Dr. David Ullman is skeptical about eVTOL and its potential for widespread use as a vehicle for an urban air taxi system. “I think a lot of people who drank the Uber [Elevate] Kool-Aid are in for some real surprises,” said Ullman, who discussed his JabirWatt eSTOL aircraft this week at EAA Airventure. Ullman, a prolific inventor and a former professor of mechanical design at Oregon State University, thinks eVTOLs simply use too much power and that a better alternative is to add small ducted fans to the wing surfaces of conventional aircraft to turn them into high-performance eSTOLs that can use runways as short as 400 feet.
“Electric VTOL kills you on the battery,” he said, pointing out that his aircraft consumes just 50kW to get airborne while a comparable eVTOL uses 250kW to take to the air. An eSTOL delivers twice the range using current battery technology, Ullman notes. Ullman calls his eSTOL “IDEAL,” for "integrated distributed electric-augmented lift." The concept uses multiple electric ducted fans that not only propel the aircraft but also shape high-velocity air over the top surface of the wing to create propulsion airframe interaction, producing aircraft that handle well at very low speeds and that reduce or virtually eliminate loss of control. “You can manage loss of control in ways that you can’t with almost any other technology. You energy the boundary layer so stall [speeds] go way down. We haven’t even begun to play with flap effect yet.
“If you double the velocity of the air on the top of a wing, you virtually double the lift coefficient,” he said, noting that the increased performance is without the use of flaps. Ullman said he tested 18 different configurations and wind tunnel data to determine optimum fan placement on the near NACA 4414 wing on a Jabiru kit plane. The aircraft made its maiden flight two weeks ago with four 120-mm ducted fans. “It sounds like a jet-powered Jabiru. It’s really cool,” he said.
Ullman said he hasn’t begun to explore all the possibilities inherent with the IDEAL design. “By changing the amount of power to an individual fan you can create more lift on that one wing. You may be able to get ride rid of the ailerons.” But by reducing the aircraft’s stall speed, possibly down to 25 knots, the potential injuries/fatalities from stall/spin accidents will be greatly reduced, he said. Ullman has plans to build a purpose-built IDEAL aircraft.