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Three-Dimensional Imaging, Visualization, and Display 2010 and Display Technologies and Applications for Defense,Security, and Avionics IV, edited by Bahram Javidi, Jung-Young Son, John Tudor Thomas, Daniel D. Desjardins,

Proc. of SPIE Vol. 7690, 769016 2010 SPIE CCC code: 0277-786X/10/$18 doi: 10.1117/12.853032

Proc. of SPIE Vol. 7690 769016-1

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This paper will highlight certain characteristics of a panoramic display produced by L-3 Display Systems with its initial application in the F-35 strike fighter. This display has an active viewing area of eight-inches high by twenty-inches wide, and represents the largest single display used today in a tactical fighter cockpit.

2. DESIRABLE ATTRIBUTES OF A PANORAMIC DISPLAY Perhaps the most important attribute of a cockpit panoramic display (or any cockpit display) is its readability under any and all conditions. This includes all ambient luminance levels from full sunlight impinging on the display surface to the ability to operate under night flying conditions and compatibility with night-vision imaging goggles. A display with an integrated touch interface has the additional requirement to have a touch technology that performs under these same conditions. The reliability of the panoramic display is even more critical than smaller displays as a result of its multifunctional usage. In the F-35 fighter, the L-3 panoramic display, shown in Figure 2, is the pilots most critical means for accomplishing the mission. Any failures of the display will severely compromise if not eliminate the pilots ability to achieve success. For this reason, system designers generally elect to incorporate a high level of redundancy into the display system from the display surface and touch screen, through the driving electronics and processing system, and even into the power supply. No single failure will cause the display to be completely blank.

Figure 2: The panoramic cockpit display with touch-screen developed for the F-35. In addition to electrical redundancy, it is important that the display surface be designed in a redundant fashion. The L-3 panoramic display consists of a single piece of glass that is partitioned into two separate halves. By incorporating this redundancy into the design of the AMLCD glass itself, the display can achieve the seamless operation necessary to take full advantage of the twenty-inch wide screen. The backlight is partitioned into two independently controlled circuits, so that it does not represent a single-point failure.

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A panoramicallowing thewearing nigcompatibility The display design is captesting speciexplosive deforces, humito pass these .

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Proc. of SPIE Vol. 7690 769016-3

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characteristics. A display that achieves very high contrast ratio with high resolution will be perceived as having a good quality image. Key factors in achieving high contrast ratio are:

Very low optical system specular reflectance; Very low optical system diffuse reflectance; Very high display brightness (use of light-emitting diodes versus fluorescent bulbs in backlight); Very high AMLCD intrinsic contrast ratio.

Other system design factors which contribute to good optical performance are:

Wide backlight daytime dimming ratio (greater than 400:1) Wide backlight nighttime dimming ratio (greater than 1000:1) Large area uniformity better than 80% over the entire viewing area Fast AMLCD response time to reduce image blur in fast moving graphics or video

One factor in good optical performance which must be considered especially in the tactical fighter application is the effect of display luminance on canopy reflections. The display and its corresponding backlight system must be designed to reduce the effects of stray light which might reflect off of the glass canopy and cause viewing problems for the pilot in his forward field of view. This may be done with special films or coatings, similar to commercial privacy filters for laptop uses. Finally, good color saturation is key to providing a quality display capable of communicating necessary information to the pilot quickly. As shown in Figure 4, light-emitting diodes (LEDs) with separate red, green, and blue components yield the best color saturation and color gamut for the display. LEDs have in general resulted in much better quality displays than the earlier generation displays which utilized cold-cathode fluorescent lamps (CCFLs) for their illumination.

Figure 4: RGB LEDs give best color quality for AMLCD.

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Another keycockpit, is thgoggles. Aldisplays in tpresented thadesigners to AMLCD maconjunction the display requirement Figure 5 sho

For a panoraoperation denormal methreach and opuser can usedrop cursorsand order the

y performance he ability of thlthough in opertheir night-moat might interfcarefully spec

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modes of kpit, the xcessive tead, the rag-and-to move

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There are several touch-screen technologies in current use for the display system designer to select from. The selection process for the proper touch screen technology for a panoramic cockpit application, must consider the following requirements:

No impact to display contrast; No visible artifacts embedded within the screen (spacer balls, internal conductors); No impact to night-vision compatibility performance; No impact to EMI performance; Must work with a gloved finger or any stylus; Must perform flawlessly under all environmental conditions; Much have sufficient touch resolution to correctly follow the users activation;

From a mechanical standpoint, the choice of touch-screen technology should result in as narrow a border as possible and should have little impact on the display system mechanical envelope and overall power dissipation. Each touch technology involves a measurement when a touch event occurs. Different technologies are designed to react to the touch event via a change in the normal condition as shown in the Table I below.

Table I: Touch Technologies and Their Method of Measurement Measurement Parameter Touch Technology

Charge/Current Surface Capacitive

Change in capacitance Projective Capacitive

Time delay or delta Surface Acoustic Wave

Absence of IR light Optical, Infrared, Vision

Voltage Resistive

Mechanical bending waves Acoustic Pulse Recognition, Dispersive Signal

Mechanical Force Force Sensing

Presence of light (AMLCD Backlight) or capacitance or voltage

AMLCD in cell

Unfortunately, there is no single optimal touch-screen technology solution for a military cockpit display. All touch technologies have particular strengths and weaknesses. The requirements for each military system must be reviewed and compared with the known strengths and weakness of the candidate touch-screen technology with the knowledge that inevitably compromises will have to be made. These trade studies must be conducted early in the display development. In the case of a panoramic cockpit display, despite its inherent disadvantages, infrared technology seems to offer the very best in optical qualities, and in general, provides the best overall performance when measured against all system requirements.

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Other Performance Attributes and Trade Studies The ultimate display design will result in a display designed to look great under all conditions and still will meet all of the other system requirements. Many times these requirements may have conflicting attributes which require the designer to compromise on one requirement in order to obtain a good blend of specification performance. Examples of performance attributes which may be mutually exclusive or conflicting include:

AMLCD response time vs. AMLCD clearing point temperature Large area uniformity vs. canopy reflection reduction Low specular reflectance vs. EMI front shield attenuation (low resistance) AMLCD transmission vs. AMLCD color saturation High luminance levels vs. low power dissipation Mechanical robustness vs. low system weight.

Design for reliability requires a display design that is made for a twenty to thirty year life expectancy. Unfortunately, typical electronic component life-cycles are significantly shorter than this time period, so a robust components obsolescence plan must be developed early in the product life. System safety considerations will typically require that all software and firmware be certified in accordance with strict development standards. For firmware embedded in field-programmable-gate-arrays (FPGAs), certification to standard DO-254 may be required. Operational software must be written, tested, and certified to the requirements of DO-178. This firmware or software includes that which controls display functionality such as backlight control, heater control, touch-screen operation, and display built-in-test. While all of these performance trade-offs require compromises, no display can be designed which is not affordable for the ultimate customer. Cost is often in direct conflict with performance. Military systems typically have very low rates of production with a relatively small number of units produced over a long period of years. These high performance expectations offer constant opportunity for cost reduction and engineering value improvement trade studies. Programs such as the F-35 fighter display program are always exploring cutting edge technologies which have the ability to maintain or increase performance while offsetting costs.

4. CONCLUSION As can be seen, performance expectations for new generation tactical fighter displays are very high. There are many requirements whose individual solutions present conflicts that need to be evaluated through trade-off analyses. Fortunately, these technical challenges are the impetus that forces innovation which yields better displays. A new level of performance has been created in the design of the panoramic cockpit display. Its size and versatility have given the aircraft system-level engineers new ways to give the ultimate user, the airborne warfighter, more tools to complete their mission and greater situational awareness to ensure a safe return from the mission.

ACKNOWLEDGEMENTS The authors wish to thank and acknowledge our technology teammates and system design experts at Lockheed Martin Fort Worth Aeronautics System Division for their support in the development of the panoramic cockpit display for the F-35 Lightning II fighter aircraft.

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