Why can't small, cheap drones do to the modern fighters what they're doing to modern tanks?
Drones that can do that are called “anti-aircraft missiles”.
Are you absolutely certain that there's no other way to take down modern fighter aircraft?
Like isn't that the lesson from the Ukraine war w.r.t. tanks? That there are cheaper, more effective tools out there to take out state of the art equipment.
We have many drones much cheaper than an f35 that can do this already. They're called AIM-9, AIM-120, Meteor. Or if you're Russian they're called R77, or R73.
These are, of course, anti-aircraft missiles.
Why or why not?
For another, R&D: we've been working on fast autonomous flying vehicles to take down aircraft for decades: as the poster above keeps explaining, they're called AA missiles, and are extremely expensive, and even still have a hard time actually hitting a plain. Drones are an innovation in fighting tanks because they are much more maneuverable than traditional AT weapons and thus can more easily find chinks in the tank's armor. You could have always used the extreme maneuverability of AA rockets to hit those same chinks in the armor, but the cost was too high; drones were cheaper. AA rockets are extremely cost effective against plains though, as those jets are monumentally more expensive than a tank.
So essentially you can't see an F-35 until it is already lined up to kill you. That tends to make it pretty difficult to hit it.
They will absolutely replace modern fighters to a degree and already have to an extent, like we've seen in Ukraine with drones serving as close infantry support etc. instead of manned aircraft.
There are still some things "cheap" drones won't be able to do.
Specifically, if you want to carry big bombs and missiles, you need a large aircraft even if it's unmanned. The drone is also presumably going to need to be able to survive enemy air defenses to some extent. So you wind up with a big expensive drone like the MQ-9 Reaper ($30mil plus, lol) that is approaching the size and complexity of a manned fighter.
Also, and I'm not sure if this is what you meant, but "small, cheap drones" are not likely to be shooting down modern fighters in the way that small cheap drones are currently killing tanks directly.
If you want an aircraft that can fly at mach 1.6+ and shoot missiles at other things (some of them stealthy) traveling at mach 1.6+, you are going to wind up with something fairly close to the size/cost/complexity of an F-35 even if you don't have a human being sitting inside.
A starship already costs around 90 million USD at cost (estimated based on parts cost currently) and is intended to cost around 10 million USD per launch commercially if it's able to be reused regularly.
And a single launch could carry a lot of bombs (like 50-400 based on the size). So on the high end after factoring in the cost of the bombs, amortising the cost of the initial orbital platform, and assuming a higher cost of like 120 million USD for a single launch, that would still almost certainly come out cheaper than sacrificing an MQ-9 or a much more expensive missile. And of course if you can get that cost down to 10 million USD per launch then other than artillery, that's going to be the cheapest way to deliver ordinance to any location in the world by far (after factoring in the cost of flight time for jets, etc).
An air-to-air missile is essentially a single-use drone
And barring some big advance, an air-to-air missile can't be any smaller than it is currently. It needs to carry enough explosive to damage the target aircraft, and it needs enough fuel to travel at supersonic speeds for a long enough distance to actually intercept the target.
That's the lesson from drones vs tanks.
Not sure what this has to do with my claims about not being able to use cheap drones for taking down fighter jets. Military ships, like tanks, are also somewhat slower and somewhat less maneuverable than fighter jets, I believe.