Iron Bird Results

An attempt was made to analyze the SP maneuver data generated from an iron bird (IB) for a fighter aircraft with the following flight condition: Mach number = 0.41, H = 3 km, undercarriage down, and alpha trim = 7.69°. An SP maneuver was excited with a pitch stick command input doublet. The pulse width was 2.8 s, and the sampling rate was 40 samples/s, and 320 data points were available for parameter estimation. The estimation results are compared with those from flight simulation (FS) and nondimensional linear (NLM) model parameters in Table 9.11. The results seem satisfactory.

It is seen that for this flight condition the aircraft is almost statically-neutrally stable or unstable. The pitch damping is also poor. It must be emphasized here that the open loop dynamics of this aircraft are unstable, and it operates in a closed loop with a control system.