Ben Goldman is the acoustics lead at Archer Aviation, the eVTOL startup that recently emerged from stealth with a full roster of experienced talent. Goldman himself came to Archer from Joby, where he served as aeroacoustics lead for the eVTOL frontrunner.
With a background in the helicopter industry as well as hands-on experience with eVTOL aircraft, Goldman has unique insight into why helicopters have failed to gain community acceptance — and how eVTOL air taxis will have to do better. We caught up with Goldman in January at the Vertical Flight Society’s Transformative Vertical Flight event in San Jose, California, where he told us more about the acoustics considerations for eVTOL aircraft.
eVTOL.com: Tell me a bit about your background and how you ended up coming to the eVTOL industry.
Ben Goldman: My undergraduate was Purdue. I studied aerodynamics — fluid dynamics largely. I was always fascinated by the beauty of the fluid equations. When I got to the end of undergraduate, I was looking around at what to do. I think I actually applied to Williams F1 for a senior engineering position. They did not respond back.
I quickly realized that, at least at that point, there’s so much work that’s already been done in CFD [computational fluid dynamics]. Noise modeling is something that has only been around for 30 years — mid-’80s was the first time there was enough computational power to let us do any noise modeling with real fidelity. I was looking around to find someone that was doing that work. Ken Brentner’s name popped up, and I called him and I said, “I would like to work with you.” He indoctrinated me with PSU-WOPWOP [an aeroacoustic prediction code], so I’m one of the co-authors and I went on to develop it.
When I was in grad school, there was a collaboration that we did, and part of the research was funded by Bell Helicopter. When I got out of grad school, I was given a terribly tough choice: go to NASA Langley or go to Bell. I really wanted to see just how gritty industry is. You learn in engineering that a straight line is a straight line, but there’s no such thing as a straight line — nothing’s straight. There’s the idealized side of things and there’s beauty to that, but I really wanted to understand more of the limitations, and going into industry allows you to do that.
I realized after being at Bell for a little while that the entire helicopter design process is not built to create a vehicle that is low-noise; it is designed around a high-performance aerospace vehicle that can hover efficiently, that can travel at high speeds. When you ask for that same vehicle to now be quiet, you sacrifice all that performance. You lose the range, you lose the hover capability — or at least efficient capability.
Helicopters are amazing vehicles, but acoustically, I felt like I was being wasted. Just having something certified is not satisfying to someone that’s trying to make a quiet vehicle. Somewhat serendipitously, around the same time, Alex Stoll, who is the lead aerodynamicist at Joby, reached out to me. He had actually talked to my advisor, who recommended me. We got in touch and they brought me on.
I recognized during the interview process that from the very beginning, Joby hadn’t simply said, “Well, we’ve got to be able to go as fast as we can; we have to carry as much weight as we can.” It was like, “We need to do the best that we can, but we have to keep an eye on the noise.” There is a hard stop at some point where you can make a vehicle go as fast as you want, but if the community doesn’t accept it, what’s the point? Seeing a group that had that fully in mind from the beginning of the design was really what solidified in my mind that this is where I wanted to be.
eVTOL.com: How do winged eVTOL aircraft [such as the Joby and Archer concepts] differ from helicopters when it comes to noise?
Ben Goldman: So many ways. When a helicopter is only just spinning up, you can hear the drive train and engine — we don’t have any of that. You don’t necessarily notice it until you think of the difference between just a conventional Honda driving down the street and a Prius and suddenly it’s like, “That’s so nice.”
We have distributed propulsion, which means we are spreading out the loading. So low disc loading means low noise below the props when we’re in hover. And we are keeping the tip speed down; the tip speed we are running wouldn’t be possible with traditional combustion engines. Even fixed-wing props, they don’t sound too bad but they’ve got that drone, due primarily to the fact that, yes they can off-load the blades, but they can’t slow them down. They have to keep spinning, so you’ve got all that thickness noise in planes when they’re flying over — we lose that, too.
That said, it seems like there has been hyping of just how quiet some of these eVTOLs would be, which has turned out in a number of cases to not be justified . . . coming out with these boastful claims of dramatic noise reductions, and then showing videos in which it’s very obvious that they might have only shaved a few decibels off. I don’t know if the public is really conscious of that, or if it’s more just other people in the industry that are taking note of it, but it concerns me because one of the things that’s going to hurt us is driving public distrust.
eVTOL.com: What is it really going to take for communities to accept these vehicles, especially at the scale that the urban air mobility industry wants to fly them?
Ben Goldman: That’s multi-faceted, and I’m of course super biased in my answer. Beyond the noise is safety. The community has largely accepted commercial flights as safe. Some of it is a perceptual thing, but it’s also statistics. We need to drive home the fact that these vehicles are safe and reliable.
There’s that side of things. I think Mark Moore yesterday was dead on when he said that we have to not surprise communities. We have to let them decide for themselves that they’re okay with this. The moment they perceive it as us forcing upon them this technology, is the moment you get people pushing back. They need to come to terms with it on their own time and recognize that, “Yes, this does provide us something, and no, it’s not such a big deal that they’re flying overhead; they’re quiet, they’re safe.”
Beyond that is also the noise, and it’s not just how loud the noise of the vehicle is in some nominal condition, but it’s how they’re operated. We’ve seen from some of the previous research that the FAA [Federal Aviation Administration] and academia have done, operating a helicopter in steady flight can be fairly quiet, but when you are aggressive in the maneuvers and disregarding the noise, you can make a huge impact on the community below you. Once you’ve annoyed them, they’re not so quick to forgive.
That’s really the fight: trying to make a distinction that this isn’t going to be helicopters round two. We’ve acknowledged that helicopters can’t be operated over the community the way we’ve tried to do it. We’re making something that might look a little bit like a helicopter, might fly a little bit like a helicopter, but at the end of the day is a paradigm shift in the way engineering is approaching the problem.
This interview has been edited and condensed.