FVA 29

Electric sustainer for our ASW-28

Since gliding is very dependent on the weather, good planning is essential before any cross-country flight. However even the best preparation cannot always protect the pilot from decreasing thermals. This often leads to to a so-called out landing. This is exactly where our electric sustainer comes in. It allows the pilot to avoid an out landing and return safely to the home airfield. Compared to conventional non-electric sustainers, it offers additional safety, reliability and lower emissions.

Background and motivation

Conventional sustainers with combustion engines require a high degree of concentration from the pilot during operation Even minor errors during use or inadequate maintenance can lead to a total failure of the system. failure. This situation poses a high safety risk, as home-return aids are primarily used at lower altitudes to enable continued flight despite the lack of thermals.
Through the use of an electric powertrain and a simple and intuitive operating concept, the described risks are minimized. at the same time, the FVA 29 achieves through aerodynamic optimization of the components - especially mast and propeller - and the explicit design for the required operating point, the FVA 29 achieves an overall efficiency of more than 70%. This will enable a range of a theoretical 120 km at a climb rate of about 2 m/s. In addition to making a direct contribution to increasing flight safety, the electric homeward bound aircraft is also expected to provide insights into the use of electric motors and batteries in small aircraft.

Development history

2021

  • Testing of the transition battery for in-flight use: charge and discharge cycles as well as safety tests
  • Functional Hazard Assessment (FHA) and System Safety Assessment (SSA) for the electric powertrain and primarily the traction battery.
  • Optimization of the kinematics Improvement of the functionality, installation of motor mount S/N 2 with low manufacturing distortion as well as correction of the mast, replacement of bushings and screw connections
  • Components and approval

    In addition to the structural components, the operational reliability of the entire powertrain must be demonstrated. For this, a battery testing program and a ground testing program have been established. More systems will be tested in stages during the test, before the full flight test program is finally flown. For example, the successful completion of ground testing enabled the first exit and entry tests at the idaflieg summer camp. The individual components are listed below, along with the associated verification and required testing.

    Battery

    Due to difficulties in implementing the cell bonding concept, an alternative battery concept based on cells of type 38.140 S of the manufacturer "Headway" is used, which is constructed from LiFePo4 cells. With a similar battery of the same modular LiFePo system, we did some ground testing of the FVA 29 successfully. For implementation in the motor box of the FVA 29, the number and arrangement of cells must be changed compared to the previous "laboratory battery". the number and arrangement of cells must be changed. The drive battery is the energy storage device in the electric drive train. It is used exclusively to supply energy to the electric motor.

    Battery box

    The battery box is designed as a black box that must not allow any objects to escape in the event of a crash. For this purpose, it must be able to absorb the total mass of the battery for all load cases and also reliably transfer these loads to the fuselage structure. The box is made of CFRP with insulating GRP layers inside and outside. The box is mounted on three fittings that are bonded to the fuselage of the FVA 29.

    Vibration and flutter behavior

    Are there changes in the vibration behavior of the aircraft when the engine is extended? This question was answered with a static vibration test. By simulating the corresponding assumed masses and excitation of the glider excitation of the glider, the reactions are checked and natural frequencies determined.

    Mast

    As a structural component, the mast must be able to withstand the applied loads without breaking. No plastic deformations may remain during a load test. For this purpose, crash accelerations of 15g must be withstood. In addition, the innovative design of the single mast is particularly resistance-efficient.

    Propeller and propeller brake

    The propeller must meet the structural requirements. The aerodynamically optimized propeller drives at the operating point of 100 km/h with best climb performance. If, due to a fault, the electrical braking force is not available due to the holding torque, windmillling must be ruled out. For this purpose, the mechanical propeller brake provides a sufficiently large braking effect for flight operation.

    System Safety Assessment (SSA)

    In order to represent sufficient safety for flight operations, a failed system must not pose a hazard. To this end, it is indicated, on the one hand, in accordance with the report on design and construction, that already aviation-proven methods and experiences are practically implemented for the design. The SSA primarily reviews the safety functions of the battery system and analyzes failure chains for severity of impact.

    ECU cooperation

    Cooperation on the development of a control unit for the electric drive train with Prof. Mysliwetz, Rosenheim University of Applied Sciences

    In a scientific work the control unit, (Engine Control Unit (ECU) or EAGLE Control Unit), was developed. Under the name EAGLE, the Rosenheim University of Applied Sciences, together with the RWTH, is preparing the further development and testing of the software for the cockpit instrument for integration into the aircraft and for flight certification. The cockpit instrument is being prepared for integration into the aircraft and flight certification. The system state machine controls the start-up and shutdown of the propulsion system. Compliance with MISRA-C:2012 development guidelines was also required for all developed source code. Algorithms for estimating the charge and "state of health" of the propulsion system's lithium battery were also evaluated in the process

    ECU Interface

    The Engine Control Unit is the so-called EAGLE Control Unit of the EAGLE project of the FH Rosenheim under the direction of Prof. Dr.-Ing. Birger Mysliwetz.

    Description

    This consists of a 36x48mm color LC display in the center, two blocking toggle switches in the upper right corner, and a rotary knob with a push button in the lower right corner. The upper toggle switch is called the Up/Down switch, it specifies with its position in which state the system should currently transition. If it is up, the system will start to extend the motor, if it is down, the system will start to retract the motor. The rotary knob is used to navigate in the software and to select the speed, the push button function is used to confirm inputs and messages. The middle toggle switch is reserved for later use and is currently not wired. The display shows the status data of motor and battery. This includes the speed (RPM), voltage as well as temperature values. This gives the pilot the correct overview of the system status.

    Subproject: Structural Health Monitoring

    Structure Health Monitoring (SHM) is a relatively new and important area of research in the context of fiber reinforced composites. The main reason for this is the increased difficulty in detecting damage to FRP structures. While plastic deformation is a clear sign of damage in metallic materials, such visible deformation in fiber reinforced plastic (FRP) materials does not occur until final failure. The original damage, which in metals would result in dents or the like, in FRP materials leaves only white fractures that cannot be seen through the paint, but still represent a similar sign of a weakened structure. In previous calculations, therefore, a damaged structure is usually assumed in order to use large safety factors to determine the thickness of the required FRP layer. This leads to unnecessarily heavy structures and reduces the efficiency of FRP materials enormously. This problem is to be solved by SHM. Different methods are used to detect possible damage, in order to be able to assume that the structure is intact during constrcution.
    The Institute for Structural Mechanics and Lightweight Design (SLA) at RWTH Aachen University and the FVA cooperated from 2017 to 2020 on the practical application of SHM in aircraft. The first research results of the institute were to be brought to the first flight application. The mast of the FVA 29 was chosen as the test component.
    Piezoelectric actuators were bonded to the insides of the two half shells of the mast for this purpose. These actuators provide different voltages depending on their vibration and deformation. This electrical voltage is then measured and can be converted into actual deformation or mechanical stress to detect the load or possible damage to the shell. Unfortunately, a first flight of the "SHM mast" could not be carried out during the project period, only ground tests were possible.

    Questions? Join us!

    Do you have questions about the project or would you like to join us? Then just write us anemail or meet us at the weekly meeting. It doesn't matter which subject you are studying or which semester you are in. We are always looking for motivated team members who are committed to take part in our project independently. With us, you will get exclusive insights into aircraft development and can gain experience in aviation alongside your studies. We are looking forward to you!

    Project lead

    teflon

    Emil Pluta

    cc

    Lucas Schwarz

    News

    Structure Health Monitoring (SHM) of the FVA 29 Mast
    Structure Health Monitoring (SHM) of the FVA 29 Mast

    For about a year now, the FVA is cooperating with the Institute of structural mechanis and lightweight construction (SLA) at RWTH Aachen University.

    ILA 2018
    ILA 2018

    Last week, the FVA presented their progress in cooperation with other Akaflieg groups from Germany at the ILA Berlin Air Show.

    FVA 29 pole: Succesful load experiment #2
    FVA 29 pole: Succesful load experiment #2

    Back in January, we conducted a first test run of the load experiment with an early model of the pole.