© Flytec USA, 2003
32
0
Bat.
3.57V
12h
4
3
2
1
m/s
1
2
3
4
70
50
40
30
m
60
The McCready indicator points to the 2 m/s
average climb rate that corresponds to a
flight speed of 62 km/h. The indicator covers
over the indicator for the average thermal
climb rate. Here the best glide speed would
be 47k m/h.
If the pilot were to further reduce his/her speed, the McCready indicator would run into the negative number range.
This is must be avoided, because the pilot will unnecessarily lose both
time and altitude. The 5030 will sound a rapid low beep tone if the pilot
flies slower than best glide speed. This will most likely happen when a
pilot flies right at best glide speed and then encounters sinking air. In
this case the pilot should speed up to remain at best glide speed.
To fly at the optimum speed, assuming that our climb rate in the next
thermal is equal to the average thermal climb rate, the pilot should
adjust his/her airspeed in such a way that the McCready indicator
points to the value that the thermal average ring has filled to on the
dial scale (See figure) or such that McCready pointer covers the
average thermal climb rate pointer on the vertical bar scale. Of
course, the next climb may be different than the previous one so the
pilot may elect to fly with the McCready indicator above or below the
Average Thermal Climb indicator. A conservative pilot might prefer to
fly with the McCready indicator between zero (best glide) and the
value of the average thermal climb.
All the functions described here can be sampled in the simulation
mode. The measured values such as speed, sink or climb, flight
direction and also ground speed can be varied by the user. Their
effects can be observed on the LCD screen and the resulting tones can be heard.
E6 Final Glide Calculation
Here, GPS data and the McCready theory and calculations go hand in hand (please also read the section E5-
McCready Theory.
Final glide calculations relate to reaching a goal as quickly as possible. Of course, the goal has to
be stored as a waypoint in the waypoint list. To aid the pilot in achieving the fastest time to goal, the 5030 will
indicate when to leave the last thermal.
To be able to make this decision, the distance to the location (goal/waypoint) must be known. The distance is
calculated using your current position, as determined by the GPS receiver. Additionally, the calculation requires the
altitude of the waypoint and the present altitude of the pilot. From this information, the required glide ratio
over
ground (L/D req.) that is necessary to reach the goal can be calculated. No other parameters, such as wind and wind
direction, flight speed and polar curve, are required to make this calculation. The required glide (L
I
D req.) ratio can
be selected as one of the user fields.
Only when the pilot’s actual glide ratio (over ground)
is calculated do the
parameters just mentioned need to be used.
Basically the final glide consists of two phases. Considered separately they are:
1. Climbing in the last thermal
2. The straightest possible glide path to goal
The last thermal
Let’s assume that our pilot is circling in a good thermal, which provides him/her with an average climb of 400 fpm (2
m/s). Besides the polar curve table in the 5030’s memory, there is a second table with the calculated speeds-to-fly),
which knows the associated McCready speed for each average climb (30 sec average) in a thermal. For each speed
to fly value, there is an associated glide ratio (through the air). While thermaling, your heading will repeatedly point in
the direction of goal. The wind component and the glide ratio over ground is calculated at that moment.
A zero wind has a wind factor =1; tail wind >1; and head wind <1. From the distance to goal and the glide ratio (over
the ground), the 5030 calculates the altitude that the pilot will lose on his/her glide path to goal. The unit considers
the altitude of the goal (input for each waypoint) and then calculates the optimum departure altitude.
The 5030 compares the optimum departure altitude with the current altitude and displays this value in the user
selectable field
Alt a. WP
. When this value goes from negative to zero the
Alt a. WP
user field will inverse (white
