Why are we writing about this topic:
A project where important solutions to problems are worked on with great idealism.
Drones are seen as the means of transport of the future. They can contribute to reducing traffic jams in the inner cities. You can also use them to transport emergency aid in disaster areas. The latter motivated students of the Master’s program in Aerospace Engineering at the University of Applied Sciences Wiener Neustadt (FHWN) to design a transport drone ideally suited for that purpose.
Master’s students have worked here since 2017 at Trogon transport drone. However, after countless project works and various master’s theses, the students and teachers also wanted to see the drone fly. With the help of the Modellflug Club (MFC) Weikersdorf, they succeeded in building a model. An initial test showed that the Trogon flies excellently.
The drone had to make fast, sharp turns, react to sudden changes in altitude and handle gusts. The demonstrator even withstood strong gusts of wind; a factor that can be taken into account in the design but is difficult to calculate precisely in advance. Drones with this performance are already being used in the military. However, the students at FH Wiener Neustadt wanted to boost the use of the transport drone for the civil sector.
Civilian transport drones
As a powerful drone, the Trogon can transport loaded Euro pallets up to 500 kg. And that with a maximum speed of around 350 km/h. But it’s not just the weight and speed that is remarkable – the range is also remarkable. This is up to 1500 kilometers. It corresponds to the distance between Vienna and Manchester (UK). For comparison, the Volodrone transport drone from the German manufacturer Volocopter, which is currently in the development phase, can transport a payload of 200 kilograms over 40 kilometers.
The trogon has wings with a wingspan of 14 meters and thus resembles a small airplane. The wings distinguish the planes from the more common category of drones that use helicopter-like technology. In the helicopter drone, the lift is generated by the rotor. It is controlled by rotor speed and blade pitch. At lower speed is elevator down and the drone goes down. If you want to go forward, tilt the plane slightly and adjust the rotor blades. It is mechanically a very big effort.
Drones with multiple propellers work a little differently. The usually four to eight propellers are fixed. You cannot adjust them. These actions are controlled by adjusting the rotational speeds of the individual propellers. This allows the drone to fly in almost any direction. The moment the propeller turns less fast, you have less lift and you lose altitude. This means that the drone and helicopter can only reach a limited height. The drone also has the advantage that it does not need a runway.
In the Trogon transport drone, the wing provides the propulsion. The forward motion causes air to flow around the wing, leading to lift. An effect that also occurs when you hold your hand out of the window of a moving car and turn it slightly. A force is created that pulls the arm up,” explains fluid mechanics Dr. Markus Trenker, who leads the project.
The idea for the transport drone with wings originally came from the students. The central task in the conceptual design was to create a suitable wing geometry and design the fuselage. The hull had to have as large a volume as possible so that piece goods could be delivered on pallets. For unloading and loading, the hull can be opened at the nose and driven over with a sled.
However, a large hull also creates a lot of air resistance, which must be compensated for. Therefore, the idea arose to shape the hull in such a way that it contributes to lift at higher speeds. This means that, like the wings, it generates an upward force that keeps it in the air. However, the wing generates much more lift than the fuselage. Both the fuselage and the wing have the shape of an asymmetrical drop of water in the vertical part. The wing and fuselage generate lift through their contours. This gives the drone higher speed, range and stability, as well as the ability to carry a larger payload.
Trenker: “Because of their shape, bodies that lift produce higher velocities at the top than at the bottom. As the speed increases, the pressure drops. This leads to a pressure difference between top and bottom, which, integrated over the wing surface, results in a lift force.”
The model building experts who built the demonstration model used balsa wood, which is low density and very light. As a result, the drone has a total weight – including battery and motor – of no more than eleven kilograms. Low weight is one of the most important parameters of aircraft. For transport drones, a low curb weight also allows for a higher payload.
There are several options for future control of the transport drone. Which ones it is depends on future legislation, explains Trenker. It is conceivable, for example, to program certain points in advance via GPS. Trogon then flies over it completely automatically. Since the model has a camera on board, it can also be controlled by a pilot via a remote control. To land and take off, the drone needs a flat surface, such as a meadow. As long as there is about 800 meters of level ground, the Trogon can land. The students’ goal has thus been achieved: the drone can transport goods to disaster and crisis areas. In cases where you do not want to risk the lives of pilots, such as in extreme weather conditions or during hostilities.
Between the demonstration model and a market-ready drone lies a significant capital investment, explains Trenker when asked about a possible market introduction. Furthermore, autonomous aircraft are subject to a lengthy certification process, which is also not sufficiently defined yet.
However, a new EU drone regulation was introduced on 31 December 2020. Since then, there are no more size and weight restrictions for professional or industrial use – and only a few in terms of mission profile. However, the certification procedures increase in relation to the risk factors identified for the intended use. Once a particular mission profile has been approved in one EU Member State, it is generally accepted by all other Member States.