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NASA Armstrong pilots flew an Italian-built Tecnam P2006T aircraft in September to collect data to compare to a modified aircraft that is under development for the agency. Once complete, Armstrong staff will integrate a specially developed wing on that aircraft with electric motors for research flights. (All images courtesy of NASA)

An X-plane for everyone?

Not too, too long ago very few amongst us ever thought we would need a phone that took pictures and video, while more recently, very few amongst us would ever not have a phone with such capabilities. Such technological changes are not limited to personal communication devices, and are destined to include personal transportation devices.

Both the automotive and aerospace industries are in midst of transformative technological disrupters. In the automotive industry, some believe we may soon approach a time when driving becomes somewhat of a lost art. In that scenario, either a “select” group of people are tasked to always remember to take a right turn on red and the significance of yellow dotted lines next to yellow solid lines, or all that knowledge is left to the coding of the autonomous (potentially multi-person) vehicle that picks up people and their laptops at their doorsteps and takes them to work, should Skype and email not be sufficient on any given day.

Or maybe daily tasks such as driving to work merely transform into something else during a commute. As it turns out, NASA may have at least one answer to what that could be.

As part of a recently announced initiative, NASA is in the midst of researching a number of strategic projects that include quiet supersonic flight, electric distributed propulsion, and hybrid wing aircraft, with goals that include demonstrating advanced technologies to reduce fuel use, emissions and noise, and accelerate possible introduction to the marketplace.

In particular, one of the initiative’s goals will be a focus on ideas that could lead to developing an electric propulsion-powered general aviation aircraft that would be more quiet, efficient, and environmentally friendly than current commuter-type aircraft, potentially opening for cleaner, faster (read: less congested, at least in theory) ways for personal and professional travel.

Along those lines NASA will be testing new propulsion technology using an experimental airplane designated the X-57 and currently nicknamed “Maxwell” in honor of James Clerk Maxwell, the 19th century Scottish physicist best known for his seminal work in electromagnetism. The aircraft will have electric motors turning propellers that will be integrated into a specially designed wing.

“With the return of piloted X-planes to NASA’s research capabilities—which is a key part of our 10-year-long New Aviation Horizons initiative—the general aviation-sized X-57 will take the first step in opening a new era of aviation,” said NASA Administrator Charles Bolden in a speech around the middle of June. It’s NASA’s first X-plane designation in a decade; as many as five larger transport-scale X-planes also are planned as part of the initiative.

The X-57 number designation was assigned by the U.S. Air Force, which manages the naming process, following a request from NASA. The first X-plane was the X-1, which in 1947 became the first airplane to fly faster than the speed of sound.

“Dozens of X-planes of all shapes, sizes and purposes have since followed—all of them contributing to our stature as the world’s leader in aviation and space technology,” said Jaiwon Shin, Associate Administrator for NASA’s Aeronautics Research Mission Directorate.

The current list of X-planes that have been assigned numbers by the Air Force stands at 56, but that doesn’t mean there have been 56 X-planes. Some had multiple models using the same number. And other experimental vehicles were designed, built, and flown but were never given X-numbers. And some X-vehicles received numbers but were never built.

In fact, the designator of X-52 was skipped altogether to avoid confusing that aircraft in any way with the B-52 bomber. Some X-planes were not experimental research planes at all, but rather prototypes of production aircraft or spacecraft, “muddying the waters over what is truly considered an X-plane and what isn’t,” according to Bill Barry, NASA’s Chief Historian.

As part of a four-year flight demonstrator plan, NASA’s Scalable Convergent Electric Propulsion Technology and Operations Research (Sceptor) project will build the X-57 by modifying a recently procured, Italian-designed Tecnam P2006T twin-engine light aircraft.

Its original wing and two gas-fueled piston engines will be replaced with a long, skinny wing embedded with 14 electric motors—12 on the leading edge for takeoffs and landings, and one larger motor on each wing tip for use while at cruise altitude.

An advantage of modifying an existing aircraft is that engineers will be able to compare the performance of the proposed experimental airplane with the original configuration, according to Sean Clarke, Sceptor co-principal investigator at NASA's Armstrong Flight Research Center. The Tecnam, currently under construction, is expected to be at Armstrong in under a year for integration of the wing with the fuselage. Armstrong flew a different Tecnam P2006T in September to gather performance data on the original configuration.

NASA engineers hope to validate the idea that distributing electric power across a number of motors integrated with an aircraft in this way will result in a five-time reduction in the energy required for a private plane to cruise at 175 mph.

Several other benefits would result as well. Maxwell will be powered only by batteries, eliminating carbon emissions and, ideally, demonstrating how demand would shrink for lead-based aviation fuel still in use by general aviation.

Energy efficiency at cruise altitude using X-57 technology is expected to reduce flight times, fuel usage, and overall operational costs for small aircraft by as much as 40%. Typically, to get the best fuel efficiency an airplane has to fly slower than it is able. Electric propulsion essentially eliminates the penalty for cruising at higher speeds. The X-57’s electric propulsion technology is expected to significantly decrease aircraft noise, making it less annoying to the public and potentially more appealing to communities that may have in the past shunned or closed smaller airports.

NASA researchers ultimately envision a nine-passenger aircraft with a 500-kW power system in 2019. (To put that in perspective, 500 kW, or ~700 hp, is about five times as powerful as an average passenger car engine.) Clarke says progress in three areas is happening to enable that timeline.

Those areas include testing of an experimental wing on a truck, developing and using a new simulator to look at controls and handling characteristics of an electric airplane, and verifying tools that will enable NASA's engineers to design and build the aircraft, which is also part of NASA's efforts to help pioneer low-carbon propulsion and transition it to industry.

The first area, in cooperation with Joby Aviation and ESAero, is the Hybrid Electric Integrated Systems Testbed, or HEIST, an experimental wing initially mounted on a specially modified truck. It is used for a series of research projects intended to integrate complex electric propulsion systems.

The testbed functions like a wind tunnel on the ground, accelerating to as much as 73 mph to gather data. Researchers have used the testbed to measure lift, drag, pitching moment, and rolling moment that can validate research tools.

"By evaluating what we measured vs. what the CFD predicted, we will know if the predictions make sense," said Clarke. "Since [this] is a new design, we need to validate we have good answers for the experimental wing."

HEIST's first experiment was called the Leading Edge Asynchronous Propeller Technology, or LEAPTech. The experiment began in May at Armstrong and consisted of 18 electric motors integrated into the carbon composite wing with lithium iron phosphate batteries.

Tests so far show the distribution of power among the 18 motors creates more than double the lift at lower speeds than traditional systems.

Developing and refining research tools is another major effort. For example, researchers plan to integrate the aircraft's systems with a NASA Armstrong flight simulator for pilots to evaluate handling qualities. Researchers also will be able to study balancing the power demands of the motors with batteries and then a turbine, according to Clarke. Of interest is whether a hybrid of distributed electric motors and gas-powered turbines could provide power to extend the aircraft's range and enable a possible nine-person concept aircraft, forever changing, perhaps, future connotations of the word "minivan."


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