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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 mywhy 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.

When we look back over the last century of innovation in flight it's sometimes hard

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客机的未来(The Future of Airliners? - Aurora D8)

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    joey joey 發佈於 2021 年 06 月 01 日
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