From Aachen to Berlin

- Faster and Cheaper than by Car

 

The electrification of transport constitutes a substantial challenge for a low emission economy. While electric cars are just on the verge of their widespread adoption, ambitions towards a sustainable transformation of aviation are also emerging increasingly. First commercial flights in hybrid-electric aircrafts are, for instance, already planned to be offered as of 2030.
Another trend we observe is a fundamental change of our mobility. “Air taxis” or small electric regional jets are supposed to serve our growing mobility needs and, for example, relieve increasing urban traffic in a climate-friendly manner. However, apart from integrating such novel concepts in our existing infrastructure, many technical challenges and open questions remain: Can electric aircrafts really provide an energy-efficient alternative? For which ranges do such systems make sense? Which pros and cons result from an electric drive train? What about noise pollution?

In the frame of our project FVA-30, we want to investigate these issues by developing a research plane designed to accomplish a defined mission with maximum efficiency and minimum environmental impact. In contrast to electric cars, a purely electric drive train for aircrafts is, however, not practical as the specific energy of current battery technologies is insufficient for most use cases (and will likely be). Therefore, we decided to develop a hybrid-electric drive concept which will be integrated in a two-seater motor glider. Our plane is specifically designed for high efficiency and low noise pollution, taking advantage of the novel propulsion system. A novel range extender is used to cover the power demand during cruise flight and shall be operated by biogas.

 
 
 

Our Concept

 
Operating Range: 650 km
This provides a useful traveling radius and additional reserves with respect to our mission profile.
Traveling Costs: < 100 €
These costs comprise fuel (methane), electricity and depreciation.
Runway Length: < 500 m
The runway length is determined by our base airport Aachen Merzbrück.
 
 
 
Speed: 150-200 km/h
Traveling speed is optimized for high efficiency.
Seats: 2
One pilot and a passenger sit next to each other.
Noise: < 60 dB-A in 200 m
This is comparable to a car in urban space.
 

Technology

 

Structure & Load Calculation

An automated load calculation tool was developed to estimate the loads in different flight phases. The aim is to compare the expected loads with other aircraft and configurations by varying aerodynamic and flight-mechanical parameters. Already in the preliminary design, structural loads in different flight phases can be estimated and evaluated. For the analysis of different manoeuvres on the ground and in the air, a specially developed load key is used, which clearly describes the flight situations prescribed by the certification.
The structural design poses a particular challenge, especially due to the unconventional tail configuration and engine position. When selecting and dimensioning the structure, the aircraft's center of gravity and the integration of powertrain components must also be taken into account at all times. A suitable structural concept is selected and dimensioned on the basis of the findings of various student projects while taking into account the expected force distribution. The front fuselage section and wings are taken from the e-Genius project.
 

Flight mechanics

The V-tail, which primarily serves as an aerodynamic control surface but also as an engine mount, is dimensioned on the basis of critical design cases to ensure flight mechanical stability and controllability. The design is optimized for the lowest possible air resistance and tested for structural feasibility. An automated tailplane design leads to optimal configurations of tailplane area, center of gravity, neutral point of the wing, tailplane lever arm, lift increase of the tailplane (aspect ratio), rudder depths and maximum deflection angles. The validation of the tailplane design is carried out by numerical simulation using a flight dynamic calculation program.
 

Propellers

In addition to efficiency, noise reduction is an important development focus in the design of propellers. For this purpose, a numerically calculated model for noise prediction was developed which is geared to the propeller drive under consideration and which is based on NASA's Aircraft Noise Prediction Program. Simulated pressure values can be superimposed for any observer position and evaluated in the frequency domain. Taking into account the frequency-dependent sensitivity of the human auditory system, it is possible to derive information about noise pollution and to optimize the propellers accordingly.
 

Battery System

The battery is made of commercial lithium-ion cells. In order to be able to meet the high power requirements during the purely electrical start, an exact consideration of energy and power density must be made when selecting the cells. In addition, it should be noted that efficiency and actually usable capacity depend heavily on the load profile selected. In the frame of the FVA-30 project, a new cell selection procedure was developed which automatically determines optimal battery pack configurations for given load profiles and operating voltage limits on the basis of public databases with manufacturer data and discharge characteristics and which provides estimates of the battery condition (current, voltage, power dissipation) at any time. Battery states are monitored during operation by a battery management system (BMS), which is redundantly structured and directly connected to the central system control via a CAN bus. Overheating of the battery due to losses is to be prevented by weight- and volume-optimised thermal management. For this purpose, a mechanically stabilizing structure with a phase change material as latent heat accumulator will be developed.
 

Drive Train & System Architecture

The placement of the drive motors on the V-tail requires very high power densities in order to maintain a stable centre of gravity. For this purpose, aerospace-proven high-performance synchronous motors and low-loss high-performance converters based on IGBT are used. In addition to the mechanical challenge of the centre of gravity position influenced by the long lever arm, effective cooling of the components and containment of electromagnetic emissions must also be ensured.
The system architecture is divided into the high-voltage network of the drive train and a galvanically isolated on-board network with a separate power supply. The drive control of the hybrid system is designed for optimum operation of the range extender, with the battery covering additional power requirements during take-off and compensating for power fluctuations during flight. Energy is also to be recovered through recuperation. A robust signal routing connects the individual components and enables a precise monitoring of the system status at any time.
 

Range Extender

The range extender is dimensioned according to the power requirement in the flight phase and designed as a Wankel engine due to the strict weight and volume limits. A particular challenge is the use of biogas as an alternative fuel, for which an appropriate tank and supply system is being developed. Reliability, efficiency, cooling, exhaust gas evacuation and after-treatment, noise reduction and positioning in the aircraft also play an important role in system design.

Implementation

 
 

The Team

 
Our team unites students of different semesters from the fields of mechanical engineering, aerospace engineering, electrical engineering, physics and computer science. We are supported by the entire FVA, various institutes of the RWTH Aachen University and our industrial project partners and sponsors.
 
 
 
 

Join us!

Are you interested in participating in this project? We always need good team members who are committed to advancing our project independently. It doesn't matter which subject you study or which semester you are in - we are rather looking for motivated people who enjoy technically challenging tasks. Simply write a mail or look every Thursday at 9pm in the lecture hall LU of the Institute of Aerospace Technology (Wüllnerstraße 7).
 
 
 
 

What do we offer you?


We give you an insight into the complete aircraft development - from the fuselage to the hybrid-electric propulsion system. With us, you can expand your theoretical knowledge and put your own ideas into practice. With our large workshop and the institutes that support us, we offer everything you need. In addition, there are regular workshops for further training with other academic aviation clubs (idaflieg), technical university groups (TechAachen) and our industrial partners. However, the FVA does not only deal with the development of new aircraft concepts - in the end, of course, we want to be able to take off with them! Therefore we also offer students the possibility to acquire a pilot licence - just according to our motto "Research - Build - Fly".
 
 

Open Positions


Structural Design and Preparation of the Fuselage Construction
- Finalization of fuselage design
- Preparation of moulds for the fuselage shell
- Construction of primary structural components (in CFRP-GFRP composite construction)

Battery Management System Development (Hardware)
- Installation of safety components and sensors
- Design of hardware interfaces on battery modules
- Practical knowledge of electrical engineering is advantageous

Battery System Testing & Certification
- Execution of profile and load tests
- Data preparation and analysis
- Experience with lithium-ion batteries as well as Python/Matlab is advantageous

 
 

Downloads

parallax background
 

Some Impressions

 
 

We thank our partners for their support!