UpLift – Ground vibration test for climate-compatible aircraft of the future
- Ground vibration testing of DLR's D328® UpLift research aircraft has been successfully completed.
- The data will be used to validate and improve the aircraft's simulation model, to enable faster and more cost-effective modifications for testing promising climate-compatible technologies.
- D328® UpLift is being converted into a flying laboratory for subjecting sustainable aviation concepts to real-world conditions, to bring them into practice more quickly.
- Focus: Aviation, climate-compatible flying
The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is using its D328® UpLift research aircraft as a flying test laboratory for climate-compatible aviation technologies. Initial measurement flights using fully synthetic fuel have already proven successful. Now, the development team has successfully carried out a ground vibration test, precisely surveying the structural dynamics of the DLR research aircraft using a specially designed air support system to isolate the aircraft from the ground. The results are being used to validate forecast models that simulate the aircraft's vibration behaviour in every flight situation, meaning experimental modifications – such as new propulsion technologies – can then be implemented more quickly and cost-effectively. DLR is leading the project, contributing its system expertise in aeronautics research to help bring sustainable technologies into practice more quickly.
"The ground vibration test has enabled us to reach a key milestone in the Uplift project," explains Julian Sinske from the DLR Institute of Aeroelasticity. "We can now also evaluate upcoming modifications to the research aircraft in terms of their aeroelasticity. I am very pleased we carried out this test so efficiently and obtained such high-quality results – in no small part thanks to our new air support system."
The aircraft's manufacturer "Deutsche Aircraft" is carrying out the conversion of the D328® UpLift on behalf of DLR, with the vibration tests taking place in its hangar in Oberpfaffenhofen over a period of approximately two weeks. "The successful ground vibration test makes a significant contribution to validating and further developing the aircraft's structural models. These are crucial for the continued modification of the D328® UpLift and enable precise predictions and well-founded analyses of its aeroelastic behaviour," explains Simon Binder, flight physics engineer at Deutsche Aircraft.
Sophisticated test setup
The Institute of Aeroelasticity's test team fitted the research aircraft with a total of 237 acceleration sensors. From the sensor data, the team determined the natural frequencies (eigenfrequencies), vibration patterns (mode shapes) and how strongly vibrations are damped (fade away) across the entire aircraft structure. 'Shakers' were used to vibrate the aircraft on the ground, including components like the wings, fuselage and control surfaces, one after another.
These shakers work in a similar way to loudspeakers, but rather than transmitting sound waves through the air, they induce mechanical vibrations via a push rod fixed to the aircraft. The vibrations of the entire aircraft are then recorded by the acceleration sensors and transmitted to the measurement system as electrical signals via cables. Researchers use software developed in part by DLR to display and process the received signals and ultimately evaluate them on standard PCs.
On site analysis under optimum test conditions
To ensure the aircraft on the ground can vibrate undisturbed, as it would during flight, the D328® UpLift was mounted on a specially designed air support. The support was attached at three points under the axles of the landing gear, ensuring the aircraft was supported gently and securely, decoupled from the ground as it moved. This provided the researchers with the best possible boundary conditions for the vibration test.
The air support was procured as part of the Uplift research project and developed in collaboration with Fabreeka Germany – a subsidiary of the Stabilus Group known worldwide for its expertise in low-frequency vibration isolation. Following its successful deployment, the new air support system at DLR is now also available for tests with other research aircraft and for industry collaborators.
By assessing the data on site, DLR's test team could check in advance how consistent the experimental measurements were compared with existing simulation models. Thanks to these preliminary analyses, the researchers were able to determine whether or not the sensors were working well during the tests, if they needed to be repositioned or if certain frequency ranges still needed to be tested. More than 50 different vibration modes were determined during the vibration test, showing the specific frequency, amplitude and direction of a vibration (graphically depicted) with which the aircraft structure responds when vibrated at a certain frequency.
Swift conversion into a flying test laboratory
The results of this extensive analysis are used to validate and improve the D328® UpLift simulation model, which will significantly speed up further upgrades and alterations – turning this DLR aircraft into a flying test laboratory. DLR's Flight Experiments facility is also contributing its long-standing experience and expertise to the aircraft modifications. The project team's plans also include installing innovative fuel tanks underneath the aircraft's wing tips to test highly promising climate-compatible propulsion technologies.
"We have obtained a very valuable dataset from the ground vibration test," emphasises Stefan Schröder from the project management team at the DLR Flight Experiments facility. "On this basis, we can now proceed with the required external modifications to the wing and fuselage faster than expected."
Our sincere thanks go to all the teams involved – and especially to our collaborators at DLR. This test was more than just a technical procedure; it was a striking demonstration of what is possible when industry and applied research work hand in hand.
As a flying test laboratory, the D328® UpLift will be made available to industry, SMEs, start-ups and research institutions to test new, climate-compatible system, fuel and propulsion technologies under real-world conditions. The project is funded by Germany's Federal Ministry for Economic Affairs and Energy (BMWE). The shared objective is to significantly accelerate the practical implementation of sustainable aviation technologies.