Welcome to this course on Aircraft Design. My name is Mirko Hornung. I'm the Head of the Institute for Aircraft Design at the Technical University of Munich. At the same time, also Executive Director of Research at Bauhaus Luftfahrt and research organization for Long-term Development of Aviation. My main industrial and research background is aircraft design which will also be the main topic of today's course. The dedicated title is Collaborative Aircraft Design. We will take a little bit into what specific on those two elements. Collaboration, at the same time as aircraft design. I will try to show it to you on some dedicated examples. The key design challenge of an aircraft design, is really to find a concept of an aircraft in the very initial phase. So we take for example, the A350 as one example of a long range passenger aircraft. We have dedicated options. How to design the aircraft. What you see, is the final product. But in the initial phase, you have to decide, is it like that? Like the competitor aircraft, the Boeing 787 or the A350. On the first look to the configurations, they look very similar. But in detail, there are huge differences in how you do the technical detailed design. But even more, in very early phases, these are not the only solutions, you can even consider a radical different configuration like you see on the Concord. So I'm looking to supersonic aircraft that could also be a viable solution. This is the design challenge you have to face at very early conceptual design phases where you have to settle the characteristics of the aircraft on that overall configuration. So going to a very old chart which is sketching a little bit the problem that we're facing in early design. So we have to consider a lot of details to get to know the final solution of the aircraft without having all the tools and measures in place really to get the details at very early phases. So the general problem is implementary design, we have a lot of know-how assembled by a variety of experts contributing to an aircraft. So this is a phase where you already know a lot of details about the general configuration. So generally sketch of the aircraft is available. You can split the work to the a lot experts that provide you the data to derive with good performance data to get an assessment of the aircraft itself. Nevertheless, the initial phase to come up with the right concepts, you are in the very early phases of the phase. So what you have to rely on limited information and to do the selection and to fix the concept already. So this, has a high flexibility but they has a high-risk of unknowns that you don't have the expertise at hand ready to do the right selections. So what you try to do now with more digital models and tools that are available to shift that knowledge base forward. So what we want to do, is get more sophisticated tools and know-how of the experts into the process at very early concept definition. So this is the target and we'll see some of the problems that arise with that and how we have to tackle that in a collaborative manner. So the aircraft design process itself. So before we go into the dedicated problems in doing aircraft design today, especially if you have multiple stakeholders involved, we have to spend a few minutes on the aircraft design process itself. So how does it work? So in January, you have a dedicated customer requirement basis. So this is about coming from market forecast, identifying which characteristics like number of passengers, range, and also destinations you want to fly to. Do specify the basis for your aircraft design. At the same time, you also have a set of technologies that are currently in research which might be viable to be inserted into a new aircraft product. So what do you do, is you started iteration to see between the specification. So the top level requirements and possible concepts of the aircraft to find the best trade off between rows. So we're looking for the compromise on the technology side with respect to requirements you want to have. So this is coming to the point where in roughly this phase over here, where you just stepping into the preliminary design, you have that concepts, one or two concepts frozen. So this is a general layout of the aircraft configuration that you want to concentrate on. So going into the phase of preliminary design, this is more or less the phase where you're in working on specifications. So this is where you try to define all the details of your different components, sub-parts, engine, landing gears onto a dedicated detail where you can start the development later on. So we have to differentiate between conceptual design, where you are laying the foundation of basic concept of the aircraft and then specifying it onto the details. The problem is that only in preliminary design, you have all the information available to see if you initial concept really worked out the way that you want to have it. Then you go into detailed design. So this is really getting down to the nuts and bolts, where you do all the sketches of detailed manufacturing sketches to support the initial production of the aircraft. So this is the different phases of the air craft design process that we have to tackle. What we're now trying to do, is to somehow combine the conceptual design with the preliniminary design if you want to shift knowledge from the expert level to early conceptual design phases. This is what we want to tackle in that. So how does it work? So we are starting from design requirements. I'm looking at the available technologies and do concept sketches. It's still like in the old days where you just take a napkin and start to sketch some aircraft configuration which you do as a baseline. Now you do it with modern tools, but nevertheless, it's still the baseline. You come up with an idea where you do some initial configuration stuff. You do an initial sizing. Sizing in that context means that you try to scale the aircraft tool in size where does fulfill exactly the mission requirements that you want to have. Then you go in that initial layout and try to work through the different disciplines. This is all the characteristics coming from aerodynamics structures, which means in the end weight, which is driving the performance of the aircraft and the propulsion system, which has a big contribution to the overall performance of the aircraft. Then you try to bring all the elements or the description of the configuration together with the sizing and the performance optimization. So once you have somehow settled and scales to dedicated configuration, which does fulfill the Requirements, you are still at the top level of the knowledge of the different disciplines, which means aerodynamics, unstructured design, and also on propulsion, and engine sizing. Then you have to go into more detail estimations of all the different disciplines. So you go into a revised layout and then you're digging much more deeper using more sophisticated and high fidelity tools and methods to grow the knowledge about the different disciplines to mature the overall concept of the aircraft. So finally, you end up on unrefined sizing and performance optimization, where you come with a more mature concept of that phase. But this already includes that you have to insert. Especially in this process, the expert know how from the different disciplines. This is what we have to tackle in an overall digital design process to feed in these models and know-how into that design process. So how does it really work in a sequence? Most of the aircraft design processes in that initial assessment do look quite similar. So once you have an aircraft design, you really start with the geometry. So this is always the baseline. So this is why still today you start with sketch of the configuration. Today it's much more sophisticated than past, but nevertheless, it stays the same. Out of the geometry, you start to define and specify your aerodynamics. You start with very low fidelity models in the beginning, and then you dig much deeper by using higher fidelity in later phases. Then you have to estimate the propulsion system over here, where you have to gain thrust data at the same time, which is very distinct and very important for the design is the fuel flow, because this finally derives your mission, fuel requirement, and describes definitely the weight of the aircraft. This is followed by the weight estimation where you have to do the structural layout or why you start with semi-empirical estimations of how the weight distribution in very early aircraft contributions looks like, and then you have to go back into aerodynamics because out of the weight assessment, you get your center of gravity. Just with the center of gravity, you are able to see which stability margin your aircraft has, and you are able to trim the aerodynamic datasets all over the mission performance and to get all the data that you need. So at the end of this assessment phase, you will get all the different data that will allow you to estimate your performance of the aircraft. So you'll have the aerodynamic datasets, you have the weights, you have the thrust, and you have the fuel consumption of the configuration, all in a consistent manner before you do the performance assessment phase. So here in the lower part of the chart, you take a look at the design performance using on one inside dedicated points, which might be due to certification aspects, and you also take a look at the design mission. This gives you finally the feedback, how much mission fuel you need to perform the mission, and this is an indicator on how well your aircraft is efficiency wise in the overall design. Nevertheless, what you also do in that design process, you'll also assess different off design emissions and of design performances, and to also see how robust is your configuration to get through [inaudible] design. So this is the overall process where we have to separate in two blocks. The one is describing the aircraft, the configuration with its characteristics like aerodynamics weight, and also the propulsive forces. The other one is the assessment with respect to the dedicated mission the aircraft has produced. So these are two blocks that we have to do and they are more or less independent of each other. So what do you do in the different phases is you start with the design space exploration. So this means you want to do a lot of trade-off investigations of multiple concepts using multiple technologies, which means you have to be fast. You have to have fast tools that allow you to sweep through all the different possibilities that you have to come up with the best compromise of the different elements in there. So this is where classical multidisciplinary optimization plays a role and more generic semi-empirical methods are used to keep the speed in the process because once you insert higher fidelity tools, it will take much longer to get to a dedicated results of the different parameters. So out of that, you define initial concepts. Out of the initial concepts, you do an evaluation, which is the best compromise and you come up with reference design, which is your baseline solution. Just from there, you now start to use much higher fidelity methods to get into the details and to mature the design in its characteristics. So you're looking to aerodynamic structures, but also systems beside the propulsion system and also mission systems that also play a role if we're not only talking about manned passenger aircraft, but also like unmanned systems as we see them today. Finally, you do with all the details that you now have available and those details can even go up until wind tunnel testing or really testing results of different disciplines, you do the scaling and optimization, which doesn't mean that you change the overall configuration anymore, but you're trying to match the size of the aircraft that it just fits the mission performance that you want to see of the aircraft. Finally, you have to bring it all together in a visualization where you have all the details visible because this in the end defines the overall concept of the aircraft. What is the problem with that? Once we start in the conceptual design, so with very fast MDO based processes to come up with a possible configuration. We are on that phase 1 according to that chart. So we are working with very rough descriptions of the overall configuration. So we have many parameters like length of the fuselage, diameter of the fuselage, the span of the aircraft, the aspect ratio of the wing, and so on. So it's very high level where you can easily address simple formulas like semi-empirical methods, but also simple numerical models to specify the characteristics of the aircraft. This is very fast, so you just take a couple of weeks or months to come up with initial concepts really to be the baseline of your design, and then once you go into the next phases, you get to much more details so the complexity drastically increases. At the same time, the fidelity of the individual tools and methods that you apply is also increasing, and therefore also the time that it takes. So you see the phase 2 where we talk about preliminary design, we are talking about a couple of months to even one or two years, where you do detailing of all the subsystems in these elements in the aircraft. In the phase 3, where you do the detailed design, this is really about structure layer buildup and also how you manufacturer dedicated part. So this is in most of the cases on the final design side itself. So we'll concentrate just on phase 1 or 2. But even in that phase, you have the problem that you have on the same baseline configuration. Now, you have to insert more sophisticated tools and models to mature your design. You don't want to lose the data that you hatch with the initial phase where you did just the estimation with rough models or with initial low fidelity tools and methods. This is what we have to take.
