The Allplane Podcast #4 - The Future of Green Aviation with Bjorn Fehrm
Although it seems that coronavirus has temporarily brushed aside any other issues the airline industry may have, the fact is that there is a lingering concern about the environmental impact of flying.
True, air travel accounts for quite a small share of overall carbon emissions (in the region of 2-3% currently), but nevertheless its high profile and visibility make it an obvious target for climate campaigners.
The good news: there is an ever growing number of initiatives from within and outside the aerospace industry that aim to tackle this issue, with electric propulsion for aircraft getting most of the attention.
The bad news: electric may not be the most promising technology when it comes to moving towards a greener aviation industry.
Our guest today, aeronautic engineer and former fighter pilot Bjorn Fehrm, has studied thoroughly a number of different technologies that attempt to get green airliners up in the air.
Bjorn has crunched the numbers and has drawn some conclusions about what the thinks are the most realistic perspectives in the field of green flying. He’s summed it up in a series of 20 blog posts full of detailed information and analysis about environmentally-friendly propulsion technologies.
The title of the series “Why e in ePlane shall stand for environment, not electric” already gives you some clues about where this is going.
Ready to listen what these are and the implications for the future of air travel?
Download this episode on:
Apple Podcasts / iTunes, Spotify, Google Podcasts or Stitcher
Topics we talk about in this episode:
What are the perspectives for electric flight?
Why is it so difficult to develop an electric airliner?
What differentiates electric propulsion in airplanes vs. cars?
What other technologies could deliver carbon-free air travel?
Is hydrogen a viable alternative?
The possibilities of biofuels and synthetic fuels
Resources
Bjorn’s series about the future of green flying “Why e in ePlane shall stand for environment, not electric”
The Saab Draken fighter jet that Bjorn used to fly in the 1970s
The unducted single fan concept that we talk about
ZeroAvia, the startup working on hydrogen power trains that we mention
About the Norwegian electric aviation plan
The two recent incidents involving electric aircraft, in Norway and Germany
The Airbus A330neo event that I mention at the beginning
Podcast Music: Five Armies by Kevin MacLeod
Link: https://incompetech.filmmusic.io/song/3762-five-armies
License: http://creativecommons.org/licenses/by/4.0/
Transcript
(please note that, although we strive to make it as close as possible to the original recording, the transcript may not be 100% accurate)
Hello and welcome to a new episode of the Allplane Podcast!
Believe it or not, in today’s episode there is hardly any mention to the current coronavirus pandemic. And this is because we have deliberately chosen to focus on an entirely different topic, one that, nevertheless, has very important long term implications for the future of aviation. And this is the relationship between airplanes and the environment.
Is there a way to make cleaner airplanes?
Are we soon going to be flying on electric aircraft?
Is it possible for the airline industry to become carbon free anytime soon?
We are going to review all these questions with one of the top independent experts in the field of aircraft propulsion.
Bjorn Fehrm is an aeronautical engineer and a former Swedish air force fighter pilot that has studied this problem in depth and crunched the numbers.
He is currently based in the South of France, from where he regularly writes about this and other aviation topics.
His blog, on LeehamNews.com is called “Bjorn’s Corner” and combines deep technical expertise with a very accessible style. This helps those who, like me, don’t come from an engineering background, to understand a bit better how aviation technology works.
So, today, I have the pleasure to have him, here, on the podcast, to talk about different ways the airline industry could become greener.
Without further ado, let me welcome Bjorn to the podcast…
-Hello Bjorn! how are you?
-I’m fine, hi there, Miquel!
-It's great to speak with you again! I remember we met at the presentation of the A330neo in Toulouse at Airbus some time ago and we had some interesting conversation with you about aircraft, because you are an expert in propulsion systems. I thought it was very interesting to speak with you today about the future of propulsion and the different technologies that are being tested to get greener aircraft. But let's let's start with a short introduction, can you tell us who you are and what’s your work in the field of aircraft propulsion?
-Yes, sure...I’m Swedish but I've been living in Europe for the last 25 years. I’ve been working on aircraft projects, I am an aeronautical engineer but I was also accepted in the Swedish air force as a fighter pilot, so I flew the Draken right back...I have a few years under my belt, but I have been working the last ten years or more with airliners, from an airliner perspective, in technology both form an airframe and propulsion perspective and I cover also jet turbine engines, electrical engines and stuff like that...And I am also an analyst right now at Leeham company and also a consultant.
-That actually something i wanted to say you have a very interesting series of publications on a website, that is Leehamnews.com and there you have a blog where you have a very thorough examination of different technologies, not just propulsion, that we are going to discuss now, but all sorts of interesting aeronautical stuff...And, by the way, I didn't know that you were flying the Draken fighter jets...if you are not familiar with the Draken I suggest (to our audience) that you go check it online because it’s a really impressive and elegant aircraft
-Yes it is! It was designed in the 1950s and it was operational almost until the year 2000 in the Swedish Air Force. I flew it in the late 1970s. So it was quite some time ago, but it was fun, very challenging aircraft, very capable. Yes, in the blog that we have at Leeham company, at Leehmannews.com we have during the week the typical articles, what’s happening in the airliner world, we focus on airliners. And then on Fridays I have my own section, called Bjorn’s corner where I go a little bit more technical and go over different themes such as avionics, aerodynamics, propulsion and I recently had several series of articles around new technologies around propulsion including electric and hybrid and other types of propulsion systems.
-Yes, this is a very interesting area, one where your fellow Swedish citizen Great is leading the crusade…
-Yeah, the crusade...sure, haha! I think Greta does a very good thing putting the focus on one of the big problems in our world right now, but then the airliner world is only 2% of the problem. Of course we can discuss what we can do with this 2%, especially the problem of burning all that fossil carbon and what it does to our nature.
-Because you have been thinking a lot about all the different alternative solutions that there are now with current technology. Of course someone may come up now with an entirely new disruptive technology...one of the points you make is that there is a lot of attention being placed on electric, but actually this may not be the best available solution to reduce the carbon footprint of the aircraft industry.
-No, I think the reason is that it works for cars, I mean it really does work for cars. You have the Toyota car that has been around for some time that has been followed by other makes, and then the Tesla electric cars, the Renault Zoe that works...so it works for cars, but unfortunately when it comes to aircraft the challenges are very different. The reason is that cars are insensitive to weight because the major resistance to moving a car is the rolling resistance of the tyres and they don't react too much to weight. The second thing is that the car doesn't really go that fast and long and you can stop anytime and reload the batteries. And the problem is not really the electric system itself, but the batteries and i can go deeper into that and compare it to other technologies.
-Yes, I remember we spoke some time ago when I was doing some research for a CNN article and I remember you mentioning that one of the problems is the energy density of the batteries, which is much lower….
-Yes, it is more than “much” it’s almost two magnitudes lower. We have to understand that the energy that is stored in the fossil fuel that we pump up and crack and turn into jet fuel or kerosene is a fantastic energy store. If we talk about the same energy measure that Tesla uses, Tesla typically talks about their car having 1.5KWh, that is one KW of power during one hour, one kg of fuel has 12 kWh of energy. 1kg of batteries ideally in a research cell in a lab, has 0.3. But when it comes to aircraft you have to look at the system, so you have to look at the fuel system with the fuel in it and compare it to a battery system and when we look at the battery system the best you can do today is 0.15, so we are essentially 70 times heavier if we run the aircraft on battery instead of kerosene.
-So in plain words one kg of jet fuel packs 70 times as much energy as the same weight in battery systems
-Correct! And the thing with the battery systems is that if you try to run it harder, you run into a dangerous zone. A lot of people are coming back and saying now batteries can get up to 0.4 and plan to be at 0.5 in x number of years and, yes, but this is a lab cell and the industry that knows most about high performance batteries and how dangerous they are and how close you can get to them is the Formula E car racing because they run on batteries. And if you go to them what they say is if you want to pack more energy in a battery system you start to become close to a thermal runaway. If you have seen a video of a Lithium-ion battery going into a runaway situation, from a mobile phone or a portable computer, they realise how dangerous this is. So you can’t do that. And The only way to stay away from a dangerous battery system is to reduce the demands on capacity demands on the system
-Basically you are putting so much of a performance demand on the system
-Correct right now the best battery system, the new one from Mclaren technology for the Formula E car. The demand of the formula e car is that it must be safe, it must be light and it must stay together as a battery system for one year, after one year you change it, this is not acceptable for aircraft, but you know, we have to give it some years so that it might be improved. A battery is a very expensive component so it must stay 5 yrs in an aircraft otherwise the maintenance cost of changing battery cells all the time will be too high, but let's say we take the example of Formula E that has the battery running for one season without having a thermal runaway...today, 2020, we are at 0.15 kwh per kg of battery system.
-So, I understood it correctly at Formula E they managed to solve some of these issues
-Yes, they have been racing now for 5 years, I am reasonably interested in racing and I also follow formula one, where they also have batteries there, but it is Formula E that is all about the battery, they are the battery example as an energy store and the Formula E has not had a thermal runaway, they have had several occasions when the system shut down, it is just too hot, somehow they are running the system to hard and they shut it down,...and this is another danger we have. You have to be surveying each cell in terms of temperature, charge, discharge everything, so you have a rather complex surveying system, monitoring system, it is rather complex, it also takes some kgs to do that. And when you do that you have to actually partition the system, because you always have the risk of a system shutting down and that actually happened in Norway...right over a lake the system shut down and they did not have any propulsion anymore, luckily they could dive into the shore and didn't die. I just want to say that electrical high performance battery systems are not safe systems unless you are very careful with what you do. We recently had two battery fires in prototypes built for electrical aircraft.
-One was Eviation...
-Yeah, one was Alice Eviation and the other one was the German eVtol...
-Lilium
-Yeah , and in both cases i think they went too close to the limit where they had a thermal runaway. It could be when you charge the battery but it could also happen when you use it. This is why the Formula E is such a good example because in 5yrs of racing they never had a thermal runaway.
-And you mentioned this Norwegian case and actually wanted to ask you because you are from Sweden and Scandinavia is one of the regions that is leading the way and Norway has very ambitious goals, they want to have full electric domestic flying in about a decade, how do you see these goals, after all what you told us....are they realistic goals? Do you expect any breakthrough that makes this possible in the medium term
-No, I don’t think it is realistic, what you can do is combine fossil fuel and battery in a hybrid system and you are going to end up with 80-90% fossil fuel and the rest battery. The battery is so heavy and thi is such a big problem for the aircraft. But they also say it should be more economic...and well, it won't be...i have done those calculations and there is no chance it will be more economical. But, then, if you want to make progress you should not say it should be battery in all aspects, you can build a hybrid that would work and kind of follow through on the promise, but it will be more expensive to produce and to run, and it won’t be more efficient than the best regional aircraft that we have at this time. But perhaps you should not ask for this, perhaps you should go for that, you have to have to creep before you can walk and you have to walk before you can run... All my calculations, all my knowledge and I have actually worked with gas turbines and propulsion systems for decades, when you sit down and start to calculate and really look at it you realize that the problem is more difficult than you think and all the OEMs, even the most positive ones, the real ones, not just some entrepreneurs that sometimes are not realistic, now say that it may be decades before we have working hybrids and even longer before we have something that is more electrical than hybrid
-Because you are duplicating systems right, adding weight, right?
-Yes, weight and complexity and I have in my corner series around the problem of hyping the electrical alternatives too much...I say that “e” should be for environmental not for electrical...even if we want to have a battery that just helps a little bit during take off and climb, because this is when more power is needed, it will weight 6 tons and this will make the whole aircraft impossible in terms of economy...
-There was some expectation that at least in the regional space...maybe in a few years...there was also this seaplane test in Canada...what about general aviation?
-General aviation has some possibilities. Pipistrel which is in Croatia...or Slovenia...Slovenia! they are really good and have made small sports planes and trainers and it is battery based aircraft, but you have one hour of action and you stay close to you airfield, it’s a good solution, it’s simple and easy to load your plane with electrical energy and then you fly and in this case, the economy works. It has its place. It has a place also for air taxis, a guy at Airbus says air taxis will have an operational range of 30 miles, because that’s typically from the airport to city center, and the battery system would work but anything beyond that...if you go into regions, the typical range of regional aircraft, turboprop or jet, is 300 to 500 nm and they fly up to 1500nm, well, so anything beyond 100nm will be a problem for a hybrid and huge problem, basically we only have proof of principle, if battery based.
-So basically one of the approaches you advocate is a number of alternative technologies that may do the trick. So the goal of making aviation more environmentally friendly and carbon free may be feasible, it may involve making existing aircraft more efficient, even if this means changing the designs, maybe coming up with new models. Others are looking at different types of fuel like hydrogen, for example. This one caught my eye recently because there are a number of projects that are exploring this possibility, for example there is this company called Zeroavia, I think that's a hydrogen powered system. There is also something called the Unducted Single Fan Propulsion, right?
-Yeah
-You discussed it in your writings...a new way of thinking engines...
-Yeah, the principle is simple and it is not really new technology, it has been worked on and talked about for decades. So, when you want to do propulsion for an aircraft what you need is an air pump, you want to throw air that is heavy, one kg per cubic meter and throw it backwards and pushes your aircraft forward, the thing is the smaller amount of air you push and the fastest you push it backwards, the less efficient this process is, the more energy you need to use to drive the aircraft forward. What we have done since the 1950s when we could only do turbojets, a small amount of air that kick backwards very fast to get the force to move forward, we have increased the amount of air and we kick it not as fast backwards, so the latest turbofans, the geared turbofans, they all have the same principle, make bigger engine diameters that suck in more air and kick it out slower, you need to kick it faster than you want to fly, but the slowest you kick it out and still get the force, the better. The principle of the unducted fan or open roller fan, is the same as turboprop, the turboprop is o more than a gas turbine that is grabbing a lot of air and kicking it back even slower than a turbofan and the open rotor, which is a variant of that that has some mechanical advantages is something in between a turboprop and a turbofan. And the advantage is that it keeps the speed of a turbofan with the economy of a turboprop, it could be a good way to go for regional aircraft, go away from normal turbofans and go to engines with higher bypass ratios.
-Would it be as fast as a current jet?
-Yes, it will keep the same travel times, that’s the key thing. There are two problems with turboprops today, one is that trips take longer, if you fly within the UK or within Germany is fine, but Berlin to Rome in a turboprop...first of all is going to take many hours and second, they are noisy, because big propellers push pressure waves close to the fuselage and you need aircraft that are quieter and today's turbojets are very quiet, comfortable. We want the efficiency of the turboprop and the speed and quietness of the turbojet. And there is an interesting development by general electric who is doing that with acceptable complexity, there are others like French Safran doing the same, but with more complex systems
-And if this technology is known why is it not more widely adopted?
-Because this prop fan has a large diameter and you need to design the aircraft around it, you can not take an existing design. Today most aircraft have engines on the wings because it is structurally very efficient, and you would need to put them in the back for safety reasons and also sound reasons, otherwise it would be too loud in the cabin.
-Just basically, to explain in plain words, it looks like taking out the casing...
-yeah, the nacelle
-As if you were taking it out and leave the engine in the open
-Yeah, and the reason you take out the nacelle is that you want to have a large diameter, because you need to suck a lot of air and push it back slowly and once you come to large diameters, the nacelle is going to be too heavy so you have to get rid of it and you need to get the fan to take the air like that...But this is one way, there are other approaches, for example, make higher bypass ratios for existing planes, make lighter nacelles using carbon fiber composites even more than we do today, so this is something we can improve on. And there is also the possibility of getting away from the actual fossil fuel, because if we use a fuel like synthetic fuel or biofuels. The key is how we get there and which techniques we use and there are many techniques that are more realistic and efficient than to say it should all be electric, just because it works for Tesla it doesn't mean it works for planes...let me tell you why it works for planes...because we have stoplights. The problem is...why does electric work for cars? Because the car engine is so outrageously inefficient. The turbofan in an aircraft is 50 to 60% efficient today and 70% tomorrow, this means it transforms the energy stored in fossil fuels to propulsive motion with a 60% efficiency, the cars we drive today when we drive them to work is 7% efficient or even less 5%, so its ten time worse!
- 7%! Wow!
-Yes, it is ten times worse! Therefore if you have a hybrid or electric car, when you are driving you are using the energy and then you brake, and they are not regenerating, so they dissipate the energy, we are destroying the motion energy, we produce and then we start the cycle again at the next stoplight. Cars are terribly inefficient and anything you do with the engine that is better than that is seen as success, but for an aircraft this is not enough, it needs to be 50-60% efficient in a propulsion system to be viable for an aircraft. And this is where the electrical system, motor, generator, inverter, etc just doesn't cut it compared with the efficient system we have today
-And is it here where hydrogen can become a viable alternative, because it has zero emissions, so if it could work at a scale...can you tell us more about the different ways to use hydrogen in an airplane and why it hasn't worked yet, bc it has been researched for years, but it has not produced anything that works at scale
-Hydrogen has many interesting features...first of all when you oxidize it to take away the energy, you get water….so its not producing a waste that is a problem. In oxidation process you need to be careful not to produce ascertain substances, but this can be dealt with. Hydrogen has almost three times more energy density than fossil fuel, almost 30 kwh per kg. There is a problem though, it is three times more demanding when it comes to volume...
-Can I stop you here for one second: in which state is hydrogen stored? Liquid, gas?
-Both you can store it as gas or liquid, the volume demand is higher when stored as gas, you need to store it in a tank under very high pressure otherwise volume demand is just impossibly large. But in order to be efficient you need to store it as a liquid, you need to cool it. The problem is that it is very difficult to store in an efficient way in an aircraft, on the other hand is almost three times more efficient as an energy store, so you don't need so many kg of energy as you have for fuel. So you can reduce the weight by three times and at the end of the day, bc of these large tanks...
-So, you need a very powerful freezer to freeze it to 235 degrees celsius and lots of space
-Correct, so the a will be larger, will have more drag, but you will need less fuel. So all manufacturers are working on it
-And actually the world's first gas turbine was started in hydrogen, bc they didn’t know if it would work with kerosene. It works perfectly well once you have solved the storage problem you can substitute the kerosene, you would still need to do some work, but it will work. In the 1950s there was some research work on reconnaissance planes bc hydrogen has some interesting properties when at high altitude
-And the byproduct is water?
-Correct
-No carbon byproduct at all
-Bc of burning process you need to be careful not to create NOXes, NOX pollution, but it is a function of burning temperature and also a problem in gas turbines and engineers are studying how to reduce it
-And the other way to use hydrogen would be to make it work through a fuel cell
-Correct you can take hydrogen into a fuel cell, and combine it with oxygen, the fuel cell will produce electrical energy that you can use to drive motors that drives fans. This is another way to do it...
-Can you explain what is a fuel cell and how does it work? It is used to run an electric motor?
-It works like a battery, but you take hydrogen, oxygen from the air and you have a chemical oxidation of the hydrogen instead of burning process and this process releases energy that you picked up as electrons, electrical power that you use to run the aircraft
-So in this case you have de facto an electric plane but instead of storing energy in batteries you store it as hydrogen
-Correct, and a high performance fuel cell generate electrical energy and the you run your fans with electric motors
-So what other limitations is has...is it dangerous?
-Well, it could be dangerous , but we have learned to master it in different industrial settings. The hydrogen we have today is produced mainly from natural gas, so you start with a fossil fuel element, so it is not ideal, there are other processes where you take the hydrogen from the air, it is more energy intensive but doable. The reason we haven't come further on the hydrogen path is mainly we don't have a good production process yet that can produce large quantities of hydrogen and secondly we don't want to transport bc of the high volume requirement, so ideally you would want a production process that produce it next ot the airport, but these are all technologies that are doable, we need to find an ecosystem, how we produce the hydrogen, how to put it in an aircraft, have aircraft that are adapted to use hydrogen...then we’ll have a capable long range propulsion system but it is a long way to go. All OEMS are starting to work on this, because they realized batteries don't work in aircraft and hydrogen has potential and longer term is the most realistic alternative to fossil fuels. Short term, biofuels, synthetic fuels, and longer term, with a lot of work, hydrogen.
-And what about performance?
-The problem with biofuels and synthetic fuels is the scale. There are 25,000 aircraft in the air every day, in normal times, when we don't have pandemics. So there is a scale problem of making those bio based or synthetic fuels, and of course there is a scale problem also in making the hydrogen, but this is something we can work on and gradually change. It is something we need to start to do. We are already flying with biofuels, starting to fly with synthetic fuels and we need to start to make research aircraft that can fly with hydrogen
-Yeah I spoke with someone in Sweden that world me that biofuels are still a bit scarce, in Scandinavia they are trying to make them from forestry products
-Yeah, this is the problem of biofuels, you don't want to compete with feeding the world and that is a problem of biofuels, otherwise it is very viable. Actually, if well produced, biofuels is best for aircraft engines than fossil fuel, the problem is the scale and the raw material. The synthetic fuel unfortunately requires lots of energy to produce, but this is a general problem we have all over the word that we have energy production in places where it is not consumed, offshore turbines, or another example, ther desserts have lots of solar energy, but no consumption, so one way to view synthetic fuel as an efficient energy storage process and then the fact it take a lot of energy to make one kg of synthetic fuel is still acceptable because that's energy that you wouldn't be using all that generated energy in the middle of the desert
-But in a context of huge capital investment, not only for airlines, but also for the oems, have to engage in programmes that cost tens of billions of euros, you can run biofuels in existing airframes, but to use hydrogen wouldn't we need new designs or need new designs?
-Yeah, this is the problem, biofuels work as a plug in replacement, the problem with hydrogen is that you need to design the aircraft from scratch but also the whole ecosystem to use hydrogen
-What is your view from the next 10 to 20 years of the industry?
-First you need to understand that 2% of the problem today is air transport and think about the use of energy and those processes that produce co2, and many of these could be changed. So going after the aviation industry as priority, before doing other things, is plain stupid, bc there is low hanging fruit. It should be the other way around, there are other processes like steel and cement that should be changed first, because they have perfectly viable alternatives that produce less co2. Then you need to realise that if you need fossil fuel use for long range air transport because you need high energy density, then you may need to accept that for some time, but over the longer term the solution is possibly hydrogen-based, but in shorter terms, we need to accept that we can replace fossil fuel as much as we can, but we certainly we should invest in taking out the carbon producing hogs we have in society, a lot of areas in society that are pushing co2 like mad and to focus on the air transport industry as priority is just a wrong way to do it
-Do you think these projects stand a real chance considering the long cycles in this industry. Are we talking about 20yrs from now?
-Yes realistically 20yrs. They stand a chance. Fuels are nothing else than energy stores, we are lucky that the earth has lots of energy in these fossil fuels, but now we are now cracking them into different fuels, but we need to realize that we need to stop this, a sustainable system and ecosystem that doesn't use what was produced before, that uses and re-uses, not just an issue for transport but for many other industries and together we will find a way to do this it, but we can not shut single out aviation and say you solve the problem first and then fix the other 99% of the problem…
-Great point to wrap up this talk...lots of interesting projects!
-It's been a pleasure Bjorn, I hope we get to speak again soon. Thank you so much and stay safe!
-Yes, it was a pleasure for me as well...until next time!
-Bye!
-Bye, bye!