LN-3 Inertial Navigation System
Encyclopedia
The LN-3 Inertial Navigation System is an Inertial Navigation System
that was developed in the 1960s by Litton Industries
. The Lockheed F-104 Starfighter was the first supersonic fighter aircraft to be equipped with this Inertial Navigation System (INS). An inertial navigation system is a system which continually determines the position of a vehicle from measurements made entirely within the vehicle using sensitive instruments. These instruments are accelerometer
s which detect and measure vehicle accelerations, and gyroscope
s which act to hold the accelerometers in proper orientation.
missile race spurred the development of smaller, lighter and more accurate inertial systems. Independent of its environment, the inertial system provides velocity and position information accurately and instantaneously for all manoeuvres, as well as being an accurate attitude and heading reference. The LN3-2A was the first inertial navigation system small and light and accurate enough to be fitted in a high performance fighter.
The early F-104's, model A through F, did not have an Inertial Navigator. It was the development of the F-104G, around 1959, for the European Air Forces with tactical bomber/strike capabilities, that brought the LN-3 into the aircraft. The LN-3 gave the F-104G the capability to navigate at low level in adverse weather and to drop a nuclear weapon at a range of 1,000 km with the best possible precision; this being vital to the F-104G program.
The LN-3 is a full 3-degrees-of-freedom, 4-gimbal inertial navigator, covering the flight performance envelope of the F-104G which ranged from 0 to 70,000 feet altitude; 0 to Mach 2+ speed, and accelerations from -5 to +9 g.
The following characteristics of the platform are described:
a. Three accelerometers in orthogonal directions provide the basic sensing elements. They measure acceleration along the two grid coordinate axes and the vertical (Z) axis. The Z accelerometer is not used by the LN3-2A itself but provides vertical acceleration data for the automatic flight control system. The east-west and north-south X and Y axes are used for the LN3-2A. The accelerometer outputs torque the gyro's in their sensitive axes, while the airplane is in flight, to maintain earth and grid north orientation of the stable platform through the platform gimbals.
b. Two gyro's stabilize the stable platform and provide for various compensations to be introduced, keeping the stable platform level with respect to earth instead of inertial space, and providing a coordinate reference system of three axes. The gyro's each have two degrees of freedom, and are oriented so that the spin axes are 90 degrees apart. The upper gyro has its spin axis oriented along the north-south grid coordinate axis and is sensitive to torques (airplane rotations) about the east-west and vertical coordinate axes. The lower gyro has its spin axis oriented along the east-west grid axis and is sensitive to torques about the north-south and vertical axes. Therefore the two gyro's control all three axes.
c. Platform gimbals are the assemblies which actually keep the platform accelerometers stable and enable the airplane to maneuver about the gyro-stabilized earth-oriented platform. The LN3-2A platform is a four-gimbal system (outerroll, pitch, innerroll and azimuth) allowing the airplane 360 degrees of rotation in all directions. The azimuth, pitch and outerroll gimbals use sliprings and brushes for electrical contacts to allow unlimited freedom. The innerroll gimbal provides a built-in redundancy to prevent a gimbal lock
situation when the azimuth and outerroll gimbal axes become aligned at 90 degrees of pitch.
The LN3-2A Computer controls the platform, computes navigational information and provides special ac and dc voltages required for equipment operation. The functions of the computer are:
a. to position the azimuth, pitch and roll gimbals of the platform. The basic sequence is that the gyro precession error due to airplane maneuvering is sensed and fed to the platform azimuth synchro resolver. The gyro signals are resolved into pitch and roll error voltages which are amplified in the computer. The computer drives the platform roll and pitch gimbal servomotors. The lower gyro is torqued to precess in azimuthh to drive the azimuth gimbal motors. The upper gyro is caged to the lower gyro in azimuth. The gimbal servomotors position the gimbals to compensate for the original deviation.
b. to provide the voltages for the starting and running of the gyro spin motors. During the start of the system the gyro's are brought up to spin speed by airplane 115VAC, 400 Hz power. After the 1 minute coarse align phase the frequency source for the gyro's is an electric tuning fork which provides a 3 kHz reference frequency which is divided by 8 to provide an operating frequency of 375 Hz and a running voltage of 90 Volts.
c. to control the heating of the component oven, the platform, the gyro's and the accelerometers. Some circuits within the computer, like amplifiers, require a very stable amplificationfactor which can only be maintained if certain components are kept under precisely held temperature. These components are placed within the Component Oven at 71 °C. Also the gyro's and accelerometers are kept at 71 °C ± 1.1 °C. The ambient atmospheric temperature inside the platform is maintained at 51.7 °C by a set of heaters and a circulating fan, and a motordriven cooling air valve controlling the flow of pressurized air through the doublewalled platformcover.
d. to compute velocity and distance information from acceleration. These navigational computations are performed with carefully designed electronic circuits in harmony with precision electromechanical components. The electronic parts are the Accelerometer Restoring Amplifier which give a voltage that is proportional to the acceleration. Ranging from micro-G's to units of G they span a very impressive dynamic range. Also the Servo Amplifiers, picking off the tiny Gyro signals and amplifying this to control the platform gimbalmotors, have tight specifications. The actual integration of the accelerometersignal to a velocitysignal is performed by an electronic amplifier which controls a velocity-motor which drives a capacitance-tachometer. This cap-tach feedback provides the basic integrator signal since the speed of the cap-tach is proportional to acceleration input. The feedback nulls the acceleration input to stop the motor. The motor positions the velocityshaft to pick-off the appropriate potentiometer signal which represents velocity. A dead zone network drives the velocitymotor in steps which are smoothed to provide the integrated acceleration (= velocity) signal.
The velocity integrators operate in a similar manner to the acceleration integrators, except that the output signal is not smoothed because the so called M-Transmitters are step-function devices. The M-transmitters send the integrated velocity (= distance) signal to the Position and Homing System PHI-4.
e. to sequence and control the coarse- and fine-align phases in conjunction with platform temperature.
f. to sense malfunctions to actuate the go, no-go circuitry of the inertial navigator.
g. Since the LN-3/PHI-4 navigation system is to be used around the globe of the earth, some systematic corrections for use on this rotating sferoid are implemented in the LN-3 : Earth rate-, Transport rate-, and Corioliscorrection. And to suppress inherent errors the system is Schuler
-tuned.
The first selection in the starting sequence is to rotate the mode selector switch of the "Inertial Navigation Control" Panel from Off to Standby.
In this mode the platform and component oven are brought up to operating temperature; indicated by the "heat" light on the IN Control Panel, which takes several minutes depending on outside and system temperatures.
All at operating temperature the system may be switched to "Align", allowing the machine to commence operation. The computer is powered up and nulls its velocity shafts; the gyro's are powered by 115V and 400 Hz and revving up; the platform is leveled in pitch, inner and outer roll relative to the aircraft using the gimbal synchrotransmitters; and the azimuth axis is driven to the grid north direction using the magnetic heading sensor. This phase of Alignment takes 1 minute and is called coarse align.
After this 1 minute the system switches to the fine align phase, during which the gyrospinmotor power is brought down to 95V and 375 Hz to avoid any magnetic interference with any other aircraft system using 400 Hz. The leveling of the platform is taken over by the X and Y accelerometers sensing even the smallest component of gravity which is an indication of not being precisely level. The leveling of the stable element is achieved by torqueing the respective gyro torquers which makes the gimbal motors to follow up and level the stable element. The distance shafts are set to zero; the gyro's are at operational speed and the computer is continuesly feeding the gyro's, and thereby the stable element, with corrections for local earth rotation. This is called the leveling phase of fine align.
Leveling ends automatically when the computer decides that the platform stable element is exactly locally level, which may take a few minutes. If level, the final phase of alignment is switched on; gyrocompassing.
The stable element is exactly level and Schuler-tuned but the gyro's are not yet aligned with the earth rotation axis. Therefore the stable element tends to turn off-level, which is sensed by the Y accelerometer which signal is fed to the gyrotorquer to rotate the azimuth axis of the stable element. This process continues for a few minutes until the correction signal is getting smaller and can be kept almost zero for 50 seconds, which gives confidence that the system is level and aligned. This is visible for the pilot because the green Nav light flashes.
The system is now ready for use and the pilot selects "Nav" on the IN Control Panel, and all circuitry that was involved in the various alignment phases is switched to the navigate mode.
Other possible modes are Compass only which may be selected after a LN3 in-flight failure, and Alert Align to shorten the alignment phase. After the last flight but before shutting down aircraft power the precise heading of the running LN3 is stored and can be used at starting up the next time, if the aircraft is not moved.
Performance
Specified navigation accuracy for the LN-3 is a 50% circular-error probability of two nautical miles after one hour's operation, which is equivalent to a 98% c.e.p. of four nautical miles. Until the -9 version of the LN-3-2A came into service (~1963) results were outside these limits by a fair margin, but since then it has been greatly exceeded in a number of groups of flights.
During manufacturer's development flying at Palmdale, some 1167 flights were made up to October 1961, and the c.e.p. of the LN-3 and PHI-4 combined was a mile or so outside specification. From October 1961 to January 1962 a further 123 flights at Palmdale were assessed, following incorporation of the -9 modifications, and the c.e.p. came almost up to specification.
At Edwards AFB, during Category 2 testing, and at Palmdale during the "avionics marriage" period, mean time between failures of pre-9 systems was considerably below the 200 hr specified, but the target has been exceeded since then.
, the Guidance and Control Systems Division at Beverly Hills CA, were one of the major producers of inertial systems in the USA in the 50's and 60's, and have made a series of systems for a number of American aircraft.
The gimballed platform of the LN3-2A is the Litton P200 platform; the Gyro is the G200 Gyro; and the accelerometer is the A200 accelerometer. (and Litton doc)
The G-200 Gyro is commonly used in the LN-2, LN-3 and the LN-12 systems.
Manufacturers designation of the F-104G system is LN3-2A. Mark the difference in notation LN-3 and LN3-2A with the position of the dividing dash "-" .
The designation LN3-2A leaves room for a LN3-1, not known to author.
The Autonetics Radar Enhanced Inertial Navigation System (REINS) of the North American A-5 Vigilante was more or less comparable to the LN-3/PHI-4. This system was derived from the XN-6 system developed for the SM-64 Navaho
, the N5G system for the AGM-28 Hound Dog
and the N2C/N2J/N3A/N3B system for the XB-70, and was related to the N6A-1 navigation system used in the USS Nautilus (SSN-571)
and the N10 inertial guidance system for the LGM-30 Minuteman
. Note that the Boeing history claims the REINS to be the first inertial navigation in a production airplane.
Nortronics had developed and produced Astro-Inertial guidance/navigation systems for the SM-62 Snark
. The system developed for the GAM-87 Skybolt was later adapted for use in the Lockheed SR-71 Blackbird and mostly referred to as NAS-14 and/or NAS-21.
The UGM-27 Polaris
missile was equipped with a MIT-developed inertial system, which later evolved to the Delco produced IMU of the Apollo PGNCS
.
The Saturn V
was equipped with a MSFC-developed ST-124-M3 inertial platform
which was a further development of the PGM-19 Jupiter's ST-90.
mode. In case of serious self-diagnosed problems the system would auto shut-down.
Flight line maintenance of the LN-3, like systemchecks and fault isolation, was performed using specific test equipment :
RNlAF operated the MATS not at flightline but shop level.
At base (nav)shop level the Platform, Computer and Adapter units were tested and repaired using the following test equipment :
For repairs beyond the capabilities of base level, the RNlAF Electronics Depot (and possibly others) were equipped with specific testequipment and tooling to handle the (higher) depot level repairs of the LN-3 system. The main teststations in use were:
Industry support
The repair of the system's sensors, gyros and accelerometers, was performed by Litton. The RNlAF had its sensors repaired by Litton Canada, which also provided all necessary spare parts.
Other European users relied on German or Italian subsidiaries/licensees as LITEF at Freiburg and Hamburg.
Exhibit of the LN3-2A system (without Alert Align Unit) in a vitrine. The Platformgimbals can be rotated by the visitor with a remote control box.
Netherlands
Display of a complete system. On request explication and demonstration of the system is given.
Inertial navigation system
An inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...
that was developed in the 1960s by Litton Industries
Litton Industries
Named after inventor Charles Litton, Sr., Litton Industries was a large defense contractor in the United States, bought by the Northrop Grumman Corporation in 2001.-History:...
. The Lockheed F-104 Starfighter was the first supersonic fighter aircraft to be equipped with this Inertial Navigation System (INS). An inertial navigation system is a system which continually determines the position of a vehicle from measurements made entirely within the vehicle using sensitive instruments. These instruments are accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
s which detect and measure vehicle accelerations, and gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
s which act to hold the accelerometers in proper orientation.
Background
The Cold WarCold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
missile race spurred the development of smaller, lighter and more accurate inertial systems. Independent of its environment, the inertial system provides velocity and position information accurately and instantaneously for all manoeuvres, as well as being an accurate attitude and heading reference. The LN3-2A was the first inertial navigation system small and light and accurate enough to be fitted in a high performance fighter.
The early F-104's, model A through F, did not have an Inertial Navigator. It was the development of the F-104G, around 1959, for the European Air Forces with tactical bomber/strike capabilities, that brought the LN-3 into the aircraft. The LN-3 gave the F-104G the capability to navigate at low level in adverse weather and to drop a nuclear weapon at a range of 1,000 km with the best possible precision; this being vital to the F-104G program.
The LN-3 is a full 3-degrees-of-freedom, 4-gimbal inertial navigator, covering the flight performance envelope of the F-104G which ranged from 0 to 70,000 feet altitude; 0 to Mach 2+ speed, and accelerations from -5 to +9 g.
Introduction to the system
The functional description of the LN3-2A requires some knowledge of some basic principles of inertial navigation to understand their application to the LN3-2A. The principal component of the system is the stable platform to which are mounted three accelerometers and two gyro's. This stable platform is mounted in a system of platform gimbals. The acceleration of the airplane in any plane or direction is measured by the accelerometers and integrated in the computer to obtain velocity. Velocities in turn are integrated to obtain distance. With a known reference point representing initial position of the airplane with respect to earth, this data can be converted to distance and heading traveled, and distance and bearing to destination.The following characteristics of the platform are described:
a. Three accelerometers in orthogonal directions provide the basic sensing elements. They measure acceleration along the two grid coordinate axes and the vertical (Z) axis. The Z accelerometer is not used by the LN3-2A itself but provides vertical acceleration data for the automatic flight control system. The east-west and north-south X and Y axes are used for the LN3-2A. The accelerometer outputs torque the gyro's in their sensitive axes, while the airplane is in flight, to maintain earth and grid north orientation of the stable platform through the platform gimbals.
b. Two gyro's stabilize the stable platform and provide for various compensations to be introduced, keeping the stable platform level with respect to earth instead of inertial space, and providing a coordinate reference system of three axes. The gyro's each have two degrees of freedom, and are oriented so that the spin axes are 90 degrees apart. The upper gyro has its spin axis oriented along the north-south grid coordinate axis and is sensitive to torques (airplane rotations) about the east-west and vertical coordinate axes. The lower gyro has its spin axis oriented along the east-west grid axis and is sensitive to torques about the north-south and vertical axes. Therefore the two gyro's control all three axes.
c. Platform gimbals are the assemblies which actually keep the platform accelerometers stable and enable the airplane to maneuver about the gyro-stabilized earth-oriented platform. The LN3-2A platform is a four-gimbal system (outerroll, pitch, innerroll and azimuth) allowing the airplane 360 degrees of rotation in all directions. The azimuth, pitch and outerroll gimbals use sliprings and brushes for electrical contacts to allow unlimited freedom. The innerroll gimbal provides a built-in redundancy to prevent a gimbal lock
Gimbal lock
Gimbal lock is the loss of one degree of freedom in a three-dimensional space that occurs when the axes of two of the three gimbals are driven into a parallel configuration, "locking" the system into rotation in a degenerate two-dimensional space....
situation when the azimuth and outerroll gimbal axes become aligned at 90 degrees of pitch.
The LN3-2A Computer controls the platform, computes navigational information and provides special ac and dc voltages required for equipment operation. The functions of the computer are:
a. to position the azimuth, pitch and roll gimbals of the platform. The basic sequence is that the gyro precession error due to airplane maneuvering is sensed and fed to the platform azimuth synchro resolver. The gyro signals are resolved into pitch and roll error voltages which are amplified in the computer. The computer drives the platform roll and pitch gimbal servomotors. The lower gyro is torqued to precess in azimuthh to drive the azimuth gimbal motors. The upper gyro is caged to the lower gyro in azimuth. The gimbal servomotors position the gimbals to compensate for the original deviation.
b. to provide the voltages for the starting and running of the gyro spin motors. During the start of the system the gyro's are brought up to spin speed by airplane 115VAC, 400 Hz power. After the 1 minute coarse align phase the frequency source for the gyro's is an electric tuning fork which provides a 3 kHz reference frequency which is divided by 8 to provide an operating frequency of 375 Hz and a running voltage of 90 Volts.
c. to control the heating of the component oven, the platform, the gyro's and the accelerometers. Some circuits within the computer, like amplifiers, require a very stable amplificationfactor which can only be maintained if certain components are kept under precisely held temperature. These components are placed within the Component Oven at 71 °C. Also the gyro's and accelerometers are kept at 71 °C ± 1.1 °C. The ambient atmospheric temperature inside the platform is maintained at 51.7 °C by a set of heaters and a circulating fan, and a motordriven cooling air valve controlling the flow of pressurized air through the doublewalled platformcover.
d. to compute velocity and distance information from acceleration. These navigational computations are performed with carefully designed electronic circuits in harmony with precision electromechanical components. The electronic parts are the Accelerometer Restoring Amplifier which give a voltage that is proportional to the acceleration. Ranging from micro-G's to units of G they span a very impressive dynamic range. Also the Servo Amplifiers, picking off the tiny Gyro signals and amplifying this to control the platform gimbalmotors, have tight specifications. The actual integration of the accelerometersignal to a velocitysignal is performed by an electronic amplifier which controls a velocity-motor which drives a capacitance-tachometer. This cap-tach feedback provides the basic integrator signal since the speed of the cap-tach is proportional to acceleration input. The feedback nulls the acceleration input to stop the motor. The motor positions the velocityshaft to pick-off the appropriate potentiometer signal which represents velocity. A dead zone network drives the velocitymotor in steps which are smoothed to provide the integrated acceleration (= velocity) signal.
The velocity integrators operate in a similar manner to the acceleration integrators, except that the output signal is not smoothed because the so called M-Transmitters are step-function devices. The M-transmitters send the integrated velocity (= distance) signal to the Position and Homing System PHI-4.
e. to sequence and control the coarse- and fine-align phases in conjunction with platform temperature.
f. to sense malfunctions to actuate the go, no-go circuitry of the inertial navigator.
g. Since the LN-3/PHI-4 navigation system is to be used around the globe of the earth, some systematic corrections for use on this rotating sferoid are implemented in the LN-3 : Earth rate-, Transport rate-, and Corioliscorrection. And to suppress inherent errors the system is Schuler
Schuler
Schuler is the surname of:* Ella Schuler, American supercentenarian* Franz Schuler , Austrian biathlete* Hans Schuler, American sculptor* Markus Schuler, German soccer player* Max Schuler, German engineer, first described the Schuler tuning...
-tuned.
Operation of the LN-3
Before starting the Inertial navigator, the pilot has to enter the coordinates of the starting point in the "Align Control" panel in the right-hand console of the F-104G.The first selection in the starting sequence is to rotate the mode selector switch of the "Inertial Navigation Control" Panel from Off to Standby.
In this mode the platform and component oven are brought up to operating temperature; indicated by the "heat" light on the IN Control Panel, which takes several minutes depending on outside and system temperatures.
All at operating temperature the system may be switched to "Align", allowing the machine to commence operation. The computer is powered up and nulls its velocity shafts; the gyro's are powered by 115V and 400 Hz and revving up; the platform is leveled in pitch, inner and outer roll relative to the aircraft using the gimbal synchrotransmitters; and the azimuth axis is driven to the grid north direction using the magnetic heading sensor. This phase of Alignment takes 1 minute and is called coarse align.
After this 1 minute the system switches to the fine align phase, during which the gyrospinmotor power is brought down to 95V and 375 Hz to avoid any magnetic interference with any other aircraft system using 400 Hz. The leveling of the platform is taken over by the X and Y accelerometers sensing even the smallest component of gravity which is an indication of not being precisely level. The leveling of the stable element is achieved by torqueing the respective gyro torquers which makes the gimbal motors to follow up and level the stable element. The distance shafts are set to zero; the gyro's are at operational speed and the computer is continuesly feeding the gyro's, and thereby the stable element, with corrections for local earth rotation. This is called the leveling phase of fine align.
Leveling ends automatically when the computer decides that the platform stable element is exactly locally level, which may take a few minutes. If level, the final phase of alignment is switched on; gyrocompassing.
The stable element is exactly level and Schuler-tuned but the gyro's are not yet aligned with the earth rotation axis. Therefore the stable element tends to turn off-level, which is sensed by the Y accelerometer which signal is fed to the gyrotorquer to rotate the azimuth axis of the stable element. This process continues for a few minutes until the correction signal is getting smaller and can be kept almost zero for 50 seconds, which gives confidence that the system is level and aligned. This is visible for the pilot because the green Nav light flashes.
The system is now ready for use and the pilot selects "Nav" on the IN Control Panel, and all circuitry that was involved in the various alignment phases is switched to the navigate mode.
Other possible modes are Compass only which may be selected after a LN3 in-flight failure, and Alert Align to shorten the alignment phase. After the last flight but before shutting down aircraft power the precise heading of the running LN3 is stored and can be used at starting up the next time, if the aircraft is not moved.
Performance
Specified navigation accuracy for the LN-3 is a 50% circular-error probability of two nautical miles after one hour's operation, which is equivalent to a 98% c.e.p. of four nautical miles. Until the -9 version of the LN-3-2A came into service (~1963) results were outside these limits by a fair margin, but since then it has been greatly exceeded in a number of groups of flights.
During manufacturer's development flying at Palmdale, some 1167 flights were made up to October 1961, and the c.e.p. of the LN-3 and PHI-4 combined was a mile or so outside specification. From October 1961 to January 1962 a further 123 flights at Palmdale were assessed, following incorporation of the -9 modifications, and the c.e.p. came almost up to specification.
At Edwards AFB, during Category 2 testing, and at Palmdale during the "avionics marriage" period, mean time between failures of pre-9 systems was considerably below the 200 hr specified, but the target has been exceeded since then.
Genealogy
Litton Systems Inc., or Litton IndustriesLitton Industries
Named after inventor Charles Litton, Sr., Litton Industries was a large defense contractor in the United States, bought by the Northrop Grumman Corporation in 2001.-History:...
, the Guidance and Control Systems Division at Beverly Hills CA, were one of the major producers of inertial systems in the USA in the 50's and 60's, and have made a series of systems for a number of American aircraft.
- The LN-1 was a development attitude reference for the XB-70 Valkyrie.
- The LN-1A was a precision attitude reference for the Grumman E-1A Tracer.
- The LN-2A (military designation AN/ASN-31 or -36) was a Doppler-inertial system for the A-6A Intruder
- The LN-2B was the system for the E-2A Hawkeye,
- and the LN-2C was the system for the P-3A Orion.
- The LN-3-2A (or LN3-2A) was the Inertial Navigation System used in the F-104G Super Starfighter. (development 195?-195?, production 1960-196?) Improved versions of the LN3-2A were -9, -11 and -13.
- The LN-3-2B is the Inertial Navigation System used in the Canadian CF-104.
- The LN-3-13 is fitted to the Italian F-104S/CI and F-104S/CB; enhanced variants of the F-104G from 1969 and onward. In the early 80's a further upgrade led to the F-104S ASA version which kept the original LN-3; but the ASA-M version of the '90s was equipped with the LN-30A2 inertial navigation system.
- The LN-4 is a miniature inertial system for "a manned orbital vehicle"
- The LN-5 is a (1963)"state of the art experimentation astro-inertial system installed in a Convair 340 R4Y ".
- The LN-7 is an astro-inertial-Doppler system for a classified application.
- The LN-12A/B series are an evolution of the LN-3 and are used in F-4C (AN/ASN-48), the F-4D and F-4E (AN/ASN-63), the RF-4C (AN/ASN-56), all with slight differences.
The gimballed platform of the LN3-2A is the Litton P200 platform; the Gyro is the G200 Gyro; and the accelerometer is the A200 accelerometer. (and Litton doc)
The G-200 Gyro is commonly used in the LN-2, LN-3 and the LN-12 systems.
- LN3-2A notation.
Manufacturers designation of the F-104G system is LN3-2A. Mark the difference in notation LN-3 and LN3-2A with the position of the dividing dash "-" .
The designation LN3-2A leaves room for a LN3-1, not known to author.
Other U.S. Inertial Systems of the early 1960s.
The Litton LN-3 was one of the first inertial navigators on a production aircraft, but other systems, either Inertial Navigators or Inertial Measurement Units, of other brands and for various applications with comparable technology existed.The Autonetics Radar Enhanced Inertial Navigation System (REINS) of the North American A-5 Vigilante was more or less comparable to the LN-3/PHI-4. This system was derived from the XN-6 system developed for the SM-64 Navaho
SM-64 Navaho
The North American SM-64 Navaho was a supersonic intercontinental cruise missile project built by North American Aviation. The program ran from 1946 to 1958 when it was cancelled in favor of intercontinental ballistic missiles...
, the N5G system for the AGM-28 Hound Dog
AGM-28 Hound Dog
The North American Aviation Corporation AGM-28 Hound Dog was a supersonic, jet propelled, air-launched cruise missile. The Hound Dog missile was first given the designation B-77, then redesignated the GAM-77, and finally designated the AGM-28, permanently...
and the N2C/N2J/N3A/N3B system for the XB-70, and was related to the N6A-1 navigation system used in the USS Nautilus (SSN-571)
USS Nautilus (SSN-571)
USS Nautilus is the world's first operational nuclear-powered submarine. She was the first vessel to complete a submerged transit beneath the North Pole on August 3, 1958...
and the N10 inertial guidance system for the LGM-30 Minuteman
LGM-30 Minuteman
The LGM-30 Minuteman is a U.S. nuclear missile, a land-based intercontinental ballistic missile . As of 2010, the version LGM-30G Minuteman-III is the only land-based ICBM in service in the United States...
. Note that the Boeing history claims the REINS to be the first inertial navigation in a production airplane.
Nortronics had developed and produced Astro-Inertial guidance/navigation systems for the SM-62 Snark
SM-62 Snark
-External links:** Air Force Magazine article about a Snark that was test-fired and rumored to have been found in Brazil** detailed article on Snark and the USAF school to train personnel for it...
. The system developed for the GAM-87 Skybolt was later adapted for use in the Lockheed SR-71 Blackbird and mostly referred to as NAS-14 and/or NAS-21.
The UGM-27 Polaris
UGM-27 Polaris
The Polaris missile was a two-stage solid-fuel nuclear-armed submarine-launched ballistic missile built during the Cold War by Lockheed Corporation of California for the United States Navy....
missile was equipped with a MIT-developed inertial system, which later evolved to the Delco produced IMU of the Apollo PGNCS
Apollo PGNCS
The Apollo Primary Guidance, Navigation and Control System was a self-contained inertial guidance system that allowed Apollo spacecraft to carry out their missions when communications with Earth were interrupted, either as expected, when the spacecraft were behind the moon, or in case of a...
.
The Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
was equipped with a MSFC-developed ST-124-M3 inertial platform
ST-124-M3 inertial platform
The ST-124-M3 is a device for measuring acceleration and attitude of the Saturn V launch vehicle. It was carried by the Saturn V Instrument Unit, a , section of the Saturn V that fit between the third stage and the Apollo spacecraft...
which was a further development of the PGM-19 Jupiter's ST-90.
LN-3 Maintenance and Test equipment
The LN-3 system was designed to constantly monitor critical parameters, and warn the pilot in case of a malfunction. Depending on the problem the pilot could switch-off the system, or continue in a dead reckoningDead reckoning
In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...
mode. In case of serious self-diagnosed problems the system would auto shut-down.
Flight line maintenance of the LN-3, like systemchecks and fault isolation, was performed using specific test equipment :
- MATS (Mobile Automated Test System)
RNlAF operated the MATS not at flightline but shop level.
- Line Test Analyzer
- Gyro Bias Test Set
At base (nav)shop level the Platform, Computer and Adapter units were tested and repaired using the following test equipment :
- System Test Console (STC).
- Bench Test Console (BTC).
For repairs beyond the capabilities of base level, the RNlAF Electronics Depot (and possibly others) were equipped with specific testequipment and tooling to handle the (higher) depot level repairs of the LN-3 system. The main teststations in use were:
- Platform Functional Test Console (PFTC).
- Module Test Console.
Industry support
The repair of the system's sensors, gyros and accelerometers, was performed by Litton. The RNlAF had its sensors repaired by Litton Canada, which also provided all necessary spare parts.
Other European users relied on German or Italian subsidiaries/licensees as LITEF at Freiburg and Hamburg.
LN-3 units on display
Germany- The Wehr Technische Studiensamlung (WTS) at Koblenz.
Exhibit of the LN3-2A system (without Alert Align Unit) in a vitrine. The Platformgimbals can be rotated by the visitor with a remote control box.
Netherlands
- Museumcollection of Navigation and Communication systems at Royal Netherlands Air Force Logistic Centre Woensdrecht, location RhenenRhenenRhenen is a municipality and a city in the central Netherlands.The municipality also includes the villages of Achterberg, Remmerden, Elst and Laareind. The town lies at a geographically interesting location, namely on the southernmost part of the chain of hills known as the Utrecht Hill Ridge ,...
, former Air Force Electronics maintenance depot (DELM).
Display of a complete system. On request explication and demonstration of the system is given.
External links
- http://www.flightglobal.com/pdfarchive/view/1963/1963%20-%200395.html Article of Flight International, 1963, on the (European)F-104G programme with good coverage of systems as the LN3-2A.
- http://cs.finescale.com/FSMCS/forums/p/51736/537625.aspx A forum for modellers with a contribution of an ex-Phantom technician explaining the Litton versions of the LN-12.
- http://www.radelow.ch/anderes/avionik/index.htm The site of a Swiss dentist who also appreciates the LN-3 system. With data of an old Litton brochure.
- http://www.navhouse.com/capabilities.htm The Navhouse capability site gives some crossreferences for Litton Inertial navigators and components.
- http://www.vectorsite.net/avf104_2.html The Vectorsite in most cases also gives details on INS equipment.
- http://www.designation-systems.net/usmilav/jetds/an-asn.html Military equipment designations with crossreferences from equipment to aircraft. Not all data correlates with other sources.
- http://www.dtic.mil/dticasd/sbir/sbir021/n104.pdf Article on celestial augmentation of inertial systems by USNO.
- http://www.bwb.org/portal/a/bwb/kcxml/04_Sj9SPykssy0xPLMnMz0vM0Y_QjzKLNzKM9_R0BslB2B4B-pFw0aCUVH1vfV- The site of the German defence technology museum in Koblenz (WTS), with a far more surprising collection than advertised, including a complete LN3-2A system in a vitrine.
- http://www.joebaugher.com/usaf_fighters/f104_33.html The Joe Baugher site with useful data on the F-104 Starfighter.