VOR System (PDF)

1 Chapter 3 Part 2 VHF OMNI RANGE (VOR)  2 Learning Outcomes  Working of VOR System  VOR Aircraft Equipment  VOR Airborne Loading  Principle of Automatic Flight Control (Auto Pilot) ...

1 Chapter 3 Part 2 VHF OMNI RANGE (VOR)  2 Learning Outcomes  Working of VOR System  VOR Aircraft Equipment  VOR Airborne Loading  Principle of Automatic Flight Control (Auto Pilot)  3 Introduction  The VOR system operates in 108-118 MHz band with channels spaced at 50 kHz  This band shares with ILS localizer frequency with first even decimals  VOR produces an infinite number of tracks (360 possible radials) from a beacon  It is practically free from static and does not suffer from night effect, consequently it can be used with confidence at any time throughout the 24 hours  4 Changi Airport VOR Ground Beacons  5 VOR BEACON RADIALS Omni Radial Concept  6 Light House Vs VOR  A simple analogy to VOR is given by imagining a lighthouse which emits an omni directional pulse of light every time the beam is pointing due north  If the speed of rotation of the beam is known, a distant observer could record the time interval between seeing the omni directional flash and seeing the beam, and hence calculate the bearing of the lighthouse  7 SIDE VIEW TOP VIEW Light House Analogy  8 Light House Vs VOR  In reality a VOR station radiates VHF energy modulated with reference phase signal- the omni directional light – and a variable phase signal similar to the rotating beam  The bearing of the aircraft depends on the phase difference between reference and variable phases- time difference between light and beam  9 Conventional VOR (CVOR) Spectrum  30 Hz AM : the variable phase signal (achieved by physical or electronic rotation of dipole)  9960 Hz AM: this is a sub-carrier frequency Modulated at 30 Hz with a deviation of ± 480Hz. The 30 Hz signal is the reference phase  10 VARIABLE 30 Hz (AM) REFERENCE 30 Hz (FM) ±480 Hz fc 30 Hz 9960 Hz VOR Frequency Spectrum  11 Reference Phase Signal  VOR carrier signal is amplitude modulated by a 9960 Hz sub-carrier which itself is frequency modulated at 30Hz  This omni directional radiation has circle as its horizontal polar diagram  At a given range from the transmitter, an aircraft’s receiver will detect the same phase on all bearings around it  In the receiver, the 30 Hz component of the transmission is used as a reference for the phase comparison which will provide the bearing  12 Rx N Rx Rx Rx Reference Signal- Same Phase in All Directions  13 Variable Phase signal  This is also transmitted on the station frequency, by an aerial which rotates either physically or electronically 30 times per second (30 Hz)  The signal is less strong than the omni directional signal, so that together the signals appear as limacon  The phase of this received AM signal will vary as the position of the aircraft changes around the circle  This phase can be compared with the phase of the FM omni directional signal, and displayed to the pilot  14 N PHASE DIFFERENCE 270º PHASE DIFFERENCE 90º LIMACON PHASE DIFFERENCE 180º Bearing by Phase Comparison  15 VOR GROUND ANTENNA  16 VOR Aircraft Equipment VOR aircraft equipment consists of  Receiver This airborne receivers picks up signals from ground station VOR antennas at the selected frequency and process the bearing information, which will be displayed on Radio Magnetic Indicator (RMI) In order to receive VOR signal, pilot has to fly on the minimum altitude of 1000 feet above ground level  Control unit The pilot should first tune the required VOR frequency and identify the station from the audio signal, at the same time he can also switch to VHF radio communication  17 RECEIVER VOR/LOC ANTENNA INDICATOR CONTROL UNIT VOR Aircraft Equipment  18  VOR indicators Omni Bearing Selector (OBS) A C ROTATING TO-FROM COURSE INDICATOR CARD B D OMNI OBS COURSE BEARING DEVIATION SELECTOR INDICATOR  19  A: Rotating Course Card is calibrated from 0 to 360 degrees, which indicates the VOR bearing chosen as the reference to fly by pilot  B: Omni Bearing Selector (OBS Knob) used to manually rotate the course card to where the point to fly to  C: TO-FROM indicator, the triangle arrow will point UP when flying to VOR station. The arrow will point DOWN when flying from the VOR station  D: Course Deviation Indicator (CDI) needle moves left or right indicating the direction to turn the aircraft to return to course  Dot: The horizontal dots at centre represent the aircraft away from the course. Each dot represents 2 degree deviation from desired course  20  Aerials Being in the VHF band, the localizer signals are often received by VEE-dipole (whip antennas) antennas on either side of the tail, which may also be used for VOR signal reception  21 VOR Station TO-FROM indicator gives the aircraft position relative to the selected VOR station radial 330º CDI FROM 330º TO 150º FROM 330º 330º FROM TO-FROM LINE 150º TO 150º-330º 330º TO VOR 150º FROM TO 330º FROM 150º TO 330º 150º  22 330º 330º FROM 330º FROM TO-FROM LINE 150º TO 150º-330º VOR 330º TO 150º FROM TO 330º 150º  23 Example 3-3: Bearing Calculation RMI N 0º RADIAL 0º RADIAL 0º HEADING 180º BEARING 270º 90º RADIAL VOR RADIAL RMI 180º RADIAL 0º HEADING 0º BEARING S 180º RADIAL 24 25 26  27 VOR Airborne Loading  Receiver sends the signal to preselector for selecting required VOR frequency and filter out all other frequency components  After the preselector, signal goes to the mixer where it mixes with synthesiser frequency to produce intermediate frequency (IF) signal  Detector demodulates the IF signal and separate it into the original signal  LOC/VOR 28 ANTENNA TUNE PRESELECTOR CONTROL MIXER VOR SYNTHESISER CONTROL UNIT DETECTOR FILTER AUDIO COCKPIT AMPLIFIER SPEAKER Airborne VARIABLE Loading FILTER 30-Hz DETECTOR MONITOR CIRCUITS FILTER FM-9960 Hz PHASE DETECTOR COMPARATOR FLAG RMI SYNCHRO VOR DRIVER RADIO MAGNETIC INDICATOR  29  The detected signal is applied to two separate circuits  30 Hz variable signal is filtered, amplified and detected by one circuit, while other circuit detects 30 Hz reference signal  The variable 30 Hz and reference 30 Hz signals are compared for phase difference in phase comparator  The detected phase difference is converted into voltage in Sync format, which can be applied to Radio Magnetic Indicator (RMI)  30  Course deviation left, right parameters and TO- FROM indications are also determined from the phase relationship between 30 Hz reference and 30 Hz variable signals  VOR equipment can detect many possible problems  A warning flag, usually red, will appear on the face of the instrument  31 Auto Pilot  ILS interface consists of Flight Control Computer (FCC), which monitors ILS deviation data and applied to autopilot inside the FCC which converts deviation data into flying commands during automatic landing by aircraft control  Localizer and glideslope deviations are displayed on electronic flight display instrument system  Flight Warning Computer (FWC) monitors the conditions of the ILS system and issue a warning SIGNAL to the pilot in case of any failure  CAP F/O 32 FLIGHT DISPLAY 1 FLIGHT DISPLAY 2 VOR VOR NAVIGATION NAV NAV NAVIGATION DISPLAY 1 ILS ILS DISPLAY 2 CONTROL UNIT ILS Auto Pilot FWC1 FWC2 ILS LOC ANTENNA ILS RECEIVER 1 G/S ANTENNA RECEIVER 2 INTERPHONE FCC1 FCC2  33 Auto Pilot  VOR interface consists of Flight Control Computer (FCC) with autopilot. VOR bearing and course deviation from a selected track is monitored and converted into flying commands for flying along the selected track  VOR station bearing data, course deviation paths and distance measurements are displayed on electronic flight display instrument system  Flight Warning Computer (FWC) monitors the reliability of VOR system and issue a warning FLAG to the pilot in case of any failure  34 VOR CAP Auto Pilot F/O FLIGHT DISPLAY 1 FLIGHT DISPLAY 2 VOR 1 VOR2 VOR VOR NAV NAV NAV 1 NAV 2 ILS ILS VOR FCC1 VOR RECEIVER 1 FCC2 RECEIVER 2 CONTROL UNIT 1 CONTROL UNIT 2 INTERPHONE LOC/VOR ANTENNA  35 The End