
Modern air travel is a marvel. It's also a source of endless delay, annoyance and planet-killing greenhouse gases. A proposed hydrogen-powered hypersonic airliner could change all that. The plane is Reaction Engines's A2 concept, a Mach-5 (3,400mph) craft for 300 passengers funded in part by the European Union's Long-Term Advanced Propulsion Concepts and Technologies project (Lapcat). Lapcat wants an airliner that can fly from Brussels to Sydney in less than four hours. If built, the A2 will do just that—without producing a trace of carbon emissions.
Engineers created the A2 with the failures of its doomed supersonic predecessor, the Concorde, very much in mind. Reaction Engines's technical director, Richard Varvill, and his colleagues believe that the Concorde was phased out because of a couple major limitations. First, it couldn't fly far enough. "The range was inadequate to do trans-Pacific routes, which is where a lot of the potential market is thought to be for a supersonic transport," Varvill explains. Second, the Concorde's engines were efficient only at its Mach-2 cruising speed, which meant that when it was poking along overland at Mach 0.9 to avoid producing sonic booms, it got horrible gas mileage. "The [A2] engine has two modes because we're very conscious of the Concorde experience," he says.
Those two modes—a combination of turbojet and ramjet propulsion systems—would both make the A2 efficient at slower speeds and give it incredible speed capabilities. (Engineers didn't include windows in the design because only space-shuttle windows, which are too heavy for use in an airliner, can withstand the heat the A2 would encounter.) In the A2's first mode, its four Scimitar engines send incoming air through bypass ducts to turbines. These turbines produce thrust much like today's conventional jet engines—by using the turbine to compress incoming air and then mixing it with fuel to achieve combustion—and that's enough to get the jet in the air and up to Mach 2.5. Once it reaches Mach 2.5, the A2 switches into its second mode and does the job it was built for. Incoming air is rerouted directly to the engine's core. Now that the plane is traveling at supersonic speed, the air gets rammed through the engine with enough pressure to sustain combustion at speeds of up to Mach 5.
That's the principle behind all ramjet designs. But the Scimitar's system goes further by adding a turbine compressor that squeezes air even more intensely. This is a big departure from traditional ramjet design; these air-breathing engines normally can't use turbines because the air enters the engine at such a high temperature—1,800ºF at Mach 5—that turbine blades would quickly melt. In the Scimitar, though, a cooling system wrapped around the inside of the engine cools incoming air enough to let it run through a turbine. As a result, the A2 has a setting for every speed.
But an even greater asset than the A2's speed is its negligible carbon footprint. It's hydrogen-powered, so it produces only water vapor and a little bit of nitrous oxide as exhaust. And although a hypersonic jet loaded with liquid hydrogen might sound dangerous, hydrogen fuel is actually no more explosive than normal jet fuel.
Joseph Schetz, a hypersonic-propulsion expert at Virginia Tech, says there's nothing fundamentally unsound in the A2's plans, "but whether it's doable or not is a whole other conversation." The engineers still face crucial design obstacles, such as building heat exchangers reliable enough for hypersonic flight.
The biggest challenge: manufacturing hydrogen fuel on a large scale without emitting carbon in the process. Indeed, Varvill is hesitant to pitch his plane as a truly green machine because he believes carbon-free hydrogen production is still a long way off. If a viable hydrogen economy comes to pass, though, the A2 could very well be the new airliner of choice.



Comments
All planes need to be built like this. This is the future of Air Travel!!
1 out of 2 people found this comment helpfulGotta love the "negligible carbon footprint" comment. How much energy goes into making the plane? How much energy goes into creating the hydrogen? Negligible... hah!
1 out of 2 people found this comment helpfulI think that with the application of solar panels (as has already been demonstrated by researchers), the carbon cost of creating hydrogen will begin to decrease. But I truly think this needs to be followed through on. Less than four hours from the heart of Europe to the capital of Australia (down from 22)? That's awesome. And for that speed, I can do without the windows.
1 out of 2 people found this comment helpful"....Less than four hours from the heart of Europe to the capital of Australia"....
Sydney is as much the capital of Australia as New York is the capital of the United States.
1 out of 2 people found this comment helpfulTo whom it may concern;
(TODAY'S REALITY SENERIO);you board a 747 heading to europe at JFK,you find your seat and stow your carryon's (jacket,hand bagg) and settle in to a semi comfortable chair and mentally prepare for a 10 hour flight.Finally the plane siftery escapes the bounds of earth and climbs to 35,000 feet at a speed of 425 knots (400 mph) for it's long night's travel.Suddenly the plane lurches and the skin exposes a small hole,the oxygen masks shoot out of a panel above your head.The noise is deafing,you find it hard to breath,the temparture has just dropped from a nice 70 degrees to -60 degrees below zero,as your reach for the oxygen mask you notice your fingers are turning blue.You feel a sinus headache comming on as you notice the aircraft starting to dive.Finally after five long minutes the plane levels out and the noise abates as the plane returns to JFK airport.
(FUTURE YOUR HYPERJET REALITY SENERIO);you board a HYPERJET TRANSPORT heading to europe at JFK,you find your seat and stow your carryon's (jacket,hand bagg) and settle in to a semi comfortable chair and mentally prepare for a 2 hour flight.Finally the plane siftery escapes the bounds of earth and starts it's climbs to 150,000 feet at a speed of mach 1 (700 mph).Suddenly the plane lurches and the skin exposes a small hole,the hole ripps into a bigger and bigger hole.You try to breath but you can't your lungs are frozen solid,the temparture has just dropped from a nice 70 degrees to -200 degrees,the pressure on your head starts to expand until your head explodes.The hole has grown to a point of catrosphre structural failure and what left of your body is plasma (friction) blasted down to the bone just before the fuel explodes!
These worst case senerio's are to draw attension to your article "HYDROGEN HYPER JET" and to the "HOLY GRAIL" promise of econimic hypro-sonic flight!I will all so address your myths about the propullsion,structural design,environent flight envelope pro's and con's as well as "egress (getting the hell out)"!
Flight Envelope Enviroment,(subspace vs atmosphere),pro;subspace starts at 100,000 feet and goes up to 100 miles above the surface of the earth,here the atmosphere is 0 to 20% air,so a gallon of gas goes a lot further than at a lower altitude.Hence the desire to fly here now that gas prices are forcing airlines to merger or go out of business.the temperature at 100,000 feet is -150 to -200 degrees atmospheric pressure is a dangerous 4 pounds per square inch,hence the need for a spacesuite or a "G" suite.It is true that the gas usage at this altitude is greatly inhanced,if designed right the craft could literially fly without fuel,surfing the shock wave at mach 3-5 (shockwave compression dynamic)!However in the senerio above I spoke of time usage in an emergency;on a 747 it takes 5 minutes to slow and dive to a breathable atmosphere,a hyperjet at 150,000 feet at mach 5 would take 15 minutes to slow down and reach a breathable atmosphere!
Structral craft design ; To attain the optimun design we have to do our history home work,I love the old M-50 design and I noticed that your hyperjet was a dirvetive of it but if you have done your home work you would have understood the design was a flawed design from the get go,bad renyonls numbers,bad pylon root design kept it from reaching supersonic capability!Now if we look at all the supersonic aircraft since WWII you will notice the engine are located close if not under the center of gravity of the craft.The only heavy bomber to reach mach 3 was the XB-70 and proved that "shockwave compression dynamic" was feasible but it was not build to fly past 68,000 feet.The SR-71 gave us vaulable data about sustained flight above 100,000 feet as well as a need to build a better "hybrid engine design" as well as the dangers involved!So what will the hyperjet really look like,I will give you a hint Boeing's X-51"Wave Runner" it has already reached "mach 5+"!
Propullsion Design; The only craft to intergrate a turbine and a ramjet was the SR-71 and they had problems from the get go,UNSTARTS (shock wave turbulation in the turbine engine) hence the horrific air dump door design after thought!The fuel was another consideration JP-8 is really thick and not really volitile hence the Sodium/Bromide ingnitors at a cost of $750,000 each.Your idea of hydrogen as the fuel is a good one,on one hand it burns at a lower flash point that JP-4 but it takes twice as much fuel (gas) but liquid hydrogen evaporates at a rate of 100 gallons of gas from 1 gallon of liquid hydrogen!The secret to this engine will be found by "radical turbine blade design" one that will have the turbine blades disappear after mach is acheived.To solve the "unstart problems" and to rework the "dump door problems".
Egress Design; The biggest mental problem to the commerical airlines and the flying public is they like window seats,in a way your suggestion of a windowless design is correct.However I believe everybody can have a window seat without windows!The averge person spends an about 6 hours a day watching television of some sort so I suggest window monitor (plasma screens).Next as I suggested in the worst cast senerio,passenger safety,should be formost!So what can be done one might ask?One method might cost more than the plane,suppling spacesuites and armed ejection chairs to 300 passangers,ah not!The other is simular to the interior shown in the movie "THE FIFTH ELEMENT" where passangers lay prone during the flight in a armored/pressurized (blastprof/fireprof/waterprof) compartment complete with window monitor door and hot and cold pockets for food and drink.The habitats are clustered and have parachute/elt/dragbags.This would call for a radical new kind of aircraft design focusing on passanger egress.So what would drive this egress situation?The master stress sensor and program now being developed by beoing for the 787 but modified to work with a supercomputer flying the hyperjet (UCAV),that is why you don't show a cockpit,right!
Sincerely
2 out of 6 people found this comment helpfulCobrapub@earthlink.net
I believe I have a solution for the no window problem. Reaction should use a Flex Screen for each window. The flex screen would be molded to the shell of the plane and give the passengers the illusion of windows. The could be framed to look like any other window.
The airline would take another plane and record the route to give the scene of each particular route. They would have to record on both sides of the plane and in various weather conditions and day times. I believe this illusion would help people not get claustrophobic in the plane.
Also another point is what do passengers really think they are going to see at MACH 5: clouds. Maybe a few minutes of scenery for take off and landing.
2 out of 3 people found this comment helpfulfrom Rock Springs, WY
@ futurenow I agree, some sort of flex screen could be used to add the illusion of windows, but I'm not sure that it matters that much. The fast majority of the passengers will be bussiness travelers who are willing to spend a little extra and take a greater risk (new technology) in order to save 18 hours of earning potential.
@cobrapub
2 out of 2 people found this comment helpfulA very intersting read. I have no doubt that many of your points are valid. However, what I think is the most important part of this article is that it's a new idea (or an old one made new) that'll keep this technology from stagnating.
How many times in the last decade has an airplane depressurized at altitude and not during climb or descent? Twice, both on climb-out. You take an interesting position to a point that is a little over dramatized. You are incorrect on several of your numbers, example being your conversion from knots to mph. I thought the article interesting and informative, as everyone who reads it can tell that it is news, not a thesis on hypersonic transportation.
0 out of 1 people found this comment helpfulLooks like there's no such thing as guilt-free flying. BusinessGreen has spoken again to the A2's designer and he's worried about water vapour release into the ozone layer and about the energy needed to make the hydrogen fuel, which he suggests will require nuclear power plants near the airport....
http://www.businessgreen.com/2209080
1 out of 1 people found this comment helpfulHow's it going to take off or land?
0 out of 1 people found this comment helpful