676 



DISPLAY SYSTEM DESIGN PROBLEMS 



in the same direction as the aircraft slippage. All these visual cues appear to 

 the operator as if he had an external reference on the ground to which he 

 can refer his own position. 



(a) Roll (b) Pitch (c) Yaw 



Fig. 12-52 Motion Display — Contact Analogue Indicator. 



The ideal radar video information displayed on such an indicator would 

 not only indicate the angular position of the objects of interest but would 

 picture the information by size and shading to indicate range and bulk. 

 The B type display of course, being cartesian, would not serve as a contact 

 analogue display, since the antenna search cone is made in a solid angle. 

 The limitation of this display is not in the CRT. The complexity of the 

 information handling requires a sophisticated computer. 



Aural Indicator. To relieve the burden imposed on the operator's 

 visual sensors — his eyes — consideration has been given to using the 

 operator's aural perception as an aid in gathering radar information and 

 control data. The ability to use the hearing sensors is limited, however, 

 since the ear is capable of resolving information of relatively low bandwidth 

 content. It works best when there is only one type of information present, 

 and it does not have the integrating capability of the eye. For example, 

 it is difficult to listen to crew command conversation and radar-processed 

 data at the same time. Because of these limitations not many airborne 

 presentations, in the past, utilized the operator's hearing ability. 



If the operator's aural perception is to be used, the parameters that can 

 be distinguished are amplitude, frequency, and duration of tone. The 

 audible range in loudness from threshold up to the pain level covers some 

 120 db over the medium frequencies and tapers off towards the high as well 

 as towards the low tones. Because of the noise level in the airplane, the 

 lower part of the loudness range cannot be used for conveying information. 

 To prevent disturbance and fatigue the louder range cannot be used. The 

 loudness range usable as an information parameter is consequently greatly 

 reduced. 



A frequency spectrum from about 30 cps to 12,000 cps can be heard by 

 most people. The sensitivity, however, rapidly decreases towards both 



