The content of this blog was contributed by the University of Bath’s Unmanned Aircraft Systems (UAS) Team Bath Droneso.
Team Bath Drones is a group of final year undergraduate engineers at the University of Bath. The University of Bath is one of the UK’s leading Engineering Universities with over 16,000 students. Each year the Unmanned Aerial Systems (UAS) team enter the IMechE UAS Challenge; a global drone competition held in North Wales, where students compete, design, manufacture and fly a fully autonomous drone. Previously the team worked together to create the ultimate autonomous Unmanned Aircraft Systems (UASs) and were the overall grand champions of the IMechE UAS Challenge 2017, as well as winning the prize for the most Innovative design in 2018. Led by a team of final year undergraduate students and supervised by Dr Pejman Iravani, Dr Jon du Bois and Dr David Cleaver, the team has interdisciplinary expertise in aeronautical, mechanical and electrical engineering.
For 2019 the team have a key aim of increasing engagement and visibility across the University and the wider public. An aim which is already underway through a ‘meet the team’ event arranged by Bath Drones for students in lower years. Team Bath Drones are excited for the younger students to get involved early in their academic careers in order to provide them with a wealth of first-hand experience in design and manufacture of drones. Over the next few weeks the team will be attending public events as part of the Bath Taps into Science week and Corsham Institute of Technology Showcase, providing a range of opportunities for student engagement.
Over the past few months, Team Bath Drones have developed a range of new and exciting drone projects! Below some of the complex processes and developments that are required to produce the drones are detailed.
Small Scale Prototyping
In order to build some heritage in multirotor design and operation, Team Bath Drones built and tested a 1/3rd scale prototype, operating in vertical mode only. Building the prototype enabled the team to test their ﬁrst tilt mechanism design, as well as gain some knowledge of the controller effectiveness in hover.
Over the last few months, members of the team have been busy running computational ﬂuid dynamics (CFD) simulations. CFD gives provides a way to make better design decisions and predict the aerodynamic performance of the aircraft quickly before building prototypes. The team’s ﬁrst course of action was to collect lift, drag, and pitching moment data in ﬁxed wing mode. The team then investigated blended winglets which were found to reduce drag produced in forward ﬂight. The effect of duct coverings was assessed; ﬁnding that it was only necessary to cover one side during ﬁxed wing ﬂight. The VTOL to forward ﬂight transition was also simulated in an effort to inﬂuence the ﬂight controller design and understand the effect of propeller thrust and rear motor tilt angle throughout the transition process.
Manufacture of the fuselage skins was the ﬁrst full-scale manufacturing process that was conducted, due to the amount of time required. The blended body fuselage CAD model was split in half and used to generate negative moulds of the body, each of which required over 15 hours to cut from Styrofoam on the team’s CNC machine. The moulds were then reinforced with ﬁbreglass and epoxy gelcoat to provide a hard and smooth surface ﬁnish for producing their parts from. The fuselage skins are lightweight ﬁbreglass and epoxy composite with a stiffened foam core to improve rigidity. Each skin consists of two layers of ﬁbreglass with the foam core sandwiched between them.
Given Bath Drones’ new, innovative ducted fan design this year, research into the performance of various conﬁgurations was essential. As a result of the help from the team’s sponsors at Create Education, Filamentive, UNMND, and Accu they were able to rapidly design, print and assemble a variety of different duct shapes and sizes to be tested.
A range of propellers were cut down to ﬁt in the ducts with minimal clearance between the duct wall and the propeller tip, increasing the thrust produced. The close proximity of the duct wall and propeller tip reduces the tip losses that all propellers experience, meaning that the chord of the propeller at the tip could be increased without negatively affecting the drag of the propeller, increasing thrust.
The team then completed numerous days of testing using a thrust measurement stand, allowing all duct and propeller combinations to be compared. The team identified and resolved problems such as the motor mount overheating and the rigidity of the duct. The optimised solution was found to be a 6 inch diameter duct, with coaxial counter-rotating 7 inch triblade propellers that had been cut down to ﬁt in the duct. The team will utilise a pair of the ducted fans on the aircraft providing 5 kg of static thrust.
Team Bath Drones have been feeding the results of their various design analyses, including the CFD Analysis and thrust testing, into their design process which has enabled them to complete the motor selection, a major building block in the design process. The results of this has seen the team shift the motors further apart and switch their orientation, reducing drag and weight and improving control authority in hover.
In the coming weeks the team are excited to be working on some new projects, manufacturing two prototype aircraft; one ﬁxed wing and one VTOL. Both drones will allow the team to test the two distinct ﬂight types prior to combining them for the ﬁnal model. With an overall aim to ﬂy both by the end of February!
The team are also looking forward to working on individual university projects with advanced research areas which will be beneficial in both this years’ aircraft and future designs. Along with this Team Bath Drones are going to be attending various public STEM events to help showcase the exciting research into drones going on at the University.
Team Bath Drones have key partnerships with technologically leading companies including Callen-Lenz, Parker, Accu, and RS Components. Working alongside industrial corporations has provided them access to manufacturing products, expertise, and helped them raise the required funds to compete and challenge for the UAS challenge ﬁrst prize.
The team also commented that their partnership with Create Education and Filamentive has greatly improved their prototyping ability and will continue to improve their educational outreach in the future!