加拿習(xí)加國學(xué)習(xí)6.altimeter

1、Section 6.4Altimeter & Encoding AltimeterThe Altimeter Is Very Important!Altimeter / Encoding AltimeterLesson ObjectivesInternal Components and ConstructionPrinciples of OperationErrorsThe ICAO Standard AtmosphereTerminologyUnderstand how to correctly set the altimeter.Encoding AltimetersAltimeterAl

2、timeter measures pressure and converts it into altitudeIndicates altitude ASL, not AGL!Airtight instrument case connected to static source and aneroid capsule sealed at 29.92”3 Hands: 100s hand, the 1000s hand and the 10,000s hand.Altimeter Altimeter/Aneroid BarometerPrinciple of OperationThe aneroi

3、d bellows expands and contracts in response to the weight of the column of overlying air.Through linkages and gears the size of the aneroid capsule is transmitted to the needle on the face of the instrument.The instrument is calibrated to read altitude in feet ( instead of pressure, which is what it

4、 is really reading). Simple Altimeter PrincipleSomewhere on earth there is a room where the ISA atmosphere exists and aneroid capsules are producedBecause the ISA hardly ever exists, altimeters have a calibration knobAltimeters cant differentiate between a change of actual altitude and a high/low pr

5、essure system passing through, you can set the current altimeter setting to indicate the correct altitudeValues of the I.S.A.Surface temperature 15C ( 59F )Surface pressure 29.92” of mercury (1013.2hPa) Lapse rate within the troposphere is approximately 2C/1,000 feet.Altimeter ErrorsPressureMust cor

6、rect for non-standard atmosphere Current altimeter setting must be placed on the subscale.“From High to Low, look out below”Altimeter will read too high if you fly into an area of lower pressure and dont reset the subscale ( and vice versa).Effect of Flying into a Low Pressure AreaAltimeter ErrorsTe

7、mperatureError if temperature is higher or lower than standard “From High to Low, watch out below” also applies when flying into an area below standard temperature.( it will read too high)There is no very simple way to correct for this. ( the formula: 4 feet /per degree /per 1000 feet, may be useful

8、)Altimeter ErrorsEffect of MountainsDue to Bernoullis Principle, there is a local decrease in pressure due to wind over mountains.A mountain wave forms where wind in excess of 50 kts. blows within 30 degrees of the perpendicular to the main axis of the mountain range.Altimeter ErrorsThe effects of a

9、 mountain wave can extend as far as 100 miles downwind of the mountains and to altitudes many times higher than the mountain elevation.The local drop in pressure, when combined with below standard temperature, can cause an altimeter to over-read by as much as 3,000 feet.Temperature and Pressure Effe

10、cts CombinedErrorsComplete Blockage of the Static vent:If the static vent es blocked then static pressure will remain fixed in the line to the Altimeter.A constant altitude will be indicated, even though the A/C may be changing altitude.PARTIAL BLOCKAGE:Under read in a climbOver read in a descent (d

11、angerous if terrain clearance is a problem)Blocked Static VentServiceability CheckThe altimeter must read within + or - 50 of field elevation before flight.Static source should be checked clean and clear during pre-flight inspection and alternate static source should be checked.Pitot-Static system a

12、nd altimeter must be calibrated every 24 months for IFR flight.Altimeter SettingChanges occurring in surface pressure are compensated for in an altimeter by means of the Pressure Adjustment Knob.This is illustrated in the next slide:-Altimeter SettingAltimeter Setting(contd)The “Altimeter Setting” i

13、s the pressure that when set on the altimeter will cause the altimeter to read station elevation when the aircraft is on the ground at the aerodrome.The altimeter setting is used during take-off and landing and in flight in the low-level airspace.Altimeter SettingWhat would you do if you had no alti

14、meter setting available at an aerodrome?If you know the field elevation, simply adjust the altimeter setting knob until the altimeter indicates the same altitude as the field elevation.Can be used to quickly cross-check to see if you were given an incorrect altimeter setting.Altimeter SettingIt is i

15、mportant to recognize how changes in altimeter setting effects the display indication on the altimeter.The next slide shows the effects on the display indication if an altimeter experiences a lower pressure after having set for example, overnight at Moncton aerodrome.Pressure Changes and Altimeter I

16、ndicationsEncoding AltimeterAn Encoding Altimeter is simply an altimeter which is equipped to transmit a digitized signal of the altitude that it sees.Encoding Altimeters are quite expensive but are necessary in certain airspace; so that A.T.C. can not only know where you are in plan view, but where

17、 you are in elevation. Encoding AltimeterA so-called “Blind Encoder” is an altimeter that sends the digitized altitude signal, but does not have a altimeter display face.In other words, there is no read-out for this instrument, it may be mounted out of sight behind the instrument panel.Blind Encoder AltimeterDefinitionsIndicated AltitudeThe reading on the altimeter when it is set to the current barometric pressure.Pressure AltitudeThe re