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hvertical motion, (4) visual scene level-of-detail control,
and (5) visual scene mean object size.
Tasks
The experiment involved two tasks.
1. In the first task, the altitude repositioning task, pilots were instructed either to double or halve their initial altitude. The initial altitudes were 15.6, 18.3, and
21.0 ft. Altitude was the only degree of freedom under the pilot’s control. No time requirement was placed on the task, and no requirements were imposed on overshooting or undershooting what the pilots felt to be their doubled (or halved) altitude.
2. In the second task, the altitude-rate control task, pilots were instructed to climb or descend at a
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The state z1 was added to approximate the effects of dynamic inflow into the rotor. All other displacements and orientations were held fixed at zero.
Simulator and Cockpit
The simulator and cockpit were the same as for the yaw experiment described in section 3. The Evans and Sutherland CT5A visual system was used, but both the hardware and software were modified to achieve the visual variations described below.
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Design of Visual Scenes
Simulated scenes are typically less dense (fewer objects per degree of field of view) at lower altitudes than at higher altitudes. In flight, objects invisible at high altitudes become visible at low altitudes, as the angle that the object subtends at the eye becomes larger. When this subtended angle exceeds an optical resolution threshold, the object can be seen. These changes in detail cannot be represented accurately owing to the required computational load in the image generator. Instead, visual databases, which are sets of objects, are stored and then faded in and out of the scene according to range. This fading is adjusted so that the transitions between databases appear natural. How an image generator accomplishes this fading of objects is called “level-of-detail management.”
For this experiment, visual databases were constructed of green polygons on a brown ground plane. These polygons were randomly positioned at locations within a 430-ft radius forward of the aircraft. Each database was associated with a particular altitude band (2.5-ft band). These bands occurred between altitudes of 5 and 45 ft. As the vehicle moved between these 2.5-ft altitude bands, one database smoothly faded out while the new database faded in.
For each altitude, whether or not a polygon was displayed at that altitude depended on which of two visual thresholds was used. The “small” visual threshold allowed objects to be drawn when their vertical visual angle spanned at least 0.1°; the “large” visual threshold allowed objects to be drawn when their vertical visual angles spanned 0.2°.
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本文链接地址：Helicopter Flight Simulation Motion Platform Requirements(45)
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