Originally Posted by
Capn Bloggs
There are two opposing scenarios here.
The theoretical scenario is where aircraft descend at the AOA for best L/D. In this case, a heavy aeroplane will descend on exactly the same path (AOA), but at a greater speed, than a light aircraft. Both will hit the ground at the same point, the only difference being that the heavier aeroplane will hit faster/quicker.
This is eloquently explained by none other than A C Kermode in The Mechanics of Flight, presented to me by my Dad in April 1975 (use my diagram below for the "Fig 6.1" discussion):
The Practical scenario is completely different. That is, we descend at (approximately) the same speed for all descents. We do not descend at Vmin+5 (or Green Dot?). We descend at say Mach 0.8 into 280KIAS. This completely changes the dynamics of the descent. Because the thrust is zero, the only way the aeroplane can counter the drag at the "fixed" speed is to use the weight, by diving. Now, if the aeroplane is heavier, the effective thrust from the weight will be more, and so it doesn't need to descend as steeply as a light aeroplane.
And that's all there is to it.
Scarebus discussion on page 159 here:
https://www.skybrary.aero/bookshelf/...-february-2002
It's "Getting a grip on" or "Coming to grips with"! But then Airbii aren't English are they!
Those vectors, explain why high performance sail planes take on water before departure. Mainly, I believe to get more speed for the optimum L/D ratio. Reduces the time flying between thermals, for example.
A heavy a/c at max landing weight, more distance is required. Takes longer to slow the aircraft down.
Hope that makes sense.
Weight does not effect the glide range within certain parameters. It does effect the TAS. Heavy = Fast.