On 14 Feb., 13:59, "stephanevdv" wrote:
Somebody wrote:


Now for the reason for making low speed finishes:

It would be interesting indeed to calculate for diverse circumstances
if the reduction of the induced drag in ground effect compensates for
the energy loss consecutive to the high speed dive (as profile drag is
directly proportional to the square of the speed) needed to get near
the ground at very nearly Vne. Given the added energy loss of having
to jump over hedges and wires (deflection of control surfaces is drag-
inducing), I think it would probably be mathematically better to make
a sensible approach aiming for the runway threshold.

If I'm right, no competitor would be justified in doing low finishes
by the idea of flying an optimal finish. Their only justification
would be "showing off" or "having fun". Now who has got the knowledge
of physics to do the maths?

There's no need to do those maths because the most efficient final
glide is clearly the one that gets you to the finishline at the
McCready speed according to the last thermal.
Unless...
1. you encounter sink on the way
2. you encounter lift on the way
3. you add a little safety margin by climbing higher than what the
calculator says

Most people do 3. because they cannot assess to what degree 1. and 2.
will happen.
So at some point, after maybe nothing or 2. happened, you have this
excess height and are confident you won't need it. I find that point
is usually at about 8-12km out. And from then on it is definitely not
the most efficient to continue at "low" speed.

Marcel Duenner