NASA expands simulations for air taxi passenger experience
By Paul Brinkmann|October 10, 2023
Steep approaches and light flicker from blades are to be studied
Corrections: An earlier version of this story included an incorrect description of the apparatus that simulates air taxi motion at NASA Armstrong. The apparatus is moved electronically, not hydraulically. The story was also updated to clarify that a lab at NASA Ames is similar to the one at Armstrong.
The electric air taxis in the works by many developers will need to descend steeply and rapidly to their vertiports to avoid siphoning too much power from their lithium-ion batteries.
Will passengers find these and other maneuvers exhilarating, nauseating or tolerable? Curtis Hanson aims to find out at NASA’s Armstrong Flight Research Center, located within Edwards Air Force Base in California.
He is principal investigator of passenger ride quality research at Armstrong. This research has come to include the ride quality of air taxis under two projects, the Air Mobility Pathfinders Project and Revolutionary Vertical Lift Technology Project.
The ride quality field traces back to the early 1970s, when airlines wanted to know how passengers would respond to takeoff, landing, turbulence and other conditions.
The situation is similar today with the coming breed of air taxis.
Landings are one area of concern. “Nobody really knows how passengers are going to respond to such flight conditions, like what is the right level of deceleration with passengers on board, where it’s good for energy efficiency,” Hanson told me during my visit last month to Armstrong and Edwards.
As we spoke, he showed me the center’s newly erected ride quality simulator for air taxis, a chair mounted on an electric stand that will expose the occupant to movements like those of an aircraft in flight.
Hanson plans to begin with generic flight profiles for air taxis, most of which will be eVTOLs, or electric vertical takeoff and landing aircraft. But in the near future, plans call for obtaining software that would simulate the flight characteristics and profiles of specific aircraft whose designers are seeking FAA type certificates.
So far, no one has completed a test on the chair: “We’re finishing up validation testing. We just did a briefing last week to get permission to move it with a person on board. That should be happening hopefully next month,” Hanson explained.
In many cases, the chair simulations will be in preparation for more elaborate research at the Vertical Motion Simulator, or VMS, housed in a 10-story building at the agency’s Ames Research Center in Silicon Valley. For decades, researchers have studied pilot, passenger and astronaut experiences there. Due to its size, the VMS can imitate six ranges or types of motion and simulate mild g-forces. But Hanson said the VMS is in high demand these days, so the chair experiments are a way to plan the VMS experiments in detail, to ensure they are run efficiently at the busy facility. In fact, a lab similar to the one at Armstrong has been set up at Ames.
The Armstrong chair simulator, while limited in range of motion compared to the VMS, also has some advantages over the larger Ames facility, such as greater rotational range of motion, NASA said.
In the Armstrong chair, test subjects will wear virtual reality goggles that can mimic the visual flight experience, and they will hear sounds that would be heard in the cabin during flight, as the chair moves. Subjects will wear sensors to measure changes in brainwaves, heart rate, sweat or skin conditions and pupil dilation. They will also have a button to push if they feel something particularly unpleasant, Hanson said.
In addition to the fast descent, the flickering of light off the rotor blades is also a concern.
“We know anecdotally from people who have flown in helicopters that the blade flicker frequency can actually cause seizures, or it could just trigger nausea in general,” Hanson said. “With these smaller air taxis, they have smaller rotors, and they spin at various speeds. And some of those frequencies are right in the potential danger zone, which is around 30 hertz [30 flashes per second].”
He added, “Some people are fine with it for like 30 seconds. But if you do it for five minutes, it’s bad. So we want to evaluate the duration and impact.”
The simulator chair at Ames has been set up at the Human Vibration Laboratory to focus on cabin noise, he said. The chair is “hooked up to accelerometers that vibrate the chair,” Hanson explained. “Some of these [air taxi] cabins are the exact size where they may kind of resonate at the wrong frequencies, which is 20 to 30 hertz.”
Further tests at Armstrong will simulate conditions when air taxis transition from vertical flight to horizontal, forward motion, and also simulate flying through urban areas where wind gusts may be affected by tall buildings.
“There’s no really good data to try to understand how passengers would respond to the different ways that aircraft transition, like what the differences are between tiltrotor and lift plus cruise,” Hanson said. He added that Armstrong won’t focus on motion sickness because that is better studied at Ames.
Plans call for testing the Armstrong chair with a helicopter pilot, who will gauge how accurately the air simulates a helicopter flight. Then researchers will move on to NASA employees and the general public.
“We’ll study each flight condition individually first and then study them together, because sometimes it’s the combination of factors that can have the most impact,” Hanson said.
He’s not sure to what extent FAA will consider the passenger experience in providing type certificates to various air taxis.
“If we find a correlation between rotor size and passenger comfort, for example, that might be of interest to the industry as a whole,” he said.