Research in the field of aircraft handling qualities is undertaken for two primary reasons. These are (i) to formulate a set of design criteria which if met will ensure that a new flight vehicle will have adequate handhng qualities and (ii) to better understand how the various vehicle and mission parameters affect the human pilot. These problems are tackled by means of experi­mental programs involving trained pilots and actual aircraft or flight simulators, or through theoretical analyses involving human-pilot describing functions. Most of the recent research has been experimental work carried out with flight simulators.

The flight simulator is a device that creates the illusion of flight to a certain extent for a pilot seated in its cockpit. This is achieved partly by con­structing the cockpit to appear like that of the real aircraft. The simulator is then programmed to respond to the actuation of the controls in a fashion which resembles the response of the actual vehicle. This is accomplished by programming the vehicle’s equations of motion on an analog or digital computer, using the pilot’s control movements as the inputs to the computer system and driving the response system of the simulator with the computer output. The realism achieved with a given simulator depends to a great extent upon the visual and motion cues provided by the response system. The motion response of the simulator can range from none at all for fixed-base simulators, through limited motion in some degrees of freedom, to complete six-degree – of-freedom motion with a variable stability aircraft, which is in fact a flying simulator. The visual cues provided can include instrument displays, closed – circuit television representations of the outside world, or the full visual and instrument display provided by a variable stability aircraft. Figure 12.10 depicts a typical simulator system.

The advantages offered by the flight simulator to researchers in the field of handling qualities are many. With the simulator it is possible to isolate a single system parameter for study, allowing it to vary while holding all other parameters fixed. Situations that would involve an element of danger if a real aircraft were utilized can be simulated with no risk to life or equipment. The lower cost of operating the simulator and the control over environ­mental factors such as turbulence also favor the simulator. However, care must be exercised in interpreting the results of simulator studies. Since the simulator is usually only an engineering approximation to the actual flight system, the pilot must extrapolate his experience in the simulator in order to relate it to an actual flight situation. The ability of a pilot to do this and hence achieve meaningful handling qualities ratings depends upon his previous flight and simulator experience. In addition, care must be taken to

provide the pilot with the pertinent stimuli. For example, it would not make sense to use a fixed-base simulator to rate a vehicle in the performance of a mission which normally requires the pilot to sense vehicle motions.