Wing Folding Research Articles

A robotic platform for mimicking the flapping flight of bats

To understand how bats control their wing movements based on biosonar inputs, it is important to identify the key kinematic synergies that need to be replicated on a robotic prototype so its wingbeat patterns and aerodynamic capabilities matches its biological counterpart. Attempting to replicate the approximately 20 degrees of freedom in each bat wing is challenging since more mechanical degrees of freedom increase mass and reduce reliability. Our proposed approach, is based on recordings of the kinematics of maneuvering bats that are obtained from high-speed camera data. The first two synergistic actions to implemented in the robot were wing flapping and folding that work together to increase net lift generation. During straight flight, these synergies follow a fixed synchronized pattern allowing a single-actuator robot model to mimic key bat flight characteristics. By recording the robot prototype's flight kinematics with the same high-speed camera setup, we can compare the flight kinematics of bats and flapping-flight robots inspired by them, quantifying differences in complexity and performance. The goal is a bioinspired robotic platform enabling detailed study of bat flight biomechanics and control strategies. This will provide new biological insights and advance flapping-flight robot development by determining kinematic complexity required for bat-like performance.

Design and Flight Test of a Tube-Launched Unmanned Aerial Vehicle

Unmanned aerial vehicles (UAVs) have already proven valuable for intelligence, search, and reconnaissance missions; however, their integration into manned aircraft to augment existing capabilities is still an emerging field. This paper describes the design of an aircraft that fits inside a G-sized sonobuoy canister, deploys from a manned aircraft in-flight, and flies for up to 111 km and 83 min while providing telemetry to a remote operator. While UAVs with similar performance requirements exist, most were designed to fit in larger canisters. Multiple UAVs can be deployed in the air to expand the search capabilities of manned aircraft, ultimately allowing a larger search area per cost compared to manned aircraft alone. Individual performance characteristics of the aircraft such as aerodynamics, weight, propulsion, and stability were developed in the preliminary design phase based on given performance requirements. The performance of the aircraft was assessed using analytical and empirical methods. Wing folding mechanisms were prototyped for use on the production aircraft for flight testing. Propulsion, aerodynamic, and structural capabilities were validated separately using experimental methods. The folding mechanisms used in this UAV allow it to achieve the benefits of a longer wingspan while remaining compact and easy to deploy.

Investigation on improving aerodynamics and flight performance for an unmanned aircraft with a span-extendable wing

The foldable unmanned aerial vehicle can reduce the storage space and improve the platform adaptability. However, the conventional foldable wing aircraft is configured with a low aspect ratio, which leads to a high aerodynamic drag and limited flight endurance. In this study, a foldable wing unmanned aircraft that can increase its wingspan to improve aerodynamic performance and flight endurance is proposed. The aerodynamic characteristics and flight performance of the aircraft is evaluated using the computational fluid dynamic method. The numerical results show that the increased wingspan can effectively decrease the wingtip vorticity and aerodynamic drag. The fully-extended wing configuration achieves a lift-to-drag ratio of 16.72, which results in an increase of 36.94% than that of the non-extended wing. The flight endurance and range of the fully-extended wing configuration are 3.81 hour and 249.89 km, respectively, which creates 86.22% more endurance and 36.88% more range than the non-extended wing. To validate the feasibility of the proposed concept, a flight test was carried out and the flight performance was obtained from flight control system. The flight data corrects well with the numerical results, which proves the effectiveness and feasibility of the variable span-morphing wing in improving flight performance for unmanned aircraft.

Design and Simulation of Foldable Wing eVTOL UAV

Design and Simulation of Foldable Wing eVTOL UAV

Design of Locking Mechanism and Locking Performance Analysis for Folding Wing

Design of Locking Mechanism and Locking Performance Analysis for Folding Wing

Aeroelasticity Analysis of Folding Wing with Structural Nonlinearity Using Modified DLM

The structural nonlinear aeroelastic analysis of folding wings is conducted by integrating the modified Doublet Lattice Method in this paper. Firstly, a modified Doublet Lattice Method is investigated to relax the aspect ratio limitation of aerodynamic elements, and its correctness is verified through numerical examples. Secondly, the rational function approximation method is discussed, and the modified Doublet Lattice Method is approximated using the minimum state method to obtain the unsteady aerodynamic forces in the time domain. Finally, the aeroelastic characteristics of a folding wing with free-play and friction nonlinearity are studied by integrating time-domain unsteady aerodynamics with the nonlinear structural dynamics model. The results show that the modified Doublet Lattice Method, which relaxes the aspect ratio limitation of aerodynamic grid elements, is feasible and effective; Friction can suppress the influence of free-play nonlinearity on aeroelastic response.

Design and numerical study of foldable wing module of air-launched underwater glider

Launching underwater gliders by aircraft could greatly expand the application of underwater gliders. However, during the process of the glider entry into the water, it will be subjected to significant impact loads, especially during the process of wing entry into the water. In this paper, a foldable wing module is proposed to reduce the water entry impact loads of the glider caused by the wings entering into the water. The effect of the foldable wing module on impact loads reduction and the influence of the foldable wing module on the water entry trajectory are studied by numerical method. The results show that the differences in mass and gravity center position caused by the foldable wing module have little effect on the water entry impact loads of the glider until the wings impact the water. When the glider enters the water obliquely, the wing module reduces the peak radial acceleration of the glider. In addition, the trajectory and time of the glider to reach the horizontal attitude are also reduced. These conclusions will be helpful for the designing of the wings of air-launched underwater gliders.

Aerodynamic Analysis of a Logistics UAV with Foldable Bi-wing Configuration

Herein, a twin-boom, inverted V-tailed unmanned aerial vehicle (UAV) featuring a foldable bi-wing configuration is proposed for logistics and transportation applications. We employed the Navier–Stokes solver to numerically simulate steady, incompressible flow conditions. By examining the effects of key design parameters on aerodynamic characteristics and bypass flow fields in a two-dimensional state, we were able to suggest a more optimized foldable wing design. Building on the two-dimensional analysis, we performed aerodynamic assessments of the three-dimensional aircraft geometry. Our results indicated that appropriate wing and gap parameters can significantly enhance lift characteristics, maintaining high lift even during large-angle flights. Specifically, when compared to a mono-wing, the lift coefficient of the bi-wing increased by 27.1% at a 14° angle of attack, demonstrating the effectiveness of our wing-and-gap design. Optimal aerodynamic performance was achieved when the gap distance equalled the chord length in both flow and vertical directions. Further, the right combination of airfoil configuration, wing axes angle, and wingspan can improve flow field aerodynamic characteristics, while also enhancing the wing’s stall capacity. The lift coefficient reached its maximum value at an angle of attack of 15°, which has the potential to reduce takeoff and landing distances, thereby enhancing the UAV’s overall safety.

Approximate global mode method for flutter analysis of folding wings

The aircraft with folding wings benefits from the ability to transform its folding wings to adapt to various flight missions but suffers from the change of the wings’ aeroelastic characteristics as a result. To clarify the change, it is necessary to study the dynamical modeling of the folding wing and also its aeroelastic response. This paper proposes a novel approximate global mode method (AGMM) for dealing with complex boundary conditions and models a folding wing consisting of separate rectangular plates for nonlinear flutter analysis. A high-precision low-dimensional dynamical model of the folding wing is developed, which is first validated by comparing the modal results obtained from the AGMM model with those obtained from an equivalent finite element model and is also experimentally validated by a comparison of forced vibration responses. On this basis, an AGMM model of the folding wing in supersonic aerodynamic loads based on the piston theory is further developed. The critical flutter velocity at different folding angles and the aeroelastic response are comprehensively studied by simulations based on the model. The result shows that the first 7th-order modes are sufficient for obtaining a converged critical flutter velocity, which varies with geometric parameters and potentially increases by 714 %. In addition, the low-order torsional modes of the wing contribute more to the vibration than the other modes during flutter. This work provides a new way of developing advanced dynamical modeling methods of folding and combinational structures for their dynamics design, optimization, and system control.

A novelty motion reliability analysis method for locking mechanism of folding wing

The locking mechanism of folding wing is investigated as an individual object while the correlation between the locking performance and the deployment process is neglected. Its performance function frequently exhibits complex nonlinear dynamic characteristics and implicity during locking process, making it described by time-consuming dynamic simulation model rather than analytical expressions. Accordingly, when it comes to motion reliability, the physical model requires frequent manual modifications, and the numerous time-consuming simulation models need to be calculated which results in low computational efficiency in motion reliability analysis, especially, in case of small failure probability. Focusing on these problems, a hybrid model, which is based on integrating ADAMS with MATALAB, is established to understand the kinematic and dynamic characteristics of the locking mechanism of folding wing. The hybrid model is composed of a control system and a mechanical subsystem, and can synchronously consider the influences on the locking performance of various critical parameters belonging to the control and controlled systems. The computational efficiency and accuracy of the hybrid model are both verified by comparing with physical and simulation models. A 1D–3D coupling reliability methodology, which is based on the hybrid model, is proposed to analyze the motion reliability for locking mechanism of folding wing. With dividing samples and constructing parallel computation on multi-machine with multiple windows, the motion reliability and sensitivity for locking mechanism of folding wing can be obtained quickly and accurately by the novelty motion reliability analysis method.

Reliability assessment of folding wing system deployment performance considering failure correlation

The reliability of folding wing deployment performance greatly impacts flight vehicle reliability. Based on the dynamic analysis theory, the deployment dynamic model of folding wing mechanism with joint clearances is established and solved. Considering the failure correlation, the system reliability models are developed for both cases, without considering synchronization and considering synchronization. For the former, a solution method combining saddle point approximation and numerical integration is proposed. For the latter, an estimation method based on a combination of the fourth order moment Pearson distribution family and the numerical integration is proposed. The efficiency and accuracy of the proposed methods are verified through examples. In addition, the trend of the system reliability change when the distribution parameters of random variables are different is also analyzed. From the perspective of improving reliability, the above study can provide theoretical guidance and data support for the design, manufacturing and service process of the folding wing mechanism system.

Design and field test of a foldable wing unmanned aerial–underwater vehicle

AbstractThis paper presents the design and field test of a foldable wing unmanned aerial–underwater vehicle (UAUV). The vehicle can complete diving and air operations, and still have the ability of multiple trans‐medium water egress and ingress under the condition of carrying mission load during a single flight. The wings can be folded back for drag reduction in underwater sailing and water egress, and unfolded to provide lift for flight after water egress. This paper presents the major components and system design of the vehicle, including the overall structure of the vehicle, the design of the mechanism for self‐locking and quick‐folding, the design of the electrical system, the selection of the propulsion system, and analyzes the performance gains from foldable wings and foldable propellers. Then the trans‐medium field test was introduced, and the analysis and discussion were conducted for the four typical operating conditions of the vehicle, including water sailing, aerial flight, water egress and water ingress. Furthermore, the endurance performance under the corresponding operating conditions is estimated based on experimental data and the current battery energy carried. The presence of foldable wings and a large pitch angle water egress strategy reduces the thrust‐to‐weight ratio requirement for the vehicle. The results of the field tests can provide important experience and data support for the subsequent application‐oriented UAUVs.

Earwig-inspired foldable origami wing for micro air vehicle gliding.

Foldable wings serve as an effective solution for reducing the size of micro air vehicles (MAVs) during non-flight phases, without compromising the gliding capacity provided by the wing area. Among insects, earwigs exhibit the highest folding ratio in their wings. Inspired by the intricate folding mechanism in earwig hindwings, we aimed to develop artificial wings with similar high-folding ratios. By leveraging an origami hinge, which is a compliant mechanism, we successfully designed and prototyped wings capable of opening and folding in the wind, which helps reduce the surface area by a factor of seven. The experimental evaluation involved measuring the lift force generated by the wings under Reynolds numbers less than 2.2 × 104. When in the open position, our foldable wings demonstrated increased lift force proportional to higher wind speeds. Properties such as wind responsiveness, efficient folding ratios, and practical feasibility highlight the potential of these wings for diverse applications in MAVs.

Reliability evaluation of folding wing mechanism deployment performance based on improved active learning Kriging method

The folding wing mechanism is essential for the normal flight of an aircraft, and it is necessary to evaluate the reliability of its deployment performance to ensure the long-term stable operation of the aircraft. In this study, a deployment dynamic model of the folding wing mechanism was developed and solved, and the essential factors affecting the deployment performance of the folding wing were analysed. The reliability evaluation models of the folding wing deployment performance were then presented for constant and non-constant random variable distribution parameters. Finally, the proposed improved AK-IS method was used to calculate the reliability of the deployment performance under the above two conditions. Through validation and analysis of the four cases, the results show that the improved AK-IS method is more efficient than the original AK-IS method, with guaranteed computational accuracy. Compared with the Monte Carlo Simulation, the improved AK-IS method also shows higher efficiency and good robustness in solving engineering problems, such as the reliability evaluation of deployment performance; thus, the proposed method can support the reliability evaluation of similar deployment mechanisms.

Feasibility study on mimicking the tail-beating supported gliding flight of flying fish

Mimicking the unpowered gliding capabilities of flying fish is challenging, due to the various technical limitations that are involved in creating a dual-modal robot that can both swim underwater and fly in the air. In this work, we suggest a modified KUFish design equipped with a pair of foldable wings for gliding flight in the air. Although the current water-leaping speed of the KUFish is lower than that of flying fish, the robot may be able to lift off by taking advantage of a head wind and forces produced by tail-beating motion, compensating for its weight, and overcoming the drag. Our series of computational fluid dynamics simulations has shown that with the unfolded wings and fully submerged tail-beating motion, when the wing and body angles are maintained in specific ranges under the head wind speeds of (9.5 and 6.5) m/s, the robotic fish after water-leaping can perform efficient gliding flight without generating pitching moment. This work can also be used to explain how flying fish perform gliding flight under tail-beating motion, and to develop an actual model of the dual-modal robot that mimics flying fish in the future.

A folding wing system for guided ammunitions: mechanism design, manufacturing and real-time results with LQR, LQI, SMC and SOSMC

AbstractIn the present work, a folding wing system (FWS) was developed for guided ammunitions, so that the swept-back angle could be adjusted during both gliding and diving phases. Unlike previous designs, the FWS does not have any fixing mechanisms or brake elements, and it provides folding functionality to reduce the drag force during the terminal phase. We conducted mechanism design, manufactured the FWS, performed system identification and designed various controllers including linear quadratic regulator (LQR), linear quadratic integrator (LQI), sliding mode control (SMC) and second-order sliding mode control (SOSMC) to adjust and hold the desired swept-back angles. Then, the performance of the FWS was tested experimentally under two different flight scenarios, with and without aerodynamic loads. While all controllers operated with almost zero steady-state error (SSE) in the absence of aerodynamic loads, the SOSMC was the most effective controller under aerodynamic loads, considering SSE, delay, chattering, and energy consumption.

Aerodynamic Characteristics of a Z-Shaped Folding Wing

Z-shaped folding wings have the potential to enhance the flight performance of an aircraft, contingent upon its mission requirements. However, the current scope of research on unmanned aerial vehicles (UAVs) with Z-shaped folding wings primarily focuses on the analysis of their folding structure and aeroelasticity-related vibrations. Computational fluid dynamics methods and dynamic meshing are employed to examine the folding process of Z-shaped folding wings. By comparing the steady aerodynamic characteristics of Z-shaped folding wings with those of conventional wings, this investigation explores the dynamic aerodynamic properties of Z-shaped folding wings at varying upward folding speeds. The numerical findings reveal that the folding of Z-shaped folding wings reduces the lift-to-drag ratio, yet simultaneously diminishes the nose-down pitching moment, thereby augmenting maneuverability. Concerning unsteady aerodynamics, the transient lift and drag coefficients of the folded wing initially increase and subsequently decrease as the folding angle increases at small angles of attack. Likewise, the nose-down pitching moment exhibits the same pattern in response to the folding angle. Additionally, the aerodynamic coefficients experience a slight decrease during the initial half of the folding process with increasing folding speed. Once the wing reaches approximately 40°~45° of folding, there is an abrupt change in the transient aerodynamic coefficients. Notably, this abrupt change is delayed with higher folding speeds, eventually converging to similar values across different folding speeds.

A New Type Bionic Foldable Wing Design for High Maneuverable Unmanned Aerial Vehicle

With the improvement of aircraft requirements in civil and military fields, aircraft are developing towards the direction of high efficiency and multi-mission. Foldable wing aircraft with large deformation capability will be able to meet flight requirements and performance under different conditions. Based on the bionic design concept, a feather-like foldable morphing wing based on a multi-link mechanism from the flight characteristics of birds was designed. In order to validate the feasibility of the proposed morphing wing conception, a UAV with bionic foldable wings was fabricated. The aerodynamic performance of the prototype model was tested under different working conditions by wind tunnel test and flight test. The simulation and wind tunnel experimental test showed that the prototype has excellent longitudinal and transverse directional aerodynamics. When the wing is symmetrically morphing, the optimal lift-to-drag ratio can be maintained under different flow velocities. When the wing is asymmetrically morphing, it can replace the aileron to achieve an efficient roll maneuver.

Dynamics simulation of folding wing UAVs launched from a high-altitude balloon platform

It is a new application of the high-altitude balloon system to launch multiple small folding wing unmanned aerial vehicles (UAVs). Based on the design of the launching system, we conduct numerical simulations of the ejection process from the balloon platform and the subsequent UAV wing deployment with trajectory leveling operation. We use the Kane method to establish the dynamic model of the balloon launching platform in the inertial coordinate system (ICS). By introducing the degree of freedom of UAV sliding along the sliding track, we realize the dynamic simulation of eight UAV launching processes and obtain the instantaneous separated states. The folding wing UAV first deploys its wings after ejection, which has the coupling characteristics between structural deformation and attitude adjustment. It is regarded as a multi-rigid body connecting structure composed of the fuselage and four wings. We establish the dynamic simulation model by the Kane method in the UAV body coordinate system (BCS). The Radau pseudo-spectral method is used to calculate the flight trajectory of each UAV. This paper is an engineering application research and can provide a simulation reference for the launching test of the balloon-borne folding wing UAV program.

Preliminary weight estimation of canister based light foldable wing electric propulsion UAV, as a platform for swarm applications

Lots of disruptive UAV technologies are rising every day. Especially in the design process, under the prism of the upcoming swarm trend, a novelty touch to new foldable designs has started. In combination with electric propulsion systems, those platforms come in reality. Because of their size, the same design can be enlarged and reduced with minor changes at its subsystems. This simplifies the construction process and minimizes the costs. Due to their application range both, civilian and military platforms started to develop their own foldable UAVs, basically for swarm applications. In this study, the basic parameters of such a scalable design will be proposed. A literature survey will be presented, to determine the most common sizes of those platforms and the battery market availability. Afterwards, a mission profile will form the basis of the conceptual process for different dimensional UAVs. Two different methods about the weight estimation of the UAV will be examined. The goal of this multilateral examination is that; enable the designer to precede to an appropriate selection of subsystems of the UAVs, i.e., battery, autopilot and telemetry systems based on the weight estimation.