://en.wikipedia.org/wiki/Fertilizer#Nitrogen_fertilizers).

Considering the reduced farming efficiency means that large part of the population is involved in food production so there are less engineers and scientists for developing alternative methods for creating cheap metals, electricity generation, or even nuclear technology. The farming efficiency will also impact the availability of bio fuels.

All that being said the Industrial Revolution would probably still be possible without fossil fuels but it's course would definitely be different. I can imagine that societies would try to find faster growing trees to supply their energy needs, maybe even bamboo which can also be turned into charcoal. Probably different furnace designs would generate cheap metals with charcoal or bio fuels. Electricity will likely start to play a role in metal smelting and refining earlier on as well, see eletric arc furnances for example. Once this thin edge of industrialisation's wedge is in the developments will continue. However the industrialisation speed and scale would be impacted by the need to constantly balance the environmental aspects to maintain healthy forests and farmland. Failing to do so would hurt a society without fossil fuels a lot quicker stalling their industrialisation.

As laid out by others aircraft would be possible without fossil fuels. However the total energy available is simply more limited without fossil fuels. Most technologies, including railroads and flying would be less wide spread and thus available only to the rich elite of society.

Hydropower is also a lot less available especially before Hydropower dams can be built, still being based on waterwheels. Wind power would be implemented more since windmills can be placed in more locations. Batteries would be a lot more important in this world dependent on electricity, as we start to see in the world today. Battery powered aircraft are possible but require more energy dense batteries than we have today. Considering the importance of batteries in your world these would surely be invented.

I expect nuclear power to be a bigger game changer than in our world, making power available more cheaply at a bigger scale. Either that or wind and eventually solar power would play a bigger role.

As for your question "Could airships remain viable in the face of electrified railroads and nuclear transport across oceans?" Probably yes, aircraft would still be faster than ships and trains generally can not cross oceans and seas. Also aircraft need less infrastructure than trains which I can imagine will be an even bigger advantage in a world where it less easy to mass produce many thing for a long time. Also don't forget the military applications that are unique to aircraft which will aid their development.

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    $\begingroup$ Coal is a fossil fuel. Sometimes literally, as it can contain fossils. $\endgroup$
    – NomadMaker
    Jan 18 at 8:26
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Piston and jet powered flight could still be developed without reliance on fossil fuels. We use fossil fuels for gasoline, diesel, and jet fuel because it's relatively easy to prepare from the oil we extract from the ground, the fuels are energy-dense and the engines are power-dense. However, both piston and jet engines can run on a range of fuels that could be synthesized or refined from sources other than petroleum. Jet fuel can be refined from vegetable oil. For piston-powered flight, you need something that behaves pretty much like gasoline in terms of energy density, combustibility, and storability - a blend of mostly alkanes in the right range (heptane, octane). It is possible (not necessarily easy or efficient) to synthesize them from hydrocarbon sources - vegetable oils and/or other plant matter. If you have cheap and abundant nuclear power, that can help to make synthesis of aviation fuels economic.

It would be far more plausible to see aircraft powered by liquid fueled piston or jet engines than compact nuclear reactors, even if the fuels have to be synthesized because nuclear power production scales up well, but doesn't scale down well, and mobile reactors bring safety issues - collisions/crashes can trigger dangerous leaks of radioactive materials.

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