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7 september 2011

7 September 2011. By R. Warning. 2. COURSE PREVIEW. TheoryEarth magnetismCompassesCompass errorsPracticeCompass swing siteCompass swingAlternative methods. 7 September 2011. By R. Warning. 3. . . . . . . Permanent Magnetism. Certain materials can be magnetized, By putting them in a magnetic field. After removing the field remnant magnetism will be kept. .

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7 september 2011

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    1. 7 September 2011 By R. Warning 1

    2. 7 September 2011 By R. Warning 2 COURSE PREVIEW Theory Earth magnetism Compasses Compass errors Practice Compass swing site Compass swing Alternative methods

    3. 7 September 2011 By R. Warning 3 Permanent Magnetism Certain materials can be magnetized, By putting them in a magnetic field. After removing the field remnant magnetism will be kept.

    4. 7 September 2011 By R. Warning 4 Electro Magnetism Around a conductor that conducts electrical current a magnetic field is also generated.

    5. 7 September 2011 By R. Warning 5 Earth magnetism The earth can be seen as a giant magnet. The magnetic poles however do not align exactly with the geographic poles. The exact place of the magnetic poles is not constant, but varies in time.

    6. 7 September 2011 By R. Warning 6 Magnetic Variation Magnetic variation is the angle at a certain point on earth between the magnetic north and the true north. Due to the fact that the place of the magnetic north is not fixed, the variation changes. In Holland about one degree every six years.

    7. 7 September 2011 By R. Warning 7 The variation is not a function of the geographical position, But can vary due to changes in the earths rock formations. Lines of equal variation around the globe are so called isogonics lines. Inser een plaatje met een variatie kaart.Inser een plaatje met een variatie kaart.

    8. 7 September 2011 By R. Warning 8 Variation must always be added to the magnetic heading to get the true heading! Variation is positive if the true north is to the right (east) of the magnetic north. Else it is negative.

    9. 7 September 2011 By R. Warning 9 Inclination (magnetic dip) The direction of the magnetic force at a certain point on earth is not always exactly horizontal. Only at the equator. At the poles they are nearly vertical. The angle of force line with the horizontal is called the inclination or dip angle. A magnetic compass uses only the horizontal component of the earths magnetic field. But the inclination tends to tilt a magnetic compass.

    10. 7 September 2011 By R. Warning 10 Inclination card

    11. 7 September 2011 By R. Warning 11 Intensity

    12. 7 September 2011 By R. Warning 12 Compasses

    13. 7 September 2011 By R. Warning 13 Aircraft compasses There are tree kinds of aircraft compasses. Direct-reading compasses or standby compasses Remote-reading compasses systems with a flux valve Inertial compass systems

    14. 7 September 2011 By R. Warning 14 Direct-reading compasses The Direct-reading compasses is a free turning magnet with a scale around it, mounted on a pivot inside a liquid. The liquid provides damping for the scale. Normally a silicon liquid is used. The center of gravity of the scale and the magnet assembly is well below the pivot point. So that the compass will mainly react to the horizontal component off the earth magnetic field. The liquid is sealed off by a membrane to compensate for volume differences due to temperature changes. Underneath the compass is a compensator unit to allow adjustments to the compass

    15. 7 September 2011 By R. Warning 15 The compensator unit There are two compensators inside the compensator unit. One for Longitudinal axis off the aircraft and one for the cross-axis. Each compensator consists of two bars that can be turned in opposite direction. In each bar two small compensator magnets are mounted. In neutral position the magnetic forces of these magnets oppose each other, giving a resultant field of zero. When the bars are turned, the resultant force will be added to the earths magnetic field, But of course only the vector part that is parallel to the earths field.

    16. 7 September 2011 By R. Warning 16

    17. 7 September 2011 By R. Warning 17 Direct-reading compasses errors There are two main errors involved in using a direct-reading compass in an aircraft. Northern turning error. Acceleration error

    18. 7 September 2011 By R. Warning 18 Northern turning error The compass card is mounted so that its center of gravity is well below the pivot point. When the aircraft is in a banked turn, the card also banks because of centrifugal forces. While the card is in the banked attitude, the vertical component of the earths magnetic field causes the compass to dip to the low side of the turn. The error is most apparent when turning trough headings close to north and south. When the aircraft makes a turn from a heading of north, the compass briefly indicates a turn in the opposite direction. Passing trough south, the compass leads the turn considerably. As the aircraft nose passes though the west, the compass should approximate the correct heading. Then, as the aircraft nose approaches north again the compass lags. In the Netherlands this error is 2,5 with a 1 bank and 25 with a 10 bank

    19. 7 September 2011 By R. Warning 19 Acceleration error A second way to tilt the compass card out of the horizontal plane is to accelerate or decelerate the airplane. With the card mounted with its CG below the pivot, acceleration causes the card to tip forward. In the Northern Hemisphere where the magnetic field has a downward component, this causes the north-seeking tip of the compass needle to swing downward.

    20. 7 September 2011 By R. Warning 20 Other compass errors Besides the dynamic errors (northern turning error and acceleration error.) and the errors caused by the aircraft it self (for witch we will calibrate the compass.) there are some minor faults in direct-reading compasses. Scale faults caused by an unjust calibration of the scale. Collimination faults, caused by a difference between the magnetic axis of the compass and the north of the scale. Lubber line alignment error. Liquid swirl error. If there is not enough room in the compass housing, the scale will be turned with the aircraft, due to the viscosity of the compass fluid. The first 3 errors will be eliminated when the A error is adjusted during the compass swing.

    21. 7 September 2011 By R. Warning 21 Checking a direct reading compass:

    22. 7 September 2011 By R. Warning 22 The remote reading compass

    23. 7 September 2011 By R. Warning 23

    24. 7 September 2011 By R. Warning 24 The electric compensator

    25. 7 September 2011 By R. Warning 25 The Remote Compensator unit The variable DC power source in the previous slide is located in the remote magnetic compensator unit. On the unit, you find also some test points to measure the DC voltage applied to the flux valve and a potentiometer to adjust the voltages. After successful adjustment of the compass system, the voltages should be measured and written down on a sticker on the remote compensator unit. This way a remote compensator unit or flux valve can be replaced without the need to do a new compass swing. Only the voltages should be taken over from the old compensator unit. Inside the remote compensator unit is also a circuit that transforms the tree wire output of the flux valve into 2-wire sine/cosine signals. And a monitor circuit thats checks the functioning of the flux valves and the remote compensator unit.

    26. 7 September 2011 By R. Warning 26 Flux valve errors Principally the flux valve suffers also from the northern turning error and acceleration errors just as the standby compass does. But because the reading of the flux valve output is stabilized with a directional gyro, The readout is much more reliable.

    27. 7 September 2011 By R. Warning 27 Aircraft errors Due to the fact that aircrafts contain a certain amount of iron and other magnetic material and there are a lot of life wires in an aircraft. The aircraft itself will generate a magnetic field that will disturb the precession of the compass systems. These aircraft errors or static errors we can divide into tree categories; Index errors, one cycle errors and two cycle errors.

    28. 7 September 2011 By R. Warning 28 Adjusting the compass We have to adjust an compass for A, B and C faults. E and F faults are generally minor and are not compensated. The A fault can be compensated by turning the compass or flux-valve in horizontal direction. The B fault is compensated by the E-W adjustment of the compensator. And the C fault is compensated with the N-S adjustment of the compensator.

    29. 7 September 2011 By R. Warning 29 Total deviation The total deviation caused by the aircraft should be compensated by means of a A-fault correction that is linear over the whole compass range. B-fault correction, that acts as a cosine function over the compass range C-fault correction thats a sine function. With the B and C correctors we only adjust the amplitudes of the sine and Cosine curves. The total Compensation is the sum of the A-fault, B- fault and C fault corrections. This total correction should compensate for the total deviation generated by the aircraft.

    30. 7 September 2011 By R. Warning 30

    31. 7 September 2011 By R. Warning 31 The compass swing location A compass swing must be carried out on an approved site! An approved site should be accessible and level. Free from magnetic fields (except earths magnetic field.) Should be at least 46 meters away from steel framed buildings and 91 meters from buildings containing electrical power generation. Large enough to swing the aircrafts its intended for. There are two compass swing site classifications. Class 1 with a permit able deviation of 10. Class 2 with a permit able deviation of 25. Periodic re-survey A class 1 site must be re-surveyed every 5 years. A class 2 site every 2 years. (??) The surveying party must work with the standards of the Admiralty Compass Observatory (ACO) and must be recognized by the CAA. (Source: CAA UK leaflet 8-1 compass base surveying)

    32. 7 September 2011 By R. Warning 32 Swing sites at Schiphol There is only one compass swing site at Amsterdam! This is the fairway near the Martinair hangars. The site near the old Fokker buildings is not surveyed and contains a lot of iron in the ground.

    33. 7 September 2011 By R. Warning 33 The Compass swing A compass swing contains two parts. The correction swing. Where the compass is calibrated and the A, B and C errors are adjusted. The calibration swing, where the remaining deviations are noted and written on the deviation table that is mounted in the aircraft. Note that with a Fokker 100 with IRS systems, the IRS may be used as reference. Else a approved prismatic landing compass mounted on a tripod should be used as a reference. Keep in mind that, when standing in front of the aircraft with a reference compass, the reading is 180 with respect to the aircrafts heading. When reading the reference compass make sure there is sufficient distance between the compass and the aircraft. Take also care not to wear any iron tools, watches, radios etc Be also aware that the reference compass comes also with a deviation card!

    34. 7 September 2011 By R. Warning 34

    35. 7 September 2011 By R. Warning 35 Preparing the compass swing Before a compass swing is undertaken make sure the following preconditions are met: Authorization of the airport authorities. Towing facilities. Daylight! Make sure you have the following equipment with you. A stairs to leave and enter the aircraft in the field (if there is no air stair on F100). Special adjustment tool for the standby compass. Flat screw driver for A fault adjustment stby compass and compensator adjustment. Wrench to loosen and tighten the locking nuts on the AHRS compensator unit Voltmeter to measure the compensation voltages on the compensator. Two Porto phones to communicate between outside and inside of aircraft. Master compass and tripod or pylorus and bracket and course list. Correction form, deviation form and deviation cards.

    36. 7 September 2011 By R. Warning 36

    37. 7 September 2011 By R. Warning 37 Example calculation

    38. 7 September 2011 By R. Warning 38 The calibration swing After the correction swing is performed, a calibration swing should be made. The calibration swing is to verify the correct adjustment of the compass and to make a deviation list and deviation cards, to make the crew aware of the remaining deviation errors. We are making a full 360 degrees swing with 30 degrees interval. On every interval we note the deviation of the standby compass and the two AHRS systems and the standby compass in emergency power condition. For the standby compass the maximal deviation may be 10 degrees but between successive (30) steps the difference in deviation may be 4 maximum! The maximum deviation for the AHRS may be 2! After the calibration swing a deviation form should be filled in for tech records and deviation cards should be made for in the cockpit.

    39. 7 September 2011 By R. Warning 39 The pylorus method With a normal compass swing a master compass is used as reference. As an alternative a pylorus can also be used if the compass swing site is approved for this method. A pylorus is an instrument with witch we can very precisely measure a angle between two points. In our case the longitudinal axis of the aircraft and a known point at some distance away. The angle between this known point and the aircraft heading is predetermined for all compass headings used during the compass swing By measuring the angle with the aircraft longitudinal axis, and comparing this with the predetermined value, we can calculate the deviation.

    40. 7 September 2011 By R. Warning 40 Before we start using the pylorus, we have to align the instrument with the aircrafts longitudinal axis. This is done by putting the instrument on a known spot (cockpit side window), Level the instrument and then point the instrument exactly to the wing tip and adjust the bottom reference ring of the pylorus to 240.25 (F50) as given on the job card. Now the zero should be exactly in line with the aircrafts longitudinal axis. After this we can shoot for every 30 heading a suitable target from the target list. By subtracting the value given on the target list , With the actual readout on the pylorus scale, the datum heading can be calculated. Subtract the readout heading from the datum and you get the deviation.

    41. 7 September 2011 By R. Warning 41

    42. 7 September 2011 By R. Warning 42

    43. 7 September 2011 By R. Warning 43

    44. 7 September 2011 By R. Warning 44 The End

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