Simulation Structure

Preface

Before entering into details on some aspect of a Simulation, it is a good idea to have the perception of the big picture, i.e. an idea on a possible structure of a simulation SW running on a Flight Simulator. We concentrate on SW and algorithms because they are matters almost time-invariant: the HW evolution is so fast that each typical piece of HW of a flight simulator wound need a weekly review: the technological advance in this fields is so fast that we leave the readers to update their knowledge directly on the website of the major simulation technology suppliers

Major components

To come back to our business, in order to give the pilot a good feeling to be on a real aircraft we need to meet several requirements:

1. the pilot environment on the simulator should be as much as possible identical with the environment on the real aircraft. This means that the simulator shall have a perfect replica of the cockpit of the aircraft with all the command and control devices (throttle, stick, switches, displays, head-up and head-down). This can be achieved or using the real AC equipment (very expansive, they are developed to fly, with the additional complication that they need to be power-supplied as in the aircraft, properly air conditioned, and linked with special data-buses at military/civil standard which require expensive interfaces) or a perfect replica in terms of look, feel and function. Also this second option can be expensive if the aircraft to be simulated is new, and no commercial equipment are available, and thus a brand new development must be carry out, In this case decision can be driven by the number of items to be purchased. Take into account that there are a lot of middle-little companies around the world specialized in manufacturing these items.

2. the dynamic of the aircraft shall be perfectly replicated. This implies mainly SW and we should be able to translate the physic laws governing the motion of an aircraft, into SW algorithms, and often it is not so easy, because in a flight simulator the input come from an human being and can be unpredictable: and the simulation SW shall react to all input from the pilot, even if unpredictable. Take into account that during AC development, flight dynamic engineers perform a lot of simulation with a wide variety of tools and even developing simulation SW, but normally they are developed to study the behavior of the aircraft in almost “nominal condition”. These pieces of SW are very useful to start the development of a flight simulator SW, but are not sufficient. Normally a lot of additional SW has to be added to make it suitable for a real time execution on flight simulator.

3. The effects of the simulated aircraft dynamics shall be presented to the pilot, through the cockpit instruments.

4. A representation of the real world, synthesized with graphics computers boards as in many nowadays video games is mandatory. This is done by means of Visual Systems, which, in addition to the graphics computer, includes

   1. the facility to develop the graphical scenario, which normally is a perfect replica of the real world (the Data Base Generation System, DBGS)

   2. the graphical data base to be displayed by the graphical computer representing the graphical scenario

5. As a consequence of 3, all the systems of the aircraft must be simulated (hydraulics and electrical systems, landing gear, fuel system, avionics , including navigation, radar, radios, and for military aircraft the store management systems, the attack system, the defense system, etc). Also in this case the avionic SW is a very good start point for implementing the same function on a flight simulator provided that:

   1. there is a clear identification of the application SW (for example the navigation function for a navigation computer), respect to other auxiliary SW winch needs to manage the data communication on the avionic buses, detect HW failures, run Build In Test (BIT) etc. While the first pieces of SW can be extensively used, the second one is quite useless, because, in a flight simulator, the SW run on a commercial HW, typically running with an Unix Operating System with real time extension (nowadays Linux Operating System), and not on an avionic computer.

All those systems provide feedback to the cockpit and consequently to the pilot: their simulation is fundamental also to train the pilot in case of failure in a safe way.

1. Optionally (nice to have but very expansive) a feedback of the accelerations on the body of the pilot: this can be achieved only partially with several devices, but often sufficient to convince the pilot he is flowing a real aircraft. This can be seen as a plus, but take into account that pilots are used to fly, and are used ”to feel” accelerations as consequence of their inputs: if accelerations are missing (like in static simulators), very often the pilots not trained to fly flight simulators, start to suffer of simulator sickness including discomfort, apathy, disorientation, fatigue, and nausea, vanishing the training session and the use of the simulator.

2. Optionally, depending on the requirements allocated to the flight simulator, a Scenario Generator, able to generate actors like other aircraft, land vehicles, ships, maneuvered by “intelligent” SW implementing programmed combat doctrines chosen during the preparation of the training session. Of course these entities have to interact among them and above all with the Flight Simulator by means of the simulated sensors, and with the Visual System in order to be seen in the scene if visible.

3. Last but not least, an Instructor Station, where an instructor can follow the flight made by the trainee, by means of a lot of facilities (virtual graphical replicas of all the systems, of all the input made by the pilot, all the geo-location facilities to follow the fly (any sort of maps), 3D representation of the external environment with the ability to change the view point (a sort of God Eye functionality), the capability to insert other actors (aircraft or land vehicles) in the scenario, friend and foe, maneuvered by artificial pilots, whom the pilot can interact with, flying in formation or combat against them, activating its armament systems (gun, missiles IR and/or AMRAAM), its sensors (IR, Radar). One of the functionality of the instructor Station is the capability to inject failures in the different systems, to train the pilot to react correctly to emergencies under stress conditions.

All the topics discussed above need to be matched with the target we want to achieve, i.e. with the scope of the flight simulator we have in mind. Here a wide discussion can be opened, implying training objectives, training planning, budget and so on, and it is out of the scope of these posts, which are thought to include only technical issues. Just to close the argument we would like to give some indication on some of these issues:

1. There are a lot of classification related to the flight simulator, and each class has its functionality and its cost, depending on the requirements allocated to them

2. There is a class named “Full Mission Simulator”, where the pilot is allowed to do all is allowed on the aircraft….and more.. This class is the most expensive and its cost per unit can be equivalent to the cost of the real aircraft. This class include the most complete simulation of all systems, including simulation of failures with all the reactions made by the systems dedicated to detect them, including the real reaction of the aircraft to human action as consequence of failure occurrence injected by the Instructor.

3. There are other intermediate Flight Simulator configurations that often are named Part Task Trainer, which focalize the training only on some aspect. Just to make an example, at the beginning of training there is the need to train pilots to interact with the Avionics System of the aircraft (this is particularly true in case of new aircraft) , and this implies interfacing with very complex systems like Navigation, Attack (with related sensors like radar), Armament System with the complex management of all the weapons the aircraft can carry out. To do that is sufficient to have a reduced system dedicated to it, with a very less sophisticated model of the aircraft (in this phase aircraft performance does not matter), with a very limited Visual System and simplified Instructor Station, very much cheaper respect to a Full Mission Simulator, leaving it for tasks with a much higher added value, like the training for Combat Ready pilots

In the post “Attitude Calculation” we start approaching bullet 2 for the part of attitude calculation.