Hybrid electric aircraft will reduce harmful emissions and noise.

Original author: Philip E. Ross
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Electric motors will appear in the air just as they appeared on the ground - first, the batteries will be used to help the engine burning fuel.

May 31, 2018 Magnus eFusion electric aircraft with a Siemens engine crashed in Hungary . His pilot Janusz B., mentioned in the article, and the passenger were killed. Siemens is working with local authorities to investigate the causes of the incident.

I sit in the cockpit of one of the most amazing airplanes in the world. This is a double light aircraft eFusion, produced by Magnus Aircraft , equipped with a motor from Siemens - a huge company, famous not for its contribution to aviation. I remove my feet from the control pedals just before the pilot turns on his car.

The propeller instantly starts spinning and becomes almost invisible. But at the same time there is such silence that we can easily communicate without headsets. This is the first sign that the plane is powered by electricity.

We begin to roll down a small airstrip in Budapest’s overgrown grass field. 10 in the morning, sunny sky, farms are visible in the distance. Suddenly, we jump up into the sky and begin to climb steeply up, farm houses shrink affectionately. The cows below do not even look up. This is a fast acceleration, the aviation equivalent of the Ludicrous mode of operation of the Tesla Model S, another sign of the electric motor. You get all the features of the engine, and immediately.

Then we dive, deviate to the side and rise again, leaving my stomach somewhere behind. Not bad for a simple airplane capable of a few aerobatics, as Gergelly György Balázs, head of the Budapest Siemens Research Office of Siemens, apologized, as if I had gotten on the plane, described it to me. Fortunately for me, the pilot of the model, capable of all aerobatics, was away on business.

After 15 invigorating minutes, the batteries had fallen by half to less than 10 kWh, and it was time to land. This is the last sign of an electric motor. Although today lithium-ion batteries, racks with which are hidden in the case in front of the cabin, store much more energy than they could just a few years ago, they are not even close to the gasoline tank. So, in the coming years, the possibilities of all electroplanes will be limited to short jumps, mainly between neighboring settlements, and not between cities.

Aviation is responsible for 2-3% of global emissionsgreenhouse gases. But its efficiency per unit volume is considered very high, since quite a lot of gases are emitted in the stratosphere. Aviation's share of emissions is expected to grow rapidly over the next couple of decades, with an increase in the number of flights and a decrease in emissions from other sources - in particular, from the generation of electricity and cars.

In 2016, 23 countries signed an agreement to limit carbon emissions committed by aircraft, which is scheduled to begin in 2020, according to standards developed by the International Civil Aviation Organization (ICAO), the UN agency. Therefore, researchers all over the world are working to find ways to meet these limitations.

But how can electrosmiths, which are limited to a ridiculously small distance, help? They are considered a critical step in technological evolution in aviation, which will repeat the migration, which is just beginning now, to the automotive industry from internal combustion engines to electric motors. After 15 years, hybrid passenger airplanes, combining electricity and fuel, may begin to work on short and medium flights. Hybrids will burn fuel, but do it economically.

Blue Sky Concept. Capable of aerobatics version of the Extra 330LE, a light aircraft, modified by Siemens to work on electricity. In the early tests of the end of 2016, he set the altitude record for electric flights, climbing 3000 meters in 4 minutes 22 seconds.

“We can seriously change the situation on the scale of small training planes that feed on electricity, because physics does not work against us there,” said George Bai, director of Bye Aerospace , who, together with Siemens, supplies electric training planes . “But to increase the speeds and masses required for liners, it is necessary to switch to a hybrid installation. The industry is actively working on this. ”

So far, hybrids are needed because, although aviation fuel gives 12,500 Wh * h of energy per kilogram, lithium-ion batteries provide only 160 Wh / kg, considering the weight of the batteries and all other equipment that ensures their safety.

To raise the hybrids in the air will require many technological breakthroughs. They, naturally, will appear as a result of work of programs on research and development. But they will also appear due to attempts, such as Siemens does, to commission electric training aircraft, and, most likely, most importantly, attempts to create an urban taxi industry in something like over-grown drones. Siemens itself is working with Airbus Helicopters on one of these all-electric projects, CityAirbus. In parallel, Airbus is working on the Vahana project , which is developing its branch in Silicon Valley. There are many other startups, including Chinese Ehang, the first demonstrations of passenger flights that took place this year, when the engineer took the oktokopter to the sky.

In aviation, most hybrids are based on a sequential architecture in which the engine that burns fuel — either ICE or a turbine — feeds a generator that feeds electric motors, rotating screws and charging batteries. In such a scheme, the batteries provide short-term bursts of energy needed for take-off, which allows technicians to tune the engines that burn fuel so that they work at ideal speeds. Massive jet engines dangling from the wings of your aircraft operate at full power only during takeoff; the rest of the time, they, roughly speaking, idle and only increase the weight of the aircraft.

There are other benefits. When distributing power over the wire, with a hybrid design, you can position the screws exactly where you need it, without adjusting everything, based only on the location of the huge engines. Some hybrid schemes try to locate the screws behind the aircraft or even on the vertical stabilizer.

Hybrids are working on two major consortia. In Europe, Airbus cooperated with Siemens and Rolls-Royce in an alliance separate from the CityAirbus project. In the US, Boeing and JetBlue are part of a competing project run by a startup Zunum Aero , located in Kirkland, Washington. Both consortia expect to raise hybrids in the air by the early 2020s.

Airbus plans to start with a modified version of the existing aircraft, British Aerospace 146 per 100 seats, in which one of the four nacelles on the wings will hold not a motor, but a two-megawatt electric motor. It will receive energy from a generator that is rotated by a small gas turbine located in the fuselage (thanks to which it does not experience air resistance). If the electrical system fails, the aircraft will be able to fly on three propellers driven by conventional motors. Airbus is preparing a hybrid for a demonstration at the next International Paris Air Show .

The US consortium reported little about its plans. In August 2017 GE Aviationissued a description of the concept and the tremendous work that she claims is being done on the creation of hybrid generators. In one of the ground-based experiments, GE Aviation used a 1 MW motor to rotate a screw with a diameter of 3.3 m. In the other, it used a compressor from a GE F110 engine to power a 1 MW generator while the engine continued to produce cravings.

Batteries insert here: this Magnus eFusion rolled the pilot Janusz B. and the author of the article in maneuvers over the field near Budapest.

Although there is very little information on the work of both consortia, the interview clearly indicates that they concentrate on improvements in four technological categories: battery capacity, weight of the motor and generator, efficiency of the power electronics, materials and frame design. In the European Consortium, Siemens is engaged in motor, generator and electronics. In addition, the company has modified several small aircraft, creating fully electric models, considering that all parts can be truly optimized only by using them all together on an aircraft.

“We gain experience in using the entire electric propulsion system, everything that is between the pilot and propeller,” says Frank Anton, head of the eAircraft department at Siemens. "The only way to learn this is to send technology on the fly."

Electric motors can be relatively small and light, which opens up many possibilities. You can install a bunch of small screws on the wings, and rotate them to facilitate takeoff. NASA even studies a circuit with a bunch of small screws placed along the entire length of the wing, which properly direct air flow over the surface, and increase the ratio of lift to frontal resistance . As a result, the wings can be made shorter and thinner.

“Separate the generation from the engine,” says Anton, “and suddenly you have a bunch of different traction vectoring options.”

The key task of reducing the weight of an electrical power plant depends on two things. First, it is necessary to increase the energy density of batteries, which will grow smoothly, at least until modern lithium-ion batteries give way to a completely new technology, like iron-air batteries . Secondly, the energy density of the system from the motor and generator should also grow. This is a Siemens case.

In the nose of the aircraft from Siemens, capable of performing aerobatics, sits their aircraft engine SP260Dwhich, with a weight of 50 kg and a power of 260 kW, has an amazing ratio of KW / kg of 5.2. The other aircraft, which is not capable of all aerobatics, has the same ratio, although its size is one and a half times larger. For the first time Extra flew in front of the public in 2016 in Germany. In 2017, he set a record for electric flights, breaking the speed bar at 340 km / h. Siemens engineers are actively working to further increase the energy density of the motor.

At the Budapest Research Center, Balasch takes me to the workbench in the laboratory and hands me a piece of motor cut in half. This is the part of the stator - the fixed part around which the rotor rotates - and in its section one can see the perpendicular sections of the copper winding, which coincide with each other, like bricks. Such straightforwardness is the key method of achieving high levels of energy. It does not leave an air gap that could prevent heat from the wires from being led to the liquid-cooled housing. This heat must be removed from the insulation of the wires, or it will melt and short circuit will occur .

“We need a more homogeneous heat exchange, which can provide a round wire, and we also hope to improve electrical insulation - all of this is important for the aircraft engine,” says Balash. Siemens specifically orders this cable from Furukawa Electric Co. Japanese supplier.

Here, engineers carry out daily research, cutting off excess weight grams per gram. Such a time-consuming approach makes these hand-made "precious stones" more expensive than any Rolex. When I lift the spare part in order to evaluate its weight, Balash noticeably shudders. I carefully put it back.

He says that in a few years, thousands of these engines will be manufactured annually for use in air taxis, which, as Siemens and all its competitors in the region predict, will flood our cities in the manner of locusts. It was then that the cost of production of engines will fall, perhaps even lower than the cost of comparable today's ICE, consisting of hundreds of parts and carrying out countless complex mechanical interactions.

But the work to eliminate excess weight gram by gram ultimately gives way to revolutionary improvements. One of these happened in the early 1980s, when General Motors and Sumitomo Special Metals independently introduced superpower neodymium magnets in motors. The next revolution will be connected with electromagnets, the winding of which will consist of superconducting wires.

With such a winding, the motor-generator will practically not lose energy in the form of parasitic heat - but this dream can be realized only after the appearance of high-temperature superconductors. Now ceramic materials reach superconductivity at temperatures of -135 ° C , which is 100 ° C warmer than the original metallic ones. So, instead of cooling the wires with liquid helium, which is not much higher than absolute zero, designers can rely on liquid nitrogen.

Siemens has been working on this concept for almost two decades. Initially, the company planned to place superconducting motors on ships, where space and weight are particularly important. And still, the current version of their engine (used as a generator) is such a cabinet, the height is greater than the height of a person. Therefore, the company's engineers are engaged in its miniaturization for use in aviation. The target power density is 10 watts per gram. Siemens did not show me these developments - only an image of a larger machine with cooling, and a diagram of a future aviation version.

Other companies are aiming for that too. GE Aviation is working on engines with cryogenic cooling for NASA, but does not disclose details. All of these companies are silent; they may not want to reveal the cards, or they simply have nothing to show yet. In any case, NASA estimates that passenger aircraft with cryogenic systems with a capacity of 30 VMT will not appear at least until the mid-2030s.

In order to fully take advantage of the superconducting motor - and the generator, in the hybrid system - it is necessary to create superconducting inverters. NASA is working with GE to produce one that can operate from 19 kW / kg with an efficiency of 99%.

Integrating the motor into the hybrid scheme — probably using a gas turbine to rotate the generator — is still in process. Siemens engineers first model everything in a computer, in an interactive simulation, from which I was shown only a couple of frames on the screen. It was part of a simulation of a machine cooled in the usual way. “This is a consistent hybrid, and the simulation shows us the distribution of capacities,” says Balash.

Currently, gas turbine plants are mainly used as a backup power supply for power grids, where the weight of the components does not matter. However,
many modern military aircraft take electricity from turbines powered by either jet engine compressors or air flow.

It may seem that too much effort is spent on saving a few pounds - but every little thing matters. The kilogram saved on the weight of the motor gives precious extra pounds for batteries. When United Airlines recently began printing its passenger magazine on paper that weighed less than usual, saving 28 grams per number, or about 5 kg per flight, it is estimated that this would save the company 640,000 liters of fuel annually, or $ 290,000.

That is why new airliners, such as Boeing 787, use such an amount of polymers reinforced with carbon fiber. Magnus eFusion does the same thing - one person’s effort is enough to roll the plane out of the hangar.

Let's go over to the final product. It will appear in ten years, and the airlines will use so quiet hybrid airplanes that they will be able to fly at night over the city. Thanks to the rotating screws, they will be able to take off from shorter lanes, possibly located right in the year. They will save energy at the expense of efficiency and low weight. This means that their maintenance and ownership will be cheaper - the situation is the opposite for today's aircraft, since the cost of their maintenance is many times higher than the purchase price.

One catch: in the next ten years, simple hybrids will be only a little more environmentally friendly than conventional aircraft. Tangible improvements will come as a result of economies of scale, when hybrids allow the industry to switch to all-electric aircraft, perhaps as early as the 2030s. “Hybridization will allow us to save from 4% to 20% of energy,” says Otto Olaf, head of sales and business development at Munich’s Siemens office. “If we completely electrify the plane, the savings will be even greater.”

Similarly, air carriers are interested in reducing greenhouse gas emissions. “The EU’s Flight Path 2050 initiative is trying to reduce emissions by more than 2 times,” says Anton from Siemens, “but by that time the passenger traffic will have to double, so we need at least a fourfold improvement.”

It is not clear how these figures are obtained. The easiest way to compare emissions with passenger miles. It will be more honest to take into account the expected source of electricity that can be generated on the ground and stored in batteries for later use in the air. The calculations also need to consider how much energy is used to manufacture batteries, motors, ultra-light carbon-composite parts of the aircraft and everything else.

The same initiative of the European Union is aimed at reducing the noise of aircraft operation by half by 2050. It turns out that now it is the greatest motivation for the airline industry. In order to meet the restrictions on night flights, air carriers are sometimes spent on work to mute old, high-profile aircraft.

“The big surprise was the moment when Siemens started communicating with air carriers,” says Anton. - I have always believed that quiet operation of engines is in priority in third place, after energy and emissions. And now this is a paramount matter. ”

This will not be the first technology successfully implemented for reasons unrelated to global warming. People buy a hybrid Prius to save on gasoline; they buy Tesla to overtake Porsche. Air carriers will buy hybrid airplanes because of their quiet operation, and reducing greenhouse gas emissions will be almost a side effect. But it will still be.

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