Shyam Chetty

Flight Control System Clearance Using Static Tests at Iron Bird

The Indian Light Combat Aircraft (LCA) has flown more than 485 flights so far without encountering any major faults in the flight safety critical fly-by-wire control software. This is partly due to the stringent quality control process and rigorous testing of the Control Laws (CLAW) and Air Data System Algorithms (ADS) carried out on various ground platforms such as Iron bird before flight. The pass/fail criteria for the tests carried out at the Iron bird test rig are defined based on the tolerance bounds provided on the expected results which take into account the characteristics of the associated hardware. These tolerance bounds guarantee that the correctness in functionality of the modules (CLAW, ADS) is retained, if the set of bounded inputs generate a set of bounded outputs. The processing of tolerance bounds is an algorithmic development that plays an important role in defining the acceptance criteria for the tests and enables clearance (certification) of the different modules. This paper presents the procedure used for the clearance of the static tests of the CLAW and ADS on the Iron Bird platform. The details on the pass/fail criteria for the static tests and the tool developed for generating the bounds are also described. The tolerance bounds for static tests were evolved based on manufacturer’s data, testers experience and engineering judgment gathered during various levels of testing of ADS and CLAW algorithms. This process yielded excellent results and was accepted as a formal clearance methodology for the onboard safety critical software.

Automated Process for Optimal Structural Notch-Filter Design

Nomenclature C, Cij = controller transfer function, i, j element of C de, da, dr = elevator, aileron, and rudder surface deflections Fk = kth second-order filter section fs = sampling frequency mx = variable magnitude for sensor x Nz, Ny = normal, lateral acceleration P, Pij = plant transfer function, i, j element of P p, q, r = roll, pitch, and yaw rates w, wc = frequency variable, critical frequency wx = weight factor for sensor x Xenv = envelope for sensor X XF, XNF = filter (notch filter) for sensor X n, d = damping of the numerator/denominator !n, !d = natural frequency of the numerator/denominator

Clearance of Flight-Control-System Software with Hardware-in-Loop Test Platform

The Indian Light Combat Aircraft has flown more than 2000 flights, including trainer and naval variants, without encountering any major faults in the flight safety-critical fly-by-wire control software. This is partly due to the stringent quality control and rigorous testing of the control-law and air-data-system algorithms carried out on various ground platforms before flight. One of these ground test platforms is the hardware-in-loop test platform (Iron Bird). The processing of tolerance bounds to define the pass/fail criteria is an algorithmic development. It guarantees the correctness of the modules, if the set of inputs generates a set of outputs within processed tolerance bounds. This paper presents the philosophy behind the design of test cases and the tools developed to evaluate the control-law and air-data-system modules on the Iron Bird platform, and the procedure to clear the test results. The computation of tolerance bounds and algorithms for their processing have been evolved over a period ba...

Nonlinear Aerodynamic Model Structure Determination using Statistical Measures

The stepwise regression is a well-established technique used to determine aerodynamic model structure from flight data. This paper discusses the application of stepwise regression to a nonlinear estimation method proposed previously by the authors, for model structure determination. The approach can also be used for updating aerodynamic database models in table look-up form. The current results obtained for model structure determination for a reference problem are compared against the results obtained using the well known least squares multivariate linear estimation. Simulated data of a transport aircraft is used to prove the concept. Finally, an application of the technique for the aero database update of a high performance fighter aircraft is discussed.