MIT Designs Aircraft That Uses 70% Less Fuel Than Conventional Planes 459
greenrainbow writes "Today a team of researchers at MIT unveiled their design for an airplane that uses 70% less fuel than conventional aircraft. The MIT design comes thanks to a NASA-funded initiative to increase fuel efficiency, lower emissions, and allow planes to take off on shorter runways. The team accomplished all of NASA's set goals with their innovative D-series plane, lovingly referred to as the 'double bubble,' which has thinner, longer wings and a smaller tail, and engine placement at the rear of the plane instead of on the wings."
Re:So Lets See, (Score:4, Informative)
Having a viable prototype design that's gone through simulations and the like is a lot more than artists renderings. What the hell do you think they do to make an airplane? Take some steel, rivets, and aluminum out to the hangar and just see where things end up?
Re:Intrigued to know more (Score:5, Informative)
There is no scale provided so you wonder what they are calculating on, is it fuel per mile per passenger? Anything else would be irrelevant.
The two designs carry the exact same number of passengers as the planes they are hypothetically replacing, the 180-passenger 737 and 350-passenger 777, so there's no difference in this case between miles per gallon and passenger-miles per gallon. :)
Re:Slower than current aircraft (Score:5, Informative)
While I'm sure you can devise a design which, as part of greater fuel economy, flies slower (turboprops might be just that...) - it won't really work for existing aircraft, like mentioned by you 737s. Airlines take care to fly them at optimal speed, not the greatest speed; optimal for fuel economy.
For example Rynair (which cares greatly about lowering costs...), some time ago, changed the guidalines for cruising speed by...2 or 3 km/h. Accidentally in this case it was lowering it, but might have been just as well an increase; what works best for given airplane / engines / routes / weight combo (didn't stop local journalists from proclaiming "Ryanair will fly slower to save fuel", which was technically correct, but....)
Re:Slower than current aircraft (Score:5, Informative)
One way they save fuel: flying slower than current aircraft.
No. While they do fly slightly (10%) slower than existing aircraft, they do that to mitigate engine stress.
will customers accept that?
Well, they seem to "accept" waiting 2-3 hours in security lines, so I'm guesing yes.
why not just fly current 737s a bit slower right now, to save on fuel?
You honestly believe that flying a 737 10% slower will reduce fuel consumption by 50%? I can tell you that if an airline reduce their costs anywhere close to that much, they'd do it in a heartbeat.
Re:Wing length is a Really Big Deal (Score:5, Informative)
According to the article the proposed 737 replacement has standard wing length and is suitable for existing airports.
Re:Great... now its up to the aerospace companies. (Score:3, Informative)
You're forgetting about Embraer or Bombardier. Companies which start to introduce ever bigger planes, ever closer to competing directly with Boeing/Airbus/Tupolev mainstray (B737, A320). And also using "classical" design...
Re:So Lets See, (Score:3, Informative)
I would like to give you the benefit of the doubt as a result of the flattering implication that engineering involves artistry, but on the whole you've got such an ignorant and insulting view of aerospace engineering that I can't call it anything but ignorant and insulting.
Burt Rutan drew up some "artists' renderings" (they're called CAD models usually) of a plane that in computer models appeared to be able to circumnavigate the world without refueling. Then they built it and it did.
Aerospace firms around the globe rely on computer models to predict the aerodynamic behavior of everything from commercial airliners to supersonic fighters. They use these models because they work. They may not be perfect, but they can be used to reliably predict the behavior of designs in the real world within a margin of error.
The idea that just having the computer model means there's "nothing to see here" is simply wrong. Anyone with a clue would be impressed that they could demonstrate these fuel savings even though they are just in a simulation.
Type D ment to work with existing airports (Score:5, Informative)
The type D is specifically designed to work with existing airports without drastically changing the terminals.
The type H, however, would require changes to current airports. The article says that these designs are planed for a 2035 deployment, though, so plenty of time to make the requisite changes, if the airlines so chose.
Re:Slower than current aircraft (Score:2, Informative)
You're correct that drag has a large influence, engines have a part to play also.
Turbofans have a 'bucket' speed where their efficiency (specific fuel consumption or the fuel they burn per second per pound of thrust) is best*
The result is that, when the aerodynamics and engine efficiency are combined, there will be a best efficiency speed (best range speed) that's not far below the theoretical 'design' speed. However many airlines fly faster than this, depending on their balance of fixed vs. hourly costs.
Generally you can get higher efficiency by flying slower but you have to make changes to the aircraft, as seen here where much of the efficiency probably comes from the lower lift dependent drag that you can get from the larger spans of these aircraft. They probably get quite a lot of gain from engine improvements also, perhaps half.
*all bets are off with open-rotor or propellor engines, broadly these like to fly slower overall and you lose efficiency steadily the faster you fly.
Re:Slower than current aircraft (Score:2, Informative)
Icing (Score:3, Informative)
Interesting designs. Looking at the first one I have some reservation to this. Structural integrity of the wings is one. A wing has to effect a mass-flow large enough to lift the aircraft, and so has to be fantastically strong, as well as large enough to cause this massflow. A problem (or rather a limitation) with gliders is that when the aspect ratio gets very high that means that there is precious little internal volume to the wing for load bearing members. This is a very real limitation on sailplane wings and means that 20 metre wingspan is a real world limit (some types have gone longer, but the extreme flex of that length of wing means that they are impractical). This seems like a very real issue here.
Of course, high aspect ratio wings are more efficient due to a number of effects, an important one being wingtip vortices affecting a smaller percentage of the wing. I have no idea how that pans out at high speeds, though. When you're reaching M0.8 I would imagine that interesting effects might start happening, but I'm sure that the MIT kids have calculated all that as well as can be done (I doubt them being dumb).
Icing would also be a concern, both for the wing (high aspect ratio, laminar flow) and (more seriously) for the whole fuselage which pollutes the airflow into the engines. MD80's (and other jets with rear fuselage mounted engines, the CL60 is another example) had some accidents due to ill visible icing forming on the wings prior to take-off, detaching from the wing on take-off and flying into the engines. This design would be quite sensitive to this sort of problem.
But all in all, a very intriguing design idea. Would be interesting to see if the real world problems can be solved as well.
Re:Slower than current aircraft (Score:3, Informative)
Fly with Air Canada next time. They offer the same amenities as Lufthansa.
Re:Both of TFA's linked sadly lacking in details (Score:1, Informative)
This is the MIT news office. It is releasing information for public consumption. If you want the nitty gritty, look at the professor's pages for publications.
Re:Wing length is a Really Big Deal (Score:3, Informative)
Oh, you can get a heavier aircraft aloft that way, but the wings in a biplane don't give anything like twice the lift. The main reason for the biplane design is not lift, but strength. If you're building a wing out of fabric covered lumber you want to make that sucker stiff so it doesn't bend and snap. That means big, heavy pieces if you have a monoplane. In the biplane the wings, struts and wires form a kind of truss that is lighter for the same stiffness.
Re:Both of TFA's linked sadly lacking in details (Score:3, Informative)
-70% less fuel? How much of that is aerodynamic savings and how much of that is engine efficiency savings?
5% here, 5% there...
the design mitigates some of the drawbacks of the BLI technique by traveling about 10 percent slower than a 737. To further reduce the drag and amount of fuel that the plane burns, the D series features longer, skinnier wings and a smaller tail. Independently, each tweak might not amount to much, but the "little 5-percent changes add up to one big change," Drela said.
-Did they do any wind tunnel testing of their model? How close were their CFD and tunnel test results?
No actual model. Just the ones in the computer.
They have proposed evaluating the interactions between the propulsion system and the new aircraft using a large-scale NASA wind tunnel. Even if the MIT designs are not chosen for the second phase, the researchers hope to continue to develop them, including testing smaller models at MIT's Wright Brothers' Wind Tunnel and collaborating with manufacturers to explore how to make the concepts a reality.
-Are they using engines based closely off existing ones, or are they projecting fuel savings 25 years into the future (the 2035 time frame from the article)?
Mostly projection and wishful thinking. Right now, they could MAYBE do 50%.
Not only does the D series meet NASA's long-term fuel burn, emissions reduction and runway length objectives, but it could also offer large benefits in the near future because the MIT team designed two versions: a higher technology version with 70 percent fuel-burn reduction, and a version that could be built with conventional aluminum and current jet technology that would burn 50 percent less fuel and might be more attractive as a lower risk, near-term alternative.
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The researchers acknowledge that some propulsion system technology still needs to be explored.
-What sort of structural weight-saving advances are they assuming, or projecting from?
Only mention of weight-saving is regarding the H-series that should replace 777s.
The MIT team designed a triangular-shaped hybrid wing body aircraft that blends a wider fuselage with the wings for improved aerodyamics. The large center body creates a forward lift that eliminates the need for a tail to balance the aircraft.
-So they made the tail smaller, what makes up for the reduction in control authority there?
The researchers acknowledge that some propulsion system technology still needs to be explored.
-Plus other more detailed questions based on the answers to those questions.
The researchers acknowledge that some propulsion system technology still needs to be explored.
Re:Icing (Score:3, Informative)
(some types have gone longer, but the extreme flex of that length of wing means that they are impractical)
I am quite sure my friend who owns an ASH 25 (26M span) http://en.wikipedia.o/wiki/Schleicher_ASH_25 [en.wikipedia.o] would disagree, he flys it nearly every weekend.
I have flown 25 hours in it myself and whilst it is slow in roll the flexibibity of the long high aspect ratio wing makes for a vey comfortable ride. (Think of the wing as a leaf spring, supporting the fuselage)
The largest production glider is the ETA
http://en.wikipedia.org/wiki/Eta_Aircraft_eta [wikipedia.org]
I do however agree that 20M gliders are easier to handle in the air, I prefer the Duo Discus and the
DG 1000 to flying the ASH.
Re:hmmm (Score:3, Informative)
It's my understanding that drag increases as the square of velocity. This leads to fuel consumption per unit of distance increasing linearly.
Go twice as fast, use twice as much fuel getting there. Your rate of fuel consumption is four times higher, but you spend half the time getting there.
Well... okay, here's the thing. The drag rises as the square of velocity, so the force required to overcome the drag rises as the square of velocity. However, since you're going faster there's another time unit involved, meaning the *power* required rises as the *cube* of velocity. "Thus, the resultant power needed to overcome this drag will vary as the cube of velocity." [wikipedia.org]. And as such your fuel costs aren't rising linearly but exponentially.
Re:hmmm (Score:4, Informative)
The FAA has prohibited overland supersonic flight except for explicitly-approved military flights for decades now. Even the military has to get permission when outside of established supersonic corridors, most of which are controlled by the FAA. (Many people are often amazed at how much authority the FAA has over military flights within US borders.)
NASA has conducted a great deal of research into quieting sonic booms, either by deflecting them upward or by canceling them out. I imagine those will be or have been factored into MIT's proposals.
Certification (Score:3, Informative)
Prototypes are fun and all, but let's see the numbers once it has customers lined up and has gone through FAA certification. That's a bit like coming up with a car that gets 175MPG (of actual gasoline or diesel, not "gallons" of electricity) -- until you've gotten it past the EPA and the DOT and can still sell the thing to more than the wealthy toy market, it's just a show car.
Believe it or not, they actually have one or two smart people working at Boeing & Airbus (possibly one at each) and it's not like they're in bed with BIG OIL!!!! or whatever other tinfoil hatted fantasy people like to believe in this week.
And, in regard to some other post here, I seem to recall winglets being there to break up parasitic drag from vortices spewing off of the wing tips. But that's just my recollection from working on MD-11 (software, not mechanical design, so take that for what it's worth). They're fairly common now.
Re:hmmm (Score:3, Informative)
Re:hmmm (Score:3, Informative)
Trips over North America can be supersonic, since it's doubtful the American government will care about sonic booms. If they do, I'm sure a few "campaign donations" will fix that....
It didn't work for Boeing in the '70s:
The anti-SST paperback, "SST and Sonic Boom Handbook" edited by William Shurcliff, which claimed that a single flight would "leave a 'bang-zone' 50 miles wide by 2,000 miles long" along with a host of problems that would cause. In tests in 1965 with the XB-70 near Oklahoma City, the path had a maximum width of 16 miles, but still resulted in 9,594 complaints of damage to buildings, 4,629 formal damage claims, and 229 claims for a total of $12,845.32, mostly for broken glass and cracked plaster.
Boeing 2707 [wikipedia.org]
Think about it, most really long flights are going to be trips like LA to Tokyo, LA to Beijing, LA to Sydney, NYC to London, NYC to Paris, etc.
There are two big problems here.
The North Atlantic run is heavily traveled.
But very competitive and price-sensitive. No matter how quick the turn-around, you need to sell a lot of seats on your SST at super-premium prices to compete against the jumbo jets and charters.
The really long runs over water - and there are not so very many of them, when you come right down to it - don't generate anything like that kind of traffic.
Re:Slower than current aircraft (Score:1, Informative)
They can save fuel by flying slower, all planes have an optimal speed for fuel above which you burn more trying to fight air resistance, and below which you burn more trying to keep yourself airborn. Fuel is not always the largest cost of a flight, however. Depending on the price of oil, the labour costs (pilots, flight attendants, operations people on the ground), and the maintenance costs for the plane (more hours in the air = more maintenance) can be higher than the fuel cost of going faster.