The Future of Airliners? – Aurora D8
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The Future of Airliners? – Aurora D8

August 31, 2019


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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  1. Had to make a small change to the video. I don't have my mic with me though so couldn't fix the "plane windows angled backwards" problem. Anywho….yeah thanks to http://squarespace.com/realengineering for supporting the channel. Please check them out or consider supporting the channel over on https://www.patreon.com/realengineering.

    Your support has allowed me to make my first part-time hire!

  2. Look at the intakes of F-4phantom, F-5, Su-27, Mig-29, concorde, etc. Their intakes arent flush with the rest of the fuselage of the plane but separated by a small gap which reduces the effects of boundary layer air flow.

  3. It is notable how the new fuselage design resembles that of a whale… It is not the first observation of how often aerodynamic designs mirror those of birds and fish… lol – One wonders if the designers saw this emerging from their design evolution by chance or perhaps did this on purpose…

  4. How to fall gracefully? Get all the Grace's, put them in the plane and then let it fall, there you go now you falling gracefully.

  5. Curious why he didn't explore over wing mounting of engines, and exclusively looked at rear mounted… also, an aft mounting would work better if it was fully shrouded/ducted so as to reduce the boundary layer velocity differential. ( Like the F-15, F-16, F-35 ). Maybe the best of both worlds, have a tri propulsion arrangement , where smaller electric forward mount fans/swept props are intended only for takeoff/climbing, and the aft engines are to sustain cruising speeds ?

  6. The Wright flyer, when it was brought over to France, blew everyone away. They'd never seen a flying machine that was completely controlled by its pilot. Until then, machines had flown, but the pilots were pretty much along for the ride as they were barely controllable. The Wiright flyer literally flew circles around its peers.

  7. Might mixing the slow and fast moving air fix the problem? Like, add some sort of small wing in front of the engine to merg the air speeds into one consistent air flow? Or will this introduce to much drag again?

  8. Why not make the engine like the b-2 spirit bomber but still have the same design with the engines at the aft of the plane

  9. How do military jets with in-board engines get around the boundary layer issue? Could military tech be somewhat easily applied to commercial airliners?

  10. I hope we can have faster international travelling in the future… crumbling yourself in the economy class seats for 12 hours is absolutely terrible! Now, before they step back from turbofan to turboprop, I hope the commercial BFR flights are ready…

  11. After flying for 24 hours over 4 consecutice flights to get to Bora Bora this spring, a slower airplane is exactly what I was looking for…

  12. one question: how so, that civilians still use half century old design, while military… 5th – 6th generation?

  13. I'm sick of watching stupid videos that put the Whright brothers as the 1st to "fly" on a plane! This is a grotesque and unreasonable lie, a phobic and ridiculous Americanism as these 2 picks only catapulted something that was unable to fly by their own means! According to the rest of the world the first human to take off, fly and land a device heavier than air with wings and an engine was the Brazilian Santos Dumont and period!

  14. Okay why the inlet of the engines just dont take air from the bottom of the aircraft, there will be much more air because its compressed under the air craft. I dont understand why the inlet have to be on the top. Can someone explain?

  15. I love music by Maeson… Also Dekobe, Lakey Inspired, Engelwood, Poldoore, Tom Misch, Llindecis. My go to travelling music, couldn't live without it!

  16. Cars should be made with the same maximized service life, minimal maintenance required principles as these planes. Or at least an "as close as is possible" approximation of these principles…. and preferably with out the massive brand name mark up of say Toyota…..

  17. maybe mixing upper low pressure air with lower high pressure air before entering the engine could balance the engine at back of the airplane

  18. "This airplane could be coming to an airport near you sooner than you may think?"
    Care to hazard an educated guess just how soon? 5 years? 10 years? 20?

  19. Another difference between under-wing jet engines and engines in the tail are line-thrust, in that under-wing engines balloon the plane on the application of thrust, and tend to nose-down when you cut thrust. Pilots train specifically for this. Tail mounted engines have no such effect.

    Also, under-wing engines ride much closer to the ground, making them much more susceptible to FOD, snow, etc. when taxiing.

    Finally, when flying engine-out, there is a much greater moment of yaw, requiring a much higher single engine minimum control speed, than with a tail mounted jet.

  20. Russians have secretly perfected the air flow and engine problems. Simple bypass technics ,etc.,etc. West won't get to see it for another fifty years or so. The Russian miissle system is their top priority for now. One under ground city that builds them is rumoured to already have enough to bomb any country for a sustainable period of time. They can reach the USA in five minutes time ! Most are armed with conventional warheads, yet the engine is nuclear based materials. Many use E-pulse that West hasn't heard of.

  21. In 1903 they might have only flown a short distance but Curtiss had not flown yet. They were trying to keep their invention under wraps and get their 3 axis control system patented. By 1908 Glen Curtiss flew 50,80 feet, and the Wrights replied with a fifty mile flight lasting over an hour. Early on, the Wrights literally flew circles around everybody. Their concern over patent infringement and lawsuits against such were the reason they languished in design. It wasn't until about 1910 that others surpassed the Wrights, and illegally, if it means anything at all.

  22. Typical United States chauvinism, 14-bis is not even mentioned, the video skips from 1903 to 1910 without the 1906 landmark of the first unaided take off (no use of catapults) actual flight with witnesses (it was just beside the Eiffel tower), not a flight in the middle of nowhere. The "bird of pray" is the facto the base for commercial flight.

  23. There is no problem to make any shape of the fuselage – you just creat separate mid pressure layers to compenasate the total difference.

  24. Electric flight propulsion is already replacing petroleum powered flight in commuters, making jet fuel conservation a non sequitur. While that is not yet the case for airliners, it is only a matter of time before it happens.

  25. You sure are full of yourself. I guess your audience is mainly people who haven't got a clue (although it's nice to see a few on here that know which end is up), but this video is as goofy as your "fatally flawed Spitfire" video. In short, you really aren't ready for prime time.

  26. D8 = Bubble butt airplane, and in the future, instead of taking 24 hrs from San fran to Japn. We get 48 hrs flight?

  27. I really dont care about the fuel efficency when i heard from 0.8 0.76 machs probably at 20.000 its over

  28. If you think the flying public is going to go along with adding 18 minutes to a 3 hour flight you are dreaming ! That is unless the ticket prices are reduced by 1/2 !

  29. Engines buried in the rear fuselage is already used on stealth aircraft, so you'd think the military will have solved this? Also, Hondajet uses pylon mounts so could perch the engines up a little, although that might cause pitch change with power; both options reduce foreign object damage though

  30. takes 4 minutes of being told what we already know (history) before the video even get to what it is named about… pfft…

  31. Right now, the fastest airliners can cruise up to Mach 0.85 or more, this plane would be 100 mph slower than a 787, which is a bigger plane, but still

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