Thanks, mountain man. Perhaps example was ill-chosen. I always thought myself that the convert speed to height routine had more to it so piety than practical value, given the speeds and drag of a Tiger. Let me put that aside. Although of course in other types one could well convert speed to height, it is not really material here.
I recognise right away your point about the weight, the lift amd the descent, because at one time I looked at it your way, and then later changed my mind. Maybe I should change it back again. My current reasoning is that there are four forces in balance, two opposing two. If any falls out of balance there is an acceleration in that pair. If it is a thrust/drag imbalance there is a speed acceleration/deceleration until balance is again reached. If it is a weight/lift imbalance there is a vertical accelaration/deceleration until balance is again reached.
The basic proposition is that an aircraft in any stable flight condition is in balance.
I see what you say about the weight vector in a steady descending glide. As you say,this element gives a forward component to weight, and balances drag. I agree. But is that not tantamount to saying that weight provides part of the thrust? The aircraft is not accelerating, and drag is not compensated by any balancing force from any source other than the descent. In a glider the weight element is the only source, in a powered descent it is a partial source.
Perhaps I did not express it well, but that really was what I was addressing to Captain Pit Bull. I think he had said that a glider does not have a thrust/drag pair, but it seems to me that it does, and the source of the "forward" component that creates the balance, commonly called thrust, is exactly the forward weight vector that you describe.
Thank you for your patience.