CR-3 CALCULATOR SIDE

1. TIME - DISTANCE – SPEED

a.

1. Place the GS (20 standing for 200)

opposite to the TIME INDEX

2. Opposite to the DISTANCE (30 standing

for 300) on the outside (white) scale �

TIME ENROUTE on the inner grey scale

ANSWER: 90 min or 1:30h

b.

1. Place DISTANCE opposite TIME. The

later on the inner scale

2. Opposite to TIME INDEX � GS

ANSWER: 252mph

NOTE: Any figure on the outer scales (white and grey) of the computer can stand for

any number containing the given digits: i.e.: 40 can stand for 0.4, 4, 40, 400, ...

2. FUEL CONSUMPTION

Is worked out in the same manner as 1

• Place FUEL CONSUMPTION opposite to TIME INDEX

• Place FUEL CONSUMED (Gallons) on outer scale

• Place TIME OF OPERATION OF THE ENGINE on inner scale

1. Place on the outer scale the amount of

FUEL CONSUMED

2. Opposite to it, on the inner scale, place

the TIME

3. Read FUEL CONSUMPTION on the outer

scale opposite to TIME INDEX

ANSWER: 70 USGall/h

GIVEN:

• GS = 200mph

• DISTANCE = 300sm

FIND:

• TIME ENROUTE

GIVEN:

• DISTANCE = 210sm

• TIME ENROUTE = 50min

FIND:

• GS

GIVEN:

• FUEL CONSUMED = 105 USGall

• TIME = 1h 30min

FIND:

• FUEL CONSUMPTION

3. CONVERSIONS

Place the arrow of the first unit of measure on one scale opposite the arrow of the other

unit on the other scale. Read corresponding values opposite each other on the two scales

SPECIAL CASES:

• ºC - ºF �Special conversion scale

• Weight of fuel and oil

• Minutes to seconds Time index opposite to the blackgrounded 10 and read

minutes on the outer white scale and seconds on the inner grey scale

4. ALTITUDE

• INDICATED ALTITUDE = Reading on the altimeter set with QNH

• CALIBRATED ALTITUDE = Indicated altitude corrected for instrument, position and

installation errors.

• TRUE ALTITUDE = Calibrated altitude corrected for non-standard atmospheric

conditions

• PRESSURE ALTITUDE = Indicated altitude when set with QNE

• DENSITY ALTITUDE = PA corrected for non-standard temperature

a. DENSITY ALTITUDE (Near the centre of the computer)

1. Place PA in front of TAT

2. Read DA � 5000’

b. TRUE ALTITUDE (Use the calibrated altitude and TAT)

Greater accuracy can be obtained if you also know the altitude of the ground

station giving you the altimeter setting.

1. Place PA opposite to TAT

2. Substract to CA the GSA in

order to get the CA above

ground level

3. Opposite to CA above ground

on the inner scale is TA

above ground on the outer

scale

GIVEN.

• PA = 3000ft

• TAT = (25ºC)

FIND:

• DA

GIVEN:

• PA = 10000ft

• CA = 9000ft

• TAT = -20ºC

• Ground station altitude = 5000ft

FIND:

• TRUE ALTITUDE (TA)

4. Add station altitude to TA above ground to get TRUE ALTITUDE ABOVE SEA

LEVEL.

5. If station altitude is at SL or unknown, find the TA on the outer scale

opposite to CA on the inner scale

5. TRUE AIRSPEED

On fast flying aircraft the air is compressed in front of the aircraft and is heated by

compression (OAT bulb feels a higher temperature than what really exist in the

surrounding non-compressed air). Also the rush of air over the OAT bulb creates a friction

causing further heating and still higher (false) reading.

This increase in temperature � TEMPERATURE RISE

NOTE: Even though both knots and mph can be used, a more accurate TAS answer will be

given using knots

Following parameters are necessary

1. CAS (or IAS if unable)

2. PA (or altitude if unable)

3. Indicated OAT (ºC)

TEMPERATURE RECOVERY COEFINCIENT (Ct): Varies with installation and design of the probe for

every aircraft (0.6 – 1.0). Can be considered constant even though it varies slightly with speed

and altitude � CR-3 only consider Ct 0.8 or 1.0

• SOLID LINE (Ct=1.0) � Standard stratosphere temperature (-55ºC)

• DASHED LINE (Ct=1.0) � Standard SL temperature (+15ºC)

Between them interpolate

NOTE: If not otherwise stated will assume Ct = 1.0

a) DIRECT METHOD

1. Place CAS opposite to PA

2. Ct 1.0 line crosses intersection between SPIRAL

LINE and INDICATED TEMP wiggly line

3. Read TAS underneath

ANSWER: 500kts

GIVEN:

• CAS = 400kts

• PA = 15000ft

• IAT = 30ºC

FIND:

• TAS

MACH NUMBER: Read at the pointer indication directly beneath TAS �

Represents different TAS at different Temperatures

b) TAS FROM M NUMBER AND TEMPERATURE

1. Place M # in front of M # ARROW underneath

TAS

2. Set Ct line over intersection of SPIRAL with

TEMP (IAT)

3. Read TAS in knots under cursor line

ANSWER: 673kts

NOTE: If OAT is not available is possible to use reported or estimate air

temperature (the result will be as accurate as the estimation)

c) DOUBLE-ENDED MACH INDEX ARROW

Relates ISA altitude with ISA temperature (ESTIMATED TAT)

1. Set MACH INDEX ARROW in front of PA in ISA

scale

2. Read on the other side of the arrow ISA temp

for that PA

ANSWER: -40ºC

d) TAS FROM TAT

1. If the aircraft is equipped with a M # indicator and you know the TAT

1. Place M # ARROW opposite to TAT

2. Opposite to M # on inner scale read TAS on outer

scale.

ANSWER: 344kts

GIVEN:

• M = 0.55

• TAT = -15ºC

FIND:

• TAS

GIVEN:

• PA = 28000ft

FIND:

• ESTIMATED FREE AIR

TEMPERATURE

GIVEN:

• M # = 0.55

• TAT = -15ºC

FIND:

• TAS

2. If the aircraft is equipped with conventional airspeed indicator:

1. Use the direct relation method matching CAS with PA

and finding the M # on the M INDEX section

underneath the TAS

2. Follow the steps above ANSWER: 343kts/0.55

TEMPERATURE RISE: Probes nowadays use recovery coefficient of 1.0. But, if temperature rise is

desired for a temperature probe with a Ct = 0.8, the Ct = 0.8 must be used, and the value for the

“TEMPERATURE RISE Cº(CT 1.0)” scale multiplied by 0.8

1. Place CAS opposite to PA

2. Move green cursor until hair line passes through

intersection of IAT line and SPIRAL line.

3. Read Trise on the section bellow MACH NUMBER

4. Must take into account: IAT = TAT +Trise

ANSWER: Trise = 13ºC / TAT = -13ºC

e) “OLD METHOD” TO FIND OUT TAS

This method doesn’t correct for temperature rise nor compressibility and ,

though, is not suited for high speed calculus (<200kts)

1. Place PA opposite to TAT

2. Opposite to CAS on the inside grey scale, read

TAS .

ANSWER: 180kts

GIVEN:

• PA = 14500ft

• CAS = 280kts

• TAT = -15ºC

FIND:

• M # / TAS

GIVEN:

• CAS = 276kts

• PA = 10000ft

• IAT = 0ºC

• CT = 1.0

FIND:

• TAS /Trise

GIVEN:

• CAS = 166kts

• PA = 5000ft

• TAT = 10ºC

FIND:

• TAS