What I experience a lot with the current su-27 fm is that I can hover the plane on the nozzles for ages. Once you have 80° Nose up you can stay there without any input and it will go on VTOLing till the fuel is out. I even once managed to land it on the nozzles without much damage. If that would be rreally possible, a manouver thats is much more spetacular than the "cobra", you would see that more often performed in RL.