Motion system

Although, according to physiologists, 70% of flying is accomplished with the eye, the ear plays also a very important role. It relates wind and motor noises to airplane speed and status of the engine. But more important than the eardrum is the inner ear with its vestibular set of sensors.

The vestibular sensors consist of the inner ear canals, which measure angular acceleration, and the inner ear otoliths (little calcium stones), which sense linear acceleration. Isn’t it interesting that an INS senses the same parameters with its gyros and accelerometers? Our brain carries out the integration, although not as accurately as the INS computer. Close your eyes while in the passenger seat of a car. Although you can sense the accelerations, to deduct the velocity or even the traveling distance is a difficult task.

This feature of the human ear is stimulated by the motion platform, which supports the cockpit. It is impossible and unnecessary to duplicate the aircraft’s velocity and position, but the accelerations are important stimuli.

The motion platform is supported at three points by a pair of hydraulic cylinders each (see Fig. 11.4). Cylinders from opposing points are paired and attached on the floor. This arrangement gives the platform three translational and three attitude degrees of freedom, a true six-DoF dynamic structure. Although the platform is restrained, the onset of linear and angular accelerations can realistically be simulated. So-called washout filters quickly fade out the signals to restrict travel.

For midsize simulators the linear travel is typically 3 m and the rotational excur­sions about ±30 deg. Powerful hydraulic lifters support the platform. They deliver

a motion bandwidth of 2 Hz, commensurate with the upper limit of typical rigid airframe dynamics.

The linear accelerations of civilian airplanes rarely exceed one g, i. e., one times the Earth’s gravity. However, fighter pilots, practicing dogfights, routinely ex­perience 3-5 g. They wear pressure suits to prevent blood from accumulating excessively in the lower part of the body, causing blackout. They certainly can attest to the seat-of-the-pants (somatosensory) feeling.

Because the motion system cannot simulate sustained g loads, the pressure suit can be enlisted to mimic g effects. Particularly in military simulators with the pilot willing to suit up, the somatosensory feedback is provided by a specially designed pressure suit. It cannot duplicate the spine-jamming agony, but still conveys the sense of sustained maneuvers.

Simulators penetrate ever-deeper flight training. They are cheaper than air time, allow practicing emergency procedures without endangering life, and are essential for single seat aircraft. The U. S. Air Force is so infatuated with simulators that it broke with tradition and bought only single-seat F-22 fighters. All flight training is done on the ground in two facilities.3 The Full Mission Trainer (FMT), set inside a geodesic dome with 360-deg view, is used for flight training and emergency egress procedures. The Weapon Tactics Trainer (WTT) is a workstation simulator with up to 21 stations, manned by blue and red pilots. Here the war fighters can hone their skills in acquiring, tracking, and attacking enemy aircraft. The F-22 pilot training lasts about 104 days, 10 days less than for the F-15, but covering a more complex aircraft. Wouldn’t you want to be part of the action? Well, you can. Go to your software store, buy an F-22 simulator, and then fly away on your home computer!