Flying High

In a flight simulation, the equations must be solved at a sufficiently fast rate that the motion (or dynamics) of the simulated aircraft appears to be smooth and continuous, with no delays or abrupt changes resulting from the computations [1]. Typically, the real-time software in a flight simulator updates at least 50 times per second. In other words, all the computations must be completed within 20ms, including the inputs from controls, levers, knobs, selectors, and switches, which must be sampled within the 20ms frame.

Data acquisition of analog and digital inputs is potentially slow. In the case of analog inputs, the signals are sampled, converted, and read into a computer as digital values, and a flight simulator might have several hundred inputs. To illustrate the problem, in a flight simulator that acquires data from 32 analog inputs at 50Hz, the overall sampling rate is 1,600 samples per second. Furthermore, the data must be sampled with sufficient resolution (or accuracy), typically 12-16 bits, and any latency resulting from data acquisition by the simulator modules must be minimized. To avoid any delays caused by simulator modules waiting to capture data, a dedicated I/O system can acquire the data and transfer it to the simulator modules over a local network.

Requirements

A real-time research flight simulator [2] currently installed at Cranfield University (Cranfield, UK), runs on a local network of eight PCs, with the simulation functions partitioned as shown in Figure 1. The I/O system provides an interface between the simulator and the software modules that comprise: the modeling of the aircraft aerodynamics and the engine dynamics, aircraft systems, flight displays, navigation, avionics, an instructor station, control loading, sound generation, flight data recording, three image generators for a visual system, and an optional connection to Matlab. Data is transmitted over the network as broadcast Ethernet UDP packets.

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