Hinge Moment Research Articles

Effect of aspect ratio variation on subsonic aerodynamics of cascade type grid fin at different gap-to-chord ratios

ABSTRACTThis paper dwells upon investigating the effect of aspect ratio (AR) variation on the aerodynamic performance of unconventional control surfaces called grid fins by virtue of a series of subsonic experiments on a simplified grid fin variant called the cascade fin. Wind tunnel tests were performed for differentAR(variable span) grid fins. The same had been investigated for different gap-to-chord ratio (g/c) variants. Results demonstrated a tangible increase in the aerodynamic efficiency as well as stall angle reduction for higherAR. Moreover, higherARleads to increased pitching moment, which emphasizes elevated hinge moment requirements. The study ensued the presence of higher deviation between the lowARfins, that is$AR<2$compared to the pertinent deviations between the highARfins, that is$AR\geq2$. The effect associated with these variations was termed as span effect in this paper. It was established that, the deviations arising due to this phenomena were lesser for higherg/cand higherAR. The analysis ofARvariation for differentg/cpresented a limiting value ofARreduction for stall performance enhancement. Thus, optimised selection of theg/candARvalues can lead to enhanced aerodynamic efficiency alongside an improved stalling characteristic.

Hinge and overturning moments due to unsteady heliostat pressure distributions in a turbulent atmospheric boundary layer

Non-uniform pressure distributions on the heliostat surface due to turbulence in the atmospheric boundary layer (ABL) have a significant impact on the maximum bending moments about the hinge of and pedestal base of a conventional pedestal-mounted heliostat. This paper correlates the movement of the centre of pressure due to the mean and peak pressure distributions with the hinge and overturning moment coefficients using high-frequency pressure and force measurements on a scale-model heliostat within two simulated ABLs generated in a wind tunnel. The positions of the centre of pressure were calculated for a range of heliostat elevation-azimuth configurations using a similar analogy to those in ASCE 7-02 for monoslope-roof buildings, ASCE 7-16 for rooftop solar panels, and in the literature on flat plates. It was found that the maximum hinge moment is strongly correlated to the centre of pressure movement from the heliostat central elevation axis. Application of stow and operating load coefficients to a full-scale 36 m2 heliostat showed that the maximum hinge moment remains below the stow hinge moment at maximum operating design gust wind speeds of 29 m/s in a suburban terrain and 33 m/s in a desert terrain. The operating hinge moments at elevation angles above 45° are less than 60% of the stow loads with a constant 40 m/s design wind speed. The results in the current study can be used to determine heliostat configurations and appropriate design wind speeds in different terrains leading to the maximum design wind loads on the elevation drive and foundation.

Actuator energy and drag minimization of a blended-wing-body with variable-camber continuous trailing-edge flaps

This article conducts a multiobjective optimization study for minimizing both the actuator energy and the total drag of a NASA aircraft, the Blended-Wing-Body (BWB), during cruising, by using the three-segment Variable-Camber Continuous Trailing-Edge Flap (VCCTEF) proposed by NASA. The metric for the electric drive actuators' energy for the BWB during cruising is characterized by summing the absolute hinge moments for all actuators. A local minimum is easily obtained for the optimization problem with a least absolute sum cost function when using a gradient-based optimizer. The minimization of the total actuator energy is converted to a linear programming problem by treating the absolute hinge moments as design variables. The induced and profile drags are considered to be the largest two contributions to the total drag. Design variables for the flap rotations and the absolute hinge moments with different orders of magnitude are scaled with respect to their maximum bounds in the optimization study to avoid numerical problems. Different VCCTEF configurations of varying deflection profiles and degrees of actuation independence and traditional flaps are studied and their performance is compared. For the BWB with four representative fuel levels, 80, 50, 20 and 0% of the maximum fuel loads, all during cruising, multiobjective optimization studies show that the VCCTEF with three individual segments can achieve a minimal total drag for the BWB while requiring a minimal total actuator energy to maintain its optimal shape for the minimal total drag.

Calculation of the Hinge Moments of a Folding Wing Aircraft during the Flight-Folding Process

A folding wing morphing aircraft should complete the folding and unfolding process of its wings while in flight. Calculating the hinge moments during the morphing process is a critical aspect of a folding wing design. Most previous studies on this problem have adopted steady-state or quasi-steady-state methods, which do not simulate the free-flying morphing process. In this study, we construct an aeroelastic flight simulation platform based on the secondary development of ADAMS software to simulate the flight-folding process of a folding wing aircraft. A flexible multibody dynamic model of the folding wing structure is established in ADAMS using modal neutral files, and the doublet lattice method is developed to generate aerodynamic influence coefficient matrices that are suitable for the flight-folding process. The user subroutine is utilized, aerodynamic loading is realized in ADAMS, and an aeroelastic flight simulation platform of a folding wing aircraft is built. On the basis of this platform, the flight-folding process of the aircraft is simulated, the hinge moments of the folding wings are calculated, and the influences of the folding rate and the aircraft’s center of gravity (c.g.) position on the results are investigated. Results show that the steady-state method is applicable to the slow folding process. For the fast folding process, the steady-state simulation errors of the hinge moments are substantially large, and a transient method is required to simulate the flight-folding process. In addition, the c.g. position considerably affects the hinge moments during the folding process. Given that the c.g. position moves aft, the maximum hinge moments of the inner and outer wings constantly increase.

FEATURES OF MODELING THE FLOW AROUND THE HELICOPTER MAIN ROTOR TAKING INTO ACCOUNT ARBITRARY BLADES MOTION

The article considers the problem of the flow around the helicopter main rotor taking into account blades flapping in the plane of rotation and in the plane of thrust as well as the elastic blades deformation. The rotor rotation is modeled by the method of converting Navier-Stokes equations from a fixed coordinate system associated with the incoming flow into a rotating system associated with the rotor hub. For axial flow problems, this makes it possible to formulate the problem as stationary at a constant rotational speed of rotor. For a mode of skewed flow around the rotor in the terms of incident flow in this system it is necessary to solve the non-stationary problem. To solve the problem, the method of deformable grids is used, in which the equations are copied taking into account the grid nodes motion determined in accordance with the spatial blades motion, and SST turbulence model is used for closure. The results of the test calculations of the main rotor aerodynamic characteristics with and without blade flapping are presented in this paper. The coefficients of the main rotor thrust cT and the blades hinge moments mh are compared. The calculations were carried out in the CFD software ANSYS CFX (TsAGI License No. 501024). The flow around a four-bladed main rotor of a radius of 2.5 meters is modeled in the regime of skewed flow. The speed of the incoming flow came to 85 m/s under normal atmospheric conditions. The rotor was at an angle of attack of −10˚. To calculate the rotor motion without taking into account the flapping movements, we used the nonstationary system of Navier-Stokes equations with the closure with SST turbulence model. The calculation was being carried out until the change in the maximum value of the rotor thrust during one revolution became less than 1%. For modeling flapping blade movements, the control laws and equations describing the angle of blade flapping as a function from its azimuth angle obtained from the experiment were used. The procedure for reconstructing the grid according to a given law was conducted using standard grid deformation methods presented in the ANSYS CFX software. When solving the nonstationary Navier-Stokes equations, a dual time step was used. The obtained results show that accounting of the effect of flapping movements and cyclic control of the blades has an impact on the character of changing the main rotor thrust coefficient during one revolution and significantly changes the shape of the graph of the hinge moment coefficient of each blade.

Numerical analysis of the effect of sweep-back angle on the stability derivatives of the grid fin

Because of high hinge moment of planar fin in supersonic flow, designers have become more attentive to the grid fin configuration in recent years. One of the disadvantages of the grid fin is its high drag force. Fortunately, this problem could be handled by implementing sweep-back angle. Few studies have been carried out to investigate the effects of the sweep-back angle on dynamic coefficients. In this paper, computational fluid dynamics is used to investigate the effect of grid fin’s sweep-back angle on the rolling and pitching dynamic coefficients in supersonic flow regime. The first step is dedicated to simulating two experimental geometries and detecting optimal mesh number and appropriate turbulence model. Unsteady dynamic coefficients along with moving mesh have been extracted by simulations. These coefficients are reported for different Mach numbers. In order to scrutinize the results, the static stability derivatives have been discussed, too. According to the simulations, each sweep-back angle has a unique trend of changing dynamic and static coefficients in terms of the Mach number. This trend is justified by studying Mach number contours for few states. Afterward, dynamic coefficients of the planar fin are presented and compared with the grid fin.

Flow Field Characterization and Visualization of Grid Fin Subsonic Flow

Grid fins are unconventional control surfaces consisting of an outer frame supporting an inner grid of intersecting planar surfaces. Although afflicted with higher drag, these have been credited for their enhanced lifting characteristics at high angles of attack and high Mach numbers, alongside reduced hinge moments accounting for the recent upsurge in their usage on numerous aerospace applications. Present investigations carry out elaborate flow field visualization and characterization underlining the rudimentary physics through a sequence of subsonic numerical simulations performed at different angles of attack and different gap (between the members) to chord ratios on a simplified grid fin variant called cascade fin. The study makes use of a new nondimensionalization technique called cumulative nondimensionalization to decipher the effect of cascading on individual members of the fin. Hence, after a comprehensive examination of the aerodynamic coefficients, pressure coefficient distribution, pressure gradient, velocity gradient, boundary layer velocity profile, and flow field visualization, the study elucidates physics associated with hastened stall angle, augmented lift-drag, and bounded efficiency accretion for gap increment.

Experimental investigation of peak wind loads on tandem operating heliostats within an atmospheric boundary layer

During the operation of a concentrating solar thermal (CST) power tower plant, heliostat mirrors inclined at different angles act as bluff bodies that are exposed to large drag loads from the wind. This experimental study investigates the aerodynamic loads on a heliostat in a tandem configuration, to determine the significance of the shielding effect from an upstream heliostat. To understand the effect of turbulence on the peak wind loads, scale-model heliostats with square facets were positioned within a part-depth atmospheric boundary layer (ABL) with a Power Law velocity profile. Peak drag coefficients on the instrumented downstream heliostat in the tandem configuration were normalized with respect to those on a single (isolated) heliostat. A range of tandem configurations were tested to determine the effects of elevation angle, azimuth angle, and gap spacing between the tandem heliostats. Findings show that peak drag loads are reduced by up to 60% on the downstream heliostat relative to an isolated heliostat at an elevation angle of 90° and a gap spacing of two chord lengths, but at higher gap spacing the shielding effect is either marginal or non-existent. Peak hinge moment coefficients on a downstream heliostat in tandem are up to seven times the load on an isolated heliostat, with the maximum occurring at 90° elevation and 180° azimuth. Base-overturning moment coefficients are less affected, as the changes in the centre of pressure location are relatively small compared to the length of the support pylon. Strouhal number analysis of the fluctuating surface pressures indicated that the dominant frequency of the pressure spectra on the downstream heliostat is over three times the value on an isolated heliostat at 45° elevation and azimuth angles. Hence, both static and dynamic effects must be considered separately in the wind load design for heliostats at typical operating angles.

Theoretical Bending Collapse of Hat-Section Tubes

This paper presents an attempt to modify an existing theoretical model to predict the bending collapse response of hat-section tubular structures. The analytical collapse model was based on Kim and Reid. Additional hinge lines created during deformation of the tube were examined and integrated with existing model to forming a modified analytical solution. Variation of the hinge moments were solved using limit analysis technique. Procedure for developing the finite element (FE) models of tube specimens was also presented. Moment-rotation characteristics from pure bending simulation were compared with analytical model and good agreement was achieved. The average of differences between simulation and calculation were found to be <5% within plastic region. In conclusion, the modified analytical solution has adequate capability to predict the moment-rotation relationship of hat-section tubes subject to pure bending..

Effect of Planar Member Cross-Section on Cascade Fin Aerodynamics

Grid fins are unconventional control and lifting surfaces consisting of an outer frame supporting an inner grid of small chord intersecting planar surfaces. Credited for their enhanced lifting characteristics at high angles of attack and wider Mach number regimes, minuscule hinge moments, and increased drag, these have been used in numerous aerospace applications. Removal of their cross-members leads to its simplified variant called cascade fins. The present study carries out numerous viscous computational fluid dynamics simulations at subsonic speed and high angles of attack to investigate and compare the impact of the horizontal planar member cross-sectional shape on cascade fin aerodynamics by elucidating the effects of using a NACA 0012 airfoil cross-section instead of a rectangular cross-section and varying the gap between their members. Appreciably higher aerodynamic efficiency attributed to drag reduction and comparable lifting characteristics along with steeper and hastened stall characteristics was deciphered for airfoil cascades. It was also found that optimally reducing the gap alleviates the stall tendency. These trends were further explained using pressure distribution plots and flow visualization analysis for the respective variant. Thus, planar member cross-section and gap selection should be done based on the aerodynamic efficiency requirement, desired maneuverability, and manufacturing cost.

Optimal performance of adaptive flap on flow separation control

The stall caused by flow separation of airfoil seriously compromises the efficiency and safety of wind turbines. Inspired by bird feathers, a passive flow control strategy was investigated by configuring adaptive flaps on the suction surface of the airfoil to delay flow separation. The Computational Fluid Dynamics (CFD) software ANSYS Fluent 17.0 using SST k–ω turbulence model was performed to study the performance of the adaptive flap with different length and location. The performance was evaluated by the comparison of total lift coefficient between the flap airfoil and clean airfoil. In addition, the performance of the double flaps configuration was investigated by Fluid-Solid Interaction (FSI) method. The results show that when the separation point is at the upstream of flap hinge point, the total lift coefficient increases with the flap rising, and when the flap reaches the optimal flap angle, the lift coefficient begins to decrease. When the flap operates in optimal angle, the closer the flap is to the trailing edge of the airfoil, the more the lift enhancement for moderate flow separation, and the closer the flap is to the leading edge of the airfoil, the more the lift enhancement for serious flow separation. For the flaps with the same location, the longer flap can block more backflow resulting in a better performance, but when the flap is long enough to block the fluid, the shorter flap has better performance. Considering the variations of the flap aerodynamic moment with the flap angle, an external hinge moment was recommended to improve the swinging flap performance.

Comparison of flutter calculation methods based on ground vibration test result

PurposeA low-cost but credible method of low-subsonic flutter analysis based on ground vibration test (GVT) results is presented. The purpose of this paper is a comparison of two methods of immediate flutter problem solution: JG2 – low cost software based on the strip theory in aerodynamics (STA) and V-g method of the flutter problem solution and ZAERO I commercial software with doublet lattice method (DLM) aerodynamic model and G method of the flutter problem solution. In both cases, the same sets of measured normal modes are used.Design/methodology/approachBefore flutter computation, resonant modes are supplied by some non-measurable but existing modes and processed using the author’s own procedure. For flutter computation, the modes are normalized using the aircraft mass model. The measured mode orthogonalization is possible. The flutter calculation made by means of both methods are performed for the MP-02 Czajka UL aircraft and the Virus SW 121 aircraft of LSA category.FindingsIn most cases, both compared flutter computation results are similar, especially in the case of high aspect wing flutter. The Czajka T-tail flutter analysis using JG2 software is more conservative than the one made by ZAERO, especially in the case of rudder flutter. The differences can be reduced if the proposed rudder effectiveness coefficients are introduced.Practical implicationsThe low-cost methods are attractive for flutter analysis of UL and light aircraft. The paper presents the scope of the low-cost JG2 method and its limitations.Originality/valueIn comparison with other works, the measured generalized masses are not used. Additionally, the rudder effectiveness reduction was implemented into the STA. However, Niedbal (1997) introduced corrections of control surface hinge moments, but the present work contains results in comparison with the outcome obtained by means of the more credible software.

Blocking force measurement of shape memory polymer composite hinges for space deployable structures

This study introduces a method for measuring the blocking force of a shape memory polymer composite hinge to quantify the performance of a shape memory polymer composite hinge for space deployable structure applications. A detailed design of how to select heating elements for a self-deployable configuration is also suggested. The shape memory polymer composite hinge consists of two reverse carpenter shape memory polymer composite tapes that were made from carbon-epoxy fabric, shape memory polymer resin, and two heating elements. The heating elements were attached to the shape memory polymer composite tape using the composite manufacturing method, and they were used as the heating source in the deployment test. The blocking force and moment of the hinge were measured using a pulley–mass system setup to examine the mechanical performance of the hinge. During the test, the shape change was recorded with a camera to calculate the moment arms. While the blocking force was 7.21 N in the initial test, it decreased slightly with the working cycle and was 6.27 N in the repeated test. The maximum hinge moment was 0.47 N m in the repeated test. In addition, the results revealed that a pop-up phenomenon occurred at the middle period of deployment. These results confirm that the shape memory polymer composite hinge works well with heating elements and provide a guideline for performance evaluation of the shape memory polymer composite hinge.

지상 및 비행 시험을 통한 플랩의 힌지 모멘트 추정

본 논문에서는 항공기 플랩 운용조건에 따라 변하는 플랩의 힌지 모멘트를 추정하는 실제적인 방법을 소개하였다. 플랩의 설계를 위하여 구조 하중해석과 풍동시험으로 산출한힌지 모멘트를 실제 비행 힌지 모멘트와 비교할 수 있었으며, 플랩 구조의 정적 안전성을 확인할 수 있었다. 이를 위해서 두 개의 변형률게이지를 플랩 힌지에 장착하였으며, 항공기 하중 모니터링 탑재장비를 사용하였다. 지상 시험을 통해서 힌지의 변형률과 모멘트의 상관관계를 해석해와 유한요소해석으로 교정하였다. 비행 시험에서는 플랩 처짐 각도 및 속도와 함께 변형률 신호를 기록하였다. 최종적으로, 계측한 변형률을 해석해와 유한요소해석으로 교정함으로서 비행 힌지 모멘트를 추정할 수 있었다.

A thermo-mechanical model for SFRC beams or slabs at elevated temperatures

The bearing capacity of steel fibre reinforced concrete (SFRC) at elevated temperatures is the subject of significant ongoing research, as the effect of steel fibres on concrete performance at higher temperatures is poorly understood. On one hand, steel fibres increase the average thermal conductivity of the concrete cross section and lead to greater heating within a concrete structural member during fire exposure, and on the other, fibres reduce crack widths and prevent excessive spalling. The former effect negatively impacts SFRC performance at high temperature, whereas the latter effect protects the inner structure from direct fire exposure. Additionally, the decreasing strength of steel at higher temperatures can result in the sudden failure of fibre or traditionally reinforced concrete. Within this contribution, a coupled thermo-mechanical model is developed in order to investigate the influence of steel fibres on the thermal loading of concrete. The effect of fibres on heat transmission within concrete, the length of time for which concrete can sustain thermal loads, and on the bending stiffness of reinforced concrete beams or slabs is investigated. The heat transfer process is modelled using Fourier’s partial differential equation of transient heat conduction. A modified plastic hinge model and moment–curvature relations are used to describe stress-dependent deformations. Thus, two alternative approaches are used to adequately track the localisation of damage for single cracks and for distributed and multiple cracking. Thermo-mechanical coupling is achieved by means of temperature-dependent stress–strain relations. These are derived for SFRC based on experimental data from the literature. Experiments are performed in which concrete slabs reinforced with variable amounts of fibres and rebar are exposed to combined thermal and mechanical loadings. The results of these experiments are used to validate the proposed model. The measured and predicted results agree well and indicate that steel fibres have a positive effect on the fire resistance of structures, assuming additional rebar is provided to prevent crack localisation. Additionally, it is shown that temperature fields within concrete remain almost unaffected by variations in fibre content.

Mechanism and Improve Methods of Rudder Lock for Mechanically Controlled Aircraft

Rudder Lock is a threat to flight safety, which should be carefully considered in the airworthiness certification. Since general aircrafts which are equipped with mechanical control system and controlled by unprofessional pilots becomes more and more popular, researches on rudder lock are still necessary. In this paper, a mechanically controlled medium sized transport is studied as an example. By analyzing the steady straight sideslip flight test data and flow field numerical simulation results, the mechanism of rudder lock is analyzed. Two aerodynamic improving methods including double-triangle dorsal fin and reducing set-back hinge balance are proposed. The flow field numerical simulation results show that double triangle dorsal fin can improve the stall characteristic of vertical tail, but the strong vortex will move the center of pressure forward, which worsens the rudder lock. Reducing set-back hinge balance can improve rudder lock effectively, while the hinge moment and rudder force will be increased, therefore the gearing ratio and tab should be carefully designed.

Hinge Moment Coefficient Prediction Tool and Control Force Analysis of Extra-300 Aerobatic Aircraft

This paper presents the development of tool that is applicable to predict hinge moment coefficients of subsonic aircraft based on Roskam’s method, including the validation and its application to predict hinge moment coefficient of an Extra-300. The hinge moment coefficients are used to predict the stick forces of the aircraft during several aerobatic maneuver i.e. inside loop, half cuban 8, split-s, and aileron roll. The maximum longitudinal stick force is 566.97 N occurs in inside loop while the maximum lateral stick force is 340.82 N occurs in aileron roll. Furthermore, validation hinge moment prediction method is performed using Cessna 172 data.

Investigation of peak wind loads on tandem heliostats in stow position

Abstract This paper investigates the effects of turbulence in the atmospheric boundary layer (ABL) on the peak wind loads on heliostats in stow position in isolation and in tandem configurations with respect to the critical scaling parameters of the heliostats. The heliostats were exposed to a part-depth ABL in a wind tunnel using two configurations of spires and roughness elements to generate a range of turbulence intensities and integral length scales. Force measurements on different-sized heliostat mirrors at a range of heights found that both peak lift and hinge moments were reduced by up to 30% on the second tandem heliostat when the spacing between the heliostat mirrors was close to the mirror chord length and converged to the isolated heliostat values when the spacing was greater than 5 times the chord length. Peak wind loads on the tandem heliostat were above those on an isolated heliostat for an integral-length-scale-to-chord-length ratio L u x / c of less than 5, whereas tandem loads were 30% lower than an isolated heliostat at L u x / c of 10. The reduced loads on the tandem heliostat corresponded to a shift to higher frequencies of the fluctuating pressure spectra, due to the break-up of large eddies by the upstream heliostat.

Simplified Numerical Approach for the Prediction of Aerodynamic Forces on Grid Fins

Grid fins are unconventional control devices used for aerodynamic control of various types of missiles. Low hinge moment requirement and superior packaging potential make grid fins attractive alternatives to conventional planar fins. Unlike missiles with planar fins, widely accepted preliminary design tools for missiles with grid fins are not available. As an alternative, aerodynamic forces and moments are obtained through full computational fluid dynamics solutions. However, generating an aerodynamic force and moment database in the preliminary design stage using full computational fluid dynamics solutions takes too much time due to the complex geometry of grid fins and the corresponding mesh requirements. In this study, the unit grid fin concept, which is a small representative portion of a grid fin, is introduced for the efficient prediction of flows around missiles with grid fin controls. The study is conducted at Mach numbers of 0.7, 1.2, and 2.5 in an angle-of-attack range between 0 and 15 deg. First, the validation of the proposed technique is done for side fins in the configuration, for which there are available experimental data. Then, the idea is applied for the simulation of the more common configuration. It is shown that, although requiring much less computational resources and time as compared to a full computational fluid dynamics solution, the unit grid fin approach can provide acceptable results for preliminary design. The body interference correction turns out to be critical in the performance of the proposed method, and the deficiency of a simple potential flow-based approach is demonstrated.

Design improvements and flap deflection evaluations with considering centrifugal load on active trailing edge flap

Purpose The purpose of this paper is to present the design, analysis and experiments of the active trailing-edge flap (Seoul National University Flap, SNUF) for vibration reduction in the helicopter rotor prior to the small-scale blades planned to test in a whirl tower. Design/methodology/approach The predictions of the hinge moment in both steady and unsteady flows were obtained through computational fluid dynamics calculations. When compared with the results originated from analytical formulations, the proposed method showed improved prediction capabilities. To validate the deflection of the flap under the centrifugal load by rotating, static analysis was conducted using both contact and rotating condition of MSC NASTRAN. The corresponding experiment also was performed using the vertical frame for simulating the effect of the centrifugal force. Findings The hinge moment of the flap is predicted through unsteady analysis in the actuation frequency of 3/rev. The material of the guide in the flap mechanism was selected through static analysis under both contact and rotating condition. Finally, reduction of the deflection occurred because of the load in the axial direction of the hinge like the centrifugal load. Practical implications The important aspects, such as design, analysis, and experiments for the active trailing-edge flap were shown. Originality/value This paper showed the relationship of the displacement, block force and voltage of the piezo-actuator, combined with the hinge moment predicted. The methodology and the experiment were presented for simulating the centrifugal force acting on the flap.