Today’s commercial airplanes are not very frugal. An average of 747, for example, burns a gallon of kerosene-based fuel every second in flight. And with, carbon-free alternatives will be needed to offset the industry’s impact on global warming. We are approaching the era of electric airplanes.
Pioneering researchers, scientists and entrepreneurs have been working on the dream of electrified flight since the second half of the 19th century, when heavy lead-acid batteries were placed on the first airships to power their propellers. We’ve also seen a number of, um, new means of powering airplanes during flight over the years, from conductor chains stretching back to the ground to to, but that wasn’t until the advent of nickel with relatively higher power. -Cadmium (NiCad) battery technology, which allowed electric planes to fly freely on a human scale, has become technically feasible.
But even as battery chemistry has evolved and energy density increased in recent decades, today’s lithium-ion cells pose the same hurdle to the aerospace industry as to the automotive industry: how to properly balance energy for the weight ratio of their batteries.
“If a jumbo jet used today’s batteries, it would take £ 1.2 million of batteries just to produce the power of a jet engine to replace it,” said Emily Pickrell, a University of Houston fellow. earlier this year. “This weight would actually need an extra eight jets just to carry that weight!”
And as Li-ion technology has fully matured, further increases in its energy density have dropped to below five percent with each annual iteration, which is why many researchers and battery companies are already looking for the next revolutionary battery chemistry – be it (Na-ion). (Li-metal), (Li-S) or (Zn-air).
Regardless of the composition, batteries must become much lighter and more energy dense if they want to attack and dethrone the jet fuel which, with an energy density of 9.6 kWh / L, makes the flammable liquid the best lions of today. To be fair, due to the inefficiency inherent in internal combustion engines, that figure drops to about 14 times the energy density of a lithium-ion battery if you compare the same weight of fuel and batteries.
For example, the Tesla Model 3 lithium-ion battery boasts an energy density of 260 Wh / kg while a sodium-ion battery with a density of 160 Wh / kg has been made (although it hopes to reach 200 Wh / kg by 2023. ). Lithium-sulfur batteries have shown capacity, although the technology is facing (i.e. chemistry tends to eat through the electrodes) before they can be widely used. Currently, 2 and 4 people typically work at 250-270 Wh / kg of specific energy, but industry experts expect the energy density to have to reach 350-400 Wh / kg before the electric aviation industry can really move – something that could be happen within the next few years, according to Tesla CEO Elon Mask.
Prevention and mitigation is another critical test for electric aviation. When a battery, or even an area within a cell, breaks down due to mechanical, thermal, or electrochemical failure, its temperature can rise above safe levels, causing the cell to first produce lithium gases, causing the cell walls to bulge, then burst, releasing all energy reserves. When a cell breaks, it can damage and overheat the surrounding cells, causing a cascading failure that results in an explosion and fire. When that happens, the car will probably be written off (they crossed their fingers if it didn’t set your house on fire as well), but if that happened on a flight on an electrified 747, the loss of life would be catastrophic.
To minimize the chances of a complete escape occurring,. As the release of gases usually occurs a few minutes before the cell bursts, the presence of a monitoring system that compares the sensors located near the lithium-ion battery with those collected further by the reference sensor can warn of the presence of a faulty cell. And in order to cancel all the gases that have already been released, fire extinguishing systems armed with inert gas can also be used – to prevent the waste gases from reaching flammability levels when mixed with atmospheric oxygen. Of course, regular maintenance and robust inspections also help prevent cell failures before the situation becomes explosive.
Battery-powered airplanes will also provide unique challenges in balancing air speed and range, though for Rolls-Royce it’s not even an issue – speed to the end. Over the past few years, Rolls-Royce has been quietly working on (accelerating the electrification of flight), building a battery-powered racing plane, called The spirit of innovation, in an effort to set a new world record in air speed.
The record was when the electric drive, using a power plant built by Siemens eAircraft, reached a top speed of 209.7 mph (337.5 km / h) on a 3-kilometer track. The World Federation of Air Sports (FAI) has confirmed this feat as the fastest electrically powered aircraft weighing less than 1,000 kg at take-off, surpassing the previous record (set in 2013) by just over 8 mph (13 km / h).
In addition to the 3-kilometer record, Rolls-Royce also has the opportunity to set FAI records for a distance of 15 kilometers and “time to altitude,” basically how fast an airplane can take off and reach a certain altitude. “That has to be a significant number,” said Rolls-Royce’s director of engineering and technology – Civil Aerospace, Simon Burr. . “We plan to fly over 300mph. We’ll see how high we can get. “
For its attempt, Rolls-Royce – which is in partnership with the British and start-up, which produces custom battery systems – has acquired a pair of two-seater air racers. One was used for ground testing, while the other will perform actual flights. The Nemesis NXT already holds a 3km FAI record with a recorded top speed of 415mph (667.8km) using a Lycoming 400hp internal combustion engine.
The Rolls-Royce team replaced that Lycoming engine with three YASA 750v electric motors that produce about 400kW (530hp), while the fuel tank was replaced with three independent batteries.
“The main challenge to electrification is weight,” Rolls-Royce flight testing engineer Andy Roberts said during a September media briefing. Not only has the 6,000-cell battery system on the Nemesis NXT shifted the aircraft’s center of balance, the 450kg battery system also doesn’t get lighter over time than conventional fuel tanks would, which could affect aircraft performance during later stages run. The batteries are so large that Rolls-Royce chief test pilot Phill O’Dell had to lose 2kg of body weight to help keep the overall weight of the aircraft within operating margins.
Thermal escape is a real concern for the Rolls-Royce team, as these batteries will push to their absolute limits during the summer. To alleviate this problem, the cells were separated by liquid cooling plates and stored in refractory housings wrapped in cork (the porous cork material helps in heat diffusion). In case the cell overheats to the point of exhaust gas discharge, the plane is equipped with both an inert gas suppression system and a ventilation system.
On September 15, The spirit of innovation made his first test flight from the airport of the Ministry of Defense of the United Kingdom, flying 15 minutes. The company hopes Nemesis will be ready for an official record-breaking ride before the end of this year.
“The first flight The spirit of innovation is a great achievement … We are focused on making the technological discoveries needed by society to decarbonise air, land and sea transport, and seize the economic opportunity to transition to net zero, ”said Warren East, CEO of Rolls-Royce. “This is not just about breaking a world record; The advanced battery and drive technology developed for this program has exciting applications in the Urban Air Mobility market. ”
Rolls-Royce is far from the only company that deals with electric aircraft technology, no matter how faster it is than the competition. From small startups to manufacturers in industry – – companies and governments around the world are racing to develop commercially viable electric aircraft for both passenger flights and cargo hauling.
, for example, builds electrified 2-seater coaching planes called, similar in function as. Slovenian aircraft manufacturer Pipistrel is selling its $ 140,000, the first FAA-certified electric aircraft since 2018. At the other end of the spectrum, you have space giants such as Airbus developing Air Race E, which the company claims is the first in the world – a series electric aerial races when it starts later this year (better to keep up with the times,), and protesters like, eVTOL with 4 seats. These electric vehicles capable of vertical takeoff and landing have become a popular option for air travel without fossil fuels, such as the Cadillac, DIY, Chinese EHang or AAV.
Unfortunately, despite all the research and hype around electrified air traffic, many industry experts are still skeptical that we will see it – at least for large aircraft like the Boeing 787 or Airbus A350. Until battery technologies become robust enough, we will most likely see that eVTOLS will be limited to short-term intra-city operations in the foreseeable future, only to eventually expand to intercity trips and regional suburban aircraft. Still, it is better to sit in traffic.
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