I'm wondering why modern widebody aircraft (such as B787/777, A330/350 etc.) don't use horizontal stabilizers with T-tail configuration. What's the difference between placement of this element? There are quite a lot of military planes (C-17) and smaller ones that use it (Fokker 70, CRJ-9) in T-tail configuration, as shown here:
A horizontal tail on top of vertical tail would require strong and heavy structures, which in turn is not good for economics of flight. The bigger the plane is, the more challenging the loads the tail has to handle are, so what might be a feasible solution on a regional jet might not work at all for a large jet.
T-tails are an obvious choice when the engines are tail mounted, and in C-17 I guess the main reason is to keep the tail away from the wake of the main wing in certain "areas" of flight envelope: C-17 is a high wing configuration, and as a military aircraft it is subjected to more "challenging" flight states.
It might have something to do with the super stall phenomenon in which a stalled wing blankets a T-tail.