Helmet-Mounted Displays

Aeromedical Issues

• Helmet-Mounted Displays

• Sensor fusion

• Aeromedical Issues associated with HMDs

Objectives

• HMDs

• Several systems in current use

• Varying degrees of function & information presented

• A general increasing trend to use the helmet as a mounting platform for sighting and display systems

• Fast jets & helicopters

Helmet-Mounted Displays

• NVGs

• Helmet-based Head-Up Display (HUD)

• Weapons sighting and display systems

• Singly or in combination

Helmet-Mounted Displays

• F-35 helmet integrates:• Weapons systems

• HUD

• NVG

• Has rendered the HUD obsolete in this aircraft

• Helmet now a critical piece of flight equipment

F-35 Helmet

• Joint Helmet-Mounted Cueing System

JHMCS

JHMCS

• Uses a magnetic head tracker system for head position referencing

• Projected collimated symbology and imagery onto the helmet visor

• A Helmet Vehicle Interface (HVI) interacts with the onboard aircraft computer system to generate the signals for the visor display

• Targets designated to air-to-air and air-to-ground weapons by simply looking at the target and activating a switch on the control stick

TopOwl

• Helmet-Mounted Sighting & Display system

• Deployed in helicopters

• Incorporates NVG function

• Side-mounted Image Intensifier tubes

Helmet-Mounted Displays

• Highly sophisticated

• The aim is to provide essential flight information, aircraft performance and tactical situation data to the pilot at all times

• Can also facilitate the designation of targets to weapons

• These systems combine:• high-resolution displays

positioned in front of the eyes • a head tracking system • an integrated sensor package

• HMDs independent of head position • This eliminates the problems associated with a fixed HUD position

• HUD only useful when pilot is facing forward

• Should improve the situational awareness and tactical performance of the pilot

Helmet-Mounted Displays

Helmet-Mounted Displays

• Increased situational awareness (SA) • Reduced pilot workload• Improved weapons employment • Better tactical outcomes • Easier weapons targeting and designation

• Faster response times • Greater accuracy • High off-boresight capability (+800 of aircraft nose)

• When maneuvering is required, essential primary flight data is still in the pilot's direct vision

Advantages of HMD

• Operations in high-threat environments • Greater time spent “heads up, eyes outside” • Generates and maintains good SA

• Reduced potential for spatial disorientation• The sudden loss of visual cues when in close proximity to the ground or in bad

weather can be countered by the ready supply of attitude, airspeed and altitude information on the pilot’s visor.

Advantages of HMD

• Sensor fusion or multi-sensor integration• The process whereby all available sensor information is integrated or

‘fused’ into a single display• Gives the pilot an integrated single-display sense of what is happening

in and around the aircraft

Sensor Fusion

• Any sensor information can be fused and displayed• In addition to what has already been discussed

• These additional information could include:• Threat detection systems (including three-dimensional localized auditory

stimuli) • Ground collision avoidance (synthetic vision systems coupled with ground

images or a stored digital topographic database)• Information data-linked from other remote sources

• Other combat aircraft• Airborne early warning and control aircraft• Ground-based stations

Sensor Fusion

• Reduced pilot cognitive workload• Increased automation

• including target selection and prioritisation

• Absence of conflicting data being presented to the pilot • Less need for cross-checking with other displays• Improved SA due to a single reference source of information• An optimised human-machine interface

Sensor Fusion Advantages

• Information overload • Task saturation • Channelised attention• Overwhelmed orientation system

• Visual, vestibular and proprioceptive mismatches

• Understanding the cognitive, psychological, biodynamic, and aeromedical issues involved in the deployment of this technology is of crucial importance• A work in progress

Sensor Fusion Disadvantages

Aeromedical Issues

• Increase in the total weight borne by the head and neck

• Forward shift of the centre of gravity of the head-helmet complex

• Especially in a fast jet operating environment with high +Gz loads

Neck Injury

• HMDs complicate the loads placed on the neck

• Potentially increases the likelihood of ejection-associated head and neck injuries

• If NVGs dislodge from the helmet mounting during the ejection catapult phase, this can lead to injuries, (eg lower limbs)

• Where possible, NVGs need to be removed prior to ejection

Ejection Considerations

• An impact while wearing a helmet-mounted display (especially NVGs) can increase the probability and severity of head injuries sustained

• In addition, there is potential for HMDs to complicate emergency ground egress

Ground Impact

• In some situations, HMDs can increase the likelihood of spatial disorientation and loss of situational awareness

• Stabilization of the projected imagery during movement of the head and/or aircraft is vital

• An unstable image will lead to:• increased perceptual difficulties • greater pilot workload• greater potential for error and loss of

situational awareness

• Helmet fit is very important

SD & Image Stability

• Hyperstereopsis is a function of increased interocular separation• Systems that have side-mounted sensors

• The greater distance between sensors than the normal inter-pupillary distance results in greater optical convergence

• This creates issues with depth perception, slope perception, and distance estimation

• To the pilot, this creates a situation where objects appear closer than they are

Hyperstereopsis

• HMDs provide all necessary and relevant information to aircrew

• Improve SA and reduce workload

• Not without their aeromedical issues• Temporary visual issues

• Neck injury

• Ejection and impact considerations

• Human factors issues (information overload)

Conclusion