I wouldn't say it is impossible.

A (relatively) simple solution would be to use something with more dense power source, maybe fuel. RC enthusiast use fueled engines routinely, it isn't something special. There are various types of advanced fueled engines for RC use from traditional 2-4 stroke miniaturized engines to turbofans.

They are not very common on small quadcopters because of lack of response. Quadcopters depend on an onboard controller for fast corrections and for this to work you need a motor that can react very fast and precisely. A liquid fuel engine in a craft that does frequent changes in direction of g forces is not an easy thing to control precisely.

But this could be easily remedied by making this at least partly hybrid (use engine to charge small battery and use this to power additional motors to improve response to help stability and maneuvers).

I never said it was impossible, but I did say that I "ruled out" a quad. I meant very unlikely, not that it was impossible. There are quads that have >1 hour endurance, and there are quads that can do 100 mph, but none that can do both, even with gas. To make a quad that can go 100 mph and stay in the air for an hour is a crazy big stretch of existing capabilities. I'd love to see an example, because none of these come close: https://blog.dronetrader.com/list-of-the-top-hybrid-gas-elec...

There are also non-hybrid quads, but again, none of them can deliver the performance observed by these pilots: https://www.mydronelab.com/blog/gas-powered-quadcopter.html

I said in another comment that my bet is on an RC plane. A fixed wing is much more likely to achieve that kind of speed with the endurance. Considering that the pilots didn't provide a good visual description I think it's the safest bet. I'm not going to worry about how it might be possible to make a quad that can do this when an obviously feasible solution is staring us in the face.

> I never said it was impossible

I never said you did.

Helicopter use variable pitched rotors. I assume a gas powered quad would as well. This would give very fast response and even let them fly upside down.

But still. This still doesn't solve why it wasn't visible on thermal and would still be an extraordinary drone doing all these things.

You can use a gas engine to hit that kind of time in a quad. There aren’t any great options on the market right now, but as a DIY project it’s not that difficult to use an engine to charge the batteries in flight.

Did they say the "quadcopter" was flying 100mph sustained for an hour, or just short bursts of up to 100mph to avoid being caught?

Could be gas powered?