A Peterbilt truck at NASA’s Armstrong Flight Research Center may never get off the ground, but, carrying a 31-foot wing outfitted with 18 propellers, it is instrumental in advancing a distributed-propulsion concept that could lead to less polluting aircraft designs. The carbon-composite wing, outfitted with load cells on a supporting truss, is called the Hybrid-Electric Integrated Systems Testbed, or HEIST. Lithium iron phosphate batteries power the electric motors that drive the propellers.
As reported in the New York Times, project engineer Sean Clarke says the truck helps simulate takeoff and landing configurations and measure lift, drag, motor efficiency, and aerodynamic performance. The Times notes that airline emissions per seat-mile are down 70% from the 1960s and account for about 2% of carbon-dioxide emissions, but that percentage could grow as the worldwide commercial airline fleet doubles, to about 40,000 airliners, over the next 15 years.
Aircraft engines don’t exactly follow Moore’s Law. The Times quotes Daniel Rutherford, a program director at the International Council on Clean Transportation, as saying average improvements in fuel reduction average 1.3% per year, which should continue through the next decade.
The goal of the NASA project—called LEAPTech, begun in 2014—is to improve that figure through new “clean-sheet” designs rather than minor upgrades to existing technologies. For example, a wing could change shape based on flight conditions to minimize drag and increase lift. With distributed propulsion, motors can be attached to the front of a wing, accelerating the airflow over it, thereby increasing lift, allowing use of a narrower wing that reduces drag.
It looks like the researchers are getting ready to park the Peterbilt and take to the air. The Times reports that the next step is to operate a modified aircraft to try out the distributed-propulsion technology.
