Originally Posted by powdermonkey
Best angle is down to max excess thrust and for a jet this will be at Vimd
This statement is only true for engines that have a thrust/speed curve almost flat in the vicinity of Vimd, which is the case for most jet engines.
Differentials in thrust being small, it's the differentials in drag that creates the optimum, hence it is the speed for minimum drag.
Otherwise, the generic formula as stated by EGBKFLYER is always true:
Vx is the speed for maximum difference between thrust and drag (for a specific power settings since both curves vary with power settings).
Similarly, Vy is the speed for maximum difference between thrust power and drag power.
These 2 speeds are not directly related to Vs.
Luc