2019年6月14日 Dr Peter Harrop
Expect seven-times the air traffic in 2050 increasing greenhouse gas X4 unless something radical happens. Elon Musk has made interesting statements about electric aircraft over the years. His Tesla will survive and prosper: if Tesla investors stop investing the Chinese will snap it up. Either way, somewhere down its list of priorities will be reinventing pure electric aircraft, so what does Tesla bring to the table?
The new IDTechEx report, Manned Electric Aircraft 2020-2030 spells it out. The energy density of batteries must improve. Close behind is the power density of motors with controllers. "Distributed thrust" involves up to 20 propeller-motors in fixed wings. This makes motors with their controllers a much larger percentage of the cost of the aircraft. Benefits include shorter take-off, half the wing mass for a fixed wing, longer endurance, redundancy and better control. Up to 36 thrusters in vertical take-off and landing VTOL aircraft reduce the inefficiency compared to helicopters and provide redundancy, plus "hands-off" stability.
Tesla CEO Elon Musk has said that once batteries are capable of producing 400 Wh/ kg, with a ratio of power cell to the overall mass of between 0.7-0.8, a pure electric transcontinental aircraft becomes "compelling". Bye Aerospace is the one to benchmark here. It has the most orders for a pure electric plane; over 400 ($165M) split between its two-seater eFlyer2 with excellent 3.5 hours endurance and four seat eFlyer4 with an even more impressive 4.2 hours endurance. More range can come from adding the solar wing option. The battery cells are from LGChem with about 260 Wh/kg cells so is Musk rational is saying 400Wh/kg gets us from these training aircraft to intercontinental flight?
The answer is yes, particularly if we consider small airliners with distributed thrust, solar bodywork like Tesla promises on its land vehicles and lighter-weight everything. The IDTechEx report, Solid State and Polymer Batteries 2019-2029 even shows that higher energy density will be combined with non-flammability. Bye Aerospace and most alternative single-propeller pure-electric aircraft use Siemens radial-flux permanent-magnet PM motors with 5 kW/kg. Two pure electric aircraft use YASA axial flux PM at 10 kW/kg and several designers promise 15-20 kW/kg -reducing weight by up to 75%. We conclude that intercontinental pure electric aircraft with 8 hours endurance are a prospect in 10 years or more.
Many key enabling technologies will support electric vehicles land, water and air beyond the usual lightweighting and drag reduction. Here they are with Tesla capability and its relevance to intercontinental aircraft.
Structural electronics varies from the Lamborghini Terzo Millennio with supercapacitor bodywork to three car companies promising energy-independent solar cars in 2020 and Tactotek using In-Mold Structural Electronics TM to reduce electrical and optical parts by 90%. Tesla sponsors research on solar bodywork. Replacing metal body with electrically smart plastic gives what Imperial College London calls "massless energy". The car then plane weight drops; space and cargo weight increase, bodywork doubles as a supercapacitor.
Electric motor-generators: Tesla 3 car excels. Its new PM reluctance motors are the most efficient and are now appearing on other Tesla vehicles. Of the volume successes, only Tesla motors are minimally exposed to neodymium price hikes. Tesla is well able to design better aero motors.
Traction battery systems: Tesla relies on cells by Panasonic which has now set up a battery joint venture with Toyota for the next generation. Tesla bought Maxwell technologies partly for its battery electrode technology and its Chinese factory will use Chinese batteries. However, Tesla global charging network with promised zero-emission, off-grid, 15-minute charging is a huge competitive advantage and the world's airports and airfields need the same.
Energy harvesting and regeneration: Tesla works in this area, but it is not a leader. The most efficient solar bodywork (Hanergy) can even be effective inside the vehicle. Mercedes has active suspension that generates electricity. The Bye Aerospace eFlyer propeller reverses when braking to generate electricity. In future, that could also occur in a cloud, during steep descent and on the airfield in wind.
Tesla's Maxwell is a world leader in supercapacitors but it does not use the non-toxic, non-flammable aqueous electrolyte favoured by East Asian users. Do not expect to see them in aircraft. Fuel cells have been unsuccessful in aircraft. Tesla does not need them.
Tesla is well ahead of competitors in power electronics, using advanced components and sharing them for many tasks. Tear-down experts admire the "military grade" quality, all directly useful in aircraft. It needs to move to the lighter, more-efficient 800V region used by some competing electric cars and trucks. Indeed, the Rolls Royce ACCEL pure-electric aircraft development seeking an airspeed record is at 750V.
In low power electronics, sensors and sensor fusion, Tesla is well ahead with technologies very useful in aircraft such as elimination of over 1km of cable in cars by using antennas on boards and by the design sophistication. Its software, wireless upgrades, user interface and integration of heating and cooling are appraised as superlative. Local energy harvesting for eliminating power cables must come next: a domestic airliner can have 100 km of cabling. Pure electric regional aircraft are more than a dream. Zunum Aero claims about $100 million in pre-orders for its nine-seater, single-pilot, pure-electric domestic aircraft, delivery 2022.
Software, connectivity and artificial intelligence are now key from cars to aircraft. Tesla is one of the most admired companies here too and its ability to add such things as camper mode, falcon wing doors and so on means it can also reinvent the aircraft to make it inspiring and exciting.
Musk even envisages a pure-electric aircraft capable of VTOL and supersonic flight at high altitudes. "The trick," said Musk, "is that you have to transition to level flight. The thing you'd use for vertical take-off and landing is not suitable for high-speed flight. The interesting thing about an electric plane is that you want to go as high as possible, but you need a certain energy density in the battery pack because you have to overcome gravitational potential energy. Once you've overcome gravitational potential energy and you're at a high altitude, the energy you use in cruise is very low, and then you can recapture a large part of your gravitational potential energy on the way down. Indeed, several developers are already working on small pure-electric aircraft with rotating thrusters."
However, "Electric cars are important, solar energy is important, stationary storage of energy is important," said Musk. "These things are much more important than creating electric supersonic VTOL." Maybe Bye Aerospace, Zunum Aero and others have a clear run after all. Meanwhile, there are about 100 pure-electric manned VTOL designs flying or planned but endurance is dangerously short. Omit the pilot in the air taxi to make endurance longer for safety? That can be dangerous and unproven, even illegal as yet. In contrast, the time for zero-emission fixed-wing aircraft has come with a place also for interim, very low-emission hybrids such as the larger Faradair solar electric-biofuel fixed-wing plane in the UK.
Top image: bye Aerospace