Commercial UAV News

Model Jet Impellers Influence UAV Performance and Innovation

The Jet Effect

In December 2018, Microdrones acquired Schübeler Technologies as part of its global expansion. Since Schübeler Technologies serves a diverse and expanding client base that can influence developments at Microdrones, we like to share news of their progress, updates, and accomplishments.

Recently, Inside Unmanned Systems featured an article demonstrating how a jet model, equipped with an electric impeller from Schübeler Technologies, helped break a speed record and establish a new direction for commercial UAV innovations. 

As seen in the February / March 2020 Inside Unmanned Systems

by Vicki Speed, technology reporter

Bruno Stükerjürgen (left) and Heinz Merschbrock (right) with their tailor-made Extreme Jet aeromodel.

The jet model equipped with an electric impeller breaks the speed record and establishes a new direction for commercial UAV innovations.

Innovation in aircraft model making doesn't seem to be the forum for progress in commercial and military UAV operations - does it? In 2019, one of the world's most successful pilots in high-speed model building, Bruno Stükerjürgen, wanted to take part in one of the largest speed competitions in the scene in Osnabrück, Germany. In order to survive in the competition, Stükerjürgen's aim was to build a custom-made flight cell instead of the conventional slim design, which could exceed the seemingly unattainable record of 400 km / h for the flight speed of model aircraft.

To achieve his goal, he relied on the expertise of his aircraft model colleague Daniel Schübeler, the founder of Schübeler Technologies GmbH, a leading German manufacturer of the latest impeller drives and lightweight components, which belongs to the commercial UAV developer Microdrones.

Schübeler recommended an electrically driven impeller (or EDF drive system), similar to the fan drives used in aircraft and airplanes, in order to achieve higher flight speeds. The result far exceeded the expectations of Stükerjürgen and opened the door for the development of a new generation of unmanned commercial and military systems in which security and speed count.

Optimized for speed

Stükerjürgens flight cell was designed by a student from the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen.

Stükerjürgen supplied the parameters such as air resistance coefficient and reference area to Schübeler Technologies to design the impeller. Whether robust fans, fans, compressors or electric motors, the products from Schübeler Technologies are designed to withstand extreme conditions and demanding outdoor use, and high-tech applications such as UAVs, professional motorsport and heavy outdoor equipment offer thrust and lightweight durability.

An impeller is a jacketed axial fan with a small diameter, ideal for generating higher pressure, lower volume throughput and high jet speed. In contrast to an exposed propeller, impellers, also known as axial fans or fans, have rotor blades that are mounted in a fairing. This design is critical to the efficiency of the rotor blades (ie high thrust, low energy). Even the smallest mistake in an aerodynamic system can lead to a loss of efficiency of 30 to 40 percent.

Schübeler believed that the electrical impeller solution would be easier to manufacture than conventional electrical drive or multi-motor solutions and would offer greater agility.

For Stükerjürgen's flight cell, Schübeler worked with dynamic performance curves - which are available for every Schübeler impeller - to predict the power consumption at different speeds. The team also designed the inlet and outlet geometries, crucial elements for any optimized drive system. The design of the rotor blades was also decisive for the development of a safe and reliable system that enables high thrust with low energy input and thus longer flight times. Initial estimates showed that the DS-51-AXI HDS (90 mm) would reach at least 430 km / h with a standard engine and would consume less than 6 kW.

Stükerjürgen and Schübeler demonstrated the concept a few months later at the model flight competition in Osnabrück.

Stükerjürgen's flight cell, which was launched from a catapult, reached a top speed of 460 km / h and an average speed of 430 km / h in the train - and that with around 500 W lower energy consumption compared to other propulsion systems.

Schübeler: “The system is fast, powerful and highly efficient. We achieved an efficiency of around 65 percent, which is comparable to fast-rotating propellers for higher speeds. ”He is particularly proud that reality came very close to the theoretical numbers and added:“ Our practical results were right the first time Time with our predictions about performance and speed. We didn't need multiple development loops - that's very satisfactory. ”

Bruno Stükerjürgen's customer-specific airframe with a Schübeler EDF-compatible drive system.

EDF in the extreme range

While the Stükerjürgen project was an entertaining and very successful experiment to demonstrate that an electric impeller can power a very fast model airplane, it has proven to be much more important in the UAV area.

"Basically, we were able to demonstrate that impeller drive systems, with good integration, represent an efficient alternative to propellers," explains Schübeler. "An electrical impeller propulsion system offers more affordable energy options for unmanned aerial vehicles compared to systems with small jet engines."

According to popular belief, additional weight is required to increase the thrust of an electric impeller, i.e. to generate more power and speed. However, the Schübeler development team can tailor the impeller systems - including the optimum pitch, number of rotors, diameter, weight and balance - to any UAV flight cell and the desired flight parameters, which corresponds exactly to what they did for Stükerjürgen's flight cell. Schübeler also develops the HST® product family, which is often required by universities for wind tunnel research. For example, the impeller / motor combination DS-51HST is available in a 1100 kV and a 950 kV version.

The Schübeler team is able to predict the performance of its impeller drive systems under very precise flight conditions, even in extreme applications. A Schübeler product is even used in the stratosphere at a height of approximately 16,000 meters (55,000 feet).

"The electric impeller drive systems of the future are moving in the direction of a balanced mixture of hover flight, slow flight and high cruise speed in combination with longer flight times," announces Schübeler.

A close-up of the Impeller DS-51-AXI HDS (90 mm).

Ahead with jet speed

Schübeler and his team also focus on the in-depth development of professional drive systems for commercial UAVs. “We face thermal and mechanical challenges in these difficult applications; there is always the possibility of continuous improvement in the development and manufacture of engines, ”he says.

The long-term assignment, according to Schübeler, is to design battery-operated electrical flight platforms so well that they can complete demanding missions. He pointed out the possible use of electrical impellers as control and propulsion systems for aircraft in applications where the size is limited and high static thrusts are required, e.g. B. with aircraft that can take off and land vertically (VTOL), with hovercraft or even with controlled hydrofoils.

Bruno Stükerjürgen and Schübeler Technologies GmbH will continue to investigate electrical impellers for high-speed flight cells in 2020. To conclude, Schübeler: “Next we will develop a drive system that can reach 500 km / h, whereby an enormous increase in performance is required for the additional 40 km / h. This kind of leap in performance doesn't just come from efficiency, but we look forward to achieving it. ”

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