Based slightly off the anime GATE, if I had excess to modern military technology and an army to operate them in medieval times like the anime, which aircraft would be better suited to destroy a city?lets say the modern army already has a base built at the medieval land and they have a good supply line. The only thing to worry about now is to figure out which aircraft out of the two would be most effective to be used by the army
I haven't seen the anime, but I would argue the biggest problem would be fuel and ammunition and spare parts (and to an lesser extent lubricating oil). They should pick the most primitive planes they can find, a helicopter is waaaay to complicated to use in medieval times. I would suggest World War 1 fighter planes, or maybe at most a World War 2 (propeller) fighter plane. A WW1 fighter can probably run on simple vegetable oil or alcohol and they can even fix broken wooden wings. They can drop primitive medieval grenades or even make ammunition for the fighters gun.
Given that a fighter jet is mainly built to attack other aircraft while an attack helicopter is mainly built to attack ground targets, the attack helicopter is the obviously correct answer.
A factor is available fuel, unless the army has large reserves of modern fuel. Many helicopters use diesel oil, which might be easier to produce than jet fuel. It might even be possible to produce biodiesel from local farm products.
How many other airplanes you need to FIGHT in the air in those times?
Or do you would need to ATTACK something? Like a castle, army or similar?
Not to mentions that for helicopter to operate you need a patch of land without trees slightly bigger than the size of rotors. For a Jet you need a large airstrip that would be flat and strong enough for a jet to take off.