Design and evaluation of a sensor fail-operational control system for a digitally controlled turbofan engine

SUMMARY A sensor fail-operational digital control system for the TF30-P-3 afterburningturbofan engine was designed and evaluated. The system has the capability of storing(learning) engine operational data when the engine measurements are valid. Four en-gine measurements, corrected to compressor face conditions, are tested for catastroph-ic sensor failure. Any valid measurements are replaced with estimates obtained fromthe valid measurements and tables of operational data previously stored in the computermemory. Data are stored for the engine bleed settings and for both steady-state andacceleration dynamic conditions. The compressor face measurements are tested forany unrealistic variations because the procedure is based upon these signals being cor-rect.The sensor fail-operational system consists of (1) a digitalization of the standardbill-of-materials (BOM) control for the TF30-P-3 engine and (2) a separate sensor fail-operational digital computer program written especially for the BOM control. It is nota completely new control system designed specifically to incorporate fail-operationalrequirements.The system was evaluated on a real-time, nonlinear, hybrid-computer simulationof the TF30-P-3 turbofan engine. Flight conditions examined were sea-level static con-dition, a typical cruise condition, and several extreme flight conditions.The study indicates that acceptable control over the range of flight conditions ex-amined is possible with certain levels of sensor failure. For nonafterburning operation,acceptable control is possible even after three of the four engine sensors have failed.For afterburning operation, adequate control can be achieved with no more than a singlefailure and then only if a modest rate limit is imposed upon engine acceleration. Ac-ceptable control means that none of the engine operating limits have been exceeded andthat nearly the same engine thrust performance is achieved.This work indicates that it is possible to design a sensor fail-operational controlsystem for an aircraft engine which will improve the engine's reliability.