DEGRADED VISUAL ENVIRONMENT

Cross Reference to Related Application

[001] This application claims priority from U.S. Patent Application No. 14/078,408, filed November 13, 2013 which is incorporated herein by reference in its entirety for all purposes.

Field of the Invention

[002] One or more embodiments of the present invention relate to illumination/visual reference systems for assisting in operating aircraft in a degraded visual environment and/or low environmental illumination.

Background

[003] Rotorcraft (e.g., helicopters) and VTOL (vertical takeoff and landing) aircraft have a natural tendency to stir particulates into the air with their downwash when operating near the Earth's surface. This typically occurs while maintaining or transitioning in or out of the hovering flight regime, at an altitude that is within one to two times the equivalent rotor diameter. In certain environments, a relatively high concentration of stirred particulates, typically dust, may significantly obscure the pilot(s) field of view (FOV). The particulates can result in the loss of outside visual references, or brownout (in a dust environment), which can induce spatial disorientation in a pilot. The pilot(s) may not be able to see the ground. Depending on conditions, particulates may comprise dust, sand, snow, or other materials that can become airborne either due to rotor downdraft or local weather conditions.

[004] The difficulty of a brownout situation is further compounded at night, because fewer visual cues are available. Further, pilots (especially military aviators) may be using night- vision goggles (NVGs) which typically restrict the FOV to 40°. Using NVGs, also referred to as flying "aided," provides a visual acuity of 20/25 at best [Army 2007 A], and is quite dependent on ambient lighting conditions. Due to the challenges involved in such operations, pilots learn to use a variety of compensatory methods.

[005] One method of compensation is to maintain enough forward airspeed during the approach and touchdown to outrun the formation of particulates and prevent the particulate cloud from enveloping the cockpit. While effective in some situations, this method is not suitable for many landing zones, particularly those that are rough, sloping, confined, or pinnacle. Another method is referred to as termination to a point OGE (out of ground effect) [Army 2007B, Army 2013]. This method requires more power. The initial approach is to a high hover position directly over the intended point of landing. The high hover position is used to stir and dissipate the dust before descending to the ground. Hovering OGE is effective is some situations, but there are disadvantages. First, depending on the aircraft gross weight and environmental conditions, the power required may not be available to hover OGE. Second, it may not be a tactically advisable maneuver, because it exposes the aircraft in its most vulnerable state for an extended period. Third, descending from an OGE hover surrounded by rapidly circulating dust can induce spatial disorientation, resulting in improper control manipulation, consequent aircraft drift, and/or an unanticipated, possibly damaging touchdown rate.

[006] Generally, in helicopters, once outside references are lost out of the windshield, the pilot's focus is directed through the chin bubble and/or other cockpit door windows. If references are lost through the chin bubble and windows, the pilot's focus transitions to the flight instruments or heads-up-display (HUD) symbology, and the approach is aborted with the application of power and a "go-around." Once above the dust with adequate visibility, the crew may continue visually and re-evaluate the situation.

[007] Regardless of the method employed, there is always the potential to become partially or completely enveloped in dust. At night, when shifting focus from the windshield to the chin bubble or other windows, NVG use provides additional limitations and when looking through NVGs, depth perception is severely limited. The pilot may not have a clear sight picture of the immediate ground surface during the final stage of an approach. Crosschecking the chin bubble or cockpit door window looking through NVGs requires a large head movement that can be hazardous during the critical final moments of an approach.

[008] An alternative, not printed in Army training manuals, is used in some cases to provide improved visibility beneath the aircraft. The landing light or search light (if non- infrared) is turned on, and the pilot looks beneath the NVG eyepieces and through the chin bubble or cockpit door window using the unaided eye. This technique can offer the best combination of available options by allowing the pilot to divide his/her attention by looking through the windshield using the NVGs (arrow 102) at horizon associated references and maintaining a good ground reference cross-check by glancing through the chin bubble unaided (arrow 104), as illustrated in FIG. 1.

[009] One problem with using landing lights or search lights in this way is that tactical considerations may be sacrificed to the intensity of the light. Further, the landing light and searchlight are considered incompatible with NVGs, because they are conventional white lights (unless the searchlight is infrared). The compatibility issue is, however, more of a misconception than a reality with modern NVGs. Modern NVGs, such as the AN/AVS- 6(V)3 (Exelis Night Vision, Roanoke VA), have automatic brightness control (ABC) and bright source protection (BSP) which are built-in features designed to prevent blinding the user or damaging the NVGs [Army 2010]. However, most white lights are still not conducive for use with NVGs, because ambient light is amplified approximately 2000-3000 times by the goggles, and BSP has the side effect of lowering resolution [Army 2007 A].

[0010] When coupled with the light amplification of the goggles, the landing light and searchlight, whether infrared (IR) or not, are beyond a practical intensity for NVG use in a degraded visual environment. This is particularly evident beyond moderate dust levels (as defined in the beginning of the Detailed Description below) with low lunar illumination or ambient light conditions. Although the infrared searchlight has adjustable brightness, it is a very coarse adjustment, has limited directional control, and, in some airframes, defaults to maximum brightness when power to it is cycled.

Summary of the Invention

[0011] Lighting/visual reference systems and methods for landing in a degraded visual environment are disclosed. The lighting systems comprise one or more lighting units mounted to an aircraft that is operable to hover near a landing zone. Each lighting unit is operable to provide adjustable illumination/visual reference to the landing zone, and has a radiant power output between a minimum and a maximum. The minimum radiant power output is just sufficient to allow a pilot to distinguish features in the landing zone when below a first altitude wherein the downwash from the aircraft rotors, propellers, or engines begins to raise particulates from the landing zone and continues to be just sufficient to allow the pilot to distinguish features as the pilot descends from the first altitude to termination at the landing zone. The particulates can include dust, sand, water, snow, or ice.

[0012] The maximum radiant power output is less than about five times the minimum power. In some embodiments the maximum radiant power output is less than about three times the minimum radiant power output. In some embodiments the maximum radiant power output is less than about two times the minimum radiant power output.

[0013] Each lighting unit can include a plurality of lighting elements collectively emitting light at a plurality of wavelengths. The plurality of wavelengths produce white, green, and infrared illumination; each illumination can be individually enabled. The plurality of lighting elements can be light emitting diodes (LEDs).

[0014] The illuminated area of the landing zone can be approximately equal in size and shape to the field of view of a pilot or crew member looking through a chin bubble or a side door or window of the aircraft. A shroud can be provided, limiting the emission of light to a direction toward the illuminated area of the landing zone as further defined by the use of various focused or collimated lenses. Each lighting unit can also include one or more lasers that can be aimed generally in the direction of the illuminated area of the landing zone (i.e., within the illuminated area). The lasers can emit light at a plurality of wavelengths including red, green, and infrared which can be individually enabled. In some embodiments, the lasers can be semiconductor lasers each having a power output of between about 0.1 mW and about 10 mW.

[0015] One or more lasers can create a pattern on the landing zone which changes as a function of altitude and/or attitude. A cross-pattern laser can improve motion cues and depth perception by providing visible quadrants on the surface, which can provide more distinct indications of longitudinal versus lateral aircraft movement, as well as surface texture.

Additionally, the size of the pattern will change as a function of altitude which can aid in depth perception. A spot projected from a laser onto the landing zone can change size as a function of altitude. A spot projected from a laser onto the landing zone can change shape as a function of altitude. Two spots projected from a laser onto the landing zone can have a separation which changes as a function of altitude.

[0016] A method for illuminating a landing zone is also provided. One or more lighting units are attached to an aircraft that is operable to perform vertical takeoffs and landings. Each lighting unit is operable to provide adjustable illumination to a landing zone, and has a radiant power output between a minimum and a maximum, wherein the minimum radiant power output is just sufficient to allow a pilot to distinguish features in the landing zone from below a first altitude wherein the aircraft rotors, propellers, or engines begins to raise particulates from the landing zone and continues to be just sufficient to allow the pilot to distinguish features as the pilot descends from the first altitude to termination at the landing zone. In some embodiments the maximum radiant power output can be less than about five times the minimum radiant power output. In some embodiments the maximum radiant power output can be less than about three times the minimum radiant power output. In some embodiments the maximum radiant power can be less than about two times the minimum radiant power output. During an approach or landing of the aircraft, the lighting units are left off until the aircraft descend below the first altitude, and then turned on below a second altitude wherein the second altitude is below the first altitude. Below the second altitude, the aircraft may be engulfed in particulates such that primary visual references are obscured. Brief Description of the Drawings

[0017] FIG. 1 shows the "cross-check" technique looking through and under NVGs.

[0018] FIG. 2 shows aircraft losses from non-combat causes for 2002-9.

[0019] FIG. 3 shows simulated airflow (3A) and dust density (3B) for a thrust-normalized advance ratio of 0.80.

[0020] FIG. 4 shows simulated airflow (4A) and dust density (4B) for a thrust-normalized advance ratio of 0.29.

[0021] FIG. 5 shows simulated airflow (5A) and dust density (5B) for a thrust-normalized advance ratio of 0.12.

[0022] FIG. 6 shows a concept illustration for a dust-light system mounted on a helicopter.

[0023] FIG. 7 shows an example of a cross-pattern laser.

[0024] FIG. 8 shows various views of a first dust-light system prototype

[0025] FIG. 9 shows an example mounting structure and connections

[0026] FIG. 10 shows various views of a second dust-light system prototype.

[0027] FIG. 11 shows the chin bubble FOV for the right pilot in a Black Hawk helicopter

[0028] FIG. 12 illustrates the inverse square law.

[0029] FIG. 13 shows two proposed mounting locations for dust-lights on a Black Hawk helicopter.

[0030] FIG. 14 shows a first mounting location with the access panel removed.

[0031] FIG. 15 shows a panel layout with dust-light mode selection switches.

[0032] FIG. 16 shows an example switch arrangement on the collective.

[0033] FIG. 17 A shows the cockpit view during heavy dust approach at 19 ft above ground level (AGL).

[0034] FIG. 17B shows the cockpit view during heavy dust approach at 9 ft AGL.

[0035] FIG. 18A shows the cockpit view during heavy dust approach at 3 ft AGL.

[0036] FIG. 18B shows the cockpit view during heavy dust approach at termination. Detailed Description

[0037] Before the present invention is described in detail, it is to be understood that unless otherwise indicated this invention is not limited to specific aircraft or specific lighting modalities. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

[0038] It must be noted that as used herein and in the claims, the singular forms "a," "and" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a lighting unit" includes two or more lighting units, and so forth.

[0039] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also

encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention. Where the term "about" is used in front of a numerical value, the value is deemed to be within ±10% of the numerical value.

[0040] As used herein, the term "degraded visual environment" (DVE) refers to any condition of reduced visibility. DVE can be caused by particulates as described below. DVE can also be caused by adverse ambient lighting conditions such as nighttime operation with low lunar illumination, low moon angle, sky obscuration, or absence of ground lighting.

[0041] As used herein, the term "particulate" refers to any small particles that can become airborne in a landing location either due to rotor downwash or due to local weather conditions. Examples include dust, sand, and snow. Examples described herein are general described using dust as an exemplary but non- limiting embodiment of particulates that can reduce visibility. Exemplary landing zones are dry, dusty surfaces, although degraded visible environments can also occur under conditions of heavy fog, rain, snow, water landings, marsh landings, and so on.

[0042] As used herein, the term "light dust" refers to a DVE in which objects can be identified beyond the region of a particulate cloud and the terrain surface is visible (i.e., an observer such as a pilot can see through the DVE). Notwithstanding, these objects and the terrain surface ("primary visual references") are "obscured" for all DVE regimes. [0043] As used herein, the term "moderate dust" refers to a DVE in which only objects within a particulate cloud can be identified and the terrain surface is visible (i.e., an observer can see part way through the DVE).

[0044] As used herein, the term "heavy dust" refers to a DVE in which no objects within a particulate cloud can be identified and the terrain surface is intermittently visible (i.e., visibility ends abruptly within the DVE).

[0045] As used herein, the term "severe dust" refers to a DVE in which no objects within a particulate cloud can be identified and terrain surface is not visible (i.e. there is virtually no visibility).

[0046] As used herein, the term "altitude" refers to the vertical position of an aircraft

(height above the Earth' s surface) relative to a position where the aircraft is stationary on the Earth's surface.

[0047] As used herein, the term "termination" refers to the end state of a landing approach where the "altitude" as defined above has reached zero.

[0048] The inventor has surprisingly found that pilots can improve their ability to land a rotary-wing aircraft by using a combination of aided and unaided viewing techniques (with and without night vision goggles) supported by a lighting system that aids visibility in DVEs. These techniques are especially useful when approaching a landing site in a dust environment at night. The inventor has identified a need for a purpose-built lighting system )a "dust-light system) that is specifically designed for night-time landing in DVEs. In addition, the lighting system can provide more adequate supplemental lighting and visual reference aids to support conventional, aided-only landing methods.

[0049] FIG. 2 shows the relative incidence of rotary wing combat non-hostile event losses for the years 2002-9 from a study on rotorcraft safety [Harrington 2010].

"Brownouts" or DVE accounted for the greatest number of combat non-hostile losses. The study concluded that an integrated systems approach would be required to overcome the hazards associated with dust environments, suggesting elements such as improved cockpit display symbology and auto-land capabilities.

[0050] Currently there are such prospective solutions and avionics-based technologies in different stages of development, testing, and use that entail the use of on-board databases and/or various sensors to construct useful imagery with corresponding flight symbology displayed inside the cockpit or on a heads-up-display monocle. While showing promise as integrated brownout landing solutions, these methods are complex in nature, and rely on multiple systems for proper functionality. They also introduce new human factors issues, formal training requirements, and extensive integration into existing platforms at a considerable price, particularly on a large-scale retrofit. The potential advantages of the dust- light system are that it is simple, lightweight, relatively low cost, and requires minimal technique adaptation for use. The dust- light system is not an attempt to stifle technology- based solutions, but rather to serve as an alternate, complementary system, or back-up system.

[0051] Researchers from the University of Glasgow conducted a simulation of helicopter brownout using fluid dynamics software to model various particle properties and their reactions under different flight conditions for both single rotor and tandem rotor

configurations. They compared dust simulation results using varying values of the "thrust- normalized advance ratio" [Phillips 2009]. This important term accounts for main rotor thrust, approach speed, and descent rate. Essentially, the larger the value, the higher forward airspeed is during the approach. FIGS. 3-5 illustrate that the predicted dust formation gains height and is more pronounced ahead of the aircraft as the approach closure rates become slower.

[0052] The images in FIGS. 3A, 4A, and 5A show the three-dimensional airflow pattern, and the images in FIGS. 3B, 4B, and 5B show the relative cross-sectional dust density.

FIGS. 3A & 3B are for a thrust-normalized advance ratio of 0.29. FIGS. 4A & 4B are for a thrust-normalized advance ratio of 0.80. FIGS. 5A & 5B are for a thrust-normalized advance ratio of 0.12. As the forward speed of the aircraft decreases (lower advance ratio), a larger cloud of dust is raised. Note that the area directly beneath and in front of the lower nose section (chin bubble area) has a very low relative dust density in all cases, suggesting that this can be a key area in which visual contact with the ground can be maintained given a suitable illumination method.

[0053] Embodiments of the present invention provide improved illumination to aid pilots in landing rotorcraft and VTOL aircraft in particulate (light dust to severe dust) landing conditions, especially under limited light conditions such as night-time landings and where tactical considerations require the use of low light levels to minimize visibility to outside observers. As will be detailed below, the lighting systems can have multiple modes and levels to provide good visual assistance to the pilot(s) to enable them to see the ground with sufficient visual acuity without making the aircraft excessively visible to outside observers. It should be further noted that, although embodiments are described for rotorcraft and VTOL aircraft that are operable to hover and perform vertical takeoffs and landings, actual landings may not be vertical. In most examples of DVE landings, the approach is not vertical.

However, the degradation of the visual environment is still a consequence of the use of a rotating blade or wing surface to generate lift or the use of thrust vectoring.

[0054] In some embodiments, dust-light systems can be installed singly or in pairs. A pair of dust-light systems, one on each side of the cockpit can be particularly useful for a typical cockpit crew comprising two pilots. Additional systems can also be provided for other crew members. These can be either mounted to the airframe or handheld, for example, by a crew member located at an open doorway.

[0055] In some embodiments, the dust-lights are adapted for use in conjunction with NVGs. For example, the pilot can look through the NVGs out of the windshield and crosscheck beneath the goggles with the unaided eye through the chin bubble and/or out of the cockpit door or door windows; the pilot need not move their head, just their eyes. Minimal adaptation by the pilots is required; the new lighting system facilitates landing using methods already familiar to trained pilots.

[0056] In exemplary embodiments, a system is provided for a Black Hawk helicopter.

The typical altitude below which dust envelopment occurs is about 50 ft. Below this altitude, pilots may transition to looking through the chin bubble during an approach. It will be apparent to one of ordinary skill that the lower the altitude from which the lights are employed, the less observable the aircraft will be from the surrounding environment. The lighting system need only provide enough light to aid the pilot in seeing the landing zone visible through the chin bubble at distances of 50 ft or less. In some embodiments, the lighting system is optimized for use below 20 ft. Some observations by the inventor suggest that operation at 20 ft and below provides sufficient light to provide adequate assistance to the pilot in heavy dust conditions.

[0057] In some embodiments visible light is used of sufficient intensity that the pilot can see the landing zone with the unaided eye below his NVGs. The light can be limited so as not to cause adverse reflections off dust during the approach, particularly through the NVGs. In some embodiments, laser light can be used to supplement depth perception by providing an identifiable point where the laser terminates on the surface. The surface immediately surrounding the laser termination point can be illuminated more generally, for example, using LED light sources or other low-level light sources as shown in FIG. 6. In some embodiments the laser light is omitted.

[0058] FIG. 6 shows the laser 602 as lines of visible light (e.g., green and/or red) with a termination point 604 shown as a sunburst symbol, exaggerated in size for the purpose of clarity. The LED beam width is represented by the dotted lines 606, and the illuminated surface is represented by the oval 608 surrounding the sunburst. Also shown is the normal FOV 610 of the right-hand pilot through NVGs and the windshield. In some embodiments, the LEDs can be white and/or green for the unaided eye, looking through the chin bubble below the NVGs. In some embodiments, the LEDs and/or laser can be infrared. When infrared light is selected (e.g., for tactical reasons to reduce visibility), the pilot makes all observations through the NVGs moving his head as necessary to look through the NVGs and the chin bubble. In some embodiments, both visible and infrared light sources are provided, and the pilot can choose light sources (and intensities) according to the needs of a particular approach and/or landing. In some embodiments, a green and red laser can be projected simultaneously to provide a beam that is visible in and out of dust conditions. Table 1 provides a reference under which conditions each illumination mode may be visible.

Table 1

Visibility of Emitters in Different Conditions

No Dust Dust

Source Unaided Aided Unaided Aided

LED

White X X X X

Green X X

Infrared X X

Laser

Red X X X

Green X X

Infrared X X

[0059] The specifications for the lasers and low level light sources can vary according to the needs of a particular aircraft and its landing characteristics. The output power can be made adjustable, either by the pilot directly, or with the assistance of some form of automated intensity adjustment aided by a reflected light sensor. An automated system can be designed to provide just enough light to provide a desired reflected light intensity returned to the aircraft with a maximum allowed level based on tactical considerations.

[0060] Any laser source providing a beam of appropriate wavelength and power can be used. In the configurations of Examples 1 and 2, three lasers, two visible and one infrared are provided to accommodate different terrain, particulate, and tactical situations. The pilot can select whichever provides the best visibility subject to operating constraints. Typically, lasers with an output power of between about 0.1 mW and about 10 mW are suitable, although other powers can also be used. In some embodiments, the laser output power is between about 0.1 mW and about 0.5 mW. In some embodiments, the laser output power is between about 0.5 mW and about 2 mW. In some embodiments, the laser output power is between about 2 mW and about 5 mW. In some embodiments, the laser output power is between about 5 mW and about 10 mW. These lasers can be semiconductor lasers such as those used in laser-pointing and laser- sighting applications. A typical green laser can have a wavelength of about 532 nm; a typical red laser can have a wavelength of about 650 nm; and a typical infrared laser can have a wavelength of about 780 nm, although these wavelengths can vary, and other wavelengths can be used.

[0061] In some embodiments, specific wavelengths for LEDs and/or lasers can be selected to be compatible with Aircraft Survivability Equipment (ASE). ASE can detect, identify, and alert aircrew to hostile threats (e.g., missiles), and can deploy countermeasures. These systems detect light (and targeting lasers) at wavelengths that are classified. Dust-light LED and laser wavelengths can be selected for compatibility with relevant ASE wavelengths.

[0062] In some embodiments, the laser light can create a pattern on the landing zone which changes as a function of altitude and/or aircraft attitude (pitch, yaw, and roll). In some embodiments, a cross-pattern (FIG.7) can be used to improve motion and depth perception, provide visible quadrants on the surface and more distinct indications of longitudinal versus lateral aircraft movement, as well as surface texture. The size of the pattern can change as a function of altitude aiding in depth perception. The rate of change of the size of the pattern with altitude can be adjusted by varying the fan angle of the laser pattern generator. For example, a fan angle of about 15-20° can provide good distance discrimination for typical degraded- visual-environment landing conditions.

[0063] Cross-patterns can be generated in various ways. For example, two lasers with cylindrical lenses can generate two line patterns that can be arranged in a cross. Diffractive or refractive optics can generate a cross pattern from a single laser. An imaging system can be used to image a cross-shaped mask. A typical cross-pattern generator produces lines that fan out at an angle that can be designed to suit application needs. Fan angles between about 10° and about 100° are readily available.

[0064] In some embodiments, the light from the laser is well-collimated such that the projected spot size on the ground is substantially constant during approach. In some embodiments, the laser can be focused or divergent with either fixed or adjustable focal length/divergence angle. A converging or diverging beam can be adjusted so that the projected spot size on the ground changes with altitude and provides an additional visual cue to the pilot as to current altitude at short range where conventional radar and barometric altimeters do not provide adequate precision and accuracy. Astigmatism can also be deliberately used such that the projected spot has an aspect ratio that changes with altitude. For example, a cylindrical lens can provide a different effective focal length along one axis compared to a perpendicular axis. A round spot will be projected at one altitude, and the spot will appear to be elongated along one axis or the other as the altitude deviates from that giving the round spot. In some embodiments, the focal lengths are adjusted to give a round spot at termination. In some embodiments two lasers can be aimed at different angles such that the separation of their projected spots varies with altitude. In some embodiments the projected spots coincide when termination is reached.

[0065] The laser spots can provide useful visual cues as to the location of a surface that may be otherwise difficult to see through the particulates and low-light conditions. A larger illuminated area can also be valuable to aid the pilot in landing at a particular target location, avoiding any local obstacles either on or above the ground. In some embodiments, the larger illuminated area is defined by a FOV around the laser spot, although it is also possible to point the laser spot and illuminated area independently toward different locations. Any low- level illumination source can be used, including conventional landing lights set at low power, although typical aircraft control systems are not configured to operate landing lights with the small FOV and low intensities optimal for particulate environments and tactical or clandestine operations. The power levels for conventional landing lights and dust-lights can be a more than an order of magnitude higher than those of an ideal dust- light system, as can the desired FOV. Accordingly, a dedicated dust- light system can be a preferred

implementation.

[0066] In some embodiments LEDs are used and can provide a suitable combination of power level and controllability. In some embodiments an array of LEDs of each color is provided. These can be arranged in any convenient geometric configuration such as the ring arrangement described in Example 1 and Example 2. Other possible configurations would be apparent to one of skill in the art. The minimum total radiant power output should be just sufficient to provide ground visibility to the pilot as he descends below a particular altitude such as the 50 ft or 20 ft suggested above for use with the Black Hawk helicopter. The maximum radiant power output should be limited so as not to provide more light than is necessary to assist the pilot, for example, no more than 2, 3, or 5 times the minimum radiant power output. For tactical use, the illumination level can be further controlled, either manually or automatically so as to maintain only the minimum level needed at any given time and location. The illuminated area can be kept small to match the FOV of the pilot looking, for example, through the chin bubble. The light assembly can be further shrouded and aimed so that the light has low visibility to any observer outside the FOV. In some embodiments, a single high-power LED with collimating optics can be used and can provide more accurate beam focusing, uniform illumination, and broad brightness range. In some embodiments, the total power for each array of LEDs can be between about 0.1 W and about 1 W. In some embodiments, the total power for each array of LEDs can be between about 1 W and about 3 W. In some embodiments, the total power for each array of LEDs can be between about 3 W and about 10 W. In some embodiments, the total power for each array of LEDs can be between about 10 W and about 20 W. In some embodiments the total power for each array of LEDs is selected based on the size and configuration of a particular aircraft. By comparison, the typical prior art landing lights and searchlights operate at or above about 600 W and 250 W respectively, and cannot readily provide the low-level controlled intensities of the dust- light system, even if it were possible to aim them in a useful direction for illuminating the surface seen through the chin bubble.

[0067] Dust- light systems can aid in maintaining or establishing outside references in what would otherwise be total darkness, or particulate-entrained NVG-green-hue. Even where general illumination cannot penetrate dust completely to a surface, laser spots and patterns can often produce an identifiable termination point.

[0068] In some embodiments, the aim of the dust-light system is fixed at installation based on an average pilot size and eye location. In some embodiments, fine tuning of the beam direction can be provided using a suitable gimble mount that allows beam direction adjustment both up and down and side to side. The adjustment can allow optimization of the aim of the dust-light system for a particular combination of pilot, seat adjustments, and aircraft. Example 1: A multiwavelen2th dust-light assembly with both LEDs and lasers

[0069] FIGS. 8A-C show views of a design for an exemplary dust- light assembly. A five-inch diameter mounting flange has a depth of about 2-3 in, and a weight of about 5 lbs. Three central recesses 802 are provided to mount red, green, and infrared semiconductor lasers. The surrounding recesses 804-808 house the LEDs by type in concentric rings. From inner to outer rings the order is infrared 804, green 806, and white 808. The chamfered outermost ring shroud is designed to shield the LED beam so that it only illuminates a target area consistent with the FOV available through a single chin bubble at 50 ft and below. In addition, the outer ring serves to shroud the light source from outside observation in a tactical environment. The inner face of the dust-light is further protected by a scratch-proof, non- reflective, tinted glass which also aids in reducing outside observation.

[0070] The outer flange of the unit mounts flush to the aircraft exterior to a fixed flange using four bolts with thread locking compound, and further sealed around the perimeter of the unit using standard nonpermanent compound (e.g., PRO-SEAL ^® made by Proseal, Adlington, Cheshire UK). The mounting configuration is similar to that of the Electro- Optic Missile Sensors (EOMS) of the Common Missile Warning System (CMWS), shown in FIG. 9.

Power can be provided to the back of the unit via a plug connection 902, supplying 28 VDC from the number 2 DC primary bus. Example 2: A multiwavelen2th dust-light assembly with LEDs, lasers and an optical pattern 2enerator

[0071] FIGS. 10A-B show views of another design for an exemplary dust-light assembly. As for Example 1 , the assembly has a five-inch diameter mounting flange, a depth of about 2-3 in, and a weight of about 5 lbs. LEDs 1002 are evenly spaced at 120° intervals around a circle. Lasers 1004 with individual lens assemblies are also spaced at 120° intervals between the LEDs. An optical pattern generator 1008 is located in the center. The optical pattern generator can be a green cross-pattern laser.

[0072] All light emitters can have individual heat sinks. As for Example 1 , an outer ring serves to shroud the light source from outside observation in a tactical environment. The inner face of the dust-light is further protected by a scratch-proof, non-reflective, tinted glass which also aids in reducing outside observation. The mounting arrangement and power connections can be provided as for Example 1.

Example 3: Aircraft Inte2ration

[0073] In order to adapt a dust-light system to a specific airframe, the ergonomics of the cockpit layout and nose section of the aircraft must be taken into account. One of the primary considerations is the FOV from the pilots' perspective through the chin bubble. In this example, integration is described for a Black Hawk helicopter. The chin bubble in a Black Hawk is reasonably sized, but does not provide much forward looking capability. Rather it provides more lateral and downward visibility as shown in FIG. 11.

[0074] A cross-pattern 1102 (generated for example by the laser cross-pattern generator of FIG. 7) shows the approximate center of the FOV through the chin bubble for the right- hand pilot. When the aircraft is on the ground, the fixed dust-lights can be aimed at their respective chin bubble FOV center. The seat position from which the image in FIG. 11 was captured is full aft, and mid-position height, in accordance with the design eye point for a 70- inch tall pilot. The design eye point for the UH-60 in accordance with the Army field manual [Army 2007 A], is to have the ground in view beginning at 12 ft from the nose (with the aircraft on the ground). Measuring from the approximate pilot's eye position, the viewing angle ranges are found to be approximately 42-49° down and approximately 18-22° outward. The seats are capable of adjusting a total of 5 inches fore/aft and up/down. The anti-torque pedals are shown full forward, but can be adjusted fore/aft a total of 6.5 inches. The FOV from the left pilot seat is approximately the same. These measurements cannot account for every possible combination of height, seat position, pedal adjustment, and anthropometric variability, but they are valid for the majority of military aviators given the constraints of the HH-60L cockpit.

[0075] Visible surface area outside the chin bubble from the pilot' s perspective is approximately 6.5 ft ² with the aircraft on the ground. Following the inverse square law in regard to area, as shown in FIG. 12, it is evident that visible area increases by multiplying by the square of the radius (distance) r, where r is the distance from the pilot's eyes to the ground along the central FOV axis, i.e., 9 ft.

[0076] At 50 feet AGL, measured from the surface to the radar altimeter antenna, the visible surface area through the chin bubble is approximately 400 ft ² , based on a 45° degree viewing angle. Shifting of the pilot's head or changing the aircraft attitude can alter this figure drastically, but it is necessary to establish a baseline figure for preliminary beam divergence for localized illumination- which in this case is approximately 18-20°. Shifting of the pilots head and changing the aircraft pitch attitude can alter this figure drastically, but these estimates can be used to establish a baseline figure for a preliminary design.

[0077] The dust-light can be located in an area which can readily provide the proper positioning for the system to work effectively, while minimizing the required modification to existing airframe structure. Two primary locations 1302 and 1304 are identified in FIG. 13.

[0078] If the AN/AVR-2B Laser Warning System is installed on the aircraft, the associated mounting structure can also serve as a potential location for the dust-lights.

Location 1302 is compatible with achieving the proper beam angle and is practical in that it only requires modification to an existing modular component, requiring no direct airframe modification.

[0079] Location 1304 offers placement of the dust-light that is more aligned with the required aiming direction for the dust-light. The drawback is that location 1304 would require more airframe modifications than location 1302. The modifications required would consist of cutting sheet metal and drilling using a circular template, which may or may not be considered a unit-level maintenance action, depending on the organizational resources. FIG. 14 shows the space behind location 1304 from a vantage point within the cockpit and behind the anti-torque pedals, with an interior panel removed. The intended location of the sheet metal modification and dust-light installation is indicated by the circle 1402. The control rod running through the circle is offset above and to the side of the mounting site, and will not cause interference.

[0080] In some embodiments, the controls for a dust-light system can be mounted on a cockpit panel as shown in FIG. 15. FIG. 15 shows a cockpit panel mounted dust-light mode selector. The selectable modes of the dust- lights are controlled using a modular panel installed in the lower console of the aircraft. The specific placement of the panel within the console can be selected for pilot convenience based on available space for any particular aircraft. The panel, as shown in FIG. 15 can allow for independent mode selection of light and lasers. Any light or laser mode can be individually selected. Particular useful combinations of lights can also be selected. For example, IR LEDs and lasers can be automatically engaged with green LEDs and lasers to smooth the transition from unaided to aided viewing (i.e., when switching to NVG viewing).

[0081] In some embodiments, the dust-lights can be controlled with switches mounted on the collective (control stick) as shown in FIG. 16. In some embodiments, the existing searchlight switch (1602 in FIG. 16) can be replaced with a split rocker switch: one side for the dust-light power, and the other side for the searchlight functions. In some embodiments, the four-way searchlight control (1604) can be replaced with a five-way control where the fifth position can be for dust-light power.

[0082] These possible control placement options would provide a seamless integration, requiring no change to the pilots' natural hand placement. The only change would be in tactile identification of the appropriate switch. One of ordinary skill would recognize that many variations of control placement are possible both for new cockpit designs and for retrofits into existing cockpit control layouts. Example 4: an approach sequence

[0083] FIGS. 17 and 18 show a photo sequence taken during a single approach into a heavy dust landing zone. Looking closely, one can observe the dust formation and visibility in relation to altitude. FIG. 17A shows the aircraft at 19 ft above ground level; the dust cloud is beginning to come into view from the cockpit.

[0084] The dust obscures the chin bubble first as the rotor downwash begins to shear material from the surface. As the helicopter closes on a landing surface, a surrounding wall of dust forms, and the FOV through the chin bubble begins to clear, as shown in FIG. 17B, where the aircraft is at 9 ft above ground level. This is consistent with the dust simulation models shown in [Phillips 2009] that are reproduced in FIGS. 3-5. As the helicopter continues to descend, the surrounding dust-entrained air mass begins to circulate through the rotor system, further degrading visibility as shown in FIG. 18A, where the aircraft is at 3 ft above ground level.

[0085] However, visibility continues to improve through the chin bubble all the way to termination on the ground illustrated in FIG. 18B. The illustrated approach was made generally into the wind to a specific point with low touchdown speed resulting in about a one foot roll-out. Conducting this approach at night using NVGs would have been far more challenging, and could have easily resulted in a go-around. The area beneath the chin bubble would have been completely dark and would have offered no outside reference to the unaided eye; the pilot would have had to repeatedly move his head downward to look through the chin bubble using his NVGs to gain reference during this critical stage. Making such head movements is not ideal and potentially unsafe.

[0086] It will be understood that the descriptions of one or more embodiments of the present invention do not limit the various alternative, modified and equivalent embodiments which may be included within the spirit and scope of the present invention as defined by the appended claims. Furthermore, in the detailed description above, numerous specific details are set forth to provide an understanding of various embodiments of the present invention.

However, one or more embodiments of the present invention may be practiced without these specific details. In other instances, well known methods, procedures, and components have not been described in detail so as not to unnecessarily obscure aspects of the present embodiments. References

[Army 2007 A] Field Manual 3-04.203 Fundamentals of Flight, Dept. of the Army, Washington, D.C. [Army 2007B] Training Circular 1-237 Aircrew Training Manual, Utility Helicopter, H-60 Series, Dept. of the Army, Washington, D.C.

[Army 2008] Army Regulation 95-1 Aviation Flight Regulations, Dept. of the Army, Washington, D.C.

[Army 2010] Technical Manual 1-1520-253-10 Operator's Manual for HH-60L Helicopter, Dept. of the Army, Washington, D.C.

[Army 2013] Training Circular 3-04.33 Aircrew Training Manual, Utility Helicopter, H-60 Series, Dept. of the Army, Washington, D.C.

[Harrington 2010] Harrington, W. et ah, "3D-LZ Brownout Landing Solution," American Helicopter Society 66 ^th Annual Forum, Phoenix, AZ, Ann. Forum Proc. - AHS, 66 (2010), 983-1001.

[Phillips 2009] Phillips, C. & Brown, R.E., (2009): "Eulerian Simulation of the Fluid Dynamics of Helicopter Brownout," Journal of Aircraft, 46 (2009), 1416-29, doi:

10.2514/1.41999.