what is a magnetometer and which instrument does it give information to aviation
- A compass is a simple magnetic bar suspended in fluid
- The float and card assembly has a hardened steel pivot in its centre that rides inside a special, bound-loaded, hard-glass jewel cup
- The magnets align with the Earth's magnetic field, and the pilot reads the direction on the scale opposite the lubber line
- When the pilot is flying North as the compass shows, Due east is to the pilot's right, but on the card "33", which represents 330° (West of North), is to the right of Due north
- The reason for this apparent backward graduation is that the bill of fare remains stationary, and the compass housing and the airplane pilot turn around information technology, always viewing the card from its behind
- A compensator assembly mounted on the top or bottom of the compass allows an aviation maintenance technician (AMT) to create a magnetic field inside the compass housing that cancels the influence of local outside magnetic fields
- The compensator corrects for divergence error
- The compensator associates has two shafts whose ends have screwdriver slots accessible from the front of the compass
- Each shaft rotates one or ii small-scale compensating magnets
- The stop of one shaft is marked E-W, and its magnets affect the compass when the aircraft points Eastward or Due west
- The other shaft is marked North-Due south, and its magnets affect the compass when the aircraft points Due north or South
- An aircraft magnetic compass has two small magnets fastened to a metal float sealed inside a basin of clear compass fluid
- The compass housing is full of compass fluid, similar to kerosene, to avoid freezing at lower temperatures/college altitudes
- The buoyancy of the float takes weight off the pin, and the fluid damps the oscillation of the float and bill of fare
- This jewel-and-pivot type mounting allows the float the freedom to rotate and tilt up to approximately 18° angle of depository financial institution 45° pitch upwards/downward
- At steeper bank angles, the compass indications are erratic and unpredictable
- The rear of the compass case is sealed with a flexible diaphragm or with a metallic bellow in some compasses to prevent impairment or leakage when the fluid expands and contracts with temperature changes
- The magnetic compass is a reliable, self-contained unit requiring no external power source
- It is extremely useful as a standby or emergency musical instrument
- A graduated calibration, chosen a bill of fare, is wrapped around the bladder and viewed through a drinking glass window with a lubber line across information technology
- The carte du jour is marked with letters representing the cardinal directions, North, East, South, and West, and a number for each 30° between these letters
- The final "0" is omitted from these directions; for instance, 3 = 30°, 6 = 60°, and 33 = 330°
- There are long and brusque graduation marks betwixt the letters and numbers, with each long mark representing x° and each short mark representing five°
- The magnetic compass is the simplest instrument in the panel, simply it is subject to several errors to consider
- The acronym "VD-MONA" helps pilots think compass errors:
- Variation
- Difference
- Magnetic Dip
- Oscillation
- Northerly Turning Error (part of magnetic dip)
- Acceleration/Deceleration Errors (part of magnetic dip)
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- Latitude and longitude are based on "true" directions meaning they provide a abiding horizontal and vertical plane with which to reference on maps and charts [Figure ii]
- The magnetic pole to which the magnetic compass points is not collocated with the geographic "true" Due north pole just is some 1,300 miles away; directions measured from the magnetic poles are called magnetic directions
- In aerial navigation, the difference between true and magnetic directions is chosen variation
- This aforementioned angular deviation in surveying and land navigation is called declination
- An "isogonic" line connects points of equal variation on a map
- The amount of variation depends on your location relative to the poles
- Variation in equatorial regions will be less dramatic, as isogonic lines are farther from each other
- Conversely, at extreme northern and southern regions, isogonic lines are more pronounced as lines are closer together
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- The line that passes well-nigh Des Moines, Iowa & Piddling Stone, Arkansas has a variation of 0°, making it the agonic line
- Right of this line, the magnetic pole is to the Due west of the geographic pole, and a correction must be practical to a compass indication to get a truthful direction
- Flying in the Washington, D.C. area, for example, the variation is 10° W
- If the airplane pilot wants to fly a true class of South (180°), the variation must exist added to this resulting in a magnetic grade to wing of 190°
- Left of this line, the magnetic pole is to the East of the geographic pole, and a correction must be applied to a compass indication to get a truthful direction
- Flying in the Los Angeles, California area, the variation is fourteen° Eastward
- To wing a truthful form of 180° there, the pilot would accept to subtract the variation and fly a magnetic course of 166°
- Right of this line, the magnetic pole is to the Due west of the geographic pole, and a correction must be practical to a compass indication to get a truthful direction
- East/Westward can be tricky to remember given they would otherwise exist considered opposite; however, if y'all recall of looking at the globe from the pole (vice your location toward the pole), then it makes sense
- The line that passes well-nigh Des Moines, Iowa & Piddling Stone, Arkansas has a variation of 0°, making it the agonic line
- The variation error does non change with the heading of the shipping; it is the same anywhere along the isogonic line
- Isogonic lines are depicted on sectional charts with a dashed magenta line and the number associated
- Used to convert true course to magnetic form
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- True class (170°) ± variation (+10°) = magnetic course (180°)
- The magnetic course (180°) is flown if there is no difference error to be applied
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- West is best (+), East is least (-), or;
- Variation E, magnetic track least (-) while variation west, magnetic track best (+)
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- Local magnetic fields in an aircraft caused by electric electric current flowing in the structure, in nearby wiring, or any magnetized part of the structure cause a compass error called deviation
- Deviation manifests itself differently betwixt aircraft and depending on heading, still, just information technology is not affected by the geographic location
- Deviation error is minimized when a pilot or Aviation Maintenance Technition (AMT) performs the maintenance task known as "swinging the compass"
- Near airports have a compass rose, which is a series of lines marked out on a taxiway or ramp at some location where there is no magnetic interference
- Lines, oriented to magnetic N, are painted every 30°
- The airplane pilot or AMT aligns the aircraft on each magnetic heading and adjusts the compensating magnets to minimize the difference betwixt the compass indication and the actual magnetic heading of the aircraft
- Any error that remains is recorded on a compass correction card and placed in a menu-holder about the compass [Figure 3]
- If the pilot wants to fly a magnetic heading of 120° and the aircraft is operating with radios on, the airplane pilot should fly a compass heading of 123°
- The corrections for variation and deviation must be applied in the right sequence and is shown below, starting from the truthful course desired
- Error due to magnetic interference with metallic components in the aircraft as well as magnetic fields from the shipping's electrical equipment
- Compensating magnets inside the compass casing can help reduce this error but not eliminate it
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- Magnetic Form ± Deviation = Compass Course
- Presume a magnetic course of 180° equally higher up, ± Deviation (-4° (180-176 = -4, bold RDO ON), from correction card) = Compass Course (176°)
- Note that intermediate magnetic courses between those listed on the compass bill of fare demand to be interpolated. Therefore, to steer a true class of 180°, the pilot would follow a compass class of 188°
- To notice the truthful grade when the compass course is known:
- Compass course ± deviation = magnetic course ± variation = true course
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- Compass tends to dip toward the magnetic pole, most dominant as latitude increases
- The lines of magnetic flux exit the Earth at the magnetic North Pole and enter at the magnetic South Pole, pronouncing magnetic dip near the poles
- At both locations, the lines are perpendicular to the Earth's surface
- At the magnetic equator, which is roughly halfway between the poles, the lines are parallel with the surface
- Inside 300 miles of the poles, the musical instrument is unreliable due to extreme errors
- The s cease of the compass is therefore weighted to minimize this fault
- The magnets in a compass align with this field; nearly the poles, they dip or tilt the bladder and bill of fare
- A small dip-compensating weight balances the float, and then it stays relatively level when operating in the middle latitudes of the northern hemisphere
- To counter this, the pin point on which the bar magnet swings is deliberately placed at a position other than the magnet'due south
- The pull of the vertical component of the Globe's magnetic field causes northerly turning error, which is apparent on a heading of north or south
- When an aircraft flight on a heading of Northward makes a turn toward East, the aircraft banks to the right and the compass carte du jour tilts to the right
- The vertical component of the Earth's magnetic field pulls the north-seeking end of the magnet to the right, and the float rotates, causing the card to rotate toward West, the direction opposite the management the turn is made
- When turning from a northerly heading, the compass will initially turn the opposite management and take hold of up by e/West [Figure 4]
- When turning from a southerly heading, the compass will indicate a plough in the proper direction but will pb the actual heading, slowing down by due Due east/W [Figure 4]
- The rule for this error is: when starting a turn from a northerly heading, the compass indication lags behind the turn
- The dominion for this error is: When starting a turn from a southerly heading, the compass indication leads the turn
- If the turn is fabricated from north to West, the aircraft banks to the left, and the compass carte volition tilt down on the left side
- The magnetic field pulls on the end of the magnet that causes the card to rotate toward East
- This indication is again opposite to the management the plough is made
- When an aircraft is flight on a heading of due south and begins a plow toward East, the World's magnetic field pulls on the terminate of the magnet that rotates the card toward E, the same direction the turn is made
- If the turn is made from south toward West, the magnetic pull starts the card rotating toward West-again, in the same direction the turn is being made
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- Undershoot North
- Overshoot South
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- New heading: ringlet-out heading ± latitude - half the banking company angle
- Compass tends to dip toward the magnetic pole, most dominant as latitude increases
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- The dip-correction weight causes the stop of the float and carte marked N (the s-seeking stop) to be heavier than the reverse end
- When the aircraft is flying at a constant speed on a heading of East or Westward, the float and card is level
- When the aircraft accelerates on a heading of East/West, inertia causes the weight to lag, and the card rotates toward North [Effigy 5]
- When the shipping decelerates on a heading of East/Due west, inertia causes the weight to move ahead, and the card rotates toward Southward [Figure 5]
- The airspeed changes that are needed to brand this noticeable are infrequent
- As presently equally the speed of the aircraft stabilizes, the card swings back to its East indication
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Acceleration/Deceleration Error -
- Accelerate North
- Decelerate South
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- South Accelerate
- North Decelerate
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- Fluid fills the compass body, which provides damping, thereby decreasing unwanted oscillations due to turbulence of the magnet and float
- Fluid should therefore fill the compass, and no air bubbling or compass fluid discoloration should exist present
- The clear compass face (window) has on it a vertical line chosen a "LUBBER LINE" so that the pilot can use it every bit a datum to prepare the required heading
- Oscillation is a combination of all of the other errors, and it results in the compass carte du jour swinging back and forth effectually the heading flown
- Turbulence causes the compass to "bounciness" or move in the container
- When setting the gyroscopic heading indicator to agree with the magnetic compass, utilize the boilerplate indication between the swings
- The floating magnet blazon of compass non but has all the errors just described merely also lends itself to confused reading
- Information technology is easy to brainstorm a plough in the wrong direction considering its card appears backward
- E is on what the airplane pilot would wait to exist the Westward side
- The vertical card magnetic compass eliminates some of the errors and confusion
- The dial of this compass is graduated with letters representing the key directions, numbers every 30° and marks every 5°
- A set of gears rotates the punch from the shaft-mounted magnet, and the nose of the symbolic airplane on the musical instrument drinking glass represents the lubber line for reading the heading of the aircraft from the dial
- Eddy currents induced into an aluminum-damping cup damp oscillation of the magnet
- As mentioned earlier, the lines of flux in the World's magnetic field have two basic characteristics: a magnet aligns with these lines of flux, and an electrical current is induced or generated in whatsoever wire crossed by them
- The flux-gate compass that drives slaved gyros uses the characteristic of electric current induction
- The flux valve is a small, segmented band made of soft atomic number 26 that readily accepts lines of magnetic flux
- An electric ringlet is wound around each of the three legs to accept the current induced in this ring past the Earth'due south magnetic field
- A coil wound around the iron spacer in the middle of the frame has 400-Hz alternate current (A.C.) flowing through it
- During the times when this current reaches its elevation, twice during each cycle, so much magnetism is produced past this whorl that the frame cannot accept the lines of flux from the Globe'southward field
- But every bit the current reverses between the peaks, it demagnetizes the frame and then information technology tin can have the flux from the Earth'due south field
- As this flux cuts across the windings in the three coils, it causes current to flow in them
- These iii coils connect in such a way that the current flowing in them changes as the aircraft heading changes
- The three coils connect to three similar but smaller coils in a synchro within the instrument case
- The synchro rotates the dial of a Radio Magnetic Indicator (RMI) or a horizontal situation indicator (HSI)
- Made of soft fe that readily accepts a line of flux
- A ringlet wound effectually the iron spacer has 400-Hz Air conditioning flowing through it
- Every bit electric current peaks, twice during each cycle, there is so much magnetism that the frame cannot have the lines of flux, but as the current reverses, it demagnetizes to have more
- The three coils connect to 3 similar but smaller coils in a synchro inside instance
- The synchro rotated the dial of a Radio Magnetic Indicator (RMI or an HSI)
- Magnetic direction indicators (of which a magnetic compass satisfies) are required by Federal Aviation Regulation 91.205 to exist installed and operational on an shipping for it to be considered airworthy
- Full of fluid; carte du jour in identify and indicating a right heading
- Compass card installed (does not need to be filled out)
- Cheque the alignment of the direction indicator to comparing to the magnetic compass (indicator) once electric power is practical and the gyros have had a chance to spin up
- A compass swing must be performed whenever any ferrous component of the arrangement (i.e. flux valve compensator, or Standby Compass) is installed, removed, repaired, or a new compass is installed
- The magnetic compass can be checked for accuracy by using a compass rose located on an airport
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- While there is no official listings of airports with compass roses, they can exist plant on many airports [Figure 6]
- Painted surfaces are of grade static, and may exist invalidated with the gradual shift in magnetic poles
- The compass swing is unremarkably effected by placing the aircraft on various magnetic headings and comparison the deviations with those on the deviation cards
- Refer to CFR fourteen 23.1327, 23.1547, and the equipment or aircraft manufacturer's manual
- A compass swing must be performed when:
- The accuracy of the compass is suspected
- After any cockpit modification or major replacement involving ferrous metal
- Whenever a compass has been subjected to a shock; for example, after a difficult landing or turbulence
- Afterward aircraft has passed through a severe electrical tempest
- After lighting strike
- Whenever a change is made to the electrical system
- Whenever a modify of cargo is probable to bear on the compass
- When an shipping operation is inverse to a dissimilar geographic location with a major change in magnetic difference (east.g., from Miami, Florida to Fairbanks, Alaska.)
- After aircraft has been parked on i heading for over a yr
- When flux valves are replaced
- Procedures and precautions are found in Advisory Round (43.13-1B CHG 1) Acceptable Methods, Techniques, and Practices - Shipping Inspection and Repair
- The magnetic compass remains a fourth dimension tested reliable instrument, although as avionics evolve, the magnetic compass is being seen increasingly as a standby or back-up instrument
- Although Non approved for use past the FAA, products such as the SUUNTO Core All Black Military Men'due south Outdoor Sports Sentinel [Amazon] provide a redundancy method of direction-finding if the magnetic compass is ever inoperable or in question
- Deviation errors are unavoidable simply is a moving target as whatsoever modification may crave a compass swing
- Still looking for something? Continue searching:
- Advisory Circular (43.thirteen-1B CHG 1) Acceptable Methods, Techniques, and Practices - Shipping Inspection and Repair
- AvFacts - Compasses
- Federal Aviation Administration - Pilot/Controller Glossary
- Federal Aviation Regulation (91.205) Powered ceremonious aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements
- Instrument Flying Handbook (3-10) Magnetism
- NASA - The Earth's Magnetosphere
Source: https://www.cfinotebook.net/notebook/avionics-and-instruments/magnetic-compass
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