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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Hydraulic Systems

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Fixed (left) and retractable (right) gear airplanes.
Figure 6-39. Fixed (left) and retractable (right) gear airplanes.

Landing Gear
The landing gear forms the principal support of an aircraft
on the surface. The most common type of landing gear
consists of wheels, but aircraft can also be equipped with
floats for water operations or skis for landing on snow.
[Figure 6-37]

The landing gear supports the airplane during the takeoff run, landing, taxiing, and when parked.
Figure 6-37. The landing gear supports the airplane during the
takeoff run, landing, taxiing, and when parked.

The landing gear on small aircraft consists of three wheels:
two main wheels (one located on each side of the fuselage)
and a third wheel positioned either at the front or rear of the
airplane. Landing gear employing a rear-mounted wheel is
called conventional landing gear. Airplanes with conventional
landing gear are often referred to as tailwheel airplanes. When
the third wheel is located on the nose, it is called a nosewheel,
and the design is referred to as a tricycle gear. A steerable
nosewheel or tailwheel permits the airplane to be controlled
throughout all operations while on the ground

Tricycle Landing Gear Airplanes
A tricycle gear airplane has three advantages:
1. It allows more forceful application of the brakes during
landings at high speeds without causing the aircraft to
nose over.
2. It permits better forward visibility for the pilot during
takeoff, landing, and taxiing.
3. It tends to prevent ground looping (swerving) by
providing more directional stability during ground
operation since the aircraft's center of gravity (CG)
is forward of the main wheels. The forward CG keeps
the airplane moving forward in a straight line rather
than ground looping.

Nosewheels are either steerable or castering. Steerable
nosewheels are linked to the rudders by cables or rods, while
castering nosewheels are free to swivel. In both cases, the
aircraft is steered using the rudder pedals. Aircraft with a
castering nosewheel may require the pilot to combine the use
of the rudder pedals with independent use of the brakes.

Tailwheel Landing Gear Airplanes
Tailwheel landing gear aircraft have two main wheels
attached to the airframe ahead of its CG that support most of
the weight of the structure. A tailwheel at the very back of the
fuselage provides a third point of support. This arrangement
allows adequate ground clearance for a larger propeller
and is more desirable for operations on unimproved fields.
[Figure 6-38]

Tailwheel landing gear.
Figure 6-38. Tailwheel landing gear.

With the CG located behind the main gear, directional
control of this type aircraft becomes more difficult while on
the ground. This is the main disadvantage of the tailwheel
landing gear. For example, if the pilot allows the aircraft
to swerve while rolling on the ground at a low speed, he or
she may not have sufficient rudder control and the CG will
attempt to get ahead of the main gear which may cause the
airplane to ground loop.

Lack of good forward visibility when the tailwheel is on or
near the ground is a second disadvantage of tailwheel landing
gear aircraft. These inherent problems mean specific training
is required in tailwheel aircraft.

Fixed and Retractable Landing Gear
Landing gear can also be classified as either fixed or
retractable. A fixed gear always remains extended and has
the advantage of simplicity combined with low maintenance.
A retractable gear is designed to streamline the airplane by
allowing the landing gear to be stowed inside the structure
during cruising flight. [Figure 6-39]

Airplane brakes are located on the main wheels and are
applied by either a hand control or by foot pedals (toe or heel).
Foot pedals operate independently and allow for differential
braking. During ground operations, differential braking can
supplement nosewheel/tailwheel steering.