Researches of the dynamic characteristics of the turbine jet engine in flight based on its ground tests

Turbine jet engines maintenance (adjustment) actions are performed during standard ground tests, but they are used during the flight. It turns out that the characteristics of the engine determined during the ground tests from the input value "w" introduced by the engine control lever DSS are significantly different from those obtained from disturbance “z" operating in the engine during the aircraft flight. It is noticed, that improvement of the engine control state made by mechanic during aircraft ground tests may cause the deterioration of the engine performance, which is felt by the pilot. The article presents a method that allows determining the basic characteristics of the engine in flight based only on the signals measured during testing ground. This method is based on measurement the major engine signals n – engine rpm, p4 – turbine discharge total pressure, p2 – low pressure compressor inlet, mp – fuel usage, then the designation of synthetic signals y=n/p4 (which describes the engine output), u=mp/p2 (describes engine input) and further their own and cross correlation function. Next, the power spectral density functions of these synthetic signals were calculated. Power spectral density functions is a basis to determine the spectral transfer function HW(jω) (during the ground tests) and HZ(jω) (in flight) which are the basis to determine the characteristics (step response) of the turbine jet engine in flight and during ground tests.