Small-scale aviation without fossil fuels

Question

In my setting, fossil fuels do not exist. I'm handwaving an alternative behavior of radioactive material, and alternative magnetism-like forces. These are explained below. My question now is:

Can there be (nuclear) small scale aviation without fossil fuels, given the constraints below?

Alternative Radioactive Decay

Electrons can be manipulated by electromagnetic fields; they can be de- or accelerated. In the same manner, I'm handwaving a field that can manipulate alpha/beta/gamma-like particles$^1$. Scientists in the setting have a late-1800's / early-1900's understanding of radiation, so we don't have to worry about explaining this.

With those fields and blissful ignorance of the laws of energy conservation, people build reactors, where the energy output of radioactive decay is harnessed to almost 100%. Therefore, power is no problem, as the radioactive material is relatively easy to mine. These reactors are extremely heavy though (we're talking 2 tons and 2x4x4m for small, low-power versions), so vehicles on the ground are usually connected to a power line (trains) or pulled by animals. Batteries are unreliable / inefficient, so only large tanks and other massive vehicles can realistically rely on local electrical energy supply. I'm willing to decrease the size/weight of the reactors to aid the solution of this question though.

Acceleration Fields

In my setting, there exists a field that induces kinetic energy in objects contained in it. The direction and strength of acceleration depend on the position in the field relative to its source's orientation. Heavier/denser matter experiences a stronger effect in this field. It's a little like magnetism, except for that the acceleration is possible in many directions, not only towards or away from the field's center / along its field lines, and that it does not only affect ferromagnetic materials, but all matter$^2$.

To give an example: Most powered vehicles on land are trains. Instead of using an electric motor with a wheel that pushes the train forward by friction on the rails, most large trains have a set of kinetic skids to drive the vehicle. These work by using a directed kinetic field that pushes the heavy rails below it backwards, and a little bit away to reduce friction / levitate. Power is supplied by either an onbort generator, or power lines (as in our electric trains of today).

Aviation

Large zeppelins are used for most civilian aviation; either a set of batteries or a very small reactor might supply the needed energy to move and steer. For military purposes, there are floating fortresses, which are essentially a reactor platform with a ton of propellers strapped to it to keep it in the air.

I want to have smaller aircraft "as we know them" too, though, for dogfight reasons. Wikipedia says that development of nuclear propulsion in aircraft has been stopped because of the severe dangers of nuclear fission. The fact that air heated from fission was thought to be enough to propel a plane makes me think that this is viable if one takes away the radiation danger (by shielding the reactor with my alternative radiation fields). I thought about acceleration fields being used as an alternative to jet engines, where instead of fuel exploding and pushing hot gasses out the back, very fine metal powder is accelerated backwards and pushes the plane forwards. Like a rocket engine, but without the burning.

Regarding the last paragraph:

Is carrying metal powder to shoot out the back a good idea? Are there any limits on the efficiency of this method, relative to the plane's speed? Or would propellers be the go-to option anyways? I'm looking for a relation between powder weight and achieved propulsion at a certain energy input.

My main question, refined:

What other alternatives are there to nuclear energy supply that are viable mid-air? Fossil fuels are ruled out, but what about plant fuels, or mechanical batteries?

Edit: To make things more simple: I have reactors that supply vast amounts of energy, but next to no means to move them. As they are heavy, smaller aircrafts have to rely on other fuels. What could those fuels be?

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$^1$ This is a massive simplification of how things work both in the real world and in my model, to the point where it may become incorrect. I hope it gets my idea across though.

$^2$ Again, a brutal simplification. I wanted to keep the question "short", but can elaborate if needed.

Answer 1

The engine depends on the power-to-weight ratio of the kinetic skids

If kinetic skids can drive trains, why couldn't they drive airplanes? Well, for one, steam engines drive trains but not planes. That is because a steam engine's power to weight ratio is very poor. But if it could be light enough, then you can make an airplane engine.

This would work, as you suggest, on some sort of reaction mass. Since your kinetic force generators affect all matter, there is no need to use metal powder as reaction mass, just use air. After all, a jet engine is just using air for its reaction mass.

So if the motive force can be provided by the kinetic skid, then you are simply limited by the available power source. The key here is that if the power source is not as mass efficient as a battery, then the kinetic skid must be that much lighter to compensate. For example, while electric aircraft do exist, they aren't great because their power to weight ratio is worse than an internal combustion engine. They also scale much worse with additional fuel: the mass of adding a gas tank is much less than adding the equivalent amount of battery storage.

Power source can be a chemical reaction

Now, the kinetic skids will need their own power source. You say that reactors are too heavy and batteries too weak. Then ideally, you will use some sort of chemical storage....although that is basically what a battery is.

A fuel cell that generates electricity from hydrogen fuel and an oxidizing agent is possible. The first fuel cells were invented in 1838, so they fit the time period. They just aren't that effective in the real world. The first fuel cells were most similar to a modern day phosphoric acid fuel cell. In operation, the cell must be heated to 150-200 C. Hydrogen fuel pumped to one side of the cell will pass electrons to oxygen from air circulating on the other side, generating an electric current. There is also exothermic exhaust, though I don't know how much use you will get out of that.

The efficiency would be low, and you'd need a tank of hydrogen to power it. On the other hand, if your zeppelins are full of hydrogen in the first place, it might not be too hard to get a hold of the hydrogen you need.

If you want zeppelin's to act as carriers, then they can be generating hydrogen fuel from hydrolysis of water, storing the excess in their shells, and then fueling up the limited range fighters when they come back to 'base'.

Alternate solution: rockets

If you like the idea of short range fighters zooming around large ponderous zeppelins a la Star Wars, you might want to go with rockets. Hydrogen peroxide was used as a mono-propellant rocket fuel. But there might be a better alternative.

Hydrazine can also be used as a rocket fuel, although it is dangerous. Hydrazine was first made from sodium hypochlorite (basically, bleach) and ammonia in 1907. Sodium hypochlorite entered industrial production in 1892; it is made by electrolysis of salt water. So the timeline is about right for hydrazine to be the big new thing.

Hydrazine is a hypergolic propellant when mixed with dinitrogen tetroxide; but that wasn't invented until WWII, so sort of out of your time spectrum. It does burn quite explosively in oxygen, so it would be a fine rocket fuel either way.

Answer 2

We use hydrocarbons for aircraft fuel because hydrocarbons have a great many beneficial properties. They have considerable energy density by volume and mass. They remain liquid at a wide range of temperatures, the kinds seen from burning hot deserts to sub-zero temperatures seen at miles into the air. They provide lubrication to pumps. They burn readily when atomized but not when pooled on the ground from a spill. This we all know because of our use of fossil fuels in our every day lives. The point I'm making is that if we could not pump them from the ground then we'd synthesize hydrocarbons for fuel. We know how to produce hydrocarbons from nuclear power, in fact this has been proposed widely as an exit from needing fossil fuels in the real world.

In short, if we could not pump hydrocarbons from the ground for aircraft fuel then we'd make hydrocarbons from whatever raw materials and energy sources were most readily accessible.

Don't try to fit a nuclear reactor into an airplane, just use a nuclear reactor on the ground to make the airplane fuel. The US Navy has been working on this for a very long time, perhaps decades, to allow nuclear powered aircraft carriers to produce the fuel for the aircraft it carries while at sea. If or when this project is successful it would remove the need for a small flotilla of oil tankers to continuously bring fuel to the carrier groups.

As they are heavy, smaller aircrafts have to rely on other fuels. What could those fuels be?

The answer is, in my mind, synthesized kerosene.

If the goal is to have the airborne equivalent of the navy aircraft carrier, a military base that floats in the air instead of floating in the sea, then a nuclear reactor on board starts to make sense. Though with something this large I'd expect a large part of the lift that keeps it in the air to be from a lifting gas. That would mean it's a large armored Zeppelin. Because airplanes are more efficient than helicopters in turning energy into lift, and a moving target is harder to hit than a stationary one, I expect this airborne military base to keep moving and use a flying wing body to provide some of the lift. That doesn't mean it can't hover, only that it does this only when necessary for the mission.

Zeppelins fell out of use because it is so much easier to produce hydrocarbons than to produce helium. Hydrogen is an easily obtained lifting gas but it's so flammable as to be impractical. Perhaps with better materials and techniques Zeppelins filled with hydrogen could be practical. If there's cheap hydrogen for a lifting gas then there's cheap hydrogen for producing synthetic kerosene.

For Zeppelins to be safe and cheap means helium has to be practically gushing out of the ground. Helium is a byproduct of nuclear reactors but I doubt that's a practical source of helium since if there's enough nuclear reactors to make travel by Zeppelins practical then that's a lot of energy going around to make kerosene. Batteries are completely impractical for powering Zeppelins. Mass is a huge issue for keeping a lighter than air vehicle flying. Nobody is going to power a Zeppelin by batteries. They'd be using something far more energy dense. If it's not kerosene being burned in turbine or reciprocating engines then it might be ammonia, hydrogen, or some other lighter than air flammable gas.

If the fuel is also a lifting gas then as it is burned the lifting capacity is diminished so some measure has to be taken to compensate, which could be as simple as dumping sand bags. Perhaps a mix of heavier and lighter than air fuels can be used, burning either as needed to maintain the desired lift. Air density varies with humidity and temperature so having a means to adjust lift during a long flight will be desirable.

A nuclear reactor on a fast moving airplane which could find itself being shot at in a war was likely a liability that few would consider. However, in a big slow moving Zeppelin, used in civilian aviation, a nuclear reactor may actually be safer than kerosene. Consider large civilian nuclear powered lighter than air airliners as an alternative to kerosene powered jet aircraft. It cuts out the conversion losses of producing the kerosene and uses the heat from the reactor directly for propulsion. With a lifting body shape it would still fly largely like an airplane but at a very leisurely cruising speed of something like 50 to 100 knots instead of the 400 to 500 knots of a jet. As a nuclear reactor doesn't need oxygen to burn fuel such an aircraft could reach altitudes a jet never could.

Answer 3

Apparently, it’s possible to fly a pedal-powered aircraft:

https://www.wired.com/2013/04/how-to-fly-a-human-powered-helicopter/

The helicopter in the article requires high-tech carbon fiber to remain light enough, but if you scaled the process up and used many peddlers on the same craft, it might be feasible using aluminum.