Longitudinal Stability Derivatives Research Articles

Mathematical modelling of a single tethered aerostat using longitudinal stability derivatives

Lighter-than-air (LTA) aerial vehicles such as airships and aerostats can be found in various strategic and commercial applications, primarily due to their capability to hover and stealth. The mathematical model of these vehicles helps in understanding their complex dynamics and designing and developing proper stabilisation systems for them. Stability derivatives have been used for developing mathematical models for heavier-than-air aerial vehicles since their introduction. This paper presents a methodology to develop a mathematical model of an aerostat based on stability derivatives. One of the major contributions of this study is the estimation of aerostat’s added mass terms expressed as longitudinal stability derivatives due to acceleration of the longitudinal motion variables. A longitudinally decoupled linear mathematical model of a single-tethered aerostat using stability derivatives is investigated in this study. A computational fluid dynamics (CFD)-based analysis of the 3D model of the vehicle is used to obtain the stability derivatives. The methodology presented considers the aerostat and tether models separately before coupling them to create the full model. The stability derivative analysis is carried out using ANSYS Fluent, and the coupled tethered aerostat model is investigated using MATLAB 2020. The negative pitch angle of the aerostat is caused by the selection of the pitching centre as the aerostat centre of volume instead of the tether confluence point. The tension force on the tether, which is proportional to the wind velocity, and aerostat velocity components are found to be stabilised within 200–400 s.

Stability Evaluation of a Fixed-Wing Unmanned Aerial Vehicle with Morphing Wingtip

Aeronautical applications of morphing technologies are continued to increase their popularity and wide spread application during last years. The technology takes place in not only military, but also civil applications that aims providing superior performances to manned or unmanned aircraft than conventional configurations. However, multidisciplinary approach is required for an aerial vehicle to have ultimate outcome from such an application due to existence of interdisciplinary interactions. Therefore, this research aims to investigate effects of morphing wingtip application on longitudinal and lateral-directional stabilities of a fixed-wing unmanned aerial vehicle, which have remarkable effect on autonomous control performance considerations. In this article, morphing wingtip refers to folding the wing from a determined spanwise location with a dihedral angle. With the aim of the study, wingtips of an unmanned aerial vehicle were folded with 15, 30 and 45 degrees of dihedral angles to be compared with original non-dihedral design. Longitudinal and lateral-directional characteristics of new variations were evaluated in terms of stability derivatives by means of linearized equations of motion that were also presented in state-space representation. Aerodynamic impacts of each variation were assessed by means of computational results obtained from analyses with three-dimensional panel method. Furthermore, taking inertial changes into consideration, concluding remarks on both longitudinal and lateral-directional stability derivatives were presented for each configuration.

Estimation of longitudinal aerodynamic parameters using recurrent neural network

AbstractThe aerodynamic modelling is one of the challenging tasks that is generally established using the results of the computational fluid dynamic software and wind tunnel analysis performed either on the scaled model or the prototype. In order to improve the confidence of the estimates, the conventional parameter estimation methods such as equation error method (EEM) and output error method (OEM) are more often applied to extract the aircraft’s stability and control derivatives from its respective flight test data. The quality of the estimates gets influenced due to the presence of the measurement and process noises in the flight test data. With the advancement in the machine learning algorithms, the data driven methods have got more attention in the modelling of a system based on the input-output measurements and also, in the identification of the system/model parameters. The research article investigates the longitudinal stability and control derivatives of the aerodynamic models by using an integrated optimisation algorithm based on a recurrent neural network. The flight test data of Hansa-3 and HFB 320 aircraft were used as case studies to see the efficacy of the parameter estimation algorithm and further, the confidence of the estimates were demonstrated in terms of the standard deviations. Finally, the simulated variables obtained using the estimates demonstrate a qualitative estimation in the presence of the noise.

Estimation and Separation of Longitudinal Dynamic Stability Derivatives with Forced Oscillation Method Using Computational Fluid Dynamics

This paper focuses on estimating dynamic stability derivatives using a computational fluid dynamics (CFD)-based force oscillation method, and on separating the coupled dynamic derivatives terms obtained from the method. A transient RANS solver is used to calculate the time history of aerodynamic moments for a test model oscillating about the center of gravity, from which the coupled dynamic derivatives are estimated. The separation of the coupled derivatives term is carried out by simulating simple harmonic oscillation motions such as plunging motion and flapping motion which can isolate the pitching moment due to AOA rate (Cmα˙) and the pitching moment due to pitch rate (Cmq), respectively. The periodic motions are implemented using a CFD dynamic mesh technique with user-defined function (UDF). For the validation test, steady and unsteady simulations are performed on the Army-Navy Finner Missile model. The static aerodynamic moments and pressure distribution, as well as the coupled dynamic derivative results from the pitching oscillation mode, show good agreement with the previously published wind tunnel tests and CFD analysis data. In order to separate the coupled derivative terms, two additional harmonic oscillation modes of plunging and flapping motions are tested with the angle of attack variations from 0 to 85 degrees at a supersonic speed to provide real insight on the missile maneuverability. The cross-validation study between the three oscillation modes indicates the summation of the individual plunging and flapping results becoming nearly identical to the coupled derivative results from the pitching motion, which implies the entire set of coupled and separated dynamic derivative terms can be effectively estimated with only two out of three modes. The advantages and disadvantages of each method are discussed to determine the efficient approach of estimating the dynamic stability derivatives using the forced oscillation method.

A Preliminary Study of Parameter Estimation for Fixed Wing Aircraft and High Endurability Parafoil Aerial Vehicle

High Endurability Aerial vehicle includes Airship, Powered parafoil aerial vehicle (PPAV). These flying aerial vehicles have excellent endurance and durability. Nowadays, research in lighter than air technology is pacing up fast. In the past years, the design and development of high endurable flying vehicle has grown due to their application in monitoring of floods/ drought, aerial photography, transportation, surveillance in terrain prone areas, reconnaissance missions etc. System Identification is a mathematical tool applied to develop mathematical model of any physical system based on measured data. Research on System Identification of these types of vehicles is on latest trends. Dynamic modelling of these types of vehicles is more complex than fixed wing aircraft. A detail Literature review in system Identification of PPAV and fixed wing aircraft is presented aiming to provide a source of information for researchers to make vehicle fully autonomous from manual controls. Various system Identification Techniques to estimate parameters of flying aerial vehicles are discussed. Longitudinal stability derivatives of fixed wing Hansa-3 aircraft and PPAV are compared. The methodology used in this study to estimate the longitudinal stability derivatives is ML Method. The results obtained in form of stability derivatives of Hansa-3 aircraft and Powered parafoil aerial vehicle are presented in tabular form. This study will give insight of identification techniques used to estimate parameters.

A numerical study into the longitudinal dynamic stability of the tailless aircraft

PurposeThe purpose of this research is a study into a mathematical approach of a tailless aircraft dynamic stability analysis. This research is focused on investigation of influence of elevons (elevator) on stability derivatives and consequently on the aircraft longitudinal dynamic stability. The main research question is to determine whether this impact should be taken into account on the conceptual and preliminary stage of the analysis of the longitudinal dynamic stability.Design/methodology/approachAerodynamic coefficients and longitudinal stability derivatives were computed by Panukl (panel methods). The analysis of the dynamic stability of the tailless aircraft was made by the Matlab code and SDSA package.FindingsThe main result of the research is a comparison of the dynamic stability of the tailless aircraft for different approaches, with and without the impact of elevator deflection on the trim drag and stability derivatives.Research limitations/implicationsThis paper presents research that mostly should be considered on the preliminary stage of aircraft design and dynamic stability analysis. The impact of elevons deflection on the aircraft moment of inertia has been omitted.Practical implicationsThe results of this research will be useful for the further design of small tailless unmanned aerial vehicles (UAVs).Originality/valueThis research reveals that in case of the analysis of small tailless UAVs, the impact of elevons deflection on stability derivatives is bigger than the impact of a Mach number. This impact should be taken into consideration, especially for a phugoid mode.

Regressor time-shifting to identify longitudinal stability and control derivatives of the Jetstream 3102

The Jetstream 31 G-NFLA aircraft is used as a national flying laboratory test vehicle for flight dynamics research and teaching purposes. It has been the subject of much theoretical and experimental modelling and therefore, the need for generating validation data through flight testing is critical. In this paper, the aircraft's short period pitch oscillation mode characteristics are identified using data from sixteen flight tests. An identification procedure based on the least squares method and reduced order state-space model is used and the need for pre-processing regressors due to the effects of sensor location and instrumentation delays is highlighted. It has been shown that time-shifting the regressors based on relative locations of the angle of attack vanes and the inertial measurement unit results in significant reductions in uncertainty bounds of the estimated aeroderivatives and also a model that provides a closer match to flight test data. The estimated models are validated using separate flight test data and the variations in aeroderivatives over a range of airspeeds and centre of gravity positions are also presented.

Development and validation of an enhanced semi-empirical method for estimation of aerodynamic characteristics of light, propeller-driven airplanes

This study is intended to introduce an enhanced semi-empirical method for estimation of longitudinal and lateral-directional stability and control derivatives in the preliminary design phase of light airplanes. Specialised for light, single or twin propeller-driven airplanes, available state-of-the-art analytical procedures and design data compendia are combined and modified in a unique compatible method, and automated in NAMAYEH software. In the present study, modified procedures and the software structure are presented. Afterwards, the proposed method is applied to a four-place, low wing, single-engine, propeller-driven general aviation airplane. In order to validate the proposed method, the estimated aerodynamic characteristics are compared with the wind tunnel test data as well as DATCOM and VLM-based method estimations. The results indicate that the proposed method is able to predict the aerodynamic characteristics in an acceptable range of accuracy from zero-lift to stall conditions in all configurations.

Numerical Study of Reduced Frequency Effect on Longitudinal Stability Derivatives of Airfoil under Pitching and Plunging Oscillations

In this study, incompressible, unsteady and turbulent flow over an airfoil with pitching and plunging oscillations is numerically studied in order to investigate the effect of reduced frequency on stability derivatives of oscillating airfoil. Linear k – e model called Launder-Sharma and Rhie and Chow model are used for turbulence modeling and overcoming pressure checkerboard problem. This means that a co-located approach is proposed in this paper to study a moving grid problem, and the results demonstrate the high accuracy of the method. Control volume and Crank-Nicholson discretization method are also used for the numerical solution. It is shown that the longitudinal stability derivatives of plunging and pitching motions trend change intensively beyond the stall angle of attack while pitching rate has a completely opposite behavior. The results also show that increasing reduced frequency leads to stability reduction in plunging oscillation but it does not have significant effect on pitching oscillation case in pre-stall, stall and post-stall conditions. Grid convergence is examined to assess the accuracy of the numerical method that shows the high accuracy of it and this is a prominent achievement of the present study. The results of the proposed method in forces and moment show a good agreement with the experimental data.

On the Determination of Longitudinal Transfer Function of the Cessna - 182 Aircraft Model

The present work focuses on the development of computer code related to the longitudinal stability analysis on a propeller driven light aircraft model. The computer code designed in such a way, so for a given aircraft data will produce the result in term of: 1) Longitudinal stability derivatives in non dimensional form as well as in their dimensional form, 2) The longitudinal stability aircraft characteristics related to position of neutral point ( stick free and stick fixed ) also the requested forces for deflecting the control surface, 3) The transfer function in response to the control surface deflection for the component velocity and pitch angle. Through this developed computer code one can make an assessment the longitudinal behavior for the propeller driven light aircraft [.

Nonlinear and Linear Unstable Aircraft Parameter Estimations Using Neural Partial Differentiation

To overcome the numerical problems faced by conventional methods for the parameter estimation of linear and nonlinear unstable aircraft dynamics, an approach based on neural partial differentiation is proposed. An equation for the relative standard deviation, which is equivalent to the Cramer–Rao bound in methods such as output error approach, is derived for the statistical analysis of the estimates obtained using the neural partial differentiation approach and verified through numerical simulation. The neural architecture to be used for the parameter estimation is also discussed. It is shown that the neural partial differentiation approach is better than the least-squares approach for noisy data. The longitudinal axis stability and control derivatives are obtained for simulated data, with and without noise for an unstable aircraft, using the neural partial differentiation approach and compared with the least-squares and stabilized output error methods. Moreover, the longitudinal axis stability and control derivatives estimated from actual flight data of the unstable X-31A aircraft are compared with the least-squares and stabilized output error approaches, proving the efficacy and superiority of the proposed neural approach.

Computational Aerodynamics Analysis of a Light Aircraft

Abstract: This work aims to study and simulate the flow field around light a/c usingnumerical solution based on solving Reynolds Averaged Navier-Stokes equations coupledwith K-ω SST turbulence model.Solution strategy began by analyzing wing alone then analyzing the whole a/c configuration.This strategy allows studying the wing flow field carefully and analyzing the vortices whichoccur over the wing and capture their effective regions at critical design conditions like stallcondition. These regions were captured by plotting pressure contours and flow pathlines.The aerodynamic behavior of this aircraft was investigated at different angles of attack andside slip angles. The x, y and z forces and moments were calculated at flight speed of 50m/sand at sea level conditions. Lift and drag curves for different angles of attack were plotted.The maximum lift coefficient for this a/c was 1.67 which occurred at angle of attack 16o , themaximum lift to drag ratio (L/D) found to be 14 which occurred at α=3o, and the zero lift dragcoefficient was 0.0342. Also the yawing moment coefficient was plotted for different side slipangles as well as rolling moment.The longitudinal stability derivatives with respect to angle of attack, speed variation (u), pitchrate (q) and time rate of change of angle of attack were calculated using obtained CFD results.Regarding lateral stability only side slip derivatives were calculated.

Stability Analysis of a Light Aircraft Configuration Using Computational Fluid Dynamics

This work aims to simulate and study the flow field around SAFAT-01 aircraft using numerical solution based on solving Reynolds Averaged Navier-Stokes equations coupled with K-ω SST turbulent model. The aerodynamics behavior of SAFAT-01 aircraft developed at SAFAT aviation complex were calculated at different angles of attack and side slip angles. The x,y and z forces and moments were calculated at flight speed 50m/s and at sea level condition. Lift and drag curves for different angles of attack were plotted. The maximum lift coefficient for SAFAT-01 was 1.67 which occurred at angle of attack 16° and Maximum lift to drag ratio (L/D) was 14 which occurred at α=3°, and the zero lift drag coefficient was 0.0342. Also the yawing moment coefficient was plotted for different side slip angles as well as rolling moment. The longitudinal stability derivatives with respect to angle of attack, speed variation (u), rate of pitch (q) and time rate of change of angle of attack were calculated using obtained CFD results. Concerning lateral stability only side slips derivatives were calculated. To validate this numerical simulation USAF Digital DATCOM is used to analyze this aircraft; a comparison between predicted results for this aircraft and Digital DATCOM indicated that this numerical simulation has high ability for predicting the aerodynamics characteristics.

강제조화운동을 이용한 SDM의 세로 및 방향 안정성 미계수 예측

This paper presents the computations of the longitudinal and directional stability derivatives for the SDM(Standard Dynamic Model). The static and dynamic derivatives are evaluated at once using forced harmonic oscillations in the pitch and yaw directions. For the numerical simulations, a 3-D Euler solver that uses a dual time stepping method for unsteady time accurate simulations is applied. This work investigates the variation of the derivatives in terms of the Mach number and the several motion parameters. Good agreement of the pitch and yaw stability derivatives with previously published numerical results and experimental results are observed.

Application of a Pendulum Support Test Rig for Aircraft Stability Derivative Estimation

This paper presents a novel technique for extracting longitudinal stability derivative information from an actively controlled wind-tunnel test model. The technique, designated as the pendulum support rig, uses a test model mounted inverted and suspended from the wind-tunnel roof via a supporting strut and a single-degree-of-freedom gimbal providing model motion in heave and forward translation. An additional single-degree-of-freedom gimbal connecting the model to the support strut was also used to allow model rotation in pitch. Overall, the technique was found to perform well at predicting the dominant longitudinal stability and control derivatives. This was assessed primarily against the results from an existing established technique obtained by an independent source and from results obtained by the author in a previous investigation, using a different technique.

Identification of Aircraft Longitudinal Stability and Control Derivatives Combining Global Search Natural Algorithms and a Gradient Based Algorithm

In this work, two optimization methods are investigated to accomplish the parameter identification of the longitudinal motion of a military aircraft within the framework of the Output Error methodology. One of these methods is based on natural algorithms, in particular, the genetic algorithms and particle swarm optimization, which combined constitute the so called Life Cycle Method. The other is the Levenberg-Marquardt optimization algorithm, which is a gradient based method. Since the methodologies differ in the way they perform the optimization, being the first based on search and so appropriate for global minima search and the second gradient based, thus, good for local minima, both are compared and used in such a way that they complement each other.

Aircraft longitudinal stability and control derivatives identification by using life cycle and Levenberg–Marquardt optimization algorithms

In this work, two optimization algorithms are investigated to accomplish the parameter identification of the longitudinal motion of a real aircraft by using the output error method. The first algorithm is the nature-inspired algorithm named the life cycle model, which is a composed strategy based on other heuristics such as genetic algorithms and particle swarm optimization. The second one is the gradient-based technique named Levenberg–Marquardt algorithm, which is a variant of the Gauss–Newton method. Flight test data, performed with a training jet aircraft (Xavante AT-26), were used to feed the output error method. In this context, both optimization algorithms were tested, in solo performance and in a cascade-type approach. Results are reported, aiming to illustrate the success of using the proposed methodology.

Software development for subsonic aircraft’s unsteady longitudinal stability derivatives calculation

Subsonic general configuration aircrafts? unsteady longitudinal aerodynamic stability derivatives can be estimated using finite element methodology based on the Doublet Lattice Method (DLM), the Slender Body Theory (SBT) and the Method of Images (MI). Applying this methodology, software DERIV is developed. The obtained results from DERIV are compared to NASTRAN examples HA21A and HA75H. A good agreement is achieved.

Design of an Aerolevitation Electric Vehiclefor High-Speed Ground Transportation System

An aerolevitation electric vehicle, acting as a tracked wing-in-ground-effect vehicle, is conceptually designed to match the design requirements. The aerodynamic interaction between the vehicle and its track is investigated using a combination of approaches. A boundary-element method is used to study the effect of steady, nonplanar ground effect on the vehicle. The more complicated flow characteristics are investigated using a Navier-Stokes computation. The data obtained from the numerical simulations are compared with the data measured from wind-tunnel tests. The results computed using the boundary-element method agree with the measured data. The longitudinal and lateral stability derivatives are estimated, and a guidance and control system is designed using intelligent techniques based on the estimated stability derivates.

Dynamic flight stability in the desert locust Schistocerca gregaria.

Here we provide the first formal quantitative analysis of dynamic stability in a flying animal. By measuring the longitudinal static stability derivatives and mass distribution of desert locusts Schistocerca gregaria, we find that their static stability and static control responses are insufficient to provide asymptotic longitudinal dynamic stability unless they are sensitive to pitch attitude (measured with respect to an inertial or earth-fixed frame) as well as aerodynamic incidence (measured relative to the direction of flight). We find no evidence for a 'constant-lift reaction', previously supposed to keep lift production constant over a range of body angles, and show that such a reaction would be inconsequential because locusts can potentially correct for pitch disturbances within a single wingbeat. The static stability derivatives identify three natural longitudinal modes of motion: one stable subsidence mode, one unstable divergence mode, and one stable oscillatory mode (which is present with or without pitch attitude control). The latter is identified with the short period mode of aircraft, and shown to consist of rapid pitch oscillations with negligible changes in forward speed. The frequency of the short period mode (approx. 10 Hz) is only half the wingbeat frequency (approx. 22 Hz), so the mode would become coupled with the flapping cycle without adequate damping. Pitch rate damping is shown to be highly effective for this purpose - especially at the small scales associated with insect flight - and may be essential in stabilising locust flight. Although having a short period mode frequency close to the wingbeat frequency risks coupling, it is essential for control inputs made at the level of a single wingbeat to be effective. This is identified as a general constraint on flight control in flying animals.