Pilot workload is rapidly approaching unmanageable proportions. Programs involving sensor fusion and technologies such as Head-up-Displays and Multi-function Displays are being pursued to help the pilot reduce workload and increase their situational awareness. The Helmet-Mounted Systems Technology program office is developing an integrated Helmet-mounted Display system which will dramatically increase the pilot's situational awareness under all operational conditions and improve weapon system mission effectiveness. In order to aëcomplish this, the program must take into account requirements, current state-of-the-art and projected availability of technologies. The HMST program office uses a System Engineering approach to tie together the key technologies and interfaces which are required in the development of helmet-mounted displays. Several of the key technologies discussed in this paper include 3-D audio, a high voltage quick disconnect connector, displays and standardized symbology.
The United States Air Force realizes there is great benefit to be gained from helmet-mounted display (HMD) technology when compared with traditional head-down displays. HMDs reduce military aircrew workload and improve their performance by mounting information display systems directly on the crew member's helmet. As the crew member concentrates outside the cockpit, information essential for successful mission execution remains within his field-of-view; regardless of his head position. However, mounting a display system on the helmet presents many design and safety related challenges. The Air Force's Interim - Night Integrated Goggle and Head Tracking System (I-NIGHTS) Program identified many of the challenges associated with HMDs. Three of these challenges discussed here are fit, weight/center-of-gravity, and ejection compatibility. Fitting a HMD involves more than just getting a head inside the helmet. The "fit equation" includes comfort, optical accommodation, and helmet stability. The lack of effective design in just one of these factors can negate any tactical advantage the HMD provides. HMDs also add to the weight supported by the crew member's head and neck. This weight generates significant forces during high G maneuvers and emergency situations such as ejection. How much weight and what center-of-gravity can the neck tolerate without injury or fatality? The Air Force I-NIGHTS Program encountered these challenges and serves as a starting point to bound their solutions
The addition of night vision devices (NVDs) to military fixed wing aircraft has resulted in the most significant increase in operational capability since the advent of computer controlled weapon systems and flight controls. This paper will briefly discuss the operational enhancements and limitations afforded by the application of NVDs to fixed wing aircraft, and then more thoroughly discuss a few of the lessons learned from testing and employment as seen from the eyes of operators. For the purpose of this paper, the term NVD will refer to both night vision goggles (NVGs) and forward-looking infrared (FLIR) systems. Other aircraft systems contributing to the night mission will be briefly discussed later in the paper.
With the development of the integrated combat aircraft cockpit, advanced display concepts will become increasingly important if pilot's workload is to be maintained at a suitable level for effective missions to be flown. The Defence Research Agency (formerly RAE Farnborough) has been involved with the development of helmet-mounted display devices since the 1970s, in order to assess their suitability for integration into the modem combat aircraft cockpit. This paper gives an operator's perspective of the helmet mounted devices trialled, covering their evolution in simulators to flight trials in fast jets. Additionally, the impact of this technology on the development of future combat aircraft and associated flight simulation is addressed.
A helmet display that has the ability to present imageiy from both NVGand FLIR sensors provides the best visual performance under a wide range of operating conditions from daylight to total darkness, because it combines the complementary advantages of the two different types of sensor. The pilot can select his sensor and operating mode to maintain imagery during natural conditions such as high humidity, thermal gradients or total darkness that would otherwise result in poor or unuseable display contrast. Design requirements for a multi image source helmet mounted display needed for this approach are severe, since aircrew expect no compromises in image quality or physiological protection, despite the extra hardware compared with a simpler HMD or NVG. The system advantages are significant however, and a new helmet display that presents both intensifier and CRT imagery is being designed for both fixed and rotary wing applications.
The applications of color symbology, graphics, and imagery in helmet-mounted displays have the potential to reduce workload and improve piloting performance. Unfortunately, there are three well-recognized paradigms that disallow the use of color in helmet-mounted displays in aviation environments. We provide evidence of three corresponding paradigm shfts that encourage the use of color in these displays. The rationales for these paradigm shifts are based on new methods of training and rehearsing, new lighting environments, and new display technologies.
The U.S. Army's AH64 Apache helicopter performance during the Panama invasion and Desert Storm has silenced years of skeptical speculation regarding the utility of a visually coupled helmet-mounted display (HMD) in combat. Unfortunately, in the fixed wing community, pilot night vision is limited to viewing a I-HiD for FLIR imagery or image intensification (12) from a helmet mounted goggle. Presently, restricted visual freedom and high head/neck ejection safety risks are accepted penalties for operating at night. Full visual freedom during night missions is a feature not yet afforded to any U.S. military fighter aircraft. This paper will focus specifically on a candidate HMD system for the night attack mission. Included are trade-off discussions relative to several specific design decisions.
A novel simulator display system is described. The display consists of a full field of view rear screen projection display and a narrow field of view high resolution helmet-mounted display (HMD). The HMD is worn by the pilot within the projection display. The virtual image of the HMD is thus superimposed upon the real image of the projection display. This hybrid approach to building a wide field of view display takes advantage of the beneficial aspects of both projection displays and HMDs. The result is a low cost total field of view display with high resolution. Several system design problems arise in the integration of the HMDwith the projection display. These issues are discussed, and include: the design of an HMD eyepiece with minimal obtrusiveness, visual blending of the HMD imagery with the projected imagery, and timing and perspective issues relating to the computer generated imagery presented by both the HMD and the projection display.
The goal of the cathode ray tube (CRT) helmet-mounted display (HMD) project was development and demonstration of a low-cost monochrome display incorporating see-through optics. The HMD was also to be integrable with a variety of image generation systems and suitable for use with low-cost cockpit trainers and night vision goggles (NVG) training applications. A final goal for the HMD was to provide a full field of regard (FOR) using a head-tracker system. The resultant HMD design included two 1 inch CRTs used with a simple optical design of beam splitters and spherical mirrors. The design provides for approximately 50% transmission and reflectance capabilities for observing the 30 degree(s) vertical X 40 degree(s) horizontal biocular instantaneous field-of-view visual image from a graphic image generator system. This design provides for a theoretical maximum of 10.8% of the CRT image source intensity arriving at the eye. Initial tests of image intensity at the eye for an average out-the-window scene have yielded 12 to 13 Foot Lamberts with the capability of providing approximately 130 Foot Lamberts. Invoking a software 'own ship' mask to 'blackout' the visual image, the user can monitor 'in-cockpit' instrumentation utilizing the see- through characteristics of the optics. The CRTs are operated at a TV line rate with a modulation transfer function (MTF) of approximately 65%. The small beam spot size and the high MTF provide for an enhanced image display. The display electronics are designed to provide a monochrome video picture based on an RS170 video input.
The goal of this helmet-mounted display (HMD) project was development and demonstration of a low-cost color display incorporating see-through optics. A full field-of-regard visual presentation was to be provided through the use of a head-tracker system and the HMD was to be suitable for use with low-cost cockpit trainers. The color imaging devices selected for the project are commercially available liquid crystal display (LCD) panels. The LCDs are 3.0 inch (diagonal) thin film transistor (TFT) types using a delta format for the red, green, blue (RGB) matrix. Fiber optic light panels mounted behind the LCDs provide a cool light source of greater than 3400 foot-lamberts (ft-L). Approximately 3 percent of the applied light source is emitted by the LCD image source. The video displayed is in a 3:4 format representing a 30 degree(s) vertical by 40 degree(s) horizontal biocular instantaneous field-of-view (IFOV) visual image from a graphic image generation system and is controlled in a full field of regard based on positional information from a head-tracker system. The optical elements of the HMD are designed as an exit pupil forming, see-through system and require the eye to be in a 15 mm volume for viewing the scene. The beam splitting function of the optics allows the user to see through the optics for reading cockpit instrumentation, while viewing outside the cockpit reveals the out-the-window (OTW) scene. The optic design allows for the IFOV to be displayed through a set of field lens, relay lens, folding mirror, beam splitter and spherical mirror system. The beam splitters and spherical mirrors for both optical paths are coated for approximately 50 percent transmission and reflectance. This approach, combined with the losses through the rest of the optical path, provides a theoretical maximum of 10.9 percent of the LCD image source intensity arriving at the eye. Initial tests of image intensity at the eye for a full white scene have measured at approximately 11 ft-L.
From very early times, as soon as man had his first thoughts, there was a strongdesire to communicate them to others of his kind. Broken branches and a rock pile, indicated trails and directions to be taken. Sketches of animals and weapons such as spears, bow and arrow, were drawn on the ground. This advanced to Hieroglyphics where complete stories were painted in picture form on cave walls for posterity to note. As man's thoughts became more sophisticated, language and communicating skills became more demanding. During this period man thought in wonderment at the first large screen display, the night display of stars, and attempted to assign meanings to the shapes and movements of the star groups and the planets. In the 'lOs Gerard Piel wrote a book called the "Acceleration of History". In one section he talks about the relationship of the various ages, where he depicted the increase in knowledge with each age and the duration of the age. From the curve (See Figure 1) we see that as we enter the nuclear age the increase in knowledge has almost become asymptote to the vertical axis and the duration of each age is shorter and shorter. Transfer of information, in this time of exploding knowledge, demands the most efficient systems available. This dictates real time visual displays to assure that the "sight" of man is most efficiently utilized. Today, the proliferation of information from the many sensing and situational requirements in a modem aircraft cockpit environment is nearing overload. Many believe that the answer to alleviate this problem is a helmet visor display capable of superimposing necessary tactical and logistical information over the pilot's panoramic view of the cockpit and the outside world. Such a display system imposes stringent requirements not only on the computer and optical interface but is pressing the state of the art on the light source that eventually projects the image onto the visor or combining glass. To have a display that is discemable both during daylight and night operation is even more challenging for the light source, with the day operation being the most difficult. Further, raster (video) displays are far more demanding than the relatively slow writing speed experienced in the stroke mode of operation.
Several techniques have been published for measuring the performance of cathode ray tube (CRT) displays. Our goal was to find a measurement technique that could be implemented with commercially available hardware, and that could be used to quickly and accurately assess the performance of a CRT display. This paper discusses several subjective and objective assessment techniques and compares the results obtained from the application of these techniques to a miniature CRT used in helmet-mounted displays.
Honeywell has developed a quantitative image quality model for the Helmet Mounted Display (HMD) electro-optical systems that will predict the optical performance and image quality of a given system configuration. The linear systems model includes modules for the image intensifier objective, image intensifier tube, fiber optic faceplates and tapers, charge coupled device (CCD) camera, liquid crystal display (LCD) or CRT image source, relay optics, electronic filtering and preprocessing, and a perception model for the eye. Sine wave and square wave system response are predicted via modulation transform function (MTF) calculations as well as the maximum resolution and a measurement of just noticeable differences (jnd's) as perceived by the human eye. The model will allow the system designer to quickly and inexpensively evaluate complex systems tradeoffs and modifications to advanced HMD systems.
The importance of fit for helmet ensembles is not limited to just comfort. It impacts most other safety and performance needs of the helmets, including helmet retention, and optical and acoustical performance. The addition of optical systems to helmet ensembles increases the need for precision in fit. Helmet systems which were previously acceptable in terms of fit do not necessarily fit well enough to accommodate new performance requirements. The increased need for precision has introduced the need for better definition of human anthropometry for helmet design as well as definition of the head and helmet interface. Traditional anthropometry (human body measurements taken with calipers, or head boards, etc.) is no longer adequate. For advanced helmet systems, data on the shape, or change in the surface curvature and how this relates to helmet systems in three-dimensional space, is now a necessity. In fact, use of the old style of anthropometry can and has created problems rather than resolve them. This paper discusses some of the problems with the old methods and introduces new technologies and research which is being done to address the needs.
The traditional head-up display (HUD) used in most modern fighter aircraft presents attitude information that is both conformal to the outside world and aligned with the body-axis of the aircraft. The introduction of helmet-mounted display (HMD) technology into simulated and actual flight environments has introduced an interesting issue regarding the presentation of attitude information. This information can be presented conformally or relative to the aircraft's body-axis, but not both (except in the special case where the pilot's line of sight is directly matched with the aircraft's body-axis). The question addressed with this study was whether attitude information displayed in an HMD should be presented with respect to the real world (conformally) or to the aircraft's body-axis. To answer this, both conformal and body-axis attitude symbology were compared under simulated air combat situations. The results of this study indicated that the body-axis concept was a more effective HMD display. A detailed description of the flight task and results of this study will be presented.
As part of the High-Angle-of-Attack Technology Program (HATP), two integrated pictorial displays have been developed for piloted simulation evaluations and, ultimately, for flight testing on board the F/A-18 High Alpha Research Vehicle (HARV). The first concept is a nosepointing display which illustrates the range of control the pilot has over the aircraft nose. The second concept is a predictive flightpath display that allows the pilot to see how his current control inputs will affect his aircraft's future position and orientation. The development of both display concepts will be discussed, as well as the results from a piloted simulation experiment in which pilots viewed the flightpath display in a wide-field-of-view Helmet-Mounted Display (HMD) while engaged in an air-combat situation.
To investigate the breadth of visual illusions experienced by aviators flying with night vision devices (NVDs), an open-ended questionnaire was distributed to the military helicopter community. Of the 242 returned questionnaires, there were 221 image intensification (I2) reports and 21 thermal imaging system reports. Most sensory events occurred at night, during low illumination, good weather, and over varied terrain. Contributing factors included inexperience, division of attention, and fatigue. Frequently reported illusions were misjudgments of drift, clearance, height above the terrain, and attitude. Also reported were illusions due to external lights and disturbed depth perception caused by differences in brightness between I2 tubes. Other respondents cited hardware problems and physiological effects. There were no obvious differences between the experiences of I2 users and FLIR (forward-looking infrared) users. Although incidence rates cannot be inferred from these data, the variety of aviator reports will be useful to all those connected with the human factors and safety of NVDs.
Visually coupled system developments have led to the concept of a Virtual Cockpit known as the Super Cockpit. Advances in Super Cockpit enabling technologies has resulted in an exciting spin-off called Virtual Environments or Virtual Reality. Press release claim almost limitless possibilities for this technology. Unfortunately the level of technology required to achieve actual Virtual Reality (VR) has still to be realized. Inspection of current VR systems readily reveals several fundamental problems. However, by fully understanding the limitations in VR technology and the complex human factors interface it is possible to apply VR to many applications, especially in training. In order to create virtual reality the technology limitations must be understood and overcome. Whatever solution is eventually derived, it must fully address the complex human factors issue. This paper will review the realities of virtual environments in terms of the limitations in technology and the apparent lack of human factors understanding. The establishment and development of the British Aerospace Virtual Cockpit Facility at Brough, one of the UK's largest Virtual Environmental laboratories has provided an insight into the key issues of virtual reality. These facilities are engaged in the evaluation of fundamental engineering and human factors issues. In order to illustrate the major problems and how they can be overcome, the results of some of these studies are given.
Present state-of-the-art technology in intensified solid state (ICCD) video cameras renders these sensors an apt candidate for use as an 'on-helmet' sensor in helmet mounted display application. This overview paper establishes the usefulness of ICCD in terms of parametric performance and suggests future trends and potential new capabilities.
We have designed a pilot's harness-mounted, high voltage quick-disconnect connectors with 62 pins, to transmit voltages up to 13.5 kV and video signals with 70 MHz bandwidth, for a binocular helmet-mounted display system. It connects and disconnects with power off, and disconnects 'hot' without pilot intervention and without producing external sparks or exposing hot embers to the explosive cockpit environment. We have implemented a procedure in which the high voltage pins disconnect inside a hermetically-sealed unit before the physical separation of the connector. The 'hot' separation triggers a crowbar circuit in the high voltage power supplies for additional protection. Conductor locations and shields are designed to reduce capacitance in the circuit and avoid crosstalk among adjacent circuits. The quick- disconnect connector and wiring harness are human-engineered to ensure pilot safety and mobility. The connector backshell is equipped with two hybrid video amplifiers to improve the clarity of the video signals. Shielded wires and coaxial cables are molded as a multi-layered ribbon for maximum flexibility between the pilot's harness and helmet. Stiff cabling is provided between the quick-disconnect connector and the aircraft console to control behavior during seat ejection. The components of the system have been successfully tested for safety, performance, ergonomic considerations, and reliability.