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The Future of Airliners? - Aurora D8

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10:49   |   Mar 31, 2017

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The Future of Airliners? - Aurora D8
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  • When we look back over the last century of innovation in flight it’s sometimes hard
  • to believe how far we have come.
  • The Wright’s first flight in 1903 was at best a proof of concept; only managing to
  • fly 37 metres before falling ungracefully from the sky.
  • We often look back at this historic event and see it as the spark that ignited a century
  • of human flight, the truth is, the event barely registered in national media and most questioned
  • the legitimacy of the news.
  • It took another 3 years of incremental improvements and public test flights before the international
  • community began to accept their achievements and by that stage others had begun to catch
  • up and even surpass their designs.
  • By 1910, Louis Blériot had flown across the English Channel, Georges Chavez soared over
  • 2 kms to clear the Alps and Glenn Curtis began to testing planes as a platform for weapons
  • and his biplane became the first to take off from the deck of a ship.
  • This marked a trend for the next 35 years of aviation history, which was dominated by
  • war and by the time World War 2 came to a close giant companies had been formed who
  • were mass producing planes capable of transporting humans across the world.
  • These companies were not going to simply vanish as the war ended and instead set their sights
  • on building a new commercial civilian transport industry.
  • In the final year of World War 2 over 4 thousand Douglas DC-3s had been built and many of these
  • would go on to be converted for civilian use.
  • The DC-3 is still the most produced airliner in history with over 16,000 built and some
  • are even still in service across the world, but it’s slowly being caught up by the Boeing
  • 737, which has sold so many units that at any single point there is an average of 2000
  • 737s in the air.
  • The 737 made it’s debut in 1968 and it’s design has essentially become the template
  • for which most jet airliners have been built on since.
  • The initial design of the 737 had the engines mounted on the tail, similar to the DC-9,
  • which the 737 was competing with, but placing the engines here reduced the amount of space
  • available towards the rear of the cabin and mounting the engine pods tight against the
  • underside of the wing freed up space at the back of the cabin for more passengers, which
  • was important for this narrow and short body, short haul plane.
  • It also reduced the bending load on the wings, counter-acting the upward bending load caused
  • by lift.
  • The success of this design has allowed the 737 to stay in service for over half a century
  • with incremental improvements and today it’s so popular that most budget airlines like
  • Ryanair and Southwest airline use no other plane.
  • It’s engines have got gradually larger and more powerful.
  • It’s cabin got larger as traffic increased, wingets were introduced to the wing to reduce
  • induced drag and later this year the latest iteration of the 737, which has already sold
  • over 3400 units, will make it’s debut with new split winglets, more efficient engines,
  • an improved flight deck and the modern cabin interior developed for the 787 dreamliner.
  • This theme of incremental improvements in the airline industry happens for a reason.
  • Introducing a totally new plane design is an incredibly risky business.
  • We need to look no further than the failed Concorde for proof of that, but even introducing
  • a new plane series like Boeing’s 787 can cause massive losses in revenue.
  • The plane was plagued with delays, originally slated to arrive in 2008, but actually made
  • its first commercial flight in 2011 and only recently has hit it’s stride in manufacturing
  • and sales.
  • New designs are simply a risky business decision and in general companies will play it safe
  • and not break the mold.
  • On top of this a plane’s service life is a huge part of its selling point.
  • Airlines want to buy planes that maintain their value over the years and can last them
  • a significant amount of time with minimal maintenance, so manufacturers have made effort
  • to increase the service life of these planes, which in turn has increased the cycle times
  • between new iterations of planes.
  • Making progress even slower again.
  • With the current status quo of the airline industry.
  • We aren’t likely to see much change any time soon, BUT what if a new industry disrupter
  • emerged.
  • One that could shake up the duopoly of Boeing and Airbus to force competition and new designs?
  • We have seen this happen in other industries recently.
  • The energy sector is being revolutionised by cheap solar panels, Tesla was the first
  • successful car start up in America in over a century and composite materials are set
  • to continue replacing metals in many every-day applications.
  • These disruptive technologies combined with rising air traffic could raise the pressure
  • to innovate.
  • In this new series of videos I am going to break down a number of future aircraft and
  • the design challenges they need to overcome to become a reality.
  • Let’s first take a look at the D8, nicknamed the Double Bubble, developed by Aurura, MIT
  • and with the help of NASA.
  • The current template of plane design at the moment consists of a tubular fuselage.
  • This shape is primarily there to resist the internal pressurisation, allowing the fuselage
  • to expand without creating dangerous stress concentrations.
  • As long as we pressurise the inside of our planes this design aspect won’t change,
  • but we can create fuselages with multiple interconnecting tubular sections.
  • This is exactly what the D8 does, with it’s double bubble fuselage.
  • So let’s look at how they came up with this design and the theory behind their design
  • choices.
  • To design this concept they actually started off with a 737 and performed a morphing study
  • by gradually introducing their design goals to the current design.
  • They started by first optimising the airframe of the current 737-800 airframe with current
  • generation improvements.
  • They then changed the fuselage to feature the double bubble.
  • This shortened and widened the fuselage considerably.
  • The wider body and shaped nose allows the body of the aircraft to generate more lift,
  • particularly at the nose.
  • This allowed the wings to get thinner and thus reduce the drag they generate, but it
  • also meant that the tail wing could decrease in size too.
  • The primary purpose of the tail wing is to generate downforce at the rear of the plane,
  • which keeps the nose of the plane up, an important stability characteristic, but when the nose
  • generates it’s own lift, the importance of the tail wing is diminished and it can
  • decrease in size, which again reduces the drag.
  • They then reduced the cruise speed of the plane from 0.80 mach to 0.76 mach, which may
  • seem like a step backwards, but remember the primary goal of this future design are to
  • improve efficiency.
  • This allowed the wing sweep of the plane to decrease, if you don’t understand this go
  • ahead and watch my “why are plane wings angled backwards video”.
  • In the next iteration they reduced the cruise speed again to 0.72, essentially removing
  • the wing sweep altogether.
  • Reducing the speed of the plane reduces the thrust requirements of the plane, which reduces
  • it’s fuel consumption, reducing the sweep reduces the wing area, which again reduces
  • the drag.
  • So reducing the speed by just 10% results in a much larger percentage of in fuel savings.
  • Consider that if you were flying on a 3 hour flight this would increase your flight time
  • by just 18 minutes and this increased transit time would be even less of an issue when you
  • factor in the reduced boarding times that the double aisle configuration facilitates.
  • The next design iteration moved engines from under the wing to the rear of the plane and
  • mounted the engines flush with the fuselage, but this requires some future tech that isn’t
  • quite ready.
  • With the current configuration, engines are placed far from the body of the plane and
  • so the air entering them is undisturbed and uniform.
  • This is ideal for the engine designers because each of the blades in the compressor experience
  • the same air pressure and speed through each cycle.
  • But if we move the engines tight against the back of the plane the engines have to ingest
  • the boundary layer air-flow, which is the slow moving layer of air that builds up on
  • the surface of the plane.
  • This type of engine is called a boundary layer ingestion engine and it has been a topic of
  • great interest for NASA and other aerospace companies, because it reduces the loss of
  • kinetic energy of the aircraft greatly.
  • In a normal plane this boundary layer of slow moving air simply rolls of the back of the
  • plane and mixes with the fast moving air.
  • This causes vortices and a low pressure zone behind the plane, which creates drag.
  • The idea behind the BLI engines is that they take this slow moving air and speed it up
  • and thus eliminate some of that drag.
  • It’s a nice idea that is far from being ready.
  • The first problem we face is that non-uniform air entering the engines.
  • The air entering the engine furthest from the fuselage of the plane is moving faster
  • than the air entering the engine near the surface.
  • This creates a discontinuity of stress, as discussed before in my dreamliner window video,
  • cycling high and low stresses is VERY bad for any part, as it results in fatigue of
  • the part and when your part is rotating through those high and low stresses a few thousand
  • times per minute...your part isn’t going to last very long and that’s just problem
  • number one.
  • The next big problem is stall.
  • Airflow normally moves uniformly through a jet engine, but when it’s distorted as it
  • enters the engine, there’s a high risk of compressor stall.
  • Compressor stall works similarly stall on a wing, where the speed and angle of attack
  • of the wing can result in flow separation behind the wing.
  • This prevents the wing from generating lift and thus stall occurs.
  • Non-uniform, turbulent air makes this far more likely to occur.
  • When this happens in a compressor it can lead to a chain reaction of stall, as the localised
  • stagnated air travels with the blade it stalled on, but lags behind slightly allowing it to
  • come in contact with other blades, which then stall too.
  • Compressor stall may just result in localised areas of stall that affect the engine's performance
  • or it can result in a complete flow reversal where the incoming air is not being compressed
  • enough to work against the previously compressed air which results in an explosive flow reversal
  • with air coming out the inlet of the engine.
  • For these embedded engines to ever make their way onto a commercial aircraft significant
  • leaps in airflow prediction and engine design & control will be needed.
  • Although there are technical challenges, their use could offer significant reduction in fuel
  • consumption over the current generation of podded engines.
  • All of these technologies combined in the D8 have been calculated to have a potential
  • fuel savings of nearly 50% over conventional technology and with the continual rise of
  • fuel prices.
  • This plane could be making it’s way to an airport near
  • you sooner than you may think.

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