With the current fleet of 50-seat regional turboprop airplanes beginning to age, why not seize the opportunity and design their replacements with a hybrid-electric propulsion system to minimize carbon emissions? That was the crux of the 2023 challenge from AIAA’s Undergraduate Team Aircraft Design Competition—a challenge which was met and awarded with first place by an aerospace engineering senior design team from the University of Illinois Urbana-Champaign.
Turboprops have a reputation for a slower, bumpier ride than a jet. Team Jackalope lead Stephanie Dutra said they wanted to design a plane that would be “an alternative that wasn’t a downgrade. It could replace those 50-seat jets with an aircraft that has a smooth experience and has reduced emissions due to the turboprop engines and batteries.”
Dutra said the team began researching designs by looking at aircraft that are similar in class and size and creating a timeline.
“In our initial historical analysis, the Fokker 50 and the Dash Q300 were about the same size and with about a 1,000 nautical mile range required by the competition,” Dutra said. “We based some of our early sizing on those planes, then reran our analysis and sizing to make our own plane. But the Q300 had its origins in the ‘80s and even the newer turboprops haven’t changed much. We’ve just been remaking the same plane. We wanted to show that Bounden is a new aircraft and not just reproducing old technology.”
A big part of the new technology was AIAA’s requirement that the aircraft use hybrid-electric propulsion.
“None of us had experience with hybrid designs, so that was a level playing field for all the teams,” said team lead Stephanie Dutra. “All of the sizing work we’d done on previous class assignments were all fuel-based. We didn't know how to do it for batteries, so it took all of the teams longer to get to the first design review. But it helped that all of us were working on the same problem together and could cross-check our numbers matched even though we approached it in different ways.”
The AIAA requirements also specified a minimum cruising altitude of 28,000 feet, which is higher than most turboprops on the market.
“We needed to make sure we had enough power required at that altitude but calculating that for a hybrid aircraft is a different process that complicated sizing the propulsion system. We had to figure out not just how to design a conventional plane that hit all of these requirements, which would already be a challenge, but then, on top of that, to make it hybrid—how to size an aircraft, how to split our power such that we are drawing from a battery, but also from fuel,” Dutra said.
Dutra said another technical hurdle came late in the process when they decided to add a truss to support the wing, allowing the plane to have a higher aspect ratio with a longer wingspan.
“Aircraft manufacturers are doing research on trusses, but there isn’t a lot of information about it available online yet. We chose to add the truss because we wanted to do something unique and to challenge ourselves, but it meant a total and rapid redesign in March. We knew the truss would set us apart, but it wasn’t about winning the competition for us. We wanted to produce something we were proud of and make it the best it could be.”
In addition to being a truss-braced aircraft and hybrid, Bounden’s avionics considered the future of autonomous flight—another aspect of AIAA’s proposal. Avionics was Dutra’s secondary role on the team and an area in which she already has industry experience, having worked two summers on the avionics team at Collins Aerospace.
“Autothrottle function is standard in jets, but not in regional turboprops which also have condition levers for each engine. We started thinking about how to organize the power quadrant since it required additional controls due to the two electric motors onboard. We brainstormed various ways to design these controls that provisioned for future autonomous operations while also limiting an increase in pilot workload for current operations.”
Senior design is a two-semester course, and although AIAA’s proposal is available in August, the class teams don’t begin working on the problem until the second semester. Dutra said Professor Jason Merret, who teaches the class, tailors the homework assignments in the first semester to areas that are relevant to the competition.
“We had a project in the fall to research and give a presentation on electric aircraft. He integrated that into our assignments to start exposing us to the things we have to think about next semester.”
Through those first-semester assignments, Merret teaches the basics of aerodynamics, performance, structures, mass properties, etc.—everything they need to know to get started.
During the second semester, Merret and the class teaching assistants met with all of the leads in their particular discipline as a group so they can be mentored in detail and learn from each other. That was true for the team leads as well, to provide guidance on any leadership issues that arose.
Dutra said everyone on her team got along with each other, which made the work easier.
“With any project there are ebbs and flows for different members. Some have midterms that other people don't, or a personal emergency and they fall off for a little bit. When that happened, no questions asked, everyone stepped in to take on their work and make sure we would get it done. Everyone was very considerate and communicated well.”
Dutra stressed that although her team won and they were excited about that, they couldn’t have done it without the support from Merret, the teaching assistants, and the other teams.
“It was such a hard problem, and it was a huge benefit to be able to work with each other constantly, giving and getting feedback about our numbers. And even when we had very different designs, we gave each other recommendations on how to move forward and make them better.”
The other team members and their responsibilities were as follows: Noor Ansari, performance, acoustics and emissions; Evher Benjamin Aponte, aerodynamics and stability and control as well as landing gear; Hsien-Kuei Chang, structures, loads and dynamics and maintenance; Sarah Erne, propulsion and certification; Anish Joshi, systems and configuration; and Krishna Modi, mass properties and cost.
For a full list of this year’s winners, visit AIAA’s website.