Flight Navigation Systems Navigation (항법) • 비행 센서를 이용하여 항공기의 위치, 속도, 자세, 각속도, 가속도 등을 알아내는 것 종류 • Automatic Direction Finder (ADF) • VHF Omni-Range (VOR) • Instrument Landing System (ILS) • Distance Measuring Equipment (DME) • LOng RAnge Navigation (LORAN) • Global Positioning System (GPS) • Doppler Navigation • Radio Altimeter standalone • Compass (나침반) • Pitot-Static Tube (Airspeed Sensor) • Inertial Navigation System (INS, 관성항법장치) based on radio principle Automatic Direction Finder (ADF) • 목적: provides direction of the radio beacon station with respect to aircraft heading radio beacon station measurement • Operating frequency range: 90 KHz ~ 1800 KHz  LF, MF  requires long antenna  Ground waves  ADF signal can follow the curvature of the earth over the horizon (not limited to line-of-sight) Beacon Station Automatic Direction Finder (ADF) • 원리: utilizes the directional characteristics of a loop antenna (in aircraft) strong signal weak signal • 이용: Pilot can “home in” to the beacon station radio beacon station no signal measurement N E cockpit display ADF indicator with two beacon station pointers VHF Omni-range (VOR) • 1950년대 도입, 널리 쓰임 • Operating frequency range: 108 MHz ~ 118 MHz N measurement user inophase line • 원리: VOR station User: detects phase difference between signals #1 & #2 VOR station sends multiple signals from closely-located several antennas Phase difference depends on the bearing of a user relative to the VOR station  Determines the direction of the user antenna #1 antenna #2 VHF Omni-range (VOR) • 이용 Step1: User set frequency to VOR station N 345o radial Step2: Set desired approach course angle to VOR station using Omni-range Bearing Selector (OBS) knob  Will bring the letter “345” on top of the indicator Step3: With the current user position shown, VOR indicator will look like course deviation bar OBS knob : to : from VOR station VHF Omni-range (VOR) For desired course angle set to 20 degrees by OBS knob VOR Station VOR Stations Instrument Landing System (ILS) • 개요: to aid landing approach Without visual reference, typical ILS will bring aircraft within 800m from runway at h=200ft typically ~3o 200 ft 800m • ILS Categories: more precise equipment runway Runway Visual Range Decision Height Category I >= 800 m >= 200 ft Category II 300 ~ 800 m 100 ~ 200 ft Category III A 200 ~ 300 m 50 ~ 100 ft Category III B 50 ~ 200 m 0 ~ 50 ft Category III C No limitation No limitation  depend on visual condition Instrument Landing System (ILS) • 원리 Localizer: - for lateral guidance - operating frequency (carrier) : 108MHz~112MHz - Transmitter at the end of runway sends two narrow waves, one is modulated with 90Hz signal and the other with 150Hz signal stronger 90Hz signal weaker 150Hz signal Glideslope: - for vertical guidance - same principle Instrument Landing System (ILS) • 이용: 계기판의 Primary Flight Display(PFD) 상에 glideslope indicator 와 localizer indicator 를 보면서 조종 glideslope indicator localizer indicator Primary Flight Display(PFD) Instrument Landing System (ILS) Localizer antenna Glideslope antenna Instrument Landing System (ILS) CAT III-A under 400m Runway Visual Range(RVR) condition Marker Beacons • 개요: - provides indication of distance from runway - can be classified as part of ILS - operation frequency : 75MHz outer marker middle 7~8 km outer marker: modulated with 400Hz signal middle marker: modulated with 1300Hz signal inner marker: modulated with 3000Hz signal ~1 km inner ~300m runway Marker Beacons Marker beacon receiver antenna Marker beacon transmitter antenna Distance Measuring Equipment (DME) at t=t1 at t=t2 - distance to the ground station DME station DT = processing time at DME station  300,000,000 m/s  t2  t1   DT 2 - The DME ground station is typically collocated with VOR station - Typically accuracy < 200 m LOng RAnge Navigation (LORAN) • 개요: - provides position information - operation frequency : 30KHz ~ 300KHz (LF)  long antenna • 원리: - A mater station and one or more slave stations send out synchronized pulses - The aircraft measures the differences among the reception times Time difference = distance difference station A B 예: a line for which the signal from A is received 100 ms earlier than the signal from B - By having more than two ground stations the aircraft position can be determined - 포항, 광주 LOng RAnge Navigation (LORAN) LORAN Coverage Global Positioning System (GPS) • provides 3D position information • 원리: - More than 30 GPS satellites (at h=20,200 km) transmit messages containing transmit-time, satellite position, etc … - GPS receiver measures the travel time of each message to computes the distance to each satellite - Receiver location can be determined by geometric trilateration using the distances to the satellites and the information of the satellite locations - The time is synchronized among GPS satellites. But, the time in GPS receiver is not synchronized with the satellite time. Therefore, at least 4 satellites are required to determine 3D position • 비고: - Accuracy : 수 m - Data output up to 10 Hz is possible - Time delay : ~ 0.4 sec - Advanced GPS receiver may provide velocity information as well using Doppler effect GPS Inertial Navigation System - No radio signal, Not dependent on ground station - Inertial sensors are used - rate gyro : measures angular velocity - accelerometer : measures specific force acceleration (필기) - Typically, the measurements from 3 rate gyros and 3 accelerometers are combined under 6 degree-of-freedom kinematic equations to further compute velocity, attitude, and position - Sometimes integrated with magnetometer to become AHRS (Attitude and Heading Reference System) - Sometimes integrated with magnetometer + GPS under Extended Kalman filter with the 6 degree-of-freedom kinematic equations to provide combined navigation solutions Doppler Navigation • Doppler Effect (shift): change in frequency of a wave for an observer by a relative motion between the source and the observer. • Doppler Navigation reflect transmit - Frequency difference between the transmitted and returned signal  velocity can be computed - standalone (requires no external signal) Radio (Radar) Altimeter - VHF - cockpit voice during landing h  (Speed of Light )  DT 2