Design Methodology for Heavy-Lift Unmanned Aerial Vehicles with Coaxial Rotors

This work presents a novel design methodology for multirotor Unmanned Aerial Vehicles (UAVs). To specifically address the design of vehicles with heavy lift capabilities, we have extended existing design methodologies to include coaxial rotor systems which have exhibit the best thrust-to-volume ratio for operation of UAVs in urban environments. Such coaxial systems, however, come with decreased aerodynamic efficiency and the design approach developed in this work can account for this. The proposed design methodology and included market studies have been demonstrated for the development of a multi-parcel delivery drone that can deliver up to four packages using a novel morphing concept. Flight test results in this paper serve to validate the predictions of thrust and battery life of the coaxial propulsion system suggesting errors in predicted flight time of less than 5 percent

Morphing Concept for Multirotor UAVs Enabling Stability Augmentation and Multiple-Parcel Delivery

This paper presents a novel morphing concept for multirotor Unmanned Aerial Vehicles (UAVs) to optimize the vehicle ight performance during multi-parcel deliveries. Abrupt changes in the vehicle weight distribution during a parcel delivery can cause the UAVs to be unbalanced. This is usually compensated by the vehicle ight control system but the motors may need to operate outside their design range which can deteriorate the stability and performance of the system. Morphing the geometry of a conventional multirotor airframe enables the vehicle to continuously re-balanced itself which improves the overall vehicle performance and safety. The paper derives expressions for the static stability of multirotor UAVs and discusses the experimental implementation of the morphing technology on a Y6 tricopter configuration. Flight test results of multi-parcel delivery scenarios demonstrate the capability of the proposed technology to balance the throttle outputs of all rotors

Rotational speed control of multirotor UAV's propulsion unit based on fractional-order PI controller

In this paper the synthesis of a rotational speed closed-loop control system based on a fractional-order proportional-integral (FOPI) controller is presented. In particular, it is proposed the use of the SCoMR-FOPI procedure as the controller tuning method for an unmanned aerial vehicle’s propulsion unit. In this framework, both the Hermite-Biehler and Pontryagin theorems are used to predefine a stability region for the controller. Several simulations were conducted in order to try to answer the questions – is the FOPI controller good enough to be an alternative to more complex FOPID controllers? In what circumstances can it be advantageous over the ubiquitous PID? How robust this fractional-order controller is regarding the parametric uncertainty of considered propulsion unit model?info:eu-repo/semantics/publishedVersio

Preliminary design of a fuel cell - battery hybrid propulsion system for a small VTOL UAV

Master's thesis in Mechanical engineeringOver the past decade, utilization of unmanned aerial vehicles (UAVs) in military and commercial applications has increased significantly. The vertical take-off and landing (VTOL) UAV is appreciated for its easy launch and versatile operation capability, but the missions are limited due to low endurance. Hybrid fuel cell systems have the potential to increase the endurance significantly. Until now, the use of fuel cell systems in VTOL UAVs have been limited to demonstrations, but as new and lightweight fuel cell systems have been developed, the technology seems to have reached the maturity level needed to realize fuel cell powered VTOL UAVs for more widespread use. This paper considers the implementation of a hybrid fuel cell – battery system on an existing VTOL UAV with maximum take-off weight (MTOW) of 25 kg. The available technology for fuel cells and hydrogen storage are investigated with the aim of determining the best solution for this UAV, and a preliminary design of the entire propulsion system is done. The selection of different components is based on power estimation from momentum theory. The hydrogen storage is a customized spherical composite pressure vessel. A comparison between cylindrical and spherical pressure vessels are performed to justify the use of a spherical pressure vessel. The calculations are based on classical lamination theory. The results indicate that a spherical pressure vessel gives weight savings of 15 %. The estimated endurance of the proposed system is 3.2 hours at MTOW with a custom spherical pressure of 21 liters. This is a 7-fold improvement compared to the current installed batteries

Design of a swarm of Unmanned Aerial Vehicle for the exploration of Mars

Mars has been a main target for exploration over the last decades, due to its closeness and similarity to Earth. Exploration landers and rovers have laid the foundation for the understanding of the planet, however, they exhibit some limitations that Unmanned Aerial Vehicles (UAVs) would overcome. Thus, this report consists of the design of a swarm of UAVs for the exploration of the red planet, which coordinates with a swarm of rovers and a constellation of orbiters that are briefly described. Firstly, the mission is preliminarily designed to define its location, architecture, objectives, and requirements. Secondly, the single UAV overview is presented, illustrating a preliminary design of all the subsystems involved in order to perform successfully. Thirdly, the swarm of UAVs is defined, introducing pre-flight check procedures. Then, two flight formation algorithms for the swarm of UAVs are suggested, although only one of them is implemented. Fourthly, there is a brief introduction to the multiplatform architecture, focused on communication and connectivity. Finally, conclusions are drawn and and the foundation for future work related to the different chapters of this thesis is included

Mars Science Helicopter Conceptual Design

Robotic planetary aerial vehicles increase the range of terrain that can be examined, compared to traditional landers and rovers, and have more near-surface capability than orbiters. Aerial mobility is a promising possibility for planetary exploration as it reduces the challenges that difficult obstacles pose to ground vehicles. The first use of a rotorcraft for a planetary mission will be in 2021, when the Mars Helicopter technology demonstrator will be deployed from the Mars 2020 rover. The Jet Propulsion Laboratory and NASA Ames Research Center are exploring possibilities for a Mars Science Helicopter, a second-generation Mars rotorcraft with the capability of conducting science investigations independently of a lander or rover (although this type of vehicle could also be used assist rovers or landers in future missions). This report describes the conceptual design of Mars Science Helicopters. The design process began with coaxial-helicopter and hexacopter configurations, with a payload in the range of two to three kilograms and an overall vehicle mass of approximately twenty kilograms. Initial estimates of weight and performance were based on the capabilities of the Mars Helicopter. Rotorcraft designs for Mars are constrained by the dimensions of the aeroshell for the trip to the planet, requiring attention to the aircraft packaging in order to maximize the rotor dimensions and hence overall performance potential. Aerodynamic performance optimization was conducted, particularly through airfoils designed specifically for the low Reynolds number and high Mach number inherent in operation on Mars. The final designs show a substantial capability for science operations on Mars: a 31 kg hexacopter that fits within a 2.5 m diameter aeroshell could carry a 5 kg payload for 10 min of hover time or over a range of 5 km

The aerodynamics of micro air vehicles: technical challenges and scientific issues

Micro air vehicles raise numerous design problems associated to the size reduction: lower aerodynamic and propulsion efficiencies, higher sensitivity to atmospheric turbulence, low-density energy of electric propulsion, etc. The paper discusses some of the most important design issues and analyses the aerodynamic challenges encountered in the field of MAVs. A number of novel aerodynamic configurations combining rotors and fixed-wing are proposed and discussed in order to recover efficiency and maneuverability at low speeds

Tri-Rotor Propeller Design Concept, Optimization and Analysis of the Lift Efficiency During Hovering

This study introduces the simulation of a tri-rotor contra-rotating propeller for thrust force and hover lift efficiency during vertical take-off. Vertical take-off or landing is a method used by many aircraft and makes the vehicle more convenient and easier to use. The second rotor revolved in the opposite direction of the first and third rotors. The proposed multi-rotor system has NACA 0012 untwisted and symmetric airfoil and includes three rotors with two blades for each. The airflow analysis was optimized with computational fluid dynamics simulation by using different pitch combinations to achieve the highest hover lift efficiency with sufficient overall thrust value. The critical angle of attack for the chosen airfoil gave the boundary conditions for the pitch of rotors. The results showed us that the most efficient combinations for three rotors work better with an increase of pitch angle from top to bottom so that there is a difference of at least two degrees between propellers. Experiments with angles of attack within the boundary conditions showed that the blade combinations starting from three degrees and increasing values gave positive and adequate results in many cases. In addition, the results showed that a regular increase in the angle of attack does not relate to a regular increment in thrust force

A review of variable-pitch propellers and their control strategies in aerospace systems

The relentless pursuit of aircraft flight efficiency has thrust variable-pitch propeller technology into the forefront of aviation innovation. This technology, rooted in the ancient power unit of propellers, has found renewed significance, particularly in the realms of unmanned aerial vehicles and urban air mobility. This underscores the profound interplay between visionary aviation concepts and the enduring utility of propellers. Variable-pitch propellers are poised to be pivotal in shaping the future of human aviation, offering benefits such as extended endurance, enhanced maneuverability, improved fuel economy, and prolonged engine life. However, with additional capabilities come new technical challenges. The development of an online adaptive control of variable-pitch propellers that does not depend on an accurate dynamic model stands as a critical imperative. Therefore, a comprehensive review and forward-looking analysis of this technology is warranted. This paper introduces the development background of variable-pitch aviation propeller technology, encompassing diverse pitch angle adjustment schemes and their integration with various engine types. It places a central focus on the latest research frontiers and emerging directions in pitch control strategies. Lastly, it delves into the research domain of constant speed pitch control, articulating the three main challenges confronting this technology: inadequacies in system modeling, the intricacies of propeller-engine compatibility, and the impact of external, time-varying factors. By shedding light on these multifaceted aspects of variable-pitch propeller technology, this paper serves as a resource for aviation professionals and researchers navigating the intricate landscape of future aircraft development