B2-13e Aircraft Systems - Navigation Flashcards

Vocabulary-style flashcards covering the fundamental laws of motion, navigation principles, components, and operation of Inertial Navigation Systems (INS) and Inertial Reference Systems (IRS).

Newton’s First Law of Motion

An object in motion will remain in motion and an object at rest will remain at rest unless acted on by an unbalanced force.

Newton’s Second Law of Motion

The acceleration of a body is directly proportional to the force causing it and inversely proportional to the mass of the body, expressed as $F = ma$.

Momentum

The product of the mass of an object and its velocity ($p = mv$).

Velocity

A vector quantity that describes both speed and direction, considering how fast a body moves and the direction it is moving at any given point in time.

Acceleration

The rate of change of velocity, calculated by the formula $a = \frac{v_2 - v_1}{t_2 - t_1}$, and expressed in units such as $m/s^2$.

Inertia

The natural property of all objects to resist any change in their state of motion; an object's tendency to resist acceleration.

Displacement

A vector or the magnitude of a vector from an initial position to a subsequent position, resulting from velocity and acceleration.

Area Navigation (RNAV)

A system that allows the pilot to fly direct from point to point without the need to fly to ground-based navigation beacons.

Azimuth

The clockwise angle from north to the longitudinal axis of an aircraft, commonly referred to as heading, ranging from $0^{\circ}$ to $360^{\circ}$.

Bearing (BRG)

The direction of a point or navigational aid measured clockwise from the aircraft’s longitudinal axis.

Latitude

The angular distance in degrees north or south of the equator, with parallels connect points of equal latitude.

Longitude

The angular distance east or west of the Prime Meridian (zero-longitude line) in Greenwich, England.

Cross Track (XTK)

The distance left or right from the desired track to the present position, measured perpendicular to the desired track.

Dead Reckoning

A basic navigational method that determines aircraft position by calculations using speed, direction, and time starting from a known previous position.

Great Circle

A circle on the surface of the earth whose plane passes through the centre of the earth, providing the shortest route between two points.

Rhumb Line

A line formed when it maintains equal angles with each meridian as it intersects them; it spirals toward the pole in a constant true direction.

Inertial Navigation System (INS)

A totally self-contained dead reckoning system that keeps track of movements in all directions to calculate present position without external inputs.

Accelerometer

A device used to measure the magnitude of aircraft acceleration along a single axis; it is nulled when the aircraft is at a constant velocity.

Cross-Couple Error

An error introduced when an accelerometer's sensitive axis moves away from null, causing it to sense accelerations at right angles to the original axis.

Torque Rebalanced Accelerometer

An accelerometer that uses signal pickoffs and rebalance torquers to hold the inertial mass at a null position, eliminating cross-couple error.

Integrator

An electronic circuit, typically using an operational amplifier and a capacitor, that multiplies signals by time to calculate velocity from acceleration or distance from velocity.

Schuler Tuning

A process that minimizes gravity-induced errors by setting a platform oscillation period of $84.4$ minutes, equal to a Schuler Pendulum.

Coriolis Force

A force acting on a body moving over a rotating surface, such as the earth, causing movement to curve (right in the northern hemisphere, left in the southern).

Strapdown INS

A late 1970s evolution of INS where gyros and accelerometers are fixed or 'strapped down' to the aircraft frame, eliminating mechanical gimbals.

Ring Laser Gyro (RLG)

A solid-state device that detects motion by measuring the frequency difference between two laser beams reflecting in opposite directions around a closed loop.

Dithering

The application of a small oscillatory vibration to a laser gyro by a dither motor to eliminate frequency 'lock-in' at low rotation rates.

Mode Selector Unit (MSU)

A control panel for the INS computer containing modes such as OFF, STBY, ALIGN, NAV, and ATT.

ATT Mode

An INS mode that provides only pitch, roll, and azimuth data, typically used as a failure mode if navigational functions fail.

Coarse Alignment (Caging)

The first stage of INS initialization where gimbals are driven to a starting position while gyroscopes spin up to operating speed.

Fine Alignment (Levelling)

The stage of initialization where accelerometer outputs are used to drive gimbals to accurately level the stable element, lasting about two minutes.

Gyrocompassing

The process by which the stable element of an Inertial Reference Unit (IRU) becomes aligned to its north reference by sensing the earth’s rotation.

ADIRS

Air Data/Inertial Reference System, which combines air data reference and inertial reference components into a single system.

Gimbal Lock

A condition occurring when gimbal orientation causes the spin axis to coincide with one of the axes of freedom, leading the system to precess and topple.

Random Drift

Errors in a gyroscope caused by defects such as bearing friction or mirror imperfections, minimized by advanced design and electronic tuning.

Centripetal Force

A force acting on a body causing it to move in a circular path, calculated as $F = \frac{mv^2}{r}$.