CHAPTER 15
UTILITY HYDRAULIC SYSTEMS
MECHANICALLY CONTROLLED NOSE
INTRODUCTION
STEERING SYSTEM
These systems may be powered by the aircraft
power or aircraft utility hydraulic systems. Some units
This nose steering system is mechanically
receive power throughout the flight, while others are
controlled and hydraulically actuated in much the same
isolated from system pressure to prevent unnecessary
manner as an electrically controlled nose steering
loss of hydraulic fluid caused by damage or system
system. The steering actuator is of a different design but
malfunction.
serves the same dual function of providing steering and
dampening, when steering is not engaged.
The systems discussed here are representative of
systems that you may be required to work on. Values,
NOSEWHEEL STEERING SYSTEM
such as tolerances, pressures, and temperatures, are
COMPONENTS
given to provide detail in the coverage. You should bear
in mind that changes in these values are sometimes
The nosewheel steering system provides direc-
necessary because of experience and data gathered
tional control of the aircraft during ground operation in
from fleet use. When actually performing the
two modes of operation. These modes are nosewheel
maintenance procedures discussed, you should consult
steering and shimmy dampening.
the current applicable technical publications for the
latest information and exact values to be used.
Operation
NOSEWHEEL STEERING
Steering on the typical aircraft is accomplished by
SYSTEMS
swiveling the lower portion of the nosewheel shock
strut. A rotary-vane type of hydraulic steering unit is
LEARNING OBJECTIVE: Identify the
mounted on the fixed portion of the shock strut, and is
types of nosewheel steering systems and their
linked to the swiveling portion to which the nosewheel,
components. Identify the applicable mainte-
or wheels, are attached. The nosewheel steering power
nance requirements for these systems.
unit, shown in figure 15-1, uses gears. The steering
Nose steering systems are hydraulically actuated
range varies with each aircraft. For specific degrees of
and can be either electrically or mechanically con-
steering range for a particular model of aircraft, you
trolled. The steering actuator serves the dual function of
must consult the applicable MIM. For turns requiring a
providing steering and dampening (when steering is not
greater steering angle, the pilot can use differential
engaged).
braking, in which case the steering unit is automatically
disengaged and the nosewheel, or wheels, swivel freely.
ELECTRICALLY CONTROLLED NOSE
A typical hydraulic steering unit (fig. 15-2) has
STEERING SYSTEM
built-in valves and a follow-up system, and
automatically reverts to the shimmy damper mode
This type of nose steering system is an electrically
when not being used as a steering actuator. The valve
controlled, hydraulically actuated system that provides
varies with the type of aircraft. One method is by means
power steering. When not engaged the system provides
of mechanical linkage tied directly to the rudder pedals.
automatic nose gear shimmy dampening.
Gearing, through a camming arrangement, gives the
The nose gear is steered by an electrically con-
necessary sensitivity range; permitting satisfactory
trolled, hydraulic powered steering cylinder, which is
maneuvering of the aircraft through all speed ranges
mounted on the nose gear recoil strut. The cylinder is
and turn rates.
connected through mechanical linkage to an eccen-
Methods of arming or activating the steering
trically mounted drive stud on the recoil strut inner
systems of the various aircraft used in naval aviation are
cylinder.
numerous, and for convenience, a typical aircraft that
15-1
