4 ms·

Is there any research being done into electric/hybrid airplanes? In 20 years oil costs could make flying very unpractical.

by utnick 18y ago

evgen 18y ago
"Hybrid" is a non-starter for an airplane. It spends 99% of its time running in the "sweet spot" of the turbine performance envelope, there are no starts and stops for which regenerative braking or a switch from the turbine to some sort of electrical propulsion would help. Electrical power is problematic because batteries and other forms of electrical energy storage still suck. There are solar-electric planes being developed for long-term station-keeping tasks, but they are slow and have almost no payload capacity. Turbine jets are basically the best thing we know of for performing this specific task. We might be able to improve the fuel they are burning, but nothing is going to replace them for the next couple of decades at least.
- ajross 18y ago
  The first paragraph is spot on, but the second is just wrong. Turbojets fly much faster than needed, for the convenience of the passengers. Drag goes as the square of speed, so per-distance fuel economy scales as the inverse of the trip time. One certainly can do much better than a turbojet simply by swapping the fan for a larger geared propeller and flying at half the speed.
  - cdr 18y ago
    And in fact, there have been news stories recently about airlines adding a few minutes per flight in this way to save fuel.
    - marvin 18y ago
      Airlines in Norway openly and publicly reduced the speed of their routes by 10%, while attempting to make up for the lost time by improving their pre-flight routines.
  - pg 18y ago
    Jets can also fly higher, which means smoother flights.
    - ajross 18y ago
      Actually, that's an issue of design choice, not fundamentals. Turbojets fly higher because they fly longer (so don't worry as much about inefficiencies due to climbing to alititude) and want to fly faster (up to the tropopause, temperature is dropping which results for mildly complicated reasons in power dropping more slowly than drag does). But there's nothing inherently "lower" about a propeller. They work just as well at altitude as they do as sea level. It's just that market forces have dictated that props are better suited to low-altitude, low-speed commuter routes. But you could design a high altitude prop without difficulty.
      - pg 18y ago
        Really? Is it an urban legend that jet engines work better at high altitudes than propellers? I wouldn't be surprised. Anyone else know about this?
        ajross 18y ago
        Pretty much. There are actually some fancy solar designs for low-speed unmanned cruisers that work up to the 80-100kft level (solar cells don't lose power with altitude, so they don't have the tropopause limitation that oxygen breathing engines do). Those things are all about efficiency, and they pick props for the same reasons that other efficiency designs do. Jets are comparatively more efficient at high speed (rather: high-radius prop losses grow with speed faster than low-radius fans), not at high altitude per se. But since tropopause-altitude is a design goal for speed designs, these two have traditionally been interchangeable. As far as credentials go, I'm the author of the "YASim" dynamics model that FlightGear (http://www.flightgear.org http://www.flightgear.org) uses. So while I'm a hacker and not an aerospace engineer, I do have at least a little domain expertise.
  - pchristensen 18y ago
    Good freaking luck trying to sell half-speed flights. Maybe as part of a national security deal - less oil used for airline fuel due to slower flights in exchange for removing some painful, slow, ineffective security screening.
    - elai 18y ago
      Why not? They can offer those flights for lower prices, so people willing to go for a longer, cheaper flight can choose to do so. If they become popular, then they've gotten new market niche.
    - khafra 18y ago
      You'd never buy a half-speed flight. I'd buy a half-speed flight from Tampa to NYC if it were 2/3 the price of the jet flight. My poorer friends would buy the route on a 1/4 speed airship if it were cheap enough. People have different sensitivities to time vs. money.
      - LogicHoleFlaw 18y ago
        I might even pay more for a trip by Zeppelin...
  - evgen 18y ago
    I might have been a bit too broad in stating that the turbojet is the best at what it does, but "speed" is a design characteristic just like any other and alternatives will need to come close on the speed side or else anything they may provide on the economy side of the equation will be ignored. Turbojets fly as fast as is practical given the market demand they are serving. If airlines offered people the choice of flying half as fast for a lower price the fast flight would still win (up to a certain point, as the supersonic option showed when Concorde was still flying.) You could do even better by putting your turbofan onto a rigid airship, but that isn't going to happen either :)
- marvin 18y ago
  We don't really need to make airplanes that use other energy sources than petroleum, if it could be manufactured or acquired at decent cost. If it should happen that we can't, we're hosed - moving through the air at 800kph is a dream unless you've got something approaching the energy density of oil. Hydrogen could be made workable, I believe - energy density per volume is something in the region of 30% of gasoline when compressed. With radical airframe changes, we might be able to uphold the status quo. We have a long way to go considering the efficiency of the airframes themselves. Fuel consumption could be reduced drastically if we could go a bit slower, or there would be some radical design change (think sailplanes). Most widebody airframes today look like flying buffalos, with the resulting air resistance. Almost all air transport of people happens on the border of the transsonic regime, where air resistance is a lot higher than it could be. Reduce speed with 30%, and you'll reduce the total energy consumption by a considerable amount. One can only guess how customers would take this. Market forces today don't look like they are convective to such change, but one can always hope that some startup is able to eat a big piece of the pie. Personally, I am very enthusiastic about companies like http://www.dayjet.com/ http://www.dayjet.com/, who specialize in slightly-expensive but pretty-painless transport. Sadly, aviation is one of the most ass-backwards industries in the world, burdened by the largest amount of politics, subsidies, bureaucracy and regulation I've ever seen. There are definitely huge business opportunities here, but there are mountains and mountains of shit to wade through before we reach them. I believe that better personal air transport would be the way to go - better and cheaper GA airplanes. The competition and politics here are still in the world class, but not quite as cutthroat as among the airlines. And the capital requirements are survivable, and the existing airplanes are even more ass-backwards. It says something about an area of business when the military has been driving the bleeding edge for fifty years.
  - sammyo 18y ago
    > Reduce speed with 30%, and you'll reduce the total energy consumption by a considerable amount. This is one of the (few?) cases where government regulation is appropriate, one airline would go out of business but if every route changed there would be a month of griping and folks would get used to it. The re-scheduling, route planning, change in maintenance schedules, etc would be a one time cost, but if that's true I can't imagine the airlines are not secretly hoping for something like that to give them some help.

Is there any research being done into electric/hybrid airplanes? In 20 years oil costs could make flying very unpractical.

by utnick 18y ago

Is there any research being done into electric/hybrid airplanes? In 20 years oil costs could make flying very unpractical.

evgen 18y ago

"Hybrid" is a non-starter for an airplane. It spends 99% of its time running in the "sweet spot" of the turbine performance envelope, there are no starts and stops for which regenerative braking or a switch from the turbine to some sort of electrical propulsion would help. Electrical power is problematic because batteries and other forms of electrical energy storage still suck. There are solar-electric planes being developed for long-term station-keeping tasks, but they are slow and have almost no payload capacity. Turbine jets are basically the best thing we know of for performing this specific task. We might be able to improve the fuel they are burning, but nothing is going to replace them for the next couple of decades at least.

ajross 18y ago
The first paragraph is spot on, but the second is just wrong. Turbojets fly much faster than needed, for the convenience of the passengers. Drag goes as the square of speed, so per-distance fuel economy scales as the inverse of the trip time. One certainly can do much better than a turbojet simply by swapping the fan for a larger geared propeller and flying at half the speed.
- cdr 18y ago
  And in fact, there have been news stories recently about airlines adding a few minutes per flight in this way to save fuel.
  - marvin 18y ago
    Airlines in Norway openly and publicly reduced the speed of their routes by 10%, while attempting to make up for the lost time by improving their pre-flight routines.
- pg 18y ago
  Jets can also fly higher, which means smoother flights.
  - ajross 18y ago
    Actually, that's an issue of design choice, not fundamentals. Turbojets fly higher because they fly longer (so don't worry as much about inefficiencies due to climbing to alititude) and want to fly faster (up to the tropopause, temperature is dropping which results for mildly complicated reasons in power dropping more slowly than drag does). But there's nothing inherently "lower" about a propeller. They work just as well at altitude as they do as sea level. It's just that market forces have dictated that props are better suited to low-altitude, low-speed commuter routes. But you could design a high altitude prop without difficulty.
    - pg 18y ago
      Really? Is it an urban legend that jet engines work better at high altitudes than propellers? I wouldn't be surprised. Anyone else know about this?
      - ajross 18y ago
        Pretty much. There are actually some fancy solar designs for low-speed unmanned cruisers that work up to the 80-100kft level (solar cells don't lose power with altitude, so they don't have the tropopause limitation that oxygen breathing engines do). Those things are all about efficiency, and they pick props for the same reasons that other efficiency designs do. Jets are comparatively more efficient at high speed (rather: high-radius prop losses grow with speed faster than low-radius fans), not at high altitude per se. But since tropopause-altitude is a design goal for speed designs, these two have traditionally been interchangeable. As far as credentials go, I'm the author of the "YASim" dynamics model that FlightGear (http://www.flightgear.org http://www.flightgear.org) uses. So while I'm a hacker and not an aerospace engineer, I do have at least a little domain expertise.
- pchristensen 18y ago
  Good freaking luck trying to sell half-speed flights. Maybe as part of a national security deal - less oil used for airline fuel due to slower flights in exchange for removing some painful, slow, ineffective security screening.
  - elai 18y ago
    Why not? They can offer those flights for lower prices, so people willing to go for a longer, cheaper flight can choose to do so. If they become popular, then they've gotten new market niche.
  - khafra 18y ago
    You'd never buy a half-speed flight. I'd buy a half-speed flight from Tampa to NYC if it were 2/3 the price of the jet flight. My poorer friends would buy the route on a 1/4 speed airship if it were cheap enough. People have different sensitivities to time vs. money.
    - LogicHoleFlaw 18y ago
      I might even pay more for a trip by Zeppelin...
- evgen 18y ago
  I might have been a bit too broad in stating that the turbojet is the best at what it does, but "speed" is a design characteristic just like any other and alternatives will need to come close on the speed side or else anything they may provide on the economy side of the equation will be ignored. Turbojets fly as fast as is practical given the market demand they are serving. If airlines offered people the choice of flying half as fast for a lower price the fast flight would still win (up to a certain point, as the supersonic option showed when Concorde was still flying.) You could do even better by putting your turbofan onto a rigid airship, but that isn't going to happen either :)
marvin 18y ago
We don't really need to make airplanes that use other energy sources than petroleum, if it could be manufactured or acquired at decent cost. If it should happen that we can't, we're hosed - moving through the air at 800kph is a dream unless you've got something approaching the energy density of oil. Hydrogen could be made workable, I believe - energy density per volume is something in the region of 30% of gasoline when compressed. With radical airframe changes, we might be able to uphold the status quo. We have a long way to go considering the efficiency of the airframes themselves. Fuel consumption could be reduced drastically if we could go a bit slower, or there would be some radical design change (think sailplanes). Most widebody airframes today look like flying buffalos, with the resulting air resistance. Almost all air transport of people happens on the border of the transsonic regime, where air resistance is a lot higher than it could be. Reduce speed with 30%, and you'll reduce the total energy consumption by a considerable amount. One can only guess how customers would take this. Market forces today don't look like they are convective to such change, but one can always hope that some startup is able to eat a big piece of the pie. Personally, I am very enthusiastic about companies like http://www.dayjet.com/ http://www.dayjet.com/, who specialize in slightly-expensive but pretty-painless transport. Sadly, aviation is one of the most ass-backwards industries in the world, burdened by the largest amount of politics, subsidies, bureaucracy and regulation I've ever seen. There are definitely huge business opportunities here, but there are mountains and mountains of shit to wade through before we reach them. I believe that better personal air transport would be the way to go - better and cheaper GA airplanes. The competition and politics here are still in the world class, but not quite as cutthroat as among the airlines. And the capital requirements are survivable, and the existing airplanes are even more ass-backwards. It says something about an area of business when the military has been driving the bleeding edge for fifty years.
- sammyo 18y ago
  > Reduce speed with 30%, and you'll reduce the total energy consumption by a considerable amount. This is one of the (few?) cases where government regulation is appropriate, one airline would go out of business but if every route changed there would be a month of griping and folks would get used to it. The re-scheduling, route planning, change in maintenance schedules, etc would be a one time cost, but if that's true I can't imagine the airlines are not secretly hoping for something like that to give them some help.