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I think there are startups making a similar sort of engine for general aviation. It's good to see that there is development of the same idea for commercial avia
by avidiax 2mo ago
I think there are startups making a similar sort of engine for general aviation. It's good to see that there is development of the same idea for commercial aviation.
This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly during cruise if needed.
This means that the battery is quite small and light, having only enough charge to take off and get to altitude.
I suspect that this system probably improves safety as well, if architected properly. If one or both of the gas engines fail, so long as they are not seized, that electric motor can still provide some power for diversion.
- SoftTalker 2mo agoThe fuel burn of take-off and climb substantially lightens the aircraft for cruise. Electric batteries have no such effect, you're carrying all that dead weight for the rest of the flight. This reduces the passenger or cargo capacity of the aircraft, which reduces potential revenue. And what if you need two go-arounds?
- 0cf8612b2e1e 2mo agoEnergy density of liquid fuels cannot be beat by batteries, so this is not competitive if you are looking to maximize cargo. However, there are plenty of short haul flights: private jets, island hopping, regional routes where you need to move little mass.
- xattt 2mo agoExactly. A hybrid passenger car can tolerate unpredictable power output that may come with an auxiliary power setup that may or may not be available when stronger dynamics are called for. A plane doesn’t have this luxury and needs predictable output. The fossil fuel engine either needs a sacrificial “overboost” mode for emergencies (at the cost of wear/long-term longevity), or has to be sized for full power at the ultimate cost of efficiency.
- Melatonic 2mo agoSo theoretically if the electric motors fail (or battery is dead) an engine could be sized and designed smaller (for cruise efficiency) but have some sort of boost mode that still ensures safety ? At the cost of increased maintenance or wear or something if it must be used
- hobonation 2mo agoValid. Perhaps it's not all negative: the electric portion could give a pilot a bit more glide than the gas portion dies.
- Tade0 2mo agoOn anything but very short flights most of the fuel is spent on cruising.
- dmoy 2mo agoI would classify 290 miles as a very short flight, that's like 1-2 hours or something?
- arijun 2mo ago> you're carrying all that dead weight for the rest of the flight If you're recharging the batteries for extra go-arounds during landing, they are as dead weight as the fuel you would otherwise reserve for that purpose. And if you have 30% more efficient engines, meaning less fuel and smaller engines, it's possible you could come out ahead, weight-wise. > what if you need two go-arounds I assume that a go-around requires less sustained power output than a full climb from takeoff, so you will probably get more than one go-around anyway, and we don't know how much over-capacity they're designing for. In any case, any design will require tradeoffs in safety, and having more engine-out capabilities might improve safety enough to overcome the higher risk with go-arounds. Not saying this project is will work out or that you're even wrong necessarily (this could be the equivalent of a concept car for Pratt & Whitney).
- dmitrygr 2mo ago> I assume that a go-around requires less sustained power output than a full climb from takeoff, No. Source 1: PE = mgh Source 2: am pilot
- arijun 2mo agoYou don't do a full climb after a go-around, so the heights are not equal, and the mass is less since you've expended fuel. You also retain some kinetic energy but I assume that is closer to a negligible effect. Also, PE = mgh is probably an not a great formula for energy cost of takeoff/go-around, as there are probably large costs it ignores (gravity loss, less efficient engine use, maybe less efficient turbines?). For your source 2 I have no rebuttal so will have to defer to you, but would ask for an explanation.
- SoftTalker 2mo agoNot a pilot, but on approach for landing you bleed off a lot of energy. For a go-around you need to reverse your descent and build up enough energy to fly away again. Take-off/Go-around tends to be the same throttle setting, AFAIK. Of course it also depends on how early you decide to throw away the approach and go around. Doing it at 1000 feet is different from bouncing it off the runway.
- repiret 2mo agoDon’t conflate airplanes with rockets. On an airplane, most of the energy in cruise is spent overcoming parasitic drag, not induced drag. It’s spent pushing the airmass out of the way as it moves forward, not creating lift to stay aloft. For that reason, a change in weight does not significantly change cruise fuel usage. Weight is still precious, but that’s because airplanes’ load are more often weight constrained than volume constrained, and capital and operating costs are such that you want to maximize the load.
- deleted 2mo ago[deleted]
- usrusr 2mo ago"And what if you need two go-arounds?" Easy: you don't try the second landing approach before the battery is sufficiently recharged to contain enough energy for the second abort. Chances are this does not take any longer than going through the pattern anyways. The saving is not just the dead weight of the bigger engine you'd need to do take-off, climb and abort without electric assist, it's also the fuel saved during cruise from running an engine that is completely designed for efficiency at cruise load instead of for some compromise between cruise efficiency and sufficient peak power for start and abort.
- kspacewalk2 2mo ago>This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly during cruise if needed. Isn't that exactly what hybrid cars (e.g. Prius) are? Extremely efficient gas engine for highway cruising, but insufficient for acceleration, which is aided by electric motors?
- arijun 2mo agoThe Prius is in series, or something like it.
- idontwantthis 2mo agoNo it’s not. The majority of power comes from the engine. It drives the electric motor mechanically, using it as a transmission. It is not just charging the battery.
- arijun 2mo agoSorry, I meant in the low speed, high acceleration regime (maybe easily confounded with takeoff?). There the engine will turn one motor to generate electricity, which will then power the second motor, like a series hybrid.
- cwillu 2mo agoNo, that's just wrong: at no point is (say) a Toyota Hybrid burning gas to generate electricity to immediately turn another motor that actually moves the wheels.
- arijun 2mo agoWhat do you imagine happens if the battery is low and the car wants to start from a stop? The engine can't shift down to first so it would just stall out if you tried to use it to drive the driveshaft directly, and there's no other source of electricity to put into the motor driving the wheels.
- idontwantthis 2mo agoHybrid cars are mostly parallel hybrids. Only the Chevy Volt comes to mind as a serial hybrid.
- mikepavone 2mo agoChevy Volt was still a parallel hybrid. The gasoline engine was used for driving the wheels for highway cruise because it was more efficient. I think the range extender version of the BMW i3 was a pure serial hybrid though
- NobodyNada 2mo agoHonda's recent hybrids (CR-V, Civic, Accord) are like this too. Mostly series, but the engine can directly drive the wheels via a single overdrive gear for better cruising efficiency.
- projektfu 2mo agoThe BMW i3.
- osamagirl69 2mo agoAnd infamously the ill fated Fisker Karma
- rsynnott 2mo agoSome hybrid buses are also serial hybrids.