At 01:30 29 March 2005, wrote:
Got to thinking about your question, Bob and actually
we shouldn't try
to hit the edge of the cylinder at red-line. Why? Because
our
sailplanes are very inafficient at red-line, in fact
they start coming
down like a stone at anything over 90 knots. We should
climb the last
thermal to 500 over home + a smidgen and then fly the
indicated M/C to
the edge of the cylinder.

I did an analysis of this and it would appear that
the minumum time solution is to dial in a finish altitude
equal to 500' minus the altitude you can gain in a
pullup from your McCready speed to minimum sink speed.
Just before the cylinder edge you pull up and hit the
bottom outside edge of the cylinder. Depending on your
McCready setting you will approach the edge of the
cylinder at somewhere between 0 feet (Mc = 6 or higher,
full ballast) and 350' (Mc = 2, dry). It's easy to
calculate that you save about 45 seconds over flying
the McCready speed to the cylinder at 500'.

Why is this? Because there is excess kinetic energy
that can be turned into altitude at all cruise speeds
(the higher the speed, the more excess energy - and
altitude). To optimize, you should not carry excess
energy through the cylinder but instead come in below
the cylinder floor and use the energy to make the minimum
altitude, in this case 500'.

Most of us carry some extra margin just in case of
unexpected sink. In this case you can wait until you're,
say, two miles from the edge of the cylinder, then
dive off even more excess energy in the last two miles.
Because you are flying off more excess energy in a
short distance, you pretty quickly get up to speeds
where you can be right on the deck and pull up to well
over 500'. In this case you are flying less efficiently,
so the time savings go down a bit, to 20-30 seconds
versus flying McCready speed to 500'.

I would add that I am not advocating that anyone do
this, since I don't want to be held responsible for
the consequences of this finishing technique. It's
only worth a handful of points per day, but then again
so is finishing at 50' versus 200-300' in a gate.

9B