Drone flying in the sky

Pushing the boundaries of drone design

13 July 2018
New solutions for propulsion and airframe design
The University of Sydney’s Faculty of Engineering is at the forefront of designing the next generation of specialised Unmanned Aerial Vehicles, making them easier to deploy, faster, and longer range.

Drone technology has made huge advances over the last decade, but the industry has struggled to fill the yawning gap between military behemoths like the Northrop Grumman Triton and the small consumer quadcopters that are available for a few hundred dollars on any high street.

At one end you have a billion-dollar marvel of aero-engineering that can travel 18,000km before having to refuel and at the other an airborne camera platform at best. If drone technology is to fulfil its potential to revolutionise aerial crop surveys, battlefield intelligence, disaster relief planning and a host of other fields, it must conquer this middle ground.

The challenges of reconciling the conflicting imperatives for the next generation of drones are formidable. Fast drones with the capacity to spend substantial time in the air need bigger and heavier propulsion systems, reducing the potential payload, and tend to require runways or other infrastructure for launch and recovery. 

Teams at the University of Sydney’s UAV Aeronautical Engineering Group, part of the Faculty of Engineering and Information Technologies, are in the vanguard of addressing these challenges, testing promising new hybrid propulsion systems and re-imagining airframe design to improve functionality.

Battery power may suffice for small recreational drones, but for more heavy-duty applications that need better range and a bigger payload, they are too heavy and discharge too quickly. Similarly, traditional piston engines are too heavy and bulky for small drones.

The main drive is to increase the endurance of the overall platform without increasing the weight, because weight equals cost.
Dr Dries Verstraete

Dr Dries Verstraete's team from the University’s School of Aerospace, Mechanical and Mechatronic Engineering (AMME) is developing what it calls a Triple Hybrid Fuel Cell system which has up to four times the endurance of current battery systems. Fuel cells coupled with a battery have a number of significant advantages over both standard electric systems and piston engines: they have a better power to weight ratio, they run on hydrogen and produce no pollution, and they produce a much-reduced heat signature, a key concern for military applications.

But fuel cells quickly degrade if they are asked to handle rapid fluctuations in power demand. The Sydney team has added an ultracapacitor to the fuel cell/battery combination, which smoothes out the load, giving significantly better engine life. Dr Verstraete says that the basic engineering problems have largely been solved, and that the team is now working on optimisation, particularly on the power electronics needed to tune the system for particular missions.

But the AMME team are looking beyond propulsion to re-engineer the shape of drones of the future. This involves solving a key contradiction: the drone has to have the efficiency and endurance of a fixed-wing aircraft but the easy launch of a multi-rotor aircraft.

One solution developed in Sydney has been the T-wing Tail-Sitter, a design that takes off vertically before transitioning in mid-air to mimic forward, fixed-wing flight. This will allow the drone to take full advantage of the extra endurance of the hybrid motor. Soldiers looking for battlefield intelligence, farmers carrying out crop surveys, oil or electricity companies looking to check the integrity of their pipelines or distribution cables can launch and retrieve the drone in the field.

Jeremy Randle, the University’s Chief Remote Pilot, has recently returned from testing a system that tracks radio transmitters fitted to one of Australia’s most endangered birds, the Swift Parrot. New software developed by the University has significantly simplified tracking.

“We designed the electronics to track the signal and the software to optimise the flight path for the aircraft to narrow down the location of that signal,” he says, but he believes that for Australia to maintain its lead in drone technology, there needs to be regulatory change.

Drone pilots are currently limited to line-of-sight flight. In the example of the Swift Parrot, this means that researchers can identify their feeding grounds, but cannot follow them back to their roost in real time, leaving significant gaps in their knowledge.

“What will have to come to maximise the potential is the ability to fly beyond visual range, and that is very difficult within existing rules,” he says. He points out that solving the problem of drone endurance is of little use if it cannot be fully utilised. “Australian rural properties tend to be very large, and if drones are to be commercially useful to farmers, they need to be able to fly beyond visual range.”

Drone technology promises to revolutionise everything from crop management to battlefield intelligence, but before that can happen propulsion and airframe technology needs to advance to improve endurance and payload capacity. With innovations like the Triple Hybrid Fuel Cell and the T-wing, the University of Sydney looks set to lead the towards a new generation of drones that will revolutionise the lives of farmers, surveyors and soldiers.

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