Keywords: Control
Abstract: The size and complexity of an airplane wing is determined by the maximum lift that it can generate, mostly for takeoff and landing purposes, and this is limited by flow separation. A change in camber provided by a simple flap is ineffective beyond a flap deflection of approximately 15o. Active control of flow separation could easily double this number therefore increasing the effectiveness of control surfaces by 50%. It could make a typical airplane lighter, its wings smaller or the approach and departure angles to and from airports steeper. Although some principles of active separation control are well known their application to commercial aircraft did not follow suit because the devices they use are either heavy, large, and complex, or they require substantial energy to operate. Sweeping jet actuators that have proven their effectiveness and possess no moving parts overcame many of the objections stated above. Thus active separation control experiments were performed at the California Institute of Technology and at The University of Arizona on a variety of swept back wing shapes some of which represented generic vertical tail models of currently manufactured airplanes. The results obtained on small scale models were so encouraging that NASA and Boeing decided jointly to test the idea on a full scale 757 vertical tail at the National Full Scale Aeronautical Complex (NFAC) at NASA’s Ames Research Center. These full scale experiments passed the required “success criteria” to be incorporated into Boeing’s Eco-Demonstrator 757 Aircraft that will be test flown within a year. According to official press release 37 actuators were used at NFAC to pass an agreed upon success criterion that improved the rudder effectiveness and a similar number will be used on the test aircraft. However a very significant result was obtained at all the wind tunnels by using a small number of sparsely distributed actuators to generate an improvement that fell slightly short of the required “success criterion”. The idea is rooted in the application of boundary layer theory to swept back airfoils of infinite span. The concept that is commonly referred to as the “Independence Principle” was considered inapplicable to turbulent flows for more than fifty years, and it cannot be rigorously applied to finite, tapered wings such as the vertical tail. Nevertheless the precept is sufficiently robust to be reduced to practice as it broadly suggests that the spanwise flow contributes to separation although its dominance is not an indicator of stall. Therefore the spanwise flow on swept back wings should be tackled first and reduced as much as possible before attempting to control separation in the customary manner. The experimental program was accompanied and sometimes led by CFD (Computational Fluid Dynamics) that proved to be woefully lacking in its predictive capabilities in this case. The various hurdles that had to be overcome when the experiment moved from a small university model to a full scale vertical tail will be discussed.

Keywords: Aerospace Systems and Systems Engineering
Abstract: In times of Net-Centric Warfare, the Air Defense Network becomes the highest echelon system of systems that in and of itself comprises complex sub systems. The combination consists - Sensor systems whose task is to create a dynamic Air Situation Picture that detects, locates, classifies and identifies the air threats (specifically when dealing with multi-stage ballistic missiles it is necessary to discriminate the penetrating body that carries the warhead from the other missile parts); - Different types of interceptors each with its own performance envelopes and capabilities against the threats (shooters); - Command and control systems for each layer separately and for the system of systems.

An incorporated command and control system is intended to perform the defense processes – threat evaluation, optimal allocation of interceptors against threats (according to the defense policy), coordination, firing and guidance to the targets according to the selected policy. The aforementioned are realized via a connectivity component that enables a coordinated operation of all system components. A multi-layer defense system is intended to increase the defense immunity by providing additional interception opportunities at different altitudes and ranges while adhering to defense economic considerations and firing additional interceptors if the first attempt fails, all subject to the levels and characteristics of threats and defense policy. A multi-layered system significantly increases the defense effectiveness and with that opens the range of possibilities for engaging targets. On the other hand new complexities also arise due to mutual disturbances and other phenomena that demand coordination between the various defense layers that cannot be operated independently.

The lecture discusses qualitative and conceptual challenges and outlines system solution approaches.

Keywords: Aerospace Sructures Design, testing and Manufacturing
Abstract: The design of lightweight composite structures, for example airframe structures, relies on extensive testing, coupled to a bottom-up, pyramidal building block approach, to ensure structural integrity and damage tolerance. Reducing the number of tests can lead to a substantial decrease in total design cost of many vehicles. Cost reduction is enabled by developing high fidelity computational models which can provide valuable information regarding the performance of a structure up to and including failure, provided the modeling is based on material parameters that can be measured, and is validated using laboratory tests that are designed to be discriminatory. This activity, which is now a major area of research falls under the broad umbrella of “virtual” testing, and also includes parallel activities such as ICME (integrated computational materials science and engineering), and “digital twin” (the process of creating a high fidelity computational model of individual aircraft, to integrate computation of structural deflections and temperatures in response to flight conditions, with a depository of local damage evolution so that the “state” of the vehicle is updated and current at any given time). In this talk, the author will provide the state of the art in virtual testing and the future challenges and opportunities in this area. Finite element models for laminated composites that can be used in ICME and “digital twin” activities of aero-composite structures will be presented and the material parameters that are needed to execute the model and how these can be measured using coupon level samples will be discussed. Validation of the models through open hole tension and open hole compression tests of composite structural panels will be presented. Finally, the many opportunities available to extend the model using multi-scaling strategies will be discussed and the many challenges that one encounters will also be presented.

Keywords: Student Competition
Abstract: SAMSON– Space Autonomous Mission for Swarming and Geolocation with Nanosatellites is a satellite mission led by the Technion, supported by the Israeli space industries and integrated with student teams. The SAMSON mission will include a cluster of three nano-satellites, based on the CubeSat standard. The mission is set to launch at 2015, and is planned for at least one year in low earth orbit (LEO). SAMSON project has two main goals – 1. Demonstrate long-term autonomous cluster flight of multiple satellites. 2. Determine the position of cooperative terrestrial emitter (geolocation). The 2012-2013 SAMSON Student Project consisted of 4th year Aerospace students from the Technion. The students took part in engineering, designing and analyzing several of the satellite's sub-systems. The student group, comprised of three teams, worked with mentors from the Technion and industries on the different sub-systems - 1. Geolocation algorithm. 2. Full system simulation. 3. Propulsion system alternatives.

Keywords: Student Competition
Abstract: The “Birdinator” project’s main goal was to understand the mechanics of a bird’s flight in nature in order to later design and build an artificial bird, resembling a real bird as much as possible to in both appearance and flight mechanics.

Keywords: Student Competition
Abstract: This article summarizes the work of a senior design project conducted at the Tel Aviv University School of Mechanical Engineering, during the year of 2012- 2013. The primary goal of the project was to design, build and fly a mini-Unmanned Aerial Vehicle (UAV). The secondary goal was to learn a practical teamwork, iterations-based, industrial method of engineering design and initial production, through the actual "hands-on" conduction of such a process.

Keywords: Student Competition
Abstract: In recent years, the Unmanned Ariel Vehicle (UAV) market has grown significantly, and has materialized itself as one of the main markets within the global and local aerial vehicle industry for military use. Nowadays, the civil market is becoming ready for it to take a leap forward. It is a great challenge to attempt entering the civil use UAV market with a useful solution that can be affordable for the majority of potential customers. A group of nine B.Sc. Mechanical Engineering students of Tel Aviv University gathered for a collective project to meet the challenge. The purpose of this project was to design, build and fly a single-engine UAV, under the guidance of Mr. Shlomo Tsach. The group designed a UAV, based on a thorough analysis of potential design and solutions and working in an iterative design manner. Upon finalizing the design, the group built the UAV in a process involving the work of the entire team which resulted in "Lucy" – a civil purpose UAV. Finally, the group performed a series of test flights, to assess the UAV’s compliance with the design’s requirements and expectations.

Keywords: Student Competition, Performance, Design Optimization
Abstract: This article summarizes the work of a senior design project at the Technion Aerospace Faculty aimed at designing and eventually building a small UAV for the DBFAIAA competition. The objective of this year’s competition was to simulate stealth UAV with the ability to carry internal and external payload. Initially the competition rules were carefully studied in order to determine the effect of different aircraft aspects on the score. This revealed that focusing on a single design parameter will not yield an overall higher flight score; therefore an optimization process was required between RAC and performance. Another important factor that dictates our design was the requirement to take off within a 30x30 square ft. austere field. The UAV designed and presented in this article has a conventional geometry of main wing, and back tail with landing gears. The aircraft’s main structure was based on carbon fiber tubes, which have the highest strength to weight ratio. The internal payload compartment was built as a separate structure, which was not part of the aircraft body. This specific design allowed easy aircraft loading with its third mission payloads. This year’s competition includes three different missions. In each mission the aircraft will be judged by different parameters. The UAV was not designed for high airspeeds, but for high lifting capabilities, aimed at maximizing the team's competition score, as well as allowing it to takeoff within the limits of the competition rules. The designed aircraft is able to lift 1.36 kg, approximately 34% of its maximum takeoff weight. The airplane’s payload compartment is designed to carry 9 internal rockets, and the wings can carry up to 6 external rockets. The maximum airspeed that can be achieved when flown without payloads is 24 m/sec, and the cruise speed of this configuration is 20 m/sec.

Keywords: Student Competition, Propulsion, Materials, Solid Mechanics
Abstract: Today the flight industry contributes 2% of the world's carbon emissions. Till 2050 it is expected to get up to 3%. This paper presents the solution for the problem - the design of a 50 passengers' electrical motorized aircraft – D2R. Creating a new innovative, multi discipline and feasible solution, the design had to overcome challenges in terms of power and energy, and so it introduces a solution of Li-Air batteries and super conducting materials. The innovative design and unfamiliar energy and propulsion systems prevents us from a weight certainty, and to make up for it the aircraft is designed with 95% of composite materials in the structure body, thus helping create high performances in many function aspects. D2R is a regional aircraft which can get up to a 1000nm range because of its aspect ratio is higher than average. This paper shows the design process including analysis and decisions that were made. The combination of electrical propulsion and aviation is not simple, but possible and should be on the flight industry agenda.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Avionics, Student Competition
Abstract: A low speed closed loop wind tunnel was designed, constructed and calibrated in Afeka, Tel Aviv Academic College of Engineering. It has a 50cm X50 cm cross section test section and can run at a maximum speed of 60 m/s. The wind tunnel was built by three students as a graduation project for the degree of B.Sc. mechanical engineering. The wind tunnel was built in the fluid mechanics laboratory and will be used for instruction, development and research activities of the college. The main objective of this paper is to review the technical justifications for the selected options of each one of the major parts, namely, the fan, motor, diffusers, corners, turning vanes, honeycomb, mashes, inlet contraction, test section, control, data acquisition and analysis system. The first author was responsible for the full construction of all the elements, integration of the wind tunnel and the required infrastructure. The second Author took care of the test section, the measuring sensors and the calibration models. The third author was in charge of the computerized and manual control as well as the data acquisition and data analysis systems. Following the completion of assembly of the wind tunnel, flow field measurements across the test section were taken. According to the design criteria of all the critical elements of the wind tunnel it is expected that the turbulence level in the test section will be below 0.2%. The flow quality and the representative force results are indicating a reliable jump start for the instructive and development work to be done in the wind tunnel facility at Afeka College of Engineering.

Keywords: Combustion, Student Competition
Abstract: The Stirling engine is an external combustion engine. Being so, and unlike in the more familiar internal combustion engine, a variety of heat sources can be used, such as solar energy, nuclear energy, residual heat etc. In application to space, where the gas combustion process as a heat source is impossible due to lack of oxygen, the Stirling engine becomes a suitable solution. Based on the prior work conducted in the author’s laboratories, a mismatch between the analytical and experimental data for assessing the Stirling engine output parameters was observed. To diminish the gap between the predictions and the measured data, this study discusses the inclusion of the air leakage effect in the numerical model. Air leakage was evaluated experimentally and the model was accordingly updated. The results demonstrate a 25% decrease in the predicted pressure within the engine and 8% decrease in the output power However, since the deviation still remains significant, further work is recomended for improving the model.

Keywords: Student Competition
Abstract: The “Parash” was designed as a senior year student project, during the period from October 2012 to July 2013. The team members gathered once a week, and gained knowledge about missiles, guidance, warheads, aerodynamics and propulsion. The main goals of the missile were set by the project’s supervisor. The “Parash” is an anti-tank missile designed to meet the needs of infantry soldiers in modern battlefield. With 1100[mm] length, 90[mm] diameter, and only 9.49 [kg] of mass, the “Parash” reaches a range of slightly above 4000 [m], and has the ability to penetrate a reactive armor and 600 [mm] thickness. An aerodynamic model was formed, including wing shapes and profiles .From the model, aerodynamic coefficients were derived and maneuvering performance was calculated. In order to verify the aerodynamic model, wind-tunnel experiments were made using a rapid prototype model (3D Printing). Results correspond with the theoretical model (which was made using the “Missile Datcom” program). Yet, an adjustment has to be made in order to verify real time conditions. Even though it requires an expensive homing device, the guidance method to be used in “Parash” is Proportional Navigation. It meets the requirements of moderate maneuvers and the ability to hit targets in motion. A test program was written, in order to determine if all operational requirements were met. Such as: range, penetration, incidents and responses, and more. A solid propellant rocket engine was defined to meet standards. The propellant is a combination of Ammonium perchlorate (AP) as the oxidizer and Hydroxyl-terminated polybutadiene (HTPB) as the binder. The unique shape of the solid propellant provides 2 [s] of acceleration and 19[s] of cruise flight at 200[ 𝑚 𝑠 ]. On top of these, the “Parash” is equipped with a launch motor in order to protect the shooter, and reduce the smoke generated at the launch zone, with may expose the shooter’s location. In order to achieve maximal penetration, a tandem shaped charge warhead is placed inside the missile. The front warhead is intended to neutralize the reactive armor, allowing the main warhead penetrate the rest of the armor left. Adjusting the warhead geometry has yield the required penetration depth. The “Parash” system has a launch unit including a lightweight bomb rack for protecting the missile till it is fired, and a tripod to stabilize and take the large loads during launching.

Keywords: Student Competition, Aircraft Maintenance, Health Monitoring
Abstract: Bearings are part of any rotating machinery. An unexpected bearing failure can cause catastrophic damage for the whole system. For this reason, good monitoring of bearing health status is required. Creating “smart” bearings with an embedded sensor continuously monitoring itself, will improve bearing monitoring. This project describes the feasibility analysis of such a “smart” bearing. The study is based on static and dynamic finite element 3D models and was experimentally confirmed.

Keywords: Student Competition, Control, Numerical Methods, Modeling Simulation
Abstract: This paper describes some of our project results where a multipurpose UAV (MP-UAV) is being developed. The MP-UAV is a VTOL UAV, which is developed with the goal of extending standard VTOL UAVs’ flight range capabilities. Its construction is based on a fixed wing with four fins holding the UAV’s four motors, In the hovering mode, the aircraft behaves very much like a quad-rotor where a hovering or slow flight is possible; this mode is also utilized for takeoff and landing. In the flight mode, the wing creates the needed high lift for holding the aircraft and enabling long flight range with an improved energetic efficiency (compared to the hovering mode). The research goals of this project are designing the multipurpose UAV, developing its dynamical model and creating a closed loop stability system based on low cost electronic components. Real flight results confirms that the MP-UAV is capable for both hovering and flight.

Keywords: Aeroacoustics, Student Competition, Aerospace Sructures Design, testing and Manufacturing
Abstract:

Keywords: Aerodynamics, CFD, Fluid Dynamics, Student Competition
Abstract: It is commonly known that the aerodynamic performance of two-dimensional airfoils suffers at Reynolds numbers below a hundred thousand. This phenomenon is associated with flow separation which induces a laminar-to-turbulent transition. Not alike high Reynolds number flows, where flow separation is restricted to a short chordwise region in comparison to the airfoil chord, at Reynolds numbers of several ten-thousands the extent of the separation region is considerably longer and cause a noticeable aerodynamic effect when it reattaches. The purpose of the current study is to analyze the flow mechanisms involved in this process using two quantitative experimental techniques. A thermography analysis yielded the heat transfer distribution from the wing surface, which can infer about the flow mechanisms that govern the flow field. The surface–based analysis was combined with two-dimensional particle image velocimetry that yielded the flow field over the wing. This approach was undertaken to determine whether a surface-based analysis is capable of replacing volumetric techniques when designing two-dimensional airfoils at Reynolds numbers of few ten thousand.

Keywords: Student Competition
Abstract: The flow regime on giant rotating spheres, such as the atmospheric flow on the bigger planets in our solar system, is characterized by jet streams flowing parallel to each other, in latitudinal directions. As the flow regime on these planets is turbulent, one could wonder how a turbulent flow regime can arrange in such steady state without the turbulence disturbing the great order. The dominance of Coriolis force in turbulent flows on rotating spheres provides an explanation to this phenomenon as it creates anisotropy in the flow, where the appearance of Rossby waves results in a new flow regime called "Zonostrophic Regime". The work that was done in this project, both restoring past simulations and performing new calculations, is in attempt to further prove the existence of a zonostrophic regime as the cause for the phenomenon as it occurs in nature. The new calculations examine the changes in values of integral scales as a function of the flow regime on a sphere.

Keywords: Student Competition, Aerodynamics, CFD, Fluid Dynamics
Abstract: Existing studies on sound wave propagation in rarefied gases examine sound generation by actuated boundaries subject to isothermal boundary conditions. We study the effect of replacing the isothermal conditions with heat-flux conditions (which are easier to implement in practice) on the propagation of sound. Towards this end, we consider the response of a rarefied gas, confined in an adiabatic (thermally insulated) channel, to instantaneous (small-amplitude) motion of its boundaries in the normal direction. The analytical problem is formulated and solved for an ideal monatomic gas at collisionless (highly rarefied) and continuum conditions, and the effect of heat-flux insulation is demonstrated through comparisonwith counterpart results obtained for a gas confined between isothermalwalls. The results, found in quantitative agreement with numericalMonte Carlo simulations, motivate further study on the effect of heat injection at the boundaries on propagation of sound waves in the gas. It is demonstrated that heat “injection” or “suction” may be applied to achieve ‘acoustic cloaking’ of actuated boundaries, a much desired property in classical acoustics.

Keywords: Student Competition, Aerodynamics, CFD, Fluid Dynamics
Abstract: Hummingbirds replace their flight feathers in a deterministic fashion which is commonly called feathers moult. The wing of Calypte anna, one of the hummingbird species, consists of ten primary flight feathers; therefore, it is expected that during the feathers moult, the absence of wing feathers will cause a considerable change of the wing aerodynamic characteristics. In this study direct measurements of the aerodynamic loads were recorded. Using dynamic similarity rules, several wing configurations were tested in water at several Reynolds numbers. This unique approach allowed obtaining the unsteady aerodynamic loads during the motion of wing models at characteristic angles-of-attack and allowed a detailed comparison between the various wing configurations. The results show that the leading-edge feathers are essential to obtain high aerodynamic lift. Moreover, the evolution of the aerodynamic loads acting on the wing, for a given geometric angle-of-attack, indicates that at increasing Reynolds numbers the aerodynamic loads reached a steady-stage further along the wing down-stroke. This result reflect the need to prescribe a characteristic wing motion rather than a steady wing rotation in order to yield proper estimations of the wing aerodynamic performance at Reynolds numbers of several ten-thousands.

Keywords: Student Competition, Structural Dynamics, Aeroelasticity
Abstract: In recent years there has been considerable interest in renewable energy resources, and specically in wind power. One of the devices that were suggested for energy harvesting in low-speed winds is the Windbelt generator, by Shawn Frayne and Jordan McRae with the Humdinger Wind Energy company [1]. The Windbelt device is a taut, high aspect-ratio membrane that flutters in low-speed winds. Magnets that are attached to the fluttering membrane move in and out of coils, thereby generating electrical power. A somewhat similar device was proposed by Sundararajan et al. [2], where the mechanical vibrations are transformed into electrical power via piezo-electric devices. These devices motivated the current study of the flutter characteristics of high aspect-ratio membranes in low subsonic flows.

The current study presents flutter analysis and wind-tunnel testing of membrane strips of high aspect ratio (6-20) in low subsonic flows. The membrane strips are tensioned at the short ends (or clamped at one end, and tensioned at the other end), while the long ends, which are the membranes' leading and trailing edges, are free. Linear stability analysis provided the utter speed and frequency as a function of the membrane geometrical and structural properties. In the wind tunnel, the membrane strip does not flutter, but rather gets to a limit-cycle oscillation (LCO). Another goal of this study was to compare the LCO onset and properties to the flutter onset and properties as predicted by the linear flutter analysis.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Formation, location and size of laminar separation bubbles is a dominant aerodynamic phenomena at domain of low Reynolds numbers. This is especially relevant for high-lift, highly cambered, thick UAV wings with their strong adverse pressure gradients and resulting tendency for formation of large laminar separation bubbles. The burst of laminar bubble at certain flight conditions produces an abrupt stall of the wing and development of strong hysteresis loop. This is unacceptable for the safe flight of air vehicles, especially for operation of small and medium size Tactical UAV flying at reduced airspeeds in windy air. Until this problem is solved, the race for high maximum lift at low Reynolds numbers is meaningless. This is important for the recently developed high-lift, mild-stall wings (MS-wings) with plateau of lift at extended range of post-stall angles of attack and remarkable capabilities to ensure safe flight up to high post-stall angles of attack. Without prevention / delay of the burst of laminar bubble and elimination of hysteresis, the feature of mild-stall cannot be realized at the flight of small UAV. This demonstrated in wind tunnel testing by evaluation of abrupt stall pattern of single-element, high-lift, mild-stall MS/DTE airfoil at domain of low Reynolds numbers. Recovery of lift characteristics for this airfoil was achieved by implementation of multi-strip transition control methodology. This prevented the burst of laminar bubble at plateau of lift and ensured high-lift, mild-stall up to high post-stall angles of attack without development of hysteresis phenomena. For operational UAV, this delay of abrupt stall to high post-stall angles of attack is equivalent to elimination of hysteresis, allowing safe flight at plateau of lift at post-stall. The obtained results were in contrast to previous experience with transition control technique that concentrated only on recovery of maximum lift at low Reynolds numbers. The developed methodology of high-lift flight at post-stall angles of attack at low Reynolds numbers is based on the combination of the concept of mild-stall airfoils and transition control technique. The achieved progress on this issue allows completely different approach to design of small UAV (W = 5-20kg) with reversal of design priorities and formulation of new and unconventional objectives in development of air vehicles. Elimination of standard speed safety margin, extension of usable lift up to the maximum lift, safe flight in windy air, post-stall flight capabilities are among the expected benefits of new design methodology. Implementation of developed concept in design of small UAV has a potential to produce a new class of air vehicles with enhanced performance and extended flight capabilities.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: This paper describes a study of transition in Couette flow initiated by the transient growth mechanism. It is shown that four modes obtained analytically are sufficient to model the transient growth. The analytical approximation allows performing a secondary stability analysis of the modified baseflow consisting of the Couette flow and a transient growth perturbation. The predictions of the secondary stability analysis are verified by checking whether transition occurs in a direct numerical simulation (DNS) initiated by the analytical expressions. Finally, the capability of the analytical expressions to capture some of the transition stages is tested.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Recent theoretical and algorithmic advances are reported in matrix-forming and time-stepping approaches to the solution of the eigenvalue problem governing global linear instability theory. Analysis tools have been developed to predict transition in flows over or through complex geometries at a cost that is orders of magnitude lower than that of full direct numerical simulation. Three configurations highlight recent progress: steady laminar supersonic and hypersonic boundary layer flow over an isolated roughness element and hypersonic flow over an elliptic cone and an orbiter model at re-entry conditions. Known instability mechanisms have been recovered, without invoking simplifying assumptions on the underlying base states. New instability mechanisms, inaccessible to classic linear theories, have been unraveled in all three configurations.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Use of high lift devices is common practice for aircraft to enhance takeoff and landing performance. They enable to use smaller wing area to obtain cruise drag reduction, while augmenting the maximum lift for takeoff and landing. They can also be used to reduce the loiter speed of an aircraft, thus enhancing its aerodynamic efficiency, especially for propeller driven aircraft. We tried to extend high lift devices usage also for low Reynolds numbers in the range 200K- 300K, which is typical of small sized UAV’s. For this class of propeller driven UAV‘s the important factor is enhancing the loiter time which is proportional to CL1.5/CD. High lift devices are used in industry including plain, and Fowler flaps. In IAI wings we also used two element airfoils. We propose to use a slotted flap (fixed hinge flap option) which may provide several benefits. It should be simpler to manufacture than a Fowler flap and may provide lower drag at cruise by closing the gap. For low Reynolds numbers there is much less data on the performance of such devices. Low Reynolds number regime is associated with longer extent of laminar flow and larger laminar separation bubbles which may cause drag increase and premature separation leading to lift loss. A design cycle of an airfoil with fixed-hinge flap for this Reynolds no. regime was done during this work in IAI and ADE. The designed airfoil models were tested in a 2-D WT in IIT Kanpur, India, and demonstrated good performance Based on the above a low Reynolds, high-lift wing concept is proposed. The inboard section is based on fixed-hinge airfoil and provides high maximum lift with deflected flap. The outboard section is based either on two-element airfoil or on plain flap (that supports deflections for both positive and negative directions) to provide flight control in roll. The presented work partially includes the results of joint ADE-IAI project "High Lift Wing Design Technology".

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: High-lift, mild-stall wings (MS-wings) are beneficial for development of Tactical UAV. The lift curves of MS-wings show plateau of lift coefficients at extended range of post-stall angles of attack, followed by gradual loss of lift at the region of actual stall of the wing. Such stall pattern is attractive for design of small and medium size Tactical UAV flying at reduced airspeeds in windy air. At stall angles of attack, no significant rolling moments are expected for MS-wings, improving air vehicle response to asymmetric stall, preventing the drop of the wing and development of spin modes of the flight. Furthermore, intended / unintended stall of air vehicles that employ MS-wings is not expected to result in safety problems, allowing controllable recovery from domain of post-stall angles of attack. High-lift, mild-stall MS-wings allow the standard speed safety margin to be revised, or eliminated, allowing better exploitation of available maximum lift. This can improve UAV take-off / landing performance and allows more efficient loitering at higher lift coefficients. MS-wings allow a fully controllable flight at stall / post-stall angles of attack, supporting development of the option of landing at post-stall at minimum possible airspeed with steep glide angles. This paper describes design and experimental evaluation of single-element, high-lift, mild-stall airfoil with divergent trailing edge closure (MS/DTE airfoil). Experimental results indicated that expectations for enhanced maximum lift and extended plateau of lift at post-stall for MS/DTE airfoil realized at real flow conditions in wind tunnel test. This was further substantiated in flight testing of fully instrumented Wing Technology Flight Demonstrator specially designed for evaluation of post-stall flight capabilities of MS-wings. Overall, it was concluded that implementations of MS-wings in development of Tactical UAV allows completely different approach to formulation of design objectives of air vehicles. Elimination of speed safety margin and safety aspects at stall / post-stall flight are the foundation for revision of aerodynamic design principles and for modification of flight control.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: A flow analysis and boundary layer control were applied to an inlet shape design that is efficient from the external aerodynamic point of view, but due to its short and high offset suffers from internal flow separations and significant engine face distortions. For simplicity, low Reynolds number and low (practically incompressible) Mach number experiments and simulations were performed on an equivalent 2D geometry. Qualitative agreement was found between experiments and simulations. Preliminary efforts to control this complex flow are presented and tested both by experiments and simulations.

Keywords: Aerospace Sructures Design, testing and Manufacturing
Abstract: It seems like just yesterday, late nights of April 1997, I was writing the COMPRES (Composite Repair of Metallic Structure for Ageing Commercial Aircraft) proposal, the first such IAI attempt to join in the EU combined research Framework Program. After extensive negotiations and some anxious correspondence, in 1998 the proposal was accepted for funding. The ice was broken and IAI entered this most coveted arena of EU Research and Development Framework Programs. We can now look back with a hindsight perspective of 15 years, over 50 projects in the Engineering Division alone, encompassing overall projects budget of 900 million Euros. Serving nearly all this period as Director of R&D for the IAI Engineering Division, I would like to share with you all a little introspection and soul searching, assessing the added value, merit and benefit of IAI's participation in these combined research projects.

This paper will firstly explain the mechanics and logistics of the EU R&D research programs as well as the magnitude of budget and other resources, the composition of the consortia and how they work together to achieve the common goals and share the intellectual property.

This paper will attempt to illustrate how the EU R&D endeavors brought added value to the IAI technical infrastructure with respect to:  Improved analytical capabilities  Superior design methodologies  Enhanced manufacturing technologies  More ecologically friendly "green" technologies  Improved metallic and composite mat capabilities  State-of-the art computer programs  Etc.

Examples will present specific benefits derived from diverse disciplines and different projects. The paper will discuss the significance of the TAURUS project which coupled the aeroelasticity effects with the CFD computer programs, the TANGO/ALCAS/MAAXIMUS projects which enhanced our composite material capabilities, as well as the Clean Sky "JTI" project which is the flagship FP7 project for Aeronautics, dedicated to the "ecolonomic" aircraft of the future.

Finally, the paper will present examples of technologies derived from some of the combined EU research projects, which found applications in present IAI state-of-the art operational aircraft

Keywords: Aerospace Sructures Design, testing and Manufacturing
Abstract: In the last 2 decades, the use of composite materials in aero-structures has increased dramatically while continuous and massive effort has been made to reduce composite structures` costs. Elbit systems – Cyclone (“Cyclone”) developed an innovative “one shot” composite control surface demonstrator that utilizes the advantages of composite materials and their associated processes in order to reduce assembly steps, production time and number of parts in the assembly. Cyclone`s demonstrator is manufactured by RTM (“Resin Transfer Molding”) technology using standard aerospace grade fabrics which are pre-formed on metallic mandrels. The demonstrator embodies innovative composite fittings that are adhered and geometrically locked to the inner frame spars with no fasteners . The combination of an innovative technology, integrated composite structure, and damage tolerant design lowers the cost by as much as 60% and improves the performance of this demonstrator compared to similar nowadays control surfaces.

Keywords: Aerospace Sructures Design, testing and Manufacturing
Abstract: Three dimensional woven composite applications are presented. This type of weaving has unique advantages, compared to conventional composites made by stacking plies. The key issues of 3D weaving will be outlined briefly, and a technological demonstrator developed at IAI is presented. Demonstrator is a single part fastenerless control surface, manufactured in a single process.

Keywords: Aerospace Sructures Design, testing and Manufacturing, Materials, Solid Mechanics
Abstract: LOCOMACHS (LOw COst Manufacturing and Assembly of Composite and Hybrid Structures) is a collaborative research and development project in which IAI is participating along with 31 partners including the European Key players in the aircraft industry. Faster and more cost efficient assembly of composite structural parts is a key enabler to high rate production. LOCOMACHS seeks to combine existing and innovative technologies to remove non-added value operations, which are time consuming and induce recurring costs, within composite production.

Keywords: Aerospace Sructures Design, testing and Manufacturing, Structural Dynamics, Aeroelasticity
Abstract: Several aspects are discussed of the laboratory condition definition process of the vibration regime in captive straight flight on an airborne store. The need is emphasized of reconsidering the statistics in the evaluation and to use the average PSD plus three standard deviations instead of the average PSD. The results of this change in the RMS versus dynamic pressure model are presented. The incorrectness is stressed of basing accelerated testing planning on the RMS values. The need is considered of changing the methodology to a combination of load cycle counting with the Miner Law, in the evaluation of the laboratory accumulated damage as an equivalent of the field accumulated damage. The advantages of PSD evaluation by the Parametric Modeling Methodology as compared to the FFT Methodology are elucidated. It can be seen that larger calculation errors of the Fourier Methodology are detrimental to the testing conditions definition.

Keywords: Aerospace Sructures Design, testing and Manufacturing, Numerical Methods, Modeling Simulation
Abstract: The Vibration Correlation Technique (VCT) is a nondestructive experimental method that can be used for the estimation of realistic boundary conditions and to improve the correlation of numerical models used to estimate the buckling load of shell structures. This paper presents initial experimental results of vibration frequencies and modes shapes of a cylindrical shell loaded in compression, up to buckling. The experimental results are used to point out the influence of the boundary conditions and material properties on the correlation with a finite element model. The results show that the application of calibrated boundary conditions and material properties are not enough to guarantee a good numerical - experimental correlation, requiring further studies suggested herein.

Keywords: Control, Guidance Navigation
Abstract: The Linear Quadratic Optimal Consensus (LQOC)control problem is a relaxation of the classical Linear Quadratic Regulation (LQR) problem, that consists of assymptotically driving the state of the system to a “consensus” point in which all coordinates are equal, in such a way that a quadratic cost function of the transient responses of the state trajectory and of the input is minimized. The generalized version of this problem requires the state of the system to converge assymptotically to a given subspace of the state space. This paper shows that, if the associated standard LQR problem has a regular optimal solution, then the existence of the open loop solution of the generalized LQOC can be readily verified and, if it exists, the solution can be readily computed by simple algebraic manipulations. The results are illustrated on a simple roll attitude regulator example.

Keywords: Guidance Navigation, Control
Abstract: The Proportional Navigation guidance law (PN) has been in use for decades within many tactical and strategic missiles due to its simple implementation and high accuracy. In some applications, however, there might arise implementation problems, for instance in the application of a design constraint on the jerk (first derivative of the acceleration) for the missile. An example of such a constraint is a missile, using Thrust Vector Control (TVC), which requires the entire missile body to be tilted in order to perform a maneuver. From design considerations, the rate of body rotation may be limited, thus limiting the rate of acceleration change, or in other words, the jerk. The main purpose of this work is to develop an optimal guidance law which minimizes the cost on the jerk, thus taking into account the limit on this property. This paper demonstrates, by introducing a jerk limit to the common PN and APN (Augmented Proportional Navigation) laws and showing that a miss occurs, under a certain jerk limit, that the foregoing motivation is justified. The new jerk limited guidance law (JLG) is developed by means of Cauchy-Schwartz inequality, ensuring its optimality. JLG is then compared to the common PN, APN and their variations (PN5 and APN5) and found to perform well, yet slightly inferior to PN in the case of an heading error and to perform better than all other guidance laws for the case of target maneuver. The results of this comparison also demonstrate the capability to tune the performance of JLG by the right choice of a jerk limit value (within the design limit on the missile) to achieve better results in terms of miss distance.

Keywords: Guidance Navigation, Control
Abstract: The paper proposes a new approach to the tuning of homing guidance laws for interceptor missiles that makes use of linear-quadratic optimal control in a different manner than the traditional approaches. Instead of looking only for the minimization of the integral square of the guidance command, the new criterion penalizes the "variability" of the guidance command. The solution is numerically as easy to obtain as the solution of the classical linear-quadratic optimal control problem and has the familiar structure of the Augmented Proportional Navigation with a compensation term for the dynamics of the interceptor and with variable navigation constant. However, it has an additional design parameter that can be profitably used to avoid saturation of the guidance law.

Keywords: Guidance Navigation, Control
Abstract: A near-optimal minimum time guidance law to a fixed point under a terminal angular manifold is developed. The planar case and the spatial case are separately considered. The problems are solved in several stages with increased level of complexity: from the simple case of a constant speed with a fixed terminal angular direction; through the case of a constant speed with a terminal conical manifold; to the more general case of atmospheric flight with the required terminal conditions.

Keywords: Guidance Navigation, Control, Performance, Design Optimization
Abstract: In an earlier study an innovative guidance strategy was introduced, based on integrating the design of a multiple model adaptive estimator and a differential game based guidance law, leading to a potential breakthrough in the interception of randomly maneuvering targets in critical scenarios, such as the Ballistic Missile Defense. Further studies indicated that while the differential game based guidance law is a robust solution for a large family of practical scenarios, the estimation process associated with it still needs improvement. Such improvement requires the definition of a suitable endgame estimator and a new estimator design approach, based on the available time-to-go information. In this paper a new criterion is proposed for a suitable estimator to be used in interception endgames and a new estimator design approach is outlined for the interception of randomly maneuvering targets. Monte Carlo simulation results show that the new design approach can reduce the 95% value of the accumulated miss distance distribution to the half.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: This work presents an effective and simple approach in Angular Momentum Unloading in Satellites. The angular momentum of the satellite is determined by the external torques acting on it. Parts of them are controlled by the on board control system, like thrusters and magnetotorquers, and some are part of the space environment like solar pressure, earth gravitation and Aerodynamic Torque. The Aerodynamic Torque is caused by air molecules that strike the satellite. It causes the satellite to decrease its orbital energy and to gain or loss angular momentum. The satellite must unload its angular momentum in order to keep functioning. It can be achieved by the use of thrusters, magnetotorquers or earth gravitation. Our work suggests an approach that uses the Aerodynamic Torque to unload angular momentum.

Keywords: Control, Space Systems, Astrodynamics, Guidance Navigation
Abstract: Satellite cluster flight is an enabling technology for disaggregated space architecture. A nonlinear distributed control law is developed considering fixed-magnitude thrust, in order to establish satellite cluster flight under perturbations. Mean orbital elements are used as feedback. Notation of partial stability is adopted to describe the stability. Uniform stability and asymptotic stability are proven for the relative motion control. State selection for establishing a low Earth orbit cluster is also discussed. Several numerical studies are performed to assess the performance of the control law. Comparisons are provided to show the fuel-balancing merits of the current control law. The effects of drag on the long-term performance are also investigated. The current control law is shown to be feasible and effective for satellite cluster flight.

Keywords: Space Systems, Astrodynamics, Control
Abstract: The problem of controlling the minimum and maximum inter-satellite distance within a satellite cluster is among the main challenges associated with multiple satellite missions, including disaggregated satellites. There are three possible ways to deal with the problem of cluster flight. The first way is to perform orbital corrections by using active control (Impulsive corrections). The second way is to define the initial conditions of any module in the cluster such that the inter-satellite distance will be bounded within proper limits, for the whole mission lifetime. Practically, it is not an easy task to launch a module with the needed orbital elements accuracy. The third way is to perform the needed orbital corrections by using passive control (i.e. without thrusters). The goal of the current research is to develop differential-drag (DD)-based cluster-keeping algorithms suitable for implementation in long-term missions, with a particular emphasis on multiple modules. To that end, in-plane nonlinear DD-based controller is developed, which include mean element feedback. In addition, a stability proof is provided. The outstanding results are validated using simulations based on the forthcoming Space Autonomous Mission for Swarming and Geolocation with Nanosatellites, showing the effectiveness of this controller.

Keywords: Space Systems, Astrodynamics, Control, Parameter Estimation, Fault Detection and Isolation
Abstract: The European Proximity Operation Simulator (EPOS) aims, among other objectives, at performing tests for verification and validation of the docking phase of an on-orbit servicing mission. The simulator includes two robots, equipped with very accurate position controllers, holding a docking interface, a probe element, and (virtual) satellites. A key feature of the simulator set-up is a feedback loop that is closed on the real force and torque sensed at the docking interface during the contact with the probe and that is used to drive a free-floating bodies numerical simulation. The high stiffness of the controlled robots causes the contact dynamics to be quicker than the robots' dynamics. This leads to inconsistencies in the docking simulation results and to potential instability and damage of the closed-loop system. This work presents a novel mitigation strategy to the given challenge, accompanied with a stability analysis and validating experiments. The high stiffness issue is addressed by combining a virtual stiffness and damping in the software with a real stiffness in the hardware, designing, thus, a hybrid docking simulator. Nonlinear state-space modeling of the closed-loop system is performed for the three dimensional case, where the tracking robots system is approximated as a pure delay. A linearized model is developed for the two dimensional case and a simplified expression is obtained by defining as states the depth and the rate of penetration along the normal to the contact surface. A stability analysis is then performed, easily extending previous results obtained in single-dimension, which provides stability regions as a function of the contact stiffness and damping, the tracking robots time delay, and the satellites masses. The design of a hardware compliance device is presented and the effective stiffness along the normal to the contact surface is developed. Finally, results of contact tests in single and three dimensions are presented, too, showing the consistency between analysis and experiment. The proposed hybrid contact dynamics model and the accompanying analysis are envisioned to enable safe and flexible docking simulation. The proposed simulator shall enable the emulation of a desired contact dynamics for any stiffness and damping characteristics within the stability region.

Keywords: Space Systems, Astrodynamics, Guidance Navigation, Control
Abstract: This work investigates the performances of several State-Dependent Riccati Equation algorithms for the estimation and control of attitude and attitude rates of a rigid-body spacecraft. The estimators are designed to process line-of-sight and gyros measurements corrupted by white noises and potentially drifting biases. The case of gyroless estimation is also addressed. The vector measurements are linear-in-quaternion with state-dependent white noises. The controllers implement single-loop and dual-loop approaches. Under equivalent conditions, the single-loop controller outperforms the dual-loop controller whether by requiring less control energy or by having a quicker pointing transient. The dual-loop approach on the other hand requires less computations and shows a less aggressive control transient. Estimation performances are the limiting factor in the proposed partial information closed-loop attitude and rate controllers. In general, the estimation transients are quicker when using gyros but they are smoother in steady-state for gyroless algorithms. With angular deviations in the vector observations of 0.5 deg, with or without gyros, and neglecting perturbations, pointing performance levels of typically 0.1 deg are demonstrated via numerical simulations.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: The performance enhancement of a vertical tail using synthetic jet actuators may allow for a decrease in tail size, which would result in a reduction of the drag, weight, and fuel consumption of the airplane. The potential for enhancement was investigated during wind tunnel experiments on a 1/19th scale model of a Boeing 767 vertical tail at a Reynolds number of 350,000. The model was instrumented with twelve finite span synthetic jet actuators placed slightly upstream of the rudder hinge-line with the objective of controlling the separation that commenced over the rudder when it was deflected to high angles. Stereo Particle Image Velocimetry (SPIV) was used to explore the interaction of the synthetic jets with the flow near the mid-span of the rudder (and at a moderate rudder deflection). Time-averaged measurements showed that along and outboard of the jets’ trajectory separation was reduced, and inboard there were recirculation regions that were visible in spanwise planes. These regions were associated with reduced total velocity. Furthermore, phase-averaged data revealed concentrations of vorticity that were related to the jets. Among these concentrations, the negative streamwise vorticity maintained their coherence farthest downstream. These features appeared to have a notable impact on the flow field. Moreover, the strength of these concentrations dissipated more quickly in the downstream direction as the number and spanwise density of jets increased. This indicated that at the conditions that were tested the jets actually had a detrimental effect on one another.

Keywords: Control, Aerodynamics, CFD, Fluid Dynamics
Abstract: An experimental study of a 2D square prism with rounded front edges is described. The purpose of the study is to reduce the aerodynamic drag by Active Flow Control (AFC) of boundary layer separation. Robust and efficient suction and pulsed blowing (SaOB) actuators are installed inside a circular cylinder that forms the upper-front curved edge. In addition and for simplicity, steady suction is applied at the lower-front round edge. The AFC results in significant form-drag reduction, narrower wake and correspondingly an increase in the base pressure.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Control
Abstract: Wind turbines are designed to operate for decades in harsh environment. Therefore, it is likely that the blades’ surface will be damaged due to environmental effects. The degraded surface quality will, unless treated, promote early transition to turbulent flow leading to premature boundary layer separation. The effects on the turbine performance could be devastating. In Addition, non-uniform and unsteady wind speed causes dynamic loads on the blade and on the overall turbine structure. Controlling those loads by changing the blade's (or its airfoil section) performance will allow building larger scale and less sensitive to contamination as well as lower wind speed starting wind turbines. The current experimental study is aimed at recovering lost performance of a thick, turbine blade airfoil due to degraded surface quality. We shall perform parallel tasks as the study of Troshin and Seifert who used 3 arrays of “Synthetic jet” (SJ) actuators to perform the above task in an closed-loop manner. The difference is the type of actuator: The Suction and Oscillating Blowing (SaOB) actuator.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Control
Abstract: The current study focuses on dynamic characterization of the Suction and Oscillatory Blowing (SaOB) actuator in still fluid as a pre-requisite to closed-loop flow control application. This stage should shed light on operational aspects, such as, the unsteady actuation characteristics, and the structure of the external, highly unsteady and complex flow. These aspects are studied through a series of experiments with a variety of experimental methods including unsteady pressures measurements, hot-wire anemometry, phase-locked and time resolved particle image velocimetry (PLPIV and TRPIV, respectively). Here we compare two TRPIV data reduction methods. We use proper orthogonal decomposition (POD) to filter the data (through small number of most energetic modes) and identify the most energetic coherent structures in the flow field. The current results should enable development of simplified boundary conditions for CFD. The suction effect, as well as the interaction of the actuation with a cross-flow boundary layer are under current study.

Keywords: Guidance Navigation, Control
Abstract: The current study is focused on unconventional ways to manipulate the forces and moments acting on an airfoil or a wing via Active Flow Control (AFC). The method relies on the use of AFC, a versatile tool for modifying flow fields. By the generation of unsteady vortices emanating from Suction and Oscillatory Blowing (SaOB) actuators, a partially or fully separated flow can be reattached or caused to be more severely separated. In this way, forces and moments acting on the wing can be dramatically altered. Experiments and simulations performed on an airfoil and a generic jet-in-cross-flow configuration are reported. The experiments included baseline wind tunnel tests on the chosen airfoil, reproduced with simulations. The simulations also included steady jet issuing from 95% chord on the lower surface. Steady and unsteady wall normal jets were tested on a simplified bench-top configuration. Good qualitative agreement was achieved between the two steady jet studies. A demonstration of the relative effectiveness of an oscillatory wall normal jet in deflecting the cross-flow was compared to its steady counterpart.

Keywords: Parameter Estimation, Fault Detection and Isolation, Aerodynamics, CFD, Fluid Dynamics
Abstract: This paper addresses the model order reduction of state estimators for plane Poiseuille flow augmented with aliased wave-number pairs, as necessitated by reduced resolution sensing. Balanced truncation is applied to the dynamic models of the augmented subsystems of individual wave-number pairs under the presence of process noise modeled as stochastic body forcing, in order to mitigate the system order expansion caused by state augmentation. The performance of reduced-order augmented estimators using reduced resolution sensing is compared to the benchmark performance full order estimators using full resolution sensing for a variety of wave-number pairs and disturbance scenarios.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Structural Dynamics, Aeroelasticity
Abstract: Limit Cycle Oscillations (LCO) is a non-linear Fluid-structure Interaction (FSI) phenomenon in which an aircraft's wing oscillates at a constant amplitude, typically sinusoidal and anti-symmetric motion. Lateral oscillations of the aircraft due to LCO may become detrimental from the point of view of handling qualities. Several hypothesis were previously suggested to explain the non-linear nature of the phenomenon, however, models which were suggested based on these hypothesis struggled to offer consistent predictions of LCO compared with flight test measurements. In the current paper, a Reynolds-averaged Navier-Stokes (RANS) computational aeroelastic investigation of the phenomenon is presented. The study is the first step towards a new computational capability currently under development to enable the prediction of the LCO phenomenon for Israeli Air Force purposes. The study presents aeroelastic simulations of the full-span F-16 fighter computational model including a detailed linear modal structural model and an aerodynamic wing model. Simulations are performed at flow conditions for which LCO was encountered in flight tests. The effects of dynamic pressure, structural damping, angle of attack and turbulence modeling on the characteristics of the phenomenon are discussed. The relationship between flutter and LCO is investigated and the origins of LCO are identified as a non-linear, self-sustained, periodic, shock-wave oscillations on the upper surface of the wing. These oscillations are suggested to suppress flutter into LCO.

Keywords: Aerospace Systems and Systems Engineering, Performance, Design Optimization, Structural Dynamics, Aeroelasticity
Abstract: It is common in modern aerodynamic platform design to have multiple design condition, which the platform is expected to function properly (such as different mach numbers, altitude etc ...). One of the solutions for this problem is designing the Aerodynamic platform using variable wing sweep angle. This design can provide essential flexibility for the different design points which the platform is expected to function (For example reducing critical Mach number on the wing etc …). Multidisciplinary design of proper structure and control system for the platform at different flight conditions and different wing sweep angles poses an engineering challenge. The different design goals such as low weight, sufficient platform performance, proper control system gain and phase margins and large enough flutter margin, forms an elaborate optimization problem with contradictory demands. This paper proposes an automated novel approach for solving the optimization problem by using the modal approach.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: Hypersonic flows are inherently complex and involve phenomena that are not present in supersonic conditions; such as dissociation, chemically reacting flow, viscous interactions and higher levels of aerodynamic heat flux. There are no suitable high speed, high enthalpy tunnels that would allow testing of scaled models of hypersonic vehicles. Furthermore hypersonic aerothermoelastic scaling laws are not available at high Mach numbers. Therefore, the development of accurate aerothermoelastic simulation capabilities is critical for the design and analysis of hypersonic vehicles. A framework for aerothermoelastic stability boundary calculation for hypersonic configurations using CFD combined with radial basis functions for mesh deformation is developed. Application of CFD enables one to consider different turbulence conditions, laminar or turbulent, and different models of the air mixture, in particular real gas model which accounts for dissociation of molecules at high temperature. The effect of transition on the flutter margin of the heated structure is also considered. The aerothermoelastic stability margin of a three-dimensional low aspect ratio wing, representative of a control surface of a hypersonic vehicle is investigated for various flight conditions. The overall objective of this study is to develop a framework for hypersonic aerothermoelastic studies using computational fluid dynamic simulations with mesh deformation based on radial basis functions (RBF) combined with a computational structural dynamic model. The specific objectives of the paper are: 1. Present a new linearization of piston theory for aeroelastic stability boundary calculations and compare it to CFD-based predictions, 2. Assess the influence of gas and turbulence modeling on hypersonic aeroelastic stability, 3. Assess the influence of transition location on hypersonic aerothermoelastic stability. The wing is found to be sensitive to turbulence modeling as well as the location of the transition from laminar to turbulent flow. Real gas effects play a minor role for the flight conditions considered. This study emphasizes the important relation between transition from laminar to turbulent, thermal stresses and stability margins of hypersonic vehicles. Additional details of the analysis and representative results on flutter margins of the heated wing are given in the extended abstract.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: A nonlinear computational scheme for structural dynamic response of an accelerating rocket to thrust misalignment forces is presented. The scheme is based on the Increased-Order Modeling approach as utilized in the Dynresp software framework. Linear aeroelastic response is calculated first using frequency-domain formulation for a nominal structure at constant flight velocity. Effects of nonlinear joints, follower thrust forces and rapidly varying flight conditions and mass properties are then introduced using time-marching solutions with convolution integrals. Response simulations of a generic rocket demonstrate the varying shortperiod and structural response properties when the Mach number changes from 0 to about 2, and the mass is reduced by about 30% in 2 seconds.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: Wake vortices generated by flight vehicles might generate large dynamic loads on aircraft encountering the wake shortly after being generated. This paper presents the challenges in the numerical simulation of the dynamic response to wake encounter and the associated structural loads. The transfer of information from the aerodynamic wake velocities generated by the lead aircraft to incidence angles in Doublet-Lattice panel model of the crossing aircraft is formulated. Frequency-domain solutions and FFT schemes are combined for an efficient, robust and adequately accurate numerical process for massive industrial applications. Some relevant parametric variations are presented, like the effect of the wake crossing angle, the effect of the crossing speed and the relation between the critical distance from the vortex core and the angle of attack. Comparisons with recent flight tests performed with the A400M military transport show good agreement that validates the numerical procedure.

Keywords: Structural Dynamics, Aeroelasticity, Aerodynamics, CFD, Fluid Dynamics
Abstract: A new capability to conduct aeroelastic flow simulations coupled with 6 degrees of freedom motion has been added to the EZNSS flow solver. The new capabilities have been tested by simulating the flow about an elastic rotating propeller under low subsonic flow conditions. The results show that elasticity does have an effect on the thrust. In the current case the thrust is reduced.

Keywords: Fatigue and Fracture Mechanics, Aerospace Sructures Design, testing and Manufacturing
Abstract: S-N diagrams are usually constructed to provide fatigue life data for a specific alloy, a specific product form (sheet, plate, forging, etc.), a specific direction of loading, and for a specific stress-concentration factor (Kt). Each diagram contains several curves,corresponding to the various mean stresses that were tested. To fully account for various stress-concentrations and mean-stress conditions, 400 – 500 specimens must be tested for each material, to provide sufficient data and to neutralize the large scatter inherent in fatigue testing. Some of the specimens will need to be tested for more than 10 million cycles. The "MMPDS Handbook", administered by the FAA, contains a large database of S-N diagrams for both 2024-T3 and 7075-T6 aluminum sheet, which were obtained by testing approximately 900 test specimens.It was found in this study, that using the modified "fatigue strength reduction factor" instead of the "stress concentration factor" could greatly reduce the number of required specimens.In addition, two methods for accounting for mean stress effects were evaluated by using two types of software and the MMPDS data. The results of this study are presented in this paper. Using the recommended approaches, the work-load for producing a full set of S-N data for a specific alloy and product form can be reduced from about 450 test specimens to approximately 20 test specimens.

Keywords: Fatigue and Fracture Mechanics, Aerospace Sructures Design, testing and Manufacturing, Materials, Solid Mechanics
Abstract: The cold-working procedure is considered as a cost-effective solution to fatigue cracks in metallic structures, and is widely used in the aerospace industries in the past two decades. The split sleeve cold expansion is accomplished by pulling a mandrel, pre fitted with lubricated split sleeve, through an undersized hole in metallic structure (mainly aluminum, steel and titanium). The removal of the sleeve results in a uniform radial expansion of the hole, creating residual compressive stresses in the vicinity of the fastener holes. These compressive stresses are still significant, even after rimming the fastener hole to its nominal size. The residual compressive stresses effectively "shield" the hole from the cyclic tensile stress loads that cause cracks to form and grow, and improve the fatigue and damage tolerance characteristics of the structure.

As part of a damage-tolerance certification program of one of Israel Aerospace Industries business jets, a structurally complete test-article is currently fatigue tested for two lifetimes (40,000 flights) followed by half a lifetime (10,000 flights) of damage-tolerance testing, with artificial flaws inflicted at critical locations. Residual strength tests, under limit loads and cabin pressurization, will be performed in the presence of large cracks at several critical locations. This will be followed by a selected teardown inspection.

During one of the scheduled inspections conducted within the full scale testing, a single crack was inspected at the side windshield retainer, between the window cutout and the nearby fastener hole. The fastener hole was cold-worked during the aircraft assembly process, to enhance its expected fatigue lifetime. The crack was detected and verified by means of two different NDI methods, namely, High Frequency Eddy Current (HFEC) and detailed visual inspection. The windshield retainer is considered as principal structural element. However, its failure does not lead to immediate catastrophic failure of the aircraft, since the loads applied on the retainer are redistributed and are taken by the cockpit side post.

As part of a root cause analysis conducted, a detailed finite element model was constructed. This model simulates the cold-working procedure that was applied to the retainer during assembly, as well as the applied loads during typical flight. The finite element analysis implied that the cold-working process at the fastener holes induced residual tensile stress in the nearby cutout. Combining this effect with the typical operating loads acting on the windshield retainer leads to crack nucleation at the window cutout. These preliminary conclusions were validated by means of fractographic analysis. However, the cold-working process has some beneficial effects. The crack propagation was further monitored during test, and it was concluded that the cold-working process slowed the crack growth rate of the continuing damage from the fastener hole up to complete f

Keywords: Fatigue and Fracture Mechanics, Aerospace Sructures Design, testing and Manufacturing, Structural Dynamics, Aeroelasticity
Abstract: Crack growth behavior is a major issue in the prediction and maintenance of aerospace structures, as well as other structural elements in mechanical and civil engineering projects. Prediction of expected life of a structural element due to a combination of a constant (static) and an alternating (fatigue) loadings is of major concern to the designers. Prediction of remaining life of the structural elements also influences the decisions of maintenance engineers (checking intervals, corrections, replacements).

Fracture mechanics has been used as the main tool with which such problems have been treated. During the last three decades, fracture mechanics scientists and engineers have made tremendous advances, from the basic practical approach dominated by Paris-Erdogan law, to more and more sophisticated crack growth models. Mathematical and metallurgical models (both deterministic and probabilistic), experimental analysis of simple models and testing of complex structures have resulted in thousands of publications, dozens of models for crack growth and life prediction, maintenance decision-making processes and numerous computer codes for crack growth analysis.

In a previous paper (presented in IACAS 53), a deterministic experimental crack growth model for aluminum 2024-T351 alloy was formulated based on published experimental results, using the “unified” approach. The “unified” approach was described in many publications in the past. According to these works the growth of the crack depends on both and , and in order for a crack to grow, two thresholds values must be met. The local driving force of short cracks is comprised of two stresses – one originated from the far field stress intensity factor and the other - from local internal stresses close to the crack tip. These local stresses “create” local R values near the crack tip, which are different from the far field R value, R being the load ratio, which defines the relative participation of static and alternating loadings. In fact, the “unified” approach claims that the crack-growth driving forces depend not only on the change in the stress intensity factor (SIF) , but on additional (mainly local internal) stresses. An initial crack length below which cracks do not propagate were found as a function of the loading stress and the stress ratio R. Using this approach, no crack closure effects need to be taken into account.

Crack growth depends on material properties (such as microstructure, initial flaws, grain boundaries etc.), geometrical properties of the structural element, and loading conditions. As most of these parameters behave randomly, the crack growth behavior should be treated using probabilistic methods. A special attention must be given to the initial crack lengths, or initial flaws, as well as to the stochastic behavior of the propagation process.

Initial flaws in a structural element originate from the material production phase and from environmental loading con

Keywords: Structural Dynamics, Aeroelasticity, Fatigue and Fracture Mechanics
Abstract: In this work, an automated application for determination of fatigue spectrum in terms of load factor based on gust PSD model was developed via Excel and Visual Basic. High order polynomial, exponential and logarithmic regression techniques were carried out for obtaining the alleviation factor and the non-dimensional zero crossing parameter from charts. These values were also found by analytical equations. The developed application was examined on typical flight cases and compared to results obtained from measured data; through this procedure, the accuracy of the application was illustrated.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Numerical Methods, Modeling Simulation, Propulsion
Abstract: A numerical study of a two-dimensional, mixed compression, supersonic intake for a ramjet engine is presented. The simulations were performed with ANSYS® Fluent Inc. code, using an inviscid, time dependent, implicit solver. Three different configurations were considered for the boost phase: closed inlet entrance, opened entrance and exit, and opened entrance with closed exit. It was found that the closed entrance configuration provides significantly low drag compared to the other two. Moreover, the ingestion Mach number for the a-priory closed inlet configuration was found to be also significantly lower than for the fully opened. Ones the configuration reaches the start conditions (shock ingestion) and the entrance opens, the transition period is of the order of few milliseconds until the flow reaches steady state. A special computational technique was derived to enforce a back pressure in a supersonic hyperbolic flow field. Using this method, the influence of back pressures on the normal shock position along the diverging diffuser was analyzed. The minimal ratio between back and ambient pressures to maintain a subsonic exit (ramjet conditions) was defined, and the total pressure recovery for each pressure ratio was calculated.

Keywords: Combustion, Numerical Methods, Modeling Simulation
Abstract: A body of experimental evidence in the literature has revealed the unusual behavior of organic gellant-based fuel droplets which, under appropriate ambient thermal conditions, evaporate and burn in an oscillatory fashion. In the current work the propagation of a laminar flame front through a fuel rich pre-mixture of organic gellant-based fuel droplets and air is studied using a numerical solution of the appropriate governing equations. For flame propagation the influence of the oscillatory evaporation of the droplets is shown to have a slight influence on the average burning velocity of the flame front. As the frequency of oscillatory evaporation increases from zero and tends to infinity the burning velocity increases by a factor of about 5%. However, rather strikingly, for a range of low values of the oscillatory evaporation frequency the flame front pulsates. The question of the location of the neutral stability curve separating regions of steady state and pulsating flame propagation is examined in the appropriate gellant-based fuel droplets-related parametric plane and conclusions concerning required operating conditions are drawn. These newly disclosed effects highlight the fact that even though gel fuel sprays may have a distinct advantage over conventional sprays in terms of their safety features it is crucial that the correct operating conditions be employed in order not to detract from attaining the desired combustion performance.

Keywords: Propulsion
Abstract: While there are many different challenges in the development of micro aerial vehicles (MAV), one of the severe limiting factors in terms of weight is the energy storage/power system. Most of the MAVs developed to date are based on electrochemical batteries coupled with an electric motor. In a previous study, several potential alternative energy storage/power systems were examined, evaluated for their specific energy and specific power, and compared to electrical batteries and hydrocarbon fuel storage. Additionally, the power and energy requirements of fixed wing MAV and rotary wing MAV were calculated, for comparison with the different alternatives. In the present study a novel PCM open cycle storage/power system for MAV applications is proposed, based on those requirements. It is an open cycle that uses the ambient temperature as its hot reservoir. Promising initial results, in terms of specific power (45-70W/kg), specific energy (24-45W-hr/kg) and open-cycle thermodynamic efficiency (22-54%), are presented.

Keywords: Propulsion, Combustion
Abstract: Hybrid rockets are a good alternative for the emerging space tourism propulsion due to the safety of the motor. On the other hand, the low regression rate of conventional polymeric fuels implies low thrust. In recent years paraffin-based fuels have been investigated because of their much higher regression rate compared to that of polymeric fuels. This paper presents experimental investigation of static firing tests of hybrid motors using paraffin and paraffin-polymer mixture, as well as polymethyl-metacrylate (PMMA, Plexiglas) as a fuel and nitrous oxide (N2O) as an oxidizer. It was found that the regression rate of paraffin is about five times higher than that of PMMA (polymer). A mixed paraffin-polymer fuel gives a lower regression rate than pure paraffin, yet it is higher by about 2-3 fold than that of PMMA. C* efficiencies obtained were in the range of 80-100%, with an average of about 90%.

Keywords: Propulsion, Aerospace Sructures Design, testing and Manufacturing, Combustion
Abstract: Since 2011 the Institute of Space Propulsion at DLR-Lampoldshausen offers the possibility of hybrid thruster test campaigns to students. A mobile test rig was developed and the applied measurement methods were widely extended. In many ways the hybrid thruster appears as an ideal research object for rocket propulsion students. The thruster provides aspects of liquid propulsion, phase transition, solid propulsion, ignition, combustion and rocket nozzle flow. System pressure and combustion temperature are in the order of the state of the art of rocket engines, but for all this the students can fully handle the thruster, rig and testing by their own. The test configuration fully applies the principle of the evacuated test position which means a complete remotely controlled test. Hence the test rig offers practically arbitrary long test duration. In the next student campaign the step from metallic to composite material for the thruster shall be fully applied and the effect of high temperature and long duration test on the thruster material will be studied.

Keywords: Control, Parameter Estimation, Fault Detection and Isolation, Space Systems, Astrodynamics
Abstract: This work is concerned with the development of a suboptimal control algorithm for Markovian jump-linear systems, and its application to fault-tolerant spacecraft magnetic attitude control. For completeness, the jump-linear quadratic optimal controller with full state and mode information is presented. Relaxing the assumption of perfect mode information, a similar optimal control problem is formulated where the mode is observed via discrete measurements. The elements of the measurement matrix, i.e. the probabilities for correct and wrong mode observations are assumed known. The optimal controller is developed, which requires an exponentially growing computational burden, and a suboptimal controller is proposed that only requires knowledge of the current mode measurement. This controller is finite memory and possess some of the classical linear quadratic regulator features such as the linear state feedback structure and a state quadratic optimal cost-to-go. The performances of the suggested algorithm are illustrated through extensive Monte-Carlo simulations on a simple numerical example. A realistic fault-tolerant spacecraft magnetic attitude controller is developed based on the proposed approach. The attitude controller succeeds in mitigating the destabilizing effect of corrupted mode observations while being computationally efficient.

Keywords: Guidance Navigation
Abstract: A conventional inertial measurement unit contains three orthogonal accelerometers and three orthogonal gyroscopes to measure acceleration and angular rate of the vehicle. A different possibility is to use a set of distributed accelerometers to measure both acceleration and angular rate. This concept, known as gyro-free navigation, was proposed over 45 years ago and recently arousing a growing interest because of the emergence of low cost MEMS based accelerometers with rapidly increasing performance. Most research in the gyro-free field had focused on seeking optimal accelerometer locations and it appears that less attention was given for deriving appropriate state-space models and analytical error assessment as in a conventional INS. In this paper, we aim to fill this gap. We derive gyro-free kinematic equations expressed in the navigation frame fitting for any set of accelerometer configurations. Such a set may be arbitrary in terms of the number of accelerometers in the configuration, their relative location and orientation. We further derive gyro-free INS error state dynamic equations in a state space model and augment them with dynamic equations representing the accelerometers residuals. In addition, simplified error models and their corresponding closed form solutions, suitable for any gyro-free configurations are derived and their characteristics are analyzed. A case study of six accelerometers configuration is used to illustrate the gyro-free concept and to analyze its performance throughout all the models derived in the paper.

Keywords: Parameter Estimation, Fault Detection and Isolation, Guidance Navigation, Aerospace Systems and Systems Engineering
Abstract: Estimating the pose, motion and structure of non-cooperative dynamic targets using on board sensors is a challenging problem. This work suggests using multiple-baseline stereo-vision for non-cooperative dynamic target relative pose, motion and structure estimation, with a particular emphasis on space applications. A computer-vision feature-matching algorithm is designed, which produces input data for a recursive filtering algorithm. A newly-developed initialization scheme is proposed, which decreases the ambiguity in the target center of mass location. The effect of varying the number of cameras is investigated. The proposed vision-based relative motion estimation method was validated at the Technion’s Distributed Space Systems Laboratory. A scalability analysis indicates that the proposed method may be potentially useful for space applications.

Keywords: Guidance Navigation, Control
Abstract: Extended target tracking arises in situations where the resolution of the sensor is high enough to allow multiple returns from the target of interest corresponding to its different parts. Various formulations and solutions may be found in the literature. We concentrate on the data association aspect involved in the tracking problem and propose utilization of a general framework that allows reformulation of many seemingly unrelated problems in a similar way. Consequently, the extended object tracking problem is stated as a single generalized dynamical system with random coefficients and solved using a standard IMM algorithm.

Keywords: Guidance Navigation, Control, Numerical Methods, Modeling Simulation
Abstract: A multilateration algorithm serves as an alternative to define and calculate the location of a moving object based on the time difference of arrival or difference Time of Arrival (TDOA) at different sensors. This article will address about results of an analysis about computational complexity, specifically on temporal complexity and precision of five distinct algorithms that use multilateration technique, with Closed-Form and Non-Closed-Form Expressions. As results we presents an comparative table about the algorithms and the selection algorithm more accurately and with the shortest execution time.