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In contrast, the pilot seldom receives any of these cues accurately in simulation. The aircraft is now represented by a mathematical aircraft model, which is likely to contain inaccuracies. The visual system, which is typically computer generated, does not provide the cueing richness of the real world. The simulator visual field of view is usually less than that of the vehicle, and the visual acuity provided today is incapable of rendering 20/20 vision. The vehicle’s force-feel system is usually the easiest to replicate, although matching the nonlinear effects (friction, free-play, and hysteresis) and the inertia characteristics can be challenging. This challenge results both from a surprising lack of flight data and from simulator force-feel system limitations. And because the simulator displacements are constrained, the motion system can typically provide only a subset of the in-flight accelerations. It is the motion system that is the focus of this report.
Of the above cueing sources, only the motion platform has practical hard technological limits in its capability to reproduce the in-flight cues. Thus, in light of those hard limits and the associated costs of providing them, estab-lishing reliable motion fidelity requirements is warranted. This is especially true for helicopters, since the pilot often stabilizes the pilot-vehicle system, and this stabilization is only possible via feedback from the simulator’s cueing systems.
The Role of Platform Motion in Flight Simulation
The role of platform motion has been the subject of great debate. Some researchers and users believe in the extreme that no platform motion is necessary. Some believe in the exact opposite. As pointed out by Boldovici (ref. 8), “Debates about whether to buy motion bases often include anecdotes, misinterpretation of research results, and incomplete knowledge of the research issues that underlie the research results.” Toward understanding the role of motion in flight simulation, the arguments for the support of each of these views are given below.
Stick
Flight
Simulator stick
Simulation
Figure 1. Flight versus simulation.
The Case Against Platform Motion. Cardullo cites many of the reasons users either do not employ motion or believe it is unnecessary (ref. 9). First, platform motion usually does not have the face validity that a simulation component such as the visual system does. Face validity is defined as a seamless one-to-one correspondence with the real world. Some subsequently argue that since the true motion environment cannot be duplicated faithfully, a subset of it should not be presented, for the cues are incorrect. It is also argued that providing platform motion is not cost effective. Finally, opponents of motion note that transfer-of-training studies have found no basis for a motion requirement. In particular, the U.S. Air Force’s standard view for training is that motion is not required in the simulation of any aircraft with centerline thrust.
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