Guten Tag Tinstaafl
Your post is right on, well written and informative. Whereas my posts were neither as eloquent nor as erudite, I am trying to say the same thing. Namely, these two different speeds are associated with different constraints. As you pointed out Best Range is a function of drag, whereas endurance is a function of power. Vx is a function of drag and Vy is a function of power. Though I realise that x and y speeds don’t appear on part 25 aircraft, it only confounded the issue. When I wrote that “lowest sink rate = a speed a bit lower than max climb rate for a jet Vy” I was being much too qualitative. And when I said I’d fly Vy in the turn I was just damn wrong. (It has since been edited for those that were going to try it). No, I would fly at max endurance in the turn and max range to get back to the aerodrome. To try to clarify for those I have unwittingly confused, mostly myself:
Max Range
Jet
Max angle of climb for a jet is derived where thrust subtract drag is the greatest, since thrust for a jet is relatively constant with speed, max T-D is at the lowest point on the drag curve vs. speed curve. The lowest drag gives the best range in glide: Vx = Best Range (jet)
Prop
Max angle of climb for a prop is derived in the same way except thrust falls off rapidly with speed so Vx in a prop is at a speed less than minimum drag speed: Vx < Best Range (prop)
Max Endurance
Jet
Vy speed in a jet is determined where the max excess power exists. In a jet the available engine power increases very quickly with speed (more so than the required power), so the greatest distance between the two curves is at a speed greater than minimum power speed: Vy >> Best Endurance (jet)
Prop
Vy speed in a prop is determined the same way, but in a prop the available engine power is relatively constant with speed so max excess power does occur at the lowest point on the power required curve: Vy = Best Endurance (prop)
Aha, and my math teacher said I couldn’t compare apples and oranges
Okay back to the original thread, let’s forget about Vx and Vy because they are only semi-relevant to the discussion of glide, we need to have a best glide endurance speed, and a best glide range speed available.