the unit can consider the head wind, this increase in the best air speed will automatically be taken into
consideration. The best glide speed arrow will indicate the best glide speed over the ground.
In contrast to sailplanes, for which the manufacturers’ measured polar curves have long-term validity, a hang
glider (and, even more so, a paraglider) has a polar curve that is dependent on the age of the surface, the
condition of the sailcloth, the weight of the pilot, the aerodynamics of the pilot’s harness and other factors. In
order to realize the best possible speed during a flight, it is necessary to have entered the most accurate polar
curve data possible – which means this should be determined by the pilot and not rely on overly-optimistic
manufacturer’s data. An overly-optimistic polar curve will cause the 6030 to indicate a speed ring setting that is
too high.
In order to receive accurate speed to fly, netto vario and glide ratio information from the 6030, you must install
an accurate polar for your flight configuration (i.e., your particular glider, wing loading, harness, air speed
sensor, etc.). You can use the 6030 to record the data to build your polar by flying data-recording flights in
smooth air. During the flight, each air speed between V
stall
and V
ne
should be maintained for several seconds.
With the aid of FlyChart 4.52.21 or later, the data attained can be analyzed and the polar curve can be
determined.
Once the polar has been developed, only two polar curve points need to be entered into the 6030: the speed
(mph or km/h) and corresponding sink rate (ft/min or m/sec) for (1) minimum sink and (2) a speed in the upper
range of your glider (best maneuvering speed). These two air speed/sink rate pairs are entered manually into
the 6030 in Menu>Pilot settings>Polar data. In addition to the two sink-rate/air-speed pairs, you must also enter
the average altitude at which you flew when conducting the testing, using the altitude field of the Polar data
menu. The polar curve points will be converted and saved as IAS pairs and the polar curve will now be valid for
all altitudes.
12.5 McCready Theory – Optimized Speed to Fly
In contrast to flying at best glide speed, which allows us to reach a goal with the least possible loss of altitude,
we can get to a goal in the shortest possible time using McCready theory and calculations. A pilot thermaling up
in an attempt to reach a goal must decide whether to leave the thermal at an altitude that will allow him or her to
reach goal at best glide, or whether it might be faster to continue climbing and then glide with a higher speed to
goal.
McCready found that with a given polar curve, there is only one departure altitude that enables one to reach the
goal in the shortest time, assuming no net lift or sink on the way to goal. This departure altitude is dependent on
the pilot’s climb rate in the thermal and the prevailing wind component. The speed for the final glide is primarily
dependent on the average climb in the last thermal.
Because the 6030 measures and calculates the relevant parameters during thermaling, it can signal when to
leave the thermal to reach the goal as quickly as possible. The calculations assume that on the glide path to
goal, rising and sinking air neutralize each other, and that the wind direction and speed measured while
thermaling are the actual wind direction and speed while gliding to goal. Because these conditions do not
always exist, experienced pilots may climb above the McCready glide path to goal before leaving the thermal.
This additional altitude can be monitored in the Alt a WP user-field. The height above best glide path to goal is
continuously recalculated, and can be displayed in the A BG WP user-field. To better indicate the point when
the pilot can make goal at best glide speed and at McCready glide speed, the A BG WP and Alt a WP user-
fields will invert (white numbers on a black background) when their respective values become positive.
When attempting to determine at what speed to fly between thermals (and not to a goal), the pilot makes a
guess as to the value of the average climb in the next thermal. This value is known for historical reasons as the
McCready speed ring value. The 6030 calculates the average climb rate, over a user-selected time period, in
the last thermal and displays this value on the outer ring on the dial display. The time interval for the thermal
averager can be adjusted in Menu>Pilot settings>Vario>Thermal averager.
In addition to the 6030’s display of the last thermal’s strength, the 6030 also displays the speed ring setting
(next expected climb rate) that coincides with the pilot’s current air speed. This pointer is known as the active
McCready indicator, and is displayed as a radial line on the analog vario scale (dial). This indicator goes up
when the pilot speeds up, or has less sink. The indicator goes down when the pilot meets stronger sink, or flies
slower. How much the value changes depends predominantly on the polar curve.
To fly at McCready speed, adjust your speed so that the radial line points to your best guess of the strength of
the next thermal, most likely the value of the thermal averager. If you have turned on the McCready sounds, the
To Next Page
Loading...
