Relaxed stability advantage...

[artik]

Modern fighter aircraft starting from F-16 are unstable by design and require fly-by-wire controls to perform adjustments all the time.

It is told that it improves maneuverability...

Indeed when the aircraft is unstable it can change its angle of attack faster... but what actually makes the turn is the lift provided by the wings. i.e. in terms of energy-maneuverability - it shouldn't help as the same wing would have to create the lift and drag (also may be somewhat less drag).

So how significant are these improvements to sacrifice natural aircraft stability (and safety related to it)? i.e. if lets say we take F-16 and make it stable or F-15 make it unstable what effect it would have on the E/M charts?

[FLS]

The relaxed static stability design allows a faster response when there is no inherent static stability to overcome. I can't think of any reason for it to affect Energy Maneuverability.

[pembquist]

Off the cuff I am thinking that stability requires stabilizing forces that come from somewhere and that that somewhere takes energy. In an abstract model which causes more drag to roll 30 degrees, a wing with dihedral or a straight wing?

I'm not sure it's the same thing as unstable but making a wing that stalls inboard first has got to be more draggy than one that flys the same along its whole length.

[Cthulhu]

The relaxed static stability design allows a faster response when there is no inherent static stability to overcome. I can't think of any reason for it to affect Energy Maneuverability.

Like FLS said, the relaxed stability allows for quicker transients. It also permits smaller control surface inputs to affect the same attitude changes, so there should be less drag associated with those smaller control surface deflections, which theoretically would minimize energy loss. Of course it's probably just a wash since the control surfaces on zero stability aircraft are constantly twitching anyway just to maintain straight flight.