Jeppesen CR-3 User manual

JS314294E
NOTE
The plastic components of your computer
may warp if exposed
to excessive heat or
sunlight . .. . 140 °F or 60 °C will do it.
© Jeppesen Sanderson, Inc., 19 81, 1988. 1987. 1994
A ll Ri gh ts Reserved
55 Inverness D ri ve East, Englewood, CO 80 11 2·5498
TABLE OF CONTENTS
PART A- CALCULATOR SIDE PART B-WIND SIDE
Time - Speed -Distance . . . . . . . . . 2 The CR "Wind'' Disc . . . . . . . . . . 30
Fuel Consumption . . . . . . . . . . 4 Addition - Subtract ion . . . . . . . . . 32
Wind Solution on the CR . . . . . . . 33
Conversions . . . . . . . . . . . . . . . . . . 5
Flight Planning with
Weight of Fuel and Oil . . . . . . . 9 Forecast Winds . . . . . . . . . . . . 37
Finding Winds in Flight . .
... . . 41
Altitude . . . . . . . . . . . . . . . . . . . . 11
T rue Cow-se (Track! and
Densi ty Altitude . . . . . . . . . . . 12 Ground Speed ....... ..... . 44
True Altitude . . . . . . . . . . . . . 12 True Heading and
True Air Speed . . . . . . . . . . . . 48
Tru e Air Sp eed . . . . . . . . . . . . . . 14 OfT -Cour se Correction . . . . . . . . . 51
Th e CR Cursor . . . . . . . . . . . . 15 Radius of Action . . . . . . . . . . . . . 53
Mach Number
... . .• . • .... 17 Wind Components for
Temperature
Ri se . . . . . . . . . . 20
"Old" M
et hod • Tru e
Air Speed
..... . ... .... 21
Takeoff and Landing . . . . . . . 55
PART C-ANSWERS ,
DEFINITIONS AND HINTS
P1 · essure Patt-ern . . . . . . . . . . . . . 23 An swers to Pract ice Pr oblems . . . 57
Slide Rule Use . . . . . . . . . . . . . . . 25 Definitions . . . . . . . . . . . . . . . . . . 58
Time
and Di sta nce to Station ... 28 Some Hints on the CR . . .. ..... 60

ii
PART A-CALCULATOR SIDE
CR-2 and CR-3
0 Unit Index
0 Cursor Hairline
0 Recovery CoefCicient 1.0
0 Nautical-Statute Conversion Arrows
0 Calibrated Air Speed Window
G Time Index
0 True Air Speed Windows
0 Base Disc
CR -5
0 Top Di sc
0 Temperature Conversion Scale
G Indicated Temperature Window
4D Mach Number Window
G) Temper ature Rise ScalP
0 True Altitude Window
G) Latitude for Pressure Pattern Scale
1

----
Time
-Speed -
Distance
"Time, speed and di~tanre probl ems are so lv ed with the CR
Computer in the conventional manner ... using the out!> idc scales
on
the calculator s ide . For the benefit ol tho~e 'k n ot so inclined,'
the CR is ' knot knecessarily knaULical' and you can get perfectly
good an~wers in ~! PH and stattHe. Let's run through ~ome quickies
so's you won't figure 'Ole Sharp' is spoofi ng you.
" fi rst a word about reading the scales on the CR. Each figure
on
the outer scales of the compu ter can stand for any number con -
taining the given digits. The poim marked '40' can ~tand lor .I, -1,
40, 400, etc. Y ou must d etermine, from the given problem, which
value is correct."
2
Ex ample
Given :
Ground peed...................200 ~I PH .
Oi
stance ...............................300 Stat. :\l1.
Fi nd : Tim e e nrout e
Fig. 1
Gi ve n: Oi~tanr e .........................210 :\[i.
Time ....... ·················-····50 ~1 in.
Find: Ground ~peed
Fig. 2
To find di\tanre il you are given g round spe('(l and time, pl~re
time index A oppmite ground speed and read di~tance on out side
,lale oppo~ite time on imide scale.
3

Proble ms 1
(Sec pa ge 57 ror an~wt·r ~ )
Tim('
c;,mud sp( ·(·d
/) istanre
I.
: ~2
180 kt~ .
2.
:I~
<4~ ~tal. mi.
3.
:l · ltl k t~.
510 rwrrt. mi.
4.
I:· 10
IIi~ . \II'H
5.
:30
I flO n< llll . 111 i.
fl.
Iii ~II'H
liliO \Lat. nli.
FUEL CONSUMPTION
P roblems involving hrcl <'OrhtllllJHion arc worked in the ~amc
man n er a~ tirne-~pced - di~tancc prohl erm. Simply plarc g:lllcHh in·
~lead o( mil es on th e olll~ide ~<"ale a nd time on the in~idc \talc.
Gallon~ per hour instead ol urile, per hour will he read oppm it e
th e time index J;.. .
II U.S. gallo ns ( ga~o lin c ) arc being uwd. porrrHI, per hour
may be read on the o ut ~ id e \< · ale oppmite th e ..SI·. C" arrow at :l li
on th e in side scale .
Ex ample
An aircraft ha, corl\llllled 105 U. S. g.lllorr, ol g .r,olinc in I hr.
30 lllrll.
f i nd : Gallon!>
J>l 'r hour and potrrrd, per hour.
4
1
CONVERSIONS
"Thing~ arcrr't al\\·ay what )OU want th em to he -
But th e C R. will help )'Oll change thcn1.
For in,t < rr Hc, il )OU wan t to change:
Na uti cal mil es to ~ tat11t e miles or kilorneter~
l l. S. g allon11 to imperial gallon~ 01 liter )
F
eet to ur eters
P ound, to l..ilograllh
Or "i cc vcr~a -
ll cr c\ how:
Note th e followirtg lab c lc ·d arrow ., on inside and om sidc ~r:rlc1.
of the calculator ,ide ol the <Ollll>ltLCr:
NAUT IC.\ L rnile:o. ............ near Ci( i on both \ C ak\
STATUTE rniles.............. nc:rr iii on bmh !>ca l C!>
K\1. ( kil ometer ") ........... nca1 I~ on bnrh 'calc •,
1 .\ 1p. (; ,\ L. . ............. .. ncar I I or1 bo th sealcs
( '. S. G. \L .. ..... ............... ncar 1:1 Oil both ~c•k~
LITERS ................... .. . .... .n ca r IH Oil both sca l e~
F 1...... . ..... .. ............ .. .... nc ar I I on Olll!.idc !>r:rle
.\I ET I·.RS.... ................... near J.l Oil i n~id c scale
LB S.
KC. (kil og rarm ) Ilear
: ~li on mrt~ide :.<.ric
.n ear 1f, on in~id e sealc
5

To convert between two different units or measure, simply find
the arrow for the first unit of measure on one scale of the comp u ter
and place it o pp osite the arrow for the second u nit of measure on
the other scale. R ead corresponding va lues op posite each other on
the two scules.
Example
Conven 40 na ut ical mil es to sta t ute miles .
2. . Oppo site 40 on outside
sca le r ead 46 on inside
s
cale.
F ig . 4
Th is m ethod is especial ly good il you h;lVe" series or yuam ities
to conven. Only one ~euing i:. necessary ror a series IJecausc every
yuantity on the out~ i dc ~cale rcprc~f'n~~ nautical miles ( vr knots)
and the correspo n di ng values in Wit • h; 1niles (or ~ I PH) <tre fou nd
oppo!> i te on the im id e scale. 80 n;nttir;tl nlilcs = 9~ stallttC 1 11 iles,
38
stat u te miles = 33 n ;l tt tira l mi l e~ . etc. It would also have been
po ss ible to 111atch t he ST ,\ TU T E arrow on the out~ i clc :.c: tl e with
the NAU TI CAL arrow on the in~ i dc s('a lc, reading ~>lat u te mi l es on
the outside scale and naut i cd mi l e~ on the i mide scale.
Usc the same method !'or all ot h er qu<tntity (ot lversion:,. Sintply
match the arrows l or tlw desired tj uantities .
vV h en convening on ly one quantity i nstead ol a ~>Cries of quan ·
titic~. the lo ll owing method may he prercrrcd:
6
Ex ample
Convert 40 nautical miles to statute mi les.
This method may be used for converting among nautical
miles, statute miles, and kilomete r s; and amo ng imperial gallo ns,
U.S. gallons, and l iters. It may not. be used to convert betwee n
feet and meters or pounds and kilograms because all arrows for
the Jailer conversions are on oppos ite scales.
Celsius - Fa hre n he it
A temperat u re conversion scale is l ocated on the ca l culator
side of the C R. R ead temperatu re con versions directly from th is
scale.
Fi g. 6
7

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Pro
bl ems 2
100 nautical miles
statute miles
196 statute miles nautical miles
90 statute mi les Kilometers
250 kilometers nautical miles
53 U.S.
gal lons imperial gallons
80 imperial gallons U.S. gallons
198 imperial gal lo ns
Hters
140 liters
U.S. gallons
117 pounds kilograms
90 kilograms pounds
-20°C
oF
50°F
oc
To help in checking "reasonableness" of yo ur
answer, NOTE:
1 km.
41iters
1 kg.
1 imp. gal.
approx .. 5 naut. mi.
a
ppro x. 1 U.S. gal.
approx. 2
lb s.
approx. 1.2 U.S. gal.
Meters to Feet
Are you perplexed because the constant pr essure charts issu ed by th e
National Weather Serv
ic e ex press altitudes in meters instead of feet? That
is no trouble at all. The CR makes the conversion by lining up the meters
arrow near 44 on the inner scale and the feet arrow near
14 on the outer
scale. T hi s sets up the co rre ct proportion of fe et and meters. Then, all
values on the inner scale represent meters and t ho se on the outer scale
repre
sent corresp on ding values in feet.
8
Ex ampl e
Change 2,500 meters
to fe et.
Fig. 7
To check the "reasonableness" of you r answer, remember that 1 meter
equals approximately 3.3 feet.
Pro bl ems 3
1. 230 feet meters
2.
3,500 meters f
eet
3.
82 feet meters
4.
5,500 meters feel
WEIGHT OF FUEL AND OIL
Want to know how much your fuel and oil weigh? Use the following
label
ed arrows:
FUEL LBS
..... . ........... near 77 on outside scale
OIL LB S ............ . .. .... at 96 on outside scale
9

Example
Find weight of 18 U.S. gal. of gasoline.
To find the weigln of imperial gallons, match the FUEL LBS.
arrow with th e l ~IP . C.\L. alTO\,. on the imide scale and proceed
as above.
To find the weight of oil, use the O IL LBS. arrow at 96 on the
outside scale and match with the proper GAL. arrow on the inside
scale, using the same method as in finding fuel weight.
Find the weight of:
I. 35 U.S. g:~l. gasoline
2. 500 imp. gal. gasoline
Problems 4
3. 50 imp. gal. oil
·L 18 U.S. gal. oil
Minutes to Seconds
At 36 on the imide sc:tlc i~ an arrow marked SEC. T o convert
minut es lO seco nds, pl ace the time index A_ opposite the number
of minutes and read ero nd s opposite SEC arrow.
Example
Find number of second) in 13 V
2
minutes. Pla ce time index
A opposite 1312. Oppo~itc SEC a11ow (ncar 3G on inside scale)
read 8 1.
Answ er: 1312 minute~
810 SC< 011<1\.
10
-;:.
ALTITUDE
Altitude comes in assorted V<ll'ieties. Ever wonder how high
1s ..up'?" No need for confusion if you remember the followinl{
points:
lndlcalt >d Altitude is the altitude reading on the altimeter,
assuming- it is correctly set. It shows the approximate height of
the aircraft above mean sea level ( MSL ).
Calibrated Alt1tude is the indicated altitude corrected for
instrument, position, and installation errors.
True Altllude is computed by eorrectinl{ calibratt>d altitude
for nonstandard atmosphet·ic conditions. It is the actual height of
the aircraft a hove st>a level.
Pressur(! Altitude is the reading on the altimeter when it is
set to 29.92. Pressure altitude is an important factor for determin-
ing aircraft performance.
Density Altitude is pressure al~itude co rrect ed for non sta n-
dard temperature. Aircraft performance is affected by density
altitude.
11

DENSIT Y ALTITUDE
Ne ar the ce nt er of th e computerat th e bottom left is the density
al
tit ude wind ow.
Example
Given:
Pr e ss ur e a ltitud e 3000'
True air tempera tur e . .. 25°C
Find: Density altitude
fig . 9
Problems 5
Find density alt i tud e for the following conditions:
1.
2.
3.
Pre ss ur e Altitude
1500'
0'
8000'
TRUE ALTITUDE
True Air Temperature
35°C
To find the approximate truealtitude, use calibrated altitude (or
indicated
if calibrated is not available) and true air temperature.
Greater accuracy can be obtained if you also know the altitude of
the ground station giving your
altimeter setting.
12
Example
Gi ve n: Press ure aI ti tude ........ .. ......I0,000'
Calibrated altitude ... .. ...... 9,000'
T rue air t emperatur c .. .....- 20°C
Ground s tation altitud e... 5,000'
Find:
True a ltitude
fig. 10
Problems 6
Fitzd true altitude:
Pr essure True Air
Calibrated
Stati on
A ltitud e T
emp.
Al titude 1\ Iti tud e
I.
10,000' 25°C 11,400' 4,200'
2.
5,000' 0° C 6,000' Sea Level
3.
7,000'
JOOC
7,400' 1900'
4. 20,000' - 1
5°C
~1,000' Unknown
13

TRUE AIR SPEED
In Lhe old days pilols listened lo Lhe wind in Lhe wires and were
happy to be
fl ying at any speed. Today we have accurate air speed
indicators.
It 's a mighty fine gadget, but it s reading is affected by
various items such
as temperature, pressure, compressibility, and
accidental misreading by the pilol who may be thinking of somclhing
else. The CR computer is effective in
co rr ecting for all errors except the
last. A
fa sl- flying aircraft. pushes through the atmosphere so rapidly
that the air can't get out of the way fa st enough. Hence the air is
compressed in front of
the aircraft and is heated by compression. As a
result,
an outside air temperature bulb 'feels' a higher air temperature
th
an really exists in the surrounding non -com pr essed air. Also, the ru sh
of air over the outside air temperature bulb creates friction, causing
further h
eating and a still higher ( fal se) reading. The amount of this
higher reading of
the thermometer is called 'te mperature l'i se· and
must be considered when computing accurate true air speed.
An automatic compensation for compressibility, temperature 1·ise
and air friction is built into the CR Computer so that no reference to
gra phs and tables and no separate figuring is nece ssa ry for correct. !.rue
air speed solutions.* For this reason the CR is especially adapted to the
problems of modern aircraft.
• Some <lircraft manufacturers prm ide air spee d co nver sion tables that already
inrlurlt • correCtions for the tcmpcrawre ri se effect of co mpr ess ibility in addition
w co rre ction for positi on and i11s11 t1111CIH error. The usc of such table s or other
air speed data :dread) ' cmTcctcd for tcmperatm c rise will result in a double
correction with erroneous rc~ull s from the C:R computer.
14
While either knots or MPH can be used with the CR Modern
True Air Speed Solution, more accurate true air speed answers
will result from using knots when dealing with speeds over 200.
The following quantities are necessary for true air speed deter·
mi nation: calibrated air speed (indicated air speed corrected for
instrument and position errors), pressure altitude (a l titude read
from altimeter when instrument is set at 29.92), and in dicated
outside air temperature in degrees Celsius. If calibrated air speed
and pressure altitude are not avai l able in a problem, indicated air
speed and al titude may be used instead. Remember , however, the
CR contains no crystal ball and gives answers only as accurate
as the data fed into it.
THE CR CURSOR
Tru e air speed calculations arc affected by a temperature re-
covery coefficient., CT, which varies wi th installalion and design
of the temperature probe on the individual ai rplane. Recovery
coefficie nts vary from .6 to l.O. Once a recovery coeff ic ient is
determined for a particular airplane, the coefficient will not vary
greatly with speed or altitude.
The cursor on the CR is marked with a straight hairline and
a curved line to the right of it (see Fig. 11 ), with recovery coeffi-
cients plotted for CT va l ues of .8 and 1.0.
Th e recovery coefficient of CT = .8 is the straight line. On
the CR-2 and CR-3 there are two lines plo tted for the CT va lue of
1.0. The solid line is for the standard stratosphere temperature
of -55 °C (35,000'), and a dashed line is for the standard sea
level tempe1·ature of +li)°C. When Oying between sea l eve l and
35,000 feet, it is necessary to interpolate between the two lines.
For instance, at an altitude of 17 ,500 feet with a CT of 1.0, note
that 17,500 feet is one-half the way between sea level and 35,000
feet. Hence, one-half of the space between the sea level curve
and stratosphere curve of CT = 1.0 must be used for the correct
CT curve.
15

In all problems in this book, it is assumed that the recovery
coefficient is the more common
1.0, unless otherwise stated.
Ex ampl e
Given:
Calilmtled air specd ........... .- 100 kts.
P res~ u re a1ti wde .................. l5,00 0'
Indic-ated air temperawre ..30°C
Find:
True air !>peed
Fi g. 12
Problems 7
Find (I lit' 11i1 S/JI'I'd:
C:tli bra ted P rc~surc I ndicate d .\ ir
.\ ir Speed
.\ltiwde
~ 1 - cnr pentllrrc
I.
180 l\ JP !l
5 ,()()()'
- 5°C
~ -
~/(i k b.
I li,OO O' - I5°C
:t
~55 l.. t~.
!!0.000' 50(.;
16
MACH NUMBER
In figu re 12, read r. J ach Number, .78, at t he poi nt er on t he
scale di rectly ben eat h the T rue Air Speed scale. This value i ndi -
cates that t he aircralt is flying at .78 times the speed ol sound. Since
1\r ath Number is dependent upon the speed of sound, which varies
o
nl y with t empera t ure, the same 1\ Iach Number represe nt s differ-
erll true air speeds at different tcnrperawres.
True Air Sp eed From Ma ch Numb er and Temperature
Jn aircraft having a ~ l ach indicator it is possible to get true air
speed from l\ lach 'lllllber and ll ' mperature.
E xa mple
Gi
ve n: 1\ Iach um her 1.16
I
ndicated air tcrnperalllre + l0 °C
Find: True air speed
Fig. 13
If outside air temperature is not av:tilable it i~ po~sible to find
t rue ai r speed by u sing reporte d or- estimated a ir · Lc nr pent ttr rc (in
wh i dr case the rc~ult is only as acwrate a-. the e~timate).
17

Us e of Double-ended Mach Index Ar r ow
To find double-ended ~ l ach Jndex arrow, set the 10 index
(outer edge of top disc) near the 60 on the base disr. (This setting is
made simply as a means of finding the double-ended arrow quickly.)
In the small window below and left of computer ccmcr you will sec
a two·directional arrow labeled :Mach Index.
The double-ended i\ fach Index arrow relates a "~tandard at-
mosphere" altitude with the standard temperature for that altitude.
The temperaLUre of the "standard atmosphere" may be of assistance
in estimating outside air temperatu re.
Ex ample
Given : Pressure altitude 28,000'
Find: EstinHtted free air temperature
f ig. 14
NO TE: The -10°C obtained in the above example is estimated
true air temperature. The methods of finding true air speed out·
lined in Figs. 12 and 13 make use of i11dicated air temperature. See
the following section for the he~t method of finding true air speed
when true air temperature is available.
18
True Air Speed From True Air Temperat u re
If your airplane is equipped with a Mach indicator, and you
know the true air temperature, simply read the indicated Mach
Number, and proceed as shown below in Fi g. 15.
H owever, if your airplane is equipped with a conventiona l
air speed indicator instead, it then becomes necessary to fir st
determine the M ach Number. This is done as follows:
Given:
Find:
Example
Calibrated Air Speed ....... 280 kts .
Pressure Altitude ........... 14,500'
True Air Temperature ....... -l5 °C
Mach Number
True Air Speed
First place calibrated air speed opposite pressure allitude (as
was done in Pig. 12, Page 16) and find the Mach Number, .55 in
the M ach Number window.
Now you have the necessary data (true air temp. -l5 °C and
Mach .55) to proceed as shown in Fig. 15 below.
fig. 15
19

TEMPERATURE RISE
In flight, particularly at high airspeeds, an outside air te mperature
thermometer will read higher than the actual free air temperature because
of friction and compre ss ion of air at the tempe ra ture prob e. The CR
Computer is designed to correct for temperature rise using the two most
popuJar recovery coefficients.
Today' s jets are equipped with temperature probes which have
recovery coefficients
of 1.0, while many older ones have a coerficient of
.8. The scaJe near the center of the computer entitled "TEMPERATURE
RISE C0
(Or 1.0)" has been designed to reflect the temperature rise
indicated by a
Or 1.0 temperature probe.
If the temperature ri se is desired for a temperature probe with a CT of
.8, the Or .8 cursor line is used and the vaJue found on the "TEMPERA-
TURE RISE C0 (Or 1.0)" scale is muJtiplied by .8.
Gi
ven:
Find:
20
E xamp le
Calibrated air speed ............ 276 kts.
Pressure
altitude. . . . . . . . . . . . . . 10 , 000'
Indicated air temperature . . . . . . . 0°C
Recovery coefficient ...... . .... 1.0
True air tempe
ra ture
fig. 16
Proble ms 8
Find temperature
rise and true air temperature: (CT 1.0)
Calibrated Pressure Indi
cated Air
Air Speed
AJtitude
Temperature
1.
190 kts.
5,000' 0°C
2.
350 kts.
17,000 ' -
10°C
" OLD " METHOD - TRUE AIR SPEED
An older method for finding true air speed consists of matching
pressure altitude and tr ue air temperature in the small true air speed
window near the lower left center of the compute r and reading true air
speed on the outside scale opp osite calibrated air speed on the inside
scale. This
method does not correct for temperature rise and com-
pressibility and is not suited to problems inuoluing high-speed aircraft.
21

Ex ampl e
Gi ve n:
Calibrated Air Speed ...... 166 kts.
Pressure Altitude ........ . ... 5000'
True Air Temperature ........ 10°C
Find: True Air Speed
Fig. 17
When taking FAA written examinations, the "o ld" method
for true air speed questions is recommended. These exams seldom
require computations involving temperature rise .
Probl ems 9
Find true air speed using the method outlined aboue:
l.
2.
22
Pr essure
Altitude
7,000'
lO,OOO'
True Air
Temp erature
0°C
-20 °C
Cal ibrated
Air Speed
210 kts .
188 MPH
PRESSURE PATTERN
"Sometimes the longest way 'round is the s hortest way home."
See the Jeppesen CR Computer Manual j\tVorkbook or a good
m1vigation text lor funher explanat ion of pressure paltern naviga -
tion. How ever, if you already know something about it, her e's how
to find cross- wind componenL with the CR Computer.
D = radio al timeter reading minu s pre ss ure al timeter reading
D1 and D ~ de1>ignate first and second readings respectively, taken
with an int ervening time interval.
In th e Northern Hemi sphere if D :.!- D1 is positive, wind is
from the right. If D~ - D1 is negative, wind is from the left. In the
Southern Hemi<,phere this rule is reversed.
Ex
ampl e
Given: D1 480'
D2 300'
Di ~tan ce traveled between readings .. ....l50 naut. mi.
.\!id- latitude ................................................41 ° N
Find: Cross wind component
23

Fig. 18
Probl ems 10
Find crosswind component :
D1
D2 Dist. Flown
Between Readings
1.
20
1
100
1
130 naut. mi.
2.
210 ' 380 '
152 naut. mi.
3.
605
1
520'
125 naut. mi.
24
(
Average
Latitude
35°N
44°N
54°S
SLIDE RULE USE
"The 41 14" diameter CR-2 log scales are approximately equivalent to
those of a 12" 'straight rule'. The
6" diameter CR-3 scales are equivalent
to those of a 17" straight slide rule and the 33 /4" CR-5 scales equal a 10"
rule."
Multiplication and division are performed on the calculator side of
the CR in t he same manner as on a straight slide rule. Be careful not to
confuse the time index J... ,which stands fo r 60, with the unit index in
these problems.
Ex ample : 28 x 15
Fig. 19
25

Example: 182 + 14
Fig. 20
25 X 12
Example: 19
F ig . 21
26
Successive multiplication and division may be done on the CR
by using the hairline of the cursor.
NOTE: l t is necessary to estimate answer by replacing numbers in
problem by numbers th at arc close in value but eas ier to multiply
and divide. For instance, in problem above, the figures are s imil ar
25 X)()
to
20 ,
which equals 12 .5. H ence the answer above must be
I5.8, not 1 58 or 1.58.
1.
2.
3.
The problem might be carried a ~tcp farther:
12 .6 X 31
2fii --:-- 156
32 X 18
25 X 12.8
Example:
25 X 12
19 X 69
Fig. 22
Problems 11
27

TIME AND DISTANCE TO STATION
Time and distance to a station using two VOR or ADF bear·
ings may be computed on the CR by using the preceding multipli-
cation and division process (see Slide Rule Use, Pg. 25) with the
following formul as:
NOTE: These formul as are based on the aircraft flying a
heading which is perpendicular to the first bearing to the
station.
Time to Station
Distance to Station
Elapsed time (min.) X 60
Degrees of change
Elapsed time (min.) x G.S.
Degrees
of change
Example
Given:
First bearing taken at 10:15
Second bea rin g taken at 10:1R
goa
= gga
A constant heading is maintained between bearings
Find: Time to station
Solu tion:
Time to Station = Elapsed time (min.) x 60
Degrees of change 3 X 60
--g
On calculator side, set 3 on outside scale opposite 9 on
inside scale. Opposite
60 (1:00) on in side scale read answer on
outside scale:
Answer: 20 minutes
Given:
Problems
12
1 st bearing 280° at 8:26
2nd bearing 269° at 8:31
G.S. = 120 mph
Find: 1. Time to station
2. Distance
to station
CONVERTING CLIMB PER MILE
TO CLIMB PER MINUTE
Some IFR departure procedures require a minimum climb
rate
to assure proper obstruction clearance. Th is climb require-
ment , stated in feet per mile, can easily be converted to feet per
minute on a CR .
Given: 120 Knot ground speed
300 feet per nautical mile climb required
Find: Feet per minute climb rate required
2. Read climb in feet
per minute over c limb
per nau ti ca l mile.
1. Set speed index un d er
groundspeed in knots
28 29

Part B
WIND SIDE
THE CR NWINDN DISC
1. Th e "2-value» scale system provides you wilh an easy way to make
accw·ate calculations, even when solving problems where the wind
velocity exceeds 100 knots. The basic solutions are the same with
either scale ... the only difference is that you have a choice of the
scale best suited to the velocities involved in a parlicular problem.
Work each problem with "a ll sma ll numb ered scales" or "a U in the
large numb ere d scales."
2. Mi nu s(-) and plus(+ )signs have been added to faci lit ate required
"corrections" for the more fr equenllypes ofapplication.
3. <C R -3 Only) Dual, 0° thru 180 scales for gri d navigation problems,
add ing and subtracting and other uses.
4. (CR -3 Onl y) Clockwise 0° thru 360° scale for ADf relative
bearing so luti ons and other u sc~.
(3 and 4 above arc more tull y ex plain ed in the new , lar ge
.J eppese n CR Compu t er M anual j W or kb oo k, the HW-2.)
CR-S COMPUTER
The CR-5 is very ~ imilar to the CR -2 Computer except a few
l
ess frc <ju e mly used Junc ti ons were e liminat ed in order tO main·
tain rea dabilit y with th e reduced site, 3% " dia. The mode rn tru e
< llr sp ee d so luti on was sli gh tl y altere d a nd th e wind scale also
l>Omew hat redu<ed 10 pe rmit this \'Ciy ~mall compu t e• to functi on.
Y our .J eppese n CR Compute r is the finest instrument of its kind
available at any pri ce ... we sincerely hope that it will become
yo ur favorite ''cockpit compa ni o n."
30 31

ADDITION-SUBTRACTION
"Even if you're a genius at mental arithmetic you'll find it
relaxin' to let the CR Computer take the work out of addition,
subtranion, multiplication and division."
"Additio n and ~ubtraction of numbers up to 360 can be ac co m-
plished on the lvind side of the CR-3 Computer, using the outside
green scale of the top disc and the black scale curv in g either side of
the TC index on the middle disc. On the CR -3 Computer th e I auer
scale can be read as high as 1 80° to the left and 360° to the right.
The smaller, CR Computers carr y the scale only as high as 30
on each s id e of the TC index .
Exampl e
fig. 23
OTE: T o s ubtract 29 from 8·1, lo cate 29 on sotle to the left o(
TC index, and above 29 read 55.
32
WIND SOLUTION ON THE C R
"Th e 'wind' side of th e CR IS a diiT crem looki ng gismo, but
thi s is nothin g to be shook-up about. Once we've brcctcd through
an illu stra ti on. I'm su re yo u'll agree th<lt it's as s impl e a solution
as you've ever used.
"First ol al l let's settle this bu~iness ol 'Mu~nelir V!>. True'.
Winds arc always given (exce pt by airport tower~) in Tm1• and
you ca n't mix magnetic and tru e any more than you e<t n oil and
oxygen. The CR Compmer ~ets you over this hump beautifully,
by providing a Magnclit-True rtHI1'('l'SiiHI Sl'afe on either side ol
the True Course Ind ex $ (sec Fig. ~ - 1) . .Just set the magnetic
course on the green scale opposite the applicable variation and
yo ur true <:o ur sc is automatically lined up oppo~ite th e tnte course
index. "

Example
Given: ~la g n e tic course............... .. ..284°
Vari a tion .................. .. ........... 11oE
Find: Tru e Course
Fig. 2-4
"Rem e mb er th e good old wind triangle?
True
Course -
Ground
Speed -
-True
Heading
True
- AirSpeed
Fig. 25
"It 's a time-honored ins tituti on but it tak es both tim e and
s pa ce. You ca n't put ,a wind triangle in yo ur poc ket , but the CR
solves the tri angle tri go nome tri cally a nd yo u co n put thl' C:R in
yo ur pockel.
"In the wi nd trian gle a bo ve, il' y ou draw a line !'r om the e nd
of the TH - TAS line pe rp endicular to th e TC -GS line, yo u will
have a small triangle at the top of the o
ri g inal triangl e.
3·1
Tailwind
Component
TC-GS
Crosswind Component
Fig. 26
" Thi s •s th e triangle that fits on th e CR Co mput er."
Fig. 27
"T his di agram a:.s um es that you can a dd the tailw ind com-
pone nt to the tru e air speed to ge t gro und s pe ed, and f or small
crab an gl es this is very clo se to tru e, any inaccuracy being t oo ~ m a ll
35

w uotht·l ahoul. I l owe' ct. lor crab angle~ ol I 11 ° or more the CR
Computer handles the m.ttter "·ith a ~implc additional :. t cp that
gives additiona l arcura< y. Th e ~tep wil l he explained btCI in a
'litmplt' pt ohlcm."
" l mtcad ol drawing atro\1·~ on )' our CO IIIJllltCr, all that i, mT ·
t'''>ary i' to place a clot at the 'pot that indic all'':> the end ol the wind
allOW. ;\J.,ke the dot small !01 antllaC\': then dr<~w "tin le ;IIOIItHI
it so yo tt can lind it again when ym t look lor it."
NO TE : Two wind scales 011 the horii'Oillal a nd Y el'l i ca l lin e~
r;nliating from the centt•r ol the computer maJ...c the CR e~pe
ciall) flexible for diflcrent t)pe~ of aircraft. l 'l>e the l;ugc
. ~calc (fr 01n 0 wHO) if tht: wind i~ less than 80 knot~ or i\1 PI I.
l ' ~e tht· s1na ll ~r:tlc (fmnt 0 to lliO) if the wind is more than
80. 011<e )Oil h,I\C < hmcn the dc'>ired 'lcalc, me it throu~hmn
the p1ohlent, taking CII T not w mix the two sca le ') within the
'a Ill(' problcnt.
FLIGHT PLANNING WITH
FORECAST WINDS
" l.t · t'l> t:t< J..lc I hi ., wind thi11 g fir,l llotn :1 'Fiighl !'Ianning '
'>LIIldpoint.
011r pwpmed flight will hc made in two kg' '>0 th.tt
1\'l' <:til dcnlon,tratc <tTtaill :H IY :tlltagt·, ol )OUr CR Computer.
Either J..noh or :\ I PI I n111 he mcd in a "·ind problem. providcd
lh<' c Jw,cn unit ol mt·a,llrc i, ti'>Cd c oihi,tentl} throughout the
p1 ohkm."
L eg No .
Giv en: ' I nit' \ir Sptcd ............... IHO :-.1 PH
;\lagrlttic (:o ll rse .................. IIO"
\ ' ;niation ...................... IW\V
Wind ................................ ... 10 ;\I I'll lto111 f(l(J v -1 111<:
Find : Cra b angle. lll:tgnctir heading and ground '>J>('Cd.
Solution : (St·t· Fig . ~H)
1. Set the llll(' air ~pt·<:d in ckx ! o1 1 IK ( l KO ;\I PH ) .
. , ,~