Airbus has pledged hydrogen airliners by 2035 - but is unlikely to deliver. What planes will actually sail the skies of the future?

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Airbus has pledged hydrogen airliners by 2035 - but is unlikely to deliver. What planes will actually sail the skies of the future?
Airbus has pledged hydrogen airliners by 2035 - but is unlikely to deliver. What planes will actually sail the skies of the future?
Anonim

The European airliner manufacturer has announced that it will be able to start producing aircraft with "zero CO2 emissions" in 15 years. To do this, he plans to fill them with hydrogen, which by that time they promise to produce from water, and not from fossil methane, as is done today. Technically, however, Airbus's plan is a beautiful-minded utopia. Real airplanes of the 2030s will be able to make the transition only to methane - for simple and technically irreparable reasons. Let's try to figure out why the European company pretends that this is not so, and at the same time find out what the airliner of the future will actually look like.

Hydrogen airliners

Modern airliners are seriously evolving only along the line of minor improvements - replacing aluminum with aluminum-lithium alloys or even carbon fiber (in the wings). Their general shape has remained unchanged since the 1950s - with the first jet airliner, the British Comet, produced by the same firm that made the wooden Mosquito bombers during World War II.

Meanwhile, it is the shape that determines the main aerodynamic features of the aircraft. The fuselage "tube" round in cross-section, only slightly sloping back wings, under which the fuel tanks and motors are suspended - all this has remained in the industry for 70 years in a row. And it would have stayed even longer - if not for the green pressure.

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However, the case of Greta Thunberg - in contrast to the slightly sagging popularity of her personally - lives on and wins. Western society increasingly hears about the "carbon footprint" and does not hear anything about the fact that one-sixth of the terrestrial biomass owes its existence to this carbon footprint of mankind. This means that the carbon footprint (and, indirectly, the biomass generated by it) will be mercilessly fought. And the aviation industry is one of its main sources.

It is already clear to everyone that electric cars from the 2030s will be the main type of cars produced, and rail transport is already largely electrified (which is why Thunberg demonstratively used it on trips across Europe).

But airliners cannot be electrified: a lithium battery for a hundred kilowatt-hours weighs half a ton (200 watt-hours per kilogram). That is, an accumulator equivalent to a hundred tons of kerosene (this is the amount of fuel, for example, in the A330) would weigh 2000 tons, which immediately makes the project unrealistic. After all, the A330 itself weighs about a quarter of a thousand tons - it is impossible to load a couple of thousand on it.

That is, a "carbon neutral" aircraft still requires fuel, not batteries - just which one? Methane has a bad reputation in Europe - it is more likely associated with the environmental problems of the US shale regions and political tensions with Russia, its largest supplier to the EU. In addition, today it is a fossil fuel - that is, burning it still leads to emissions of carbon dioxide into the atmosphere.

That is why Western concerns are constantly promising a transition to hydrogen aircraft "on the horizon in 15-20 years." And yet, so far these are only promises. Most likely, such machines will not take the lead in the sky after any period of time.

Soviet experience: hydrogen won't take off?

The fact is that European aircraft manufacturers, to put it mildly, are not the first to think about switching from kerosene to gas fuel. This was first done by the USSR Academy of Sciences in the 1970s, initiating a program to introduce liquefied fuels - including hydrogen - into a wide variety of sectors of the economy. The thought behind this was obvious: the fuel crisis of the 70s sharply raised the price of oil products, and gas fuel, both then and today, was much cheaper than kerosene or gasoline. In the West, in those years, state and scientific institutions did not have direct leverage over the industry, so there they did not launch R&D programs of this magnitude.

In the aviation industry, within the framework of the Cold program, the Tu-155 airliner (based on the Tu-154) was created. This plane took off in 1988 - 47 years before Airbus promised the debut of its hydrogen airliners. However, he spent only five flights on liquid hydrogen - and there was a reason.

No, technically all the systems of the liner worked fine, despite the fact that this was the first experience of its kind in the world. But here are the details …

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When we talk about aircraft fuel, the most important indicator is the heat of combustion in megajoules per liter of volume. For liquid hydrogen, it is less than 9 megajoules per liter, and for aviation kerosene, 35 megajoules per liter. The difference, as we can see, is fourfold.

Therefore, the tank with liquid hydrogen on the Tu-155 occupied 20 m³ and required vacuum thermal insulation. At the same time, a cubic meter of liquid hydrogen weighed 71 kilograms - that is, quite large, by aviation standards, the fuel tank contained only 1400 kilograms of fuel! Recall: the basic Tu-154 took on board almost forty tons of kerosene.

Of course, when combusted, hydrogen gave 121 megajoules per kilogram, and kerosene - 43-46 (its composition often varies) megajoules per kilogram. But due to a dozen times lower fuel density and the need for thick walls, the tank for liquid hydrogen still came out too large, four times more than kerosene. To make it equal in capabilities to the Tu-154 kerosene tanks, the tank would have to be made for more than 200 cubic meters.

Moreover, if the kerosene tanks could be taken out into the wings, then with the hydrogen tanks it did not work: with the size of its thermal insulation, it came out thicker than the most expedient wing thickness. Hundreds of cubes had to be taken away from the fuselage capacity - that is, both the passenger compartment and the cargo compartment of the aircraft. Such an airliner with a classic layout could carry mainly fuel and crew. There was simply not enough space for passengers and cargo.

All this put an end to the projects of the Tupolevites for the creation of strategic bombers Tu-160V (B - hydrogen) and a supersonic airliner Tu-144V, as well as a hypersonic strike aircraft of the "360" project and an aerospace aircraft Tu-2000 capable of going into space. but at the same time starting and taking off like an airplane.

Methane turn

They responded to the problem quickly. By 1989, the hydrogen tank of the Tu-155 was replaced with a methane one and the tests continued, completing another 95 flights. The density of methane in the tanks was not lower than 0.41 kilograms per cubic meter - six times higher than that of hydrogen. The heat of combustion of a kilogram of CH4 is only 55.7 megajoules per kilogram - half that of H2. But six times the high density of the liquid phase of the gas easily interrupted this factor: the tank for liquid methane can be 2.5 times smaller than for hydrogen.

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In addition, methane becomes liquid at -161.5 ° C, and hydrogen at -252.9 ° C. This huge gap leads to a big difference in economics: a kit for a hydrogen refueling station, even the smallest, costs millions of dollars, and an order of magnitude less for liquid methane. And the walls of the fuel tank with liquid CH4 on the Tu-155 required only 5 centimeters of thermal insulation - and no difficulties with vacuum-screen thermal insulation. The methane tank (or rather, two, to maintain alignment) on the experimental aircraft had a capacity of 20 cubic meters and allowed to fly for two hours in a row.

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It is clear that this is not enough for a production aircraft; but it is no less clear that the problem can still be solved. To do this, the Tupolevites created the Tu-156 project, with 16 tons of methane on board (the equivalent of almost 20 tons of kerosene), and later - the Tu-206, with 22.5 tons of methane on board (almost 54 cubic meters).

To squeeze fuel into the fuselage without sacrificing space for passengers and cargo, the tanks were placed in a "hump" above the passenger compartment. At the same time, according to calculations, fuel consumption increased by 15%. But due to the fact that a kilogram of liquefied methane gives at least 15% more energy than a kilogram of kerosene, the mass fuel consumption per kilometer of flight did not deteriorate. And economically (fortunately, liquefied methane is much cheaper than kerosene), the liner became more profitable than the usual one.

It is clear that none of this could be realized, since 1991 followed the flights of methane planes in the USSR. Following this date, the country's leadership made a decision on the massive import of airliners, while abroad there were no “methane” projects of the same degree of elaboration. Even if the decision to launch the Tu-206 into production had been made, it is not a fact that something would have worked out. In the 1990s, the death rate in the country soared by 30% and did not drop to zero. In such a situation, there is no time for money for R&D for aircraft.

How should European hydrogen projects be assessed?

From the history of the development of technology in the West, it is known that only a few take into account the Soviet experience there. For example, Musk, who studied rocket science from a Soviet textbook, followed Korolev using supercooled oxygen, and no one else in the Western world did this (however, the creators of the Russian Angara did not bother with this either: studying our own history is generally our weak point).

Therefore, it is natural that no one at Airbus seriously thought about hydrogen experiments with the Tu-155, and they will begin to realize all the problems with liquid hydrogen described above on their own experience already in the 2030s, closer to the promised construction of prototypes.

Purely theoretically, the hydrogen problem can be solved by creating an aircraft not according to the classic airliner scheme inherited from the British Comet of the 1950s, but more suitable for large gas tanks.

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For example, according to the "carrying fuselage" scheme, as in the Russian project M-60 of the Myasishchev Design Bureau: due to the broadened fuselage, which creates a lifting force, it is quite possible to get much more internal volume in the fuselage, where gas tanks can be placed - as we remember, in the wing, unlike kerosene, they cannot be placed.

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There is another way: to create an aircraft with a "flying wing" fuselage, similar to the DSB-LK developed by designer Moskalev from the 1950s (the project is almost a contemporary of Comet). In such a scheme, the fuselage is almost "flat", and the actual wings are small, since it is the fuselage that creates a very large part of the lift.

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True, the Moskalev project itself is not directly suitable: it was created for supersonic flight at altitudes up to 35 kilometers, that is, its capabilities for modern passenger airliners are deeply redundant. At subsonic sound, the "flying wing" can be made noticeably thicker, which will not only accommodate a hundred or two cubic meters of liquefied methane in the fuselage, but also provide greater comfort to passengers.

By the way, one of the Airbus concepts in the illustration vaguely resembles a hybrid between such a flying wing and a monocoque fuselage like the M-60. Such a scheme is called "mixed wing". True, the likelihood of its implementation in this form is doubtful: the company claims that the concept is designed for 200 passengers, and as calculations show, for such small aircraft, there is simply no noticeable advantage over the usual scheme of the flying wing and the supporting fuselage. In addition, it is not noticeable in the sketches that a noticeable place for hydrogen tanks remains inside the concept (in the case of such an aircraft, they should take about 200 cubic meters).

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But in practice, we would not expect the implementation of the "mixed wing" schemes in practice - neither in Russia nor in the West.Let's face it: Russia at the present stage, from a technical point of view, outside the military sectors, acts as an intellectual colony of the West. In aviation, it is precisely those projects that are developing in terms of layout that copy the standard Western solutions - Sukhoi Superjet and MS-21. This means that no M-60 and even more so "flying wings" will not take off in our country, because they simply will not be given money for their construction.

The typical businessman or high-ranking official is not a fanatic, like Musk, who started the rocket business by reading a rocket science textbook. He did not read any textbooks and works on the "load-bearing fuselage" and "flying wing", and therefore will treat such a solution as untested. Moreover, to paraphrase Comrade Stalin, there are no fools in the West, and if it were possible, "they would have built something like this long ago." It is precisely such sentiments among the elites that we mean by the phrase “intellectual colony”.

But it is also doubtful that Airbus will take this path. For the ZEROe concept above, we have already explained why it does not look like a truly "hydrogen" one. It is also doubtful that something similar will be implemented in the future. Yes, the company recently proposed a V-shaped aircraft design, where, in theory, larger tanks can also be placed.

But on closer inspection of the news, it becomes obvious that the V-shaped concept was not proposed by Airbus (he only supported it, and the performers were people from a Dutch university). In addition, the project has a big drawback: the V-shape creates a "Dutch step" - vibrations of the fuselage during flight, which will not be easy to compensate. Finally, this project simply does not have the space required for hydrogen tanks.

Let's remind: the methane tank, equal in capabilities to the kerosene tank on the A330 (139 cubic meters), will have a size of only 216 cubic meters. But hydrogen is about 560 cubic meters. The second digit simply cannot be crammed into a flying machine that is traditional or has a V-shaped layout. It is already crowded there, no half a thousand additional cubes are observed in this place. At the very least, not to cram without a sharp loss of space for passengers, which will make such an aircraft unprofitable.

Therefore, we can say with a noticeable degree of certainty that hydrogen energy will not take off in Europe either - there is simply not a single hydrogen airliner project presented there that would take into account the problem of lack of space in conventional aircraft.

Maybe such a project will appear there? Not a fact: Western builders of airliners today are as conservative as Western rocket builders of the “Domask” era. They could not abandon the close to traditional layout even when they made the Concorde - as a result of which the aircraft had an unacceptably high fuel consumption, which made it a narrowish product. There is no reason to change this status quo.

Western manufacturers of large liners today simply have no competitors, and out of competition, large corporations tend to churn out similar technological solutions indefinitely. This is elementary less risky, and risk is what large corporations fear most of all.

How will the aviation industry actually develop?

Of course, the “risk-free” strategy that suits large corporations does not suit the rest. Today, airliners (the same A330) cost about a million dollars per ton of mass, and partially reusable space rockets cost a million dollars per ten tons of mass. And even at the unit price of "dry weight" (without fuel), passenger aircraft are comparable to the cost of the Falcon 9 rocket.

In the coming years, with the advent of Starship, reusable spaceships and rockets per dry mass unit will become even cheaper than Airbus and Boeing. In addition, the latter also use expensive kerosene, while Starship uses much cheaper liquefied methane.It is not surprising that SpaceX is making plans on how to squeeze liners in the long-distance flight market: economically, this is quite feasible, even despite the probably less resource of Starship in comparison with aircraft.

But here's the trouble: for flights at ranges of less than 4-5 thousand kilometers, rockets still cannot replace liners. It would be good for the producers of the latter to do something to reduce the cost of flights and, at the same time, to fulfill the “green mandate”. In principle, methane is as good as hydrogen for this. In some chemical reactions, carbon dioxide and hydrogen eventually produce methane. That is, having obtained hydrogen with the help of "green" electricity, it can be used to produce equally "green" (and not fossil) methane.

At the same time, about the same amount of carbon dioxide will be released during the combustion of "green methane" as during its synthesis by the Sabatier reaction. That is, formally, the "original sin" of fuel - CO2 emissions - will be completely "redeemed" here. Yes, the cost of such a synthetic fuel should be much higher than that of natural methane - probably even more expensive than that of kerosene.

However, this is not a problem. The inhabitants of the Western world are not too poor and will quite tolerate the increase in airfare associated with the transition to "green methane". The real plus is that methane significantly less kerosene pollutes the atmosphere with microparticles, which are one of the main causes of death from cardiovascular diseases. And she, we recall, is still the main cause of death on our planet.

Moreover, the transition to "green methane" will be ideal for manufacturers of Western airliners. They are too conservative to switch to "main fuselage" and "flying wing" for large aircraft. On the other hand, having made a "hump" on a liner of conventional aerodynamic shapes - as on the Tu-206 project decades ago - both Airbus and Boeing will be able to cope with the task of "zero CO2 emissions". Here, new aerodynamic solutions are not particularly needed, and ecologists will be happy.

This is practically the only happy ending imaginable for today in the airliner industry. By the way, it may have indirect advantages for us as well: after the appearance of methane planes in the West, we will inevitably switch over to them. But it is unlikely that gas for them in our country will receive a reaction from Sabatier. Most likely, it will be regular "fossil" methane. That is, in the future, several decades in Russia, the prices for air tickets may well decrease - at least for domestic lines.

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