Lateral-directional Modes Research Articles

A Simple, Correct Pedagogical Presentation of Airplane Lateral-Directional Dynamic

This paper offers a clean and correct pedagogical presentation of the theory of airplane lateral-directional dynamics. In this work, the definition of the dynamic (rate) derivatives has been corrected, distinct timescales corresponding to the standard lateral-directional modes have been identified, and a multiple timescale procedure including static residuals has been followed to derive new literal approximations to the modes. The lateral-directional small-per-turbation equations have themselves been written without having to first derive the complete 6-degree of freedom equations of airplane motion. New, physically meaningful results for the Dutch roll and spiral mode parameters are obtained and discussed. This work complements the revised presentation of airplane longitudinal dynamics in a companion paper.

Small-Perturbation Analysis of Airplane Dynamics With Dynamic Stability Derivatives Redefined

The first successful powered and controlled heavier-than-air flight and the subsequent meteoric rise of aviation in the 20th century also brought with it mathematical models to understand the phenomenon of flight. Though successful to a large extent as is obvious from their longevity, these models still suffer from the odd anomalous result. Upon careful examination, the source of this problem can be traced to an inappropriate choice of dynamic stability derivatives that is inconsistent with the aerodynamics. In order to correctly distinguish between the different mechanisms that are responsible for the aerodynamic forces and moments generated due to body angular rates in flight, this paper refines the existing model for flight mechanics by redefining the dynamic stability derivatives with respect to, i) relative rate of rotation between the body and wind axes, and ii) the rate of rotation of the wind axis with respect to the earth axis, sometimes called flow curvature effect. Further, new literal approximations to the longitudinal and lateral-directional modes have been obtained in terms of the redefined dynamic stability parameters. The new approximations, for instance, correctly relate the short-period natural frequency to the longitudinal static stability parameter Cmα.

Flight testing verification of lateral-directional dynamic stability of gliding birds due to wing dihedral

PurposeUnlike conventional aircraft, birds can glide without a vertical tail. The purpose of this paper is to analyse the influence of dihedral angle spanwise distribution on lateral-directional dynamic stability by the simulation, calculation in the development of the bird-inspired aircraft and the flight testing.Design/methodology/approachThe gliding magnificent frigatebird (Fregata magnificens) was selected as the study object. The geometric and mass model of the study object were developed. Stability derivatives and moments of inertia were obtained. The lateral-directional stability was assessed under different spanwise distributions of dihedral angle. A bird-inspired aircraft was developed, and a flight test was carried out to verify the analysed results.FindingsThe results show that spanwise distribution changing of dihedral angle has influence on the lateral-directional mode stability. All of the analysed configurations have convergent Dutch roll mode and rolling mode. The key role of dihedral angle changing is to achieve a convergent spiral mode. Flight test results show that the bird-inspired aircraft has a well-convergent Dutch roll mode.Practical implicationsThe theory that birds can achieve its lateral-directional stability by changing its dihedral angle spanwise distribution may explain the stability mechanism of gliding birds.Originality/valueThis paper helps to improve the understanding of bird gliding stability mechanism and provides bio-inspired solutions in aircraft designing.

Fighter Aircraft Closed Loop Handling Quality Simulation on Lateral-Directional Modes

Fighter Aircraft Closed Loop Handling Quality Simulation on Lateral-Directional Modes

Experimental Study of Aircraft Achieving Dutch Roll Mode Stability without Weathercock Stability

Weathercock stability is usually considered essential to achieve normal flight, while the Dutch roll mode stability can still be achieved without weathercock stability which has been algebraically proved. This paper proposed a flight experiment to investigate the characteristics of an airplane with Dutch roll mode stability but no weathercock stability. Firstly, the algebraic analysis based on a standard lateral-directional mode approximation was made to demonstrate the effect of yawing stability derivative Cnβ on the Dutch roll mode characteristics. The flight experiment was organized after that using a model glider which was modified to have zero Cnβ but with marginal change on Cyβ. The convergence of Dutch roll mode in flight meets the algebraic and numerical analysis as expected. However, the difference of handling characteristics between the original and modified configurations indicates some other roles the weathercock stability plays in flight as well as some limitations of utilizing mode criterion in flight quality analysis.

Aerodynamic Modeling and Flight Simulator Evaluation of Aircraft's Response to Varying Crosswind

Varying crosswind is the crosswind with varying magnitude and/or direction as that being encountered by an aircraft. It includes horizontal gust wind and horizontal wind shear. As a result of this encounter, the aircraft may develop roll oscillation with large amplitude to affect flight safety. The main purpose of this paper is to show that this phenomenon can be reproduced in an existing flight simulator with high fidelity for pilot training based on unsteady aerodynamic models developed in a tabulated form. Five sets of flight data involving various varying crosswind in landing are available and are combined for developing into one set of unsteady aerodynamic models for six aerodynamic coefficients at low Mach numbers. A least-square-error method is used to smooth any discrepancy among these five sets of flight variables which are in the form of dynamic similitude. The tabulation is arranged only in the subspace of angles of attack because of low Mach numbers. It has been demonstrated that the same set of aerodynamic models in tabulated form is applicable to all five flights with good prediction accuracy. In this paper, the prediction accuracy will be demonstrated only for one flight. One unique feature of the aerodynamic models is that the models can predict the main reasons for flights becoming uncontrollable in a motion with large amplitudes and highly coupled longitudinal and lateral-directional modes. Another feature is that in addition to predicting accurate response for display in a simulator, it can predict the unsteady aerodynamic loads as well. These aerodynamic models, when implemented in a flight simulator, are shown to produce realistic response to varying crosswind. Fidelity of the simulation has been verified by pilots.

Experimental Investigation of Aerodynamic Hysteresis Using a Five-Degree-of-Freedom Wind-Tunnel Maneuver Rig

The high-incidence aerodynamics of a lightweight jet trainer aircraft model has been investigated using a novel five-degree-of-freedom (DOF) dynamic maneuver rig, recently updated with improved actuation and data acquisition systems, in the closed-section low-speed wind tunnel at the University of Bristol. The major focus was to identify the nonlinear and unsteady aerodynamic characteristics specific to the stall region and which affect free-to-move aircraft-model behavior. First, the unstable equilibrium states in the limit-cycle regions were stabilized, and so observed, over a wide range of angles of attack using a simple elevator feedback control law based on pitch angle and pitch-rate sensor measurements. Tests with two DOF, namely, the aircraft model and rig-arm pitch angles, revealed the existence of static hysteresis in the normal force acting on the aircraft model in the stall region. Unlocking the aircraft model in roll and yaw accompanied by feedback stabilization of the lateral–directional modes of motion demonstrated the onset of asymmetric aerodynamic rolling and yawing moments in this four-DOF configuration. This observation implicitly indicates a link between the static hystereses in the normal aerodynamic force with an onset of aerodynamic asymmetry. The experimental results show the efficiency of the updated multi-DOF actively controlled maneuver rig in providing insight into complicated aerodynamic effects within the stall region.

Nonlinear aircraft system identification using artificial neural networks enhanced by empirical mode decomposition

This paper aims to improve the performance of artificial neural networks used for the aircraft system identification by taking flight dynamic characteristics into consideration. In the proposed method, flight dynamic modes are recognized, isolated, and inputted individually to feed-forward neural networks. This method has several advantages such as being adaptive, involving all observable modes in the identification process, considering interactions between longitudinal and lateral-directional modes, and reducing noise effects. Simulated and real flight data of the HARV aircraft at high-angle of attack maneuvers are employed to train the neural networks and evaluate them. Results demonstrate improved accuracy and generality of the proposed method in comparison with the conventional ones.

Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing

Computational simulations of aerodynamic characteristics of the Common Research Model (CRM), representing a typical transport airliner are conducted using CFD methods in close proximity to the ground. The obtained dependencies on bank angle for aerodynamic forces and moments are further used in stability and controllability analysis of the lateral-directional aircraft motion. Essential changes in the lateral-directional modes in close proximity to the ground have been identified. For example, with approach to the ground, the roll subsidence and spiral eigenvalues are merging creating the oscillatory Roll-Spiral mode with quite significant frequency. This transformation of the lateral-directional dynamics in piloted simulation may affect the aircraft responses to external crosswind, modify handling quality characteristics and improve realism of crosswind landing. The material of this paper was presented at the Seventh European Conference for Aeronautics and Space Sciences EUCASS-2017. Further work is carried out for evaluation of the ground effect aerodynamics for a high-lift configuration based on a hybrid geometry of DLR F11 and NASA GTM models with fully deployed flaps and slats. Some aspects of grid generation for a high lift configuration using structured blocking approach are discussed.

Flight Dynamics and Stability of Kites in Steady and Unsteady Wind Conditions

The flight dynamics and stability of a kite with a single main line flying in steady and unsteady wind conditions are discussed. A simple dynamic model with five degrees of freedom is derived with the aid of Lagrangian formulation, which explicitly avoids any constraint force in the equations of motion. The longitudinal and lateral–directional modes and stability of the steady flight under constant wind conditions are analyzed by using both numerical and analytical methods. Taking advantage of the appearance of small dimensionless parameters in the model, useful analytical formulas for stable-designed kites are found. Under nonsteady wind-velocity conditions, the equilibrium state disappears and periodic orbits occur. The kite stability and an interesting resonance phenomenon are explored with the aid of a numerical method based on Floquet theory.

Unified Algebraic Approach to Approximation of Lateral-Directional Modes and Departure Criteria

Introduction L ITERAL expressions involving aerodynamic derivatives and inertial data provide physical insight into the behavior of the aircraft motion. For instance, they are well suited for the optimization of flight control systems, both for the setup of nominal system design and for the prediction of motion characteristics in off-nominal problems.1 In fact, such literal expressions show the direct connection between the transfer function poles and zeros as a function of the relative values of certain key derivatives and give valuable insight into the nature of the associated control problem. More precisely, they show the detailed effect of particular stability derivatives on aircraft characteristics. Also, they are of fundamental importance in obtaining stability derivatives from flight data and in developing analytical departure criteria to be used in the design process of new aircraft configurations.2 However, it is difficult to find exact closed-form solutions, especially to the aircraft modes, because both the longitudinal and the lateral aircraft eigenvalues come from fourth-order characteristic equations. Therefore, an approximation is required to arrive at reasonably compact and usable expressions that delineate the dominant effects. In many cases this process of approximation is useful for the designer. Indeed, the omission of certain terms, which are relatively unimportant, allows such important simplifications to be made that the relation between cause and effect becomes apparent. Very often such effects vary among vehicle types, so that literal approximate factors, which apply to all vehicles for all flight conditions, are quite difficult to obtain. This conclusion is particularly apparent when aircraft lateral–directional modes are considered. In particular, an accurate expression for the Dutch-roll damping is traditionally known to be a difficult task, although relatively satisfactory approximations for the spiral, roll, and Dutch-roll natural frequency are available, for example, see McRuer et al.,3 pp. 367–377. This is a serious difficulty when analytical approximations to aircraft departure criteria are sought. In fact, a natural approach to this problem is to set to zero the Dutch-roll damping expression to predict its instability. However, this is impractical as long as the Dutch-roll damping approximation is inaccurate. The main reason for this difficulty comes primarily from the physical behavior of lateral–directional motion. In fact, the easiest way to obtain accurate simplified models is to resort to a timescale analysis of the problem, separating slow from fast modes. However, when applied to the lateral–directional motion, this approach is not fully satisfactory because the complete

Analysis of the stability modes of the non-rigid airship

AbstractThis paper describes and compares various analyses leading to the development of approximate models for the linear stability modes of the non-rigid airship. The progress of the analyses was variously dependent on assumptions made from the detailed scrutiny of linear numerical models for three airships. For each airship studied, the linear models were obtained from non-linear simulation models by linearising about a number of chosen trim speeds representative of a typical speed envelope. The decoupled linear models comprised the longitudinal and lateral-directional state equations of the neutrally buoyant airship, for speeds from the hover to 30m/sec. Since the fidelity of the earliest airship models was not known, the principal purpose of this paper is to re-visit the original analysis using a later airship model of known excellent fidelity.The longitudinal modes of the airship comprise the surge mode, the heave-pitch subsidence mode and the oscillatory pitch-incidence mode. The lateral-directional modes of the airship comprise the sideslip subsidence mode, the yaw subsidence mode and the oscillatory roll pendulum mode. Approximate models for these modes are derived and expressed in terms of concise aerodynamic stability derivatives. The mode characteristics are discussed, and the approximate models are compared with the actual airship modes over the typical airspeed envelope.

Robust control law design for lateral-directional modes of an F-16/MATV using μ-synthesis and dynamic inversion

A manual flight control system for the lateral-directional dynamics of a modern fighter aircraft incorporating thrust vectoring is presented. Design goals are posed in terms of maintaining acceptable flying qualities during high angle of attack (α) manoeuvring while also achieving robustness to model parameter variations and unmodelled dynamics over the entire flight envelope. The need for gain scheduling a dynamic controller is eliminated by using an inner loop dynamic inversion/outer loop structured singular value (μ)-synthesis control structure which separately addresses operating envelope variations and robustness concerns, respectively. Performance objectives are based on commanding sideslip angle and stability axis roll rate. Realistic representations of both structured (real parametric) and unstructured uncertainty are included in the design/anlysis process. A flight condition dependent control selector maps generalized controls to physical control deflections, considering actuator redundancy, effectiveness and saturation issues. An angle of attack dependent command prefilter shapes commands to produce desired responses. Structured singular value analysis, low-order equivalent system (LOES) fits, and linear step responses demonstrate satisfaction of design goals. Simulation shows excellent control at both low and high angles of attack. © 1997 John Wiley & Sons. Ltd.

Stability boundaries for aircraft with unstable lateral-directional dynamics and control saturation

Aircraft that do not possess inherent (aerodynamic) stability must rely on closed-loop control systems for stable operation. Because there are limits on the deflections of an aircraft's control surfaces, the region of stable operation also is bounded. These boundaries are investigated for a lateral-directional example in which vertical fin size is inadequate to provide directional stability and where aileron and rudder deflections are subject to saturation. Fourth-order models are used in this study, with flight control logic based on minimum-control-energy linear-quadratic-regulatory theory. It is found that the stability boundaries can be described by unstable limit cycles surrounding stable equilibrium points. Variations in regions of stability with gain levels and command inputs are illustrated. Current results suggest guidelines for permissible limits on the open-loop instability of an aircraft's lateral-directional modes.

Parameter Identification Technology Used in Determining In-Flight Airload Parameters

An investigation was conducted to determine the feasibility of utilizing a modified Newton-Raphson computer program, developed by Taylor and Iliff of NASA, to determine the airload and the aircraft parameters concurrently from in-flight empennage and aircraft response data. Only the lateral directional mode was considered in this study. The airload responses consisted of the horizontal stabilizer rolling moment and the vertical tail sideforce. Pilot rudder pedal force time history responses were also included in the investigation. Comparisons of the in-flight coefficient parameters are made with wind-tunnel results. The a priori feature of the program was not utilized. Although there are many other techniques available, this technique is becoming recognized throughout the industry as the preferred or standard approach. The results of this investigation substantiate the practicality of the technique for the purpose of evaluating airload derivatives.