13 ms·
Rolls-Royce concludes testing of plane technology to break electric speed record
- hinkley 6y agoIs there any world where a series hybrid jet engine makes sense the way that series hybrid diesel engines used for trains does? It seems like weight and displacement could be more of a concern. And turbines run at higher temperatures than diesel engines...
- jnsaff2 6y agoWell, Airbus had an event[0] last week about their hydrogen-hybrid passenger planes. And there the main power would come from adapted jet engines that combust hydrogen but the hybrid aspect would be fuel cell sourced electrical motor that would give some additional boost for some phases of the flight. [0] - https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html#hydrogen https://www.airbus.com/innovation/zero-emission/hydrogen/zer...
- deleted 6y ago[deleted]
- Pick-A-Hill2019 6y agoYes. Or at least the concept/idea is being explored. From [1] "The hybrid version would generate electric power through a turbine within the plane. That power would be used to turn the fan blades of the single electric turbofan engine." [2] Uses a slightly different approach "The propeller is powered by an electric motor with 65 kilowatts of continuous output. The electricity is supplied through a generator by a small Wankel engine that consumes little fuel" [1]https://phys.org/news/2017-11-airbus-rolls-royce-siemens-hybrid-plane.html https://phys.org/news/2017-11-airbus-rolls-royce-siemens-hyb... [2] https://phys.org/news/2013-07-electric-hybrid-aircraft.html https://phys.org/news/2013-07-electric-hybrid-aircraft.html
- jeffreyrogers 6y agoThe Wankel engine one is interesting. It seems the only way any of these make sense is with a new type of engine. Makes no sense to put a turbine in a plane just to run an electric motor, since it's more efficient to just use the turbine directly.
- Pick-A-Hill2019 6y agoAgreed re the concept of [1]. Since the link in [2] was from 2013 I was curious to see if there were any updated PR releases but couldn't find any. I did stumble across [3] which seems to be the successor which uses a 3 cylinder diesel engine as the power source [3] https://wiki2.org/en/Siemens-FlyEco_Magnus_eFusion https://wiki2.org/en/Siemens-FlyEco_Magnus_eFusion
- hinkley 6y agoMy recollection is that the problem with Wankels is the emissions, which they are claiming this system still reduces. I wonder what a different engine option would do.
- hinkley 6y agoThat Rolls Royce proposal seems to be based on the fact that airplanes draw power from the turbines and/or and auxiliary power unit. They're driving one of the fans off of power parasitized from the other turbines. Technically that's a hybrid, but I was thinking more of a self-contained unit.
- dokem 6y agoBy singling our trains I’m thinking you are referring to diesel electric which is not the same as hybrid. On a train the generator to motor link it to act as essentially a clutch/gearbox allowing theoretic full torque at 0 rpm.
- SigmundA 6y agoMost diesel-electric trains are not hybrids, they have no batteries and therefore always get power from the single source, the diesel engine. There have been attempts to make them hybrid by putting a car in that contains a lot of batteries for say storing power down a mountain to use going back up the next mountain rather than converting the power to heat in the dynamic braking grid. My understanding is so far it is not worth the cost or complexity for the minimal savings. Diesel-electric is actually less efficient than a mechanical coupling at steady speed due to double conversion losses which is about 80% efficient vs high 90's for gears through standard mechanical transmission. Trains use the an electric drivetrain because they need precise traction control with huge torque to get the train moving, a mechanical transmission with torque converters, clutches and gears would be difficult to route power and wear out too easily due to the low speed lugging. Once up to cruising speed however it would be more efficient. This is why there are no hybrid semis or even diesel electric semi's, standard mechanical transmission are more efficient and hybrids only have significant gains in stop and go traffic where as for mostly highway travel the hybrid would normally disengage and simply be dead weight in a parallel hybrid or simply a efficiency drain in a series hybrid. This is also why most hybrid cars are not series, they mechanically couple the engine to wheel for efficiency once up to speed. Planes again would have little gains from being a hybrid as they would spend most of their time at cruise running the combustion engine and a straight mechanical connection from engine to prop is much more efficient and lighter than any electric double conversion scheme. Electric planes might make sense because there is no double conversion or engine in the plane itself, but you still have the issue of energy density with batteries.
- deeg 6y agoExcellent and well-written answer. I hadn't considered the dead weight of the generator. It's more proof that questions with seemingly simple answers rarely exist in the real world. As a friend of mine (a data analyst) likes to say: "the real world is messy".
- SigmundA 6y agoYes most people don't seem to realize the hybrid system tends to just shut down at highway speeds. The reason a hybrid car has good highway mileage is because it has skinny tries and good aerodynamics, if you ripped out the hybrid gear its would get even better highway mileage due to less weight. There is another aspect specifically of gas hybrids they typically use Atkinson cycle engines to increase efficiency but have reduced torque. This makes it ideal for a hybrid setup as the electric motor can make up for the lack of torque off the line. Notice there are basically no diesel hybrids, this is because a diesel engine is more efficient than a Atkinson cycle gas and has even better torque than a Otto gas but they weigh more and cost more, so it makes little sense to add more weight and cost to a diesel drivetrain that is already very efficient and has plenty of torque. City buses are the exception due to the extreme stop and go low speed duty cycle that can really take advantage of a hybrid drivetrain.
- Gibbon1 6y agoYeah much higher bypass ratio. Current turbofans bypass ratio is limited by the fan diameter. With a series hybrid you can power multiple fans from one engine. Or more likely engines. So you could design a plane with two engines and four fans. For a reaction engines thrust is proportional to mass flow X delta V. And power is proportional to mass_flow X delta V squared. You can see why high bypass turbofans are more efficient. More thrust/less power. Couple of other benefits. Much safer in an engine out condition because you can power your fans off the remaining engine. With a battery hybrid you could power the fans for a limited time with all engines out. Probably less throttle lag with an battery hybrid. Throttle lag is what kills people during take off and landing in bad weather. Wind shear causes the airspeed to drop, pilot needs more power but the engines take seconds to respond. Take off and landing under battery power --> way less noise.
- dredmorbius 6y agoSpeed is comparatively easy for electric propulsion -- on land (Tesla) or air (here). Range is quite another issue. A Cesna 172 has a 1,289 km range, four times the Rolls-Royce prototype, and carries more than just the piolot and fuel. https://en.wikipedia.org/wiki/Cessna_172#Specifications_(172R) https://en.wikipedia.org/wiki/Cessna_172#Specifications_(172... For both land and air, total payload is another hard limit. Tesla achieves admirable results for a passenger vehicle by using high energy/volume and energy/mass batteries integrated into the vehicle structure itself. Battery EV trucks have had range limits of measured in single-digit kilometers. Their fuel-based counterparts exceed four digits (1,000 km). Accellerating, decellerating, and managing mass costs joules.
- NovemberWhiskey 6y agoThe basic problem with electric aircraft vs. electric cars is that aircraft spend a much larger proportion of their journeys operating at high power levels. A slow, economy cruise setting in a Cessna 172 is a 45% power setting - ~80 hp, and climbs will be at full power (180 hp). On the other hand, you might only need ~20 hp to maintain 65mph on a level road in a sedan; and most people never use anything like the full power of their cars for more than seconds at a time.
- dredmorbius 6y agoThat, and the fact that fuel-powered aircraft will shed half their takeoff weight during flight. Battery-powered aircraft either maintain constant mass or gain mass in the case of metal-air batteries, as energy is discharged. Long-haul alt-energy aircraft utilise very low airspeed (low drag), extreme mass budgets (they're wonders of materials and structural engineering), and altitude profiles (potential energy0 to manage overall energy budgets and use.
- sandworm101 6y ago>> fuel-powered aircraft will shed half their takeoff weight during flight. While that is true of jets optimized for altitude, small piston aircraft (cessnas) do not burn nearly that much fuel on takeoff. Small aircraft can generally do a dozen or more takeoff/landing cycles on a single tank.
- hikerclimb 6y agoNot good...
- dapids 6y agofor who?
- aerospace_guy 6y agoI find it interesting that Rolls-Royce Motor Cars is developing this, as opposed to Rolls-Royce plc - the company that works more closely with aviation.
- lb1lf 6y ago-Even more interesting given that Rolls-Royce plc has a number of boffins at a subsidiary in Trondheim, Norway working on exotic PM motor designs, including for aviation. (The company is called SmartMotor, was purchased by what was then Rolls-Royce Marine, then was retained under the RR umbrella when the rest of the Marine division was sold to Kongsberg a couple of years ago.
- BorgHunter 6y agoThat appears to be an error in the article. Rolls-Royce plc has a press release on this, not Rolls-Royce Motor Cars: https://www.rolls-royce.com/media/press-releases/2020/24-09-2020-rr-completes-ground-testing-of-technology-set-to-power-worlds-fastest-electric-plane.aspx https://www.rolls-royce.com/media/press-releases/2020/24-09-...
- aerospace_guy 6y agoThanks, I didn't notice the link to the press release at the bottom of the article.
- deleted 6y ago[deleted]
- deleted 6y ago[deleted]
- kkotak 6y agoFrom fuel efficiency and aerodynamics perspective, CELERA 500L is a great advancement that could possibly also be converted to electric in the future - https://www.ottoaviation.com/ https://www.ottoaviation.com/
- quattrofan 6y agoDoubt it's Roll Royce Motor cars, more likely the other Rolls Royce that builds aircraft engines, related but not the same.
- aerospace_guy 6y agohttps://news.ycombinator.com/item?id=24631093 https://news.ycombinator.com/item?id=24631093
- psadri 6y agoIs it possible to assist the plane during its take off phase? Maybe with a electric wire that supplies energy and detaches. I know it’s messy. Or maybe using something like balloon to gain altitude and then engines to cruise? Or a special battery bank that gets depleted during take off and detached + a recovery mechanism?
- virtue3 6y agoI was just htinkin the same thing. Having a huge battery pack attached and then parachuted off after takeoff in a designated spot could work really well. Or even like a "plane assister" that just stayed attached for takeoff and then dropped off and landed back at the airport to re-charge / help the next plane. I think it's all moot tho. Airbus seems to be going hydrogen for their next planes to have 0 emission.
- nickff 6y agoThe hydrogen project was basically started to take advantage of a grant from the French government, there are many doubts as to its viability.
- virtue3 6y agoThe major issue with Hydrogen is usually containment (it just leaks through almost everything). Do you have any links to the doubting of it's viability?
- nickff 6y agoAviation Week has had some coverage on the matter, their podcast is pretty good: https://aviationweek.com/aerospace/podcast-airbus-ambitious-hydrogen-plans https://aviationweek.com/aerospace/podcast-airbus-ambitious-...
- blendo 6y agoElectric motors in the wheels might help on the takeoff roll during initial acceleration to rotation speed (100-150 mph). Perhaps also regenerative braking on landing. And taxiing.
- korantu 6y agoElectric propulsion is very cool in and of itself. If the goal is to fly without adding CO2, there are other approaches as well, though. One could synthesize fuel usable by nornal existing airplanes from atmospheric CO2. This would require a lot of CO2-free energy though. There is an ongoing project [1] by US NAVY to turn seawater into jet fuel. This way we would not need to burn fossil fuels and would not need to throw away much of existing aviation technology. [1] https://www.eurekalert.org/pub_releases/2020-07/uor-lch071520.php https://www.eurekalert.org/pub_releases/2020-07/uor-lch07152...
- vlovich123 6y agoWouldn't converting seawater into jet fuel effectively just have us contribute to global warming even more aggressively by converting CO2 sequestered in the ocean to atmospheric CO2 (+ huge energy consumption for the intermediary step of jet fuel)? I'm sure I must be missing something there.
- korantu 6y agoIf source of energy is low CO2, such as nuclear, then losses dont contribute to CO2 increase. As for taking CO2 from the ocean, it is done for this project as it is military for airplane carriers. CO2 can be had from atmosphere as well, with more energy cost.
- vlovich123 6y agoI see how you're thinking about it. In your experience does this chemical process transfer from seawater to atmosphere? I'd love to learn about the details of this process based on your expertise. I've only taken public high school chemistry & it's been a while so I consider myself here a total novice. From a logical perspective though, to me this has to be a net production of energy reaction though since otherwise it wouldn't be extending the operational time (an external power source would be needed & thus you may as well just use that power source to power your ship). My guess would have been that the seawater -> CO2 + Hydrogen conversion is the part that produces the energy needed for the rest of the process as I would think CO2 -> CO1 -> liquidcarbons requires energy somewhere or is at best roughly neutral with a mix of +/- steps. I could easily be wrong there though in that assumption (again, don't know these reactions). If that is actually a correct guess, I would have expect CO2 density differential between air & seawater to be a critical component. I then checked CO2 for density and water on Google [1]: 1.98 kg/m^3 in air, 997 kg/m^3 in water (didn't know these densities in advance of making my hypothesis). This is a wild guess on all fronts, but given the magnitudes involved & how much fuel it requires to power ships (i.e. how much CO2 you'd need to extract from seawater to turn it into liquidcarbons to power a ship), that disparity in density would seem crucial to being able to produce the fuel at all. Even without that, from a physical aspect, I would think the combination of density & how long the process takes could be the next limiting factors even if it did map. The 1000x disparity in density would mean that you could need 1000x the volume to produce the same amount of liquidcarbon fuel. Now of course there are differences between the use-cases that will alter the needs but I don't have an intuition if it would increase or decrease net, and if it were to decreae, would it be sufficient to make the disparity manageable. Would love your thoughts on this nuance.
- torpfactory 6y agoElectric planes will replace car and bus trips before they replace gas planes. Short range, on demand, point to point, cheap travel could really be a game changer. Think what you used to do as a two hour drive- battery electric planes will be able to do that, a distance that today isn’t economical because of the high cost of jet and turboprop maintenance and fuel, and the need for runways. All those commenting- “but the energy density” are right, but don’t miss the forest for the trees. The sky is an underutilized asset.
- tonyedgecombe 6y agoI hope not, we've already exploited too many "underutilized assets".