Successful Flight Research Articles

Cascade control for heterogeneous multirotor UAS

PurposeDespite of the numerous characteristics of the multirotor unmanned aircraft systems (UASs), they have been termed as less energy-efficient compared to fixed-wing and helicopter counterparts. The purpose of this paper is to explore a more efficient multirotor configuration and to provide the robust and stable control system for it.Design/methodology/approachA heterogeneous multirotor configuration is explored in this paper, which employs a large rotor at the centre to provide majority of lift and three small tilted booms rotors to provide the control. Design provides the combined characteristics of both quadcopters and helicopters in a single UAS configuration, providing endurance of helicopters keeping the manoeuvrability, simplicity and control of quadcopters. In this paper, rotational as well as translational dynamics of the multirotor are explored. Cascade control system is designed to provide an effective solution to control the attitude, altitude and position of the rotorcraft.FindingsOne of the challenging tasks towards successful flight of such a configuration is to design a stable and robust control system as it is an underactuated system possessing complex non-linearities and coupled dynamics. Cascaded proportional integral (PI) control approach has provided an efficient solution with stable control performance. A novel motor control loop is implemented to ensure enhanced disturbance rejection, which is also validated through Dryden turbulence model and 1-cosine gust model.Originality/valueRobustness and stability of the proposed control structure for such a dynamically complex UAS configuration is demonstrated with stable attitude and position performance, reference tracking and enhanced disturbance rejection.

Three-dimensional Computational Analysis of Transverse Injection in a Supersonic Combustor

The scramjet engine plays a promising role for a successful future hypersonic flight system. The performance of scramjet system depends on many factors like mixing rate of fuel and air, proper flame stabilization mechanism and suitable injection system. The flame stabilization is provided by means of introducing a Cavity along the wall of the combustor. The cavity effects on the performance of supersonic combustion will be studied here with the help of three-dimensional combustor CFD model. The reliability of the numerical results obtained by using the computational approach depends on the proper validation of the CFD code with their corresponding experimental results. The corresponding experimental results from the literature will be identified and used here for the validation of the numerical code. The final CFD results after its validation with the experimental results will be presented in terms of x-y plots and contours for the discussion.

Airbus Active Debris Removal Service

With the increasing number of both functional and defunct space assets being present in orbit, and having a better understanding of the space environment, it is clear that there is a need for active debris removal (ADR) today if not in the very near future. Previous demonstrators have been successful such as the RemoveDEBRIS mission which was co-funded by the European Commission and produced by a set of partners. Airbus have also worked extensively on other projects to develop the capability to rendezvous and capture objects in space (such as the ATV with 5 successful flights, e-Deorbit, DEOS, and Space Tug). Airbus have been working with agencies and industry to create a removal service with the aim of being both technically feasible and at an attractive price point to potential customers. The capture solutions have been outlined and an example mission profile is shown for providing the service for a mega-constellation operator. With this setup, a total of 20+ spacecraft could be deorbited with a single ADR vehicle which would provide an affordable price point.

A High-Order Load Model and the Control Algorithm for an Aerospace Electro-Hydraulic Actuator

It is difficult to describe precisely, and thus control satisfactorily, the dynamics of an electro-hydraulic actuator to drive a high thrust liquid launcher engine, whose structural resonant frequency is usually low due to its heavy inertia and complicated mass distribution, let alone one to drive a heavy kerolox engine with high-order dynamics. By transforming classic control block diagrams, a baseline two-mass-two-spring load model and a normalized actuator-engine system model were developed for understanding the basic physics and methodology, where a fourth-order transfer function is used to model the multi-resonance-frequency engine body outside of the rod position loop, another fourth-order transfer function with two pairs of conjugated zeros and poles to represent the composite hydro-mechanical resonance effect in the closed rod position loop. A sixth-order model was thereafter proposed for even higher dynamics. The model parameters were identified and optimized by a full factor search approach. To meet the stringent specification of static and dynamic performances, it was demonstrated that a notch filter network combined with other controllers is needed since the traditional dynamic pressure feedback (DPF) is difficult to handle the high-order dynamics. The approach has been validated by simulation, experiments and successful flights. The models, analysis, data and insights were elaborated.

A Low-Cost Solution for Leader-Follower Formation Control of Multi-UAV System Based on Pixhawk

In recent years, cooperative multi-UAV systems have shown great performance in a variety of potential applications. Aiming at the problem of fixed-wing UAVs cooperative formation flight, this paper presents a low-cost system based on Pixhawk autopilot for keeping the shape of the formation. The kinematic relationship of a leader-follower UAV formation is established and a fuzzy PID control law is designed for the follower to maintain the expected position relative to the leader. Wireless data transmission between the leader and followers is achieved by using several radio telemetry modules. The proposed formation control system is validated by a series of successful flight experiments using 3 small-scaled UAV models, which has proven its feasibility and reliability.

Unmanned aerial vehicles (UAV)-based canopy height modeling under leaf-on and leaf-off conditions for determining tree height and crown diameter (case study: Hyrcanian mixed forest)

Tree height and crown diameter are two common individual tree attributes that can be estimated from unmanned aerial vehicle (UAV) images thanks to photogrammetry and structure from motion. This research investigates the potential of low-cost UAV aerial images to estimate tree height and crown diameter. Two successful flights were carried out in two different seasons corresponding to leaf-off and leaf-on conditions to generate a digital terrain model and a digital surface model, which were further employed in calculation of a canopy height model (CHM). The CHM was used to estimate tree height using low pass and local maximum filters, and crown diameter was estimated based on an inverse watershed segmentation algorithm. UAV-based tree height and crown diameter estimates were validated against field measurements and resulted in 3.22 m (10.1%) and 0.81 m (7.02%) root mean square errors, respectively. The results showed high agreement between our estimates and field measurements, with an R2 of 0.808 for tree height and an R2 of 0.923 for crown diameter. Generally, the accuracy of the results was considered acceptable and confirmed the usefulness of this approach for estimating tree heights and crown diameter.

Dynamic Characterization of a High-Altitude Balloon during a Flight Campaign for the Detection of ISM Radio Background in the Stratosphere

Sounding balloons, available at very low cost from commercial vendors and operable with minimal training, have an excellent potential as testing platforms in the near-space environment. The work reported here was motivated by the need to perform an experimental assessment of the radio frequency (RF) background present in the ISM (Industrial, Scientific and Medical) bands, namely 868 MHz (Ultra High Frequency—UHF) and 2.4 GHz (S-Band), simulating the operational environment of a Low Earth Orbit (LEO) constellation forInternet of Things (IoT) telecommunications. To this end, five balloons were flown with a dedicated RF payload. Along with the radio measurements, the flights provided a convenient opportunity to collect data on the dynamic behavior of the payload gondola. We report on the system design and the operational phase of the mission, and discuss the data collected throughout the successful flight campaign. As a result, a preliminary understanding of the gondola dynamics has been gained, including both linear accelerations and attitude oscillations. It is also concluded that the two ISM bands considered are actually suitable for IoT ground-to-LEO links.

Identification of Wind-Induced Hazard Zones Impacting UAS Bridge Inspection

Unmanned Aerial Systems (UAS) continue to grow in both popularity and utility within the national airspace system. The use of commercial UAS for civil inspection, specifically that of bridge structures, is becoming commonplace among practitioners and academics alike. The development of an integrated bridge-inspection hazard model provides a way for UAS operators to prepare for and respond to changing environmental conditions that could otherwise prevent a successful UAS flight. The interaction of wind-induced airflow with bridge surfaces creates an aerodynamic wake that can result in hazardous conditions for a UAS platform operating in close proximity. An analysis of this airflow surrounding an overpass bridge using computational fluid dynamic (CFD) models shows where these hazardous areas exist, based on initial wind conditions, existing functionality of UAS platforms, and mitigating systems that exist within current UAS technology. Altering the initial conditions by modifying wind velocities allows for a baseline understanding of which areas surrounding an overpass bridge structure are not suitable for successful UAS flight. Hazard zones range from severe, moderate, and mild, to no appreciable hazard. Moderate to extreme hazard zones are located in areas where high levels of wind shear, vorticity, or general turbulence exist, making UAS operations difficult. This study develops a practical model that may be utilized by UAS operators to better understand and potentially avoid unsafe flight environments during bridge structure inspections.

Never landing drone: Autonomous soaring of a unmanned aerial vehicle in front of a moving obstacle

Increasing endurance is a major challenge for battery-powered aerial vehicles. A method is presented which makes use of an updraft around obstacles to decrease the power consumption of a fixed-wing unmanned aerial vehicle. A soaring flight controller has been developed that can autonomously soar while the unmanned aerial vehicle keeps its relative position to that of a moving object. Multiple simulations have been performed to analyse the limitations of the soaring controller under different conditions. The effect of a change in wind velocity and updraft has been analysed. The simulations showed that an increase in updraft decreases the energy consumption of the flight controller. An increase in wind velocity results in a higher updraft requirement, while a decrease in the wind velocity requires less updraft. The simulations achieved sustained flight at 0% throttle. The controller has been validated experimentally using the updraft generated by a moving ship. The practical, autonomous tests reduced the average throttle down to 4.5% in front of a ship. The method presented in this study achieved successful hovering flight using an energy control module for longitudinal positioning.

Preliminary Design Method and Prototype Testing of a Novel Rotors Retractable Hybrid VTOL UAV

Conventional hybrid VTOL (Vertical Take-Off and Landing) aircraft are always designed by directly mounting multicopter rotors to a fixed-wing plane. This type of VTOL aircraft may suffer from terrible drag due to the copter rotors. To tackle this problem, this paper describes a novel rotors retractable hybrid VTOL UAV (RR VTOL) that combines the hovering capability of multicopters and the high cruise velocity property of pure FW aircraft. Computational fluid dynamic (CFD) analysis on rotors folding and unfolding models proves that the retractable rotors can increase the lift-to-drag ratio by approximately 2 times compared to that common hybrid VTOL UAV. Moreover, some aerodynamic performance data of the rotors folded model are also acquired. A preliminary design method of this creative UAV is proposed with some new empirical equations derived from many hybrid VTOL UAVs’ data. Emphasis is given on the method for determining the center of gravity position and horizontal tail dimensions as they are the unique aspects of the RR VTOL configuration. Subsequently, the manufacturing process and rotor retraction mechanism of two UAV generations are reviewed and a rapid prototyping method for RR VTOL is summarized. Finally, a successful flight test confirms that the proposed VTOL concept is practical and the drag reduction effect of rotors retracting function is remarkable.

From Space Tourism to Commercial Suborbital Travel

After several announcements last years, the recent successful flights with Jeff Bezos and Richard Branson as passengers have brought the space tourism topic back at the top of news headlines. Indeed, several projects have undergone incremental and careful development steps last years to ensure a sufficient reliability of such flights with passengers on board. The perfect re-entry of both the New Shepard system of Blue Origin and the Unity system of Virgin Orbit in July 2021 are now opening the path for commercial space tourism flights, with several hundreds of candidates having paid either substantial advance payments or even the total ticket price and a rising demand after these demonstrations. This evolution can be compared with the first flights in the aeronautical field starting in 1919, when, at the end of WW1, experienced pilots and proven (ex-military) planes were used to carry air tourists at short turn-around flights. This rapidly evolved a few years later in regular commercial Point-to-Point air traffic, with the first air connection Paris London Paris. We can easily forecast a similar evolution in suborbital transport of cargo and passengers after the first wave of space tourism. Similar as with the first aviation tourism, where passengers got a first sensation of flying and were then brought back to the starting point after a few minutes, suborbital space experience will soon evolve in so called pointto-point suborbital flights, covering intercontinental travel in 60-80 minutes in one go, which now takes up more than 21 hours, like a trip London-Sydney with one stopover. This article will focus on the feasibility of such development, focusing in the first place on the potential business case and the economic rationale. It will be demonstrated that for ‘time-poor, cash-rich’ people such suborbital intercontinental travel will be a viable option and a potential market.

Increasing the reliability of stress tolerance prediction as part of aptitude screening of flight specialists

Aim . The paper describes a research aimed at improving the reliability of stress tolerance prediction as part of aptitude screening (AS) of flight school applicants using a proprietary objectifying method of Stress Tolerance Assessment. Stress tolerance (ST) is an important psychophysiological professional quality and serves as one of the factors ensuring both successful flight training, and further professional flight work. However, the methods recommended in regulatory documents for the purpose of ST identification as part of AS are not efficient enough and are affected by subjective factors. Therefore, an objective and thus more efficient method is still required. Methods . The method was developed based on the analysis of subject-matter literature and own experience. Stress stimuli and methods of indicator recording were selected based on their empirical verification. The stress-inducing property of the stimuli was confirmed by the pulse rate increase by 40 – 100% and higher, associated behavioural manifestations and significant dynamics of mental productivity in the course of tests. Out of the methods of mathematical statistics, the authors used correlation analysis. Results . The method of ST assessment is based on the Reakor multifunctional psychophysiological system by the Medicom MTD research and development company from Taganrog, Russia, with a proprietary procedure built in the system’s software. As stress stimulus material and for performance assessment, arithmetically complicated problems were selected, whose solutions involve a larger portion (areas) of the brain than verbal tests. In order to eliminate the effect of habituation and learning, the arithmetic tests were displayed one by one on a computer screen in a random order. The 3-4-second time interval between individual problems was selected based on premises of aviation psychology and tests conducted on a group of students. The sample consisted of 1135 male applicants to the higher flight school in 2016. Correlation analysis shows that the correlations between the external criterion indicators (successful simulator training and flying practice) and the integrated ST indicator are statistically significant: the higher is the ST indicator measured in the course of AS using the respective method, the higher are the expert estimates of the simulator training and flying practice. Conclusion . Thus, the conducted research showed that the application of the developed method of ST assessment in the course of higher flight school AS ensures higher predicted stress tolerance in the selected candidates as the psychophysiological factor of professional efficiency and reliability of flight personnel.

Simulation of response characteristic of VTVL system with hybrid rocket engine

To determine the suitability of the control performance of the VTVL system with hybrid rocket engine, simulations were done for the vertical and horizontal motion using various engine data. In the simulation, the thrust modulation characteristics of each engine were modeled with the same second-order transfer function in all cases. The results showed that the VTVL system with HRE showed better performance in terms of vertical motion error and touch down speed. In addition, this confirms the possibility for successful VTVL flight missions using HRE. In the next step, a better control algorithm and an efficient control technique will be attempted for developing the VTVL demonstrator.

An Analysis of the Benefits and Difficulties of Aerial Magnetic Vector Navigation

Recent successful flight tests have demonstrated scalar magnetic anomaly navigation to be a viable GPS-alternative navigation system. These flight tests matched magnetic field measurements to maps of the Earth's crustal magnetic field in order to navigate. Scalar magnetic navigation uses only the magnetic field intensity, not direction, in order to navigate. While it appears obvious to extend aerial magnetic navigation to use the full vector field, in practice there are substantial obstacles to doing so. This article explores the key challenges of magnetic vector navigation including current sensor limitations, lack of high frequency magnetic vector maps of the Earth's crust, and proper integration of the magnetic data with an inertial navigation system. In overcoming these challenges several key benefits of magnetic vector navigation over scalar magnetic navigation become apparent, including modestly improved navigation accuracy and greatly improved platform attitude.

BVLOS UAS Operations in Highly-Turbulent Volcanic Plumes.

Long-range, high-altitude Unoccupied Aerial System (UAS) operations now enable in-situ measurements of volcanic gas chemistry at globally-significant active volcanoes. However, the extreme environments encountered within volcanic plumes present significant challenges for both air frame development and in-flight control. As part of a multi-disciplinary field deployment in May 2019, we flew fixed wing UAS Beyond Visual Line of Sight (BVLOS) over Manam volcano, Papua New Guinea, to measure real-time gas concentrations within the volcanic plume. By integrating aerial gas measurements with ground- and satellite-based sensors, our aim was to collect data that would constrain the emission rate of environmentally-important volcanic gases, such as carbon dioxide, whilst providing critical insight into the state of the subsurface volcanic system. Here, we present a detailed analysis of three BVLOS flights into the plume of Manam volcano and discuss the challenges involved in operating in highly turbulent volcanic plumes. Specifically, we report a detailed description of the system, including ground and air components, and flight plans. We present logged flight data for two successful flights to evaluate the aircraft performance under the atmospheric conditions experienced during plume traverses. Further, by reconstructing the sequence of events that led to the failure of the third flight, we identify a number of lessons learned and propose appropriate recommendations to reduce risk in future flight operations.

Advanced Supersonic Parachute Inflation Research Experiment Preflight Trajectory Modeling and Postflight Reconstruction

The Advanced Supersonic Parachute Inflation Research Experiment (ASPIRE) was a series of sounding rocket flights aimed at understanding the dynamics of supersonic parachutes that are used for Mars robotic applications. Although the 2012 Mars Science Laboratory (MSL) had a successful deployment of a supersonic parachute, postflight analysis and the results of the Low-Density Supersonic Decelerator project called into question some of the assumptions underlying MSL’s parachute qualification program. The ASPIRE project was a key part of the risk-reduction program undertaken by Mars 2020, the follow-on to MSL. The first sounding rocket (SR01) flight of ASPIRE occurred near Wallops Island, Virginia on 4 October 2017, and demonstrated the successful deployment and inflation of an MSL build-to-print parachute in flight conditions similar to the 2012 MSL mission. ASPIRE SR02 and SR03 were successful follow-on flights on 31 March 2018 and 7 September 2018 that demonstrated the new, strengthened supersonic parachute designed for the Mars 2020 project. The SR02 and SR03 parachutes were targeted to 100 and 140% of the expected flight limit load for Mars 2020 to confirm new margins expected from the strengthened parachute. Prior to all flights, a multibody flight dynamics simulation was developed to predict the parachute dynamics and was used, in conjunction with other tools, to target Mars-relevant flight conditions. After each flight, the onboard data were used to reconstruct the flight trajectory and to validate the preflight dynamics simulation. Postflight analysis showed that all three tests achieved their targeted conditions and preflight modeling bounded the key performance metrics for the parachute. This paper describes the flight mechanics simulation, postflight reconstruction, and the reconciliation process used to validate the flight models.

The Effect of Climatological Variables on Future UAS-Based Atmospheric Profiling in the Lower Atmosphere

Vertical profiles of wind, temperature, and moisture are essential to capture the kinematic and thermodynamic structure of the atmospheric boundary layer (ABL). Our goal is to use weather observing unmanned aircraft systems (WxUAS) to perform the vertical profiles by taking measurements while ascending through the ABL and subsequently descending to the Earth’s surface. Before establishing routine profiles using a network of WxUAS stations, the climatologies of the flight locations must be studied. This was done using data from the North American Regional Reanalysis (NARR) model. To begin, NARR data accuracy was verified against radiosondes. While the results showed variability in individual profiles, the detailed statistical analyses of the aggregated data suggested that the NARR model is a viable option for the study. Based on these findings, we used NARR data to determine fractions of successful hypothetical flights of vertical profiles across the state of Oklahoma given thresholds of visibility, cloud base level (CBL) height, and wind speed. CBL height is an important parameter because the WxUAS must stay below clouds for the flight restrictions being considered. For the purpose of this study, a hypothetical WxUAS flight is considered successful if the vehicle is able to reach an altitude corresponding to a pressure level of 600 hPa. Our analysis indicated the CBL height parameter hindered the fractions of successful hypothetical flights the most and the wind speed tolerance limited the fractions of successful hypothetical flights most strongly in the winter months. Northwest Oklahoma had the highest fractions of successful hypothetical flights, and the southeastern corner performs the worst in every season except spring, when the northeastern corner performed the worst. Future work will study the potential effect of topology and additional variables, such as amount of rainfall and temperature, on fractions of successful hypothetical flights by region of the state.

Design and Development of Multirotor UAV with Automatic Collision Avoidance using Stereo Camera

The operation of drones in cluttered environments like forests and hilly areas is extremely difficult; it is impossible to use drones autonomously without having built-in information to detect and avoid obstacles. The vision based obstacle avoidance algorithm is presented in this paper, with extensions to UAV navigation. The proposed method is incorporated on a stereo vison multi copter using a block matching algorithm. The stereo vision baseline is based on horizontal configuration and computes the depth using a sum of absolute difference algorithm. The image processing node (LabVIEW vi) and the controller node are run on a remote laptop. This vi computes the distance between the multirotor and an obstacle and transmits depth data to an onboard flight controller through the MAVLink protocol. The algorithm efficiency was tested using the software in the loop on Gazebo simulator to analyze the performance of the UAV. The hardware in loop results are also shown in this paper after the successful flight test.

Rehabilitation of a whiskered screech-owl (Megascops trichopsis) in a wildlife care center in Mexico City

A whiskered screech-owl (Megascops trichopsis), the second smallest owl of the genus Megascops in Mexico, was admitted at the Wildlife Care Center of El Pedregal de San Angel Ecological Reserve. After performing the physical examination we found no pathologies, but the owl was not able to fly or to hunt successfully. Based on these we determined that the owl was candidate for rehabilitation for the purpose of reintroducing it to the wild. During the rehabilitation, short indoor, long outdoor and vertical flights were carried out. In addition, we offered different live preys to simulate hunting behavior. After rehabilitation, we take blood and fecal samples. Also, a complete ophthalmological examination was carried out. Before the release, a general physical evaluation was carried out where the owl showed an adequate weight (120 g). We did not find endoparasites, or alterations in the ophthalmological exam. The owl was alert and elusive, with no signs of habituation to human contact. Also, a successful flight and hunting behavior was observed. Their hematological values were within the optimal ranges reported for Megascops asio and Asio flammeus. This is the first report of hematological and biochemical values of this species.

From aviation tourism to suborbital space tourism: A study on passenger screening and business opportunities

Due to the significant amount of cost for privately paid passenger to travel the Earth orbit and beyond, orbital space tourism (OST) is not affordable for the general public in the coming decades. Therefore, the second best could be the suborbital space tourism (SST). According to the following facts, SST could be right at the corner: in October 2017, the Saudi Arabia intended to invest 1 billion USD into Virgin Galactic; on December 11, 2019, Blue Origin's New Shepard had a wholly successful 12th flight test mission (NS-12); and then on February 13, 2020, Virgin Galactic's spaceplane SpaceShipTwo, named VSS Unity, has been successfully relocated to its commercial headquarters at Spaceport America. Referring to the possible or potential effects of reusable suborbital launch vehicle (RSLV) trajectory dynamics on the neuro-vestibular system of passenger, this paper studied and discussed the pre-flight passenger screening contents and the related business opportunities for SST. Requirements for the third class medical certificate of the Federal Aviation Administration (FAA) of the USA have been proposed as a major reference. Since the SST is a new emerging market, contents for pre-flight screening of tourist need be rigorous, but could be adjustable based on accumulated flight experience in the future. The related business opportunities, either academic or commercial, in pre-flight training, pre-flight adaption, post-flight adaption, and data analysis, are expected to form a new industry chain gradually from 2020s to 2030s or 2040s.