air navigation part 2 distance speed & time. recap if two places are on the same meridian then...
TRANSCRIPT
AIR NAVIGATION
Part 2
Distance Speed & Time
RECAPIf two places are on the same meridian
then it is possible to calculate the distance between them,
rather than having to measure it.
We don’t use a speedometer for aircraft speed.
We use an Air Speed Indicator (ASI)
Speed Corrections•ASI readings can be wrong for two reasons –
•Instrument and Pressure Errors.•
•Instrument Error •caused by poor manufacturing tolerances
•when the instrument was built.•
Speed Corrections•ASI readings can be wrong for two reasons –
•Instrument and Pressure Errors.•
• •Pressure Error
•(previously known as position error) •caused by sensing incorrect values
•of static pressure due to the static vents position•relative to the airflow around the aircraft.
Speed Corrections
Once the two errors have been accounted for, we are left with
Calibrated Air Speed (CAS), (formerly known as Rectified Air Speed (RAS))
+-+-IAS Pressure Error Instrument Error CAS=
Speed Corrections
Thus an IAS (Indicated Air Speed)of 118 kts
with an overall correction of +2 kts
would give a CAS (Calibrated Air Speed)of 120 kts.
+-+-IAS Pressure Error Instrument Error CAS=
Speed Corrections
If flying at speeds greater than 300 kts, you also need to apply a correction for
Compressibility Error, caused by air being compressed in the Pitot Tube.
To obtain True Air Speed (TAS) from CAS
you need to correct for air density changes
caused by temperature and altitude.
Speed Corrections
+-+-CAS Density Error Compressibility Error TAS=
Thus a CAS of 120 kts with a correction of -2 kts
would give a TAS of 118 kts.
When these two corrections have been made, we are left with
True Air Speed (TAS),
Speed CorrectionsSUMMARY
+-+-CAS Density Error Compressibility Error TAS=
+-+-IAS Pressure Error Instrument Error CAS=
Calibrated Air Speed (CAS), (formerly known as Rectified Air Speed (RAS))
True Air Speed (TAS)
Calculation of Time
•We are all familiar with •days, hours and minutes;
•But when working with aircraft knots,•it’s only necessary to use hours,
•as this speed is nautical miles per hour.•
Calculation of Time
•In aviation the 24 hr clock is used, •set to Greenwich Mean Time GMT
•or Coordinated Universal Time (UTC) •(also known as Zulu Time)
• •Summer Time or Daylight Saving Time
•is always ignored.
Calculation of Time
•If a car travels 120 miles at 60 mph, •it will take 2 hours to complete the journey.
•This is calculated using the
•Distance - Speed - Time
•formulae
Speed Time
Distance
Calculation of Time
Speed Time
Distance
Provided 2 quantities are knownthe 3rd can be calculated -
Time (T)
Distance (D)Speed (S) =
Speed (S)
Distance (D)Time (T) =
Speed (S) Time (T)Distance (D) = x
Calculations• How fast (in knots) must we go to cover
• 1500 nm in 5 hours?
Time (T)
Distance (D)Speed (S) =
5 hours (T)1500 nm (D)
Speed (S) = = 300 kts
3
1
Calculations• How long will it take to travel
• 960 nm at 160 knots?
Speed (S)
Distance (D)Time (T) =
160 knots (S)960 nm (D)
Time (T) = = 6 hrs
6
1
Calculations• How far (in nm) will we cover
• at 270 knots in 3 hours?
= 810 nm
Speed (S) Time (T)Distance (D) = x
270 kts (S) 3 hours (T)Distance (D) = x
Check UnderstandingWhich of the following statements about
Calibrated Air Speed (CAS), (formerly known as Rectified Air Speed (RAS))
is true?
CAS is always less than IAS
CAS = IAS after corrections
CAS always equals IAS
CAS = IAS before corrections
Check UnderstandingCalibrated Air Speed equals
Indicated Air Speed with corrections for what?
Altitude and Pressure error
Instrument and Pressure error
Air Density and Pressure error
Compressibility and Pressure error
Check Understanding
An ASI has an instrument correction of +3 kts and a pressure correction of -1 kts.
If the ASI reads 130 kts what is the CAS?
130 Kts
132 Kts
133 Kts
134 Kts
IAS ± Pressure Error ± Instrument Error = CAS
130 kts + 3 kts – 1 kts = CAS
CAS = 132 kts
Check UnderstandingTrue Air Speed equals Calibrated Air Speed
with corrections for what?
Air Density and Compressibility error
Compressibility and Altitude error
Air Density andPressure error
Compressibility and Pressure error
Check Understanding
A Tornado is flying at a TAS of 400 kts. How far will it travel in 2 hrs?
200 nm
200 Km
800 nm
800 Km
Speed (S) Time (T)Distance (D) = x
400 kts (S) 2 hours (T)Distance (D) = x
= 800 nm
Check Understanding
A Tornado is flying at a TAS of 320 kts. How long will it take to travel 80nm?
15 mins
30 mins
2 hours
4 hours
Speed (S)
Distance (D)Time (T) =
320 knots (S)80 nm (D)
Time (T) = =
1
4
15 mins=
AIR NAVIGATION
End of Presentation