Longitudinal Robust Controller for Excellent Handling Qualities Design of a General Aviation Aircraft using QFT

Abstract

Handling Qualities improvement by means of active Fly-by-Wire Flight Control Systems has been applied successfully since decades. In contrast small general aviation aircraft are still missing such valuable pilot assistance in terms of the manifold benefits offered by advanced Active Fly-by-Wire Flight Control Systems featuring a wide range of functionalities and applications. In order to bring such a system to a real aircraft as well as allowing the system to be certified in future, controller design layout must be tailored to the general aviation aircraft constraints, e.g. available actuators, sensors and sensor signals, mechanical linkage design, control surface deflection limitations and aircraft dynamics. E.g. in order to minimize the number of sensor signals, the controller should be designed featuring maximum robustness and hence, to yield the capability to operate with fixed gains (not requiring any velocity/dynamic pressure based gain scheduling) both for the whole flight envelope as well as any configuration changes with respect to flaps or landing gear. For that purpose the Quantitative Feedback Theory (QFT) has been applied to the controller design in order to meet the desired handling qualities criteria, including the Control Anticipation Parameter (CAP), Neal Smith, C-Star (C*), Drop Back and others.Consequently, an integrated approach is presented which incorporates and combines all these criteria. Moreover the often neglected part of the inceptor and feel system design, respectively, is addressed in order to provide excellent handling for the pilot. The presented technology work is applied in a joint Research project of an Austrian aircraft manufacturer and the Technische Universität München.

Fault Tolerant Control Design for the Longitudinal Aircraft Dynamics using Quantitative Feedback Theory

“…However, the additional phase lag mainly changes the time delay in the LOES and has little influence on the short period damping and the eigenfrequency. 11 As the control anticipation parameter, the short period damping and the value of n zα are not influenced by the time delay, the use of the second order longitudinal model for the selection of the scheduling variables based on the mentioned flying quality parameters is sufficient.…”

“…As obviously (10) and (11) have different frequency responses, fulfilling the design margins during the design of the second controller K C * (s) based on the open loop (11) does not mean that the frequency response of (10) fulfills them as well. However one can tell what happens by looking at both transfer functions: In equation (11) the augmented plant G C * qc (s) shows a different but similar pole location than G C * η (s) in (10). Mainly the poles of the short period mode are modified, but as the gain K q tends to be small they are quite similar.…”

Synthesis and Flight Test of Automatic Landing Controller Using Quantitative Feedback Theory

“…Santander and Aranda [24] present multi-input/multi-output (MIMO) longitudinal and lateral/directional QFT controllers validated in nonlinear simulation. More recently, Schuck et al [25] use QFT to achieve level 1 handling requirements for a manual control of a manned aircraft. Although the utility of QFT for MIMO control design has been questioned [26], recent results in the literature suggest that the QFT approach provides a sound basis for low-dimensional MIMO systems [27].…”