Vertical Take-off Research Articles

Prop-Plane — new convertible VTOL UAV as a combination of a longitudinal bicopter and a flying wing with a tilt-rotor powertrain

Vertical take-off and landing (VTOL) unmanned aircrafts are the newest and rapidly developing topic which is not only capable of improving Unmanned Aerial Vehicles (UAV) potential but also to create new use cases. This paper proposes a new convertible VTOL concept designed to obtain optimum flight characteristics for monitoring or flying over long objects. The distinctive feature of the proposed design is a combination of a flying wing with a longitudinal bicopter. The aircraft folds the wings down along the main axis of the aircraft during vertical take-offs and landings to descend the center of gravity and increase stability in bicopter mode. The convertible plane maximizes performance during horizontal flight while maintaining vertical take-off and landing capabilities.The design has been implemented in prototype, and the internal systems and the airframe have been designed and manufactured. As a result, the calculated technical characteristics of the UAV including wind resistance capability were described, the principal elements and components of the design were discussed, and the flight tests of the prototype created were conducted and results presented. Furthermore, the advantages and disadvantages of the concept are reviewed and further development of the project is discussed. The conducted work allows us to confirm the assumption that the developed concept can be used for real-world monitoring missions and to continue developing the concept for a full-scale UAV.

Urban Air Mobility (UAM) in Türkiye: Evaluating Existing Aviation Laws and International Practices

Urban Air Mobility (UAM) has emerged as a solution to transport challenges such as traffic congestion, environmental impacts, and lack of adequate public transport systems in urban areas. As the interest in UAM objects such as electric vertical take-off and landing aircraft (eVTOL) is increasing, it is important to understand whether the current regulations are sufficient to address the sui generis difficulties of this brand new technology. This article examines the adequacy of Türkiye's current legal framework to ensure the safe, effective, and sustainable integration of UAM. This article analyses Türkiye's existing aviation legislation, in particular the Turkish Civil Aviation Law and the instructions issued by the Directorate General of Civil Aviation (DGCA) and examines their applicability to UAM. The article discusses various regulatory gaps such as the lack of standards specifically designed for UAM, inadequate safety, environmental and operational regulations, and unclear guidelines on airspace integration. The article also discusses various UAM regulations prepared by the International Civil Aviation Organisation (ICAO), the European Union Aviation Safety Agency (EASA), and the approaches of pioneer countries in this area, such as the US, Germany, and Japan. Through a comparative analysis, it demonstrates the key lessons learnt from these international practices and presents suggestions for improving Türkiye's regulatory environment. The study emphasises the need for targeted reforms, introduction of specific standards, and a new regulative framework to foster the successful integration of UAM. The findings aim to contribute to the establishment of a solid legal framework to ensure that Türkiye is prepared for the future of UAM.

Gravity-assisted Takeoff of Bird-inspired Flapping-Wing Air Vehicle Using Cliff-drop

AbstractFlapping-Wing Air Vehicles (FWAVs) have been developed to pursue the efficient, agile, and quiet flight of flying animals. However, unlike lightweight FWAVs capable of vertical takeoff, relatively heavy FWAVs face challenges in self-takeoff, which refers to taking off without both external device and energy input. In this study, a cliff-drop method is implemented for an independent takeoff of a heavy FWAV, relying solely on gravity. In the takeoff process using the cliff-drop method, the FWAV moves on the ground to a cliff edge using a wheel-driving motor and then descends from the cliff to achieve the necessary speed for flight. To demonstrate the cliff-drop method, the KAIST Robotic Hawk (KRoHawk) with a mass of 740 g and a wingspan of 120 cm is developed. The takeoff tests demonstrate that the KRoHawk, significantly heavier than the vertical-takeoff capable FWAVs, can successfully take off using the gravity-assisted takeoff method. The scalability of cliff-drop method is analyzed through simulations. When drop constraints are absent, the wheel-driving motor mass fraction for cliff-drop method remains negligible even as the vehicle’s weight increases. When drop constraints are set to 4 m, FWAVs heavier than KRoHawk, weighing up to 4.4 kg, can perform the cliff-drop takeoffs with a wheel-driving motor mass fraction of less than 8%.

A Study on the Aerodynamic Impact of Rotors on Fixed Wings During the Transition Phase in Compound-Wing UAVs

Compound-wing unmanned aerial vehicles (UAVs) are highly valued for their performance. However, during the transition from vertical take-off to the cruise phase, the rotor wake can be coupled with the fixed wing. In this study, the aerodynamic effects of a DJI 9450 rotor on a NACA2415 fixed wing during transition were investigated using the computational fluid dynamics (CFD) method. The rotor-to-wing distances (R/L = 0.25, 0.5, and 0.9) were varied to analyze their impact on aerodynamic performance. The results show that increasing the distance between the front rotor and the fixed wing enhances the lift and drag of the fixed wing, while increasing the distance between the rear rotor and the fixed wing decreases the lift and drag of the fixed wing. During the rotor’s rotation, the fluctuation in the lift and drag of the fixed wing changes periodically due to the rotor wake, and the smaller the distance between the rotor and the fixed wing, the larger the fluctuation. When R/L = 0.25, the fluctuation of the fixed wing is minimized. Compound-wing UAVs with rotors mounted at R/L = 0.25 during the design stage can improve the flight stability during the transition phase in UAVs.

Influence of Airfoil Geometry on VTOL UAV Aerodynamics at Low Reynolds Numbers

This study examines the impact of airfoil geometry on the aerodynamic properties of a low Reynolds number flying wing unmanned aerial vehicle (UAV). The investigation was conducted at three Reynolds numbers (1×106, 2×106, and 5×106), all under a constant Mach number of 0.3 during subsonic flight. Four distinct airfoils from the NACA and Selig series were analyzed using XFLR5 v6.61, with the angle of attack varying from -5° to 15°. Among the airfoils, NACA 6409 consistently demonstrated superior aerodynamic performance across all Reynolds numbers. Notably, at a Reynolds number of 1×106, NACA 6409 achieved a peak lift coefficient (Cl) of 1.584 at an angle of attack of 11.1°, indicating high efficiency. Additionally, the study explored the angles of attack where the drag coefficient (Cd) increased sharply, as well as the lift-to-drag ratios (Cl/Cd), providing a comprehensive understanding of stalling behavior and the balance between lift and drag. These findings offer valuable insights into the aerodynamic efficiency of airfoils in the context of vertical takeoff and landing (VTOL) UAV design, underscoring the importance of further research to optimize airfoil designs for enhanced VTOL UAV performance.

The Diverse Applications of Aerospace Drones: From Defense to Humanitarian and Commercial Uses

This research investigates the extensive applications of aerospace drones across defense, humanitarian, and commercial sectors, showcasing their transformative impact on modern industry. Aerospace drones have become pivotal tools in diverse settings—from defense and tactical operations to humanitarian aid and infrastructure management—offering operational efficiencies, cost savings, enhanced safety, and innovative solutions to complex challenges. This study explores defense applications such as military reconnaissance, where Vertical Take-Off and Landing (VTOL) drones enable effective surveillance in challenging terrains. In humanitarian settings, drones are utilized for disaster response in earthquake and flood zones, providing critical functions like search-and-rescue, real-time damage assessment, and medical supply delivery. Commercially, drones support long-range infrastructure inspections, smart agriculture, and environmental monitoring, driven by advancements in imaging and remote sensing. The project emphasizes the technical challenges and ethical considerations associated with drone deployment, particularly the need for robust AI and autonomous navigation systems in dynamic and unpredictable environments. Collaborations with international aerospace firms and humanitarian organizations have further refined drone integration strategies in both civilian and military contexts. The research concludes with a discussion on regulatory frameworks and environmental impacts, aiming to provide a comprehensive view of thefuture of aerospace drones and their role in addressing global challenges.

Modeling and Transition Flight Control of Distributed Propulsion–Wing VTOL UAV with Induced Wing Configuration

The integration of propulsion and wing in distributed propulsion–wing UAVs (DPW UAVs) introduces significant propulsion-aerodynamic coupling, complicating dynamic modeling and flight control. This complexity is heightened by using induced wing surfaces for vertical takeoff and landing, requiring controllers to adapt to configuration changes and disturbances during transition flight. This paper develops a propulsion-aerodynamic coupling model for a medium-sized DPW UAV with induced wings (DPW-IW), enabling real-time aerodynamic performance calculations. Furthermore, a unified flight-control framework is proposed to avoid controller scheduling and switching during flight mode transitions. The proposed control framework employs the time-scale separation principle, divided into an outer loop and an inner loop. The outer loop uses a fuzzy controller to adjust allocation parameters, while the inner loop applies incremental nonlinear dynamic inversion (INDI) and control allocation (INCA) methods, providing robustness to nonlinear changes during flight transitions. Finally, simulations under various conditions demonstrate the controller’s effectiveness in ensuring smooth and robust transitions.

Lightweight aircraft design: Integrating biomechanics and algorithm optimization for drone construction using paper materials

Lightweight aircraft design emphasizes materials like composites, alloys, and advanced polymers to reduce weight while ensuring structural integrity. Streamlined aerodynamics, efficient propulsion systems, and optimized component layout further enhance performance. The purpose of this research is to develop an innovative aircraft design model for drones, integrating algorithm optimization techniques and lightweight materials to enhance the performance and efficiency of drones with the utilization of open-source software. We apply this structure to the construction of drones with fixed-wing (FW) and vertical take-off and landing (VTOL) configurations. The aircraft’s body is constructed using lightweight materials such as glass fiber fabric (Gff) and extruded polystyrene foam (XPS), employing a vacuum-assisted wet layup technique for fabrication. Multi-objective Co-evolving Ant Colony Optimization (MC-ACO) was used to improve the construction of drones with VTOL and FW capabilities. This strategy enabled it to be easier to achieve the trade-offs required for a generalist drone design, such as range, payload capabilities, and swarm operations, which were then evaluated against commercially available software to evaluate the effectiveness. Incorporating biomechanics into the design method permits higher consideration of user interaction with drones. The findings indicate that low-fidelity architecture is a suitable starting point for prototyping under limited time frames. The paper concludes with a discussion of the technical constraints of employing free software, as well as some practical concerns for flight testing drones with hybrid configurations.

Fast-Time Simulations to Study the Capacity of a Traffic Network Aimed at Urban Air Mobility

This article investigates viable solutions to implement an Urban Air Mobility network in Milan, Italy, and analyzes its influence on the airspace capacity. The network comprises eight vertiports for passenger transport among two main airports in the area and the city using electric vertical take-off and landing aircraft (eVTOLs). A Fast-Time Simulation (FTS) model with the software AirTOp (Air Traffic Optimization) allowed the evaluation of the ideal capacity of the network by varying two configurations, which differ from each other in terms of the number of Final Approach and Takeoff areas (FATOs). The results show how it is possible to reach high hourly capacities (in the order of one hundred), thus allowing the use of the service for about 4% of the total passengers passing through the two airports during the reference day chosen for this study. However, the results are ideal due to the strong idealism of the system, which overlooks several factors, and they should be considered as the maximum limit that can be obtained. Despite this, the method presented in this article can also be adapted for other urban areas with high population densities. In addition, the use of a simulation tool of this type allows, in addition to a numerical analysis, a qualitative analysis of the network behavior in terms of traffic, thus highlighting the criticalities of the proposed systems.

Options for future European reusable booster stages: evaluation and comparison of VTHL and VTVL return methods

AbstractIn the past, the majority of system studies on reusable space transportation performed within Europe focused on concepts relying on lift-generating wings for recovery. Recently, vertically landing concepts similar to those deployed successfully by SpaceX have moved to the center of technical attention. Both recovery and landing strategies have their pros and cons and it is not obvious what would be a sound choice for Europe. Therefore, the German Aerospace Center DLR initiated a parametric system study, named ENTRAIN, that evaluates the impact of different return options on the launcher design on a technical level: the vertical take-off, vertical landing method (VTVL) as used by SpaceX compared to the vertical take-off, horizontal landing (VTHL) method as used for the Space Shuttle. Within this study, launchers were designed using different propellant combinations, staging velocities and engine cycles. The designed launchers are evaluated in this paper regarding performance, technical difficulties, operational aspects, size, mass and complexity.

Design and implementation of a nonlinear observer for a novel Quadrotor UAV: the HELIPLANE

This study presents the design and dynamic modeling of a new type of quadrotor UAV, referred to as the Heliplane, which integrates the vertical take-off and landing (VTOL) capabilities of a multirotor with the horizontal flight efficiency of a fixed-wing aircraft. The modeling process involved creating a dynamic representation of the Heliplane, with special attention to the determination of its aerodynamic coefficients, which were calculated using SolidWorks Flow Simulation. The aerodynamic forces, including lift and drag, were analyzed based on the flow characteristics around the Heliplane's structure. To further enhance the system's performance, a nonlinear observer based on a sliding mode approach was synthesized. This observer was designed in a triangular form to ensure accurate state estimation and robust control, even in the presence of model uncertainties. The observer's key advantage lies in its finite-time convergence, which guarantees quick and precise tracking of the Heliplane's state variables. Simulation results demonstrated the effectiveness of the proposed observer in estimating the rotational and translational velocities with minimal deviation. The sliding mode observer's performance suggests its suitability for control and fault detection tasks in UAV applications, particularly in challenging operational environments.

The Design of Improved Series Hybrid Power System Based on Compound-Wing VTOL

Hybrid power systems are now widely utilized in a variety of vehicle platforms due to their efficacy in reducing pollution and enhancing energy utilization efficiency. Nevertheless, the existing vehicle hybrid systems are of a considerable size and weight, rendering them unsuitable for integration into 25 kg compound-wing UAVs. This study presents a design solution for a compound-wing vertical takeoff and landing unmanned aerial vehicle (VTOL) equipped with an improved series hybrid power system. The system comprises a 48 V lithium polymer battery(Li-Po battery), a 60cc internal combustion engine (ICE), a converter, and a dedicated permanent magnet synchronous machine (PMSM) with four motors, which collectively facilitate dual-directional energy flow. The four motors serve as a load and lift assembly, providing the requisite lift during the take-off, landing, and hovering phases, and in the event of the ICE thrust insufficiency, as well as forward thrust during the level cruise phase by mounting the variable pitch propeller directly on the ICE. The entire hybrid power system of the UAV undergoes numerical modeling and experimental simulation to validate the feasibility of the complete hybrid power configuration. The validation is achieved by comparing and analyzing the results of the numerical simulations with ground tests. Moreover, the effectiveness of this hybrid power system is validated through the successful completion of flight test experiments. The hybrid power system has been demonstrated to significantly enhance the endurance of vertical flight for a compound-wing VTOL by more than 25 min, thereby establishing a solid foundation for future compound-wing VTOLs to enable multi-destination flights and multiple takeoffs and landings.

Efficient conversion of Euler angles to quaternion for practical aerospace applications

Abstract Current methods for converting Euler angles to a rotation quaternion are computationally intensive and have limited practical applications in aerospace. This study introduces an efficient approach that directly converts Euler angles in any desired sequence to a rotation quaternion, eliminating the need for intermediate Euler angle transformation matrices, which leads to a significant improvement in computational efficiency. Moreover, it is general because it works with all 12 possible sequences of rotations. A case study is presented, demonstrating the application of the algorithm in converting between the launch frame and the missile frame of a vertical takeoff vertical landing (VTVL) rocket. The results show more than a ninefold improvement in computational efficiency compared to the classical Euler angle method while maintaining consistency of results.

Dynamics and control of a high-altitude balloon with slung load

Abstract The high-altitude balloon proposed in this paper is a long-life balloon carrying a payload through a cable that flies at 20km altitude in near space. A dynamic model of the system, including the thermodynamics of the buoyancy body coupled with a hanging model of the pod, is developed using the Newton–Euler method. The buoyancy body consists of a helium balloon and a ballonet. A differential pressure difference-based altitude adjustment is achieved by tracking the pressure difference at the target altitude. A dynamic simulation of the buoyancy body with a slung pod in autonomous vertical takeoff and altitude regulation processes is presented. The internal thermodynamic variations and pressure differential of the buoyancy body are given. The air mass exchange and blower flow control of the ballonet are validated. The altitude holding error is analysed. The maximum pull force that the cable can withstand is calculated, and the maximum attitude angles of the pod during the ascending and descending processes are depicted. Simulation results provide basic knowledge for the structural design and payload installation of pods.

Transition flight of a concept of lifting-wing quadcopter

Abstract This paper presents the concept of a lifting-wing quadcopter unmanned aerial vehicle (UAV), a vertical take-off and landing vehicle (VTOL) with a rear wing, a canard at its front and four propellers. The aerodynamic surfaces are designed so that their mounting angle can be adjusted and fixed before flight, so its performance in transition flight can be studied for a combination of wing and canard mounting angles. A dynamic model using rigid-body equations of motion is presented, which is used to compute the transition flight trajectory from hover to cruise in horizontal flight. The trim conditions were computed for a range of fixed wing and canard mounting angles to study the effects of these variables on transition trajectory parameters such as required power, body pitch angle and propeller rotation speeds as a function of flight speed. Furthermore, a transition flight control algorithm is presented, which has a cascaded PID controller and a reference scheduler to switch between the proper reference states, controls and control allocation matrix. Finally, the transition control algorithm of the conceptual UAV is numerically simulated. Results show that this configuration can perform a fast and smooth transition from hover to cruise flight using the proposed flight control algorithm, substantially reducing required propulsive power in cruise of up to 64%. The application of the control algorithm made notable a transition manoeuver that consists of negatively inclining the aircraft at a negative pitch angle, initially at high intensity, and as the final cruising speed approaches, the inclination is attenuated until the equilibrium pitch angle is reached. Simultaneously with the negative inclination of the pitch angle, there is a slight drop in altitude, which is quickly resumed as the trajectory develops until the final cruising speed. Lastly, this aircraft configuration can be widely used in applications where performance gains in operations currently carried out by multicopters, which cover large distances and need long flight time, would bring great operational advantages.

The Overview of Vertical Take-Off and Landing Technology

Vertical takeoff and landing (VTOL) technology is garnering significant attention in the aviation industry due to its distinct benefits and wide range of potential applications. A long runway is not necessary when using VTOL technology, which allows aircraft to take off and land vertically straight from the ground. Air mobility in cities, military activities, and emergency response are just a few of the areas where this technology is beneficial. This essay will provide an overview of the development, application, and future of vertical takeoff and landing technology. The technologys operating principles, advantages and limitations will also be explored. Overall, VTOL technology offers a tremendous leap in aircraft technology, with numerous possible uses. Even though there are still difficulties, more research and development will probably result in improvements and broader use.

Position and reduced attitude trajectory tracking control of quadrotors: Theory and experiments

Multirotor aerial vehicles are versatile flying robots that perform hovering, vertical take-off and landing, and aggressive maneuvers in a 3D environment. Due to their underactuated nature, the aerial vehicles' position and orientation cannot be controlled independently. For this reason, most of the quadrotors' tasks involved position tracking or regulation tasks. This paper focuses on the position-tracking problem of quadrotors using the reduced orientation of the vehicle, meaning that only two degrees of freedom of the robot's orientation are controlled. We propose an almost global exponential reduced attitude control law that aligns the aerial robot's thrust direction with the desired force that drives the robot along the desired position trajectory. For the translational subsystem, we propose a dynamic control law that drives the position and velocity of the quadrotors asymptotically to the desired trajectories. The proposed attitude control law is computationally simple, and thus, it is suitable to run on board. Finally, we provide experimental results performed on a low-cost quadrotor and a comparison study with a full-attitude controller to illustrate the performance and advantages of the proposed control laws.

A vertical take-off and landing (VTOL) unmanned aircraft vehicle trajectory control model with air-launched missiles

PurposeIn today’s technology, the significance of unmanned aerial vehicles is steadily increasing. Many unmanned aerial vehicles design, especially those used for military purposes, have achieved autonomy from human operators. Undoubtedly, one of the most crucial features of these aircraft is their vertical take-off and landing (VTOL) capability. Inspired by quadrotor methodology, this paper aims to conduct, a modeling of an aircraft with VTOL capabilities.Design/methodology/approachThe impact of releasing air-launched missiles, considered as the useful payload carried during the flight of the aircraft, has been taken into account in this modeling. The release of air-launched missiles disrupts both the symmetric structure of the system and alters the mass and inertia parameters. Simulations were conducted to investigate scenarios involving the simultaneous release of all air-launched missiles and their release at different times.FindingsThe investigation focused on determining how quickly an aircraft, aiming to consecutively hit targets, can return to its desired trajectory. The time interval between the consecutive releases of two air-launched missiles has been identified.Originality/valueIt is crucial for a VTOL-capable aircraft to possess a unique modeling structure to examine its capability of releasing air-launched missiles in various scenarios. This entails understanding not only the aircraft’s VTOL functionality but also its ability to effectively release missiles in different operational conditions.

Design and Simulation of eVTOL Aircraft Thermal Management System

Abstract Vertical Take-off and Landing (VTOL) aircraft with hybrid or fully-electric propulsion systems are becoming popular for Urban Air Mobility (UAM) applications. However, they face challenges such as limited power and energy density, stringent operating temperature constraints, and the generation of low-grade waste heat. These issues emphasize the need for effective Thermal Management Systems (TMS) design. In light of the above, this paper aims to design the TMS for a parallel hybrid electric XV-15 aircraft, a widely known civil tiltrotor concept. The TMS is integrated into the aircraft system to assess its impact on energy efficiency and emissions at both aircraft and mission levels. This study considers current state of the art technology and expected advancements over the next two decades to identify the benefits of electrification. In the designed TMS, liquid cooling cold plates serve as the main heat acquisition and cooling system for each electric component. An air-coolant heat exchanger is also incorporated to dissipate the accumulated heat load. The study conducts a comparative analysis to determine the optimal TMS design point. It involves a comparison between two design scenarios: one focused on the cruise condition, which constitutes a significant portion of the flight mission, and another designed specifically for peak heat load conditions. This ensures a holistic evaluation of the TMS's performance across various flight phases, balancing efficiency and resilience to peak demands. Finally, the energy efficiency and emission penalty associated with the TMS integration are quantified and discussed in the study.

Active Disturbance Rejection Flight Control and Simulation of Unmanned Quad Tilt Rotor eVTOL Based on Adaptive Neural Network

The unmanned quad tilt-rotor eVTOL (QTRV) is a variable-configuration aircraft that combines the features of vertical takeoff and landing (VTOL), hovering, and high-speed cruising, making its control system design particularly challenging. The flight dynamics of the QTRV differ significantly between the VTOL and cruise modes, and are further influenced by rotor tilt and external wind disturbances. Developing a unified, highly coupled nonlinear full-flight dynamics model facilitates flight control system design and simulation verification. To ensure stable tilt of the QTRV, a tilt corridor was established, along with the design of its tilt route and manipulation strategy. An adaptive neural network active disturbance rejection controller (ANN-ADRC) is proposed to ensure stable flight across all modes, reducing the control parameters and simplifying tuning while effectively estimating and compensating for unknown disturbances in real time. A hardware-in-the-loop (HIL) simulation system was designed for full-mode flight control simulation, and the results demonstrated the effectiveness of the proposed control method.