4 ms·

Honestly, I'd feel better knowing it has a reserve system in case there's any issues, even if the batteries have more than enough power, beats having it and nev

Honestly, I'd feel better knowing it has a reserve system in case there's any issues, even if the batteries have more than enough power, beats having it and never using it, than needing it and suffering as a result.

IrishTechie 1mo ago
Do current aircraft have a backup in-case their fuel tanks run dry?
- ben-schaaf 1mo ago
  There's reserve tanks or more generally reserve fuel for emergencies. Other than that there's no propulsion backup for when the fuel runs out, instead redundancy comes from multiple independent fuel tanks.
  - SideburnsOfDoom 1mo ago
    > redundancy comes from multiple independent fuel tanks. And in larger aircraft, multiple independent engines. See for instance ETOPS https://en.wikipedia.org/wiki/ETOPS https://en.wikipedia.org/wiki/ETOPS From the pictures, I see that this new aircraft has 4 engines. So it should be adequately resilient to single engine failure.
- dmitrygr 1mo ago
  Current aircraft have * MULTIPLE HOURS* of fuel tanks. Compared to dozens of minutes of battery that this thing has.
  - tonyarkles 1mo ago
    Typical reserve requirement is 30 min for a turbine aircraft (45 for piston). Given the 125 mile battery-only range and the probability that it flies at at least 200 kts (230 mph), it’s pretty unlikely to hit even a 30 min reserve on only batteries. I like the design, I think they get the problem and have a decent solution for it
    - Kaliboy 1mo ago
      The most common flight on my island is to the island about 50 miles away from us. We pay about $120 for the privilege, which takes 20 minutes of flying. So I think even in this case the reserve capacity is "needed" (for the reserve requierement), but I can see them realistically being able to fly between the islands purely on electric power.
    - dmitrygr 1mo ago
      > and have a decent solution for it Unless we ignore the additional maintenance cost of having to completely different proportion systems to maintain (and it is worse than a twin engine plane, because the propulsion systems are different, so you have to stock up on more different kinds of parts and possibly have different kinds of mechanics on staff to understand them)
      - tonyarkles 1mo ago
        Something that wasn’t super clear to me was whether the turbines are actually used for propulsion or if they’re used solely as generators to recharge the batteries/power the electric motors. I could honestly see it going either way. Having the turbine, electric motor, gearbox, and potentially clutches to isolate the turbine or electric motor from the transmission seems pretty viable though. This would waste a little bit of power keeping the turbine spinning (unless there are clutches) but would also ensure that the turbine’s been spun recently, the oil pumps are primed and the bearings are lubed and ready to go. Not that I’m saying a turboprop turbine like a PT6A is a simple device, but compared to a high-bypass turbofan like you’d see on a 737 or A320, they are considerably simpler. Edit: looking quick, the time-before-overhaul (TBO) on modern PT6As can be up to 6000 hours, with a ~2000hr Hot Section Inspection. I’m not sure how “spinning but not burning fuel” counts on TBO, but it should at least mean the HSI is simple.
        labcomputer 1mo ago
        Yea, that wasn't super clear to me, either. But... given that turbine APUs already exist for ground power and are already engineered to be as light as practical, my naive guess would be that it's easier, simpler and faster to just use a COTS APU as a series hybrid rather than trying directly couple a turbine to the propeller. On inspections and overhauls: I'd expect that not needing to start the turbine at all on a given flight massively helps the economics of the airplane. Turbines often have parts that must be replaced after a given number of (startup) cycles, and that's going to be especially important for a turbine that is only expected to run for a short time (if at all) at the end of a flight. If you only start the turbine on, say, 5% of flights, that means you get 20x as many flights before overhaul/inspection. I could see that being incredibly attractive to airlines.
  - deleted 1mo ago
    [deleted]
- mmanfrin 1mo ago
  Yes, they also have ramjet turbines which generate electricity from the movement of the plane on a backup circuit.
- ZiiS 1mo ago
  Yes the are strict regulations requiring them to carry extra fuel; despite its weight having a real cost. Carrying extra battery would be too heavy even compared to having a whole extra engine.
golem14 1mo ago
The real benefit really seems to be that the electric motors have a much smaller failure rates than mechanical ones running near their top rpm. The hybrid motor can run at a much optimized RPM, so the idea is that this will improve the overall safety margin of the overall design. I could be wrong, but that's what the video said.
- dist-epoch 1mo ago
  One would assume that all combustion engines used in aviation run at an optimized RPM?
  - FredFS456 1mo ago
    At cruise, yes. However during takeoff and go around they run at higher RPM to develop more thrust. Using batteries for takeoff and only using fuel for cruise or backup power is smart.
    - golem14 1mo ago
      I think it's even more than that. The hybrid engine has to run one single RPM to drive a generator, it can be vibration insulated, probably needs to be only smaller because it doesn't have to provide the high max power the conventional motors have etc. It's why I believe hybrid cars that use a gas motor only to charge the batteries are more reliable and more efficient.
  - Tade0 1mo ago
    RPM is one thing, but the other is that engines run more efficiently at altitude due to the temperatures being much lower there.
- chermi 1mo ago
  So basically like diesal-electric trains? My understanding that's almost certainly outdated was that the issue with electric planes was weight due to batteries, so added mass from a generator sounds bad.

IrishTechie 1mo ago

Do current aircraft have a backup in-case their fuel tanks run dry?

ben-schaaf 1mo ago
There's reserve tanks or more generally reserve fuel for emergencies. Other than that there's no propulsion backup for when the fuel runs out, instead redundancy comes from multiple independent fuel tanks.
- SideburnsOfDoom 1mo ago
  > redundancy comes from multiple independent fuel tanks. And in larger aircraft, multiple independent engines. See for instance ETOPS https://en.wikipedia.org/wiki/ETOPS https://en.wikipedia.org/wiki/ETOPS From the pictures, I see that this new aircraft has 4 engines. So it should be adequately resilient to single engine failure.
dmitrygr 1mo ago
Current aircraft have * MULTIPLE HOURS* of fuel tanks. Compared to dozens of minutes of battery that this thing has.
- tonyarkles 1mo ago
  Typical reserve requirement is 30 min for a turbine aircraft (45 for piston). Given the 125 mile battery-only range and the probability that it flies at at least 200 kts (230 mph), it’s pretty unlikely to hit even a 30 min reserve on only batteries. I like the design, I think they get the problem and have a decent solution for it
  - Kaliboy 1mo ago
    The most common flight on my island is to the island about 50 miles away from us. We pay about $120 for the privilege, which takes 20 minutes of flying. So I think even in this case the reserve capacity is "needed" (for the reserve requierement), but I can see them realistically being able to fly between the islands purely on electric power.
  - dmitrygr 1mo ago
    > and have a decent solution for it Unless we ignore the additional maintenance cost of having to completely different proportion systems to maintain (and it is worse than a twin engine plane, because the propulsion systems are different, so you have to stock up on more different kinds of parts and possibly have different kinds of mechanics on staff to understand them)
    - tonyarkles 1mo ago
      Something that wasn’t super clear to me was whether the turbines are actually used for propulsion or if they’re used solely as generators to recharge the batteries/power the electric motors. I could honestly see it going either way. Having the turbine, electric motor, gearbox, and potentially clutches to isolate the turbine or electric motor from the transmission seems pretty viable though. This would waste a little bit of power keeping the turbine spinning (unless there are clutches) but would also ensure that the turbine’s been spun recently, the oil pumps are primed and the bearings are lubed and ready to go. Not that I’m saying a turboprop turbine like a PT6A is a simple device, but compared to a high-bypass turbofan like you’d see on a 737 or A320, they are considerably simpler. Edit: looking quick, the time-before-overhaul (TBO) on modern PT6As can be up to 6000 hours, with a ~2000hr Hot Section Inspection. I’m not sure how “spinning but not burning fuel” counts on TBO, but it should at least mean the HSI is simple.
      - labcomputer 1mo ago
        Yea, that wasn't super clear to me, either. But... given that turbine APUs already exist for ground power and are already engineered to be as light as practical, my naive guess would be that it's easier, simpler and faster to just use a COTS APU as a series hybrid rather than trying directly couple a turbine to the propeller. On inspections and overhauls: I'd expect that not needing to start the turbine at all on a given flight massively helps the economics of the airplane. Turbines often have parts that must be replaced after a given number of (startup) cycles, and that's going to be especially important for a turbine that is only expected to run for a short time (if at all) at the end of a flight. If you only start the turbine on, say, 5% of flights, that means you get 20x as many flights before overhaul/inspection. I could see that being incredibly attractive to airlines.
- deleted 1mo ago
  [deleted]
mmanfrin 1mo ago
Yes, they also have ramjet turbines which generate electricity from the movement of the plane on a backup circuit.
ZiiS 1mo ago
Yes the are strict regulations requiring them to carry extra fuel; despite its weight having a real cost. Carrying extra battery would be too heavy even compared to having a whole extra engine.

golem14 1mo ago

The real benefit really seems to be that the electric motors have a much smaller failure rates than mechanical ones running near their top rpm. The hybrid motor can run at a much optimized RPM, so the idea is that this will improve the overall safety margin of the overall design. I could be wrong, but that's what the video said.

dist-epoch 1mo ago
One would assume that all combustion engines used in aviation run at an optimized RPM?
- FredFS456 1mo ago
  At cruise, yes. However during takeoff and go around they run at higher RPM to develop more thrust. Using batteries for takeoff and only using fuel for cruise or backup power is smart.
  - golem14 1mo ago
    I think it's even more than that. The hybrid engine has to run one single RPM to drive a generator, it can be vibration insulated, probably needs to be only smaller because it doesn't have to provide the high max power the conventional motors have etc. It's why I believe hybrid cars that use a gas motor only to charge the batteries are more reliable and more efficient.
- Tade0 1mo ago
  RPM is one thing, but the other is that engines run more efficiently at altitude due to the temperatures being much lower there.
chermi 1mo ago
So basically like diesal-electric trains? My understanding that's almost certainly outdated was that the issue with electric planes was weight due to batteries, so added mass from a generator sounds bad.