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Instrument Flying Handbook
Aerodynamic Factors
Slow Speed Flight

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Instrument Flying
Handbook

Preface

Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Flying
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Flying
Using an Electronic Flight
Display

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight
Display

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency
Operations

Delaying the boundary layer separation is another way to
increase CLmax Several methods are employed (such as
suction and use of a blowing boundary layer control), but the
most. common device used on general aviation light aircraft
is the vortex generator. Small strips of metal placed along
the wing (usually in front of the control surfaces) create
turbulence. The turbulence in turn mixes high-energy air from
outside the boundary layer with boundary layer air. The effect
is similar to other boundary layer devices. [Figure 2-12]

Small Airplanes
Most small airplanes maintain a speed well in excess of 1.3
times Vso on an instrument approach. An airplane with a
stall speed of 50 knots (Vso) has a normal approach speed
of 65 knots. However, this same airplane may maintain 90
knots (1.8 Vso) while on the final segment of an instrument
approach. The landing gear will most likely be extended at
the beginning of the descent to the minimum descent altitude,
or upon intercepting the glide slope of the instrument landing
system. The pilot may also select an intermediate flap setting
for this phase of the approach. The airplane at this speed has
good positive speed stability, as represented by point A on
Figure 2-10. Flying in this regime permits the pilot to make
slight pitch changes without changing power settings, and
accept minor speed changes knowing that when the pitch is
returned to the initial setting, the speed returns to the original
setting. This reduces the pilot's workload,

Aircraft are usually slowed to a normal landing speed when
on the final approach just prior to landing. When slowed to
65 knots, (1.3 Vso), the airplane will be close to point C.
(Figure 2-10) At this point, precise control of the pitch and
power becomes more crucial for maintaining the correct speed.
Pitch and power coordination is necessary because the speed
stability is relatively neutral since the speed tends to remain
at the new value and not return to the original setting. In
addition to the need for more precise airspeed control, the pilot
normally changes the aircraft's configuration by extending
landing flaps. This configuration change means the pilot must
be alert to unwanted pitch changes at a low altitude.

Various Types of  Flaps.
Figure 2-11. Various Types of Flaps.

If allowed to slow several knots, the airplane could enter
the region of reversed command. At this point, the airplane
could develop an unsafe sink rate and continue to lose speed
unless the pilot takes a prompt corrective action. Proper pitch
and power coordination is critical in this region due to speed
instability and the tendency of increased divergence from
the desired speed.

Large Airplanes
Pilots of larger airplanes with higher stall speeds may find the
speed they maintain on the instrument approach is near 1.3
Vso, putting them near point C (Figure 2-10) the entire time
the airplane is on the final approach segment. In this ease,
precise speed control is necessary throughout the approach. It
may he necessary to temporarily select excessive, or deficient
thrust in relation to the target thrust setting in order to quickly
correct for airspeed deviations.

Vortex Generators.
Figure 2-12. Vortex Generators.

 

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