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First, the task needs to be analyzed to determine if fundamental motion frequencies are present. Some tasks
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have a predominant task frequency. For instance, nap-of-the-Earth flight over regularly varying terrain can necessitate low-frequency heave cues (the frequency determined by hill separation divided by vehicle forward speed). In these instances, the motion-filter natural frequency and gain should not be set independently in an attempt to satisfy the motion-fidelity criteria. Otherwise, pilots do not feel like they are falling or climbing when the visual scene indicates they are falling or climbing. Setting the motion-filter natural frequency should take priority over setting the gain. The filter natural frequency should be selected such that less than a 30° phase error at that predominant task frequency exists. Then, the motion gain can be selected by trying to maximize the criteria shown in figure 78. Once these two parameters are selected, the motion-filter configuration should be evaluated with a pilot flying the task in simulation to determine if simulator excursions reach their physical limits. If the physical displacement limits are reached,
Set motion gain per criteria
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then the motion gain should be lowered until the ensuing motion remains off the limits.
If fundamental motion frequencies do not exist, then the gain and natural frequency of the motion filter can be set independently. In this instance, the highest fidelity should be sought in accordance with the criteria in figure 78. Iteration with a pilot still needs to be performed to determine the reachable fidelity level. At the end of either of these paths, a certain achievable fidelity level will be reached.
If the desired fidelity level cannot be achieved for a given simulator’s displacement capability, then the user should consider changing the task. Often the task is considered a given and is treated as inviolate, since its origins may be from flight test experience. However, trying to extrapolate simulator results to flight when the simulator can only duplicate the task with low fidelity will usually result in a poor extrapolation.
Poor extrapolations from simulation to flight have occurred frequently because of a control sensitivity that is too high. Pilots improperly perceive vehicle sensitivity to control stick inputs if tasks are not developed in concert with a simulator’s displacement capability. Rather than change the task, the simulator’s gain is reduced, which gives the pilot a false reading of the true sensitivity.
If the process of developing a task is considered as a feedback process with the attained simulator fidelity as a performance metric, then modifying both the motion cues and the task itself should be considered. It may be the only method for achieving high simulation fidelity. Extrapolations to flight can then be made with improved confidence.
Generally, this method should serve as a useful guide for configuring motion systems and for selecting tasks to minimize differences between simulation and flight. Although the method is iterative, it is possible that its combination with the expert system ideas of Grant and Reid (refs. 68, 69) might prove useful.
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本文链接地址：Helicopter Flight Simulation Motion Platform Requirements(57)
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