Virtual flying with ground simulators

The country's prestigious aerospace laboratory, the Aeronautical Development Establishment, has designed three kinds of ground-based simulators. Even as each one of them has a role-specific function, they are also interconnected.

"Making and configuring simulators to user's requirements indigenously has proven to be more economical than imported ones," says VS Chandrashekar, head of flight simulation, Aeronautical Development Establishment (ADE). Chandrashekar was talking with domain-b during the recently concluded Aero India 2007 show held at Air Force Station, Yelahanka, Bangalore.

PC Based Cost Effective Simulators
Today, designing and building simulators for complex, high performance military aircraft is turning out to be a considerable challenge. Normally, these simulators are configured around high-end graphic workstations, which provide out-of-the-window visual scenery, and dedicated proprietary computers that provide the necessary computational resources to meet the high update rates and high-speed data links to manage the Input/Output (I/O).

But now, thanks to recent advantages in PC technology, a cost effective design alternative can be considered to meet the computational and graphic capabilities required for some of the simulator applications.

"A paradigm shift in simulator technology allows one to use commercial-off-the-shelf (COTS) concepts for the development of training and engineering simulators to provide a good and effective training," says Chandrashekar. Using COTS technology, a low-cost flight simulator is developed, and configured, around a cluster of high-end PC systems under a Linux environment, interconnected with high-speed data links.

The task of the host computer for computation of the flight model and data acquisition functions, are performed by the PCs. A three-channel, out-the-window visual scenery, is generated by PC systems using high performance graphic processor boards. Three flat non-collimated LCD monitors, mounted in front of the cockpit, provide the external visual cues, including the HUD symbology in the central monitor, to the simulator pilot. A generic head down LCD display monitor, driven by a PC based system, provides the HSI, ADI, Flight plan and other navigational pages for situation awareness to the pilot.

The cockpit environment is generic and is provided by a fibreglass plastic (FRP) based cockpit shell with typical fighter control stick and throttle. The cockpit has been wired with typical membrane switches for functional simulation of aircraft systems. The presentation of the out-the-window visual scenery can be easily configured with projectors or collimated displays for providing realistic visual cues.

Engineering Simulator
The pilot-in-loop flight simulator, also called Real-Time Simulator (RTS), is a sophisticated facility that has been designed and developed for evaluating the handling qualities of the Light Combat Aircraft (LCA) Flight Control System. This enables verification of an aircraft even before a prototype is built.

This engineering simulator, which is unlike a flight-training simulator, emphasises on control law (CLAW) evaluation and on pilot interface studies. Configured to simulate the dynamic performance of highly maneuverable fighter aircraft, the system updates simulation computation at very high rates with low latency.

The fixed base cockpit is equipped with controls and synthetic displays appropriate to the aircraft being simulated. A fully textured, high fidelity computer generated imagery of the out-the-window visual scene is presented to the pilot in a wide angle, collimated display with realistic aural simulation of engine and aerodynamic noise as well as noises generated during take-off and touch down. A digitally controlled variable feel system can be integrated into this cockpit in place of the conventional spring feel, if needed.

Test pilots are using this simulator extensively for evaluating the handling qualities of the LCA. The role of RTS has been crucial in the evaluation of CLAW, as this has led to more than 600 successful flights of various proto types of LCA. In addition to CLAW evaluation, the facility is continuously being used to plan, and practice, mission sorties for most of the LCA test flights.

Avionics Part Task Trainer for upgraded fighter Aircraft (APTT) - (ADE & DARE)
A state-of-the-art fighter aircraft, with modern avionics and weapon release capabilities, is a necessary component in the inventory of any armed force. Indigenously upgrading avionics and weapon release system of existing aircraft is an optimal route to be adopted in the modernization of an air force fleet, rather than the purchase of an entire aircraft with modern capabilities.

In an upgrade programme, many aircraft systems of a candidate aircraft have undergone major changes in terms of avionics and weapon delivery systems. These include the entire instrument panel, which have been upgraded as a glass cockpit with MFD, UFCP, HUD and other subsystems. Training is necessary for combat pilots, with experience of non-upgraded aircraft, as well as for new pilots, on the modernised upgraded aircraft.

Training on a ground-based simulator becomes all the more important for a single-seat aircraft without a trainer version. The main emphasis in the APTT is to provide functional simulation of all the avionics sub-systems of the upgraded aircraft, EW systems and weapon release systems. It provides training both under normal flying (take off, landing and en route navigation) and failure conditions.

Distributed computer architecture is used for simulation of various sub-systems of the APTT. The system architecture is modular and configured around a suitable mix of PCs and custom built hardware. The inter sub-systems communications are effected through Ethernet, and embedded USB interfaces.

Functional independence and real time communication are the key factors in arriving at optimal system architectures. The architecture is flexible to the extent that 'scale up' and 'scale out' in terms of adding more computing power, and addition of new LRUs (Line Replaceable Units) respectively are easily achieved. Rack mounted, customized PCs are used to compute intensive and graphics intensive tasks, whereas custom-built hardware with synthetic displays, indicators and switches are used for simulation of various panels and EW systems.

A 6-DOF (Degrees Of Freedom) flight model for the aircraft has been developed based on the aerodynamic data available. Further, this flight model is fine tuned by interactions with test pilots to meet the requirements of Avionics Part Task Trainer (APTT). The Flight model along with the navigation model is hosted on a PC under LINUX and RTLINUX.

The MFD (Multi-Function Display) and the front panel instruments are simulated on PCs and displayed on a flat TFT monitor with frontal bezels. Audio cues are generated through the rendering of digitally recorded cockpit sound. COTS based data acquisition system provides an interface between the various sub-systems and cockpit.

"The cockpit shell is fabricated in fiber glass with appropriate metal stiffeners. Pilot controls like control column, rudder pedal, and throttle are designed and developed in-house as per the standards of the aircraft. Spring-dashpot based dampers are designed and developed in house to provide force feedback. The visual cues with superimposed HUD symbology are simulated using PCs with advanced graphics boards. The 'out the Window' scenery is created by generation of terrain database using geo-specific satellite images, and Digital Elevation Model (DEM) created using digital maps/ topo sheets. Several real time rendering techniques were implemented for effecting real time visualization of the 'out-the-window' visual scenery."