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After entering the starting position, an inertial navigation system provides continuous information on the aircraft's position by measuring the (1) _____ in the vertical, horizontal and lateral planes. A first integration over time outputs the (2) _____; a second integration over time gives (3) _____.
  • A
    (1) distance travelled; (2) velocity; (3) horizontal position
  • B
    (1) acceleration; (2) height; (3) present position
  • C
    (1) velocity; (2) last position; (3) acceleration
  • D
    (1) acceleration; (2) velocity; (3) distance travelled

Refer to figures.
An Inertial Navigation System (INS) provides the aeroplane’s velocity and position by continuously measuring and integrating its acceleration. This system relies on no external references, is unaffected by weather, and can operate during the day or night.

The products of an INS are position (latitude/longitude), speed (kt), distance (nautical miles), and other navigational information.

This system is composed of a stable platform consisting of high quality gyros and accelerometers and a computer.

The purpose of the computer is to integrate the accelerometer outputs with time to give velocity and then integrate velocity with time to give distance travelled. From this is available pitch and roll attitude, true heading, true track, drift, present position in latitude and longitude, ground speed and wind.

For navigation in a horizontal plane, two accelerometers are needed, which are normally aligned with True North and True East. These acceleration measuring devices sense any change in the aircraft’s velocity either as an acceleration or deceleration very accurately.

The acceleration signal from the amplifier is sent to an integrator which is a time multiplication device. It starts out with acceleration which is in feet per second squared. In the integrator, it is multiplied by time and the result is a velocity in feet per second.

With an input of feet per second, it is then sent through a second integrator, which is multiplied by time, the result is a distance in feet or nautical miles.

The computer associated with the inertial system knows the latitude and longitude of the take-off point and calculates that the aircraft has travelled so far in the north and east direction. The computer can then compute the new position of the aircraft and give a digital read-out.

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