BEN CRAVEN: PART ONE

CALCULATIONS AND ESTIMATIONS 



It was nice to get a talk from Ben, the man from our screens in first year, who gave us a nice introduction to the importance of calculations in product design. The idea that a project or concept can be justified very early on with a simple rough calculation.

It is important to include calculations like these in projects to ensure you aren’t wasting your time. You can design something amazing in theory but if the numbers don’t add up it means nothing. He gave a good perspective on this, stressing that accuracy is not always that important. Simple rough calculations in your head are enough to give a clear indication if something will work and it is something I plan to take into consideration with my current and future projects.

D&T RESEARCH


Naturally my takeaway from this was this very calculation we were asked to do, regarding sustainable aviation fuel (SAF). We see more and more today that airlines and aircraft manufacturers boast their investment into SAF’s but Ben raised questions about how conceivable this may be. It is very easy to say we can solve the issues with aviation by switching to SAF but is this as easy as it sounds.

The current trend with aircraft these days seems to be updating older air frames with newer and more efficient engines. The Boeing 737 for example is one of the most common and commercially successful jet aircraft of all time. This was first released in 1968. Since then, the aircraft has been gradually upgraded with newer and more efficient engines. These engines have allowed the aircraft to use less fuel and fly longer distances. 

Boeing 737 Family Comparisons 
You can see from this diagram, the first few generations of the Boeing 737 aircraft. Each on slightly modifying the existing air frame to fit these improved engines. So, this has worked up until now, an industry standard across other manufacturers like AIRBUS. However, we are reaching the point where we have pushed these designs almost as far as we can push them. 





I have found it difficult to truly understand exactly why these larger engines are more efficient and how to put it into words. I would generally consider myself more of a designer rather than an engineer if that is any justification. I feel the above video gives a quick idea of how this works in the simplest way possible. It shows how these engines have become more efficient over time by harnessing higher bypass ratios. In summary, traditional aircraft engines from the 50s to the 70s worked by funnelling all of the air through the combustion chamber, igniting with the fuel and providing thrust. It was then discovered that this wasn’t the most efficient way of doing this. Allowing some air to flow around the core of the combustion engine increases efficiency and reduces noise, this is known as a higher bypass ratio. So modern engines have an extremely high bypass ratio.

GE9X Engine for the Boeing 777X being tested on an old Boeing 747 Test Platform 
We can only innovate so far based off these older air frames and I feel the Boeing 737 illustrates this well. In 2017 yet another iteration of this aircraft released, the range of now infamous 737-MAX aircraft. Boasting significantly improved engines this aircraft could cut fuel and operation costs for airliners and is one of the most popular aircraft of the modern age. Unfortunately, this aircraft quickly started showing strange behaviour which resulted in two devastating crashes in 2018 and 2019, which claimed a total of 346 lives. This is unheard of in modern aviation, and this shows the human cost of cutting corners in design.


Boeing 737-400 Engines compared to the MAX-8
So, what was the issue with this newest plane? The previous generations such as the 737-400 were already pushing space under the wing to the limits, with the large engines almost touching the ground. When Boeing decided to add even larger engines they simply would not fit. This required them to be moved further forward on the wing to allow them to be positioned higher. So instead of updating the aging air frame, they cut corners. This minor repositioning of the engines caused some issues in the way the plane behaved, causing it to tilt upwards gradually. To counter this Boeing added software called MCAS to automatically tip the nose of the aircraft down. The problem was that they didn’t tell pilots or airlines, as this change would require further training. This costs airlines money, and Boeing knows this, so they kept it quiet to try and improve sales. Ultimately this became an absolute disaster for the company and its reputation, something they are still trying to recover from to this day.

The way the industry currently works almost doesn’t allow for innovation. The two main companies Boeing and Airbus, are continually trying to make their aircraft more efficient and cost effective while not pushing the design too far so as to require further training from pilots. The lack of competition and desire for airliners to evolve means we are almost stuck in this cycle of minor upgrades. Any radical change in design would require significant benefits for the finances of airliners to actually be adopted. It’s clear to see that aircraft manufacturers and airlines simply don’t care enough. They value money over innovation and even human life so why would they care about sustainability.

So, the current industry basically only allows for one solution, SAFs. There’s no evidence pointing to anything substantial that will make a dramatic shift in the direction the industry is heading in within the next few years. This leads back to the questions about feasibility that Ben raised. He gave the example of how much land would be required to produce enough fuel for one A380 flight, and it was a massive plot of land. It makes it sound like it’s a complete pipe dream but is that true?




Waste product from a variety of sources can be used to make SAF’s including:
  • Corn grain
  • Oil seeds
  • Algae
  • Other fats, oils, and greases
  • Agricultural residues
  • Forestry residues
  • Wood mill waste
  • Municipal solid waste streams
  • Wet wastes (manures, wastewater treatment sludge)
  • Dedicated energy crops.

It is difficult to estimate whether there is enough waste to meet the demand of air travel, especially given the ever increasing passenger numbers year on year. The US department of Energy have estimated that there is around 1 billion dry tons of bio-mass can be collected sustainably each year in the US alone, a number which they say can meet the projected fuel demand of their country. So in theory the bio material is there to meet with the demand. The rest of the world consumes at a similar rate to the US. If the proper infrastructure is put in place, the demand can be met. So this all sounds great. We have all we’d ever need to make aviation sustainable. That is until you take a closer look.

Other sources claim that to meet the demands, extensive land would have to be used for bio-crops. The act of using extra land would required a decrease in food production or expanding crop lands into wooded areas. Destroying forests also releases stored carbon and means the land won’t be able to absorb carbon anymore. Many beleive this would actually be more harmful to the environment than traditional fuel. Whether this is entirely true or not will have to be seen as production is ramped up, but again this is another sign that it maybe is not as simple as it sounds.

SAFs are still a blend of traditional aviation fuels. The ratio is somewhere in the ballpark of 50/50. It is actually not legal to fly an aircraft using 100% SAF fuel due to strict regulations. On the 23 November 2023, Virgin Atlantic flew a test flight using 100% SAF to test whether this would negatively affect the engines. Air BP, Rolls Royce, Boeing, and an independent fuel test laboratory conducted detailed tests on the proposed fuel blend to check the safety, concluding that there were no issues with performance, handling or fuel consumption. So, in theory, future regulatory changes and infrastructure adaptations would allow for SAF to replace traditional jet fuel. They also reduce soot content, water vapor, and sulphates in the exhaust. This will mean a reduction in contrail formation which is also another huge benefit in stopping climate change. 


Virgin Atlantic Flight 100, Boeing 787 flying on 100% Sustainable Aviation Fuel, Nov 2023 
In terms of a quick fix for aviation, this might be the easiest solution. It wouldn’t require a whole new fleet of aircraft, which in itself would damage the environment. Looking into companies such as BP, they mention wanting to reduce emissions but emphasise they require policy change from governments to ensure their investments in the infrastructure are worthwhile. Producing 100% SAF that could fuel most jet flights will take years to come to fruition and they don’t want to take a massive risk. SAF adoption of 10% by 2030 would require 40 million tonnes of SAF. Out of all aviation fuel in use, SAF only counts for about 0.1%. This shows how slow advancement is in this industry. There is a possible solution to increase the sustainability, but no one is adopting it quickly enough.

If it is not cost effective for everyone involved or forced through by government bodies it simply won’t happen and that is the sad truth. It also only really deals with the problem of using fossil fuels. Burning fuel like this still releases harmful emissions. Research does show this could reduce emissions by around 80%. It does release emissions but they can claim it is lower because it primarily uses carbon that is already part of the current carbon cycle in various feedstocks. Traditional fuel uses resources from the ground releasing carbon that was previously stored there. So technically it doesn’t really stop emissions it just means the emissions are in theory re-absorbed my the bio-mass that is used in its production. It basically just reduces the amount of carbon taken out of the ground.
 
While it is definetely a step in the right direction, I think it is also like those sort of green washing buzzwords like net zero and carbon footprint. It is being seen a lot more in the industry as a sort of justification for the out-of-control increase in flight numbers and emissions every year, but it only makes up a tiny portion of total aviation fuel. It is also being adopted very slowly and would require a large amount of infrastructure change. When you look closer it ultimately doesn’t solve everything like they say it does. It actually gives us a way to keep releasing emissions even when we run out of fossil fuels. Ultimately going forward the industry might require a more significant mix up to really make a change.


USEFUL LINKS



ARTICLE ON THE LIMITATIONS OF CURRENT ENGINE EFFICIENCY
https://simpleflying.com/risks-of-engines-running-hot-amid-efficient-improvements/

ARTICLE ON THE TECHNICAL DETAILS OF THE NEWEST GE9X ENGINE FOR BOEING
https://simpleflying.com/general-electric-boeing-777-engine-power-comparison/

INFORMATION ON VIRGIN ATLANTIC FLIGHT100
https://corporate.virginatlantic.com/gb/en/business-for-good/planet/fuel/flight100.html

US DEPARTMENT OF ENERGY ON SUSTAINABLE AVIATION FUELS DEMAND
https://www.energy.gov/eere/bioenergy/sustainable-aviation-fuels

AIRBUS ON HOW SAF
https://www.airbus.com/en/sustainability/respecting-the-planet/decarbonisation/sustainable-aviation-fuels#:~:text=When%20burned%2C%20SAF%20still%20produces,carbon%20cycle%20in%20various%20feedstocks.

ARTICLE ON THE PROBLEMS WITH SAF
https://www.wri.org/insights/us-sustainable-aviation-fuel-emissions-impacts