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.
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).
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?
$^1$ 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.