my turn
CJ: I think that you might have made a manipulation mistake with your vectors or the trig.
With your definitions (and references), I get:
L = W*cos(angleofclimb),
D = T - W*sin(angleofclimb)
This happens to satisfy all extreme cases of horizontal flight and vertical flight (if power setting allows such a steady state).
(1) Total drag D is what the poster asked about.
My answer:
Some assumptions are missing in the question.
If he doesn't touch the throttles as he levels off, the aircraft will accelerate and D will progressively increase to match T.
If he keeps his airspeed as he levels off, he will have to reduce the throttles. In this maneuver, D will be constant throughout.
(2) The second question is even more open.
You can't maintain speed and transition to climb without touching the throttles.
If you don't touch the throttles, we still need to know something about the vertical speed. Are they supposed to be the same? You will need less angle of climb for the same VS the faster you go.
I'm not waiting for the return fire - I'm going to bed - bm.