曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
Midwest in the United States, landable fields may be
present every few miles, allowing a delay in field selection
to a lower altitude. In areas of the desert southwest
or the Great Basin, landing sites may be 30 or more
miles apart, so focusing on a landing spot must begin at
much higher altitudes above the ground.
Once committed in the pattern, do not try to thermal
away again. Accidents occur due to stalls or spins from
thermalling attempts in the pattern. Other accidents
have occurred as pilots drifted away from a safe landing
spot while trying to thermal from low altitudes. When
the thermal dissipated, the pilot was too far beyond the
site to return for a safe landing. It is easy to fall into this
trap! In all the excitement of preparing for an off-field
landing, do not forget a pre-landing checklist.
A common first cross-country flight is a 50-kilometer
(32 statute miles) straight distance flight with a landing
at another field. The distance is short enough that it
can be flown at a leisurely pace on an average soaring
day and also qualifies for part of the FAI Silver Badge.
Prepare the course well and find out about all available
landing areas along the way. Get to the soaring
site early so there is no rush in the preflight preparations.
Once airborne, take time to get a feel for the
day’s thermals. If the day looks good enough and
height is adequate to set off on course, go!
Committing to a landing away from the home field for
the first time is difficult. The first landing away from
the home field, whether the goal was reached or not, is
a notable achievement.
SOARING FASTER AND FARTHER
Early cross-country flights, including small practice
triangles within gliding range of the home field, are
excellent preparation and training for longer crosscountry
flights. The FAI Gold Badge requires a 300-
km (187 statute miles) cross-country flight, which can
be straight out distance or a declared triangle or out
and return flight. An average cross-country speed of
20 or 30 MPH may have been adequate for a 32-mile
flight, but that average speed is too slow on most days
for longer flights. Flying faster average cross-country
speeds also allows for farther soaring flights.
Improvement of cross-country skills comes primarily
from practice, but reviewing theory as experience is
gained is also important. A theory or technique that
initially made little sense to the beginner will have real
meaning and significance after several cross-country
flights. Post-flight self-critique is a useful tool to
improve skills.
In the context of cross-country soaring, flying faster
means achieving a faster average ground speed. The
secret to faster cross-country lies in spending less time
climbing and more time gliding. This is achieved by only
using the better thermals and spending more time in lifting
air and less time in sinking air. Optimum speeds
between thermals are given by MacCready ring theory
and/or speed-to-fly theory, and can be determined
through proper use of the MacCready speed ring or
equivalent electronic speed director.
On most soaring days there is an altitude range,
called a height band, in which the thermal strength
is at a maximum. Height bands can be defined as the
optimum altitude range in which to climb and glide
on a given day. For instance, thermals in the lowest
3,000 feet AGL may be 200-300 fpm, then increase
to 500 fpm up to 5,000 feet AGL and again weaken
before topping out at 6,000 feet AGL. In this case,
the height band would be 2,000 feet deep between
3,000 feet and 5,000 feet AGL. Staying within the
height band gives the best (fastest) climbs. Avoid
stopping for weaker thermals while within the height
11-11
band unless there is a good reason. On another day,
thermals may be strong from 1,000 feet to 6,000 feet
AGL before weakening, which would suggest a
height band 5,000 feet deep. In this case, however,
depending on thermal spacing, terrain, pilot experience
level, and other factors, the height band would
be 2,000 feet or 3,000 feet up to 6,000 feet AGL.
Avoid continuing on to the lower bounds of strong
thermals (1,000 feet AGL) since failure to find a thermal
there gives no extra time before committing to a
landing. [Figure 11-10]
Determining the top of the height band is a matter of
personal preference and experience, but a rule of
thumb puts the top at an altitude where thermals drop
off to 75 percent of the best achieved climb. If maximum
thermal strength in the height band is 400 fpm,
leave when thermals decrease to 300 FPM for more
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
Glider Flying Handbook(155)
