5 ms·

The big win would obviously be electric aircraft, but I doubt we'll see that in my lifetime (barring a massive breakthrough in battery technology). The problem

The big win would obviously be electric aircraft, but I doubt we'll see that in my lifetime (barring a massive breakthrough in battery technology). The problem is even the best batteries have a much lower energy density compared with traditional fuels. Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Real Engineering did a pretty good video on the topic https://www.youtube.com/watch?v=VNvzZfsC13o https://www.youtube.com/watch?v=VNvzZfsC13o

moltar 7y ago
World's first fully electric commercial aircraft takes flight in Canada https://www.theguardian.com/world/2019/dec/11/worlds-first-fully-electric-commercial-aircraft-takes-flight-in-canada https://www.theguardian.com/world/2019/dec/11/worlds-first-f... Of course far from intercontinental jet, but it’s a start :)
- cgrealy 7y ago
  Did you watch the video I posted? It specifically talks about converting a small aircraft and says you could get "about 20 minutes". Building an actually useful commercial plane (i.e. something along the lines of 737 or A320) is an order of magnitude more difficult, in fact, basically impossible with current battery technology.
  - benhurmarcel 7y ago
    For electric airliners, most promising research centers on hydrogen fuel cells, not batteries. It brings a lot of issues (mainly volume and cooling), but still it's being seriously considered.
    - anovikov 7y ago
      Why not just liquid hydrogen, burned in a jet engine? Yes it has density about 12x lower then kerosene, but specific energy is about 3x higher so for the same fuel volume, we get 4x less range. In fact better than that, because of much lower weight and about 2/3 power ratio of fuel burn to aircraft weight and about 40% of weight of a typical plane being fuel, it being gradually burned during flight... it adds about 11% of range, so like 28% of the kerosene-powered range for the same fuel tank volume. So about 4500-5000km, with added benefit of fantastic takeoff performance (low weight). Enough for cross-USA travel, and non-Arctic cross-Atlantic flights (anywhere in CONUS->Bangor, Maine->Shannon, Ireland->Anywhere in EU)... solves the problem as i see it?
      - leetcrew 7y ago
        it solves the greenhouse gas issue, but burning hydrogen still produces NOx.
        ed_balls 7y ago
        Is NOx an issue if it's far away from humans?
        leetcrew 7y ago
        probably not, but the plane still has to takeoff and land sometimes. tbh, I'm not sure exactly how hydrogen combustion compares to hydrocarbon combustion in terms of environmental harm. I suspect it's still a lot cleaner overall. a lot of people think hydrogen combustion is totally clean and just creates water as exhaust, so I like to point this out.
Ididntdothis 7y ago
I think hydrogen would be a candidate but then you have to deal with cooling.
- danaliv 7y ago
  The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.
  - Ididntdothis 7y ago
    Interesting! I didn't think about volume. Is that why the Saturn V first stage also used kerosene?
    - m4rtink 7y ago
      Pretty much - the rocket is smaller & you can usually also get more thrust, while loosing some efficiency. There are were more rockets like this (kerolox for first stage & hydrolox for upper stage), like for example Atlas 5. Other rockets used kerolox boosters, such as for example Energia & IIRc some of the new Chinese rockets.
    - labster 7y ago
      That probably went into the decision, but rocket science is complicated. While not on the Saturn V, you there’s a good discussion on fuel tradeoffs here, after explaining the engine cycles: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
    - danaliv 7y ago
      Oh, good question - not a rocket scientist but this history seems to say that’s the case: https://history.nasa.gov/SP-4206/ch7.htm https://history.nasa.gov/SP-4206/ch7.htm ”Liquid hydrogen was only one half as dense as kerosene. This density ratio indicated that, for the necessary propellant, an LH2 tank design would require a far larger tank volume than required for RP-1. The size would create unacceptable penalties in tank weight and aerodynamic design. So, RP-1 became the fuel.” (RP-1 And Jet A are almost identical.) In applications where cross-sectional area is an exponential factor (read: atmospheric flight), volume is significant!
JumpCrisscross 7y ago
> big win would obviously be electric aircraft Why batteries over synthetic jet fuel? Hydrocarbons are great for this purpose. The problem is where the carbon is coming from. Burn jet fuel made from atmospheric carbon and you solve the problem overnight.
- cgrealy 7y ago
  Simple answer: I wasn't aware of synthetic jet fuel! If it can solve the problem, I'm keen to learn more.
  - dredmorbius 7y ago
    I'd learnt of this a few years ago when the US Naval Research Lab released some papers with a bit of a splash. The announcements (and references) made this sound like entirely novel technology. In truth it dates in part to WWII and German production of fuel from coal (also practiced by South Africa), and was suggested as an alternative to fossil fuel consumption in the 1960s by M. King Hubbert (of Peak Oil fame) and the Brookhaven National Laboratory. There's been substantial additional work at Brookhaven, M.I.T., USNRL, and a (failed) Google X-Project attempt. The fundamental chemistry is sound, scaling and costs are the principle concerns. Costs are strongly influenced by the grotesque underpricing of fossil fuels, by a factor of millions, based on the geological processes of formation. Account properly for those, and the economics straighten out. (Though much of the present world turns out to be much more expensive than we'd accounted for.) Numerous posts and references at my subreddit: https://old.reddit.com/r/dredmorbius/search?q=fischer-tropsch&restrict_sr=on https://old.reddit.com/r/dredmorbius/search?q=fischer-tropsc... Specifically, history of research to the 1960s: https://old.reddit.com/r/dredmorbius/comments/28nqoz/electrical_fuel_synthesis_from_seawater_older/ https://old.reddit.com/r/dredmorbius/comments/28nqoz/electri... Compilation of papers from Heather Willauer et al: https://old.reddit.com/r/dredmorbius/comments/22k71x/us_navy_electricitytofuel_synthesis_papers_and/ https://old.reddit.com/r/dredmorbius/comments/22k71x/us_navy...
  - bluGill 7y ago
    https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_proces... Problem is it used a lot more energy than pumping oil out of the ground. In theory we can get the energy from solar or something, but still it needs a lot of energy. Good news it the process as been successfully used on the scale of providing fuel for entry countries. Thus we know it scales to something larger. There are other options that look promising in a test tube but don't seem to work at larger scales yet.
ShorsHammer 7y ago
It is a certainly an untenable problem for longhaul, though with the current pace of advances in battery tech (mainly driven by smartphone companies of all things) shorthaul electric flight could certainly find some support in the near future. Electric offers dramatic reductions in engine noise and maintenance, along with far more reliability/safety. I can see that being a selling point to some aviation execs, Norway has been trying it out, hope it works for them. > Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Offtopic: The discussion on that fact is an excellent question/answer to read on SE: https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-discharged https://physics.stackexchange.com/questions/34421/does-the-m...
- cgrealy 7y ago
  I think .5 micrograms falls under "pretty much" :D But that was interesting to read... thanks!

moltar 7y ago

World's first fully electric commercial aircraft takes flight in Canada https://www.theguardian.com/world/2019/dec/11/worlds-first-fully-electric-commercial-aircraft-takes-flight-in-canada https://www.theguardian.com/world/2019/dec/11/worlds-first-f... Of course far from intercontinental jet, but it’s a start :)

cgrealy 7y ago
Did you watch the video I posted? It specifically talks about converting a small aircraft and says you could get "about 20 minutes". Building an actually useful commercial plane (i.e. something along the lines of 737 or A320) is an order of magnitude more difficult, in fact, basically impossible with current battery technology.
- benhurmarcel 7y ago
  For electric airliners, most promising research centers on hydrogen fuel cells, not batteries. It brings a lot of issues (mainly volume and cooling), but still it's being seriously considered.
  - anovikov 7y ago
    Why not just liquid hydrogen, burned in a jet engine? Yes it has density about 12x lower then kerosene, but specific energy is about 3x higher so for the same fuel volume, we get 4x less range. In fact better than that, because of much lower weight and about 2/3 power ratio of fuel burn to aircraft weight and about 40% of weight of a typical plane being fuel, it being gradually burned during flight... it adds about 11% of range, so like 28% of the kerosene-powered range for the same fuel tank volume. So about 4500-5000km, with added benefit of fantastic takeoff performance (low weight). Enough for cross-USA travel, and non-Arctic cross-Atlantic flights (anywhere in CONUS->Bangor, Maine->Shannon, Ireland->Anywhere in EU)... solves the problem as i see it?
    - leetcrew 7y ago
      it solves the greenhouse gas issue, but burning hydrogen still produces NOx.
      - ed_balls 7y ago
        Is NOx an issue if it's far away from humans?
        leetcrew 7y ago
        probably not, but the plane still has to takeoff and land sometimes. tbh, I'm not sure exactly how hydrogen combustion compares to hydrocarbon combustion in terms of environmental harm. I suspect it's still a lot cleaner overall. a lot of people think hydrogen combustion is totally clean and just creates water as exhaust, so I like to point this out.

Ididntdothis 7y ago

I think hydrogen would be a candidate but then you have to deal with cooling.

danaliv 7y ago
The problem with hydrogen is that it has a lot of mass-specific energy but its density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is a measly 8500.
- Ididntdothis 7y ago
  Interesting! I didn't think about volume. Is that why the Saturn V first stage also used kerosene?
  - m4rtink 7y ago
    Pretty much - the rocket is smaller & you can usually also get more thrust, while loosing some efficiency. There are were more rockets like this (kerolox for first stage & hydrolox for upper stage), like for example Atlas 5. Other rockets used kerolox boosters, such as for example Energia & IIRc some of the new Chinese rockets.
  - labster 7y ago
    That probably went into the decision, but rocket science is complicated. While not on the Saturn V, you there’s a good discussion on fuel tradeoffs here, after explaining the engine cycles: https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
  - danaliv 7y ago
    Oh, good question - not a rocket scientist but this history seems to say that’s the case: https://history.nasa.gov/SP-4206/ch7.htm https://history.nasa.gov/SP-4206/ch7.htm ”Liquid hydrogen was only one half as dense as kerosene. This density ratio indicated that, for the necessary propellant, an LH2 tank design would require a far larger tank volume than required for RP-1. The size would create unacceptable penalties in tank weight and aerodynamic design. So, RP-1 became the fuel.” (RP-1 And Jet A are almost identical.) In applications where cross-sectional area is an exponential factor (read: atmospheric flight), volume is significant!

JumpCrisscross 7y ago

> big win would obviously be electric aircraft Why batteries over synthetic jet fuel? Hydrocarbons are great for this purpose. The problem is where the carbon is coming from. Burn jet fuel made from atmospheric carbon and you solve the problem overnight.

cgrealy 7y ago
Simple answer: I wasn't aware of synthetic jet fuel! If it can solve the problem, I'm keen to learn more.
- dredmorbius 7y ago
  I'd learnt of this a few years ago when the US Naval Research Lab released some papers with a bit of a splash. The announcements (and references) made this sound like entirely novel technology. In truth it dates in part to WWII and German production of fuel from coal (also practiced by South Africa), and was suggested as an alternative to fossil fuel consumption in the 1960s by M. King Hubbert (of Peak Oil fame) and the Brookhaven National Laboratory. There's been substantial additional work at Brookhaven, M.I.T., USNRL, and a (failed) Google X-Project attempt. The fundamental chemistry is sound, scaling and costs are the principle concerns. Costs are strongly influenced by the grotesque underpricing of fossil fuels, by a factor of millions, based on the geological processes of formation. Account properly for those, and the economics straighten out. (Though much of the present world turns out to be much more expensive than we'd accounted for.) Numerous posts and references at my subreddit: https://old.reddit.com/r/dredmorbius/search?q=fischer-tropsch&restrict_sr=on https://old.reddit.com/r/dredmorbius/search?q=fischer-tropsc... Specifically, history of research to the 1960s: https://old.reddit.com/r/dredmorbius/comments/28nqoz/electrical_fuel_synthesis_from_seawater_older/ https://old.reddit.com/r/dredmorbius/comments/28nqoz/electri... Compilation of papers from Heather Willauer et al: https://old.reddit.com/r/dredmorbius/comments/22k71x/us_navy_electricitytofuel_synthesis_papers_and/ https://old.reddit.com/r/dredmorbius/comments/22k71x/us_navy...
- bluGill 7y ago
  https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_proces... Problem is it used a lot more energy than pumping oil out of the ground. In theory we can get the energy from solar or something, but still it needs a lot of energy. Good news it the process as been successfully used on the scale of providing fuel for entry countries. Thus we know it scales to something larger. There are other options that look promising in a test tube but don't seem to work at larger scales yet.

ShorsHammer 7y ago

It is a certainly an untenable problem for longhaul, though with the current pace of advances in battery tech (mainly driven by smartphone companies of all things) shorthaul electric flight could certainly find some support in the near future. Electric offers dramatic reductions in engine noise and maintenance, along with far more reliability/safety. I can see that being a selling point to some aviation execs, Norway has been trying it out, hope it works for them. > Also, a battery that weighs 100kg when full weighs pretty much 100kg when empty. Offtopic: The discussion on that fact is an excellent question/answer to read on SE: https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-discharged https://physics.stackexchange.com/questions/34421/does-the-m...

cgrealy 7y ago
I think .5 micrograms falls under "pretty much" :D But that was interesting to read... thanks!