Aircraft Landing Research Articles

Autonomous Emergency Gliding Landing Guidance and Control of Tilt-Wing Electric Vertical Take-Off and Landing for Urban Air Mobility Missions Using Control Barrier Functions

Urban Air Mobility (UAM) aims to transform urban transportation through innovative applications of electric Vertical Take-Off and Landing (eVTOL) aircraft. This paper focuses on tilt-wing eVTOLs, which offer significant advantages in energy efficiency and operational versatility. However, their unique flight characteristics present challenges, particularly during emergency landings. To address this, we propose a novel control framework that utilizes control barrier functions (CBFs) to ensure safe landings within urban environments, characterized by numerous obstacles and varying conditions. By integrating trajectory generation, tracking, and attitude control under stringent safety constraints, our method prioritizes occupant safety while complying with FAA airworthiness standards. We illustrate the framework’s effectiveness through simulations, demonstrating its ability to guide eVTOLs to safe touchdowns despite power loss or other emergencies. This study not only advances the understanding of emergency landing mechanisms for eVTOLs but also contributes to the broader field of urban air traffic management, offering a foundation for future research and practical implementations of UAM. The innovative combination of CBFs and global optimization techniques sets a new precedent for resilient aircraft control in complex urban scenarios, paving the way for the safe integration of eVTOLs into everyday urban life.

Study on the Identification of Terminal Area Traffic Congestion Situation Based on Symmetrical Random Forest

As the demand for air transport continues to increase, air traffic congestion in the terminal area is becoming more and more serious. In order to assist the controller in efficiently handling the symmetrical activities of aircraft take-off or landing and alleviate traffic congestion, this paper proposes a method for identifying traffic congestion situations based on complex networks and a multiclass random forest algorithm with symmetrical characteristics. First, the approach points, departure points, waypoints, and navigation stations are used as nodes, the flight paths as edges, and the busyness of the paths as edge weights to construct a traffic network model for the terminal area. On this basis, five congestion situation recognition indicators are selected from the perspective of network topology, and a symmetric multiclass random forest algorithm is proposed to recognize the congestion situation. Finally, this method is compared with the situation recognition method based on the traditional random forest algorithm. The results of the simulation experiment show that compared with the traditional random forest algorithm, the proposed recognition model improves the recognition accuracy by 17.5%, can better handle symmetry information, and can accurately determine the traffic congestion situation in the terminal area.

Aerial e-mobility perspective: Anticipated designs and operational capabilities of eVTOL urban air mobility (UAM) aircraft

We collected data about 13 urban air mobility (UAM) electric vertical take-off and landing (eVTOL) aircraft from 12 UAM companies in the world. While none of these models has yet reached a large-scale commercial operation (particularly as air taxis), some of them progressed well in the certification process and may have their UAM models widely operated within a few years. This article focuses on the variability in the configurations of these UAM eVTOL aircraft for aerial e-mobility; such as single-fixed-wing, tandem-tilt-wing, canard wing, fixed-rotor fixed-wing, full tilt-rotor, partial tilt-rotor, V-shaped tail, tailless, twin tail, conventional tail assembly, distributed propulsion, multicopter, rear forward thrust propeller, ducted fans, and a hybrid airplane-helicopter design. The 13 UAM eVTOL aircraft covered here are: (1) EH216-S (by EHang), (2) VoloCity (by Volocopter), (3) Lilium Jet (by Lilium), (4) VoloRegion (by Volocopter), (5) CityAirbus NextGen (by Airbus), (6) Passenger Air Vehicle - PAV (by Boeing), (7) S-A2 (by Hyundai), (8) Joby (by Joby Aviation), (9) VX4 (by Vertical Aerospace Group), (10) Midnight (by Archer Aviation), (11) Eve (by Eve Air Mobility), (12) Jaunt (by Jaunt Air Mobility), and (13) Generation 6 (by Wisk Aero). Out of these 13 UAM eVTOL aircraft models for aerial e-mobility and/or air taxis, we found that 11 models utilize a wing configuration, while only two use a wingless multirotor concept (as in hobbyist drones). A fixed-wing design is associated with a faster travel speed, at the expense of added restrictions on maneuvering and low-speed travel (or hovering). Six models are intended to have an onboard human pilot, while the remaining seven models are designed to be pilotless. One model demonstrated the ability to use hydrogen as a clean source of energy through a fuel cell system.

Ducted Fan Design for VTOL Aircraft Flight Mission Based on Bayesian Optimization

Vertical takeoff and landing (VTOL) aircraft have great potential in both military and civil applications. Due to the high power and energy requirements of VTOL and its potential widespread use in the future, it is important to improve the overall efficiency of VTOL aircraft, where one promising way is using the ducted fan concept because of the potentially higher aerodynamic performance and noise shielding effects. The goal of this paper is to adopt an approach that can efficiently include both continuous and discrete ducted fan design variables and further to design and to optimize the ducted fan for conceptual VTOL aircraft design study. Firstly, the open-source Ducted Fan Design Code (DFDC) tool is employed for fast and efficient ducted fan analysis. Then, we formulate the ducted fan design and optimization problem as mixed integer nonlinear programming to include both class-shape-transformation-based parameters and intuitive ducted fan parameters. The performance of the ducted fan was optimized for hovering, cruising, and the overall flight mission based on the Bayesian optimization approach. The results showed that optimization considering only hovering or cruising can enhance the performance of the ducted fan at the corresponding phase, but the overall aircraft performance might not be improved. As such, the whole aircraft flight mission performance was set as the design objective while carrying out the ducted fan optimization, which in the end led to the reduction of fuel consumption from the original 828.41 kg to 713.46 kg, i.e., about 15.9% fuel saving for the selected flight mission.

Some Comments on the Aircraft Landing Problem: How Optimal is the First Come First Serve Policy?

Some Comments on the Aircraft Landing Problem: How Optimal is the First Come First Serve Policy?

Retraction and extension characteristic simulation of aircraft landing gear/hydraulic system

Retraction and extension characteristic simulation of aircraft landing gear/hydraulic system

Flamingo Search Algorithm for aircraft landing scheduling

جدولة هبوط الطائرات (ALS) هي عملية تنظيم وصول ومغادرة الطائرات في المطار. تتم إدارة هذه العملية من قبل مراقبي الحركة الجوية الذين يستخدمون أدوات وتقيات مختلفة لضمان هبوط الطائرة وإقلاعها بأمان وكفاءة. الهدف من جدولة هبوط الطائرات هو تقليل التأخير وزيادة عدد الطائرات التي يمكن استيعابها في المطار. يتم ذلك من خلال التنسيق الدقيق لمواعيد وصول ومغادرة الطائرات، بالإضافة إلى عدد الطائرات التي يمكن استيعابها بأمان. بحث الفلامنغو هي خوارزمية تحسين مستوحاة من سلوك طيور النحام. إنها خوارزمية metaheuristic تعتمد على السكان وتستخدم سربًا من طيور النحام للبحث عن الحل الأمثل لمشكلة معينة. تعمل الخوارزمية من خلال جعل كل فلامنغو في القطيع يبحث عن الحل الأمثل المحلي. ثم تتواصل طيور النحام مع بعضها البعض وتتبادل الحلول. بالمقارنة مع تقنيات التحسين التقليدية، أظهرت التجارب أن الحل الذي قدمه أسرع بشكل ملحوظ وأكثر ملاءمة لمشاكل جدولة هبوط الطائرات في الوقت الفعلي فلقد اظهرت النتائج تفوق الخوارزمية المقترحة على بقية الخوارزميات بنسبة تجاوزت ٩٠ %. يمكن للطريقة المقترحة تحديد الحلول المناسبة بسرعة لجميع مجموعات البيانات الـ 8.

Design and Modeling of a High-Peak-Power Distributed Electric Propulsion System for a Super-STOL UAV

Electric short takeoff and landing (eSTOL) aircraft utilize the slipstream generated by distributed propellers to significantly increase the effective lift coefficient and reduce the takeoff and landing distances. By utilizing the blown lift, eSTOL UAVs can achieve similar takeoff and landing site requirements as electric vertical takeoff and landing (eVTOL) UAVs, while having lower takeoff and landing energy consumption and thrust requirements. This research proposes a high-peak-power distributed electric propulsion (DEP) system model and overload design method for eSTOL UAVs to further improve the power and thrust of the propulsion system. The model considers motor temperature factors with the throttle input, which is solved through three-round iterative calculations. The experimental and simulation results indicate that the maximum error of the high-peak-power propulsion unit model without considering temperature is 19.52%, and the maximum error when considering temperature is 1.2%. The propulsion unit ground test indicates that the main factors affecting peak power are the duration of peak power and the temperature limit of the motor. Finally, the effectiveness of the propulsion system model is verified through ground tests and UAV flight tests.

An Objective Handling Qualities Assessment Framework of Electric Vertical Takeoff and Landing

Assessing handling qualities is crucial for ensuring the safety and operational efficiency of aircraft control characteristics. The growing interest in Urban Air Mobility (UAM) has increased the focus on electric Vertical Takeoff and Landing (eVTOL) aircraft; however, a comprehensive assessment of eVTOL handling qualities remains a challenge. This paper proposed a handling qualities framework to assess eVTOL handling qualities, integrating pilot compensation, task performance, and qualitative comments. An experiment was conducted, where eye-tracking data and subjective ratings from 16 participants as they performed various Mission Task Elements (MTEs) in an eVTOL simulator were analyzed. The relationship between pilot compensation and task workload was investigated based on eye metrics. Data mining results revealed that pilots’ eye movement patterns and workload perception change when performing Mission Task Elements (MTEs) that involve aircraft deficiencies. Additionally, pupil size, pupil diameter, iris diameter, interpupillary distance, iris-to-pupil ratio, and gaze entropy are found to be correlated with both handling qualities and task workload. Furthermore, a handling qualities and pilot workload recognition model is developed based on Long-Short Term Memory (LSTM), which is subsequently trained and evaluated with experimental data, achieving an accuracy of 97%. A case study was conducted to validate the effectiveness of the proposed framework. Overall, the proposed framework addresses the limitations of the existing Handling Qualities Rating Method (HQRM), offering a more comprehensive approach to handling qualities assessment.

Unlocking the Potential: How Flying Taxis Will Shape the Future of Transportation

The advent of flying taxis, also known as vertical take-off and landing (VTOL) aircraft, presents a revolutionary approach to urban transportation by offering faster, more flexible, and less congested travel options. This research aims to explore the potential impact of flying taxis on urban transportation systems, focusing on their implementation, regulation, and benefits across various industries. This study investigates the role of government in monitoring and regulating flying taxis to ensure safety and compliance with regulations, addressing key considerations such as licensing, air traffic control, safety standards, insurance requirements, and privacy concerns. Through a comprehensive review of the existing literature and case studies, this paper presents the advantages of flying taxis, including time savings, accessibility to remote areas, reduced traffic congestion, and enhanced travel experiences. Additionally, the economic benefits of manufacturing flying taxis, such as job creation and technological advancements, are discussed. The findings suggest that flying taxis have significant potential to transform urban transportation, but their adoption requires collaboration among stakeholders, robust regulatory frameworks, and substantial infrastructure investments. The conclusions highlight the practical application value of flying taxis in promoting sustainable urban mobility and driving innovation in transportation.

Dynamic effects on different rotor profiles for eVTOL applications

Electric Vertical Take-Off and Landing (eVTOL) aircraft, commonly known as eVTOLs, represent a recent and promising concept for enhancing urban mobility, particularly in densely populated areas. However, the development of eVTOLs has been accompanied by various technical and technological challenges, primarily due to the rapid introduction of new concepts. Among these challenges, this study focuses on investigating the dynamic effects on rotor blades designed for such aircraft. Rotor blades, being subject to rotational dynamic effects, exhibit behavior distinct from components lacking angular velocity. Therefore, they are of particular interest for dynamic analysis. The study begins by defining a simplified geometry representative of a rotor blade, which serves as the basis for applying finite element methods using Ansys software. This approach enables the observation of the system's response to rotation. Following, more detailed geometries representing rotors are modelled, respectively in NACA 0012, VR 08 and VR 12 airfoils, which are then subject to the rotational effects numerical calculations. The results obtained for the different aerodynamic profiles are then compared, presenting the differences caused by the different geometries and mass distributions implied. The results obtained from the analysis highlight the significant impact of angular velocity on the fundamental frequencies and modes of the dynamic system. These findings suggest the presence of effects such as spin softening and strain stiffening, along with identifying important frequency coupling points.

Flight Safety Risk Prediction for Civil Aircraft Approach and Landing

The approach and landing phase is the critical juncture in flight operations, where flight-state risks must be meticulously identified and mitigated to avert significant safety incidents. This paper proposes a risk prediction model that enhances the Light Gradient Boosting Machine (LightGBM) using the Whale Optimization Algorithm (WOA). First, a six-degree-of-freedom model is used to establish a system of differential equations to describe the aircraft’s flight states. In conjunction with longitudinal and lateral motion risk analyses, parameters prone to typical flight accidents are selected as risk prediction indicators, focusing on abnormal flight states. Subsequently, the LightGBM algorithm is employed to construct a flight safety risk prediction model using WOA to optimize hyperparameters within the LightGBM framework, enhancing the predictive accuracy of the model. Finally, a data set is created using actual flight data from a particular airline, aggregating flight-state parameter data from 910 flights for model training and testing. The proposed model’s performance is compared with similar machine-learning methods, including LightGBM, XGBoost, and Random Forest. The results demonstrate that the WOA–LightGBM model achieves 95.6% accuracy in predicting flight safety risks during the approach and landing phase, demonstrating a significant advantage in predictive precision over other methods.

Failure analysis of flight damage to a composite outer door of a civil aircraft landing gear

Failure analysis of flight damage to a composite outer door of a civil aircraft landing gear

Characterization of aircraft landing impact loads: Effects on vertical tire-pavement contact characteristics and pavement performance

The comprehensive understanding of the mechanistic behavior of airport pavements under aircraft landing loads is essential for ensuring safety and durability. Addressing the limited understanding on the interaction between aircraft landing gear and airport pavement during landing, this study proposed a measurement method for the vertical dynamic contact characteristics of tire-pavement interface and internal dynamic responses based on a laboratory dynamic test device. This involved the experimental design and testing method for the dynamic characteristics of landing gear landing loads, utilizing the Tekscan pressure measurement system to evaluate the vertical dynamic contact characteristics between the aircraft tires and pavement during landing. Through comparative analysis with the static results, the study revealed the importance of landing load measurements for mechanical response analysis and durability design of airport pavements. Additionally, the study investigated the dynamic response of airport pavements under different simulated aircraft landing speeds and weights, and further quantified the impact effects of aircraft landing loads on airport pavements. The results show that the vertical tire-pavement contact characteristics under landing impact are significantly different from those under static conditions, and need to be considered. The proposed quantitative equations with acceptable good fitting effect provided more accurate and efficient vertical load inputs for numerical simulation and durability design of airport pavements, which laid the foundation for understanding the failure mechanisms of airport pavement and enhancing the safety of aircraft and airport operation.

Application of fiber-optic strain sensing technology in high-precision load prediction of aircraft landing gear

In this paper, a compact and lightweight high-precision airborne fiber-optic strain sensor is designed, and a strain-load prediction model based on convolutional neural network and long short-term memory network (ConvLSTM) is proposed to validate the collected landing gear strain data. Firstly, based on the fiber Bragg grating (FBG) sensing principle and simulation validation, small and lightweight strain and temperature sensors were fabricated, and key performance parameters such as sensitivity and linearity were comprehensively investigated, and they were mounted on the left landing gear of the aircraft to conduct strain monitoring by loading a three-way load, and the ConvLSTM model was used to train and test the strain-load mapping with the maximum relative error, average relative error and variance as indicators to evaluate its prediction accuracy and stability. The experimental results show that the strain measurement accuracy is maintained within 2.5 % and the strain sensitivity is as high as 1.3 pm/με within the ± 5000 με measurement range of the strain sensor; the maximum relative errors of the X, Y, and Z load predictions are 6.03 %, 3.75 %, and 4.12 %, respectively, and the overall average relative errors are 2.38 %, 0.27 %, and 0.76 %, with variances of 0.23 N, 0.61 N, and 0.61 N, respectively. 0.23 N, 0.61 N and 0.12 N, indicating that the model predictions are stable and highly accurate, demonstrating higher prediction accuracy when compared with traditional multiple linear regression methods. The results of this research have important application value in the field of aircraft structural health monitoring.

Examining the behavior of a two-connected-spring pendulum according to non-resonance and resonance conditions

This paper focuses on the planar forced oscillations of a particle linked to its support point through a system comprising two nonlinear springs arranged in series with two viscous dampers. The motion of this point is restricted to being on an elliptic route. Three degrees-of-freedom (DOF) characterize the system’s motion, explained by two differential equations (DEs) and another algebraic equation derived using Lagrange’s equations. The traditional method of multiple-time scales (MMTS) is applied in the context of the time realm. The dynamics of forced and damped oscillations is explored in this work, highlighting non-resonant conditions along with two distinct external resonances. Furthermore, stationary periodic states influenced by external resonances are examined, and the stability of each case is evaluated. The asymptotic solutions of the controlling equations are solved up to the third approximation. The classification of resonance cases is based on the second and third order of the approximate solutions. Therefore, the solvability criteria and the modulation equations (ME) are obtained. The Routh–Hurwitz conditions (RHCs) serve as the basis for assessing the stability and instability criteria. A discussion and graphical representations of the time histories, frequency response curves (FRC), and stability regions are provided to demonstrate the beneficial effects of different physical parameter inputs on the system’s performance. The obtained outcomes can improve the performance of spring-based mechanical systems like vibrational isolation devices, shock absorbers, and suspension mechanisms. Additionally, they have the potential to enhance stability and control in robotic limbs and aircraft landing gear systems, ensuring better stress absorption and stability.

Variable stroke fatigue test for aircraft landing gears

The fixed stroke fatigue test cannot simulate the real loading conditions of the landing gear, and the variable stroke fatigue test has increasingly become mainstream. A modular test device for fatigue tests for aircraft landing gears was designed, and the automatic control of the buffer stroke was realized with ectopic displacement control technology effectively. The horizontal loading cylinder could follow the wheel axis actively with the displacement active control technology. The follow-up loading along the vertical direction was realized by constructing a polar coordinate system and making the loading line automatic alignment. A split-type dummy wheel was designed to improve the loading accuracy, and a booster cylinder was designed to realize the control loading of high pressure combined with the hydraulic control system. The test results show that the technical scheme meets the design requirements, and the fatigue test was completed successfully. The device for landing gear variable stroke fatigue testing is appropriate for other landing gear static/fatigue tests.

(Invited) Analyzing Effect of Battery Design Characteristics and Thermal Dynamics on Battery Performance in Electric Aircraft

One the biggest challenges in achieving net-zero in the aviation sector through electrification of electric aircraft is the limitation of current battery systems in terms of simultaneously providing high gravimetric energy density and power density combined with suboptimal performance and safety issues at extreme temperatures. Much of the current literature related to electric aircraft focuses on aircraft design and optimization with overly simplified battery analysis such as linear voltage profile approximation or the use of equivalent circuit models which do not help understand and quantify material limitations of battery systems in electric aircraft application1-3. This is particularly relevant due to the fact that battery cells used in both fixed-wing electric aircraft and eVTOLs (electric vertical take-off and landing aircraft) see unique operating requirements that are often significantly more demanding than those seen in electric vehicles (EVs)4. Recently, there have been a few studies analyzing battery performance in more detail 5-7. However, there is a lack of investigations on the effect of battery design parameters and material properties on battery performance under real-world operating conditions, such as dynamically varying power demand, and the resulting effect on electric aircraft performance characterized by range, speed, and endurance. This type of study is necessary in guiding design of batteries and battery materials tailored to electric aircraft applications, particularly in dealing with the highly dynamic nature of such an application.In the present work, we perform coupled simulation studies of longitudinal flight dynamics and battery dynamics using high fidelity electrochemical battery models. First, we study the effect of model fidelity on the prediction of battery dynamics and key battery states, particularly in the context of studying the effect of battery design parameters. This results in the identification of an appropriate battery model for an in-depth analysis on the effect of battery design parameters and material properties on battery dynamics and the resulting effect on aircraft performance. Additionally, we consider the effect of dynamically changing battery temperature obtained from experimental testing under simulated flight conditions. This is particularly important due to the significant battery temperature variation expected during a typical flight and its implications on battery performance and safety. Overall, this work provides detailed analysis on the effect of battery design on its electrochemical performance and the overall system level performance considering real-world operating conditions.References M. Kaptsov and L. Rodrigues, Journal of Guidance, Control, and Dynamics, 41, 288 (2018).N. Biju and H. Fang, Applied Energy, 339, 120905 (2023).L. Kiesewetter, K. H. Shakib, P. Singh, M. Rahman, B. Khandelwal, S. Kumar and K. Shah, Progress in Aerospace Sciences, 142, 100949 (2023).X.-G. Yang, T. Liu, S. Ge, E. Rountree and C.-Y. Wang, Joule, 5, 1644 (2021).A. Ayyaswamy, B. S. Vishnugopi and P. P. Mukherjee, Joule, 7, 2016 (2023).Dixit, M., Bisht, A., Essehli, R., Amin, R., Kweon, C. B. M. and Belharouak, I., ACS Energy Letters, 9, 934-940 (2024).M. Wang, S. Kolluri, K. Shah, V. R. Subramanian and M. Mesbahi, IEEE Transactions on Aerospace and Electronic Systems, 59, 1084 (2022).

DRT Characterization of Lithium-Ion Batteries for eVTOL Applications

The demand for electric vehicles (EV) and electric vertical take-off and landing (eVTOL) aircraft is growing exponentially. The lithium-ion battery (LIB) is commonly selected for such applications due to its promising relatively high energy and power density. However, range limitations, capacity fade, and durability of Li-ion systems limit EVs. These questions become even more vital when discussing aerospace applications of eVTOL, which have more stringent requirements for safety, power, and durability. Additionally, cell-to-cell-variations (CtCv) play a major role in pack performance. To address the current needs, this work employs a characterization method combining the techniques of electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT), allowing for better characterization of cell performance and degradation at relevant high C-rates. In this work, cells are cycled at high-rate discharge (10C and 25C) at various temperatures to mimic eVTOL applications, with characterization tests being performed at beginning of life and every 50 cycles for a total of 500 cycles.By applying DRT to the EIS data, the electrochemical processes inside the cell can be deconvoluted and examined [1-3]. Gaussian peaks are fit to the DRT distribution function, and the resistance of each process can be predicted, thereby monitoring changes in HFR, interfacial particle-particle interactions, SEI/CEI interphase layers, and charge transfer/intercalation kinetics at various states of charge (SOC) and cycle number. Furthermore, diffusion related processes can also be identified and estimated from DC current-interrupt/application methods.Degradation tests were performed to simulate various thermal boundary conditions faced by eVTOLs ranging from 20°C to -20°C. The results reveal that, at high discharge rates operating at room temperature, cells reached up to 90°C and signatures of degradation in the SEI layer are seen in the DRT data. Other cells cycled at 0°C show evidence of lithium plating due to the cold environment. Active cooling at 20°C showed the least degradation as identified from the various internal processes. This method of testing provides an approach to comprehensively analyze individual internal degradation modes of a Li-ion battery.

Multi-nozzle thrust matching control of STOVL engine

Abstract A multi-nozzle thrust matching control method is proposed in this paper to provide the thrust vector required of lift-fan type short takeoff and vertical landing (STOVL) aircrafts during hover. Attitude-matched thrust commands for each nozzle of STOVL engine are generated based on a six-degree-of-freedom aircraft model. The thrust controller is divided into two blocks according to the coupling analysis. Based on the combination of linear matrix inequality and differential evolution algorithm, a multi-target controller parameters optimization method is proposed to achieve stable disturbance suppression and fast command tracking. Simulations results show that the proposed command generated model is effective and the decoupling control method can effectively suppress the coupling between the loops and realize the matching control of thrust.