Vertical Tail Research Articles

Influence of Fluid Viscosity and Compressibility on Nonlinearities in Generalized Aerodynamic Forces for T-Tail Flutter

The numerical assessment of T-tail flutter requires a nonlinear description of the structural deformations when the unsteady aerodynamic forces comprise terms from lifting surface roll motion. For linear flutter, a linear deformation description of the vertical tail plane (VTP) out-of-plane bending results in a spurious stiffening proportional to the steady lift forces, which is corrected by incorporating second-order deformation terms in the equations of motion. While the effect of these nonlinear deformation components on the stiffness of the VTP out-of-plane bending mode shape is known from the literature, their impact on the aerodynamic coupling terms involved in T-tail flutter has not been studied so far, especially regarding amplitude-dependent characteristics. This term affects numerical results targeting common flutter analysis, as well as the study of amplitude-dependent dynamic aeroelastic stability phenomena, e.g., Limit Cycle Oscillations (LCOs). As LCOs might occur below the linear flutter boundary, fundamental knowledge about the structural and aerodynamic nonlinearities occurring in the dynamical system is essential. This paper gives an insight into the aerodynamic nonlinearities for representative structural deformations usually encountered in T-tail flutter mechanisms using a CFD approach in the time domain. It further outlines the impact of geometrically nonlinear deformations on the aerodynamic nonlinearities. For this, the horizontal tail plane (HTP) is considered in isolated form to exclude aerodynamic interference effects from the studies and subjected to rigid body roll and yaw motion as an approximation to the structural mode shapes. The complexity of the aerodynamics is increased successively from subsonic inviscid flow to transonic viscous flow. At a subsonic Mach number, a distinct aerodynamic nonlinearity in stiffness and damping in the aerodynamic coupling term HTP roll on yaw is shown. Geometric nonlinearities result in an almost entire cancellation of the stiffness nonlinearity and an increase in damping nonlinearity. The viscous forces result in a stiffness offset with respect to the inviscid results, but do not alter the observed nonlinearities, as well as the impact of geometric nonlinearities. At a transonic Mach number, the aerodynamic stiffness nonlinearity is amplified further and the damping nonlinearity is reduced considerably. Here, the geometrically nonlinear motion description reduces the aerodynamic stiffness nonlinearity as well, but does not cancel it.

Free as a Bird: Event-Based Dynamic Sense-and-Avoid for Ornithopter Robot Flight

Autonomous flight of flapping-wing robots is a major challenge for robot perception. Most of the previous <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sense-and-avoid</i> works have studied the problem of obstacle avoidance for flapping-wing robots considering only static obstacles. This letter presents a fully onboard dynamic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sense-and-avoid</i> scheme for large-scale ornithopters using event cameras. These sensors trigger pixel information due to changes of illumination in the scene such as those produced by dynamic objects. The method performs <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">event-by-event</i> processing in low-cost hardware such as those onboard small aerial vehicles. The proposed scheme detects obstacles and evaluates possible collisions with the robot body. The onboard controller actuates over the horizontal and vertical tail deflections to execute the avoidance maneuver. The scheme is validated in both indoor and outdoor scenarios using obstacles of different shapes and sizes. To the best of the authors’ knowledge, this is the first event-based method for dynamic obstacle avoidance in a flapping-wing robot.

Accuracy Analysis for a Flow Line Process using a Mobile Holding Fixture for Machining CFRP Components

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The aerospace sector is challenged to produce airplanes more efficiently and resiliently in the future. This leads to an increasing demand for improving productivity and flexibility as well as providing solutions for sustainable developments. A bottleneck in production is the machining of large-scale components. Apart from the machining tasks, non-productive operations like fixture adjustment, component handling, referencing and localization are performed within the machining station and can constitute up to 50% of the overall workload. In the UniFix project, Fraunhofer IFAM is participating in the development of a mobile fixture system for large-scale aircraft components, like vertical tail plane and landing flap components of the single aisle aircrafts. By installing components into a mobile holding fixture with an according referencing scheme, a flow line can be established that is composed of specialized workstations discharging the machining station from non-productive processes, leading to higher productivity.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;This paper focusses on the component localization and referencing strategies for this mobile holding fixture. Here, specific challenges are caused by the transport in between the referencing and the machining process. Therefore, influences that contribute to the overall geometric uncertainty of the referencing process for machining are evaluated in detail. In this work, an automated laser scanner based localization of the components will be presented. Furthermore, estimations on the uncertainty in the involved systems will be conducted and propagated through the localization process.&lt;/div&gt;&lt;/div&gt;

Online Surface Roughness Prediction for Assembly Interfaces of Vertical Tail Integrating Tool Wear under Variable Cutting Parameters.

Monitoring surface quality during machining has considerable practical significance for the performance of high-value products, particularly for their assembly interfaces. Surface roughness is the most important metric of surface quality. Currently, the research on online surface roughness prediction has several limitations. The effect of tool wear variation on surface roughness is seldom considered in machining. In addition, the deterioration trend of surface roughness and tool wear differs under variable cutting parameters. The prediction models trained under one set of cutting parameters fail when cutting parameters change. Accordingly, to timely monitor the surface quality of assembly interfaces of high-value products, this paper proposes a surface roughness prediction method that considers the tool wear variation under variable cutting parameters. In this method, a stacked autoencoder and long short-term memory network (SAE–LSTM) is designed as the fundamental surface roughness prediction model using tool wear conditions and sensor signals as inputs. The transfer learning strategy is applied to the SAE–LSTM such that the surface roughness online prediction under variable cutting parameters can be realized. Machining experiments for the assembly interface (using Ti6Al4V as material) of an aircraft’s vertical tail are conducted, and monitoring data are used to validate the proposed method. Ablation studies are implemented to evaluate the key modules of the proposed model. The experimental results show that the proposed method outperforms other models and is capable of tracking the true surface roughness with time. Specifically, the minimum values of the root mean square error and mean absolute percentage error of the prediction results after transfer learning are 0.027 μm and 1.56%, respectively.

Design Evolution and Wind Tunnel Tests of a Three-Lifting Surface Regional Transport Aircraft

This paper deals with the experimental assessment of the aerodynamic characteristics of an innovative large turboprop aircraft. The configuration is a three-lifting surfaces airplane with rear engine installation at tail tips, conceived to carry up to 130 passengers and targeting a minimum economic and environmental impact, which is competitive with regional jets on short and medium hauls. The three-lifting surfaces layout is the output of previous research made by the authors, and it has been selected to fully comply with the market and design constraints. An experimental test campaign was required to validate the aerodynamics, stability, and control of this innovative configuration. From the results of the first campaign, it appeared that the aircraft had insufficient longitudinal and directional stability. Thus, the authors worked to improve these characteristics, updating the design and executing a second wind tunnel test campaign. The evolution of the design is described in the first part of the paper. In the second part, the authors discuss the aerodynamic interference effects among aircraft components, detailing how the combined downwash coming from both the canard and wing, as well as their wakes, affects the empennage aerodynamics. Experimental tests have revealed a significant reduction of the longitudinal stability due to canard additional downwash, especially at low attitudes. Furthermore, it was found that the canard generates a non-linearity on the aircraft directional stability derivative at moderate sideslip angles because of its tip vortex impinging on the vertical tail. Despite the detrimental interference due to the canard, the updated aircraft proved to be statically stable with sufficient margin at the most rearward center of gravity. Lessons learned in this research may be useful to aerodynamicists and aircraft designers facing similar issues.

Research on dynamic aerodynamic characteristics of flying wing model with low aspect ratio

The flying wing with low aspect ratio removes the horizontal and vertical tails and adopts configuration of wing-body fusion, which has better lift and drag characteristics and stealth than the traditional wing-body split configuration. In this paper, with the help of the semi-reflux transient transonic wind tunnel of China Aerodynamics Research and Development Center, a single-degree-of-freedom pitching dynamic force test is carried out on the standard model of flying wing with low aspect ratio, and the mechanism of some cases is analyzed through numerical calculation. The study found that when the fuselage is forced to pitch at f=1Hz: The normal force coefficient curve will form a hysteresis loop in the shape of a spoon; during the pitching process, the angle of attack of stall is delayed from the 40° which is the angle of attack of stall in static case to 45°; the pitching movement will delay the dissipation of the energy of leading edge vortex along the flow direction and increases the vortex suction at the rear of the wing; the flow pattern of the suction surface is similar during the upward elevation process, and spanwise flow is more severe than the static case under the same angle of attack.

Real-Time Vision-Based Aircraft Vertical Tail Damage Detection and Parameter Estimation

The need for reliable, fast, and accurate detection of fault is the key to fault-tolerant control reconfiguration of any flight control system. It is known that faults such as structural damage greatly modify the aerodynamic characteristics, often represented by stability and control derivatives. They also result in abrupt deterioration of flight performance and handling quality, which impairs safety. Since no detection technique is as reliable and fast as the Human Visual System (HVS), this paper demonstrates how popular vision algorithms such as edge detection and structural similarity index can be used for real-time detection of vertical tail damage of a fighter aircraft. A novel geometric method is proposed for fault identification using traditional mathematical geometry. Empirical techniques are used for the estimation of stability and control derivatives to generate a mathematical model of damaged aircraft instead of relying on expensive wind tunnel data. Flight mechanics analysis of the data generated confirms the effects of vertical damage in terms of reduction of static and dynamic directional stability and its control effectiveness. The parametrized state matrix thus obtained for the given flight condition thus leads to efficient real-time control reconfiguration of a damaged aircraft for safe recovery. The importance of this paper lies in using the established techniques of image processing for fault detection of damaged aircraft and parametrization for subsequent control reconfiguration, which is a novel application.

Investigation of propeller slipstream effects on lateral and directional static stability of transport aircraft

ABSTRACT The aerodynamic characteristics of turboprop aircraft are greatly affected by the running propellers. In this paper, propeller slipstream effects on the static lateral-directional stability characteristics of a typical twin-engine turboprop aircraft with clockwise rotating propellers were investigated through unsteady computational fluid dynamics (CFD) simulations and wind tunnel experiments. The propeller slipstream led to a significant decrease in the lateral static stability contribution of the wing-body-nacelle (WBN), and the most affected wing sections were located near the left boundary of the port propeller slipstream region. Moreover, the influence of the propeller slipstream on the lateral static stability contribution of the vertical tail plane (VTP) significantly altered the rolling moment curve slope of the entire airframe. Due to the effects of the propeller slipstream on the local dynamic pressure and therefore the effectiveness of the VTP, the aircraft showed significantly different directional static stability behaviors between the positive and negative sideslip conditions. Furthermore, it was found that the configurations with clockwise rotating propellers readily experience dramatic losses in directional static stability at large negative sideslip angles.

Dry carbon fiber applications in aerospace sector and automation options

Considering the latest introduction of the dry multiaxial fabrics into Aeronautical applications/programs (wing skins, Vertical Tail Plane [VTP] skins, winglets, bulkheads, cargo doors, etc.), together with the lack of automation for the preform creation and its deposition onto the corresponding molds, this paper will cover different potential solutions for the manufacturing of skins and stiffeners. In all cases, looking to the automated dry multiaxial fabric preform creation, lay-up and forming.

Effect of Twin Vertical Stabilizers on Lateral Directional Static Stability of an Aircraft – A Computational Study

The advantages of twin vertical Stabilizers over a single vertical Stabilizer of an aero plane are the rationale for this study. For conventional aero planes, the use of double vertical Stabilizers is being considered. The contribution to lateral stability has been examined for this application. XFLR5 software was used to conduct the overall analysis. The analysis was conducted for a single vertical Stabilizer as well as twin vertical Stabilizers, and the findings were compiled and correlated. It is critical to be able to fully explain and evaluate the stability and control parameters. It is crucial to understand the relationship between the aerodynamics of the airframe and its stability characteristics in order to increase flight endurance and deployment effectiveness. The stability analysis based on the dynamic model of the twin boom vertical Stabilizer is presented in this paper. The lateral-directional stability of an aero plane with a single vertical tail is determined to be 20% more efficient than that with twin boom vertical Stabilizers. The trim condition is moderately satisfied by an aircraft with twin vertical Stabilizers.

Investigation of Wing, Fuselage and Tail Design Parameters in Boeing and Airbus Aircraft

The study aims to examine the wing, fuselage and tail design parameters of Airbus and Boeing aircraft and to reveal the design criteria for the sizing of large commercial jets. Tin the study, the design and sizing data of 11 Airbus models and 14 Boeing models were compiled. The number of abreast seats, maximum seats, fuselage length, fuselage width, fineness ratio, tail section length, cockpit length and cargo compartment length are the main parameters studied about the fuselage design. Wing area, wingspan, aspect ratio, mean aerodynamic chord (MAC), taper ratio, dihedral angle, quarter chord sweep angle, and winglet lengths are the main parameters studied about the wing design. The area, span, aspect ratio, taper ratio, and quarter chord sweep angle of vertical and horizontal tail are the main parameters studied about the tail design. As a result of the study, exceptional designs and average design criteria for Airbus and Boeing aircraft have been revealed with the help of charts presented. In addition, the obtained linear correlations reveal that the MAC has about 0.14 times the wingspan and about 1.168 times the average chord length.

Aircraft Configuration Parameter Boundaries Based on Closed-Loop Flying Qualities Requirements

For aircraft employing the fly-by-wire technique, the closed-loop dynamic characteristics are determined by both the configuration design and the flight control system. As the capacity of the control system has certain limitations, the configuration parameters are also constrained by the requirements of the closed-loop flying qualities. This paper presents an aircraft configuration parameter boundaries determination method based on closed-loop flying qualities requirements independent of the actual flight control law design, mainly aiming at the parameters that affect the stability and control characteristics. First, a nonlinear dynamic inversion-based flight control law is adopted to decouple the control law gains from the configuration parameters and to study the relationship between the configuration parameters and closed-loop flying qualities. Second, a flying qualities evaluation scheme is established by selecting the most severe flight conditions and the evaluation criteria that are most sensitive to changes in the parameters. Finally, the parameter boundaries according to the requirements of Level 1 flying qualities are determined by searching for the critical values that lead to degradation of the flying qualities. The proposed method is verified by an application example of the design ranges of a sample aircraft’s wing position, horizontal tail area, center of gravity, vertical tail area and vertical tail position.

Prediction of Vertical Tail Buffet Using CFD/CSD Coupling Method

The vertical tail buffet induced by the vortex breakdown flow is numerically investigated. The unsteady flow is calculated by solving the RANS equations. The structural dynamic equations are decoupled in the modal coordinates. The radial basis functions (RBFs) are employed to generate the deformation mesh. The buffet response of the flexible tail is predicted by coupling the three sets of equations. The results show that the presence of asymmetry flow on the inner and outer surface of the tail forced the structural deflection offsetting the outboard. The frequency of the 2nd bending mode of the tail structure meets the peak frequency of the pressure fluctuation upon the tail surface, and the resonance phenomenon was observed. Therefore, the 2nd bending responses govern the flow field surrounding the vertical tail. Finally, the displacement of the vertical tail is small, while the acceleration with a large quantitation forces the vertical tail undergoing severe addition inertial loads.

Stability characteristics and airworthiness requirements of blended wing body aircraft with podded engines

Blended-Wing-Body (BWB) aircraft have a relatively short fuselage and no horizontal tail, and they usually adopt podded engines and a V tail instead of a vertical tail. Generally, BWB aircraft have decreased longitudinal and directional static stability and damping. In this paper, the three-axis static and dynamic stability characteristics of an example BWB aircraft with podded engines are studied. According to the differences in flight characteristics of BWB aircraft and conventional aircraft, the different airworthiness requirements for BWB aircraft are analyzed: first, based on current airworthiness regulations and transport aircraft flying quality specification, the relaxation requirement of longitudinal static stability for BWB aircraft is studied; second, the influences of podded engines on longitudinal trim, attitude and trajectory responses and maximum directional control power requirement of BWB aircraft are analyzed; third, the changes in the proportional relationships between the takeoff characteristic speeds of the example BWB aircraft are analyzed. In view of these variations in directional control power requirement and relationships between takeoff characteristic speeds, new recommendations for airworthiness evaluation are proposed for BWB aircraft. The conclusions of this paper are helpful references for configuration design, flight control law design and airworthiness evaluation of BWB aircraft.

Guidance, Navigation, and Control for Fixed-Wing UAV

The purpose of this paper is to develop a fixed-wing aircraft that has the abilities of both vertical take-off (VTOL) and a fixed-wing aircraft. To achieve this goal, a prototype of a fixed-wing gyroplane with two propellers is developed and a rotor can maneuver like a drone and also has the ability of vertical take-off and landing similar to a helicopter. This study provides guidance, navigation, and control algorithm for the gyrocopter. Firstly, this study describes the dynamics of the fixed-wing aircraft and its control inputs, i.e., throttle, blade pitch, and thrust vectors. Secondly, the inflow velocity, the forces acting on the rotor blade, and the factors affecting the rotor speed are analyzed. Afterward, the mathematical models of the rotor, dual engines, wings, and vertical and horizontal tails are presented. Later, the flight control strategy using a global processing system (GPS) module is designed. The parameters that are examined are attitude, speed, altitude, turn, and take-off control. Lastly, hardware in the loop (HWIL) based simulations proves the effectiveness and robustness of the navigation guidance and control mechanism. The simulations confirm that the proposed novel mechanism is robust and satisfies mission requirements. The gyrocopter remains stable during the whole flight and maneuvers the designated path efficiently.

Empennage sizing with the tail volume complemented with a method for dorsal fin layout

Purpose: Provide good values for the tail volume coefficient and the lever arm as a percentage of the fuselage length. Provide a statistical method for dorsal fin layout. – Methodology: Based on an understanding of flight physics, the statistical correlation of real aircraft parameters is investigated. This is based on the firm conviction that high fidelity parameters for future aircraft need a checked against parameters of existing successful aircraft. – Findings: Typical tail volume coefficients are between 0.5 and 1.0 for the horizontal tail and between 0.03 and 0.08 for the vertical tail depending on aircraft category. Empennage statistics have clear trends. The often weak correlation shows that aircraft design allows for sufficient designer's choice. Only a minority of aircraft feature a dorsal fin. Designers see it as an added surface rather than as part of the vertical tail. It is used to limit the hypothetical risk of vertical tail stall due to high sideslip angles. – Research Limitations: Results obtained from statistics are close to reality, but not a proof to fulfill requirements. – Practical Implications: Methods from the paper can be used for quick initial sizing of a vertical tail with or without dorsal fin or sizing of a horizontal tail. These results can also be used as good starting values for optimization tools in aircraft design. – Originality: Estimation of the tail lever arm is necessary for sizing with the tail volume coefficient, but had not been investigated to any detail. A method for the layout of dorsal fins was missing.

Design of Low Altitude Long Endurance Solar-Powered UAV Using Genetic Algorithm

This paper presents a novel framework for the design of a low altitude long endurance solar-powered UAV for multiple-day flight. The genetic algorithm is used to optimize wing airfoil using CST parameterization, along with wing, horizontal and vertical tail geometry. The mass estimation model presented in this paper is based on structural layout, design and available materials used in the fabrication of similar UAVs. This model also caters for additional weight due to the change in wing airfoil. The configuration is optimized for a user-defined static margin, thereby incorporating static stability in the optimization. Longitudinal and lateral control systems are developed for the optimized configuration using the inner–outer loop strategy with an LQR and PID controller, respectively. A six degree-of-freedom nonlinear simulation is performed for the validation of the proposed control scheme. The results of nonlinear simulations are in good agreement with static analysis, validating the complete design process.

Layered Mastopexy with Augmentation in Muscle Splitting Biplane: A Modification for Lower Pole Safety and Stability.

Single-stage mastopexy with augmentation is a commonly performed procedure. The single-stage procedure can be performed in primary cases or a secondary procedure in patients with previous history of augmentation, mastopexy or mastopexy with augmentation. The procedure is challenging and not without its risks. A retrospective chart review of all consecutive cases of layered mastopexy with augmentation mammoplasties, carried out from September 2015 to August 2019, was performed. All patients had their implants placed in muscle splitting pocket first and access for the pocket was closed prior to the commencement of mastopexy. During the period of 4years, 102 consecutive layered mastopexy with augmentations were performed in muscle splitting plane. Of these 102 patients, 74 (72.5%) patients had it as a primary and 28 (27.5%) as a secondary procedure. Of these 102 patients, 53 (52.0%) had textured, 37 (36.3%) had smooth and 12 (11.8%) had microtextured implants and 72 (70.6%) patients had high profile and 30 (29.4%) had medium profile implants. Same size implant was used in 89 patients with a mean of 298cc, and 13 patients had different size implants with a mean of 362cc on the right and 395cc on the left. In current study, bilateral periareolar, vertical scar cat's tail and Wise pattern mastopexies were performed in 11, 51 and 27 patients, respectively. Of the 102 patients, 5 had unilateral right periareolar, 5 unilateral right vertical scar cat's tail, 2 unilateral left periareolar and 1 patient had a combination of periareolar and vertical scar combination. There was no nipple loss or periprosthetic infection. There was a minor wound breakdown seen in 4 (3.9%), haematoma in 2 (2.1%), nipple sensation loss in 2 (2.1%) and 12 (11.8%) had layered mastopexy as a part of a combined procedure. Revision was performed in 6 (6.5%), drains were used in 14 (13.7%), and 92 (90.2%) had the procedure performed as a day case. Layered mastopexy with augmentation is a safe procedure with added stability and safety to lower pole of the breast as well as nipple-areolar complex. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Investigation of vertical tail buffeting alleviation controlled by nanosecond plasma actuators

An experimental study was conducted with the aim of alleviating the vertical tail buffeting of a 55° delta wing using pulsed nanosecond dielectric barrier discharge plasma actuators. The flow physics in the event of wing stall, flow reattachment, vortex breakdown, shear layer under plasma actuation were obtained and analyzed, and results indicate that plasma actuation promotes flow attachment and manipulates the shear layer. The acceleration results indicate that the structural response of the vertical tail increases with an increasing angle of attack, and the first bending mode response increases most significantly at the post-stall angle. Manipulation of flow field by plasma actuation produces a considerable reduction in buffeting response and mainly controls the first bending mode. The characteristics of velocity fluctuations show two important factors affecting buffeting: the redistribution of loads and the spectrum change of fluctuations, both of which are related to the movement of the impingement point of the shear layer onto the vertical tail controlled by plasma actuation. Theoretical analysis indicates that the impingement point moving downward in the vertical direction of the vertical tail under plasma actuation is the main reason for reduction of the first bending mode response.

Vertical tail sizing of propeller-driven aircraft considering the asymmetric blade effect

An engineering approach is presented to analyse the asymmetric blade thrust effect with the help of analytical and semi-empirical methods. It is shown that the contribution of the asymmetric blade thrust effect in the lateral-directional stability of multi-engine propeller-driven aircraft is significant particularly in critical flight conditions with one engine out of service. Also, in some cases where the engines are rotating in one direction, the asymmetric blade effect has substantial effects on the handling qualities of the aircraft even in normal flight conditions. Overall, due to the significant contribution of this phenomenon in the lateral-directional stability of propeller-driven airplanes, it is important to consider it in the design of the vertical stabilizer and rudder. The resulting analytical method has been used to determine the vertical tail incident angle and desired rudder deflection in accordance with the most critical flight condition for two different cases and validated to ensure the accuracy of the result. In this work, the aerodynamic coefficients as well as the stability and control derivatives have been predicted using analytical and semi-empirical methods validated for light aircraft.