[notlefthanded]

Short answer: that is not correct for heavier than air aircraft.

https://www.grc.nasa.gov/www/k-12/airplane/forces.html

Lift requires energy, usually kinetic, like the forward motion of an aeroplane being converted to lift (and drag) via the wings, or the blades of a helicopter pushing air down, or real hot and fast gases pointed downwards (think harrier jump jet).

A blimp, on the other hand, relies on buoyancy for lift, so yeah, in that case, given an altitude at which it's stable, to maintain velocity it only needs to add enough thrust to counteract the drag created by its forward movement.

[skelsey]

Yes it is correct. Lift always creates drag. You can think of drag as the work necessary to gain lift. When lift is generated, it produced what is called induced drag[0]. Induced drag and parasitic drag, which is the drag generated from the aircraft structure itself, are where all the energy goes in unaccelerted flight.

[0] https://en.wikipedia.org/wiki/Lift-induced_drag

[notlefthanded]

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.