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Inertial Navigation Systems
Pavel Pačes
Introduction into
Prerequisites
Subjects:
Aircraft sensors systems
(Přístrojové systémy letadel)
Navigation
(Navigace)
Content
Introduction
◦ Requirements
Inertial Measurement Systems
Sensors
Area Navigation (RNAV)
Instrument Flight Rules (IFR)
◦ Navigation Beacons – 1970, and later
◦ Inercial Reference Systems
Navigation
Land navigation
Very high frequency Omnidirectional
Radio range (VOR)
Distance Measuring Equipment (DME)
Over ocean
Inertial Measurement Systems (INS)
Precision
System precision
◦ Definition of airspace and obstacle clearance
Delays
New method of defining equipment
requirements =>
Performance-based Navigation (PBN)
Current Status
Performance based Navigation
◦ Area Navigation (RNAV)
◦ Required Navigation Performance (RNP)
related to Actual Navigation Performance (ANP)
Differences:
the requirement for on-board performance
monitoring and alerting
What about service assurance? => RNAV
(coexistence of both systems)
Source [4]
Performance Based Navigation
RNAV (Area Navigation) umožňuje letadlu vybrat vhodnou trasu za využití soustavy navigračních prostředků (majáky, GPS, INS) –šetří se čas, délka dráhy a doba letu.
◦ Nejde to použít všude, je nutné definovat požadavky (na vybavení, posádku, letadlo, …)
Required navigation performance
Rozdíly se stírají – poslední dobou (od 1990) jsou i RNAV systémy vybavované funkcí performance monitoring and alerting= tj. vše je RNAV.
RAIM
RAIM – Receiver Autonomous Integrity
Monitor
Poskytuje varování v případě, že systém
není možné použít pro navigaci.
U GPS je kontrola například použitím
několika čtveřic viditelných satelitů.
RNP
Lepší spolehlivost a funkce garantující
funkčnost zařízení.
Přesnější navigace
◦ Menší rozestupy mezi letadly
◦ Navigace pouze pomocí RNP systému
Problém je cena, ale předpokládá se, že v
budoucnosti se budou využívat už jen
RNP systémy.
RNAV requirements
continuous indication of aircraft position relative to track to be displayed to the pilot flying on a navigation display situated in his primary field of view;
display of distance and bearing to the active (To) waypoint;
display of ground speed or time to the active (To) waypoint;
navigation data storage function; and
appropriate failure indication of the RNAV system including its sensors.
RNAV Lateral Navigation
Navigation Accuracy
◦ path definition error (PDE),
◦ flight technical error (FTE) and
◦ navigation system error (NSE)
Total System Error (TSE) =>
σ = sqrt(σPDE+ σFTE+ σNSE)
RNAV Longitudinal navigation
Position along a track
It is not considered important
◦ Except , e.g. Descent points
Designation
RNAV X – whre X is a number in nautical miles representing 95% probability of aircraft operation within lateral distance from a path
RNP
Used in specific airspaces
Permitting closer route spacing
Offer significant safety, operational and efficiency benefits
RNP designation
An RNP of 0.3 means the aircraft
navigation system must be able to
calculate its position to within a circle
with a radius of 0.3 nautical mile
What is it for?
Nose reduction along a path
Source [3]
What is it for?
Precise approach over a
a river – no noise
polution of residential
areas
Source [5]
Airplanes categories (SBAS)
Landing minimums
RNP-0.3 required
Source [4]
What do we have? Precision?
System Precision [m]
Loran, GPS 9-180
DECCA 200
Transit, Tacan 400
INS (after 1 hour) 650
VOR/DME & Doppler 900
Omega 2200
Inertial Navigation System (INS)
Includes
A computer and
a module containing
◦ Accelerometers,
◦ Gyroscopes or
◦ Other devices
It is necessary to provide its position and velocity (GPS,
FMS, etc.) and then it calculates its own position,
velocity and orientation by integration from motion
sensors.
Definice
• Polohové úhly
– Théta , pitch – podélný sklon
– Phi , roll – příčný náklon
– Psi , yaw, headind, azimuth - kurz
+
+
+
Sensors
Mechanical gyroscopes – rotating mass
Accelerometers – movement of a mass
point transferred on electric signal
Micro Electro Mechanical Structures
(MEMS)
Porovnání MEMS a RLG
Křivky výkonnosti RLG1308 a MEMS
Gyro
Coordinate Frames
Body frame
◦ North-East-Down (NED)
Navigation frame
Earth Centered xxx Frame
Image source [7]
Roll, Pitch and Yaw
Coordinate sysems
C TargetOriginal , or CTo
From
Euler angles singularity problem => Use
quaternions
Covariance matrix = measure of trust in
measurement
INS Systems
Gimbaled platform
Gimbaled frame with an inertial center
gyro
Strap-down systems
Image source [Wiki] Image source [8]
Gimbaled platform
Gimbaled frame with an inertial
center gyro
Strap-down system
Strap-down systems alignment
Image source [8]
INS algorithms
Examples
◦ Flat Earth
◦ Non-rotating Earth
◦ Rotating Earth
Strap-down system
Flat Earth
Image source [7]
Non-rotating Earth
Rotating spherical Earth navigator
GPS system coupling
A
Tightly coupled
Other system
Gravitační pole
Nerovnoměrné rozložení se kterým se
musí počítat. Závislost na:
Geografické lokaci
Výšce
Schulerovo kyvadlo
Kyvadlo s dobou kyvu 84.4 min – takové jehož délka je stejná jako délka poloměru země.
Unikátní vlastností je, že vektor vedoucí ze závaží kyvadla do bodu uchycení (počátku) zůstává stále vertikální vzhledem k povrchu navzdory jakémukoliv pohybu jeho počátku (závěsu).
V inerciálních systémech je zaváděno jako jeden z výpočetních bloků. Zavádí se jako změna úhlu, která závisí na rychlosti pohybu v horizontální rovině dělená poloměrem země.
Schuler pendulum
/v R
6378 kmR
2. . =6.28. 637,8 km 84.4377 minl
Tg
-110 m.sv
61.5679e
• Kompletní oscilace
Sensor Fusion
Magnetometers
GPS systems
Pressure Reference System
Image source [8]
In-flight alignment and system
precision
Image source [8]
AHRS
Altitude heading and reference system
◦ low-cost INS
◦ A magnetometer unit
AHRS
INS
Magnetometer
Aircraft instalation
Characterization of sensors
Is the sensor good for INS?
Alan Variance – movement of an average
value in time
Errors
Raw data
Allan Variance
Literatura1. Establishment of Area Navigation Routes (RNAV),
http://www.epa.gov/EPA-IMPACT/2003/May/Day-09/i11638.htm
2. Navigation Systems - Level 3 Area Navigationhttp://www.allstar.fiu.edu/aero/RNAV.htm
3. Space Communication and Aviation Navigation: The United States Moves towards Performance-Based Navigation http://spacejournal.ohio.edu/issue9/aviation_navigation.html
4. RNP - What is it?http://www.overtheairwaves.com/airwaves/vol2-5a.htm
5. Example of the RNP ’River’ approach to Brisbane runway 01 - 03/08http://www.airservicesaustralia.com/media/pressreleases/pr3_08.asp
6. Airbus, getting to grips with modern navigation
7. Stovall, Sherryl H. Basic Inertial Navigation. California : Naval Air Warfare Center, Weapons Division, 1997. NAWCWPNS TM 8128.
8. Weed, Doug, a další. GPS Align In Motion of civilian strapdownINS. Development, Honeywell Commerzial Aviation Products, Honeywell Interantional. Picastaway : IEEE, 2004. stránky 184- 192. 0-7803-8416-4/04.