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angle. The control bar is pulled in to achieve this steep
approach—the further the bar is pulled in, the steeper
the descent rate. Each WSC aircraft is different, but
pulling the control bar to the chest may be necessary
to achieve the required angle.
• Descent at minimum safe airspeed—a nose-high
descent. This should only be used for unusual
situations such as clearing high obstacles for a short
runway in an emergency situation. The only advantage
is a steeper than normal descent angle. This is similar
to the best angle of climb speed and should only be
used with caution because stalling near the ground
could have catastrophic consequences for the pilot,
passenger, and people/property on the ground.
• Glide—a basic maneuver in which the aircraft loses
altitude in a controlled descent with little or no engine
power; forward motion is maintained by gravity
pulling the aircraft along an inclined path, and the
descent rate is controlled by the pilot balancing the
forces of gravity and lift. [Figure 6-15]
Although glides are directly related to the practice of poweroff
accuracy landings, they have a specifi c operational purpose
in normal landing approaches and forced landings after engine
failure. Therefore, it is necessary that they be performed more
subconsciously than other maneuvers because most of the
time during their execution, the pilot gives full attention to
details other than the mechanics of performing the maneuver.
Since glides are usually performed relatively close to the
ground, accuracy of their execution, the formation of proper
technique, and habits are of special importance.
The glide ratio of a WSC aircraft is the distance the aircraft,
with power off, travels forward in relation to the altitude
it loses. For instance, if it travels 5,000 feet forward while
descending 1,000 feet, its glide ratio is said to be 5 to 1.
The glide ratio is affected by all four fundamental forces that
act on an aircraft (weight, lift, drag, and thrust). If all factors
affecting the aircraft are constant, the glide ratio is constant.
6-15
Increasing Lift-to-Drag Ratio
Increasing Speed
Stall
LD-MAX
VNE
Figure 6-16. LDMAX.
Although the effect of wind is not covered in this section, it
is a very prominent force acting on the gliding distance of the
aircraft in relationship to its movement over the ground. With
a tailwind, the aircraft glides farther because of the higher
groundspeed. Conversely, with a headwind the aircraft does
not glide as far because of the slower groundspeed.
Variations in weight for an aircraft with a rigid wing
do not affect the glide angle provided the pilot uses the
correct airspeed. Since it is the lift over drag (LD) ratio that
determines the distance the aircraft can glide, weight does
not affect the distance. The glide ratio is based only on the
relationship of the aerodynamic forces acting on the aircraft.
The only effect weight has is to vary the time the aircraft
glides. The heavier the aircraft, the higher the airspeed must
be to obtain the same glide ratio. For example, if two aircraft
having the same LD ratio but different weights start a glide
from the same altitude, the heavier aircraft gliding at a higher
airspeed arrives at the same touchdown point in a shorter
time. Both aircraft cover the same distance, only the lighter
aircraft takes a longer time.
However, the WSC aircraft has different characteristics
because it has a fl exible airframe. As more weight is added
to the WSC wing, it fl exes more creating more twist in the
wing decreasing aerodynamic effi ciency, as discussed in
chapter 2. For example, a pilot is accustomed to a glide ratio
of 5 to 1 fl ying solo; a passenger is added, and this glide ratio
may decrease to 4 to 1. This decrease in glide ratio for added
weight is true for all descent speeds. The amount of decrease
in glide ratio varies signifi cantly between manufactures and
models because each wing fl exes differently. The more
fl exible the wing is, the greater the decrease in glide ratio.
Pilots should become familiar with glide ratios for their
aircraft at all speeds and all weights.
Although the propeller thrust of the aircraft is normally
dependent on the power output of the engine, the throttle is
in the closed position during a glide so the thrust is constant.
Since power is not used during a glide or power-off approach,
the pitch attitude must be adjusted as necessary to maintain
a constant airspeed.
The best speed for the glide is one at which the aircraft travels
the greatest forward distance for a given loss of altitude in still
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Weight-Shift Control Aircraft Flying Handbook(75)
