. Workstation Simulator

Workstation simulators are CRT screen-based, man-in-the-loop simulators with processors of high-end workstations. Several processors, linked by Ethernet pro­tocol, support distributed computing. The aircraft and missiles are executed si­multaneously with their display utilities. Typically, the pilot sits at a two-screen display with throttle, stick, pedals, and keyboard as input devices. The upper screen displays the background scene, superimposing the heads-up display. It also can contain the radar, tactical display, and an attitude indicator. The lower screen is re­served for the remaining aircraft instrumentation—the so-called lookdown display.

The number of piloted stations depends on the objective of the simulation. Flight training requires just one station, whereas air-to-air combat calls for multiple sta­tions, simulating blue and red aircraft. The maximum number is determined by the outlay of the processors. Workstation simulators make it possible to conduct studies with many piloted aircraft without large investments. Military tactics, like engagement maneuvers, choice of weapons, and egress maneuvers, can be devel­oped and practiced. However, their utility for flight training is restricted because of limited situational awareness: the pilot’s view is confined to the flat screen display, and no tactile feedback is provided. In workstation simulators you will find a mixture of models. Highly detailed aircraft dynamics with six-DoF aero­dynamics, multimode flight controls, high-bandwidth actuators, navigation aids, gears, and flaps. The missile trajectories are often modeled as simple three-DoF or pseudo-five-DoF simulations. Rarely will you encounter a full six-DoF missile representation. The reason is simple. The pilot’s attention is focused on the air­craft’s behavior as he delivers and evades missiles. Any obvious discrepancy with his flying experience will distract him from the simulation’s objective. The missile fly-out, on the other hand, is autonomous, and only the flight time and the effect on the target are of interest to the pilot. Therefore, simplified missile simulations are acceptable as long as they have been validated previously by full six-DoF models.

Most of the simulation code is programmed in FORTRAN. A long legacy exists of flight dynamics, autopilot and radar models, adapted to the characteristics of new
systems, as required. The graphics interface is highly dependent on the simulation hardware and has changed drastically over the past decade. Today, C++ is the preferred language to interface the hardware and the displays. Both FORTRAN and C++ interact harmoniously in workstation simulators, although the purists would like to deal only with a single language.

Let us observe the genesis of a project from planning to execution. Assume the objective is to study the effectiveness of a new air-to-air missile in an air combat environment. Well before the pilots arrive, in some instances 12 month in advance, a planning meeting is held with the customer, the aircraft and missile designers, and the simulator personnel. The objectives are defined, the aircraft and missiles identified, and the scenarios discussed. If new flight systems are introduced, the facility programmer is given their code, which he will integrate into the simulation environment. Here, the first problems can arise. The new missile or aircraft must run as subroutines callable from the main program, usually referred as the man – in-the-loop (MIL) frame. The input and output to the subroutines must be well defined, preferably formalized by an interface document.

You will encounter two approaches to the integration. The older technique, the distributed integration, breaks the flight system into its individual components and incorporates only the new subroutines like aerodynamics and flight controls into the MIL frame, while reusing such basic equations as translational and attitude motions. With today’s abundance of computer memory, the newer approach, the compact integration, inserts the complete missile or aircraft into the MIL frame. It has the advantage that the code, after having been thoroughly checked out in a batch environment, is executed in its entirety in the MIL frame, thus eliminating the time-consuming validation phase.

After the MIL frame programmer has updated his simulation environment, the engineering trials are conducted as final system check. An experienced pilot at this point would be helpful in uncovering any flight anomalies. Once checkout is complete and the air combat simulation has been validated, the test-planning meeting is convened, attended by the customer, the designers, the programmers, and the pilots. They establish the scenarios, concur on the parameter space of the design variables, and lay out a detailed run schedule.

Finally, the time has come to call the pilots for the combat trials. During the first week, they are briefed on the mission objectives and the scenarios and given an opportunity to develop their tactics. Sometimes they question the fidelity of the simulator and the “feel” of the aircraft response. If you are the facility programmer, you have the difficult task to convince the pilots of the adequacy of your simulation for the planned trials. Once they understand that the compromises you had to make do not adversely affect their combat skills, you have won them over, and you can start with the actual test.

The conduct of the trials closely follows the established plan. The engagements are flown, the missiles launched, and the intercepts recorded. Then the parameters are changed, and the cycle repeated. All data are recorded for analysis.

During the post-trial analysis, before the measures of effectiveness are evalu­ated some of the stressing engagements must be validated. The recorded data are replayed and scrutinized. Miss distance values, which depend on the fidelity of the missile fly-out simulation, must be verified. The analyst may even have to take recourse to the original six degrees of freedom. He or she drives it with the actual
target motions and duplicates the engagement based on the high-fidelity simula­tion. Eventually, the results will be expressed in blue and red fighter exchange rates and conclusions drawn as to the best aircraft and missile designs.

Workstation simulators are particularly effective training tools for managing the aircraft’s systems. Radio communication, flight planning, and troubleshooting faulty devices are some of the exercises that can be practiced. The U. S. Air Force uses them as weapon tactics trainers, giving the pilot hands-on experience with fire control radars and weapon release switchology without expending missiles. However, to submerge the trainee into the complete flight experience the more elaborate cockpit simulator is essential.