Many previous rotorcraft nap-of-earth visual simulators were designed by the "seat of the pants" method: infant technologies mated with "best guess" estimates of what a visual simulation scene should contain. Experience with the successes and weaknesses of these earlier systems (many still in valuable active use) provided the right questions, and recent empirical quantitative studies have offered first and second generation answers. Unfortunately, the technology's solutions have too often been, "This is as good as we can do, and so we'll prove it's good enough." It is now possible to approach the problem from the researchers point of view. Maturing hardware and emerging software technologies have made possible the design of a system that provides the content demanded by the research, not just to marginal but to desirable levels of performance.

The nap-of-earth visual simulation project had as a practical objective tailoring a visual data base designed for rotorcraft to the requirements of a comprehensive research study. The projected performance envelope was designed to be nap-of-earth and contour flying from five feet up and from hover to 100 knots. Empirical issues to be addressed in the implementation included: mix of 2D and 3D cueing, and total cue densities to provide optimum visual flow; elimination or minimization of negative cueing; value of terrain fidelity versus dense generic scene content; maximization of detail in the aircraft performance envelope; and scene reality versus training value. Other perceived deficiencies of some earlier systems that are addressed by this system are multiple, properly occulting, dynamic ground and air threats, and special weapons effects (cannon, rockets, FLIR, etc.) In addition, consideration was given in the structuring of the data base to provide maximum flexibility as new research and experience dictate modifications. What has evolved is a good example of visual flight simulation specifically designed for the nap-of-earth regime.