Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
DUAL MODE LIGHT SOURCE FOR AIRCRAFT EXTERNAL LIGHTING
Field~of the Invention
This invention relates to navigation light sources provided for aircraft that
are
used to render the aircraft visible, and more particularly to navigation
lights for military
aircraft that may wish to exercise an option of going to a covert mode of
operation in
which the only light generated by the aircraft is infra red ("IR") light that
can only be
seen by friendly militazy wearing appropriate night vision goggles. The
invention also
relates to methods of upgrading the covert capabilities of existing aircraft
that do not yet
have covert IR navigational lights.
Ba~ound of the Invention
The Federal Aviation Administration and the aviation authorities of many
countries require that aircraft have navigational lighting, generally red
Lights on the left
side and green lights on the right side of the plane, to improve their
visibility at night.
Military aircraft, when in civilian airspace on non-covert activities, are
also
required to have such lighting. Normally, the external lighting is provided by
incandescent light bulbs in sockets on the outside of the plane. These are
conventionally
powered by electricity from the internal electronics of the aircraft, which in
most U.S.
fighter aircraft is 400 Hz AC at 115 volts. A single double wire runs to each
light bulb.
The pilot can adjust the intensity of the navigation lights, or turn them off
completely,
with a brightness control dial in the cockpit which varies the voltage of the
AC current
sent to the light socket. In situations where visibility would be a
disadvantage, these
military aircraft would in the past simply turn off the external lighting.
In recent years, it was noted that in covert activities the aircraft was not
visible
to the enemy, but also not visible to friendly aircraft, and planes began to
be supplied
with covert mode IR light sources in addition to the visible navigational
lights. The IR
light emitted is not visible to the unaided human eye, but can be seen with
appropriate
viewing equipment, e.g., night vision goggles.
To upgrade aircraft to covert IR capability, IR light sources of this type
have
ordinarily been additional arrays of IR diodes added to the outside of the
plane in
addition to the existing navigational lights. Alternatively, filters have been
mounted
-1-
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
over the existing navigational lights and IR diodes mounted in the light bulb
fixtures.
These kinds of additions, however, require substantial structural work to
create the
mounts and to wire the new fixtures into the aircraft body, which usually does
not have
very much extra room for more wiring. In addition, the extensive modifications
result in
considerable expense for an upgrade to covert IR capability.
Summary of the Invention
It is accordingly an object of the invention to provide an aircraft lighting
system
that can function both as a visible navigational light system and also as a
covert IR light
system for friendly eyes only. It is also an object of the invention to
provide a design
and method that allows for relatively easy upgrade of existing visible
navigation lights
to give an existing aircraft 1R covert capability without the need for any
substantial
mechanical adaptation of the plane's structure.
These and other objectives are accomplished by providing according to the
invention a dual mode light source unit configured so that it can be secured
into a
conventional incandescent bulb socket on the aircraft. The light source has a
connector
portion that fits in the socket and receives the electrical current supplied
thereto by the
aircraft electrical system. The unit also comprises electric circuitry
connected with the
connector portion and a visible light source and an IR light source.
The electric circuitry is configured to process the input current from the
socket
and, based thereon, operate in either a civilian, visible mode or a covert IR
mode.
Where the current is in one electrical state, such as for example a certain
voltage, the
electric circuit sends power to the visible light source. When the current is
in a different
electrical state, e.g., a different voltage level, the circuitry sends power
only to the IR
source, and no visible light is emitted. The electrical states of the current
may be any
variation of electrical parameters thereof, including amperage, voltage,
frequency, or
data encoded therein, etc.
Such a system allows for ready upgrade of existing aircraft because all
control
may be accomplished over a single pair of wires, as are already in existing
systems that
do not have IR mode capability. To upgrade, light source units according to
the
invention are simply inserted into the existing navigational light sockets.
Other objects and advantages of the invention will become apparent from the
specification herein.
-2-
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
Brief Description of the Drawings
Fig. 1 shows a schematic top view of an aircraft graphically illustrating one
of
the placements for a navigational light and showing the required light
intensity in
varying angles, as required by the FAA.
Fig. 2 shows a side view of the dual mode light source unit of the present
invention.
Fig. 3 shows a front view of the LED mounting board used in the unit, showing
the arrangement of the LEDs and the )R emitter thereon before it is flexed
into position
in the unit.
Fig. 4 is a graphical illustration of the operation of a typical installation
of the
dual mode unit of the invention.
Fig. 5 is a functional diagram of the electronic circuitry of the dual mode
light
source unit.
Fig. 6 is a more detailed schematic of the circuitry of the dual mode light
source
unit.
Detailed Description
Referring to Fig. 1, all aircraft flying in civilian airspace are required to
be
equipped with visible navigational lights to allow them to see each other at
night or in
conditions of bad visibility. The FAA has defined the parameters for
acceptable
navigational light intensity based on the angle of viewing thereof. A
navigational light
on top of an aircraft must project at least 40 candelas luminous intensity
directly ahead,
i.e. zero degrees, and in a 10-degree angular spread to the side of the plane.
Between 10
and 20 degrees off the nose of the plane, 30 candelas luminous intensity are
required.
Between 20 and 110 degrees, an illumination of only 5 candelas is required.
Military aircraft are also required to have such visible navigation lighting
systems for operation in civilian areas in a non-covert, visible mode.
Accordingly, even
military aircraft are equipped with a number of navigational lights, which
have '
traditionally been incandescent bulbs. For each bulb, the aircraft has an
electric bulb
socket, usually the type of socket that is referred to as a bayonet socket,
which is wired
into the aircraft's electrical system. The socket is configured to receive and
secure a
bulb therein and make an electrical contact with it. Power from the electronic
system of
the aircraft is then supplied through the socket.
-3-
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
Normally, the pilot has a brightness control dial or similar control device in
the
cockpit that allows him to adjust the brightness of the external navigational
lights up or
down. Adjusting this control dial in prior art systems changes the voltage of
the 400 Hz
AC current sent to the bulb over the plane's internal electrical wiring.
As best seen in Fig. 2, the dual mode light source unit 3 comprises a
connection
portion 5 which is preferably a standard single-contact bayonet base, which is
configured to fit in and connect with a standard bayonet socket for an
incandescent bulb
in the aircraft. When secured in the bayonet socket, connection portion 5
makes the
necessary contacts and receives the control current from the aircraft
electrical system in
the same way as the incandescent bulbs of the prior art.
The electrical current received is transmitted to electronic circuitry in the
form
of circuit board 7 mounted fixedly on connection portion 5 and double-sided
copper
cixcuit board 9 fixedly attached to circuit board 7 and extending upwardly
therefrom.
Connected with both boards 7 and 9 is light source mounting board 11, made of
thin
flex circuit board and supporting the light emitting components of the unit.
As best seen in Fig. 3, the thin flex board 11 has an array of components
secured
thereto. The board 11 supports a visible light source in the form of thirty-
four (34)
visible light-emitting diodes 13 or LEDs (3500 MCD) mounted thereon, in two
4x4
arrays and one on either side of IR light source 15. These LEDs 13 are wired
in parallel
and connected to board 7 to receive power therefrom, as is IR source 15. A
different
number of LEDs may be used as required, and also, alternatively, other array
configurations may be used to achieve the required luminous intensity
distribution as
well, especially if LEDs specified in the preferred embodiment are used.
The near-infrared emitter 15 is preferably an emitter such as the super high-
power GaAIAs IR emitter sold as model no. OD-50W by the Opto Diode Corp., of
Newbury Park, California. The preferred IR emitter generates IR at a range of
wavelengths centered at about 880 nm, and with a fairly wide angular spread,
necessitating only a single emitter for each unit. However, more than one IR
emitter
may be used, optionally supported in several orientations relative to each
other. Night
vision goggles used in covert operations are particularly sensitive to the
deep red and
near-infrared region of the spectrum, and friendly military equipped with
night vision
goggles are readily able to see the IR produced by the IR emitter 15. Without
appropriate night vision equipment, however, the IR light is impossible to
see.
-4-
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
The LEDs are selected and configured to emit light conforming to FAA
luminous intensity requirements, angular coverage requirements, and
chromaticity
requirements for Aviation Red or Aviation Green. All of the LEDs for a given
light unit
are either red or green, depending on whether the unit is to be installed on
the left-hand
(red) or the right-hand (green) side of the aircraft. The LEDs are high
intensity
directional LEDs, such as those manufactured by Purdy Electronics of
Sunnyvale, CA,
with Model number AND180HSP, Motorola, Inc., with Model number HSMC-5690, or
Nichia Corporation of Japan as model number NSPG-5105, or equivalent products.
LEDs of this type generally project fairly intense light only within a cone of
about 10 to
15 degrees. To meet the FAA requirement for an angular spread of luminous
intensity
levels as shown in Fig. 1, the board is bowed, as seen in Fig. 2, so that the
LEDs point
in a plurality of angled directions and achieve the luminous intensity
distribution
required.
The LEDs generate visible light, but unlike incandescent lights, which are
copious emitters of near-infrared energy at any brightness setting, the LEDs
are selected
for having spectral emission characteristics such that they do not generate
much, if any,
infrared light. As a consequence, these LEDs will not overpower or unduly
degrade an
intensified image of the LED when viewed at close range using night vision
goggles.
The dual mode light source is configured to be installed by simply
substituting
the dual mode light source unit for an existing navigation light bulb. The
shape,
volume, power requirements, and external physical configuration of the dual
mode unit
of the disclosed embodiment are substantially the same as for the Grimes type
72914/11631, a 6.2-volt, 40-watt incandescent bulb. It will be understood
however that
virtually any type of light source might be replaced by a suitably configured
dual mode
light source unit according to the invention.
The electronics of the dual mode unit are preferably set up to interface with
the
electronic current supplied by the aircraft electrical system so that no
further
modification is necessary, and covert mode or visible mode may be selected by
the pilot
by the dimmer control already present for the navigational lights.
In most current navigation light systems which provide for adjusting the
brightness of the navigation lights, the control of the brightness is
effectuated by
varying the voltage of the AC power current sent to the light between a
minimum value
of about five volts and a maximum value of about 115 volts. According to an
aspect of
-5-
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
the present invention, this varying voltage control is used to give a pilot
control over
whether the aircraft is operating in visible civilian mode, or covert IR mode.
Figure 4 illustrates the functionality of the electronic circuitry 7 of the
unit 3.
The circuitry analyses the incoming current from the aircraft, and if the
voltage exceeds
a preselected threshold voltage V,~eshold~ the dual mode unit is placed in
visible mode,
and only the visible LEDs are illuminated. No power is sent to the IR light
source. The
intensity of the visible LEDs remains constant irrespective of any changes to
different
voltages in this range of voltages A.
To enter covert mode, the pilot needs only to turn the existing navigation
light
brightness control down low enough, thereby reducing the input voltage to the
unit.
When the unit's electronics detect that the input voltage has dropped below
the
threshold voltage, the dual mode unit shifts to covert mode; all power is cut
to the
visible light source (the LEDs 13), and power is sent to illuminate the IR
light source.
The IR light source is fed a constant level of power over the entire range B
of
voltages from Vn,;n to the threshold voltage. However, it is desirable, where
a number of
aircraft are flying covert mode and viewing each other's IR emissions through
their
night vision goggles, that the IR have a distinctive appearance for some or
all of the
aircraft. This can be accomplished in the present system by causing the IR
light source
to pulse on and off periodically so that individual aircraft will have a
recognizable cycle
or "blink rate" to the pulse of their IR. Adjustment of the voltage by the
pilot in this
voltage range B results in adjustment of the periodic frequency of the pulsing
of the IR
emission on the aircraft. Higher voltages result in faster pulsing, and
reducing the input
voltage slows down the IR pulsing rate. The pulse is preferably a square wave,
and in
the preferred embodiment the square wave keeps the IR source on about 75% of
the
time.
The operation of the electronic circuitry of the dual mode unit is illustrated
best
in Fig. 5. The schematic of Fig. 6 parallels Fig. 5, but shows the individual
components
in greater detail. Equivalent paxts are indicated by the same reference number
in the
figures.
The input AC power current is introduced from the socket connector base
through line 17, which feeds the current into rectifier doubter 19, which
converts the
AC to equivalent voltage DC current. This DC current is delivered to the
visual light
source (LEDs 13) through visual mode switch 21, to switch mode voltage
regulator 23,
-6-
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
which converts the variable voltage current to a steady DC output, and also to
voltage
comparator 25, which determines the mode of the unit, and to IR light source
15
through switchable control mode timer circuitry 27.
The determination of which mode the unit is to be in is made at comparator 25,
which receives the input voltage along line 28 and compares this input voltage
to a
preset reference voltage from line 29 from a divider network which corresponds
to the
threshold voltage for the change between covert and visible modes. This
reference
voltage in the preferred embodunent is about 5.8 volts, although this
threshold value
could vary considerably. If the input current is in an electrical state
indicating visible
' mode (e.g., voltage higher than threshold), the comparator output 31 snaps
to low. This
low voltage is sent by line 33 to switchable timer 27 for the IR light source,
and
switches it off so no power goes to the IR light source. The low output on
line 31 is also
inverted by inverter 35, and this high output is sent via line 37 to turn on
the switching
regulator 21, allowing the constant DC current to flow through to the visible
light
source LEDs 13. The LEDs thus remain at a constant intensity despite any
variations in
input voltage at this level.
If the input current is in an electrical state that indicates covert mode
(e.g.,
voltage below threshold, range B in Fig. 4), then the comparator 25 produces
an output
that snaps to high. This high output is inverted by inverter 35 to produce a
low signal to
the switch mode regulator 21, cutting the flow of power to the visual light
source. At
the same time, the high output on line 31 switches timer 27 on.
When switched on, timer 27 acts as a voltage controlled oscillator, and the
high
output 33 applied thereto runs it in an astable mode, oscillating at a
frequency based on
the voltage applied thereto along line 41, with higher frequency oscillation
produced by
higher input voltage. This rate of oscillation is in a range that can be seen
by the human
eye, and provides the adjustable blink rate for the IR light source based on
the pilot-
controlled level of input voltage.
The output of the oscillation of the timer goes to a follower 43 and causes it
to
switch a 5 volt power supply to the IR light source on and off responsive
thereto. The
resulting pulsing current flows to IR source 15 and causes it to pulse
periodically. Since
the rate of pulsing IR is dependent on the input voltage, it can be adjusted
by also
adjusting the input current voltage by adjusting the cockpit brightness
control in the
lower range that corresponds to covert mode.
_7_
CA 02422826 2003-03-18
WO 02/28711 PCT/USO1/29110
An existing aircraft with variable brightness control for its navigational
lights
can be upgraded to an infrared covert capability by substituting a dual mode
light
source unit for each of the incandescent navigation light bulbs thereof. When
this is
done, existing brightness controls may be used to operate in visual or covert
mode as
follows.
In normal civilian airspace, the pilot illuminates the navigation lights by
setting
the brightness control at a high setting corresponding to a voltage above the
threshold at
the sockets. When covert operation is desired, the pilot dials down the
brightness
control until the visible navigation lights go out. If the pilot puts on night
vision
goggles, he will see the IR emitters blinking at a certain rate. He can adjust
this rate to
be slower by further dialing down the brightness control. The settings for
specific
recognizable pulsing rates may be incorporated into the control as desired to
aid in
coordination of the speed of pulsing between aircraft.
New aircraft may also be equipped with dual mode light sources according to
the invention with substantial benefits as well. The dual mode unit has an
enhanced
lifetime over that of incandescent bulbs, and also obtains an advantage over
separate
visible/IR systems by use of only a single wire pair for control of both types
of light,
reducing labor and cost of manufacture, and to a degree, weight of the
aircraft.
It will be understood that the invention herein extends well beyond the
embodiments of the disclosure, and the terms used in this specification should
be
understood to be language of description, not limitation, as those of skill in
the art with
this specification before them will be able to make changes and modifications
therein
without departing from the scope of the invention.
_g_
