Flight Investigation of the Tradeoff Between Augmentation and Displays For NOE Flight in Low Visibility

The missions proposed for the next generation helicopter involve requirements to operate in essentially zero visibility in the nap-of-themarth (NOE) environment. Such operations will require the use of pilot vision aids, which gives rise to the question of the interaction of such displays and the required aircraft handling qualities. This research was conducted to: 1) investigate the required visual cueing for low speed and hover, and 2) determine if an increase in stabilization can effectively be used to compensate for the loss of essential cues. Two flight test experiments were conducted using a conventional helicopter, and a variable stability helicopter, as well electronically fogged lenses and night vision goggles with daylight training filters. The primary conclusion regarding the essential cues for hover was that fine grained texture (microtexture) is more important than large discrete objects (macrotexture), or field-of-view . The use of attitude command augmentation was found to be effective as a way to makeup for display deficiencies. However, a corresponding loss of agility occurred with the tested attitude command/attitude hold system resulting in unfavorable pilot comments. Hence, the favorable control display tradeoff must be interpreted in the context that the best solution would be to improve the vision aid. Such an improvement would require an increase in the visible microtexture, an advancement in display technology which is unlikely to be available in the foreseeable future. Therefore, a criterion was developed to systematically evaluate display quality, and the associated upgrade in required stabilization as a function of increasingly degraded visual cues.