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A structural battery powered drone has almost doubled its endurance in recent flight tests.
Professor of Mechanical and Aerospace Engineering Vikas Prakash – along with state government and private partners – launched an otherwise unremarkable, single-propeller fiberglass airplane into the skies at Springfield-Beckley Municipal Airport, Dayton, USA, and waited to see how long it could fly before running out of juice.
In previous tests, the same automated plane stayed airborne for 91 minutes before the batteries died. This time, with a different set of specialised wings, it kept going for 171 minutes total.
The difference: Tucked inside the 1.8 m wingspan of the 2.1 m long UAV were “structural battery” components.
That innovation, being developed by Prakash over the last three years, turns the wings themselves into an extension of the batteries powering the plane. The technology not only extends flight time and distance, but allows more room in the fuselage for critical payload.
“[Electric regional passenger aircraft] is what we’re aiming for in the long run,” said Prakash, who gained media attention in October 2017 when he was awarded a NASA grant to work toward developing more-electric regional aircrafts.
His latest work is funded by the Partnership for Research in Energy Storage and Integration for Defense and Space Exploration (PRESIDES) programme. That partnership is sponsored by the Ohio Federal Research Network (OFRN) and managed by the Great Lakes Energy Institute at Case Western Reserve. The programme “focuses on advancing energy storage and integration technologies that have demonstrated commercial viability in defense and space exploration”.
Prakash’ two-year, $450,000 project, officially known as “Hi-Performance Multifunctional Structural Energy Storage,” is one of 22 OFRN applied-research projects in the state, all of which emphasise collaboration among research universities, government and private companies.
The flight test on 22 Feb 2019 at Springfield-Beckley Municipal Airport was conducted under a Certificate of Waiver or Authorization granted to the U.S. Air Force Research Laboratory in Dayton by the Federal Aviation Administration.
Prakash and Jeff Taylor, founder and chief executive officer of Event38, an Akron-based drone company that specializes in mapping and surveying applications, led the test.
“The new structural battery system offers benefits that will appeal to our customers,” Taylor, a 2009 Case Western Reserve aerospace engineering graduate, said in the OFRN news release. “Use of this technology will open new doors to build crafts with more complex and sensitive sensors that small drones usually struggle to carry.”
Structural batteries are a great way to increase your battery capacity while reducing the usable volume of the aircraft dedicated to batteries. CBE aircraft have been doing this since the early days, with fuel tanks dotted all over the airframe but mostly in the wings. Such systems leave the fuselage mostly free for the aircraft’s cargo, but mean complex systems for shifting fuel around to engines and maintain the aircraft’s balance.
Electrical propulsion systems and batteries avoid both these problems. The wiring system to move the electricity around is less complex to install and maintain (although it may become very complex if HTS systems come online), and the weight of the batteries does not change throughout the flight, so the aircraft’s balance remains constant.
One major downside is recharging them. Current battery technology means long recharging times – longer than it takes to refuel a CBE aircraft. For an operational aircraft, turn round time is critical, and one idea to assist with reducing recharge time is replaceable batteries – you take the flat set out and put a fully charged set in. When the batteries are part of the aircraft…. well, you can’t replace the wings of an airliner in under 30 minutes.
The idea of using the battery as a structural element – although not what Prakash et al are doing here (yet) – in the airframe is popular in other fields (see this 2011 presentation on Multifunctional composite materials for energy storage in structural load paths). Automotive is looking at using structural batteries to replace body panels and also in the chassis. Aircraft have different and in some ways more critical loads to manage, which may be beyond structural batteries for now.
So a system which spreads batteries throughout the aircraft has benefits and issues. But the killer app for structural batteries: you don’t have the weight of both airframe and battery frame, and in aircraft, weight is king.