I think we're interpreting op differently. No, not
all the energy added to a heavier than air aircraft (thrust) in straight-n-level flight* is used to counteract drag. Yes, where there is lift, there is induced drag. But the kinetic energy being added to maintain velocity is also being used for lift.
Imagine if the airfoil on an aeroplane were replaced with a symmetrical airfoil mounted with no angle of incidence. Thrust could be reduced because there's less drag from no lift. No lift, no induced drag, only parasitic drag, and the plane starts to lose altitude. Would you agree that not all the energy added to straight and level flight goes towards counteracting drag?
*where a' and v' are zero, and where for argument's sake, the thrust vector is perfectly horizontal
edit: by a' I mean change in vertical airspeed, by v' i mean change in true airspeed.
Imagine if the airfoil on an aeroplane were replaced with a symmetrical airfoil mounted with no angle of incidence. Thrust could be reduced because there's less drag from no lift. No lift, no induced drag, only parasitic drag, and the plane starts to lose altitude. Would you agree that not all the energy added to straight and level flight goes towards counteracting drag?
*where a' and v' are zero, and where for argument's sake, the thrust vector is perfectly horizontal
edit: by a' I mean change in vertical airspeed, by v' i mean change in true airspeed.