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is raised too high without an increase of power, the
airplane will settle very rapidly and touch down
short of the desired spot. For this reason, the pilot
should never try to stretch a glide by applying backelevator
pressure alone to reach the desired landing
spot. This will shorten the gliding distance if power is
not added simultaneously. The proper angle of descent
and airspeed should be maintained by coordinating
pitch attitude changes and power changes.
The objective of a good final approach is to descend at
an angle and airspeed that will permit the airplane to
reach the desired touchdown point at an airspeed
which will result in minimum floating just before
touchdown; in essence, a semi-stalled condition. To
accomplish this, it is essential that both the descent
angle and the airspeed be accurately controlled. Since
on a normal approach the power setting is not fixed as
in a power-off approach, the power and pitch attitude
should be adjusted simultaneously as necessary, to
control the airspeed, and the descent angle, or to attain
the desired altitudes along the approach path. By lowering
the nose and reducing power to keep approach
airspeed constant, a descent at a higher rate can be
made to correct for being too high in the approach.
This is one reason for performing approaches with partial
power; if the approach is too high, merely lower
the nose and reduce the power. When the approach is
too low, add power and raise the nose.
USE OF FLAPS
The lift/drag factors may also be varied by the pilot to
adjust the descent through the use of landing flaps.
[Figures 8-3 and 8-4] Flap extension during landings
provides several advantages by:
• Producing greater lift and permitting lower
landing speed.
• Producing greater drag, permitting a steep
descent angle without airspeed increase.
• Reducing the length of the landing roll.
Flap extension has a definite effect on the airplane’s
pitch behavior. The increased camber from flap deflection
produces lift primarily on the rear portion of the
wing. This produces a nosedown pitching moment;
however, the change in tail loads from the downwash
deflected by the flaps over the horizontal tail has a
significant influence on the pitching moment.
Consequently, pitch behavior depends on the design
features of the particular airplane.
Flap deflection of up to 15° primarily produces lift with
minimal drag. The airplane has a tendency to balloon
No Flaps
Half Flaps
Full Flaps
With: Constant Airspeed
Constant Power
Flatter Descent Angle
Steeper Descent Angle
With: Constant Airspeed
Constant Power
No Flaps Half Flaps Full Flaps
Figure 8-3. Effect of flaps on the landing point.
Figure 8-4. Effect of flaps on the approach angle.
Ch 08.qxd 5/7/04 8:08 AM Page 8-3
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up with initial flap deflection because of the lift
increase. The nosedown pitching moment, however,
tends to offset the balloon. Flap deflection beyond 15°
produces a large increase in drag. Also, deflection
beyond 15° produces a significant noseup pitching
moment in high-wing airplanes because the resulting
downwash increases the airflow over the horizontal tail.
The time of flap extension and the degree of deflection
are related. Large flap deflections at one single point in
the landing pattern produce large lift changes that
require significant pitch and power changes in order to
maintain airspeed and descent angle. Consequently, the
deflection of flaps at certain positions in the landing
pattern has definite advantages. Incremental deflection
of flaps on downwind, base leg, and final approach
allow smaller adjustment of pitch and power compared
to extension of full flaps all at one time.
When the flaps are lowered, the airspeed will decrease
unless the power is increased or the pitch attitude
lowered. On final approach, therefore, the pilot must
estimate where the airplane will land through
discerning judgment of the descent angle. If it appears
that the airplane is going to overshoot the desired
landing spot, more flaps may be used if not fully
extended or the power reduced further, and the pitch
attitude lowered. This will result in a steeper approach.
If the desired landing spot is being undershot and a
shallower approach is needed, both power and pitch
attitude should be increased to readjust the descent
angle. Never retract the flaps to correct for undershooting
since that will suddenly decrease the lift and cause
　
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