TECHNICAL VIABILITY

As this concept combines many different technologies and new ideas into one VTOL, these ideas have to be validated thoroughly in terms of safety, weight impact and economic impact. What you can see in this concept are many ideas with advantages and also technical challenges.

To get a better understanding of the technical functionalities, we published some information of our technical development for you.

WHY HYDROGEN?

Despite the fact that kerosene is the most appropriate fuel for aviation, we should think about new possibilities for a more environmental friendly aerospace industry.

The question is, what is the best propulsion technology for VTOL aircraft?

The current battery technology offers good energy densities for electrical cars already (0,5MJ/kg). Electric VTOL can also fly with today’s battery technology, but for a real commercial use-case, the energy density needs to be higher (minimum 2 MJ/kg).

Hydrogen has a much higher energy density (120MJ/kg). Including the weight of the pressured hydrogen tank, the energy density of hydrogen can be 15MJ/kg. On this aspect, kerosene has almost a three times higher energy density (43MJ/kg excl. storage) than the hydrogen storage system and would be better suitable for aircraft.

To effect a compromise between an environmental friendly and a technically realizable aircraft, the only real solution for now is the combustion of hydrogen. Hydrogen does not perform as good as kerosene, but it is still good enough for designing a large VTOL aircraft.

One advantage for direct combustion of hydrogen is the relatively low weight, compared to other propulsion systems and the low effort for adapting state-of-the-art combustion propulsion systems.

Below you can see some graphs. (Data source: Calculations from Martin Etzl)

VTOL CAPABILITIES

TILT WING DESIGN

There are different methods for an aircraft to start and land vertically. For this concept, we decided to design a tilt wing aircraft. The main reason for a tilt wing design is the good forward flight capability, combined with the capabilities of vertical starting and landing.

The wings are double-deck wings with the propulsion units in between the wings. This design allows to have wings with integrated propeller ducts.

Is this specific tilt wing design a good choice for an aircraft?

As it would be necessary to have expensive, heavy and technically critical wing-to-body suspensions, this tiltwing design might not be the best choice for a VTOL-aircraft. However, this design might offer some interesting ideas for future concepts.

DIMENSION OF THE ROTOR DISC AREA

The projected area of the impellers has to be as high as possible for an efficient vertical take-off and landing as well as small enough for a fast forward flight. Therefore, different settings were calculated thoroughly to find the best configuration for the concept.

RANGE AND FUEL CONSUMPTION

To find an optimum between range and fuel consumption (at a higher fuel capacity, the weight and so the fuel consumption increases), this graph was created for visualizing the non-linear characteristics and choosing the right size of the hydrogen tank.

FUSELAGE SPACE CONCEPT

The hydrogen volume problem

Hydrogen has a very low density, even in compressed or liquefied state. On the one hand, it is necessary to save volume (by pressurizing the hydrogen), and on the other hand the hydrogen tank must not be to heavy (by keeping the pressure low).
The best performance for an aircraft will be reached at a pressure between 30 and 40 MPa.

For this aircraft concept it is necessary to store 200kg usable hydrogen. To do so 10 m³ of spherical or cylindrical tank volume are necessary. The tanks are positioned in the rear of the aircraft, so that the total aircraft mass is balanced and the center of gravity is in the right position. With this configuration, unfavorable tail-heavy or top-heavy loading conditions will lead to an additional power demand of no more than 10% on the main wings or canards.