Control Surface Design Research Articles

Best Design of Wing Aerodynamic Control Surfaces Based on Aeroelastic Instability Consideration

Best Design of Wing Aerodynamic Control Surfaces Based on Aeroelastic Instability Consideration

Hydrodynamic characteristics of an Asian sea bass-inspired underwater body

A novel underwater body geometry inspired from the morphology of Asian sea bass (Lates calcarifer) fish is developed, and its hydrodynamic coefficients for different combinations of angle of attack and drift angle are investigated using RANS-based CFD methods. The six degrees of freedom manoeuvring performance is evaluated by the calculation of surge, sway and heave forces and roll, pitch and yaw moments at Reynolds number 3.7 × 106. The numerical model is validated using experimental results for DARPA SUBOFF model. The sea bass sectional geometry has an inherent asymmetry about the horizontal plane, and this is observed in the force and moment coefficients. A detailed study for pressure coefficient and skin friction coefficient is presented, both along the length and circumferentially at specified locations for varying angles of attack and drift angles (-15° to 15°). Due to transverse pressure gradient, cross-flow structures are observed resulting in vortices from the mid-body that grow downstream, the strength depending on the angle of manoeuvre. It is observed that the sea bass-inspired body generates greater roll and pitch moments and heave force as compared to a symmetric tuna-inspired body for drift angles greater than 10°. The differences show the influence of asymmetry in underwater vessel geometry on its stability and performance during horizontal and vertical plane manoeuvres. The study of the hydrodynamic characteristics will aid the design of control surfaces and development of estimation of manoeuvring and propulsion performance for fish-inspired autonomous underwater vessels.

Designing aerodynamic devices for UAV – lessons learned

PurposeDesigning new aircraft that are state-of-the-art and beyond always requires the development of new technologies. This paper aims to present lessons learned while designing, building and testing new UAVs in the configuration of the flying wing. The UAV contains a number of aerodynamic devices that are not obvious solutions and use the latest manufacturing technology achievements, such as 3D printing.Design/methodology/approachThe design solutions were applied on an airworthy aircraft and checked during test flights. The process was first conducted on the smaller UAV, and based on the test outcomes, improvements were made and then applied on the larger version of the UAV, where they were verified.FindingsA number of practical findings were identified. For example, the use of 3D printing technology for manufacturing integrated pressure ports, investigation of the adverse yaw effect on the flying wing configuration and the effectiveness of winglet rudders in producing yawing moment.Practical implicationsAll designed devices were tested in practice on the flying aircraft. It allowed for improved aircraft performance and handling characteristics. Several of the technologies used improved the speed and quality of aerodynamic device design and manufacturing, which also influences the reliability of the aircraft.Originality/valueThe paper presents how 3D printing technology can be utilized for manufacturing of aerodynamic devices. Specially developed techniques for control surface design, which can affect adverse yaw problem and aircraft handling characteristics, were described.

Collaborative design method of aerodynamic stability and control for modern advanced symmetrical tailless high-speed aircraft

Tailless and small control surface design is usually used in the new generation of plane-symmetrical hypersonic vehicle (HSV). However, this design greatly reduced the vehicle's stability and make the vehicle's lateral and directional control seriously coupled. We consider increasing the stability and controllability of the lateral and directional channel while maintaining the lift-drag ratio and other key indicators as a major problem for such HSV. In order to solve this problem, this paper establishes a collaborative design method of aerodynamic stability and control (CDMAC) based on the space criterion diagram (SCD) composed of three core stability parameters. And through the single-state point and multi-state points collaborative design cases of a plane-symmetrical tailless HSV with static instability in lateral and directional channels, it is verified that the CDMAC method can avoid the problem of degradation of key aerodynamic performance such as lift-to-drag ratio and the problem of rudder saturation and inability to track control commands in non-cooperative design. The CDMAC proposed in this paper provides a fast and effective tool for the design of modern advanced symmetrical tailless HSV.

Flight mechanical analysis of a solar-powered high-altitude platform

The German Aerospace Center (DLR) is currently developing an unmanned experimental solar-powered fixed-wing high-altitude platform designed to be stationed in the stratosphere for several days and to carry payload for earth observation missions. This paper deals with a flight mechanical analysis of the aircraft within the preliminary design phase. For this purpose, it briefly describes all disciplines involved in the preliminary design and gives an insight into their methods used. Subsequently, it presents an assessment of the aircraft in terms of stability and control characteristics. Doing so, it first deals with a dynamic stability investigation using a non-linear 6-degrees-of-freedom flight dynamic model with a simple quasi-stationary approach to account for flexibility, in which the aerodynamic derivatives are given for different airspeed-dependent flight shapes. The investigations show that the aircraft is naturally stable over the complete flight envelope. It does not have a typical short period mode. Instead, the corresponding mode involves altitude and airspeed changes to a large extent. At low airspeeds, the Dutch roll and spiral modes couple and form two non-classical modes. Second, it presents a control surface design evaluation process for the aircraft based on a flight mechanical requirement. This requirement addresses the necessary control authority to counteract the aircraft’s responses due to gust encounters to not exceed afore-defined limits and to prevent the aircraft from entering a flight condition that it cannot be recovered from.

Gliding Motion Optimization for a Biomimetic Gliding Robotic Fish

In this paper, we present a gliding efficiency optimization strategy based on deep reinforcement learning (DRL) for a gliding robotic fish. For the gliding motion in shallow waters, the non-steady motion strongly impacts the gliding range and also reduces efficiency. This paper presents a concept of transient gliding motion and illustrates its importance for small-scale gliding robotic fish. For better gliding performance of active fins, several pectoral fins with different sizes are designed and their hydrodynamics and optimizing capabilities are analyzed by computational fluid dynamics (CFD) simulation. Then, a double deep Q network (DQN) based optimization strategy is proposed to improve gliding efficiency by active pectoral fins, in which an adversarial model and a two-stage reward function are presented for the adequate calculation of gliding range. Simulations are conducted to validate the convergence and effectiveness of the proposed strategy. The aquatic experiments are carried out to further verify the proposed strategy. The results reveal that the optimization strategy can save about 4.88% of energy and 19.45% of travel time. This study provides clues to the design of active control surfaces and improvement of gliding efficiency for underwater vehicles. Remarkably, the proposed strategy can significantly improve the duration and endow the robot with the potential to perform complex tasks.

Development and Evaluation of Control Architectures for a Mechanically Deployed Entry Vehicle

The NASA-funded Pterodactyl Project seeks to advance the current state of the art for atmospheric entry vehicles by developing novel guidance and control technologies for deployable entry vehicles (DEVs). This paper details the efforts of the Pterodactyl team to develop, implement, and evaluate different control hardware effectors on an asymmetric, mechanically deployed DEV. Multiple control effector designs are developed for a baseline vehicle including propulsive control systems (reaction control systems) and nonpropulsive control systems (aerodynamic control surfaces and internal moving masses). For each control system, state-feedback integral controllers based on linear quadratic regulator optimal control methods are designed to track the guidance commands of either the bank angle or the angle of attack and sideslip angle. Using a lunar return reference mission, a comparative analysis of the performance and maneuverability of the DEV using the different control system configurations is conducted. The aerodynamic control surface design is demonstrated to be the most suitable architecture, primarily due to its ability to achieve acceleration rates that supersede the other designs. Considering performance, maneuverability, and guidance tracking during entry, the aerodynamic control surface design is recommended for this DEV and chosen reference mission.

Investigation on a Flow Coupling Rudder for Directional Control of a Low-Aspect Tailless Configuration with Diamond-Shaped Wing

To solve the issues of directional control and aerodynamic moment coupling for a low-aspect tailless configuration with a diamond-shaped wing, we herein propose the concept of a flow coupling rudder (FCR). The FCR was composed of two basic control surfaces: a spoiler slot deflector (SSD) on the upper surface of the wing and the corresponding elevon. With the constraints of the fixed area and spanwise position of the SSD, the effects of the leading-edge sweep angle, chord position of the SSD, and collocating deflection angles of the SSD and elevon on the control characteristics of the configuration were analyzed using a numerical method. Based on the analysis, the selection principle of the key parameters for designing the FCR for the configuration was proposed. This proves that the leading edge of the selected SSD should be swept back instead of being parallel to the trailing edge of the wing to design an FCR with favorable aerodynamic performance for such a configuration. By accurately adjusting the parameters of the SSD and elevon, the FCR on the one-side wing could supply an effective yawing moment while simultaneously weakening or even eliminating the coupling pitching and rolling moments of traditional drag-type control surfaces. In this study, we provide a method for the directional control surface design of a low-aspect tailless configuration with a diamond-shaped wing.

Increase in Stability of an X-Configured AUV through Hydrodynamic Design Iterations with the Definition of a New Stability Index to Include Effect of Gravity

A study about the effect of different configurations of stationary and movable appendages on the dynamic stability of an autonomous underwater vehicle (AUV) is presented. A new stability index that can be used to assess dynamic stability in the vertical plane is derived. It improves upon the vertical plane stability index by accurately accounting for the contribution of hydrostatic forces to dynamic stability, even at low speeds. The use of the new stability index is illustrated by applying it to a set of AUV configurations based on an AUV initially designed at Virginia Tech and built by Dive Technologies. The applicability of this index depends on the speed of the craft. The range of applicability in terms of speed is presented for the DIVE craft as an example. The baseline design of the DIVE craft has asymmetry in the vertical plane and symmetry in the horizontal plane. A virtual planar motion mechanism (VPMM) is used to obtain the hydrodynamic coefficients of the hull. Design iterations are performed on the baseline design by varying the appendages in shape and size, adding appendages and adding features on appendages. The best and the baseline design from this effort are incorporated in a 6 DOF lumped-parameter model (LPM) to compare results of a straight line maneuver. A computational fluid dynamic (CFD) tool is used to obtain the trajectory comparison of turn-circle maneuver for these two designs. A principal conclusion is the important contribution of a hydrostatic restoring force at low-moderate speeds by using GVgrav and the influence of design of control surfaces, both stationary and non-stationary, in the achievement of control-fixed course stability.

Control surface design for radio-controlled aircraft. Case: SAE Aero Design Micro-class prototype

This research article presents a design methodology for primary control surfaces (Ailerons, Rudder and Elevator) for experimental unmanned radio-controlled aircraft. The methodology is based on the proposal and standardization of the required mechanical and aerodynamic analysis for each control surface sizing, considering the SAE Aero Design competition objectives within Micro Class. It is used on empirical results previously described in references about aeronautical design, computerized fluids dynamics (CFD) software, and aircraft controllability regulations in order to obtain the design variables. Based on this information, the iteration sequences required for design were automated by a C++ language code to obtain the optimal characteristics for each surface, thereby reducing the possibility of calculation errors, overall time, and workload invested in the design process. The application of the methodology to the latest aircraft design reduced the total control systems weight to the aircraft’s empty weight ratio to a minimum of 3.4%.

Controllability Gramian as Control Design Objective in Aircraft Structural Design Optimization

Because of their higher aerodynamic efficiency and lighter structural weight, thin composite wings with large aspect ratios are increasingly being used for civil transport aircraft wing design. However, the increased flexibility can induce several performance issues, such as high deflections, reduced control authority, coupled flight dynamics, and, possibly, a reduction in the flutter speed. Therefore, including control surface and control law design at the conceptual design stage is becoming increasingly important. This paper presents a novel approach for integrating a control objective into an aircraft design optimization at the conceptual design stage by proposing the use of the eigenvalues of the controllability Gramian to enhance the controllability of an aircraft. The individual eigenvalues of the controllability Gramian quantify the energy required to move along the corresponding eigenvector, which is observed to be dominated by one state-space variable. A higher eigenvalue implies lower energy requirements for controlling that eigenvector, thus the corresponding state-space variable. This approach does not rely on a control law design but on modifying the open-loop system such that it is easier to control. The approach is applied to conduct multidisciplinary design analysis and optimization (MDAO) of a composite flying-wing test aircraft. A previously developed MDAO framework is used to design the internal structural layout, using curvilinear spars and ribs (SpaRibs) and straight spars and ribs. It is found that the optimal control designs have up to 8% higher flutter speed with a 3.7% weight penalty. Moreover, the frequencies of the vibration mode shapes are higher for the optimal control designs. The active flutter suppression controllers are designed after the MDAO process, and it is found that the optimal control designs have significantly higher gain and phase margins. As a result, the optimal control designs yield higher robust closed-loop flutter speed as compared with the weight-minimized design.

Grid-Based and Polytopic Linear Parameter-Varying Modeling of Aeroelastic Aircraft with Parametric Control Surface Design

The main direction of aircraft design today and in the future is to achieve more lightweight and higher aspect ratio airframes with the aim to improve performance and to reduce operating costs and harmful emissions. This promotes the development of flexible aircraft structures with enhanced aeroelastic behaviour. Increased aeroservoelastic (ASE) effects such as flutter can be addressed by active control technologies. Control design for flutter suppression heavily depends on the control surface sizing. Control surface sizing is traditionally done in an iterative process, in which the sizing is determined considering solely engineering rules and the control laws are designed afterwards. However, in the case of flexible vehicles, flexible dynamics and rigid body control surface sizing may become coupled. This coupling can make the iterative process lengthy and challenging. As a solution, a parametric control surface design approach can be applied, which includes limitations of control laws in the design process. For this a set of parametric models is derived in the early stage of the aircraft design. Therefore, the control surfaces can be optimized in a single step with the control design. The purpose of this paper is to describe as well as assess the developed control surface parameterized ASE models of the mini Multi Utility Technology Testbed (MUTT) flexible aircraft, designed at the University of Minnesota. The ASE model is constructed by integrating aerodynamics, structural dynamics and rigid body dynamics. In order to be utilized for control design, control oriented, low order linear parameter-varying (LPV) models are developed using the bottom-up modeling approach. Both grid- and polytopic parametric LPV models are obtained and assessed.

Control device effectiveness studies of a 53∘ swept flying wing configuration. Experimental, computational, and modeling considerations

The present investigation covers studies of different control devices on several 53∘ swept flying wing configurations without a vertical tail plane. The wings considered share the same planform but differ in their spanwise profile shapes. The planform, developed under the NATO AVT-251 Task Group, is referred to as the MULDICON (or MULti-DIsciplinary CONfiguration). The objectives of this article are twofold: (1) to design yaw control surfaces for the MULDICON wing using an experimental/computational approach and (2) to develop aerodynamic models that rapidly and accurately predict the effectiveness of control surfaces over a wide range of flight conditions. The yaw control surface design (position and size) should provide sufficient yaw moment with almost no contribution in roll and pitch moment. To identify such concepts, a number of preliminary experiments on a generic flying wing configuration have been conducted. Two promising concepts from wind tunnel tests were then numerically examined for being implemented in the MULDICON baseline wing. Concepts with spoilers and a split flap were specifically considered. For medium to high angles of attack, the flow topology of the baseline wing is dominated by a vortical flow field on the upper outer wing. This leads to interactions between vortex and the control device which influences the flow and the attitude of the control device on the upper wing side. Furthermore, this work considers developing aerodynamic models for predicting stability derivatives of several MULDICON designs over a wide range of flight conditions. Aerodynamic loads models are only developed for normal force and pitch moment coefficients, however, the developed approach can easily being extended to include lateral aerodynamic coefficients as well. Quasi-steady models of this work are power series expansions of traditional linear aerodynamic models to capture nonlinear effects. Additionally, the models can estimate static and dynamic stability derivatives and the control surface powers.

Control surfaces of aquatic vertebrates: active and passive design and function.

Aquatic vertebrates display a variety of control surfaces that are used for propulsion, stabilization, trim and maneuvering. Control surfaces include paired and median fins in fishes, and flippers and flukes in secondarily aquatic tetrapods. These structures initially evolved from embryonic fin folds in fishes and have been modified into complex control surfaces in derived aquatic tetrapods. Control surfaces function both actively and passively to produce torque about the center of mass by the generation of either lift or drag, or both, and thus produce vector forces to effect rectilinear locomotion, trim control and maneuvers. In addition to fins and flippers, there are other structures that act as control surfaces and enhance functionality. The entire body can act as a control surface and generate lift for stability in destabilizing flow regimes. Furthermore, control surfaces can undergo active shape change to enhance their performance, and a number of features act as secondary control structures: leading edge tubercles, wing-like canards, multiple fins in series, finlets, keels and trailing edge structures. These modifications to control surface design can alter flow to increase lift, reduce drag and enhance thrust in the case of propulsive fin-based systems in fishes and marine mammals, and are particularly interesting subjects for future research and application to engineered systems. Here, we review how modifications to control surfaces can alter flow and increase hydrodynamic performance.

Integrated design of flight control surfaces and laws for new aircraft configurations

Control architecture sizing is a main challenge for new aircraft design like blended wing-body design. This aircraft configuration typically features redundant elevons located at the trailing edge of the wing, acting simultaneously on pitch and roll axes. The problem of integrated design of control surface sizes and flight control laws for an unstable blended wing-body aircraft is addressed here. Latest tools for H∞ non-smooth optimization of structured controllers are used to optimize in a single step the gains for both longitudinal and lateral control laws, and a control allocation module, while minimizing control surfaces total span. Following constraints are ensured: maximal deflection angles and rates for 1) pilot longitudinal pull-up 2) pilot bank angle order and 3) longitudinal turbulence. Using this coupled approach, significant gains in terms of outer elevons span compared to the initial layout are demonstrated, while closed-loop handling qualities constraints are guaranteed.

Design and flight test of the generic micro-aerial vehicle (GenMAV) utilizing piezoelectric conformal flight control actuation

A novel morphing control surface design employing piezoelectric macro-fiber composite actuators is compared to a servo-actuated system. The comprehensive comparison including aerodynamics, size, weight, power, bandwidth, and reliability has been extended to include flight test comparisons. Three flight vehicles were designed, built, and evaluated: a servo-controlled generic micro-aerial vehicle aircraft and two conformal actuator controlled versions based on thick and thin wing designs. Flight agility and control response of the morphing-actuated and servo-actuated configurations were quantified through state measurement during identical automated maneuvers. The morphing actuation scheme demonstrated control bandwidth that was an order of magnitude greater than for the servo-actuated system, but showed a 12% decrease in roll rate when compared to the servo-actuated baseline aircraft. The flight vehicles allowed system-level comparisons of conventional and morphing control, where conformal actuation occupied less volume, consumed equivalent power as micro servos and provided effective control power for maneuvering.

Single propeller airplane minimal flight speed based upon the lateral maneuver condition

This paper presents the application of the previously presented general analysis method to determine the safe flight boundaries of the asymmetrically loaded airplane within the terminal flight phases as applied to the case of inherently asymmetric single propeller airplane. As the lateral control surface design is done for the flight conditions out of the terminal flight phases, the key objective is to improve the flight safety of the asymmetrically loaded airplane by introducing the lateral flight controls verification at the low flight speeds. The concept of the authority of control surfaces presenting their capability to generate the forces and moments needed by the airplane to perform required maneuvers is the basis of the analysis. Control surface authority is the function of the control surface aerodynamic properties, structurally available flight control displacements and dynamic pressure. The analysis method scope is based upon the requirement to supplement the safe flight boundaries of symmetrically loaded airplane within the terminal flight phases, with the lift coefficient observed as the function of the angle of attack being at the linear limit. Control surface demands are lateral maneuver execution and asymmetric load and lateral wind compensation, the method scope permitting them to be addictive. Thus defined, the method is based upon the comparison of the available control surface authority and demands. For the defined flight conditions, the analysis is reduced to the comparison of the demanded and structurally available flight control displacement. The method combines the simple roll dynamics model, the stationary equations of the airplane lateral-directional motion and several numeric analysis procedures to obtain the results. This new combination possesses synergy properties and is implemented as the computer program. The method is applicable for any combination of airplane asymmetric loads and can be used throughout entire airplane life cycle. The contemporary trend of downsizing training and light combat airplane types with the rising number of the introduced medium and high power single propeller airplane types increases the significance of the method application in the design procedure.

PrandtlPlane Joined Wing: Body freedom flutter, limit cycle oscillation and freeplay studies

Dynamic aeroelastic behavior of a joined-wing PrandtlPlane configuration is investigated herein. The baseline model is obtained from a configuration previously designed by partner universities through several multidisciplinary optimizations and ad hoc analyses, including detailed studies on the layout of control architecture. An equivalent structural model has then been adopted to qualitatively retain similar aeroelastic properties.Flutter and post-flutter regimes, including limit cycle oscillations (LCOs), are studied. A detailed analysis of the energy transfer between fluid and structure is carried out; the areas in which energy is extracted from the fluid are identified to gain insights on the mechanism leading to the aeroelastic instability. Starting from an existing design of control surfaces on the baseline configuration, freeplay is also considered and its effects on the aeroelastic stability properties of the joined-wing system are investigated for the first time.Both cantilever and free flying configurations are analyzed. Fuselage inertial effects are modeled and the aeroelastic properties are studied considering plunging and pitching rigid body modes. For this configuration a positive interaction between elastic and rigid body modes yields a flutter-free design (within the range of considered airspeeds).To understand the sensitivity of the system and gain insight, fuselage mass and moment of inertia are selectively varied. For a fixed pitching moment of inertia, larger fuselage mass favors body freedom flutter. When the moment of inertia is varied, a change of critical properties is observed. For smaller values the pitching mode becomes unstable, and coalescence is observed between pitching and the first elastic mode. Increasing pitching inertia, the above criticality is postponed; meanwhile, the second elastic mode becomes unstable at progressively lower speeds. For larger inertial values “cantilever” flutter properties, having coalescence of first and second elastic modes, are recovered.

Nonlinear Flutter Analysis for the Scaled F-35 with Horizontal-Tail Free Play

A nonlinear flutter analysis is performed to study the limit-cycle-oscillation characteristics of an F-35 wind-tunnel model with horizontal-tail free-play effects using a direct simulation method. The result of this study is first validated with the wind-tunnel data. Then, a set of free-play design charts is generated to investigate the limit-cycle-oscillation-occurrence domain at various free-play angles and hinge moments of the horizontal tail. It is found that, as long as the horizontal tail is unloaded, the limit-cycle oscillation is inevitable even with a very small free-play angle. Furthermore, the free-play angle cannot be the only significant parameter involved in the free-play criteria. Therefore, it is suggested that an improved military specification for free-play limits of all-movable control surfaces be established. This effort will make a substantial impact on the control-surface design that may lead to a paradigm shift in the design criteria of aircraft structure.

Investigation on Aerodynamic Configuration of Monitoring Long Endurance UAV

In recent years, monitoring long endurance UAV is widely used in civil fields such as earthquake relief, it has certain particularities in comparison with conventional UAV; this paper studied and summarized its key technologies in aerodynamic configuration. The research of aerodynamic configuration is based on a general scheme, research indicates that: (1) monitoring long endurance UAV has the characteristics of low-Reynolds number, so laminar airfoil is needed to increase lift-drag ratio; induced drag can be reduced by optimizing wing twist angle; (2) subsection control surface and new design method on flight-quality would improve control reliability and flight quality, which are indispensable for the UAV to guarantee safety in bad weather condition; (3) take-off/landing/taxiing performance should be considered in order to improve the runway adaptability of the UAV.