Flexible wings, COVID-19, and the future of commercial aviation
In the Spring of 2016, Cesnik says that he was contacted by Airbus about their desire to establish new university-based research centers, and that the University of Michigan was among a handful of others in the US that had been preselected to come to Washington DC to learn about the company’s future and needs.
After an early Fall visit by Airbus to Ann Arbor to hear the Michigan’s proposal in response to the company’s requirements, Airbus decided at the end of 2016 to enter into a formal agreement with UMich, which was signed at the 2017 Paris Air Show by Dean Alec Gallimore and Airbus officials, creating the Airbus-University of Michigan Center for Aero-Servo-Elasticity of Very Flexible Aircraft, or CASE-VFA for short, that began operation at that time.
“I believe that the reason Airbus chose an American University among all universities in the world that they preselected and got their proposals back from is because we really understood their needs and can help them reach their vision,” said Cesnik. “We responded the best to their needs, so for the first time, as far as I understand, they left the EU to support a non-EU university in a sizable way. They are doing that because they believe it to be in their best interest, and we do have an edge – not just Michigan. I think the whole American research university system has a natural connection with industry and knows how to make our work relevant to them as well. They see a clear potential for practical applications of our basic research.
I believe that the reason Airbus chose an American University among all universities in the world that they preselected and got their proposals back from is because we really understood their needs and can help them reach their vision.Carlos Cesnik, AERO
“I think that aspect was there at the beginning. Since then, all our review meetings with Airbus have been super positive. Everyone seems very pleased with the amount of progress in our studies. For Airbus, I believe this kind of engagement is very important for them. Certainly they have to continuously respond to their stakeholders, because that’s vital for the immediate health of Airbus, but for a high tech company, they also need to look in the future in terms of research and technology investments that will pay off later.” The purpose of the Center is to study various aspects related to aero-servo-elasticity of very flexible wings. The aero part is aerodynamics, the servo part is controls, and the elasticity is the structural aspects of it. The idea is to take a holistic approach to what happens when an advanced flexible aircraft wing encounters air turbulence, as well as during takeoff, landing, and in-flight maneuvers. That may seem simple, but how air moves over even a rigid wing makes three-dimensional chess look like checkers. Make that wing flexible and you need a new word for “complex.”
“Basically, when an airplane is flying, there are significant interactions between it and the air,” said Cesnik. “Its performance and characteristics are dependent on the wings. The very flexible wing comes from the need for future aviation concepts to provide lower fuel consumption and, therefore, lower emissions and lower operating costs. One of the ways to achieve it is by having lighter structures with new materials and longer wings with lower induced drag. But the mix of longer wings and lighter structures make these wings more flexible. When the wing becomes more flexible, the interaction with the air becomes more pronounced and more complex.
“From an engineering perspective, the problem becomes non-linear. That means that several of the design tools that the industry currently uses may not be applicable anymore. We need new methodologies and this is what we had been developing internally. This supports the design of this new, longer, more flexible wing.”
Dealing with these problems at the Center is primarily through computer modeling to support multidisciplinary design optimization and simulation. In particular, it involves learning how to control wing loads, including maneuver loads and the gust loads for flexible wings.
To help with this, the Center’s studies go beyond just computational methods. Cesnik’s group has designed and built a remote-controlled aircraft with a six-meter wingspan that is so flexible that it looks like a bow in flight. This allows Cesnik and his team to study experimentally interactions between the aircraft structure and these other dynamics, along with new control strategies.
The point of all of this is to support a new, holistic approach to engineering. This is because the traditional engineering “divide-and-conquer” approach does not work well with the increasing complexity of flexible wing aircraft with the various parts interacting in ways that cannot be separated from one another.
“The aerodynamics, the structures, the flight dynamics, and the controls are much more coupled, and if they are coupled, conventional designing sequences don’t get you much of a result compared to designing simultaneously,” said Cesnik. “In the past, you refined the aerodynamics. You go to the wind tunnel, you do tests, assemble the configuration, and then you go into the structure and then you optimize it. But the aerodynamics was already fixed. The outcome may not be as good as if we consider all pieces simultaneously.”
According to Cesnik, this is an industry-wide effort in bringing these whole-aircraft considerations to bear very early on in the design process. This means that before even preliminary wind tunnel tests, a new wing will already have a structural design, a controller design, and much more. This means doing a lot of design work simultaneously and doing trade-offs between different requirements. This is different from how aircraft have been typically designed.
“We don’t do this today,” says Cesnik. “We don’t trade all disciplines in greater detail early in the design process. In particular, dealing with the flight control system happens after the basic aerodynamic design is completed. We already have the airframe design. Now, we design the controller on top of it. We don’t change the size of the wing or position of the wing with respect to the fuselage when we are designing the flight control system. That’s frozen by then. So how can we actually bring in the controls consideration early on in the design cycle?”
At the Center, much of this work is being done on a fundamental or, what Cesnik calls, a low technology readiness level (TRL). That means that as the technology and computational tools being developed there matures, it’s then transferred to Airbus, who take on the task of developing these for their own products.
The impact of all of this goes beyond coming up with flexible wings. It could also be disruptive across the entire aerospace industry. Today, it takes up to 10 years to develop a new airplane, but that is changing fast.
“The goal is to cut the development cycle to a third of what it takes today,” said Cesnik. “So when I come up with a new way of doing something, I am not solving the problem of how that can be deployed in regard to the existing way a company has its processes implemented. Whenever you disrupt the design process, you also disrupt the organizational structure behind it. This is super challenging. So while we are tackling the technical aspects of the processes, you can imagine that the structure of the organization might be impacted too. Industry won’t do this out of nothing. You have to have some serious level of certainty about the benefits of the new approach.”
When we asked Cesnik what he sees the aircraft of the future being like, we got a bit of a surprise and it’s because of the ongoing COVID-19 pandemic and the measures taken around the world to respond to it.
“If we are having this conversation in early March, I could give you an answer based on what we’re doing. Today. I’m not sure if I can answer the question.
“Here’s the big issue. First, the aviation industry has been riding on a five to six percent increase in passenger demand on a yearly basis. Basically, it rides with the world GDP and the anticipation of the number of new aircraft and so forth. It drives a lot of development, a lot of sales, a large backlog of orders. On top of that, the aerospace industry has committed to seriously reduce aircraft emissions. For that, the things the Center is doing will play a significant role. Now, suddenly, all got disrupted in a very short period of time. It’s scary, but it looks like we are living through a major rescaling of our air transportation system.
“There’s a lot of injection of funds, of course, but the airlines are taking serious losses. We are not traveling. The airlines are not flying. They are not buying new airplanes. Suppliers can’t sell as much. I don’t know what the demand is going to be in the near future. How long is it going to take for us to get back to doing a normal volume of operations?
“Let’s say that we’re all vaccinated in a year or so and this becomes like the flu. Are we going to do the same amount or more of traveling that we did before? From the business travelers, it’s uncertain because a lot of them, who never knew how it would look if they didn’t have face to face meetings and the traveling involved, are now experiencing that and making it work.”
According to Cesnik, in the short term, we should see airlines running at 50 percent passenger capacity. To offset the loss, expect much higher ticket prices. Even if this happens, aircraft interiors with their close quarters would need to be heavily modified.
“How are you going to do that,” he asked. “Separate passengers with Plexiglas? How does that impact safety, evacuation? I don’t know. I don’t even know exactly if there is a reasonable solution for this while keeping passenger capacity. Moreover, what are the demands for long duration flight? The very long range flights versus the short hauls? And the size of the airplanes. Maybe the planes that are actually going to benefit from this are the smaller regional jets – the kind of thing where you have fewer people on board.”
If the industry does go to smaller, regional aircraft, it could also mean trying to reduce costs by designing slower aircraft for long-haul flights, like a hybrid electric prop plane flying at 460 mph rather than 640 mph.
“The technology of lower drag wings, lighter wings, is still going to be applicable,” he said. “I think that the kind of knowledge we are developing at our Center and the kind of advanced methodologies that we are developing are going to be applicable regardless of what configuration in the future we’re going to have. The only part we’re really not doing is the interior. We’re not thinking about how we solve the problem of packing passengers inside the airplane.”
But it isn’t all pessimism. Cesnik says that, while the disasters caused by COVID-19 are disruptive, these disruptions also lead to great opportunities. There are great uncertainties today and the situation is continuing to evolve, but this is the time for research to continue and for companies to continue to invest in that research. In doing so, companies can be ready and possess a bigger edge than their competitors when the economy starts opening up again. And it will.
“There’s a lot of uncertainty,” said Cesnik. “However, this is an investment in the future where we can actually make a difference. We still must address the high-stakes aircraft emission reduction goals if we want to continue flying people as well as goods. These aircraft have to be fuel efficient and so forth, and how we design them must be done in a much shorter turnaround time than today’s standards. Anyone in the high-tech industry knows that it is essential to continue pursuing research, development, and new technologies even during difficult financial times. It is critical for the future success of its products and of the companies. We need to continue addressing today the future challenges and opportunities that will come.”
Clarence L. (Kelly) Johnson Professor, Aerospace Engineering; Professor and Director, Active Aeroelasticity and Structures Research Laboratory