The realisation, in the academic community, of a Uninhabited Aerial Vehicle (UAV) capable of acquiring autonomous flight capabilities, represents a technological challenge and, at the same time, a rare opportunity for teams of researchers in different disciplines to be involved in well defined and highly cooperative research activities.
Programme goals also deserve a specific consideration when reference is made to scientific activities of monitoring and survey that may require observation of defined areas by means of aircraft or satellites. Recent studies have shown that use of UAVs in the so-called D3 (Dull, Dangerous, Dirty) types of missions is safer, less expensive and more efficient in comparison with manned aircraft and, in many cases, use of satellites is limited by poor resolution in spatial domain and/or because they do not supply real-time information.
In this context, the UAV here proposed is the only original project to date in Italy of a vertical take-off and landing (VTOL) aerial platform to be used for developing and testing maturing technologies in civil applications. The vehicle configuration, with two counter-rotating rotors enveloped in an annular shroud and driven by three engines, is in many respects highly innovative and rather complex. Since the very early stages of the research program, it quickly became apparent that the vehicle would be of value not only to the immediate research tasks of the involved departments but also to various applications. In particular, provided that reliability and smooth/safe flight characteristics are demonstrated and fully autonomous capabilities are incorporated in the flight management system (FMS), size and performances of the UAV will allow its operations in several mission areas, including geological surveying, reconnaissance, environmental monitoring and remote delivery.
The primary (and rather challenging) objective of the programme is to demonstrate the capabilities built by the participating research teams in the core UAV technologies of design optimisation, advanced airframe design and construction, guidance and control strategies, real-time flight control software synthesis and UAV flight testing. A significant result of the programme also concerns the development and dissemination in the scientific community of advanced methods and technologies in the areas of control system design for UAVs, rapid prototyping of controllers, sensor-fusion as well as remote sensing, miniaturisation and onboard integration of airborne sensors for environmental remote monitoring.
Following a preliminary phase dedicated to feasibility studies and conceptual design, construction of the shrouded-fan UAV started in 1998 at the University of Rome "La Sapienza" (DMA) and Polytechnic of Turin (DIASP). The prototype was completed in 2005. Following a 50% reduction of funding with respect to the planned budget, the envisioned activities in the project are focused on a limited set of well-defined objectives that can be summarised as follows:
- Design review aimed at improving vehicle reliability, performance and payload capability;
- Demonstration of vehicle reliability and performance in the envisioned operational field, by ground and flight testing;
- Development and implementation of technologies for enhancing vehicle autonomy in managing the mission profile, so that neither skilled ground operators nor special ground equipment will be necessary for the execution of envisioned missions;
- Demonstration of the UAV concept as an airborne sensor platform with precision navigation capability through the study of onboard integration of a Lidar fluoro-sensor for superficial water monitoring.
The principal task of the project was the development of a novel concept of a VTOL UAV for civil applications, with potential of being developed into a highly integrated and autonomous sensor platform.
In this respect, activities finalise the work carried out by the same team in recent years to design build and fly a vehicle characterised by a rather complex - from the points of view of mechanical systems, aerodynamics and dynamics and control - configuration, where the annular shroud provides a significant advantage, in terms of lift performance and safety (for both the support personnel and the vehicle itself) in comparison with a classic configuration of rotorcraft.
At the same time the proposed application as a mobile sensor platform where a miniaturised Lidar fluoro-sensor is implemented onboard, appears as either a natural follow-on of the project to be recognised by end-users interested in further development and industrialisation of the vehicle, and a significant step forward to conceive an innovative airborne system specifically modified and instrumented for operations in the field of environmental research in the atmospheric, marine and terrestrial sciences.
DIASP research group (RG) with the support of DIMA group, also manage the planning and organisation of the flight test programme. The tasks of (i) vehicle automation (take-off, landing, precision navigation) to increase safety of operations and (ii) sensor payload miniaturisation and integration will be addressed by DIMA RG, with participation, in the second activity of the team of ENEA laser remote sensing lab, with support from DIASP for the mechanical aspects of sensor integration on board of the vehicle and evaluation of its functionalities.
The relatively high number of external personnel to be hired stems from the heavy workload required to carry out the planned activities in the programme. It would be unrealistic to underestimate the significant amount of work, in terms of month/man necessary to keep the project on schedule and to complete it with reasonable confidence. The research team involves personnel from DIASP and DIMA that have been actively cooperating for many years. The group at ENEA has relevant technical expertise in the development, miniaturisation and integration of Lidar spectroscopic systems applied to waters and vegetation monitoring and, in general, in remote sensing diagnostic techniques for environmental applications. In conclusion, the small consortium, w
Results obtained can be summarised as follows:
- Analysis and revision of the UAV design according to results and indications of ground tests. The rotor control system has been redesigned and the engine system has been developed to improve reliability, landing gear had been realised and, as a major improvement of the original design, a set of linear actuators has been designed and built to satisfy the strict performance requirements on these critical elements of the UAV. Finally, the construction of the UAV prototype has been concluded in all his parts and the whole system has been tested, particularly for the aspects of power system and mechanical reliability.
- Development and validation of control software/hardware to enhance the flight characteristics of the vehicle, particularly for the purpose of automatic/autonomous flight. The autopilot has been upgraded and fully validated in hardware-in-the-loop simulation. Control software for the management (pointing, focusing etc) of the onboard video camera has been developed, and algorithms for trajectory planning, automatic take-off/landing and way point navigation have been implemented and tested.
- The vehicle has been extensively tested on its ground stand.
- A miniaturised (very light weight and size) Lidar fluoro-sensor has been realized by the ENEA RG, that is ready to be on-board implemented and integrated with the power and avionic system of the vehicle. The sensor is to be used to monitor concentration of pollutants on the surface of marine ecosystems.
Project activities have resulted in two national patents, on the Lidar payload and on a personal transportation system based on the concept of counter-rotating coaxial rotors adopted for the present UAV.
Academic departments involved in the project have advanced with the UAV programme successfully. Despite having proven capabilities in involved technologies, their progress was hindered by lack of funding and, to a certain extent, by lack of national industry interest and involvement in rotary-wing UAV research and development. Nevertheless, while operating on limited budget, expertise and experience of the team in the rather demanding and risky technical arena of rotary-wing UAV research have ever been growing, as an increasing amount of results has been acquired from experimental tests and simulations, and many problems have been discovered and solved. As a major drawback, the planned campaign of flight tests has not been conducted in the programme time frame, due the issue of insufficient funding as well as to the longer that expected time necessary to address and solve a number of technical problems, particularly when the realisation of mechanical parts was involved.