Fly like a bird, hover like a bee

William Thielicke loves flying ‘micro air vehicles’ (MAVs), small helicopter-like aircraft that he designs and builds himself. And on 31 October, he will be awarded a PhD by the University of Groningen. His thesis reveals the secrets of avian wings. These are special because they not only allow birds to fly efficiently at higher speeds, but also to hover and manoeuvre like insects.

The six-rotor ‘hexacopter’ in the YouTube clip looks like a big black beetle. In the next scene, we see blades of grass from the beetle’s perspective before it takes off and treats us to a rollercoaster ride through a park. Right at the start of its flight, it passes a strange-looking guy wearing video goggles. This is William Thielicke with the control unit for his ‘GEMiNi’ hexacopter. The images from the camera on the ‘copter are transmitted in real-time to the video goggles, allowing Thielicke to manoeuvre with great agility.

His multicopters ( helicopters with more than one rotor) fly through parks and buildings, and he has won an impressive number of MAV competitions. Although it may seem like a strange hobby for a biologist, it’s not, as Thielicke explains. ‘I have long been interested in biomimetics, the science that takes its inspiration from nature to come up with new technological solutions.’

He built a robotic fish as an undergraduate at the Humboldt University in Berlin and TU Darmstadt, and his Master’s thesis (partly completed at the University of Groningen) focused on bird flight. ‘We wanted to find out why birds can fly so incredibly well, and how they can both fly efficiently at high speed and perform extreme manoeuvres at a lower speed.’ This question also formed the basis of his PhD project at the University of Groningen and the Biomimetics Innovation Centre at Bremen University of Applied Sciences.

‘Scientists already have a pretty good idea of what allows birds to fly efficiently’, explains Thielicke. This has been thoroughly investigated. Basically, a bird wing uses the same aerodynamics as a fixed wing on an airplane. The difference in air velocity above and below the wing creates low pressure above the wing, which provides lift.

‘But little work has been done on birds when they are flying slowly or hovering. In my research for my Master’s thesis, we found evidence that slow-flying birds benefit from similar aerodynamic mechanisms to those of insects.’ During the downstroke, vortices are created at the ‘leading edge’ on top of the wing. These leading edge vortices (LEVs) create the additional lift that is required for slow and hovering flight.

Thielicke tested the aerodynamics of slow flight by placing a simple model of a bird wing in wind and water tunnels. A special system generated 3D images of the air flow around the flapping model wing. ‘We showed that the base of the wing acts in a similar way to a conventional airplane wing, but that towards the tip, where the wing becomes thinner, prominent LEVs are created during slow flight.’ Birds can adjust the wing to harness the features of the base or the outer part according to the situation. This is mainly governed by the ‘angle of attack’ of the wing and the shape of its sections, which helps to explain how birds can effectively switch between flight modes.

In his thesis, Thielicke used the results of his study and his experience as an MAV designer to create a flapping robot prototype with wings inspired by those of a swift. Such mechanical birds would make ideal search and rescue drones. ‘The challenge is to arrive at an incident quickly and efficiently, and to perform a detailed search once you are there.’

A small helicopter is well suited to search rooms, but is not very efficient on long flights, while a fixed-wing plane can reach the site of an incident rapidly, but doesn’t have the manoeuvrability to search a collapsed building. ‘A flapping MAV would combine both.’ So, is he itching to build one? He laughs. ‘Sure, but that would still require a lot of effort and expense.’

Thielicke already has some expertise in search and rescue missions: he recently won second prize in an international competition organized by Delft Technical University. ‘It was held in a training village. We had 30 minutes to localize several houses, fly into them, identify several objects, land on the roof etc. The tasks were pretty challenging, and on top of that, it was rather windy.’

Since finishing his PhD project, Thielicke has taken a break from academic research to join the consumer electronics company TobyRich GmbH as an MAV designer. ‘For me, it is also very important to stay in touch with the real world and apply the findings of my research.’ One of his earlier designs has been licensed by a Swiss company. The days when everything he made was purely open source are coming to an end.

‘When I started designing MAVs in 2007, there was a lively community of enthusiasts who would all work together. But now that there are plenty of MAVs available off the shelf and people are making money from it, things have changed.’ But if you are interested in building your own multicopter, you can still visit Thielicke’s website.