You may define navigation as the process of
directing a vehicle from one point to another.
Basically, navigation can be divided into two
categories: (1) position fixing and (2) dead
reckoning. In the first category, you determine
your position relative to positions of known
objects such as stars and landmarks. The most
common example of navigation by position
fixing is celestial navigation. Use of loran is
another example of navigation by periodic
position fixes. Dead reckoning, the second
category, is the process of estimating your
position from the following known information:
Previous position
Course
Speed
Figure 7-26.--Attitude direction indicator.
Time elapsed
REVIEW SUBSET NUMBER 2
Two examples of navigation by dead reckoning
are Doppler radar and inertial navigation systems.
Q1. What is the purpose of the four-gimbal
All navigation systems, except the inertial
type, rely on some bit of information external to
system in inertial navigation systems?
the vehicle to solve its navigational problem. In
this respect, the inertial navigation system stands
alone; it is completely self-contained within the
Q2. When operating the AN/ASN-50 attitude
vehicle. It is independent of its operating environ-
heading reference system, when do you use
ment, such as wind, visibility, or aircraft attitude.
the compass mode?
It does not radiate RF energy; therefore, it is
impervious to countermeasures. It does not
depend on ground transmission or any other
outside source to determine its instantaneous
INERTIAL NAVIGATION SYSTEM
position. The inertial navigation system simply
makes use of the physical laws of motion that
Learning Objective: Recognize the
Newton described three centuries ago.
operating principles and characteristics of
the inertial navigation system, to include
BASIC PRINCIPLES
Schuler loops and tuning; and identify
navigation errors and aligning and calibra-
The operating principle of the inertial
tion procedures.
navigation system (INS) is Newton's first law of
The following paragraphs describe a heading
motion. This law states "Every body continues
reference system found on the latest model high-
in its state of rest, or of uniform motion in a
speed aircraft and some patrol aircraft. The
straight line, unless it is compelled to change that
inertial navigation system (INS) is sometimes
state by forces impressed on it." In laymans
maintained by the Aviation Electronics Technician
terms, this law says that a body at rest tends to
(AT) rating. Some squadrons use a concept called
remain at rest. It also says a body in motion tends
to remain in motion, unless acted upon by an out-
an integrated weapons team (IWT). It is composed
of the three avionics/armament division (work
side force.
center 200) ratings--AT, AO, and AE. Regardless
The full meaning of Newton's first law is not
of who maintains the INS, you, must be familiar
easy to visualize in the earth's reference frame
with the theory and operating principles of such
because Newton's laws apply to an inertial
reference system. You may define an inertial
a system.
