Applied Mechanics and Materials Vol. 225

Abstract: This work proposes a novel and simple fabrication process of a nickel-copper thermal bimorph actuator. This new fabrication process employs only two-step electroplating technique that is easy, cheap and compatible for various materials. In this study, the total thickness of fabricated cantilever actuator is around 80 μm, i.e. 30±10 and 50±10 μm for nickel and copper, respectively, and its length is equal to 22.5 mm. For actuator’s width, it is varied as 258±7, 351±7 and 447±7 μm. After heating by applying current through the actuator’s structure, the actuator bends up due to the elongation mismatch between copper and nickel elements. It is found that the deflection becomes larger for a narrower actuator. From the experiments, the deflection at current of 2.5A for 258±7 μm wide actuator is approximately equal to 4 mm. In addition, the response of all actuators is faster than 1 Hz. With obtained large deflection and fast response, the fabricated actuators are viable to employ for flow control applications.

Abstract: Phugoid mode is a lowly damped, low-frequency oscillatory motion representing vertical translation usually related to kinetic and potential energy interchange. MIL-F-8785C standard has ruled out qualitative specification requirements on measurement of flying and handling qualities of piloted aircraft. For phugoid mode, these requirements lie in the value of its damping ratio. Small aircraft is sensitive to atmospheric conditions and poor phugoid mode performance is observed in many unmanned aircraft. This paper discusses the effect of airspeed and altitude to phugoid mode of small, unmanned blended wing-body (BWB) aircraft named Baseline-II E-2. Baseline-II is a low subsonic, remotely-piloted UAV used to study the behaviour of a BWB-type aircraft. The case presented here is an E-2 version in which a specifically-designed canard is incorporated as its longitudinal control surface. Five Category B flight cases (airspeeds) per altitude-case, and three altitude cases (low, medium and high) are studied. Model-N dynamic model is introduced here to become the basis of flight simulation. The model is compared to models derived by other authors and approximation equations. The mean of simulating phugoid behaviour is using state-space representation of the aircraft using Matlab SIMULINK. The computations show that Baseline-II E-2 undamped natural frequency of phugoid mode is inversely-proportional to airspeed and reduces as altitude increases. These have adverse effect on its damping ratio that increases near parabolically when the aircraft flies faster, and reduces when it climbs up. The cause of these trends is looked into in detail and issues concerning Baseline-II E-2’s unsatisfactory and unstable phugoid mode oscillation at low speed are addressed.

Abstract: Conventional aircraft designs have been highly successful within commercial passengers transport markets for a very long time, as evident from current fleet of many airlines. However, with the anticipated stricter environmental regulations to be imposed on future flight operations by the related governing bodies, the relevance of conventional aircraft designs to remain competitive has been questioned. On the other hand, some research ventures have been made to pursue revolutionary designs like blended wing body (BWB). This study aims to preliminarily assess the comparison of expected future emission performance between conventional aircraft design and blended wing body design. It addresses the ongoing debate on whether conventional aircraft designs can be expected to be able to cope with impending stricter environmental regulations and/or whether the venture into revolutionary designs is really necessary. Analyses done are largely based on the historical trends of conventional aircraft designs with regards to the lift-to-drag ratio and fuel consumption parameters. As for the blended wing body, its projected emissions performance is based on published data in the literature. The outcome from these analyses solidifies the belief that conventional aircraft designs will face tougher chances to remain operational under new environmental regulations and the search for revolutionary design with better aerodynamic efficiency such as blended wing body is becoming rather necessary.

Abstract: 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.

Abstract: To maintain flight safety, all transport aircraft designs should satisfy airworthiness standard regulation. One fundamental issue of the aircraft design that relates directly to flight safety as well as commercial aspect of the aircraft is on the evaluation of the maximum speed within the designated flight envelope. In the present work, a study is performed to evaluate the negative altitude requirement related to aeroelastic instability analysis as one requirement that should be fulfilled to design the maximum speed. An analytical derivation to obtain the negative altitude is performed based on the airworthiness requirement that a transport airplane must be designed to be free from aeroelastic instability within the flight envelope encompassed by the dive speed or dive Mach number versus altitude envelope enlarged at all points by an increase of 15% in equivalent airspeed at both constant Mach number and constant altitude. To take into account variation in atmospheric condition as function of altitude, the international standard regulation is used as referenced. The analysis result shows that a single negative altitude can be obtained using these criteria regardless of the dive speed or dive Mach number. A further discussion on the application of the negative altitude concept to UAV (Unmanned Aerial Vehicle), in relation to UAV Standard Airworthiness Requirement STANAG 4671, is presented.

Abstract: An area under consideration of improving the mission effectiveness of small-scale, autonomous Uninhabited Aerial Vehicles (UAVs) has been the increase of speed. One method is to incorporate dynamic slope soaring maneuvers as part of the flight path during waypoint navigation. Research into autonomous dynamic soaring capability in small-scale UAVs began with selecting a suitable maneuver heuristic. The output from the heuristic model has then been used to formulate a non-iterative trajectory forming algorithm. By utilizing Dubin’s curves, a viable trajectory can be generated between the exit point of the dynamic soaring maneuver and the next waypoint. The result is a complete, easily implemented three-dimensional autonomous dynamic soaring capability.

Abstract: Tethered Satellite Systems (TSS) have been used in various applications such as in performing space interferometry, orbit transfer and other relevant fields. As far as the operation system of a TSS is concerned, it is crucial to ensure that the tether will not go slack as its slackness would adversely affects the overall operation outcome due to an undesirable system dynamics. Therefore, it is important to investigate the types of conditions that will cause the tether slackness. Investigations on in-plane and out-of plane libration angles can be utilized to measure at what point that the tether will go slack. Based on previous research works, usually a rigid tether comprising of a uniformed mass is considered while the connecting two satellites are regarded as point masses in order to simplify the governing dynamics equation of motion. However, in order to develop a much more accurate modeling, a flexible tether is chosen by further incorporating the reeling mechanism, attitude dynamics of rigid bodies and tether deformations. Furthermore, a tether has a tendency to go slack if the in-plane and out-of plane libration angle exceeds 65° and 60° respectively regardless of the types of tether utilized whether it being a rigid or a flexible one. Thus, the tension of the tether will serves as a constraint and plotted against the in-plane and out-of plane libration motions that would be attained via the generalized forces. The results will then be analyzed to establish in-plane and out-of plane libration boundaries. Subsequently, the in-plane and out-of plane operation contrains are established for TSS corresponding to a reference mission.

Abstract: This paper deals with attitude determination, parameter identification and reference sensor calibration simultaneously. A LEO satellite’s attitude, inertia tensor as well as calibration of Three-Axis-Magnetometer (TAM) are estimated during a maneuver designed to satisfy persistency of excitation condition. For this purpose, kinematic and kinetic state equations of spacecraft motion are augmented for the determination of inertia tensor and TAM calibration parameters including scale factors, misalignments and biases along three body axes. Attitude determination is a nonlinear estimation problem. Unscented Kalman Filter (UKF) as an advanced nonlinear estimation algorithm with good performance can be used to estimate satellite attitude but its computational cost is considerably larger than the widespread, low accuracy, Extended Kalman Filter (EKF). Reduced Sigma Points Filters provide good solutions and also decrease run time of UKF. However, in contrast to nonlinear problem of attitude determination, parameter identification and sensor calibration have linear dynamics. Therefore, a new Marginal UKF (MUKF) is proposed that combines the utility of Kalman Filter with Modified UKF (MMUKF). The proposed MMUKF utilizes only 14 sigma points to achieve the complete 25-dimensional state vector estimation. Additionally, a Monte Carlo simulation has demonstrated a good accuracy for concurrent estimation of attitude, inertia tensor as well as TAM calibration parameters in significantly less time with respect to sole utilization of the UKF.

Abstract: Injector is one of the vital devices in liquid rocket engine (LRE) as small changes in its configurations and design can result in significantly different LRE performance. Characteristics of spray such as spray cone angle, breakup length and Sauter mean diameter (SMD) are examples of crucial parameters that play the important role in the performance of liquid propellant rocket engine. Wider spray cone angle is beneficial for widespread of fuel in the combustion chamber for fast quiet ignition and a shorter breakup length provides shorter combustion chamber to be utilized and small SMD will result in fast and clean combustion. There are several mechanisms of liquid atomization such as swirling, e.g. jet swirl atomization or introducing bubbles into the liquid and effervescent atomization. Introducing a swirl component in the flow can enhance the propellant atomization and mixing whereas introducing bubbling gas directly into the liquid stream inside the injector leads to finer sprays even at lower injection pressures. This paper reviews the influence of both operating conditions and injector internal geometries towards the spray characteristics of swirl effervescent injectors. Operating conditions reviewed are injection pressure and gas-to-liquid ratio (GLR), while the injector internal geometries reviewed are limited to swirler geometry, mixing chamber diameter (d_c), mixing chamber length (l_c), aeration hole diameter (d_a), discharge orifice diameter (d_o) and discharge orifice length (l_o).

Abstract: Parametric optimization study is carried out on performance measure for assessing the benefits of relevant ground-track parameters and Instantaneous Overlap Area (IOA) in near earth and near-equatorial twin-satellite formation flying to explore its potential as space platform oriented towards Tropical Resources and Environment Monitoring mission. The present study also emphasizes two aspects: the dynamics of relative motion of multiple spacecrafts and the desirable ground tracks such missions. Relative motion dynamics incorporating Clohessy-Wiltshire Equation for circular orbits is used as a reference. The performance metric is synthesized as a tradeoff between exact definition and intuitive judgment.