Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~83338
Photo Electronic Astro Com~ass
,_
This invention relates t~ a device for reading the angle of a radiant
body, and more particularly to a navigational aid.
In Transport Canada's Flight Information Manual 1976 Civil Aeronautics
Page 2-13 is stated, "In response to a need for the provision of directional
information simply and to within one degree (1) the Legislation and ~tan-
dards Branch of Civil Aeronautics has arranged for the development of tables
from which the Sun's True Bearing can be quickly extracted knowing only the
date, Local Civil Time and approximate latitude and longitude". The publi-
cation is entitled "Finding the Sun's True Bearing precomputed tables", and
states the following:-
From aviation's earliest days, pilots of aircraft havs been con-
cious of the need for accurate directional information. The developmen-t of
the magnetic and gyro compass has, for general purposes, kept pace with
aviation needs in most areas of the world. ~light operations in Northern
Canada, ho~ever, present problems which are unique by virtue o~ the posi-
tion of the North Magnetic Pole.
Navigation by referencs to the magnetic meridian in this general
area poses practical problems in taking account of the large changes in
magnetic variation and the errors which occur in aircraft magnetic compass
systems due to the reduction in the horizontal directional properties of the
earth's magnetic field as one nears the North Magnetic Pole".
Radio Navigational Aids are very limited and landmarks few and far ;~
between in these northern areas further increasing navigational problems.
Close to the Magnetic Pole, the earth's Magnetic Lines of Force dip
vertically to~ards the Pole. The compass needle lies in a horizontal plane,
and as the strength of the horizontal component of the sarth's magnetic
field tends to disappear in the close vicinity of the Pole, the magnetic
compass loses its ability to point the ~ay, and becomes anything but a de-
pendable companion. In a large area of Northern Canada the magnetic compass
is therefore unreliable. Within this area, called the Northern Domestic
Airspace, ~IOT regulations require that airplanes weighing 12,000 lbs. or
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~83338
over must be fitted with an Astro Compass or some other means of determining
direction that is not dependent on a magnetic source. The Astro Compass is not
influenced by the earth's Magnetic Field, but indicates direction with refer-
ence to the Sun, Moon~ Planets or Stars. These heavenly bodies ha~e been man's
guiding beacons in the skies since time immemorial. The examinations for
Commercial, Senior Commercial and Transport Pilot licenses in Canada require a
knowledge of the Astro Compass.
The ASTRO COl~ASS is an instrument designed to enable a pilot or naviga-
tor to determine the True Heading of his airplane. tIt can also be used to
take a bearing on an abject.)
In the simplest possible terms, the As~ro Compass is a Bearing Plate with
a movable Sighting Device mounted above it. The bearing of a heavenly body
can be set on the bearing plate, and when the movable sights are properly
aligned on the heavenly body, the North Mark on the bearing plate will coin-
cide with True North. The bearing plate can now be read off against a Lubber
Line ~aligned in the fore and aft axis of the airplane) to indicate the TRUE
B ADING. The Directional Gyro can now be set to the True Heading and the air-
plane steered with reference to the Directional Gyro in lieu of the magnetic
compass.
How do you find the true bearing (or aæimuth) of the heavenly body to set
on the bearing plate? The Astro Compass automatically does this for you pro-
vided you supply it with the following information:-
1. Your Latitude.
2. The Local Hour Angle of the body.
3. The Declination of -the body.
Your position, in latitude and longitude, is that assumed by yourself,
based on your own D.R. navigation.
The position of the Sun, Stars and other as-tronomical bodies can be ac-
curately predicted for any given moment of time. They are recorded in a
handy volume called the AIR A~MANAC. By opening the Air Almanac to the
Greenwich date, hour and minute of time on which you wish to check your
True Heading, you can look up the Greenwich Hour Angle and the Declination
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108333~
of the Sun, Moon, Aries, or the particular Planet you wish to sight on.
The Sidereal Hour Angle and Declination of any navigation Star can similarly
be found. (From The Ground Up, Sandy A. F. MacDonald's)
The Astro Compasses are, however, too large and clumsy for general
aviation use, and impractical since they must be operated manually by a
pilot in flight.
It is, therefore, the object of the present invention to provide a new
instrument for measuring the direction of a radiant body, and more partic-
ularly to a new navigational aid which is relatively small and gives directly
the direction or position of an aircraft without manual operation by the
pilot. The instrument in accordance with the present invention comprises an
apparatus having a plurality of wells oriented at different angles in both a
horizontal and a vertical plane toward the sky, a light sensitive device at
the base of each well and adapted to be illuminated by the radiant body
depending on the position of the radiant body, and means for electrically
connecting the output of the light sensitive devices to a microprocessor for
detecting the angle of the radiant body.
In an alternative embodiment of the invention, the instrument comprises
a light tight container having a plurality of light sensitive devices
located on the bottom and a small hole in the ceiling to allow a shaft of
light originating from the radiant body to fall on some of the light sensitive -
devices depending on the angular position of the radiant body and means for
electrically connecting the output of the light sensitive devices to a
microprocessor for detecting the angle of the radiant body.
The invention will now be disclosed, by way of examples, with reference
to the accompanying drawings in which:
Figure 1 is a cross section of Tube and Photo Cells Design.
Figure 2 is a cross section of ~alf Sphere and Fiber Optic Design.
Figure 3 is a cross section of Saucer Design.
Figure 4 is a cross section showing the light effect on a tube and
photo cell design.
Referring to figure 1, a dome of many light tight tubes 10 are mounted
together in such a manner that they all point in different directions through-
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~083338
out 360 of the hori~ontal plane and throughout about 180 in a vertical plane.All tubes have a co~non focal point below or under the instrument. At the
central or core end of the tubes are inserted photo cells 12 in a ligm tight
manner. Flat black paint on the interior sides of the tubes may help in
cutting down bounce light reaching the photo cells from the open end of tubes.
Large numbers of photo cells and tubes would increase the number of angles
the instrument is capable of measuring~ making it more accurate. Len~th and
inside diameter would also effect angle measurement. Photo cell wires 14
would lead to a microprocessor (not shown) informing the system of the sun's
angle indicated by the strongest signal received. Such microprocessors are
well known and need not be disclosed in detail.
Figure 2 shows a design which may be much superior in being much more
compact and more precise and ~ith half the number of leads to deal with, not
to mention no power source required for this section. As ~hown in figure 2
the cross section shows a sphere 20 with the central core remo~ed. As an
example the sphere could be solid aluminium. Fine fiber optical size (hair
si~e) holes 22 are drilled at many angles throughout the sphere all leading
to a common central point. In the core or interior ends of holes 22 photo
optic leads 24 are plugged tor glued) in the bottom of each hole in a llgm
tight manner. The photo optic leads lead off to a microprocessor ~not shown).
At the microprocessor the strongest signal would determine the sun's angle,
and combined with the microprocessor's internal clock, date, time and sun's
angle pass through a flow chart, producing a read ouk in a cockpit indicating
the aircrafts heading. Such microprocessors are also well known.
Figure 3 shows a design which is quite different from the preceding and
may be superior in simplicity of construction. Photo cells 30 are closel~
mounted in a saucer shape body 32 with a lid 34 across the top enclosing the
area making it light tight except for a pin hole 36 in the central lid allow-
ing a beam of light to penetrate the area hitting a photo cell in a straight
line between the light source and the hole, and itself. Agaln wires 3~ tor
optical fibers) would lead to a microprocessor. IDue to cons~ruct,ion design
some angles are be~ond it's range and would not be detectable. This problem
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~83338
could be easily overcome by the use of more than one instrument for the
particular application, each pointing differently. (On a helicopter, more
than one instrument would be preferable to overcome the obstruction of the
light path between the instrument and main rotor mast.)
Figure 4 shows the light effect on a cross section of an instrument
designed with tubes and photo cells. The light source casts shadows over all
photo cells except those of which the wells are directed in line with the
light source. The well directly oriented to the light source allows the
light to penetrate to its bottom, where the accompanying photo cell becomes
illuminated allowing a current to flow through it.
It can be clearly seen that many designs could be developed in different
combinations of photo cells and fiber optics, tubes and half spheres, and/or
similar to the saucer design in order to read the angle of a radiant body.
In service, light would stimulate a particular photo cell or optical
fiber of the instrument. This would allow a current to flow or light to be
carried from that particular well, indicating the angle of the radiant body
relative to the instrument in the computer system. Through a flow chart of ,
sorts combined with other information such as that of an internal clock, the
microprocessor would give a readout to a pilot in his aircraft in degrees true
indicating the headlng of the aircraft.
The apparatus was originally invented with the idea of application to
rotor wing aircraft (helicopters) measuring the sun's angle. But its
application is clearly not limited to these, but could be applied to fix wing
airplanes, ships, ground vehicles and space craft, to measure angles of any
radiant body for navigational or other purposes. It may be applied possibly
for surveying, and also be specialized to be sensitive to particular light by
the introduction of filters, lenses or devices sensitive to the particular
light spectrum desired. (Infrared to ultraviolet). In designing the
instrument sensitive to ultraviolet or polarized light, the apparatus may be
functional even in overcast weather, because these forms of light vibrations
are capable of penetrating clouds, though overcast weather is, perhaps, less
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~08~33~3 i
common in the extreme north where the cold does not allow the air to hold
moisture.
For aviation purposes, if need be, an electrical system of sorts could
allow a readout only during straight and level flight.
a) DIRECTIONAL: In this application, the instrument would be set up
with its computer system to give directional information only.
B) LOCATIVE: In this application, the computer system would be
more complex in its flow charts and informational inputs. This system would
give it the ability to produce a readout in an aircraft's cockpit indicating
the aircraft's location on the earth's surface in degrees, minutes and
seconds of longitude and latitude.
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