Appendix C: Glossary of Terms
From X-Plane Wiki
Here is some basic terminology that people misuse every day. Knowledge of these terms is crucial to working with X-Plane. These are the same terms that will be used by customer support if or when a user calls.
Working with the Program Itself
Download: To download something means to get files from some remote server on the Internet and receive those files on your computer. Users can download lots of airplanes and scenery packages for X-Plane from the internet. Downloading is receiving files from the Internet; it is not the same as installing those files.
Install: To install something means to move a copy of something onto your computer so that it can be run. When a user gets a DVD with X-Plane on it, he or she runs the installer to install the program from the DVD—this is not downloading the program. It is installing it. One would only be downloading it if the files were coming from the Internet (though once such files were downloaded, one would install them to have them ready for use).
Update: To update a piece of software is to convert it to a newer version. This should be done every couple months or so in order to take advantage of new features in the simulator. To update in X-Plane, the user first downloads and then installs a newer version. The updater program (available for free at X-Plane.com) does both of these things for you very easily.
Parts of an Aircraft
Anti-torque pedals: In a helicopter, the foot pedals which modify the collective pitch of the tail rotor. Because the helicopter's throttle governor keeps the rotors turning at a constant RPM, changing the pitch also changes the thrust generated by the rotor, so the tail rotor can swing the helicopter's tail to the left or right. This is referred to as yaw motion.
Collective: In a helicopter, the lever that modifies the collective pitch of the main rotor's blades; called collective because the pitch of all the blades is modified at the same time. Because the engine keeps the rotor moving at a constant RPM, increasing the rotor blades' pitch with this control will also increase their lift.
Cyclic: The control (a joystick in real life) which changes the pitch of the main rotor's blades as they go through each cycle, used to steer the craft left, right, forward, or aft.
Joystick: A control device used in aircraft. It consists of a base with a handle attached to it. The handle can be tiled around within the base to control the pitch and roll movement of the aircraft. Computer joysticks often have the ability to twist the handle to control yaw movement also. Real airplanes have either a joystick or a yoke to control them, while helicopters are controlled with joysticks only.
Rotor: The rotating part of a helicopter that generates the craft's lift; similar in appearance to an oversized airplane propeller, though different in its operation.
Rudder pedals: Foot pedals in an airplane used to steer the plane down the runway and to control its yaw motion in flight (that is, the wagging of its tail left or right). This becomes very useful when starting turns and counter-acting crosswinds. Note that these are not spelled “petals,” as they are not named after the fragile leaves of a flower.
Yoke: The yoke, named after a wooden device draped across oxen to tow things, is the “steering wheel” of the airplane. It is used to steer the plane in flight by dipping the wings up or down and by pulling the nose up and pushing it down. Note that this is not spelled “yolk,” as it is not named after the center of an egg.
Movement of an Aircraft
Pitch: Movement of the aircraft's nose up or down (see the image above).
Roll: Movement of the aircraft's body along the line formed by its body; in an airplane, this is easily seen as the dip or rise of the wings (see the image above).
Yaw: Movement of the aircraft's body left or right, most easily pictured as a wagging of the aircraft's tail (see the image above).
Other Aviation Terms
ADF: Automatic Direction-Finder. This is the old-style navigation device that just points a needle at a transmitter on the ground. These are not used too often any more because modern navigation involves staying on a pre-defined course (a line), not just taking any random routing to get to a pre-defined point, like an ADF typically provides. Additionally, with GPS navigation, the whole idea of going to pre-defined points (like picking up bread-crumbs to find one’s way home) is thankfully disappearing. The GPS will take pilots all the way to where they want to go in a straight line, not a zig-zaggy one like would be achieved in flying from one navigation transmitter to another, wasting fuel with an indirect routing simply because of the locations people chose to plant navigation transmitters fifty years ago.
AGL: Above Ground Level. When holding an altitude requested by air traffic control, a pilot will hold an altitude MSL (above mean sea level). This lets the pilot stay at a constant level while flying. In order to avoid a horrific and instant death, however, pilots should be aware of their altitude AGL (above ground level) as well! The altimeter in the aircraft works on air pressure, so it measures the altitude above sea level (MSL), so awareness of minimum allowable altitudes in one’s region is always needed in order to stay at least that high. The radio altimeter measures the height above the ground (AGL). Most planes, however, do not have these installed. This is increasingly okay, though, because in theory a pilot can follow the en route and approach charts, which list safe MSL altitudes, and more and more planes have moving maps that clearly show the terrain elevation, so pilots can be sure that their elevation is safe.
Airspeed indicator (ASI): The ASI is driven by the pressure of the air impacting a little tube on the nose or wing of the plane. More pressure means the craft is moving faster. See the discussion in “Indicated airspeed (IAS)” below.
Altitude: An aircraft's altitude is its height above sea level. This is typically displayed on the aircraft’s altimeter, which is driven by air pressure.
ATC: Air Traffic Control.
BC: Back Course. This is the part of the ILS that goes beyond the touch-down zone. Read all about it in Chapter 6, Navigation, Autopilots, and Flying on Instruments.
CDI: Course Deviation Indicator. This instrument (part of the OBI or HSI) displays which direction the aircraft needs to turn in order to intercept the VOR course. This is discussed in Chapter 6, Navigation, Autopilots, and Flying on Instruments.
Density altitude: As the temperature of the air increases, its density decreases. The barometric pressure can vary based on a number of other factors, too, so at sea level on a hot, low-pressure day, the density of the air may be the same as standard air density at 10,000 feet up in the air! This is a 10,000 foot density altitude. This means there is less air for the engines, less air for the propeller, and less air for the wings. All of this adds up to say that it will take the aircraft longer to get off the ground.
DME: Distance Measuring Equipment. An instrument used in navigation which measures distance using the delay between the sending and receiving of a radio signal. Aircraft use this to determine their distance from a fixed NAVAID.
Drag: The aerodynamic force (created by a fluid such as air flowing around an object) that slows the object's motion.
EFIS: Electronic Flight Instrument System. A flight instrument system (found in an aircraft's panel) with electronic displays rather than the mechanical gauges of a standard panel.
GA: This can stand for either general aviation (light planes) or Go Around, an autopilot mode that raises the nose in a wings-level attitude and calls for lots of power in order to get back to altitude after a botched landing approach).
Glideslope (G/S): The angle at which an aircraft approaches (or needs to approach) a runway; often used when discussing navigation by instruments. See Chapter 6 of the manual.
GPS: Global Positioning System. A form of navigation using data from satellites.
Heading (HDG): An aircraft's heading is the direction that its nose is pointing. This is also a mode in the autopilot that lets the pilot hold a pre-defined heading, typically magnetic. A magnetic heading is heading to the magnetic north pole, something a hair different than true north, which is a geographic heading that will take one to the true geographic North Pole. Remember, since the magnetic north pole is separated from the geographic north pole by a bit, true and magnetic heading are not typically the same! They may be off by 5 or 10 degrees in the medium latitudes. The difference between the true and magnetic north poles is called the magnetic variation.
HLD: Hold. Pressing this button will engage the autopilot in altitude hold mode. See the Autopilots section of Chapter 6 for more information.
HSI: Horizontal Situation Indicator. This instrument is found in the panel of many aircraft in X-Plane. It serves the same function as an OBI—that is, it indicates course deviation. See Chapter 6 for more information.
IFR: Instrument Flight Rules. The procedure for flying an aircraft based solely on the craft's instrument panel. Environmental conditions requiring such flight (such as the poor visibility on a rainy day) are referred to as IFR conditions. This is contrasted with VFR conditions (those operating under visual flight rules). In bad weather or above 18,000 feet, pilots need to fly by Instrument Flight Rules, following their instruments and air traffic control instructions carefully to avoid hitting the ground or other planes, or going off course and messing up the carefully laid plans of the air traffic controller. When flying IFR, it really makes no difference whether the pilot can see out the front of the plane or not, since he or is on a carefully mapped procedure to stay on a safe course. Seeing out the window in this case is an unneeded luxury.
ILS: Instrument Landing System. A ground-based system for guiding approaching aircraft into the runway via radio signals. See the Chapter 6 for more information.
IMC: Instrument Meteorological Conditions. When pilots are in clouds or rain and cannot see out the window, they are required to fly by IMC rules. In such conditions, they need to be on an instrument flight plan.
Indicated airspeed (IAS): The presumed airspeed of a craft as determined by measuring the pressure acting on a little tube attached to the craft which points into the wind. This differs from true airspeed in situations where the air has very little density (for example, at 80,000 feet in an SR-71 Blackbird or in orbit in the Space Shuttle). This error, though, can be useful, because if there is less pressure pushing on the airspeed indicator, then there is also less pressure pushing on the wings of the aircraft. Therefore, the airspeed indicator tells how much air pressure is available for the props and wings (which is what a pilot really cares about, as more pressure gives more lift and drag). So, if a pilot is going 120 mph in thin air, but the pressure is only strong enough to measure 100 mph on the airspeed indicator, then that means the aerodynamic pressure on the wings is only 100 mph-worth of pressure! It is this pressure that determines how much lift and drag the wings can put out.
Lift: The aerodynamic force (created by a fluid such as air flowing around an object) that pushes an object upward.
Localizer (LOC): A localizer is part of an instrument landing system (ILS). It serves as a lateral (left and right) guide to the centerline of the runway.
Mach speed: The speed of sound through the air. Mach's number actually describes the speed of sound through any fluid (that is, liquid or gas). In application to aeronautics, though, it is implied that the fluid is air. Note that this number is dependent on a number of factors, such as temperature, humidity, and pressure. Generally, "Mach 1" is cited as 768 miles per hour (the speed of sound at sea level in dry air at 68˚ Fahrenheit).
NAV: Short for “navigate.” This is an autopilot mode that follows an ILS, localizer, VOR, or GPS path. See Chapter 6 for more information.
NAVAID: A navigation aid transmitter (typically a VOR, NDB, or ILS) which is used as a reference when flying. These are often found on or near an airport, but they can also be scattered between airports to use a node points in an airway. Pilots often fly from NAVAID to NAVAID on long flights, as a VOR is only useable from about 50 miles away. See Chapter 6 for more information.
NDB: Non Directional Beacon. See the ADF note above.
OBI: Omni-Bearing Indicator. This instrument, used for navigation, is found in most general aviation aircraft. It consists of a moving arrow (called the course deviation indicator, or CDI) which points the way to whatever VOR frequency is tuned in the navigation radio. The instrument is set using the Omni-Bearing Selector (or OBS), the knob in its lower left corner. A more expensive version of this is an HSI. See Chapter 6 for more information.
RPM: Rotations per minute; a way of measuring the speed of a rotor or propeller. In a helicopter, the RPM of both the main rotor and the tail rotor are held constant.
Speed: The change in the position of an object over time; unlike velocity, speed does not take into account the direction of the object's movement.
Thrust vector: The direction in which the engine or rotor’s thrust is going; for a helicopter sitting on a helipad with its controls at neutral, this is straight down.
Thrust vectoring: The ability of helicopters and some other aircraft (such as the Harrier or the F-22) to change the direction of the thrust from its engines/rotors.
Vector airways: Vector airways are the pre-charted airways that are defined by a series of VORs. Pilots fly from VOR to VOR until they reach their destination, thereby staying on a vector airway. Each segment of the vector airway thoughtfully lists the minimum altitude that pilots can fly that airway segment with to avoid crashing.
Velocity: The combination of an object's speed and the direction of its movement; for example, an aircraft might have a vertical velocity of 500 feet per minute (meaning it moves upward at a rate of 500 feet per minute) or a vertical velocity of -500 feet per minute (meaning it moves downward at 500 feet per minute).
Vertical speed/vertical velocity: The rate at which the aircraft is gaining or losing altitude, typically given in feet per minute.
Vfe: Velocity Flap Extension. This is the maximum speed at which the aircraft can deploy its flaps without damaging or breaking them.
VFR: Visual Flight Rules. This is flying done using a combination of the pilot's view of the outside world and the aircraft's instruments. Environmental conditions permitting such flight (such as a sunny day with 10 mile visibility) are referred to as VFR conditions. It is assumed in such conditions that pilots are always able to see out the window well enough to avoid collisions with terrain and other aircraft. To use visual flight rules, one typically needs about 3 miles visibility and to stay about 1000 feet from the clouds.
VMC: Visual Meteorological Conditions. These are environmental conditions suitable for flying by sight (VFR).
VOR: Very High Frequency Omnidirectional Range. This is a type of NAVAID that sends out signals that pilots can follow to get to or from the transmitter. While an NDB simply lets the aircraft’s ADF needle point right to it, the VOR actually lets pilots fly to the station along a programmed radial. So, for example, rather than just “flying to the VOR,” a pilot can be sure to fly to the VOR along the 090 radial (from the east), guaranteeing his or her location to be along an airway for the entire trip to the VOR. This is nice because once the airway is charted, the aircraft will be over mapped terrain height for the entire trip, and if the wind starts to blow it off course, then the pilot will see it quickly due to a deflected needle, at which point he or she can turn the nose into the wind to stay on the desired radial. Light airplanes often track these VOR signals using an Omni-Bearing Indicator, or OBI, while more expensive craft often use a Horizontal Situation Indicator, or HSI. See Chapter 6 for more information.
Vne: Velocity Never Exceed. This is the maximum speed that a given airplane can go. Going faster than Vne can result in “structural damage.” Please be aware that "structural damage" is very conservative language for "ripping your wings off so you plunge to a horrible death."
Vno: Velocity Normal Operating. This velocity should not be exceeded unless the air is very smooth. Even then, it should be exceeded “with extreme caution,” as the operating handbooks say.
VSI/VVI: Vertical Speed/Velocity Indicator. By looking at how fast the air pressure is changing, the VSI deduces how quickly the aircraft must be climbing or descending.