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a self-launch glider under power at a constant indicated
Figure 11-5. Navigational plotter.
11-6
speed and altitude. This also assumes the winds at altitude
do not change along the course, which is reasonable
for a course of 100 miles or so. For longer
distances, winds aloft may change along the course.
Normal soaring flight involves glides that vary in altitude
(so the winds will vary), drifting off course while
thermalling, deviations from course to follow the best
lift, and frequent speed variations for lift and sink. So
the wind triangle is of limited use on soaring flights,
and usually glider pilots simply estimate the crab angle
needed for a given crosswind component. It is a useful
exercise to devise a few scenarios and note the crab
angle needed for varying airspeeds. For instance, cruising
60 knots will require about 20° of crab with a 20
knot direct crosswind, while only 15° is needed for the
same crosswind cruising at 80 knots.
A SAMPLE CROSS COUNTRY FLIGHT
For training purposes, plan a triangle course starting at
Portales Airport (Q34), with turn points at Benger
Airport (Q54), and the town of Circle Back. As part of
the preflight preparation, draw the course lines for the
three legs. Using the plotter, determine the true heading
for each leg, then correct for variation and make written
note of the magnetic heading on each leg. Use 9°
easterly variation as indicated on the sectional chart
(subtract easterly variations, and add westerly variations).
For the first leg, the distance is 47 NM with a
true heading of 48° (39° magnetic), the second leg is 38
NM at 178° true (169° magnetic) and the third leg is 38
NM at 282° true (273° magnetic). [Figure 11-7]
Assume the base of the cumulus is forecast to be 11,000
MSL, and the winds aloft indicate 320° at 10 knots at
9,000 MSL and 330° at 20 knots at 12,000 MSL. Make
written note of the winds aloft for reference during the
flight. Mentally note the estimated crab angle needed
to remain on course along each leg. For instance, the
first leg will have almost a direct crosswind from the
left; on the second leg, a weaker crosswind component
from the right; while the final leg will be almost
directly into the wind. Knowing courses and approximate
headings aids the navigation and helps avoiding
getting lost, even though deviations to stay with the
best lift are often needed. During the flight, if the sky
ahead shows several equally promising cumulus
Figure 11-6. Construction of the wind triangle.
11-7
clouds, choosing the one closest to the course line
makes the most sense.
As further preflight preparation, study the course line
along each leg for expected landmarks. For instance,
the first leg follows highway and parallel railroad
tracks for several miles before the highway turns north.
The town of Clovis should become obvious on the left.
Note the Class D airspace around Cannon Air Force
Base (AFB) just west of Clovis—this could be an issue
if better clouds lead to a north of course track. Also,
with the northwesterly flow, it is possible to be crossing
the path of aircraft on a long final approach to the
northwest-southeast runway. Note that Clovis Airport
(CVN) has parachute activity—be aware that they will
drop upwind of the airport if they are active. Next the
towns of Bovina and then Friona should come into
view. The proximity of the Texico VOR near Bovina
indicates that alertness needs to be taken for power traffic
in the vicinity. The second leg has fewer landmarks.
After about 25 miles, the town of Muleshoe and the airport
will be straddled. Note that the Reese 1 MOA covers
part of this leg of the flight and the next leg. The
dimensions of the MOA can be found on the sectional
chart, and the AFSS should be consulted concerning
the active times of this airspace. Approaching the sec-
Figure 11-7. Cross-country triangle.
11-8
ond turn point it is easy to confuse the towns of Circle
Back and Needmore. The clues are the position of
Circle Back relative to a 466 feet AGL obstruction
(south and east) and the lack of a road that heads north
out of Needmore. Landmarks on the third leg include
power transmission lines, Coyote Lake (possibly dry),
Salt Lake, the small town of Arch and a major road
coming south out of Potales. About eight miles from
Portales a VOR airway is crossed.
After a thorough preflight of the glider and all the
appropriate equipment is stowed or in position for use
in flight, it is time to go fly. Once in the air and on
　
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