US Air Force Approves New Green Aircraft Demonstrator Project

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The US Air Force has been pushing the sustainable aviation fuel envelope since the early 2000s, with mixed results. Apparently they are tired of messing around, because they have just conferred official X-plane status on a new green aircraft demonstration project aimed at slashing fuel consumption by 30%. Spearheaded by Boeing and NASA, the new project is the first Air Force designated X-plane to focus on sustainability since the program first began in the 1940s.

Green Aircraft Demonstration Project To Focus On Single-Aisle Fleets

X-plane is the Air Force designation for aircraft devoted to testing and validating revolutionary new technologies. NASA’s Armstrong Flight Research Center in Edwards, California has been the key testing site for X-planes since the 1940s.

The newest X-plane, dubbed the X-66A, will sport a new fuel-saving wing configuration called a Transonic Truss-Braced Wing (TTBW). NASA and Boeing have been fine tuning TTBW technology over the past 10 years or so, and they are finally ready to develop a full scale version for a test flight.

NASA announced the funding plan for developing and flight-testing the TTBW aircraft last January. The project won’t come cheap. NASA puts its investment at $425 million over the next seven years, with Boeing and its partners chipping in another $725 million.

As an X-plane project, the demonstration will not result in a new bespoke green aircraft built from scratch, but it will produce technologies that can be applied to others. With that in mind, the project applies TTBW technology to single-aisle aircraft, which NASA describes as “the workhorse of many airline fleets.”

That may sound rather unambitious, but NASA estimates that single-aisle aircraft account for almost 50% of all aviation emissions globally, because of their heavy usage.

The plan calls for Boeing to convert an existing MD-90 single aisle jet, which is undergoing “extensive modification” at the company’s facility in Palmdale, California. The MD-90 jet was developed by McDonnell Douglas in the early 1990’s, prior to its merger with Boeing in 1997.

What Is A Transonic Truss-Braced Wing

Back in 2009, CleanTechnica took note of a US Air Force Academy project that involved a new application for winglets, a 20th development in green aircraft technology that reduces drag by giving a slight upward tilt to the ends of airplane wings.

The TTBW project will go a giant step farther to improve drag reduction along the entire length of the wing.

“The Transonic Truss-Braced Wing concept involves an aircraft with extra-long, thin wings stabilized by diagonal struts,” NASA explains. “This design results in an aircraft that is much more fuel efficient than a traditional airliner due to a shape that would create less drag — resulting in its burning less fuel.”

The technology looks futuristic but NASA anticipates near-term results, with NASA’s Aeronautics Research Mission Directorate confirming that TTBW technology has a “clear and viable path to informing the next generation of single-aisle aircraft.”

NASA anticipates that TTBW engineering will be adopted by the new aviation industry in the 2030’s, leading to a 30% cut in fuel consumption with an assist from additional new technologies related to propulsion, materials, and systems architecture.

That’s just the first step. The ultimate goal is net-zero carbon emissions from the aviation industry by 2050, as articulated in the Biden Administration’s Aviation Climate Action Plan and the International Civil Aviation Organization, too.

US Air Force Taps Green Aircraft Of The Future For X-Plane Status

The TTBW project took a big step forward last June, when NASA announced that the official name of the new green aircraft is X-66A, making it the newest demonstration project to attain X-plane status from the US Air Force.

In terms of the Air Force’s record of X-plane designation, X-66A is a really big deal. NASA has been testing X-planes for almost 80 years, since the 1940’s, and the X-66A is the very first one to focus on green aircraft technology.

NASA emphasized that X-66A is the “first X-plane specifically focused on helping the United States achieve the goal of net-zero aviation greenhouse gas emissions.”

Bob Pearce, the associate administrator of the NASA Aeronautics Research Mission Directorate, also connected the green aircraft dots between fuel efficiency and the 2050 net zero goal.

“With this experimental aircraft, we’re aiming high to demonstrate the kinds of energy-saving, emissions-reducing technologies the aviation industry needs,” he explained.

For the record, the X-66A project comes under the Sustainable Flight Demonstrator wing of NASA’s Integrated Aviation Systems Program.

Green Aircraft & The Sustainable Aviation Fuel Of The Future

If the TTBW fuel-saving venture pays off, the end result will be a more economical environment for sustainable aviation fuels.

The US Air Force and the US Navy tried mightily to promote bio-based aviation fuels during the Obama administration, with algae biofuel, a weedy oil-producing plant called camelina, and used cooking oil among the sustainable resources in play.

Now another round of green aircraft fuel is in the hopper. This time the focus is on electrofuels (also called e-fuels), which deploy water-sourced green hydrogen and captured airborne carbon to formulate synthetic, fossil-free hydrocarbon fuels (see more e-fuel coverage here).

The Project FIERCE initiative of the US Air Force Research Laboratory is one recent development. Project FIERCE aims to produce and test e-fuels for green aircraft, in partnership with the Brooklyn startup Air Company and a flight test team at the Hsu Educational Foundation.

The partnership launched in 2021. In December of 2022 the Air Force reported that the new e-fuel has been confirmed as “the first fuel made entirely from carbon dioxide emissions that matches the properties and performance of Jet A-1, and contains all necessary components of jet fuel, including aromatics.”

The Air Force already anticipates that the technology will enable its aircraft to shake loose from fossil energy price spikes and the cumbersome supply chains.

“For now, just a few gallons [of electrofuel] can be produced in a day, but as this technology scales, forward bases could benefit from diversified supply, or operate independently without fuel resupply requirements,” the Air Force noted.

The Air Force has also partnered with the startup Twelve, another US e-fuels innovator, in support of green aircraft fuel. Twelve broke ground on a full scale production facility in Washington State last month.

The US Navy is emerging as another force propelling the e-fuels movement forward, including systems that deploy seawater as a source of green hydrogen.

Critics have scoffed at e-fuels in general and green hydrogen in particular, but US Department of Defense is known for its power to push new markets through its buying power. The agency’s singular focus on managing threat risk also comes into play.

Last February, the Defense Innovation branch of DoD took note of Air Company’s new $65 million contract with the Air Force, explaining that the ideal sustainable aviation fuel is “capable of leveraging a variety of locally-available CO2 feedstocks, sourced from air or seawater in a small, mobile form-factor that will enable agile basing concepts around the world.”

DoD is not flying solo. In support of green aircraft, the ARPA-E high risk, high reward office of the US Department of Energy has also been pouring dollars into e-fuels R&D. The office launched in 2010 with a suite of electrofuels projects ready to roll.

More recently, the Energy Department rolled five of its national laboratories into a collaborative effort called CO2RUe, short for “CO2 Reduction and Upgrading for e-Fuels.”

The consortium is tasked with formulating technologies that leverage electricity from renewable resources to upcycle carbon dioxide into fuels and other chemicals.

In addition to decarbonizing the aviation industry, CO2RUe is taking aim at maritime industries as well as chemical production and heavy industries.

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Image (artist rendering): A green aircraft demonstrator project will focus on the use of Transonic Truss-Braced Wing to reduce drag and help reduce aviation fuel consumption by 30% (courtesy of Boeing via PR Newswire).

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