Mon. Dec 6th, 2021

Today’s commercial aircraft are not exactly fuel efficient. The average 747, for example, flies through one gallon of kerosene-based fuel per second. And with , Carbon free alternative It will be necessary to offset the impact of industry on global warming. We have moved closer to the era of electric aircraft.

Pioneer researchers, scientists and entrepreneurs have been working on the dream of electrified flights since the late 19th century when heavy lead-acid batteries were loaded on early airships to power their pilots. We’ve also seen fancy ways to power aircraft during years of flight, from conductive tethers to the ground. Per But it was not until the advent of relatively high-power nickel-cadmium (NiCad) battery technology that human-scale free-flying electric planes became technically possible.

But even as battery chemistry has evolved over the past few decades and energy concentrations have increased, today’s sophisticated lithium-ion cells have created the same problem for the aviation industry as for the automotive industry: how to properly balance energy – their battery weight ratio.

“If a jumbo jet were to use today’s battery, a 1.2 million pound battery would be needed just to generate the power of the jet engine that would replace it,” said Emily Pickerel, an energy fellow at the University of Houston. Earlier this year. “An additional eight jet planes will be needed to carry this weight effectively!”

And since Li-ion technology has fully matured, further increases in its energy concentration have dropped below five percent with each annual recurrence, which is why many researchers and battery companies are already looking for the next groundbreaking battery chemistry – whether (Non-ion), (Li-metal), (Li-S), or (ZN-Air).

Regardless of the composition, batteries need to be much lighter and have a higher energy concentration if they are to attack and detonate jet fuel which produces a combustible liquid, with an energy density of 9.6 kWh / L As the best Li-ion of today. To be fair though, due to the inherent inefficiency of internal combustion engines, if you compare the equivalent weight of fuel and battery, this figure drops to about 14 times the power density of a Li-ion battery.

For example, a Tesla Model 3 Li-ion-based battery with a power density of 260 Wh / kg That it has produced a sodium-ion battery with a density of 160 Wh / kg (although it is expected to reach 200 Wh / kg by 2023). Demonstrated lithium-sulfur battery power , Though facing that technology (I.e. the tendency to eat through chemical electrodes) before they can be widely used. Currently, 2- and 4-person Typically 250-270 Wh / kg operates at a specific power but industry experts expect the power concentration to be 350 – 400 Wh / kg before the electric aviation industry is truly launched – which could happen in the next few years, according to Tesla CEO, Elon Musk. .

Prevention and mitigation Another important test for electric aviation. When a battery cell, or even an area within a cell, is defective due to mechanical, thermal, or electrochemical failure, its temperature may exceed safe levels causing the cell to first produce lithium off-gas, causing the cell walls to swell. Then bursts, leaving all of its energy reserves. When a cell explodes it can damage and overheat the surrounding cells, creating a cascading failure that leads to explosion and fire. That’s when one happens , The car will probably be a write off (if the fingers crossed it did not set your house on fire) but if If an electrified 747 could happen on the flight, the loss of life would be catastrophic.

To reduce the chances of a complete escape, . Since off-gassing usually occurs a few minutes before a cell explodes, the presence of an observation system that compares with sensors located near a Li-ion battery can warn of the presence of a failed cell further collected by a reference sensor. And to repel already emitted gases, fire extinguishers equipped with inert gases – when mixed with atmospheric oxygen to prevent offgases from reaching combustible levels – can be employed as well. Of course regular maintenance and strong inspection help prevent cell failure before the situation explodes.

Rolls Royce

Battery electric planes will also present a unique challenge in balancing wind speed and range, although for Rolls-Royce, this is not a question – speed everywhere. For the past few years, Rolls-Royce has been working silently (Accelerate in-flight electrification), build a battery-powered racing plane, dub The spirit of innovation, In an effort to set a new world wind speed record.

There were records When an electric powered , Using a Siemens e-aircraft-built power plant, achieved a maximum speed of 209.7 mph (337.5 kph) over a 3-kilometer long course. This achievement was certified by the World Air Sports Federation (FAI) as the fastest electric powered flight of an aircraft weighing less than 1,000 kg at takeoff, surpassing the previous record (set in 2013) at just 8 mph (13 kph).

In addition to the 3-kilometer record, Rolls-Royce also has the opportunity to set FAI records for distances of 15km and “time at altitude”, depending on how fast the plane can reach a certain altitude. “That should be a significant number,” said Simon Burr, Rolls-Royce’s director of engineering and technology at Civil Aerospace. . “We are planning to fly at 300mph. We will see how high we can go. ”

The spirit of innovation

Rolls Royce

For its efforts, Rolls-Royce – which is partnering with the UK And start-ups , Which makes the Bespoke battery system – has achieved a pair Twin-seat air racer. One has been used for ground testing while the other will handle the actual flight. The Nemesis NXT already holds a 3km FAI record with a maximum speed of 415mph (667.8km) using a 400hp liking internal combustion engine.

The Rolls-Royce team replaced that Lycoming engine with a 400kW (530hp) generating YASA 750v electric motor trio while the fuel tank was replaced with three separate battery packs.

The spirit of innovation

Rolls Royce

“The main challenge of electrification is weight,” Rolls-Royce flight test engineer Andy Roberts said during a media briefing in September. Not only has the 6,000-cell battery system in the Nemesis NXT shifted the center of balance of the aircraft, the 450kg battery system also does not lighten over time as will conventional fuel tanks, which could affect aircraft performance at later stages of the aircraft. The consignment batteries were so large that Rolls-Royce’s chief test pilot Phil O’Dell had to lose 2 kg of body weight to help keep the overall weight of the aircraft within the operating margin.

Thermal escape is a major concern for the Rolls-Royce team, as they will push these batteries to their absolute limit during flight. To alleviate this problem, the cells are separated by a liquid-cooling plate and stored in cork-wrapped fireproof cases (perforated cork material helps dissipate heat). A cell should be overheated so that off-gas escapes, the plane is equipped with an inert gas suppressor and ventilation system.

15 September, The The spirit of innovation Made the first test flight from the UK Ministry of Defense Airfield, flying for 15 minutes. The company expects Nemesis to be ready for the official run on record before the end of this year.

“Its the first flight The spirit of innovation A great achievement … We are focused on the technological advances we need to make to decarbonize transportation across air, land and sea and capture the economic opportunity to convert to Net Zero, ”said Warren East, Rolls-Royce CEO. . “It’s not just about breaking a world record; The advanced battery and propulsion technology for this program has exciting applications for the urban air mobility market. “

Rolls-Royce is far from the only company that follows electric aircraft technology, no matter how fast it competes. From small startups to industry leaders: – Companies and governments around the world are running to build commercially efficient electric aircraft for passenger flights and cargo transport.

A prototype of an electric air taxi from the German company Volokopter was seen during a presentation at Fumicino Airport in Rome, Italy, on October 27, 2021.  REUTERS / Guglielmo Mangiapane

Guglielmo Mangiapane / Reuters

, For example, builds an electrified 2-seat trainer plane called , Similar to the function . Slovenian aircraft maker Pipistrel is selling its $ 140,000 , The first electric plane to achieve FAA certification since 2018. At the other end of the spectrum you have space giants like Airbus who are developing Air Race e, which the company claims is the world’s first all-electric air race series when it launches later this year (better to keep up with the times, ), And the like , A 4-seater eVTOL. These electric vertical take-off and landing-capable vehicles have become a popular alternative to fossil fuel-free air travel, such as the Cadillac , Create your own , Of China EHang AAV, Or .

Unfortunately, despite all the research and publicity surrounding electrified air travel, many industry experts remain skeptical that we will see it. – At least for larger sized airframes like the Boeing 787 or Airbus A350. Until battery technology becomes strong enough, we will probably see EVTOLS limited to short-hop intracity duty for the foreseeable future, eventually expanding into intercity giants and regional commuter jets. Still, sitting in traffic gets beaten up.

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