Navigation Ground School CI Pesto

Topics Discussed Today The Magnetic Compass Variation - Isogonic Lines, Agonic Lines Compass Errors - Deviation, Magnetic Dip, Northerly Turning Error, and Acceleration/Deceleration Error

Topics Discussed Cont. Units of Distance Units of Time Units of Speed Converting questions

The Magnetic Compass An instrument containing a magnetized pointer that shows the direction of Magnetic North Uses magnets (usually two) attached to a float mounted on a pivot suspended in alcohol or white kerosene The liquid damps out oscillations, reduces the weight of the magnets, and lubricates the pivot point as well as making sure the compass does not freeze in subzero temperatures.

Magnetic Compass Components

Variation The angle between True North and Magnetic North in which the compass needles lies.

Correcting for Variation True Heading −East Variation= Magnetic Heading True Heading +West Variation= Magnetic Heading

Variation True Heading Magnetic Variation Magnetic Heading 300 ∘ 6 ∘ East 5 ∘ West57 ∘ 210 ∘ 207 ∘ 4 ∘ West180 ∘ 360 ∘ 12 ∘ West

Isogonic Lines Lines on a map joining places of equal variation. Also known as Isogonals. These are numbered east and west according to whether the magnetic variation is to the east or west of true north.

Agonic Lines Lines on a map joining places of zero variation.

Compass Errors COMPASS DEVIATION The angle between the magnetic heading and the compass heading.

Correcting for Deviation Magnetic Heading −East Deviation= Compass Heading Magnetic Heading +West Deviation= Compass Heading

Deviation Magnetic Heading Deviation Compass Heading 65 ∘ 2 ∘ East 320 ∘ 325 ∘ 7 ∘ West40 ∘ 120 ∘ 117 ∘

So we can now use what we’ve learned of Variation and Deviation to find our Compass Heading. Using our True Heading and Variation to get our Magnetic Heading, then using Deviation to get our Compass Heading. TV Makes Dumb Cadets TVMDC TRUEVARIATIONMAGNETIC DEVIATION COMPASS

Magnetic Dip The earth's lines of force are horizontal at the equator but become vertical towards the poles. This causes the compass to tend to dip in higher latitudes.

Northerly Turning Error The compass will misread when the aircraft is in a banked attitude and turning. Error is most apparent on headings of North and South and is greatest over the poles. Always make sure the wings are level while reading the compass on North or South headings.

Northerly Turning Error Cont. On turns from NORTH northerly turning error causes the compass to LAG. On turns from SOUTH northerly turning error causes the compass to LEAD.

Helpful Tip: The compass always wants to be pointing North, so when you are turning FROM North TO South, the compass will lag. While turning FROM South TO North, the compass will lead.

Acceleration and Deceleration Error On East and West headings, acceleration causes a turning moment, causing deflection of the compass towards North. When the airplane decelerates, a similar effect is seen but the deflection will be in the opposite direction, towards South.

Acceleration and Deceleration Error Cont. The effect of acceleration and deceleration compass errors is nil on North and South headings. When reading the compass on East or West headings, always make sure the airspeed is constant.

Helpful Tip: ON EAST OR WEST HEADINGS: ACCELERATION makes the compass turn NORTH. DECELERATION makes the compass turn SOUTH. Aacceleration NnorthD decelerationS south

Units of Distance Statute Mile ft Nautical Mile ft (average length of one minute of latitude) Kilometre meters

Units of Speed and Conversions Knots to MPH - Multiply by 1.15 MPH to Knots - Divide by 1.15 KPH to Knots - Multiply by 0.54 KPH to MPH - Multiply by 0.62

Units of Time and Conversions Hours to Minutes-Multiply by 60 Minutes to Hours-Divide by 60

Questions: 108 Knots 5 Hrs 135 MPH 180 Mins 250 KPH 115 Knots = = = = = = ? MPH ? Hrs ? Knots ? Mins ? KPH

Reading and Questions Please read pages There will be a quiz next class Have a Great Week!