4 flight optimisation, 1 final glide calculation, Flight optimisation – Flytec 6020 * User Manual
Page 51: Final glide calculation
Operating Manual Flytec 6020
9.4 Flight optimisation
9.4.1 Final
glide
calculation
Here the GPS-Data and the McCready theory go hand in hand. Principally it is
about reaching a goal (of course it must be logged as a waypoint in the list)
as fast as possible, or rather, to get a signal from the instrument of when the last thermal can
be left in order to arrive at the WP as fast as possible. In order to be
able to establish a statement about this, the distance to this location must be known. This
distance will be calculated with help of the GPS-Receiver. In addition, we need the altitude of
the waypoint (is mentioned in the list of waypoints), as well as the current altitude of the pilot.
From this smallish amount of information it is possible
to calculate the required glide ratio over ground (L/D req.) which is necessary
to reach the goal. For this purpose all other conditions, such as climb, sink, wind
and wind direction, flight speed and polar curve, are left entirely unconsidered.
The required glide ratio can be displayed in the user defined fields: L/D req.
It is only when the flyable glide ratio (over ground) has to be determined, that the before
mentioned conditions have indeed an important role.
Basically the final approach consists of two phases which are to be considered separately:
1.)
climbing in the last thermal and
2.)
the straightest possible glide path to the goal.
The Flytec 6020 does not calculate with the McCready theory, but only with
the speed of best glide. In order to reach the goal under optimal conditions all
the same, the pilot can take nonetheless some decisions based on the final glide display
screen, which will help him to reach goal safely in the shortest possible time.
For this purpose it is helpful to keep part of the McCready theory at the back of one’s mind.
The McCready theory declares that one is flying time optimised if, after having
left the thermal, one would be flying as fast as one would be in a descending air mass at the
same speed as would be the day specific climb in the thermal.
This speed value has to be calculated from the polar curve and the resulting figure is the
speed to fly. Given the fact that the 6020-GPS does not compute with the polar curve, one
needs to estimate this „optimal“ speed by himself.
1.) Let’s assume that the pilot is circling under a cloud in quite a good thermal which provides to
him an average climb of 2 m/s. While circling he will naturally try
to fly with the speed for minimum sink. If, while circling, the nose of the aircraft turns again and
again in the direction of the goal, the wind component, and, derived from this the wind factor,
may be determined at this moment and consequently the glide ratio over ground (Gnd) can be
calculated.
From the distance to goal and the glide ratio (gnd) the 6020-GPS calculates the loss in height
which the pilot requires on his glide path to the goal. If the altitude of the goal is added (for each
WP also its altitude is saved), then we obtain directly the minimum departure altitude. The own
altitude is known, therefore the instrument can now display directly by comparison at which
altitude is reached the path of best glide and if we still have to thermal up to arrive safely.
It is of course subject to the pilot’s experience whether he wants to take-off immediately upon
positive „Diff. BGWayp“, or whether he will prefer to climb up further and take some reserve
altitude.
The 6020-GPS naturally does not know whether in the course of the glide path lifting
or sinking air mass zones are incorporated, or if the wind intends to change.
The instrument calculates with the current wind and assumes that no lifting or sinking zones are
to be expected.
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