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Boeing's Sweet Vision For SUGAR Concepts

The concept vehicles proposed could potentially enter service within 15 to 20 years.

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NASA’s Fundamental Aeronautics Program was launched with the goal of visualizing future passenger airplanes with greatly reduced fuel consumption, noise, and emissions. The concept vehicles proposed could potentially enter service within 15 to 20 years.

One of these concepts, the SUGAR Volt, is being developed through the Subsonic Ultra Green Aircraft Research (SUGAR) program, a line of research being pursued by Boeing as part of NASA’s Fundamental Aeronautics Program.

While the Volt is the current model under development, various SUGAR concepts studied throughout the process included, the SUGAR Freeze, which explored power by liquefied natural gas; the SUGAR High which featured a truss braced wing; and the SUGAR Volt with a hybrid electric propulsion system.

Besides Boeing Research and Technology and Boeing Commercial Airplanes, other companies involved with the program, include GE, Georgia Tech, Virginia Tech, NextGen Aeronautics, MicroCraft, and Tri-Models. Additionally, NASA experts were both active participants and test facility providers.

The GL-10 prototype takes off in hover mode like a helicopter. (Image credit: NASA Langley/David C. Bowman)

Boeing’s contract was awarded in 2008 with Phase I, and is funded through 2016 into Phase III. After narrowing the concept ideas, the SUGAR Volt concept was studied in Phase I and II from 2008 to 2014.

The last milestone for the SUGAR team will be conducting high speed aerodynamic tests of the truss braced wing design in 2016, as well as publishing the Phase III Final Report.

Boeing recently presented its research and development efforts at the 2015 Paris Air Show in June, specifically, the alternative propulsion systems that are being developed as part of the SUGAR concept program. “We’re building on gains we’ve made on our newest airplanes to raise the bar for our next generation of airplanes,” says Mike Sinnett, vice president of Product Development, Boeing Commercial Airplanes.

SUGAR Volt Design

The SUGAR Volt concept grew from abstract ideas paired with several realistic aircraft designs, called “vision vehicles,” that are used to focus and evaluate the technology’s development.

“We started with ideas on a white board, then progressed to back-of-the-envelope calculations, spreadsheet tools, then finally transitioned to our standard design tools for CAD, aircraft performance, structural analysis, etc., making modifications all along the way for the unique aspects of our designs,” explains Dr. Marty Bradley, Technical Fellow, Boeing Commercial Airplanes, Advanced Concepts.

Once the team had completed the vision vehicle configurations, they designed sub-scale models to test the key structural and aerodynamic performance metrics.

“The SUGAR concepts were developed by bundling together advanced aerodynamic structures, propulsion, and systems technologies, and integrating them into advanced configurations,” explains Bradley.

According to Bradley, the biggest design challenge in developing the SUGAR Volt was the aircraft-level optimization of the hybrid electric system.

“There are many design variables, including turbine and electric motor size and battery performance and size,” explains Bradley. “You are trying to minimize fuel consumption, but also energy use, lifecycle emissions, and operating cost; all the while maintaining airliner mission requirements.”

Engineers at NASA’s Langley Research Center test a 15% scale model in its Transonic Dynamics Tunnel, a unique wind tunnel for testing at transonic speeds. The 13-foot semi-span model was used to assess the aeroelastic qualities (how an aircraft flexes during flight in response to aerodynamic forces) of the truss-braced wing (TBW) configuration. (Image credit: NASA Langley/Sandie Gibbs)

In the design, the hybrid electric system adjoins an electric motor to the vehicle’s turbine fan shaft and would allow the fuel to be throttled back (or even turned off) during periods of the flight in order to reduce emissions. Energy is stored in battery pods located on the wings for an ideal weight and balance distribution.

To further increase fuel consumption through improved aerodynamics, the SUGAR Volt also features a truss braced wing that enables a higher span, aspect ratio, and lift-to-drag ratio.

“The strut bracing significantly reduces the weight penalty for increasing span, so the aircraft will optimize to a higher span and better aerodynamic efficiency than a conventional cantilever wing aircraft,” explains Bradley.

The SUGAR Volt concept’s foldable wings, advanced jet engines, and battery pods each enable reduced fuel burn, greenhouse gases, NOx (mono-nitrogen oxides) emissions, noise, and field length. Most importantly, these features have already been adapted for use in various other NASA programs.

“A lot of the results from the SUGAR study were used to help NASA define their technology research and development roadmaps,” explains Bradley. “SUGAR technologies will live on in the technology research activities in high span wings and hybrid electric propulsion that are continuing at organizations around the world.”

This article originally appeared in the July/August print edition of PD&D.

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