Aerospace engineering specialist at Siemens Digital Industries discusses the airworthiness challenges of the new generation of aircraft
With greater levels of autonomy and the pressures to reduce carbon emissions, the aviation industry is undergoing significant technical changes and whilst innovation is in plentiful supply, the brakes have to be applied to progress due to the high levels of regulation thatâs required in the industry and the need for multiple levels of certification including that of airworthiness.
An aerospace expert at Siemens Digital Industries Software with over two decades of experience in the field of acoustics and vibration, RaphaĂ«l Hallez, Aerospace Business Development Manager explains whatâs involved in obtaining type certification for manufacturers and whether the requirements are any different for the latest generation of aircraft to conventional aeroplanes.
Having been involved in many projects relating to the development of traditional and next-generation aircraft using a variety of simulation and testing techniques, Hallez and his team are now very active in the transition of the industry to greener, quieter and easier aviation.
Airworthiness Certification
Airworthiness certification is a mandatory step in the accreditation process of any new aeroplane or aircraft. It is a standard procedure that every aircraft manufacturer must undergo to certify that a specific aeroplane model is safe to fly within the set flight envelope. Airworthiness certification comes at the end of the development process of a new aircraft. At this stage, it is crucial to complete the certification procedure as quickly as possible. Engineers want to shrink the testing time and avoid any potential redesigns of the product in order to speed up the time-to-market.
An example of one of the steps in the certification programme is the ground vibration test, which is a structural dynamics test performed on the ground before the aircraftâs maiden flight. Since it comes at the end of the development cycle, there is a lot of pressure to complete this labour, data and sensor-intensive test as quickly, accurately and flawlessly as possible.
Ground Vibration Test
Siemens has been providing the means for the manufacturers of traditional aircraft to perform ground vibration testing for many years and the industry has become accustomed to performing such tests and getting their aircraft designs validated. Now that theyâve mastered the steps of this well-known procedure and can rely on the data obtained in the tests of predecessorâs models, they can more adequately plan, prepare and speed up their tests.
According to Hallez, their focus has now shifted to getting the tests done as quickly as possible so that costly prototypes are not immobilised for too long. They also take the opportunity of this mandatory test to obtain additional insightful data that helps validate simulation models, for flutter analysis, for example.
âWeâre constantly working on improving our Simcenter Ground Vibration Testing Solutions to help manufacturers speed up their test procedures and get more insights from it,â he says.
However, with the changes taking place within the world of aviation and given the stringent regulations for reduced emissions, many aircraft manufacturers are designing and developing innovative aircraft architectures and lightweight structures that use more composite materials.
Concerning architecture, electric propulsion systems, for example, offer more possibilities for disruptive aircraft configurations. Electric vertical take-off and landing (eVTOL) aeroplanes open new horizons for enhanced mobility. Personal or urban air mobility (UAM) concepts flourish. However, these new architectures as well as new materials bring uncertainties around the aircraftâs structural dynamics performance. They increase the workload required to validate and tune their performance, while the time constraints remain and engineers strive to meet tight programme deadlines. The issue is that they are lacking both experience and physical data about these next-generation aircraft structural dynamics performance.
With all of this flux in design, there are as many aircrafts variants as there are companies making them. The development of new electric propulsion systems and the evolution in material composition and designs are changing the industry although the stringent safety requirements remain the same. In such an environment, Itâs hard to apply any conservative rules and so more flexibility is needed in the design and prototyping phases. A safety culture pervades the aviation industry much more than it does the automotive industry, for example.
Manufacturers need to address certain issues to ensure the safe operation of next-generation aircraft and more specifically eVTOLs. Certification agencies such as the European Agency for Space and Aviation (EASA) have taken the specificities of VTOLs into account and issued special conditions to enable the safe operation of hybrid and electrical VTOL aircraft. The industry is learning every day from experimental aircraft and engineers at Siemens are closely monitoring the evolution in the industry.
Testing Modern Designs
One of the differences in performing ground vibration tests on new era aircraft is that modern aviation companies are developing very innovative designs, which are very often completely new and completely different. It is therefore impossible to rely on existing data from previous designs to speed up the certification process. On top of that, these companies are operating in a very competitive market. They donât have much time ahead to iterate on design variations. Prototyping and trial-and-error are too costly and time-intensive methods for those programmes.
When it comes to ground vibration testing, sometimes the test engineers need to adapt to a fully new configuration. They are faced with such questions as where to place the shakers and sensors to properly capture all modes of interest, which excitation force is required, how to account for non-linear responses into account and How should the tests be documented to ensure successful aircraft certification.
Digital Twins
The use of digital twins allows companies to fly an aircraft before it is built. This means that there are savings in cost and time on demonstrators and prototypes. If it were possible to certify a digital twin for its airworthiness, additional time and effort could be saved but the certification process still requires acquiring a large portion of physical data on prototypes or first models. Only a portion of the process can rely on simulations.
Next-generation aircraft manufacturers build actual demonstrators to experimentally verify and validate the performance attributes of the aircraft. Today, a certification process cannot rely exclusively on the digital twinâs performance either for traditional or for next-generation aircraft. Despite this, the use of digital twinning technology yields considerable time and cost benefits in new aircraft development and testing.
The tight integration of test and simulation tools (pre-test) is even more critical when it comes to designing and developing innovative aerial vehicles. This integration helps to better address the unknowns linked to the usage of new materials or to innovative configurations. It also helps to de-risk the test. Simulation, for example, is essential to pre-empt any testing issue by supporting careful test preparation in the pre-test phase. This is just one example of the many advantages of the integrated test and simulation approach that can be taken with tools like Simcenter.
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