Flight Simulation Software

10 Validation

It is necessary to look at the results of observation objectively, because you, the experimenter, might like one result better than another.

Richard P. Feynman

Many years ago, the author developed a real-time flight model for a 16-bit microprocessor using integer arithmetic, with many of the variables computed using look-up tables. During a demonstration, as the aircraft climbed through 20,000 ft, it suddenly stalled. Subsequent inspection of the weather module showed that the entry in the table for air density around 20,000 ft was 0.0080 rather than 0.0880, reducing the aircraft lift by a factor of 10. The error should have been detected during testing of the weather module, but the testing coverage had failed to spot this anomaly.

Recalling points made in Section 2.2 that testing can take up to 50% of project development time, online debugging, that is, on the simulator, can take up valuable simulator time. Moreover, only one set of tests can be run at any time and may require pilot input to undertake specific tests. An alternative approach is to transfer much of the development and testing to offline facilities, such as the SimPlot tool described in Section 4.2, which is used to obtain the results of many of the examples in this chapter.

10.1 Software Verification

In developing software for any project, verification is a measure of the rigour of software development, whereas validation ensures that the software is fit for its intended purpose. As Boehm observed, ...