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Double bubble aircraft design would use 70 percent less fuel


May 19, 2010

The D double bubble aircraft design promises a 70 percent improvement in fuel economy (Ima...

The D double bubble aircraft design promises a 70 percent improvement in fuel economy (Image: MIT/Aurora Flight )

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The contribution of aircraft to greenhouse gas emissions has been well documented - a 2009 study [PDF] by Friends of the Earth found that air travel is the world’s fastest growing source of greenhouse gases like carbon dioxide, generating nearly as much CO2 annually as that from all human activities in Africa. Biofuels are being trialled in an effort to combat the issue, but with air traffic expected to double by 2035 it would seem that a fundamental shift in technology is needed to make real progress. That's the starting point for the D “double bubble” – a design concept presented to NASA by an MIT led research team which promises a 70 percent improvement in fuel economy, reduced noise, lower nitrogen oxide (NOx) emissions and the ability to use shorter runways.

The D double bubble design uses long, skinny wings, a small tail and - hence the name - replaces the traditional cylindrical fuselage with a two partial cylinders placed side-by-side. The engines sit at the rear of the fuselage rather than on the wing to make use of a technique called Boundary Layer Ingestion (BLI). This approach sees slower moving air from the wake of the fuselage enter the engines, resulting in less fuel consumption for the same amount of thrust. The downside is slower speeds and more stress on the engine.

The result is a plane that travels 10 percent slower than the Boeing 737 it is designed to replace, but according to lead designer of the D series Mark Drela, the longer flight times would be partially mitigated by the ability to load and unload the plane faster. Another advantage is that it could also be used with current airport infrastructure.

Along with the 180-passenger D series, the research team has also produced a blueprint for a much larger (350 seat) H series that would be equivalent to a Boeing 777. This design uses the BLI technique and a wider fuselage with an aerodynamic triangular-shaped hybrid wing body.

The H series on the right, and the D series on the left (Image: MIT/Aurora Flight )

A second version of the D series has also been put forward. This design doesn't save as much fuel (around 50 percent) but is a more viable near term alternative because it that could be built using current jet technology and materials.

The MIT led project is the result of a $2.1 million contract awarded by NASA in 2008 as part of an aeronautics research program aimed at putting greener planes in the sky by 2035. Boeing, GE Aviation and Northrop Grumman are also taking part in the program.

The team from the MIT's Department of Aeronautics and Astronautics was headed by principal investigator Ed Greitzer and Aurora Flight Sciences Corporation and Pratt & Whitney also contributed.

NASA is expected to announce a second phase of the program in coming months.

About the Author
Noel McKeegan After a misspent youth at law school, Noel began to dabble in tech research, writing and things with wheels that go fast. This bus dropped him at the door of a freshly sprouted in 2002. He has been Gizmag's Editor-in-Chief since 2007.   All articles by Noel McKeegan

I've often wondered how much fuel must be consumed during take off. Would it not save literally tons of fuel if a catapult system (similar to an aircraft carrier) could be used to assist during take off?

19th May, 2010 @ 07:15 am PDT

@Noel McKeegan

You blew your precis. That Friends of the Earth report does NOT say air travel is the world's largest source of greenhouse gases. Fastest-growing is not largest. Later on it says "Aircraft cause about 3.5% of global warming from all human activities"; that's much smaller share than emissions from individual driving, trucking, or heavy-duty vehicles.

Air travel is definitely a big contributor and "could contribute up to 15% of global warming from all human activities within 50 years." Take the train if you can.

ED note: thankyou skierpage. This error has now been corrected.

19th May, 2010 @ 05:21 pm PDT

I don't think many people would want to fly if they used a catapult system for take off...most people would faint at launch. Besides unless you could launch the aircraft to over supersonic speeds it would never gain much height from the resulting speed of the catapult. Aircraft carriers only use catapults because of the restricted space on deck, and if you have a look at most launches, they come of the deck straight and then rotate upwards after. They also steer the carrier into the wind and run the carrier at speed to make sure the aircraft can produce enough lift to get off the deck, despite the powerful catapult. Most aircraft can't even launch when the carrier is stationary.

I think the only way to reduce fuel consumption is to do what they are doing...improve the aerodynamics and propulsion systems, that is until we get seriously fast maglev trains. Then air travel would only need to occur across the Pacific and Atlantic, and the maglevs could run renewables or the like to cut down emissions. Plus none of the crazy chk-in or 'security' procedures that can easily double the length of travel times throughout Europe.

19th May, 2010 @ 08:50 pm PDT

Launching with the engine serves an important safety purpose which is to strain the engine to its maximum thrust just before takeoff. If an engine is going to fail you want it to happen on the runway rather than someplace awkward, like flying over the ocean.

They should ditch the tailplane though. Drag is a function of lift, and the tailplane generates something like 30% negative lift (downwards push) in order to keep the heavy nose up. That means the main wing has to develop 130% upwards lift - 130% of the weight of the aircraft. So the drag that the engines are pushing against is due to a total of 160% of the weight of the craft - you could remove lift-induced drag by as much as 60%! Removing the tailplane is just another one of the simple, common sense ideas from the Rutans (not just the winglets on jumbo jets). Oh, and why are airplanes so nose heavy in the first place? It's another safety idea - if the aircraft ever stalls, it will tend to fall downwards nose-first and thus develop airflow over the wings so the pilot has a chance to get control again. But the tailplane isn't the only way to do to provide that important safety feature, only the most wasteful way to do it.

19th May, 2010 @ 10:29 pm PDT

Hey Grunchy if you read this...

Spot on with the tailless design. Rutans rules should be the standard by now for aircraft design. At least he is designing stuff thats going to space like the Spaceship One...aircraft must be getting either to boring or frustrating for him with all the conventional designs still floating around. Nature has always displayed superior designs in all areas of engineering, maybe after a 100 years of flying around and only 40 or so wing profiles in use in the world today to show for it, we should take another look how it should really be done. Flying wings or canards (ie Ducks!) are next logical step, and using the wings for propulsion might also assist in getting rid of the laminar flow issues with common aerofoils.

Also I've been trying to catch up with you on this from the dDrive article:

Which version of the Ikona transmissions are you referring to? The non-involute profile gears (aka Harmonic Drive) were used on the Lunar Rover in the sixties, but I have not yet found a variable speed/ratio version. Could you post a link to the actual drive please? Thx

19th May, 2010 @ 11:47 pm PDT

there is just one BIG problem with both of these designs, the distance the inner passengers would be from the nearest exit. before a design can enter passenger service it must be able to be evacuated in the dark, with up to 30% of the exits unusable, within one min and a half IIRC. the A-380 took a few tries to pass, during which one person broke their leg and many sustained sprains and bruises, they were all airbus employees who volunteered and without them the A-380 would not be flying now.

Facebook User
20th May, 2010 @ 03:04 am PDT

Okay sure, here's a link:

And they have a paper published or posted online somewhere about it, but ultimately it is just another planetary geartrain. That whole Ikona geartooth technology originated in Russia and was bought out & brought to North America, where it has never taken off at all. Too bad....

Incidentally, the way that Rutan's winglets work is to disturb the vortices falling off the wing tips, but the way I think of it is it keeps that high pressure air beneath a wing from 'leaking' around the wing tip onto the top of the wing, diminishing lift & creating drag. Rutan is one of those guys who "looks with eyes that see".

20th May, 2010 @ 11:47 am PDT

I wouldn't mind going a little slower if the airlines would share some of the fuel savings in the form of lower ticket prices?

Will, the tink
21st May, 2010 @ 10:59 pm PDT

It look great, but remember Concord only fragility, and the Concord had two groups of engines.

3rd June, 2010 @ 12:02 pm PDT

A very similar design was actually also purposed by a group of students at the University Of Michigan independently of NASA and MIT. The design is known as a blended wing body with recessed engines. This design isn't great for passengers, as there are a distinct lack of windows. Also, these suckers probably wont fit at standard airport terminals.

The notable design features here are the C-wing tip design, which helps eliminate wing-tip vorticity, the submerged engine, and of course the biiiiggg flat body. Wing tip vorticies induce drag on the aircraft and slow them down, thus requiring more thrust/ fuel. By minimizing this, you increase fuel economy. It is still debatable if the boundary layer ingestion engines are more effective over the lifetime of the aircraft. More stress on the engine means more repairs and more time on the ground out of the fleet. The big lifting body takes an element on traditional planes that just creates drag (the fuselage) and uses it to generate lift, thus eliminating/reducing the need for wings.

@Grunchy: While I agree that the taillless design is good in many situations, they lend themselves to dynamic instability without careful implementation. Yes tails as they are implemented are not the most efficient, but they are statically stable and more usually more dynamically stable then tailless planes. I like planes that dont need a bank of computers onboard to fly. Also, Rutan did not first develop the tailless aircraft. That achievement goes back to the Nazis in WWII.

21st June, 2010 @ 03:27 pm PDT


Good to hear that at least another sees its potential in reducing energy used in jets, provided that you can "wind it up" using the energy from an incoming plane.

Perhaps an electronic mag system could be developed that could eliminate the mechanics?

Another interesting possibility. Airports with runways that are severely sloped at some point, using gravity to stop and assist in landing and takeoff?

28th June, 2010 @ 01:49 pm PDT

Ryno, I have had the catapult idea as well. The thing is, it need not be a sudden acceleration as in an aircraft carrier launch, It could be an electrically powered cable launch. Engines would still be working, but eased up to full throttle near take-off speed. I like the idea by ADVENTUREMUFFIN for taking off downhill, and landing uphill. Is this why Biggin Hill is an airfield?

8th July, 2010 @ 11:37 am PDT

The projected tail and vertical stabilizer removed from the triangular shaped hybrid wing body design, the successful development of multiple control surfaces on the BWB for stability and control will lead to a large number of new design variants, with much better maneuverability, which will decide the future of the aviation industry. How the design performs with respect to rate of climb and high speed cruising will be interesting to observe.

S P S Sabharwal
15th August, 2010 @ 02:51 am PDT
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