Captain Pit Bull, Following this with interest. I agree with your example of the glider and the airbrake, but I have one question. I am flying along in my Tiger Moth, engine working, straight and level, thrust/drag, lift/weight all happily balanced. The engine quits, so I no longer have "thrust" from that source. I am now in a biplane glider
I remember the mantra "convert speed to height". I do that. Naturally, as per instruction's warning voice, I always had a forced landing field selected and now I want to land on it. So now glider, I reconvert height to speed, or potential energy to (I hope I have this right) kinetic energy. I establish a new, albeit now descending, flight stability. Gosh, I am doing this well, I think I am going to make it, and here at my lap top my pulse rate is also steady.
Everything nicely balanced. Constant speed. I still have weight, and I am not dropping like a stone, but at steady speed, so I must have lift, and it must balance the weight. I still have drag, and I am not decelerating, so the drag must be balanced by ...................? Would we not in the normal case call it "thrust" or "thrust equivalent"?