Automated Low-Altitude Air Delivery

The project Automated Low Altitude Air Delivery–ALAADy is a study on the design of a heavy-lift transportation drone in the context of certification based on operational risks. This chapter is the opening of a book providing the results of the initial phase of the project within the years 2016 to 2019. Conceptually, in ALAADy, unmanned aircraft systems (UAS) are envisioned to provide a payload capacity of around one metric ton. Research questions on how the newly established EASA Specific Category of drone operation and its acceptable means of compliance, the Specific Operations Risk Assessment (SORA), influences the UAS are introduced and motivated in this chapter. Applying the SORA imposes limits to the operation to ensure safety. The project focus is investigating the impact on the UAS design if the operational limitations are maximized by restricting the flight over sparsely populated areas and below common air traffic only, while exploring large-scale UAS at the same time. The aspects considered include UAS design, aircraft configuration, system architecture, datalinks, safe autonomy, and airspace integration. The impact on the use-cases of such a UAS as well as the effect on the economical perspective are also addressed. Finally, this chapter introduces the need to design and implement scaled technology demonstrators and presents the overall project’s perspective to experimental analysis. One demonstrator is based on a manned micro light gyrocopter converted into a cargo drone. It enables payload transportation of around 150–200 kg and is applied to validate the conceptual part of the ALAADy project beyond simulation.

There is a growing interest in large unmanned cargo aircraft (UCA) with payload capacity and range significantly larger than drones for last-mile parcel delivery. Several fields of application for such types of UCA were suggested. In this chapter, the usability of such a large UCA is discussed for three use cases, namely spare parts logistics, supply of people in hard-to-reach areas, and disaster relief. Performance parameters of the UCA are based on the large cargo drone concept developed by the DLR (German Aerospace Center) within the project Automated Low Altitude Air Delivery – ALAADy. We describe specific characteristics of each use case and how the use of an UCA could result in improved transport solutions. UCA can be a suitable transport solution when spare parts with high criticality and high value and with low and irregular demand have to be supplied. Furthermore, UCA can improve the transport of essential goods in hard-to-reach areas. For usage in disaster relief operations the UCA needs additional capabilities like to detect people in need and to supply them by airdrops.

The project Automated Low Altitude Air Delivery (ALAADy) focuses on a transportation drone supposed to transport one metric ton of goods over a distance of 600 km with a cruise speed of 200 km/h. The aircraft is planned to operate under a newly established category of certification (EASA’s Specific category) that is intended to make certification less constraining and operations more affordable and equally safe compared to other means of air transportation. The present chapter introduces two possible applications of this aircraft, namely a commercial flight network for the delivery of agricultural spare parts in Europe, and a catastrophe relief mission for overflooded areas. In order to illustrate the parameters of the respective operations, both concepts are assessed using cost models as well as flight schedules and mission trajectories, respectively. This chapter’s purpose is to give impressions on the operational environments, particularly regarding economics and business-case establishment, that longer-range transportation drones have to comply with.

This chapter deals with the selection process of three different aircraft configurations that are appropriate for automated cargo operations at low altitudes and above sparsely populated areas. The selection process starts with a conceptual assessment of various aircraft types with respect to their suitability as an unmanned cargo aircraft (UCA) and subject to a set of specific top-level aircraft requirements (TLAR’s). Based on the TLAR’s and further characteristics like fuel efficiency, cargo space accessibility, technical simplicity or size, five fixed-wing aircraft and two rotorcraft are chosen for further investigations. A subsequent preliminary design study dimensions the fixed-wing aircraft for different wing spans based on flight performance requirements according to the TLAR’s. A possible mean to enhance take-off and landing performances is the integration of additional small propellers and to make use of the propeller slipstream effect. Therefore, this chapter furthermore investigates the benefits from the integration of additional electrically driven propellers. The second part of the study focusses on the comparison of a helicopter and a gyrocopter, presenting performance key parameters and discussing their respective advantages and disadvantages. This chapter concludes with the selection of a twin boom aircraft of 16 m wing span, a box wing of 12 m span and a gyrocopter with a rotor radius of 7 m and small supplementary wings for the use as UCA.

This chapter focuses on the work done to examine in more detail how three configurations, namely double tail boom fixed wing aircraft, box wing aircraft and gyrocopter as proposed in a pre-study (Hasan YJ, Sachs F (2021) Performance-based preliminary design and selection of aircraft configurations for un-manned cargo operations. In: Dauer JC (ed) Automated low-altitude air delivery - towards autonomous cargo transportation with drones. Springer, Heidelberg) are suited for the task described in the project Automated Low Altitude Air Delivery (ALAADy). It is investigated which specific properties and features of each configuration are rather contributing or contravening for the ALAADy purpose. These investigations comprise, above all, the conduction of wind tunnel tests and a flight experiment. In order to identify and investigate inherent safety features 6-degree-of-freedom flight dynamic simulations of the three configurations are set up. To provide sufficiently precise simulation models many details of the configurations and the according power train variations are created and examined. For the gyrocopter wind tunnel tests of a scaled gyrocopter demonstrator are conducted as well.

This chapter presents the conceptual loads analysis and the structural design of the unmanned cargo aircraft concepts within the Automated Low Altitude Air Delivery (ALAADy) project of the German Aerospace Center, DLR. Three concepts of a gyroplane, a fixed high-wing with a twin boom v-tail aircraft and a box wing aircraft are concerned in the project. The main focus is on the estimation of the structural weight of each unconventional aircraft configuration. However, the application of empirical formulations based on conventional aircraft configurations is not suitable for this task. Instead, the task is performed with a parametric design process which is designed to be used for the structural design of an unconventional aircraft. In this process, the structural models are set up as finite element models in a parametric manner. The loads analysis and the aeroelastic structural dimensioning are then performed using these finite element models. This process is developed by the DLR and it is called the MONA process. The major result of the process is the structural weight of each unmanned aircraft (UA) concept. Finally, the structural weights of all aircraft are compared. The weight comparison contributes to the global evaluation of the aircraft concepts within the ALAADY project. Based on the considered aircraft requirements, the considered load cases and the considered system masses, the gyroplane has the minimum structure weight of 2,720 kg.

Besides lower environmental impact, full and hybrid-electric propulsion systems offer an opportunity to set-up a highly redundant powertrain. As safety is one of the important topics for the design of unmanned aircraft systems (UAS), concepts of full-electric and hybrid-electric propulsion have been investigated in terms of meeting: mass, volume, power, energy and safety constraints. In the first step, the powertrain system has been sized according to preliminary design data described in the project Automated Low Altitude Air Delivery (ALAADy) using generic data of state-of-the-art system components. In the next steps the powertrain system has been analyzed and modelled with simulation models to investigate the system performance in more detail. Optimal powertrain system architectures concerning system overall mass and redundancy have been set up especially for the vehicles designed for the ALAADy project. The differences between full-electric and hybrid-electric powertrain systems is discussed as well.

The steadily growing share of air freight transport in the entire logistics industry is mainly due to the three major advantages of speed, safety and reliability. In order to meet increasing demands, more and more automated transport and delivery processes are used. As part of the DLR (German Aerospace Center) research project Automated Low Altitude Delivery (ALAADy), a fully automated Unmanned Cargo Aircraft (UCA) with a payload of one ton is being developed in cooperation with eight DLR institutes. As a general area of application, the UCA is responsible for the so-called “penultimate mile” in the air freight logistics chain. In order to achieve an optimal integration of a UCA into the freight supply chain, this research focuses on ground handling and in particular on the loading and unloading processes. The theoretical and practical concepts of the integration of UCA were examined within this research under the premise that no infrastructure exists at the destination in order to obtain the most automated process possible for future logistics. The research shows that the interaction between a UCA and an automated robot container system can solve both problems of the “last mile” and the “penultimate mile” within the logistics chain.

Current initiatives to integrate UAS into airspace mostly target small or medium-sized drones. However, it is foreseeable that there will be a demand for cargo UAS with a payload in the range of about 1000 kg. It is proving to be a challenge to integrate these larger drones into a national airspace. The concept of choice for this problem is to use the EASA Specific Category. In this category it is possible that the reliability of the vehicles is not maximised by increasingly complex system components, but that the drones are guided on special trajectories so that any accident that occurs does not result in fatalities and only financial losses. The advantage is that the concept can be realized with existing technology and only moderate effort for new equipment on board and on ground.

However, this poses some further challenges to air traffic procedures. In Germany and Europe in general, the airspace is densely occupied, especially near airports. UAS missions should disturb this existing structure as little as possible. An integration concept must therefore ensure that the future air cargo system can strategically or at least tactically avoid any potential risk, regardless of whether it is a conurbation, an industrial infrastructure or other aircraft.

We present an integration concept for airspace structure, communication infrastructure and information management. Based on publicly available data on population and ground infrastructure, we present exemplary calculations that show the concept’s feasibility.

This work develops a set of high-level system architectures for an Unmanned Aircraft System (UAS) for the low altitude transport of one ton payload within the Automated Low Altitude Air Delivery (ALAADy) project. These architectures are further analyzed regarding their development effort. Based on the Specific Operation Risk Assessment (SORA) as Acceptable Means of Compliance (AMC) for the Specific Category of the new EU regulation for UAS, requirements are derived and processed into the architectures. A reference architecture for a certified system is developed for comparison as well. Overall, four major architectures are found. Within SORA, regarding the use case of a large cargo drone, only flights over sparsely populated areas are possible. Consequently, for flights over populated areas a certified system is needed. Requirements in SORA are based on the intrinsic risk of an operation. The risk can be modified by applying mitigations. Therefore, different levels of requirements have to be used for the same mission depending on the mitigations used. Within the analysis of the development effort a nondimensional relative effort factor is found. As a result an ALAADy mission within SORA with limited mitigations and high-risk requirements has little difference to a certified system. Furthermore, a gap is found between two adjacent requirement levels. It is shown that the development effort ranges from the least demanding to the most demanding architecture in half an order of magnitude.

Long-distance cargo transport is one of the manifold applications envisaged for highly automated unmanned aircraft (UA), which operate in the very low-level airspace below 150 m. Despite the level of automation, remote pilots need an interface for command and control of UA, which is typically provided by a digital data link. In this contribution, we investigate the impact of certification based on operational risk, which the European Aviation Safety Agency (EASA) introduced for UA within the specific category on the data link concept. In order to reach the required level of safety, which is the outcome of the Specific Operation Risk Assessment (SORA), the data link concept has to fulfill certain safety objectives. At the same time, the data link concept should be as cost-efficient as possible from an economical point of view. Keeping these boundary conditions in mind, we present an operation risk-based data link concept based on commercial off-the-shelf technologies. In dependence of the mission profile and the required safety level, cellular networks, satellite networks, as well as a combination of both, are viable options. Specifically, we evaluate by simulations the suitability of 4^th generation Long Term Evolution (LTE) cellular networks for long-distance cargo UA. With regard to the concepts of operation, the goal of our simulations is estimating low-altitude cellular coverage in rural areas and we factor in radio propagation effects, link budgets, and the distribution of cellular base stations. The results of our system simulations with realistic flight routes show that LTE cellular networks offer good rural coverage in Germany and ensure operational safety in general. Nevertheless, connection disruptions in the order of some seconds can occur in valleys that are not served well by LTE and have to be considered in the risk assessment process.

Regular aviation does usually not utilize the very low level airspace below 150 m. Even so, this altitude range cannot be exclusively reserved for the operation of unmanned aircraft. Therefore, measures have to be implemented to avoid mid-air collisions, especially with manned aviation. Primarily, the mid-air collision risk is supposed to be reduced on a strategic level preflight by thorough flight route planning and making use of advanced unmanned aircraft system traffic management concepts. Besides, the residual mid-air collision risk is supposed to be reduced on a tactical level through the use of detect and avoid systems, which support remote pilots especially during flights beyond visual line of sight. However, an accepted technical solution for unmanned aircraft does not exist at the moment. On that account, the contribution of this chapter is three-fold. First, we identify suitable detect and avoid system architectures. Second, we review suitable cooperative sensor technologies. Third, we determine the minimum required sensor range in simulations. As a result, we propose a solution for operation in European airspace that is already available: FLARM cooperative sensors onboard the UA surveille the surrounding airspace and the remote pilot tracks intruders and commands avoidance maneuvers.

A key challenge for low-altitude unmanned air transportation is to minimize operational risks by all means. Besides many other measures to be considered, the aircraft’s trajectory must be planned carefully and optimized as there are inevitable remaining risks which should be minimized when flying over sparsely populated areas. The risk may be mitigated by a safe termination of the flight if circumstances permit. Also, the probability of violating any operational constraints that would lead to a flight termination should be reduced as much as possible. Adequate risk models and efficient algorithmic risk assessment techniques are required to perform such optimizations. Furthermore, the aircraft may have to react to certain events such as high-priority traffic by changing its trajectory online during flight. As command and control (C2) links may have limited reliability, it must be possible to perform trajectory re-planning onboard with limited computational resources. This poses high demands on the runtime efficiency of the planning algorithms. In this work, we present conceptual approaches to risk modeling and assessment based on geospatial datasets and aircraft dynamic models. We further present the design and experimental results of a software framework for onboard and online trajectory planning. Our results demonstrate that risk-based motion planning for unmanned aircraft can be performed with limited onboard computational resources allowing for safe autonomous flight.

Future unmanned aircraft systems are allowed to incorporate operational aspects for flight approval due to the new EASA “specific” category. Incorporating operational aspects offer new possibilities for the verification and validation of complex functions used especially in highly automated vehicles. For these functions, verification and validation can focus on predefined operational aspects prior to flight. In-flight, limits of the operation are monitored to assure the correct working environment for these functions resulting in a safe operation. In this paper, we present the notion of safe operation monitoring and depict operational limits to be supervised. One prominent example for such an operational limit is geofencing. Geofencing prevents an unmanned aircraft from entering a forbidden airspace by using virtual fences. Specifically, in this paper, we present an algorithm and describe parameters for the buffer distance used for the geofence boundary values. The algorithm can be highly parallelized which is important when considering realistic geofences of future operations. Further, we highlight the use of a formal specification language and simulation results which support the verification and validation of geofencing, respectively. The chosen specification language is not limited to geofencing, other operational limits can be expressed and monitored in-flight to assure the safe operation.

The design and development of unmanned aircraft is a complex multi-disciplinary task. In the context of risk-based and operation-centric assurance and certification, operational constraints play a key role. Consequently, technologies that impact operational risks such as flight termination, command-and-control links, and onboard autonomy have to be addressed holistically and within the context of the operation. A scenario simulation combines these various aspects originating from different disciplines into one versatile tool. It allows making informed design trade-offs and validating operational requirements at early development stages. In this work, we give insight into the scenario simulation framework developed within the research project ALAADy (Automated Low-Altitude Air Delivery) which addresses unmanned freight operations at low-altitudes within the context of operation-centric certification as introduced by EASA with the so-called specific category. We describe use-cases and requirements derived from research objectives. Furthermore, we present the simulation architecture as well as details on implementation and modelling. Results from an exemplary simulation study regarding safe flight termination in the event of an operational constraint violation are shown to demonstrate the applicability and usefulness of the simulation framework as a tool for holistic unmanned aircraft design.

Within the project ALAADy (Automated Low Altitude Air Delivery) several options for start and destination of a cargo transport mission are discussed. One option in the concept study is the integration of larger transport drones in regular airport operations. In this case, integration of the vehicle in air space class B, C, or D (depending on the country) is required. The feasibility of this option was evaluated at the Air Traffic Validation Center at DLR (German Aerospace Center). As an example, the approach sector of Dusseldorf airport (EDDL) was simulated with different arrival traffic flows with and without a drone included. In a Human in the Loop (HITL) simulation the test persons controlled the air traffic in the sector according to ICAO rules assuring separation between all aircraft (including the drone) at any time. The resulting traffic flow with and without drone was compared to analyze the capacity effects of that vehicle. In addition, the test persons performed a questionnaire asking for workload and situational awareness. Based on the information gained by the analysis and the questionnaire, possible operational improvements were developed.

An unmanned gyrocopter is selected as a technology demonstrator to check the feasibility of the ideas discussed in the automated low altitude air delivery (ALAADy) project in 2016. A gyrocopter airframe is chosen, based on experience in the operation of unmanned aircraft systems (UAS) and manned light aircraft gyrocopters. The specific operations risk assessment (SORA) draft by the joint authorities for rulemaking on unmanned systems (JARUS) served as a basis and guideline for the operational concept. A key aspect of the concept is the choice of flying over sparsely populated areas. Therefor the capability for safe termination of the flight in case of an unexpected failure or other unsafe condition is considered as the main risk mitigation. The development of the demonstrator is characterized by the balance between cost-efficiency, functionality and reliability of hardware and software components. A rapid prototyping approach allows the aircraft to take off as early as possible. Findings from flight tests are leading to the development of several additional features and functions, which illustrates the importance of an agile development. The demonstrator proves to be a capable platform for research on unmanned freight transportation and one of the largest transport drones in civil operation at the time.

Using Unmanned Aircraft Systems (UAS) for transportation is an increasingly widespread concept. However, the majority of UAS only carry payloads of a few kilograms. This payload limitation will change in the future. New regulatory approaches facilitate the use of larger UAS with significantly increased payload capacities by incorporating the operational risks during certification. To assess the risk, the Specific Operations Risk Assessment (SORA) can be used, which defines a method that incorporates all safety affecting factors holistically. However, so far these factors ranging from automation or autonomy, aircraft configurations and design, airspace infrastructure and integration, certification and assurance, to the economics of potential use-cases have been studied in literature independently. The reason for this separation is the complexity of such holistic analysis of the aircraft system and operation. To overcome this complexity, this chapter identifies four segments of particularly strong interdependencies. This segmentation allows to map the air and ground risk classes of the SORA to the different system and operational components. At the same time, it supports balancing the level of autonomy with the reliability of required external services. Furthermore, it allows to study and adjust potential use-cases with the resulting system and operational requirements. The segmentation is discussed in detail based on the results of the research project Automated Low Altitude Air Delivery (ALAADy). The project conceptually studied transport UAS with payload capacities of up to one metric ton. Several technology demonstrations and flight experiments are included within this project. The following sections present a comprehensive view of the project’s results and conclude four years of research on unmanned aerial transport at the German Aerospace Center (DLR).