Skai made big waves last month with the launch of its long-range hydrogen-powered eVTOL air taxi prototype. In an interview with New Atlas, Skai’s CTO tells us these flying commuter vehicles will cost about the same per mile as an Uber ride, and that he expects to be able to land them just about anywhere.
Brian Morrison, CTO of Skai and its parent company, Alaka’i Technologies, is not shy about what his company is proposing: a democratization of air transport that doesn’t have to wait for a huge leap in lithium battery technology. Battery energy density is one of the two biggest challenges facing eVTOL developers at this stage, the other being FAA certification.
Morrison says his company’s use of liquid hydrogen fuel completely leap-frogs the issue of how to get electric air taxis flying for more than 20 minutes, and that Skai is working “hand in hand” with the FAA to complete the certification process for this completely new type of aircraft – a process he believes will be completed and allow for commercial flights by the end of 2020.
This is an audacious plan, but if it comes together, it might put Skai well ahead of the rest of the pack in bringing affordable vertical commuting to the masses. We spoke with Morrison over Skype this morning. What follows is an edited transcript.
Skai’s flight testing progress
Loz: The first thing everyone wants to know is: have you got it flying yet?
The test vehicle is up at Minuteman Field up in Stow, and all the tests we’ve been conducting to date have been with it tethered to a concrete pad, which is part of the FAA requirements.
If not tomorrow, then Monday we’ll be ready to take the tethers off, but we can’t until the FAA comes out to do another site inspection to make sure that they’re happy with all the documentation. Once that happens, we’ll take the tethers off and be able to lift off.
Loz: What will the flight testing program look like for you guys?
Until this point, it’s been rotor run-ups to a certain power level, increasing power to full power. Running through the regime that the motors operate in. We’ve run individual motors before, this is the first time we’ve had all six on a single structure, running off hydrogen fuel cells. We’re making sure we evaluate it every step of the way before we take the tethers off.
Dealing with the hydrogen
Loz: how are you storing the hydrogen?
We use liquid hydrogen on board. The fuel cells actually use it in gaseous form, so it’s stored in liquid but it comes out and goes through an expansion chamber which allows it to change from the liquid state into a gaseous state. Then we put it through a heat exchanger to warm it up a little bit, and that’s what goes into the fuel cells.
Loz: What size tank are you running in there?
We have tanks ranging from 110 liters all the way up to 400 liters. The 400-liter tank is the one that’ll give us, in round numbers, four hours of flight time and 420, 430 miles (676, 692 km) of range.
Loz: There have been a lot of people making manned multicopter designs, but not a lot of fuel cells. What made you guys decide to go down this path?
When I started this exercise back in 2012, I too was trying to find a way to do it with lithium-ion batteries. I’m a systems engineer by training, and I spent literally months running different simulations. Looking at the lift provided, looking at how long we could stay in the air, how long you could hover, versus how much energy you need.
I determined that from an air taxi standpoint, 15 or 20 minutes flight was never going to be enough. Because you have to have emergency reserves as well. If you only have the ability to stay in the air for 20 minutes, the FAA would only let you fly 10 minute routes so you’d have some reserve left over. That didn’t seem practical, so I started casting about for a better solution, and started looking at hydrogen fuel cells for that. We’ve been working with that ever since.
Loz: I’ve been writing about fuel cells in the auto industry for a long time, and it’s always seemed to me like a technology that was never going to take off, just because of the difficulty around storing the stuff, and integrating it into the fuel station supply chain. It all seemed too difficult. But I guess in the aviation world you don’t need hydrogen stations on every third corner?
You really don’t. And by the way, more and more corner fuel stations – particularly in California, now Connecticut and Massachusetts – are starting to have gaseous hydrogen dispensing capability.
I spent yesterday with a major hydrogen supplier, talking about having them offer not just gaseous hydrogen but also liquid hydrogen at those stations – that would solve the source of supply problem quite easily for us.
They already have liquid hydrogen on site, because it’s most efficient for them to store it in bulk form in liquid, then convert it to gas and pressurize it before they put it in somebody’s car. This way we’d be able to siphon off some of the liquid and use it to fuel our vehicles directly.
Loz: You wouldn’t operate out of depots using your own supply?
Well, there’s lots of opportunities. One is you take advantage of what’s already commercially available. Another is, perhaps in parts of the state where you don’t have a lot of that, you have your own electrolysis and liquefaction capability.
Or you just have your own tanker truck. We have our own tanker truck right now. It only carries about 3,500 liters of liquid hydrogen, but that’ll fuel the vehicle a number of times. So you could literally have the aircraft meet a movable vehicle somewhere in a parking lot, just land next to it when you need to refuel, and then take off again. That gives us a nice mobile refueling capability.
On the Skai aircraft’s design and safety considerations
Loz: Changing tack a little, it’s a six-rotor design. You’ve got some redundancy there. You chose not to go with coaxial props, ducted fans, or any kind of tilt-wing design that’d give you wing lift for extra efficiency in the air. What was the thinking there?
All true! The core philosophy is keep it simple. And by keeping it simple, we’ll get certified sooner and we’ll be a much lower cost vehicle than the more complex designs. You add complexity, you add weight, and you add certification risk.
Loz: So these multi-mode VTOL takeoff jiggers that switch forward into winged flight with pusher props or whatever, you feel that’d be a longer path to certification?
I do, yeah.
Loz: One thing that fascinates me is the worst case safety thing, whereby everyone’s got ballistic ‘chutes on these things, but they just don’t work under a certain altitude. I’m really interested to hear how you’re dealing with that problem.
We’re working very closely with the ballistic parachute manufacturer to engineer it as a system rather than just tacking on a parachute.
Part of that system is the flexion you’ll get out of the landing skids. Part of the system is the flexion you get out of the seat itself. So you can protect the occupants up to a pretty significant G impact just through a combination of the skids and the deflection of the seat. And the vehicle itself can deform or crush to absorb some of the energy.
Our expectation is for that to absorb enough energy that above a certain altitude, you’ll have time to deploy the parachute and descend safely from the parachute. But you’re right, there are concerns that everyone’ll be facing about how to do that.
On Skai’s own air taxi service, and what it will cost
Loz: Now, it seems you guys have designs on running the air taxi service rather than just making the vehicles and plugging into something like Uber Elevate, is this correct?
That’s correct. In part because three of our principles have all operated air taxi services in the past. So we know a bit about setting up and operating an air taxi service. We’ve already got an app up and running that lets you book a flight.
We’ll happily sell to others if they want to acquire some to use in their air taxi service – indeed we’ve already had enquiries from some. But we also plan to be operating our own, yeah.
Loz: What’s the advantage of these things over helicopters, are they going to be that much cheaper?
Well, say a traditional helicopter – unless you’re talking about a Robinson – but a traditional turbine helicopter is four, six, seven, eight million dollars depending on how it’s outfitted. You’ve got an engine running at 6,000 rpm, and you have to use a complex transmission to get it down to typically 300 rpm at the rotor blade.
Those transmissions are heavy, and they fail. One of the sensors you’re required to have on board is called a chip detector, so you can detect when the gears in the transmission are starting to come apart.
Here what we’re doing with electric motors, they’re all direct drive, so there’s no transmission involved. They use electronic speed control, electronic computation to control the speed and direction of the motors, so it focuses on simplicity and safety and making the vehicle as light and safe as we can.
The other big advantage you get with six rotors spread out from the center of the vehicle is you can actually have a parachute on board.
Loz: Right, it can fire straight upwards. So in terms of ride cost, obviously the average everyday Joe isn’t getting around in helicopters as part of their transport mix these days. What kind of cost reduction are your numbers showing at this point?
Without going into a lot of specifics, more than a ten-fold reduction.
Loz: OK, and have you done any modeling on how long a flight would have to be before it becomes cheaper than driving a car, or anything like that?
Well, the price right out of the box will be comparable to what a generic Uber would charge to go the same distance. The difference, of course, is that you’d get there much faster in the sky than you would on the roads.
Loz: Really? Comparable to the cost of a land based Uber?
Yep
Loz: Holy moly. That changes everything.
Yeah. And to answer your question, we’ve done a lot of modeling on that, a lot of analysis using not only our own tools, but some industry leading tools to evaluate how different modes of transportation work, and are picked up by the traveling population.
Loz: Where does that massive cost reduction come from? Is it the cost of the vehicle? The fuel? Pilots? What’s driving it?
All of those things. Hydrogen right now is on a par with gasoline, but it’ll become cheaper over time. The pilot, we’re certifying the vehicle initially with a pilot on board, but very quickly we’ll be able to operate the vehicle over a tactical datalink from the ground, so we won’t have to carry the weight of the pilot around. So you get more passengers or payload capability with a pilot still in full command of the vehicle.
Obviously longer term you’d get to an autonomous version, where you don’t need a pilot involved at all.
Loz: So your intermediate step is basically a data center full of kids playing video games, effectively?
Absolutely! I think they’ll have to be 21, but you get the idea. The other big factor … well, we’ve all been involved in air taxis before, so let me give you an example. If you have a fixed wing Cirrus aircraft, that’s a piston engine making 330-350 hp. Every 2,000 hours you have to do a complete teardown and overhaul of the engine, and it costs US$60,000.
That operating cost has to be factored into your cost per seat mile that you’ll offer to the public. That’s every 2,000 hours with a piston engine.
Along come fuel cells, where you don’t have to do anything until 20,000 hours, and all you have to do is swap out the stack. All the rest of the fuel cell stays in place. That’s a big reduction in terms of OpEx.
Interview: Skai claims its air taxis will cost the same per mile as taking an Uber [New Atlas]