The Coming Age of Emissions-free Aircraft
An interview with Professor Dr. Josef Kallo of the German Aerospace Center (DLR)
On September 29, 2016, a 10-minute test flight at Stuttgart Airport in Germany took place that could end up changing the entire future of air travel.
The flight was of the twin-cabin HY4 aircraft, the first four-seater aircraft in the world using emissions-free hybrid fuel cells to fly. It uses hydrogen to generate electricity in flight and has a cruising speed of 165 kilometers per hour (or 102.5 miles per hour) and a travel range of up to 1,500 kilometers (932 miles). It uses conventional batteries to handle the power boost needed for takeoffs and landings. And the only emission it produces is water vapor.
This revolutionary aircraft is the brainchild of a team coming from four different organizations: the aircraft designer Pipistrel, the fuel cell specialist Hydrogenics, the University of Ulm and the German Aerospace Cen- ter (DLR). And if the development of the project continues as planned, in as little as six or seven years from now the world could see slightly larger planes like this as a minimum servicing short-haul flights throughout the world, all without adding a single molecule of greenhouse gas emissions as part of their travel.
To learn more about this incredible achievement, Trillions had the honor to speak with the aircraft’s project leader, Professor Dr. Josef Kallo of the German Aerospace Center and the University of Ulm, at his offices in Germany on October 22.
Trillions: Congratulations on the impressive test flight of the HY4 emissions-free aircraft that had its public maiden test flight just a few weeks ago. My understanding is you have the position of Head of Project for the German Aerospace Center for the program.
Dr. Kallo: My role is to have the project lead from the German Aerospace Center, and I’m also working [as]
the project lead for the University of Ulm. So, these two entities had the chance to work on this project.
Trillions: Could you talk a bit about the genesis of the project, how it got started and even how you put together some of the partners?
Dr. Kallo: Approximately 10 years ago we had the idea in our group to look at the fuel cell as a propulsion unit for an aircraft. And then we started – in 2009 – the first one-seater, which was the DLRH2 airplane. And we had a one-seater which flew with the fuel cell. After that, we had some achievements. We achieved to fly, like, 1,500 kilometers with that plane. Then it became a little bit quieter. So we took the challenge to improve the technology and to improve the power of the system, so we could start working on the HY4, which is what formed this [aircraft] by Pipistrel, and then which was also implemented with the fuel cell from the DLR.
So, we started … two years ago. We worked together with Pipistrel, the University of Ulm, Hydrogenics. We had a chance to bring very good people together. And then we joined with H2fly, which is the owner and operator of the HY4 plane. And then we had a chance to start the project implementation.
The integration itself was started in May 2016. And then we had a very interesting and exciting time until September, when the first flight was taking place. Trillions: That’s an intense schedule. I guess it helps that you had the earlier version, where you had a lot of experience with what worked and what things you wanted to improve. As a project manager myself, I can appreciate that was a quick turnaround even with some of that background under your belt.
In terms of the project itself, I’m curious about the whole nature of the design of the aircraft and what’s very different from traditional aircraft. One thing I know about, for instance, is that fuel cells provide a good steady stream of power, but if you need that initial boost to take over or whatever, they aren’t necessarily as effective at things like that. I’m sure the engine’s different. And I can already tell, from the images of the aircraft and all, that there are things you did to take advantage of efficiencies in flight, of having the Bernoulli effect have some [larger] effects. What was different about the aircraft versus other types of aircraft that one might consider in short-haul flights – and things like that?
Dr. Kallo: First of all, I think formally [that the] G4, which was built by Pipistrel and was developed for a battery – electric – propulsion, was a very, very good start. So, when I saw the plane a couple of years ago, then I could instantaneously imagine to see where the hydrogen storage system can be built in, where the fuel cell can be implemented and also where the remaining batteries for the high-power phase can be im-
plemented. Then we had to change the battery loads from the G4 to the HY4, and we minimized the battery, from something like 500 kilograms to something like 100 kilograms. In addition, we installed hydrogen storage systems in [the] fuselage, behind the passengers. And then we had also the fuel cells implemented in the middle part. So I think this is the big difference comparing [to] the G4.
Also the range can be improved. With our hydrogen systems today, we have a range of around 750 to 800 kilometers. With improved technology for the storage units, we can achieve 1,300 to 1,400 kilometers of range. I think this is due to the very high efficient shape of the aircraft, so we can fly with speeds up to 250 kilometers per hour but cruising at about 160 to 170 kilometers per hour. And there the plane is very, very efficient. So I think these two points, the efficient airplane and the high efficiency of the fuel cell providing electric energy for the motor in flight, during cruise, these are the specialties of this plane.
We still need a battery. We could fly also without [the] battery, also during the start phase. But then we are carrying too much fuel cell installed power, comparing to a battery. So the perfect match is to have a small energy battery with high power and a very high energy fuel cell hydrogen system with middle power. So this is what we have done, and this matches very well.
Trillions: Did your fuel cell developer, Hydrogenics, use anything unusual for this? Either more compact, higher energy storage capacity or a different type of cell?
Dr. Kallo: First of all, we have to look at the hardware. And there were some changes which Hydrogenics brought in due to our requirements. And in the second step, we learned a lot from Hydrogenics, so we understood how they deal with the controls. Then we made some suggestions how to change it, and they had some suggestions for us for the low-pressure operation. It was a very fruitful work together, and we had to change the hardware [and] also to change the software and the controls.
I think that has to be done also, in the next version, then, to get to much higher altitudes than we are flying today.
Trillions: You talked about how fast it can fly, as well as the range. What is the altitude that you’re able to achieve with the current aircraft?
Dr. Kallo: With the current aircraft, which is the first step, it’s something around 3,000 meters, which is 10,000 feet. We could fly higher, but we didn’t adjust the controls for it. So it’s a software thing which we have to adjust. We know how to deal with higher altitudes and what is important, but we had 10 hours of flight, all around a couple of thousands of feet. And at the moment the plane is [designed] for 10,000 feet maximum.
The next step will be to go to 5,500 meters, which is then something around 16,000 to 17,000 feet.
Trillions: That’s impressive that you’re able to make that jump, because I’m sure the aircraft itself changes, to accommodate thinner air, lower pressures, some of the things that you were talking about, and it sounds like [you have] well under control.
When you think of conventional aircraft, there is servicing of the aircraft when it lands. If this becomes a commercial type of thing, what is the concept of servicing and things like that like for this kind of an aircraft? Imagine the future, as opposed to where it’s at right now.
Dr. Kallo: Our concept is, for this kind of plane, to have high range, to minimize the needed infrastructure for refueling. I don’t think we will travel in such a plane for, like, five to six hours. This is the endurance of this plane. I think this plane can be used for traveling 100 to 200 kilometers, to connect big cities or to connect places in the outdoors where there is no road infrastructure or it’s not easy to go there.
So this could be something which we could use as a four-seater, maybe as a six-seater.
What we see is that this technology is able to be improved, in terms of power, by using modular systems. Our calculations and also our models show that, let’s say, an eight-seater is definitely feasible to fly around 150 knots and also have a range of around 1,000 kilometers. With that, we can do small regional traffic.
That’s not the end of the vision. From today’s perspective, I can say our models show that we could build a 40-seater with a range of also around 1,000 kilometers and with a cruise speed of around 220 to 230 knots. This could be something which is interesting then as a regional aircraft, flying from smaller airports. We have something like 300 of them in Germany, flying from smaller airports to bigger airports or connecting regional airports.
There could be a very good business case, yes.
Trillions: I could certainly see that in a lot of places. There are both the emerging markets that are getting very busy where this could be used, [as well as in places like] California, for example, [where] there are a lot of short-haul flights that might be more efficient with something like this.
What is next in your plans for this? I know that you’re going to go through further demonstrations of this aircraft, but maybe you could give some ideas of what’s going to happen next.
Dr. Kallo: From our perspective, we now have to look at higher efficiencies on the fuel cells. We will improve from something around 50 to 53, 54 efficiency on the fuel cell itself. This will be done in the next six to nine months.
And then we would like to start a campaign to test the airplane under realistic daily conditions. So [as] to see how robust is the system, to see what is not only the calculated range but also what is also the realistic range, with climatic changes and things like this. This is our next step. We will go into improving the robustness of the system. My feeling tells me that there is no “no go” on the physics side. It’s only engineering work and development. And if this happens the next three years, then we have a very good [chance] to put also not only a permit to fly on this plane but also then to have a certification for this power train.
Our goal is to have, in three years from now on, a highly efficient electric power train based on hydrogen and batteries and fuel cells. And then we can start thinking about implementing this power train into new aircraft concepts like concepts with maybe shorter takeoff capability with distributed propulsion, but maybe also in concepts for small helicopters and so on.
Trillions: In terms of commercialization, do you have a guess at when you think it might be possible for aircraft like this to start being used commercially? Just based on your own feeling on how long it’s going to take to get there, as well as, I’m sure, that little minor issue of funding to make all that stuff happen.
Dr. Kallo: [Laughs] I know this. At the moment, with the right funding, I can imagine to say, from now on in three years we can start with the certification for a product. Then in something like six to seven years I can envision a first product. But I think we need this time to step into this product.
HY4 team: Tine Tomasic, Vid Plevnik, Fraci Popit, Steffen Flade, Thomas Stephan, Henry Erhardt, Paolo Romagnolli and the Pilots: Saso Knez, Johannes Anton and Nejc Faganelj. Photo © Jean-marie Urlacher
HY4 in flight.
HY4 taking off.