Note: Descriptions are shown in the official language in which they were submitted.
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International Patent Application
LIGHT SOURCE ASSEMBLY FOR VEHICLE EXTERNAL LIGHTING
Related applications
This application is a continuation-in-part of U.S. patent application serial
number 09/665,600
entitled DUAL MODE~LIGHT SOURCE FOR AIRCRAFT EXTERNAL LIGHTING filed on
September 19, 2000 by inventors John J. Martin and Cary H. Leach, which is
still pending and herein
incorporated by reference.
This application also asserts priority of U.S. provisional patent application
serial number
60/356,854 filed February 13, 2002.
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 civilian
or military aircraft that use
light emitting diodes (LEDs) to generate visible light. The invention also
relates to apparatus and
methods of upgrading the navigation lights of existing aircraft.
Backg-mound of the Invention
The aviation authorities of many countries require that commercial aircraft,
and also military
aircraft, when in civilian airspace on non-covert activities, have
navigational lighting to improve their
visibility at night. Under U.S. regulations, when any aircraft (military or
civilian) is flown during
darkness in unrestricted airspace or in a military operations area (MOA), the
external lighting of the
aircraft must conform to FAA requirements for chromaticity ('color'), luminous
intensity
('brightness'), and angular coverage. Generally, the navigation lighting
comprises red lights on the
left side and green lights on the right side of the plane, and this external
lighting normally is provided
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by incandescent light bulbs in sockets on the outside of the plane,
conventionally powered by
electricity from the internal electronics of the aircraft.
The lifetime of incandescent lamps, especially in military aircraft exterior
lighting
applications, is limited, and replacement of incandescent lamps in the
exterior lighting fixtures of
vehicles, in particular aircraft, is a frequent maintenance task. For example,
interviews of squadron
maintenance personnel indicate that the average lifetime of incandescent lamps
in the main left and
right navigation light fixtures in F-16 aircraft is approximately 75 hours. A
means of increasing the
reliability of exterior light sources while maintaining levels of luminous
intensity required to meet
Federal Aviation Administration (FAA) regulations is therefore needed.
Compared to conventional incandescent lamps, light emitting diodes (LEDs)
contain no
filaments and can theoretically provide lifetimes measured in thousands of
hours. Also, LEDs are far
more efficient in converting electrical energy into light energy. However,
LEDs are not perfect
converters of electrical energy into light energy, and some energy always will
be lost as waste heat.
- This creates a problem for possible use of LEDs in aircraft navigation
lighting, because the
heat created increases the temperature of the LEDs, and, for a given drive
voltage, the hotter an LED
gets, the less light that LED emits. The problem is even greater in the area
of navigation light aviation
applications, because to achieve luminous intensity levels conforming to
FAA/ICAO.regulations a
number of high intensity LED diodes (individual light emitters) must be
integrated and co-packaged.
However, the added LEDs generate substantial heat, which elevates the
temperature of the LEDs.
This elevated temperature in turn tends to reduce the intensity of the light.
Sufficiently high
temperatures will ultimately degrade the LEDs so that they either go out
entirely, or function at a
greatly reduced illumination level. Use of LEDs in aircraft light systems is
consequently subject to
problems of overheating.
As mentioned above, military aircraft are required to have visible navigation
lights similar to
those of civilian and commercial aircraft. When flying a wartime night mission
or night training
sortie, a military aircraft may transit through unrestricted airspace in which
civilian aircraft also
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operate, and it must have aircraft external lighting that conforms to FAA
requirements during this
transit. However, during night flight operations in wartime conditions, or
during night flight training
in restricted airspace, aircraft external lighting that is visible to the
unaided eye is undesirable.
For military aircraft in covert activities or other military situations where
visibility would be a
disadvantage, one approach was for the pilot of the military aircraft to
simply turn off the external
lighting. The pilot can adjust the intensity of the navigation lights, or turn
them off completely, with a
brightness control dial in the cockpit that varies the voltage of the AC
current sent to the light socket.
In recent years, however, it has been noted that, in covert activities, while
the aircraft was not
visible to the enemy, it was 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.
In covert operation, only
emissions in the near-infrared of appropriate intensity are used, and visible
navigation light is not
emitted. 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 (NVGs) that are
utilized during night
oper'~tions in many military aircraft, which are very sensitive to the deep
red and near-infrared region
of the spectrum.
To upgrade to covert IR capability making military aircraft external lighting
to be selectable
between visible and covert modes at will during flight, IR light sources 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 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.
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Summary of the Invention
It is therefore an object of the present invention to provide a navigation
light for aircraft that
makes use of LEDs, but that avoids the heat-related problems of the prior art.
It is further an object of the invention to provide an LED light source that
efficiently carries
heat away from the LED source and radiates the heat to the environment outside
of the aircraft.
It is also an object to provide such a system in a modular design that affords
easy replacement
of the lighting assembly, and also provides a relatively easy upgrade from
existing navigation lights to
the improved system, especially as an upgrade that does not require
modification to the existing
aircraft structure.
According to the invention, an aircraft light assembly is provided for an
aircraft having a body
with an outer surface exposed to an external airflow. The assembly comprises a
light apparatus
configured to be supported on the body of the aircraft and including one or
more light emitting diodes
generating visible light. The apparatus also includes an outer structure
overlying the light apparatus.
The buter structure includes a light transmission portion through which
visible light from the LEDs
can pass, and a metallic portion with an outer surface exposed to the external
airflow. The metallic
portion secures the light transmission portion on the aircraft. A heat-
transmitting connection
thermally links the LEDs to the metallic portion so that heat from the LEDs
flows to the outer surface
and is dissipated to the external airflow.
Preferably, the outer surface of the metallic portion and the light
transmission portion are
configured so that the outer surface thereof is conformal to the outer contour
of the aircraft body, at
least on one edge, e.g. the leading edge of the assembly.
It is further an object of the invention to provide a method for installing an
LED-based aircraft
light assembly.
It is further an object of the invention to provide for a dual mode visible
and infra-red aircraft
light source for military aircraft that avoids the heat-related problems of
the prior art.
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It is also an object of the invention to provide a dual mode light source that
provides for
different flashing patterns of the infra-red emitter when in covert mode.
Preferably, the different flash
patterns are pre-programmable and selectable by existing controls without
modification to the
electronics of the aircraft.
It is also 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 IR
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 an
aspect of 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.
According to another aspect of the invention, 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.
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Other objects and advantages of the invention will become apparent from the
specification
herein.
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 IR 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.
Fig. 7 is a horizontal cross-sectional view through an aircraft wingtip,
showing a conventional
incandescent bulb fixture and glass lens of the prior art.
Fig. 8 is a schematic illustration of an upgrade to an aircraft lighting
system with another
embodiment of light source module according to the present invention.
Fig. 9 is a horizontal cross-sectional view of a wingtip having an upgraded
aircraft lighting
system with embodiment of light source module shown in Fig. 8.
Fig. 10 is a plan view of a preferred embodiment of a modular aircraft light
unit.
Fig. 11 is a side view of the aircraft light unit of Fig. 10.
Fig. 12 is a partially cut-away view as in Fig. 11 showing the interior of the
aircraft light unit.
Fig. 13 is a perspective view of the bottom of the metallic outer portion of
the modular unit of
Figs. 10 to 12.
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Fig. 14 is a perspective view of an aircraft light unit as shown in Figs. 10
to 13 installed in an
aircraft wingtip.
Fig. 15 is a perspective illustration of the relative position of the infra
red emitter and a
reflector plate in the aircraft light unit of Figs. 10 to 14.
Fig. 16 is a chart showing the relative visible and covert emissions from a
device according to
the invention for the settings of the five-position navigational light
intensity switch in an F-15 cockpit
control panel.
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 a
plurality of
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. The
incandescent bulb
navigation lights of the prior art 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 with a single
double wire running to each light bulb.
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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 for a military
aircraft 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
circuit 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-SOW 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
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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.
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 AND 180HSP, Motorola, Inc., with Model number HSMC-S690,
or Nichia
Corporation of Japan as model number NSPG-S10S, 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
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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 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 Va,~esno,a, 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
Vm;" 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
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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
parts 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, 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 1.5 through switchable control mode timer circuitry 27.
The determination of which mode the unit is to be in is made at comparator 25,
which
~eceives 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 ttu-eshold
voltage for the change
between covert and visible modes. This reference voltage in the preferred
embodiment 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.
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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
~o 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.
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.
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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.
Another embodiment of the invention is shown in Figs. 8 and 9, as well as a
method of
upgrading an aircraft with an incandescent light fixture.
An existing incandescent light fixture is an aircraft as shown in Fig. 7. The
aircraft has a
body 51, which for illustrative purposes in Figs. 7 and 8 is a wingtip, with a
space 53 therein in which
a socket 55 is supported. Socket 55 is part of the electrical system of the
aircraft, and is supplied with
AC power, usually by a single pair of wires, not shown, as discussed
previously herein. Incandescent
bulb 57 is removably secured in socket 55 by a bayonet portion 59 thereof.
The body 51 of the aircraft has an aperture therein through which the bulb 57
in space 53 can
be accessed. This aperture is closed during normal operation of the aircraft
by a lens 61 that is held in
aperture by security plate 63 that is secured by Allen bolt 65, and also by a
lip structure generally
indicated at 67 on the lens 61 that fits in engagement with the aircraft body
51 at the edge of the
aperture.
Referring to Fig. 8, an existing incandescent bulb light can be retrofit or
upgraded to an LED-
based lamp by installation of a self-contained light assembly or unit 71 in
the aperture of the aircraft
body S1. Installation involves removal of the Allen bolt 65 and retaining
plate 63. The lens 61 and
bulb 57 are then removed from the socket 55.
Electrical connection portion, or bayonet fitting, 73 of the unit 71 is
inserted into socket 55 so
as to receive electrical power therefrom and transmit the power through a
flexible electrical umbilical
cable 75 that links bayonet fitting 73 to lighting circuitry housed in unit
71. By use of the bayonet
connection 73, power for the unit 71 can be drawn from the existing electrical
system without
modification.
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The unit 71 includes a housing 75 that holds control circuitry connected with
a metallic outer
housing 77. The outer housing 77 supports a window or light portion 79 through
which visible light
can pass. The outer housing 77 also supports, for military applications, a
second window or IR light
transmitting portion 81 of material through which infra-red light can pass for
covert mode operations.
The outer portion 77 of the unit 71 exactly duplicates the shape of the pre-
existing lens 61,
and is configured to fit in the aperture in the aircraft body 51 in place of
and mount identically to lens
61. In the method of Fig. 8, the bayonet fitting is secured and electrically
connected in the socket 55,
and the umbilical cable is coiled and fit into the space 53. The unit 71 is
then placed in the aperture
and a lip structure 83 of the unit 71 interlockingly engages the edge of the
aperture, as the lens 61 was
held. Plate 63 is then secured with Allen bolt 65 over unit 71, fitting into a
recess 85 at a rear edge of
the assembly housing 77.
The outer portion 77 and windows 79 and 81 together define an outer surface
that is also
identical to the outer surface of the lens 61. The unit 71 thus becomes the
lens 61 duplicated in metal,
with appropriate windows or ports flush with and maintaining the pre-existent
profile of the outer
surface. By virtue of its exposed profile and shape matching that of the
original lens, the unit 71 thus
does not affect, compromise or degrade the aerodynamic characteristics of an
aircraft in which the
lens forms an integral or important part of the airfoil shape and/or design.
Referring to Fig. 9, the light module 71 also includes a housing 87 that
extends inwardly of
the aircraft body into space 53. Housing 87 supports inside it light control
circuitry, which is
preferably voltage discrimination and control circuitry similar to the
circuitry shown in Figs. 5 and 6,
and discussed above. The circuitry is connected with umbilical cable 75 and
receives electrical power
therefrom. The circuitry in housing 87 is connected by wiring to power supply
and/or power
conditioning circuitry 88 and to a plurality of visible-light LEDs 89 and an
infra-red emitter 91.
Depending on an electrical condition or parameter, e.g., voltage, of the
electrical current received
from socket 55 and the electrical system of the aircraft, the light control
circuitry sends power to and
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illuminates the visible light LEDs 89 or the IR emitter 91, as with the first
embodiment discussed
above.
The visible LEDs 89 are preferably high intensity LEDs, and especially
preferred are LEDs
sold by Lumileds Lighting LLC of San Jose, California under the name Luxeon TM
Star. Preferably
three of these LEDs are used, supported at appropriate angles on mounting
portion 93 so that the
visible light emitted from the LEDs is transmitted through window 79 in said
housing 77 and is
angularly distributed according to specific patterns, e.g., FAA requirements.
To aid in proper
distribution of the light from the LEDs, a mirror 95 is also provided inside
the outer housing 77.
In addition to replacing the lens, the unit 71 also replaces the internal
incandescent lamp in
aircraft red (left), green (right), or white (tail) external navigation light
fixtures, and therefore must
emit light of the correct color. The LEDs used in the unit in these different
positions are preferably
color LEDs that emit a light of the appropriate color for the location of the
fixture in the aircraft, i.e.,
red, green or white. Since these LEDs have the correct color light output, the
window 79 may be of
clear material, and not a color filter.
The LEDs 89 are mounted on mounting portion 93 so as to readily transmit heat
created to the
mounting portion 93. This heat must be carried away (heat-sinked), or light
emission from the LEDs
will decrease. Both the mounting portion 93 and the outer housing 77 are of
thermally conductive
metal, preferably aluminum, and, to remove the heat, mounting portion 93 is
connected thermally and
mechanically to the metallic outer housing 77, which has an adequate surface
area to dissipate the heat
produced by the LEDs. The mounting portion 93 and outer housing 77 are
preferably a continuous
aluminum structure or connected by a metal-to-metal contact to form a thermal
link with a suitable
cross sectional area to the direction of heat flow, such that heat in mounting
portion 93 flows to the
outer housing 77 and is dissipated to the external airflow passing over the
aircraft body, and the
temperatures of the LEDs remain within an acceptable operating range.
By virtue of the unit 71 substituting for a fixture of lens, the external
surface of the metal
housing 77 is directly exposed to moving airflow, and the unit 71 thus is
particularly efficient in
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radiating waste heat internally generated by the circuitry and LEDs contained
within it. The metal
housing 77 also functions as a mounting chassis for the light control
circuitry and the infra-red
emitter, which are also physically integrated into, heat-sinked, and protected
by said housing 77. By
such means of heat radiation, which is far more efficient than in a structure
in which an array of high
intensity LEDs is located beneath or behind an existing lens but not directly
thermally bonded to a
metal surface exposed to outside airflow, the unit 71 permits higher intensity
light emission from
LEDs than otherwise is possible with existing "plug and play" LED substitutes
for incandescent
lamps. Also, the LEDs used are smaller physically than the incandescent lamp
and can be mounted
closer to the outer glass lens and connected with the metal part of the
fixture nearer the outside of the
aircraft, reducing the distance heat must flow to be released outside the
aircraft.
As stated above, the illustrative unit 71 of Figs. 8 and 9 is configured for
placement in a
military aircraft for which infra-red emission is desired for covert
operations. Consequently, the unit
71 includes IR emitter 91 that selectively into IR light through window 81.
The IR emitter 91 is
preferably surrounded by a shroud 97 that directs all IR emissions in angular
directions that can only
be seen with NVGs from desired aspects, usually upward, above the horizontal
horizon of the aircraft.
The light control circuitry for a military aircraft light assembly or unit is
preferably dual-mode
circuitry, similar to or such as shown in Figs. 5 and 6. This circuitry
receives power from the aircraft
electrical system, preferably through the fixture socket. The electric
circuitry is configured to process
the input current from the socket and based thereon operate in either
civilian, visible mode or covert
IR mode. Where the current is in one electrical state, such as for example at
a voltage above a preset
threshold, the electric circuit sends power derived from the incoming current
and illuminates the
LEDs. When the current is in a different electrical state, e.g., at a voltage
below the preset threshold
voltage level, the circuitry cuts power to the LEDs and sends power only to
the IR emitter, and no
visible light is emitted.
The detected electrical states that are most compatible for interface with
existing aircraft
controls without modification are different voltages. Depending on the cockpit
electronics, the
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existing aircraft electrical system may supply electrical current at any of
several voltage levels set by
the lighting intensity control in the cockpit. Most military aircraft have
navigational light dimmer
controls in the cockpit with at least two brightness settings, to as many as
five settings. For example,
F-15's usually have a cockpit control switch with five different illuminations
intensity levels
producing voltages of, e.g., 30, 50, 70, 90 and 115 volts, while F-16's have
only two switch positions,
producing 55 or 110 volts. In either aircraft, however, the light control
circuitry , in the embodiment
of Figs. 5 and 6, detects the different voltage levels using a comparator 25
(Fig. 5), and causes the IR
emitter to pulse at different frequencies set by a timer 27 based on different
input voltage levels. The
different pulsing makes the aircraft easier to recognize and distinguish from
other aircraft by other
pilots using NVGs.
To make the assembly more adaptable to different aircraft electronics, the
light circuitry of
the preferred embodiment is modified from the circuit of Figs. 5 and 6 in two
ways.
First, instead of the comparator 27, the light control circuitry in the unit
71 preferably
includes a microcontroller which senses the voltage of the input current
supplied from the existing
external lighting control located in the cockpit. The microcontroller is pre-
programmable (or re-
programmable) by a user to respond to different AC or DC voltage inputs from
the existing aircraft
lighting electrical system and to drive based on the programmed voltage level,
driving the visible light
emitting diodes (LEDs) or infrared emitting diodes (IREDs) to emit steady
(constant) output or
flashing output of different rates, patterns, duty cycles, etc as desired.
Because the voltage value
corresponding to each given external lighting intensity setting may differ
slightly from aircraft to
aircraft due to tolerances or aging of aircraft electrical system components,
the microcontroller also
allows the unit to be tailored to individual aircraft and give the same
desired light output (or infrared
output) response for a given intensity setting even when installed in
different aircraft having different
electrical characteristics.
Second, instead of the timer that adjusts frequency of the flashing IR emitter
on the aircraft,
the light control circuit is provided with a pre-programmable feature through
which different flash
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patterns can be entered and assigned to different voltage levels of current
from the aircraft. These
flash patterns are used to turn the IR emitter on and off in time-dependent.
repeating patterns, which
aid in visual identification of the aircraft with NVGs at a distance. An
example of different flash
patterns that might be used in an aircraft such as an F-15 with a five-
position intensity control are
shown in the chart of Fig. 16. The flash patterns may be quite varied, but
generally are arrangements
of short pulses, longer pulses, and intervals of varying duration between
pulses.
Both the setting of the voltage levels for different IR or visible emissions
and the
programming of the IR flash patterns are accomplished by input to the light
control circuitry.
Preprogramming, or re-programming, of different covert flash characteristics
(e.g., simple pulsing at
different rates or more complicated patters for flashing, such as a short
flash followed by a long flash,
or irregularly spaced flashes) may be accomplished on the ground by a user by
means of a hand-held
programming device that interfaces with programmable circuitry in the unit.
The hand-held
programming device can input commands, data and selections of the flash
patterns or the electrical
states or characteristics, such as voltage levels, on which the circuitry
makes a determination of which
mode the unit should operate in. The input from the hand-held programming
device may be
accomplished even after installation directly through the window and through
an infra-red data port
99, best shown in Fig. 9, or by a jack or a pin connection on the housing 87
that can be accessed
before the unit 71 is installed, by a mechanical plug-in connector from a hand-
held device. The circuit
can be reprogrammed if necessary to set specific voltage levels or ranges to
be detected, and to set the
specific visible or covert emissions and patterns associated with each of the
defined voltage levels or
ranges.
It will be understood by those of skill in the art that different
characteristics of the current,
e.g., amperage or digital data in the current, may also be used to detect from
the input current at the
socket the desired covert or visible action, and that the light control
circuitry may be programmed to
modify those parameters and actions as desired.
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For civilian or commercial aircraft, the light unit 71 is built to emit light
energy only in the
visible part of the electromagnetic spectrum, and the unit is a self-contained
assembly that contains
high intensity LEDs that emit visible light, and associated voltage
conditioning circuitry. No separate
IR emitter 91 or IR window 81 is supplied in the civilian version of the unit,
but the general form of
the housing copying the external shape of the original lens and being
conformal to the shape of the
contour of the aircraft is similar to the military light unit.
Since there is no need to selectively control infra-red covert lighting in a
civilian aircraft, the
light control circuitry functions mainly to condition the electricity received
from the aircraft
electronics to be used to directly power the LEDs. Even though configured to
emit visible light only,
'~owever, a commercial aircraft assembly nonetheless benefits from the heat
transfer to direct
exposure of the metal housing to external airflow to facilitate the liberation
or radiation of heat from
the high-intensity visible-light LEDs contained within the housing, thus
permitting greater luminous
intensity output from said LEDs cluster than otherwise would be possible. The
LEDs in a civilian
version are therefore also thermally bonded to a mounting portion 93 that is
connected thermally and
mechanically to the outer portion 77 of the unit 71.
The most preferred embodiment of the light source unit of the invention is
shown in Fig. 10.
Tl-~e light source module 101 of this embodiment is configured to have an
external shape identical to
that of level 61 and securement plate 63 combined. As best seen in Fig. 10,
the light source unit 101
has a metallic outer portion 103 that serves as a frame that supports therein
a window or light
transmissive member 105. Outer portion 103 has a bore 107 therein configured
to receive Allen bolt
65 therethrough securing the unit 101 in the aperture on the aircraft. Unit
103 also has a lip structure
109 that engages the edge of the aperture to hold the unit 101 on the aircraft
body 51.
As best seen in Figs. 11 and 12, below the outer portion 103, the unit 101 has
an inward
housing or electronics envelope 111 that contains light control circuitry as
described for any of the
preceding embodiments, connected by a flexible electrical umbilical cable 115
with a bayonet fitting
113, which connects with the socket 55 connecting to wiring in the aircraft
that connects with pilot
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interface circuitry (e.g., cockpit controls) and receives electrical current
therefrom, as discussed with'
respect to the earlier embodiments. The light control circuitry is similar to
the light control circuitry
of the preceding embodiments, especially the programmable form above with the
relevant input port
or pins, and it receives the electrical current from the aircraft and
selectively transmits power derived
therefrom to connecting wiring (not shown) leading to visible-light LED
sources or a near infra-red
emitter.
The LEDs on the unit 101 preferably are three Luxeon TM Star LEDs of
appropriate color and
intensity to produce illumination satisfying the FAA or other applicable
regulations. These LEDs
have an aluminum core that is a built-in heat sink that can be engaged against
a suitable surface to
transmit heat thereto. Two LEDs 117 are each secured thermally and
mechanically on mounting
structure 119 on a thermally conductive inclined surface thereof, facing
forward and outward of the
unit 101 at respective angles to achieve the desired distribution of visible
light therefrom. The third
LED is housed in a prismatic lens structure 121, but is also mechanically and
thermally bonded to a
face of mounting structure 119. The positions of LEDs 117 and lens structure
121 distribute the
visible light from the LEDs so as to achieve the requisite angular and
intensity distribution.
Mounting structure 119 is itself mounted on support plate 123 by fastener on
bolt 125.
Support plate 123 is supported in a continuous manner by being secured by
fasteners or bolts 127 that
fixedly attach to the lower end of interior rib 129 of outer housing 103.
Mounting structure 119,
support plate 123, and outer portion 103 each are of thermally conductive
metal, preferably
aluminum, and are thermally connected with each other with adequate cross-
sectional area to the
direction of heat flow such that heat from the LEDs 117 is transferred to
mounting structure 119, and
then transmitted to support number 123, through interior rib 129 into the
metal outer portion 103,
which has adequate surface area to dissipate the heat into the external
airflow over the aircraft. The 1R
emitter and the circuitry of the unit 101 are also preferably thermally linked
to metal outer portion 103
to dissipate any heat therein as well.
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The form of the metallic outer portion 103 is best shown in Fig. 13. The outer
portion 103 is
preferably formed as one piece of aluminum. Ribs 129 are each provided with
threaded bores 130 to
receive bolts 127 securing the face 132 in engagement with the support plate
123 to provide for a
thermal connection and good heat flow between the parts, and at a minimum,
adequate heat flow to
dissipate enough heat that the LEDs remain in an acceptable range of operating
temperatures. The
outer portion 103 includes a frame structure 131 that receives therein the
material of the window 105,
where it is secured by adhesive or otherwise and preferably caulked in place.
The window 105 itself is
symmetrical and the frame structure 131 has an aperture therein for receiving
and securing the
window 105 that is symmetrical in terms of the shape of window 105 that it can
receive. As a result,
the same window 105 can be used with the outer portion 103 on either side of
the plane, even though
the outer portions 103 from opposite sides of the plane are mirror images of
each other.
The unit also includes infrared emitter 133 supported on plate 135, which is
preferably a
printed circuit board that is linked thermally to sink heat to the outer
portion 103. The near-infrared
emitter 133 is preferably an emitter such as the super high-power GaAIAs IR
emitter sold as model
no. OD-SOW 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.
Plate 135 is preferably also
thermally linked to the metal outer surface of the unit 101 to dissipate heat
in the IR emitter 137 to the
outside airflow.
It is desirable that infra-red radiation be directed only upwardly from the
source to be visible
with NVGs from other aircraft that are level with or above the aircraft with
the light unit installed, and
to prevent viewing of the aircraft from below with NVGs. When the unit 101 is
installed in an aircraft
(see Fig. 14) the IR emitter 133 is actually oriented to face downwardly. To
prevent IR emissions
from radiating downwardly, a reflector 137 is provided. This reflector has
roughly hat-shaped cross
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section and reflects all IR from the emitter upwardly. The spatial
relationship of the reflector 137 and
the IR emitter is illustrated schematically in Fig. 15.
IR radiation downward is also blocked by IR opaque paint or foil mask 139 on
the inside of
part of the window 105 where it does not obstruct desired visible light from
the LEDs when they are
illuminated. The mask 139 shown in Fig. 14 is partially cut-away to show the
IR emitter 133, but
normally, the IR emitter 133 would not be visible from the angle of the view
of Fig. 14. The mask 139
in fact extends upward to whatever height and whatever shape is necessary to
block downward
radiation of the infra red light.
The window 105 is preferably otherwise of transparent material, especially
glass, that
transmits therethrough both visible light from the LEDs and infra-red
radiation from the emitter 137
without substantial diffusion. In addition, the window is preferably provided
with an electro-magnetic
interference (EMI) shield to reduce or eliminate emission of susceptibility to
radio frequency energy,
and with a metallic coating or sieve to create a conductive skin on the unit
101 that is less affected by
various RF radiation.
Installation of the unit 101 is similar to the method of Fig. 9, and the unit
functions as a plug-
and-play heat sinked module foe the LEDs and other parts of the unit 101
without the need to
structurally tie in with any other structure of the aircraft. The existing
lens 61 and securing plate 63
are removed. The bayonet fitting 113 of the unit 101 is placed in the socket
55, and the unit 101 is
then secured in the aperture in place of lens 61 and plate 63. The Allen bolt
65 is re-used to secure the
unit 101 to the aircraft body S 1 through aperture 107. The apparatus is then
ready for use.
The civilian or commercial aircraft variation of the unit 101 does not have
the IR emitter 133
or retroreflector 137. Accordingly, the window 105 can be reduced in size to
cover the portion of the
interior of the unit 101 that emits infra-red light in the military version.
This increases the metal
surface area of metal outer portion 103, which is an added benefit because it
improves the dissipation
of heat created by the LEDs 117.
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As with the previous embodiment, the light control circuitry in a unit 101 for
civilian use is
greatly simplified because there is no need for the unit to screen the input
current for possible
indications of various covert IR mode actions. The circuitry rather primarily
functions as voltage
conditioning circuitry, i.e., to convert the input current to a form of
electrical power, e.g., lower
voltage DC current, that can be applied to power the LEDs 117.
Whether applied to civilian or military applications, the subject invention
provides benefits in
terms of direct exposure of the metal housing to external airflow to
facilitate the liberation or radiation
of heat from one or more high intensity visible light LEDs contained within
the housing, thus
permitting greater luminous intensity output from the LEDs than otherwise
would be possible, and
this heat sinking is achieved in a plug-and-play application without need for
metal surgery on the
aircraft. The commercial and military versions of the light unit afford
substantial advantages,
including:
i. The cost of the system and method of the invention is comparatively lower
than that
of previous approaches.
ii. Implementation requires no change to existing voltage or power
characteristics in the
aircraft, nor modifications to any part of the existing aircraft electrical
system.
iii. Implementation is quickly accomplished through simple substitution of the
device for
existing lenses and lamps.
iv. By virtue of its direct exposure to the air stream, the light assembly
provides
improved radiation of internally generated waste heat compared to previous
approaches, thus allowing
the LEDs contained therein to operate at greater efficiency and thus provide
greater luminous intensity
for a given physical size.
v. When installed, the exterior shape or profile of the invention matches that
of existing
light fixture lenses, thus causing no change in airfoil and/or aerodynamic
characteristics of an aircraft
on which it is installed.
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vi. Covert emissions are visible only from locations level with and above the
aircraft, and
different selectable flash characteristics in covert mode facilitate
recognition of different aircraft with
NVGs at long ranges, without modification of the aircraft electrical system.
vii. Preprogramming of appropriate voltage levels allows adaptation of the
light unit to
different aircraft electronics, and also allows multiple different covert
infra-red flash characteristics to
be set up in the unit before used using a hand-held programming tool.
The light assembly is not limited to any single particular shape or size, and
its shape, profile
and/or configuration may be tailored to match virtually any existing lens and
interface with virtually
any existing exterior lighting fixture configuration. Lenses on existing
external light fixtures typically
are secured by at most three screws, and the lamp within said fixtures
typically is mounted via~a
simple twist-lock bayonet base shown in the embodiments herein, so through the
simple expedient of
its substitution for the existing lenses and lamps, the invention provides
implementation of visible-
only or dual mode lighting for aircraft requiring such external lighting more
rapidly and at less
expense than any other known approach, using the existing fixtures if desired.
An assembly according to the invention also may be implemented as a 'new
start' design for
exterior light fixtures, where its configuration is original, and it need not
duplicate the profile of an
existing lens or fit an existing fixture. In whatever the application,
however, the light assembly
according to the invention preferably has an outer surface that is conformal
to the outer contour of the
aircraft body on at least one edge, e.g., the leading edge of the assembly
meaning that the outer
surface of the assembly smoothly merges without substantial interruption or
discontinuity into the
contour of the outer surface of the aircraft body adjacent thereto.
An additional way to reduce the heat from the LEDs (or the arrays of LEDs)
while
maintaining an adequate brightness standard is accomplished using a brightness
enhancement effect
produced by flashing. All of the LEDs of the fixture are flashed on and off
together at a rate of lOHZ
to 20Hz, and most preferably at a rate of 12 to 15 Hz so as to produce the
psycho-optical effect known
as brightness enhancement, which makes a human see such flashing lights as
brighter than if they
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were on 100% of the time. Since the LEDs produce no heat for the portion of
the cycle during which
they are off, this reduces the amount of heat that must be dissipated, while
providing a perceptibly
similar level of brightness.
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.
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