Necessity is the mother of invention / How fossil fuels have stifled progress / Electric aeroplanes part 3.
The expression "necessity is the mother of invention" really came home to me thinking about electric vehicles. There is so much readily available power in those hydrocarbon droplets we as a civilisation have been lulled into a slumber of innovation. It was not until the EV revolution that automakers really started to think about efficiency, and the same will happen with air travel.
According to the US EPA the average fuel economy of US cars in 2016 was a measly 25.1mpg. (This is in US imperial, for UK readers you should read it as 30mpg) Whilst this is an average across the whole fleet it also shows that the best non-EV cars are only getting about 50 mpg (and those are hybrids).
Car efficiency
Looking at the graph over time, whilst we see some improvement especially around 1980 and 2005 mostly there hasn't been a lot of progress in the last 20 years despite government mandates trying to encourage it.
Enter the EV. In 2012 the Tesla model S entered the market with an EPA rated 89 MPGe. This is already 50% better than the best non-EVs. Electric motors are inherently more efficient that ICE engines, but that's not the story here. The 2020 model S has an EPA rated 117 MPGe, 30% better than the 2012 model (in only 8 years), despite having a higher capacity battery. This improvement has come on the back of hundreds of innovations each responsible for tiny improvements. (Such as flush door handles, better designed wheels and tyres, smaller/non existent wing mirrors, improvements to energy management, and more recently, turning off AC fans for unoccupied seats).
Why did Tesla work so hard to improve the efficiency of their car? Because the range of an EV is currently something people are concerned about, and improving the range of EVs is more pressing due to the lower energy density of batteries vs fossil fuel.
Car manufacturers could have implemented many of the efficiency gains Tesla made on their ICE vehicles, but didn't because no-one cared enough about efficiency because fuel was abundant and cheap. Humans are efficient with their innovation and brain power, why invent something to solve a problem that isn't bothering you?
I believe the same is true and more so for electric flight. Whilst jet fuel is very expensive compared to electricity, its still relatively cheap (especially as in many countries aviation fuel is exempt from taxation). Whilst aircraft manufacturers have made some improvements to efficiency over the years, the pace has been somewhat glacial.
Enter electrified aircraft.
I believe that the electrification of air travel will have a similar stimulus to aircraft efficiency as the electrification of passenger cars had, but even more so as the need is even greater. In fact we can already see this happening.
According to Wikipedia, the NASA X-57 started life as a commercially available Tecnam P2006T. With modifications to improve the efficiency, and taking advantage of the benefits of electric propulsion it has gained efficiency improvements of possibly over 5 X or 500%. Its hard to make sense of the numbers exactly (as given in that article), but it seems that its safe to say there is at least a 30% efficiency improvement gained from redesigning the wing shape and placement of the engines. Some of the stated 5X is due to the efficiency of electric engines vs ICE (as stated in the first article in this series, electric engines are about 3x as efficient as their combustion counterparts), so possibly up to another 2X from their design changes.
Regardless of the actual numbers, even if this vehicle is only 30% more efficient, the changes were only to the wings and placement of the engines. With additional innovations, such as removing all control surfaces, or changes to the fuselage, significantly greater efficiencies could be obtained. Thats why when I said 50% in part 2 I don't believe I was being unrealistic.
Aircraft currently have the ratio of the weight of the vehicle (including fuel) to the weight of the payload (or carrying capacity) or "payload fraction" of between 25 and 55% What this means is that the (vehicle and fuel) weighing between 75 and 45% of the total weight. There are practical limits on how low you can make this number (e.g. a flying battery that weighed 100 tonnes but carried only 100kg would have little practical value), however there could be value in going as low as 5%, or 95% of the weight is aircraft (including batteries) with only 5% payload.
Why would you want such a small number? Well, ideally you want the largest number possible, but bear in mind the reduced costs of operating an electric plane and you can see that even if you have a much more expensive to build and heavier vehicle, in time it can return that investment. Of course a heavier vehicle would also cost more to run, but with the fuel costs so much lower even a heavier vehicle is still worth considering.
There are diminishing returns on lowering the ratio, however with current long distance vehicles around the 55% mark, there is extra range to be gained in an electric plane by redesigning it to hold more weight of batteries than a current design holds (of fuel).
As battery technology improves over time and the batteries of those planes get replaced their carrying capacity and/or range would be improved too.
For reference, this is why Tesla vehicles have so much more range than non-Tesla. They completely redesigned the way a car is built, putting a 'skateboard' of batteries under the car. Other automaker were trying to fit batteries into spaces that used to be occupied by the ICE power-train such as engine compartment, fuel tank and transmission tunnel, which are non-optimal spaces for batteries.
I believe that in the future we will look back at the fossil fuel burning era and consider how our technological innovation was stifled by it, and how quickly it fired back up once we started abandoning them.
Please leave your thoughts and examples of this in the comments.
Why did Tesla work so hard to improve the efficiency of their car? Because the range of an EV is currently something people are concerned about, and improving the range of EVs is more pressing due to the lower energy density of batteries vs fossil fuel.
Car manufacturers could have implemented many of the efficiency gains Tesla made on their ICE vehicles, but didn't because no-one cared enough about efficiency because fuel was abundant and cheap. Humans are efficient with their innovation and brain power, why invent something to solve a problem that isn't bothering you?
Plane efficiency
I believe the same is true and more so for electric flight. Whilst jet fuel is very expensive compared to electricity, its still relatively cheap (especially as in many countries aviation fuel is exempt from taxation). Whilst aircraft manufacturers have made some improvements to efficiency over the years, the pace has been somewhat glacial.
Enter electrified aircraft.
I believe that the electrification of air travel will have a similar stimulus to aircraft efficiency as the electrification of passenger cars had, but even more so as the need is even greater. In fact we can already see this happening.
According to Wikipedia, the NASA X-57 started life as a commercially available Tecnam P2006T. With modifications to improve the efficiency, and taking advantage of the benefits of electric propulsion it has gained efficiency improvements of possibly over 5 X or 500%. Its hard to make sense of the numbers exactly (as given in that article), but it seems that its safe to say there is at least a 30% efficiency improvement gained from redesigning the wing shape and placement of the engines. Some of the stated 5X is due to the efficiency of electric engines vs ICE (as stated in the first article in this series, electric engines are about 3x as efficient as their combustion counterparts), so possibly up to another 2X from their design changes.
Regardless of the actual numbers, even if this vehicle is only 30% more efficient, the changes were only to the wings and placement of the engines. With additional innovations, such as removing all control surfaces, or changes to the fuselage, significantly greater efficiencies could be obtained. Thats why when I said 50% in part 2 I don't believe I was being unrealistic.
Payload Fraction
In addition to efficiency improvements, I want to also elaborate a little on how range can be improved simply by efficiency-neutral design changes.Aircraft currently have the ratio of the weight of the vehicle (including fuel) to the weight of the payload (or carrying capacity) or "payload fraction" of between 25 and 55% What this means is that the (vehicle and fuel) weighing between 75 and 45% of the total weight. There are practical limits on how low you can make this number (e.g. a flying battery that weighed 100 tonnes but carried only 100kg would have little practical value), however there could be value in going as low as 5%, or 95% of the weight is aircraft (including batteries) with only 5% payload.
Why would you want such a small number? Well, ideally you want the largest number possible, but bear in mind the reduced costs of operating an electric plane and you can see that even if you have a much more expensive to build and heavier vehicle, in time it can return that investment. Of course a heavier vehicle would also cost more to run, but with the fuel costs so much lower even a heavier vehicle is still worth considering.
There are diminishing returns on lowering the ratio, however with current long distance vehicles around the 55% mark, there is extra range to be gained in an electric plane by redesigning it to hold more weight of batteries than a current design holds (of fuel).
As battery technology improves over time and the batteries of those planes get replaced their carrying capacity and/or range would be improved too.
For reference, this is why Tesla vehicles have so much more range than non-Tesla. They completely redesigned the way a car is built, putting a 'skateboard' of batteries under the car. Other automaker were trying to fit batteries into spaces that used to be occupied by the ICE power-train such as engine compartment, fuel tank and transmission tunnel, which are non-optimal spaces for batteries.
Other (non plane) things
There are so many other devices that use hydrocarbon fuels I sometimes wonder how much better they could get if they were replaced by battery versions. My mind drifts to things like drones which seem to be getting better every year, and how fast that development has happened since batteries become good enough to power them.I believe that in the future we will look back at the fossil fuel burning era and consider how our technological innovation was stifled by it, and how quickly it fired back up once we started abandoning them.
Please leave your thoughts and examples of this in the comments.
Part 4 is now available here: Part 4
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