Forty-Five Pounds of Automatic Navigation
FORTY-FIVE POUNDS
OF
AUTOMATIC NAVIGATION
BY Grorce Lirsxe, Project Supervisor,
Forp InsTRUMENT CoMPANY
. a description of the Computer Set, Latitude and Longitude,
AN/ASN-6, a new dead-reckoning computer for aircraft.
Db 8 designed and manufactured by Forp INSTRUMENT ComPaANy,
Division of Sperry Rand Corporation.
REPRINTED FROM
SPERRYSCOPE, Quarterly Publication of SPERRY RAND GORPORATION
Lacking all ground-to-air communication,
pilot of plane can rely on AN/ASN-6 Ground
Position Indicator to give him position.
HE need for increased automatic-
ity in aircraft has been made criti-
cal by high-speed jet planes. The pilot
navigator, occupied with flying his
plane at 500 miles an hour or better,
has no opportunity to plot his position
with plotting board and computers, In
time of war, not only must he give his
attention to the panel full of dials, but
he must also elude pursuing enemy
planes, and be on the alert against
ground antiaircraft fire. Moreover,
radio blackout will have silenced all
signals from his home base. It was
therefore inevitable that he would
have to be provided with an automatic
dead-reckoning instrament dependent
on no ground-to-air communication
whatever. The Ford Instrument Com-
pany developed and is now manufac-
turing for the USAF such an instro-
ment. It is called the AN/ASN-6
Ground Position Indicator.
The AN/ASN-6 weighs approxi-
mately 45 pounds, and although it
contains almost 2,000 different items,
its total volume is just over one cubic
foot. Only the dials of the instrument
take up space on the instrument panel,
its operational gear may be located
in a remote part of the plane where
Space is available.
Hermetic sealing provides con-
trolled atmosphere for most working
parts. Corrosion is reduced, and the
instrument is capable of operating
over a temperature range of from
—54°C to 71°C in widely varying
Forty-five Pounds of
Automatic N avigation
By Grorcr Lirsxz, Project Supervisor,
Forp InstRUMENT ComMPANY
environments such as high humidity,
dust - laden atmospheres, and high
altitudes.
WHAT IT DOES
To furnish the information needed,
the Ground Position Indicator must
add to the pilot’s initial longitude and
latitude the changes in these position
factors that result from the plane’s
movement through space. To accom-
plish this, it must mathematically con-
sider speed and true heading and
the speed and direction of the wind.
Using this information, it calculates
the plane’s present position and dis-
plays the changing longitude and lati-
tude continuously on counters mount-
ed in windows of the instrument.
Provided the pilot has been given
correct set-in-data, the plane’s position
will be displayed accurately to within
1.5 per cent of the distance traveled.
TAKE-OFF
The pilot climbs aboard his plane,
turns to his Ground Position Indicator,
sets in his present position, his mag-
netic variation for the location he is
starting from, and the wind speed and
direction as indicated by his meteoro-
AN/ASN-6 consists of four units.
The AN/ASN-6 Ground Position
Indicator System was designed
and developed by Ford Instrument
Company under the auspices of
the United States Air Force, in con-
junction with the Communications
and Navigation Laboratory, Wright
Air Development Center, Dayton, O.
logical charts. Once he is in the air,
he releases a departure switch, and the
computer begins computing continu-
ously his position. He need not mon-
itor his GPI, It is another “man”
aboard, one who is charged with the
sole responsibility of continuously re-
cording the position of the plane. If
an enemy attacks and the pilot must
interrupt his original flight program to
fly an evasive course, all he need do
when he has escaped is consult his
“helper’’ to learn his present position
and from that proceed to get back on
his original course.
The Ford Instrument Company’s
AN/ASN-6 Ground Position Indi-
cator is not an end in itself. Although
the AN/ASN-6 is in full production
for the Air Force, Ford engineers are
developing new potentials for the basic
The Indicator unit below fits in the standard mounting-
hole for a three-inch indicator in an aircraft instrument panel and is eight inches deep.
LATITUDE AND LONGITUDE
COMPUTER
S. |, FRANGOULIS
Project Supervisor
Ford Instrument Company
Long Island City, New York
PERATION of most aerial navigation systems
depends principally on some contact with the
‘ground, or in rare cases with some celestial body.
For all the improvements in modern radio and radar
navigation systems, it is frequently desirable and
sometimes imperative to enable the pilot to navigate
over considerable distances without depending on
ground contact, and to permit him to make all navi-
gational computations from information developed
solely within the aircraft.
The system developed for this purpose performs
simultaneously the function of dead reckoning the
SET ASN-6
airplane ground position and of computing the course
and distance of the airplane to its destination. The
dead-reckoning part of the system represents in itself
an independent useful navigational instrument, the
ground position indicator. Originally developed for
the US Air Force, the ASN-6 Latitude and Longitude
Computer Set, computes automatically and continu-
ously the map coordinates of the present position of
the airplane. Another variant, which is known as the
lightweight version of the ground position indicator,
computes east-west and north-south coordinates of the
aircraft relative to a selected base or origin.
Addition of several simple auxiliary devices permits
use of outputs of the ground position indicator to
obtain the course and distance to a destination of
known coordinates. Specifically, use of the additional
equipment (known as the ASN-7 Computer Group)
provides rhumb line course and rhumb line distance
. RESOLVER CORECTOR
Hi Vi cOSH #5 Lap)
‘| INIT. LONG.
[Fo -T can HoTOR
wD Lh — awd FLO
7) DIFFERENTIAL CONTROL
INIT. LAT.
RESOLVER |
Figure 1—Flow diagram, Ground Position Indicator.
in nautical miles, and provides the pilot with a com-
plete navigational system, telling him where he is,
how far he has to go, and what course to fly to get
there.
@ @ Inputs and Outputs
The input data are obtained from instruments solely
on board the aircraft, with the following automatic
inputs necessary for the proper operation of the
computer set:
1} magnetic heading from a slaved gyro magnetic
compass. ©
true air speed from a true air speed computer
and transmitter,
3) compass transmission error correction.
The computer set also requires the following three
inputs which are inserted manually into the system:
1) wind force.
2} wind direction.
3) magnetic variation,
2)
The outputs, naturally, are thé coordinates of the
present position of the aircraft and the distance (in
nautical miles} and course to go. While normally
displayed by means of counters and pointers, some
outputs can also be relayed by synchro transmission
te dependent equipment on beard the airplane, such
as for operation of dead-reckoning tracers, for remote
indication, or for tie-in with the autopilot.
Block diagrams of the equipment, showing inputs,
outputs and principal computing elements, are given
in Figures 1 and 2.
Two basic navigational computations are performed
by the equipment: computation of the map coordinates
of the airplane position, and computation of the
course and distance to go. These are calculated in
two steps—first finding the aircraft ground position,
then calculating the course and distance to go.
To find the aircraft ground position, the instrument
has to add to the coordinates of the take-off point the
coordinates covered by the plane from the take-off to
the present position. The ground distance an airplane
covers is ground speed integrated over flying time.
The airplane ground speed is obtained by measuring
MAGNETIC VARIATION Wy * TRUE NORTH
MAGNETIC NORTH
/
DIRECTION OF
WORTH INDICATED
OW AIRCRAFT
COMPASS
Figure 3—Geometry of aerial navigation.
Loapine|-L POT} {sin ge}
St RESOLVER
{Pe oT} ¢{ cos Har Fe
@
COURSE
LATITUDE SERVO
BARREL
CAM PoTL_.
in fo POINTER
Lop DISTANCE ITIL)
SERVO
_] POL} COUNTER
ra
Lag LAD-La 4 {Por }+H—»
Figure 2—Flow diagram, Course and Distance Computer.
the speed of the airplane relative to the surrounding
air (measuring the true air speed) and by adding to
this air speed the speed of the air mass relative to
the ground (wind speed), which the pilot ascertains
before take-off. (He can also receive this information
by radio while in flight, but this is not essential.)
if Cos Hy t¥y cos Hy
Figure 4—Resolution of ground velocity & wind vectors.
ta”
$ PRESENT POSITION
LATITUDE LONGITUDE
E
>
DESTINATION
o—
LATITUDE
STORAGE
INSERT RQ STORE
GONTRDE SWITCH
Figure 5—Contrel Unit, Course and Distance Computer.
Thus, the ground position of an aircraft at any
time during flight depends on its true air speed (V;),
irue heading (H;), wind speed (Vv), and wind head-
ing (Hw). Figure 3 shows the geometry and the rela-
tionship of the various quantities used in the ground
position indicator. True airspeed, wind force and
wind heading are direct inputs to the system, while
true heading is derived from the remaining inputs,
namely magnetic heading (H,), compass transmission
error (T,), and magnetic variation (V,). Therefore,
Ay =A, +T. + ¥,,
WIND DIREOTION VARIATION
T 8
pis 4s
‘ip WIND'FORCE
sat = A
Figure 6—Control Unit, Ground Position Indicator.
where T, and V, are positive when measured clock-
wise from their reference axes.
The N-S ground speed of an aircraft is the alge-
braic sum of the latitudinal components of true air
speed and wind speed, V+ cos H; + Vy cos Hy.
A vector diagram relating the various velocity and
heading components is given in Figure 4.
The length of arc traversed in the N-S direction
is equal to
i
f (V, cos H; + Vw cos Hw)dt,
o
with a similar expression holding for the are traversed
in the E-W direction.
Conversion from distances to geographic longitude
and latitude is a simple matter. If the airplane speed
is given in knots, the distances are in nautical miles
and one nautical mile equals one minute along the
meridian. Nautical miles can be converted directly
into degrees latitude; additional multiplication by
the secant of latitude, to correct. for meridian con-
vergence, is automatically performed by the equip-
ment to change the east-west nautical miles into de-
grees of longitude.
Thus, by automatically adding the number of de-
grees latitude and longitude covered by the airplane
from the time of take-off to the degrees latitude and
longitude corresponding to the take-off point, the
computer determines continuously the latitude and
longitude of the airplane’s present ground position,
AERO DIGEST
The next step is to compute the remaining distance
to go and the course the airplane must follow to
reach its destination. With the latitude and longitude
of the destination point known and set into the instru-
ment, the instrument automatically subtracts the co-
ordinates of the destination from the present ground-
position coordinates and calculates the remaining ‘air
distance and the course.
if LOP, LOD, Lap, and Lad are respectively the
longitudes and latitudes of the present position and
destination, the course and distance. computer section
LATITUDE
(| \9 519.N)
GROUND
CG) Position (Cy
“INDICATOR Ya
LONGITUDE
Figure 7—Ground Posi-
tion Indicator. counters,
solves the following equation for the course to desti-
nation (Hgrj: .
tan Hgr = (LOD — LOP)/{in(sec Lad + tan Lad)
-— In(sec Lap + tan Lap)];
and for the distance to destination,
D = (LOD — LOP) cos La sin Hgr
+ (Lad — Lap) cos Her,
where cos Le is a complicated function of latitude:
cos La = (Lad — Lap}/[In (sec Lad + tan Lad) -
— In (sec Lap + tan Lap)],
which is instrumented with a three-dimensional cam.
@ @ Presentation
Performance of the equipment is automatic. Before
take-off, the pilot sets the present longitude and lati-
tude counters to the coordinate of the air base. He
next sets the coordinates of the destination. This:
causes a dial indicator on the panel board to show
automatically either the present position alone or the
present position plus the course and distance to desti-
nation, Figures 5, 6, 7 and 8.
After take-off, when the plane has reached its alti-
tude, the present position and the course and distance
to go are continuously displayed on the indicator.
But the pilot can make some refinements and adjust-
ments at any time. These adjustments. are sometimes
necessitated by changes in wind speed and some-
times are made merely to check on the present-posi-
tion indication should the plane be passing over a
landmark with known coordinates.
The ground position indicator alone weighs approx-
imately 45 pounds; adding the course and distance
computer increases the weight to 65 pounds.. The
respective volumes are 1.3 and 1.8 cubie feet, The
equipment operates at aircraft speeds from 70 to 800
knots, Meridian convergence considerations and vaga-
ries of the earth’s magnetic field limit its latitude to
+ 70°,
The weight and space limitations inherent in all
Fieure 8—Pointer and Counter,
Course and Distance Computer.
airborne equipment were successfully coped with in
the design of this equipment by using precision cams
to generate the non-linear and non-sinusoidal func-
tions used in the computer. Such 2 non-linear func-
tion is the residual deviation and the compass-trans-
mission-error correction. A special cam is also used
to compensate for the loading error of. some of the
potentiometers used. A rhumb-line computation is
used for the course and the distance; a precise three-
dimensional cam gives the intricate functions of lati-
tude necessary for the computations. Electric poten-
tiometers and resolvers are used for the linear and
sinusoidal functions. Electronic amplifiers are used
to control the servo motors in the system, for resolver
isolation, and to produce an accurate time standard.
While the principal functions of the system are
as described above, many other features are incorpo-
rated for greater versatility: For example, an alter-
nate destination or a second destination can be set
into the equipment when necessary. Deviations from
the flight path, such as detours around storms, are
permissible without affecting the instrument’s opera-
tion,
Flight longer than 1000 miles can be accommodated
through an information-storage device built into the
computer, which enables the pilot to breakdown his
set-in flight plan into segments shorter than 1000
miles. While the equipment is designed to operate
between 70°N and 70°S latitude, corrections can be
made to maintain accuracy of the calculations should
the airplane fly beyond the latitude limits. END
The AN/ASN-7
- . . AN AIRBORNE NAVIGATIONAL SYSTEM
WHICH DISPLAYS COURSE AND DISTANCE
An outgrowth of Ford Instrument’s ASN-6, the ASN-7,. is an automatic
Navigational system which continuously displays the rhumb-line course a pilot
should follow and the rhumb-line distance he has to go to get to his destination -
regardless of how his flight path changes. In addition, it displays the present
position (latitude and longitude) of the plane at all times,
_ . This computing system is designed-for distances up to 1000 mites with-
out resetting and for operation between 70° north and south latitude. It can easily
handle flights over 1,000 miles by simple resetting, Course and distance are dis-
played on the small indicator illustrated on the other side ofthis page - which
shows direction and nautical miles,
The ASN-7 employs some of the units-from the ASN-6, and includes a new
control unit, as well as the course-distance indicator shown. The control unit, also
illustrated, serves both as an indicator, displaying present latitude and longitude,
and as an input into which the pilot sets the latitude and longitude of his destination,
using slew switches. This destination can be set in at any time, and changed at any
time ~ but the system will continue to tell the pilot what direction to fly and how far
he has to go to his new:destination. Provision is made so that an alternate or succeed-
ing destination can be set in prior to take-off in a storage circuit.
‘Otherwise, the inputs to the ASN-7 are the same as in the ASN-6. The
Pilot sets in his magnetic variation, wind speed and wind direction on the control
unit illustrated, In addition, the ASN-7 has an automatic magnetic variation con-
puter permitting automatic compensation if desired,
A top feature of the system is that it permits a pilet to take off from
one point and fly to accomplish’. a mission - using thé ASN-7 to guide him there. Then,
when his mission is accomplished, he can set in the latitude and longitude of his home
field, another field, or his carrier ( or insert.a previously stored destination) and
follow the system's direction on return. .
Total weight of the present version of the ASN-7 is about 65 lbs. and its
volume is about 2 cu. ft. Its accuracy matches that of the ASN-6 (1.5% total distance
traveled for. present position) and is 6 miles on course and distance.
FORD INSTRUMENT COMPANY
Division of Sperry Rand Corporation
31-10 Thomson Avenue
Long Island City 1, N.Y.
PP
Alii oe Fea) niaiieiomen
VARIATION ®
— *
(x) DEGREES
WIND DIRECTION
4 )
(Gee
\)
WIND SPEED
ong wy .
wo E INSERT | » STORAGE (A)rors «q
ad ®@
TMOMAZOO sI-2ZM>
.
ey
Control and indicator units of ASN-7
Course and Distance Computer shown
full size.
se | ae
Many super-fast jet aircraft of the USAF similar to sepublic’e sleek, swept-wing F-84F
Thunderstreak will be equipped with this new aid to fli
Upper photo is of Computer Control] Unit.
Hermetically sealed to provide controlled
atmosphere for working parts, it is mounted
in cockpit console. Below is photo of the
Computer, which is also hermetically sealed
and ig remotely mounted from the Control.
engineering done in connection with
this instrument.
SOME POTENTIALITIES
The AN/ASN-6 tied in with other
devices, such as radio or radar naviga-
tional aids, could become an instru-
ment to give more accurate wind
information to the pilot and navi-
gator. Its adaptation into a course
and distance computer would not be
impossible—the position of the ulti-
mate destination would be set on the
instrument and the indicator would
t control and plane navigation.
tell the pilot if he is on the right
course and what distance he has yet
to fly. Or the same information might
be fed directly to the automatic pilot,
and the entire flight would become
automatic. There are adaptations
that would be valuable aids to aerial
cameras used for mapping; and since
the AN/ASN-6 is a passive system, it
could be used with initial guidance
for a missile or bomber to bring it to
a target area, at which point some
other guidance system could direct it
to its pin-point target.
Amplifier, which is remotely mounted and gasket sealed, houses instrument’s electronic
units. All are in sub-units that can be pulled out and plugged in for easy maintenance.
Ag wOrs Tr
larat i ey
Friend or foe? Tactical defense officers in MINK control center watch movements of aircraft as reported from
radar warning sites. This is equipment developed under the direction of Rome Air Development Center.
ROME AIR DEVELOPMENT CENTER PROVIDES
AIR DEFENSE EQUIPMENT FOR OUR AIR FORCE
One development agency for the Air Force’s ground-
based electronic equipment is Rome Air Develop-
ment Center, located at Griffiss AFB in Rome, N. Y.
One of the ten centers of the Air Research and
Development Command, RADC is concerned with
the air defense of our nation, with providing equip-
ment for tactical supremacy, and with developing
ground complexes for various navigation systems to
aid all aircraft. In addition, RADC is charged with
data handling improvements for the Air Force
intelligence mission.
RADC is the responsible center for development,
DIVISION OF SPERRY RAND CORPORATION
41-10 Thomson Ave., Long Islend City 1, N.Y.
Thisas-one ofa Series obads on the technical
ietimittes (oF the Wepariment of Det
a4
FORD INSTRUMENT COMPANY
Engineers at Ford Instrument Company
working on a special Air Force preject
in one of the company's laboratories.
through its various contractors, of such end products
as radar sites, including improved tubes, circuits,
antennae, and shelters; ground communications
equipment and associated support items; IFF
{Identification Friend or Foe) environments, and
electronic countermeasures.
Bringing complex systems from the written re-
quirements to the actual hardware items to be used
in the various Air Force commands is a long and
tedious business which draws upon the skills of
RADC’s 500 civilian and military engineers and
their many counterparts in private industry.
PRINTED IN 8.4,
smyth ee rtm LSS Tan ween asp OE
Official U.S. Air Force Photograph
+
“ety