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air. This best glide speed corresponds to an angle of attack
resulting in the least drag on the aircraft and giving the best
lift-to-drag ratio (LDMAX). [Figure 6-16]
Any change in the gliding airspeed results in a proportionate
change in glide ratio. Any speed, other than the best glide
speed, results in more drag. Therefore, as the glide airspeed
is reduced or increased from the optimum or best glide speed,
the glide ratio is also changed. When descending at a speed
below the best glide speed, induced drag increases. When
descending at a speed above best glide speed, parasite drag
increases. In either case, the rate of descent increases and the
glide ratio decreases.
This leads to a cardinal rule of aircraft fl ying that a student
pilot must understand and appreciate: the pilot must never
attempt to “stretch” a glide by applying nose up pressure and
reducing the airspeed below the aircraft’s recommended best
glide speed. Attempts to stretch a glide invariably result in an
increase in the rate and angle of descent and may precipitate
an inadvertent stall.
To enter a glide, the pilot should close the throttle and
obtain the best glide speed. When the approximate gliding
pitch attitude is established, the airspeed indicator should
be checked. If the airspeed is higher than the recommended
speed, the pitch attitude is too low; if the airspeed is less than
recommended, the pitch attitude is too high. Therefore, the
pitch attitude should be readjusted accordingly by referencing
the horizon. After the adjustment has been made, the aircraft
should be retrimmed (if equipped) so that it maintains this
attitude without the need to hold pitch pressure on the control
bar. The principles of attitude fl ying require that the proper
fl ight attitude be established using outside visual references
fi rst, then using the fl ight instruments as a secondary check.
It is a good practice to always retrim the aircraft after each
pitch adjustment.
6-16
A stabilized power-off descent at the best glide speed is
often referred to as a normal glide. The fl ight instructor
should demonstrate a normal glide, and direct the student
pilot to memorize the aircraft’s angle and speed by visually
checking the:
1. Aircraft’s attitude with reference to the horizon.
2. Noting the pitch of the sound made by the air.
3. Pressure on the controls, and the feel of the aircraft.
Due to lack of experience, the beginning student may be
unable to recognize slight variations of speed and angle of
bank immediately by vision or by the pressure required on
the controls. The student pilot must use all three elements
consciously until they become habits, and must be alert when
attention is diverted from the attitude of the aircraft. A student
must be responsive to any warning given by a variation in
the feel of the aircraft or controls or by a change in the pitch
of the sound.
After a good comprehension of the normal glide is attained,
the student pilot should be instructed of the differences in
the results of normal and abnormal glides. Abnormal glides
are those conducted at speeds other than the normal best
glide speed. Pilots who do not acquire an understanding and
appreciation of these differences experience diffi culties with
accuracy landings which are comparatively simple if the
fundamentals of the glide are thoroughly understood.
Gliding Turns
Gliding turns have a signifi cant increase in descent rate than
straight glides because of the decrease in effective lift due to
the direction of the lifting force being at an angle to the pull
of gravity. Therefore, it should be clearly understood that the
steeper the bank angle, the greater the descent rate.
In gliding turns, the decrease in effective lift due to the
direction of the lifting force being at an angle to the pull
of gravity make it necessary to use more nose-up pressure
than is required for a straight glide. However, as discussed
earlier for steeper turns, airspeed must be maintained well
above stall speed which increases during turns or the WSC
could stall in the turn.
When recovery is being made from a medium or high banked
gliding turn, the pitch force which was applied during the turn
must be decreased back to trim, which must be coordinated
with the roll back to level.
In order to maintain the most effi cient or normal glide in a
turn, more altitude must be sacrifi ced than in a straight glide
since this is the only way speed can be maintained without
power. Attention to the front tube angle with the horizon and
the reference point on the front tube provide visual reference
　
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