Flight Control System Synthesis for High-Speed Unmanned Vehicle, Considering its Elastic Properties

The evolution of large transport aircraft is characterized by longer fuselages and larger wingspans, while efforts to decrease the structural weight reduce the structural stiffness. Both effects lead to more flexible aircraft structures with significant aeroelastic coupling between flight mechanics and structural dynamics, especially at high speed, high altitude cruise. The lesser frequency separation between rigid body and flexible modes of flexible aircraft results in a stronger interaction between the flight control system and its structural modes, with higher flexibility effects on aircraft dynamics. Therefore, the design of a flight control law based on the assumption that the aircraft dynamics are rigid is no longer valid for the flexible aircraft. This paper focuses on the design of a flight control system for flexible aircraft described in terms of a rigid body mode and four flexible body modes and whose parameters are assumed to be varying. In this paper, a conditional integral based sliding mode control (SMC) is used for robust tracking control of the pitch angle of the flexible aircraft. The performance of the proposed nonlinear flight control system has been shown through the numerical simulations of the flexible aircraft. Good transient and steady-state performance of a control system are also ensured without suffering from the drawback of control chattering in SMC.

Download Full-text

Structural Coupling and Whirl-Flutter Stability with Pilot-in-the-Loop

Journal of the American Helicopter Society ◽

10.4050/jahs.66.032003 ◽

2021 ◽

Author(s):

Vincenzo Muscarello ◽

Giuseppe Quaranta

Keyword(s):

Control System ◽

Flight Control ◽

High Speed ◽

Sensitivity Analyses ◽

Critical Parameters ◽

Flight Control System ◽

Structural Coupling ◽

Yaw Control ◽

Whirl Flutter ◽

Biodynamic Model

This paper investigates structural coupling problems for tiltrotors, considering not only the interaction of the flight control system with the flexible structure but also the potentially adverse effects on the aeroservoelastic stability that may be caused by the pilot's involuntary, high-frequency, biodynamic response. The investigation is focused on the analysis of the side effects that could appear at high speed in the airplane flight regime, where the whirl flutter boundaries may be significantly reduced. A detailed tiltrotor model, representative of the Bell XV-15 and of a flight control system has been built and joined with a pilot biodynamic model acting on the power-lever and on the center stick, available in the literature. Additionally, a modified version of the XV-15 using differential collective pitch for yaw control in airplane mode instead of rudder has been investigated to show the effect of different yaw control designs.The stability analyses presented demonstrate that the structural coupling analysis and the flutter boundaries for tiltrotors must be evaluated not only considering the closed loop created by the flight control system but also the effect of involuntary pilot response. Sensitivity analyses examine the most critical parameters impacting tiltrotor aeroservoelastic stability. Finally, the employment of notch filters as a means of prevention is discussed.

Download Full-text

Designing a Control Failure Survival System for High Speed Transport Aircraft Using Eigenvalue Assignment Method

Jurnal Teknologi ◽

10.11113/jt.v36.560 ◽

2012 ◽

Author(s):

Zairil A. Zaludin

Keyword(s):

Control System ◽

Flight Control ◽

High Speed ◽

Control Surface ◽

Longitudinal Motion ◽

State Variables ◽

Flight Control System ◽

Short Period ◽

Control Failure ◽

Eigenvalue Assignment

Jika kerosakan berlaku kepada permukaan kawalan penerbangan, tujuan “Sistem Pereka Bentuk Kawalan Penerbangan” ialah untuk membahagi dan menyelaras usaha kawalan antara permukaan-permukaan kawalan yang masih aktif untuk tujuan mengekalkan mutu penerbangan yang diingini. Tugas utama ‘Sistem Pereka Bentuk Kawalan Penerbangan’ adalah untuk menyelaraskan unit kawalan semasa kerosakan berlaku ataupun menukar unit kawalan kepada sistem kawalan yang lebih sesuai untuk tujuan membaiki kerosakan tersebut. Dalam kertas ini, cara yang kedua dipertimbangkan. Reka bentuk “Sistem Keselamatan Kegagalan Kawalan” untuk pesawat hipersonik dibentangkan. Cara tersebut adalah berdasarkan cara penetapan nilai eigen dan teori pengatur kuadratik linear. Terdapat tiga masukan kawalan ke pesawat tersebut. Jika cara yang dibentangkan di dalam kertas ini digunakan, keputusan analisis yang dibentangkan menunjukkan bahawa sistem kawalan penerbangan untuk pesawat ini boleh direka bentuk sehingga kestabilan pesawat tersebut dicapai semula apabila salah satu ataupun gabungan permukaan kawalan gagal berfungsi pada masa yang sama. Didapati juga gerakan tabii pesawat yang mengalami kerosakan dapat dibaik pulih seperti sebelum kerosakan berlaku. Satu contoh disertakan dalam kertas ini menggunakan model matematik pesawat hipersonik. Kata kunci: dinamik penerbangan; penerbangan hipersonik; kawalan optimal; penetapan nilai eigen; Teori LQR In the event of a control surface failure, the purpose of a reconfigurable flight control system is to redistribute and coordinate the control effort among the aircraft’s remaining effective surfaces such that satisfactory flight performance is retained. A major task in control reconfiguration deals with adjusting the controller gains on-line or switching to a different control law to compensate for the failure. In this paper, the former option is considered. The design of a Control Failure Survival System (CFSS) for a hypersonic transport (HST) aircraft is presented. The method is based on eigenvalue assignment which was developed using Linear Quadratic Regulator theory. There are three control inputs available on board the HST; the change in the flaps deflection, the change in the propulsion diffuser area ratio and the change in the total temperature across combustor. Using the method discussed in this paper, the results showed that it was possible to reconfigure the flight control system such that the aircraft stability is regained when either a single or a combination of, control failures occurred simultaneously. In addition, the natural motion characteristics (i.e short period, phugoid and height motion) of the aircraft before the failure occurred are conserved and the transient response of the aircraft state variables after failure was almost the same as before failure occurred. An example is included in this paper using the mathematical model of the longitudinal motion of the HST. Key words: Aircraft dynamics; hypersonic flight; optimal control; eigen value assignment; LQR Theory

Download Full-text

Helicopter load alleviation using active control

The Aeronautical Journal ◽

10.1017/s0001924000002633 ◽

2008 ◽

Vol 112 (1137) ◽

pp. 663-672

Author(s):

M. Voskuijl ◽

D. J. Walker ◽

B. J. Manimala

Keyword(s):

Control System ◽

Flight Control ◽

High Speed ◽

Flight Control System ◽

Order Model ◽

Longitudinal Control ◽

Handling Qualities ◽

Control Techniques ◽

Maneuvering Flight

Abstract This paper discusses how structural load objectives can be included in a rotorcraft flight control system design in an efficient and straightforward way using multivariable control techniques. Several research studies have indicated that pitch link loads for various rotorcraft types can reach high or even unacceptable values, both in steady state and maneuvering flight. This is especially the case for high-speed aggressive maneouvers. Pitch link loads at high-speed flight are therefore taken as a case study. A novel longitudinal control system is presented, designed to reduce helicopter pitch-link loads during high-speed longitudinal manoeuvres whilst providing a pitch attitude command attitude hold response type. The design is based on a high-order model of a helicopter representative of the UH-60 Black Hawk. New metrics are presented for the analysis of structural loads that can be used in combination with ADS-33 handling qualities requirements.

Download Full-text