Glossary of Aviation Terminology

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Quaternion: A system of representing attitude by measuring angle of aircraft center line with respect to three orthoginal axes plus rotation about centerline; quaternions are used over Euler angles (pitch, roll, yaw) when pitch can approach 90deg because of a singularity on Euler angles at 90deg; discrete-time computations using quaternions can run more slowly than those with Euler angles while producing results of the same accuracy See Also: Euler parameters;

RADALT: Radar Altimeter

Radar altimeter (RADALT): Measures height above terrain. The altitude is monitored to provide a low altitude warning during TF operations and landing operations. It can also be used as input to the Terrain Reference Navigation algorithm for position updates.

Radar altitude: Height with respect to the terrain below (distance above closest dirt); Synonyms: above ground level; Symbols: h sub r; Typical Units: ft; Dimensions: Length;

Radar altitude select (RALT SEL): A basic guidance mode, providing vertical guidance to an operator selected radar altitude;

Radial error probability (REP): A probability that a percentage of one-dimension measurements will lie on a radial (line) of given length, with the origin centered at truth or mean of the measurements; used to specify test cases for measurement errors of sensors of one dimension, such as vertical velocity; Compare: circular error probability, spherical error probability;

Radio navigation: Navigation relative to radio station, providing, for example, of relative bearing, range, lateral deviation, and glideslope; Examples include VOR, TACAN, and PLS. Radio navigation differs from other navigation in that the transmitter signals often dropout for a long period of time, like minutes. This can occur because of natural obstructions, or because the transmitter was shut down intentionally. In hostile territory, a PLS can locate a downed pilot, who would be foolhardy to be continuously transmitting, but would transmit infrequently with small bursts of data. The Radio- Navigation system accommodates this phenomenon by simulating range and bearing to the fixed site when it is not transmitting. After reacquiring a mobile transmitter, the mobile station's position is re-determined. The navigation component supports wash-out filters on output data.

RALT SEL: Radar altitude select

Range (rng): Standard aviation term Synonyms: distance; Symbols: r; Typical Units: ft,nmi - method of measurement dependent on use; Dimensions: Length;

Ranging: Act of determining a range

Rate limiter: A filter that passes the input as the output, except that rate of change of the output is limited to a maximum absolute value; Compare: limiter;

Raw: Data taken directly from the sensor; Compare: derived, estimated, filtered, measured, selected, smoothed

Real time: Time in a computational process which runs at the same rate as a physical process; for example, algorithms designed to run a fixed period t (filter time constants at set for t) and actually execute with frequency 1/t execute in real time; Avionics systems must run in real time;

Real-time engineering simulation (rtes): A simulator designed to test avionics algorithms with a pilot in the loop, consisting of a simulated cockpit, an aircraft model, sensor models, and algorithms to be tested; rtes is often used during development to check algorithms, such as the navigation, radio navigation, guidance and flight director, prior to full-scale software development; rtes gives systems engineers early insight in human factors problems, pilot complaints, algorithm bugs, unstability in the algorithms, expected performance (accuracy), and pilot-machine interaction; Synonyms: piloted simulation; Compare: built-in simulation;

Reasonableness: A test to determine if data is reasonable, for example, radar altitude must be positive, and two devices should return similar data within known limits of each other

Receive: To absorb rf energy

REFACC: Reference acceleration

Reference: What must be achieved in order to match a plan; Synonyms: desired;

Reference acceleration (REFACC): A guidance control law parameter, generated by the longitudinal guidance modes; Typical Units: ft/s-squared, g; Dimensions: Length / Time-squared

Reference acceleration gain (KLA): A guidance control law parameter, generated by the longitudinal guidance modes; Typical Units: s; Dimensions: Time.

Reject: To disallow a position update, usually by an operator; Compare: accept

Relative: Applies to measurements, in a non-standard, moving reference, as opposed to fixed reference; Compare: absolute;

Relative bearing: Angle from aircraft center line to bearing of the destination; Symbols: B sub R; Typical Units: rad, deg;

Remote terminal (RT): Term defining role of a device on a MIL-STD-1553 bus as being a slave; Compare: bus controller;

Remote Terminal Unit: Signal Data Converter;

Rendezvous: To meet with another aircraft in the air, for refueling or other mission objectives

Rendezvous approach: To approach a planned rendezvous point

REP: Radial error probability

Reported: Data from a device

Ring-laser gyro (RLG): A gyroscope based on a laser beam instead of a rotating mass, providing to same data as a gyroscope;

RLG: Ring-laser gyro

RMS: Root mean square;

RNG: Range

Roll: Bank angle; Symbols: phi,Phi; Typical Units: rad, deg;

Roll cue: Flight director cue to control roll; in fixed-wing aircraft, a wheel cue; in rotary-wing aircraft, a lateral cyclic cue

Roll rate: Rate of change of roll; time derivative of roll; Symbols: q; Symbols: phi dot; Typical Units: rad/s,deg/s; Dimensions: 1/Time;

Root mean square (RMS): A statistical measure of data; the root of the mean of the square; for variables with mean of zero, the standard deviation is equal to the rms; Compare: root sum square;

Root sum square (RSS): A statistical measure of data; the root of the sum of the square; for a vector, its length is equal to the rss of its scalar elements; Compare: root mean square;

Rotary wing: A helicopter;

RSS: Root sum square;

RT: Remote terminal

RTES: Real-time engineering simulation

RTU: Remote Terminal Unit

Rudder: A control surface on fixed-wing aircraft, usually mounted at aft end of the fuselage sticking up (like a dorsal fin), that controls yaw (heading), and is controlled by the pedals; Symbols: delta sub R; Typical Units: rad, deg;

A , B , C , D , E , F , G , H , I , J - K , L , M , N , O , P , Q - R , S , T , U , V, W, X - Z