LOL, you guys need to go read CNN!
"
The FC-31's flight routine shows that it "bleeds" too much energy -- so when it enters into a turn it begins to lose altitude. Even during straight and level flight the pilot has to engage the engine's afterburners in order to keep the aircraft from sinking to a lower altitude. These are defects in the aircraft's aerodynamic design that a Russian design team would not have made.".
So, either the airframe design is horrible, or the engines they are using right now is underpowered.
BTW, I have yet to see the video of this supposedly "bleed to much energy" aerial demonstration anywhere. The youtube video I saw it seems to perform fine. Perhaps someone can enlighten me?
[video=youtube;NLQEtRxflEU]https://www.youtube.com/watch?v=NLQEtRxflEU[/video]