4 ms·

I am curious, the aero-engines are know to be reliable but electric engines are considered to be good too. What kind of complexity variation does a battery intr

I am curious, the aero-engines are know to be reliable but electric engines are considered to be good too. What kind of complexity variation does a battery introduce in providing reliable power vs gas tank. What can be possible weaknesses if any with electric planes?

csours 8y ago
Liquid fuel is volatile, but generally does not catch on fire on its own. Batteries can catch on fire if over or under charged. Batteries can catch on fire if punctured - liquid fuel can as well, but batteries do not need an external source. This means you need thermal management for your energy source and your power unit. It's not as applicable for this class of aircraft, but batteries do not get lighter as they are expended. Liquid fuel provides the same amount of unit energy until it is completely gone; batteries lose power over time, leading to lower horsepower at the end (this is a simplified point of view).
- VectorLock 8y ago
  Also you can't shoot batteries out the back of your plane to create thrust like you're doing with liquid fuel.
  - AnimalMuppet 8y ago
    Sure you can. Encase them it metal, and use the remaining batteries to power a railgun...
- aeternus 8y ago
  The per-unit energy is the biggest issue. It's true that fire is a problem for batteries, but that is manageable with very small sensors and casings. There are many more systems required to deal with the many failure modes of internal combustion engines: - Heating systems to address carburetor icing. Typically manually activated by pilot since they have a performance cost. - Fuel pumps since gravity cannot always be depended upon especially in acrobatic airplanes. - Fuel sump systems which must be checked before every flight to address water in the fuel tanks & lines. - Lubrication systems which require pre-flight fluid level checks. - Magneto system to ensure that sparks can be generated independently from the electrical system. - Redundant magneto system since carbon tends to build up and prevent proper sparking. - Possibility of an engine running rough/cylinder firing out of sync due to carbon or other issues. - Fuel/air mixture control so that the optimal mix can be selected based on altitude. Requires pilot intervention. - Extreme thermal stresses on the engine, requiring engine run-up checks before takeoff. - Radiators, and airflow rediretion to address cooling issues resulting in loss of performance and weight. - Exhaust system, and noise vs. weight tradeoff
  - Robotbeat 8y ago
    Indeed. ICEs only don't catch fire constantly because of a century of safety improvements.
    - mannykannot 8y ago
      Outside of combat, fuel fires are very rarely in the fuel tanks (TWA 800 being a notable exception, and there are ways it could have been avoided), and a for a fire in an engine, the fuel can be cut off and fire extinguishers used. On the other hand, liquid fuel is probably much more dangerous in a crash.
asparagui 8y ago
Electric engines have a number of properties that are great for aviation, namely the ability to provide torque at low speeds and easily handle high rotation rates, which removes the need for complicated gearboxes and simplifies design. They have been proposed a number of times over the years, the historical problem has always been getting the electricity to drive things: batteries are heavy and diesel->electric converters (eg. hybrid trains) are too large to be practical.
- Zak 8y ago
  It's worth pointing out that piston aircraft engines usually don't use gearboxes. Instead, they drive the propeller directly, which dictates very low engine speeds relative to where car engines usually produce their peak power since any part of the propeller blade nearing the speed of sound results in a loss of efficiency.
- chungleong 8y ago
  I wonder if progress being made in micro-turbine generators would one day allow them to be used in planes. Having a bank of generators inside the fuselage could making flying a lot safer. I imagine planes can be made much more aerodynamic as well.
  - starpilot 8y ago
    Turbines are more efficient with larger sizes due to the fluid mechanics, and they need air, so then you end up at gas turbine engines externally mounted.
rmah 8y ago
I imagine the primary weakness is the rather low energy density of li-ion batteries vs gasoline. This means less energy per kg of battery/fuel, which means lower power (speed/payload) or range or both.
ccleve 8y ago
I remember reading that electric motors are much lighter than gas engines for the same amount of power. This difference can at least partially offset the added battery weight. Also, it's possible to have multiple, small electric motors with no loss of efficiency. That isn't possible for a gas engine. Multiple motors could add some redundancy, and therefore reliability. I think we're going to see a lot of interesting designs over the next few years.
- nbadg 8y ago
  > electric motors are much lighter than gas engines for the same amount of power That varies wildly based on what kind of engines and motors you're talking about; it's not consistent enough to be applied as a generalization, especially when it comes to aircraft (turbines are some of the most power-dense engines available). See here [1] for examples. [1] https://en.wikipedia.org/wiki/Power-to-weight_ratio#Examples https://en.wikipedia.org/wiki/Power-to-weight_ratio#Examples
- ScottFree 8y ago
  Something else to keep in mind: a plane gets lighter as it burns fuel. Electric batteries don't get lighter as they expend energy. Chip Yates flew a few experimental electric airplanes a few years back. The last I heard, he had devised some sort of battery hot-swap system so he could fly from NY to England in one go. I don't think that one ever made it off the drawing board.
- mikeyouse 8y ago
  Smaller motors unfortunately means smaller propellers which means smaller swept area and a large decrease in available power.
  - thrill 8y ago
    Propellers are generally limited by torque, which is something that electric motors excel at.
- WrtCdEvrydy 8y ago
  > are much lighter than gas engines for the same amount of power The issue will always be that fuel is consumed and causes the aircraft to be lighter the longer you fly.
itsyaboi 8y ago
Off the top of my head, both lithium polymer/lithium ion cells are much more temperature sensitive when compared to most liquid fuels. When flying fpv quadcopters in cold weather, (speaking from a anecdotal hobbyist experience here), I get a much lower maximum current for the first minute or so until the individual cells warm up due to the internal resistances. This translates to less total raw wattage. Total battery capacity is reduced as well. I imagine a big challenge would be keeping the batteries at a happy temperature. A quick google search shows the Solar Impulse team ran into this problem: (https://www.theverge.com/2015/7/11/8933295/solar-impulse-sustains-battery-damage-after-record-flight https://www.theverge.com/2015/7/11/8933295/solar-impulse-sus...) Edit: The above in regards to providing reliable electric power. Disregarding this, the main downside by far is energy density of currently available batteries. From https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density, a kilogram of gasoline has about 53x as much energy as a comparable 1 kilogram lithium ion battery. Gasoline 46.4 Lithium-ion battery 0.36–0.875 (MJ/Kg)
sowbug 8y ago
These are some differences that I can think of after mentally running through a C172SP checklist. In a gas plane, checking fuel level during preflight is a matter of direct observation. It's at a certain level, it's the right color, and it doesn't have any gunk in it. In an electric plane, you can't directly observe a battery's state of charge; rather, you can measure the voltage using a device of some kind, and then extrapolate range/capacity from that. That's not hard to do correctly, but it does involve more moving parts than just looking at the gas. Batteries don't change their weight based on state of charge, which is nice for flight planning that normally has to take into account a heavier plane at takeoff than landing. But it is nice to be able to trade off range for performance by fueling to different levels in a gas plane, and you can't do that in an electric one. Batteries perform worse in the cold. Gas engines don't (though normally aspirated/carbureted engines do). The eFlyer is a pretty small plane, though, and it probably won't go high enough to reach altitudes that are consistently very cold. If your gas engine catches fire, there are a bunch of things you can do to put it out without killing yourself. But I'm not sure what you do if your batteries catch fire, except hope you're very close to a surface you can land on.
cmurf 8y ago
Cold weather operations might differ. It's not uncommon to heat a fuel powered engine in the winter, whereas with battery it might be mandatory. Also, cabin heat affect on range will need to be well understood and incorporated in performance and endurance charts for flight planning purposes. For pressurized airplanes, the power cost of pressurizing and cooling. I'm not sure what that cost to endurance would be, but it would need to be accounted for.

csours 8y ago

Liquid fuel is volatile, but generally does not catch on fire on its own. Batteries can catch on fire if over or under charged. Batteries can catch on fire if punctured - liquid fuel can as well, but batteries do not need an external source. This means you need thermal management for your energy source and your power unit. It's not as applicable for this class of aircraft, but batteries do not get lighter as they are expended. Liquid fuel provides the same amount of unit energy until it is completely gone; batteries lose power over time, leading to lower horsepower at the end (this is a simplified point of view).

VectorLock 8y ago
Also you can't shoot batteries out the back of your plane to create thrust like you're doing with liquid fuel.
- AnimalMuppet 8y ago
  Sure you can. Encase them it metal, and use the remaining batteries to power a railgun...
aeternus 8y ago
The per-unit energy is the biggest issue. It's true that fire is a problem for batteries, but that is manageable with very small sensors and casings. There are many more systems required to deal with the many failure modes of internal combustion engines: - Heating systems to address carburetor icing. Typically manually activated by pilot since they have a performance cost. - Fuel pumps since gravity cannot always be depended upon especially in acrobatic airplanes. - Fuel sump systems which must be checked before every flight to address water in the fuel tanks & lines. - Lubrication systems which require pre-flight fluid level checks. - Magneto system to ensure that sparks can be generated independently from the electrical system. - Redundant magneto system since carbon tends to build up and prevent proper sparking. - Possibility of an engine running rough/cylinder firing out of sync due to carbon or other issues. - Fuel/air mixture control so that the optimal mix can be selected based on altitude. Requires pilot intervention. - Extreme thermal stresses on the engine, requiring engine run-up checks before takeoff. - Radiators, and airflow rediretion to address cooling issues resulting in loss of performance and weight. - Exhaust system, and noise vs. weight tradeoff
- Robotbeat 8y ago
  Indeed. ICEs only don't catch fire constantly because of a century of safety improvements.
  - mannykannot 8y ago
    Outside of combat, fuel fires are very rarely in the fuel tanks (TWA 800 being a notable exception, and there are ways it could have been avoided), and a for a fire in an engine, the fuel can be cut off and fire extinguishers used. On the other hand, liquid fuel is probably much more dangerous in a crash.

asparagui 8y ago

Electric engines have a number of properties that are great for aviation, namely the ability to provide torque at low speeds and easily handle high rotation rates, which removes the need for complicated gearboxes and simplifies design. They have been proposed a number of times over the years, the historical problem has always been getting the electricity to drive things: batteries are heavy and diesel->electric converters (eg. hybrid trains) are too large to be practical.

Zak 8y ago
It's worth pointing out that piston aircraft engines usually don't use gearboxes. Instead, they drive the propeller directly, which dictates very low engine speeds relative to where car engines usually produce their peak power since any part of the propeller blade nearing the speed of sound results in a loss of efficiency.
chungleong 8y ago
I wonder if progress being made in micro-turbine generators would one day allow them to be used in planes. Having a bank of generators inside the fuselage could making flying a lot safer. I imagine planes can be made much more aerodynamic as well.
- starpilot 8y ago
  Turbines are more efficient with larger sizes due to the fluid mechanics, and they need air, so then you end up at gas turbine engines externally mounted.

rmah 8y ago

I imagine the primary weakness is the rather low energy density of li-ion batteries vs gasoline. This means less energy per kg of battery/fuel, which means lower power (speed/payload) or range or both.

ccleve 8y ago

I remember reading that electric motors are much lighter than gas engines for the same amount of power. This difference can at least partially offset the added battery weight. Also, it's possible to have multiple, small electric motors with no loss of efficiency. That isn't possible for a gas engine. Multiple motors could add some redundancy, and therefore reliability. I think we're going to see a lot of interesting designs over the next few years.

nbadg 8y ago
> electric motors are much lighter than gas engines for the same amount of power That varies wildly based on what kind of engines and motors you're talking about; it's not consistent enough to be applied as a generalization, especially when it comes to aircraft (turbines are some of the most power-dense engines available). See here [1] for examples. [1] https://en.wikipedia.org/wiki/Power-to-weight_ratio#Examples https://en.wikipedia.org/wiki/Power-to-weight_ratio#Examples
ScottFree 8y ago
Something else to keep in mind: a plane gets lighter as it burns fuel. Electric batteries don't get lighter as they expend energy. Chip Yates flew a few experimental electric airplanes a few years back. The last I heard, he had devised some sort of battery hot-swap system so he could fly from NY to England in one go. I don't think that one ever made it off the drawing board.
mikeyouse 8y ago
Smaller motors unfortunately means smaller propellers which means smaller swept area and a large decrease in available power.
- thrill 8y ago
  Propellers are generally limited by torque, which is something that electric motors excel at.
WrtCdEvrydy 8y ago
> are much lighter than gas engines for the same amount of power The issue will always be that fuel is consumed and causes the aircraft to be lighter the longer you fly.

itsyaboi 8y ago

Off the top of my head, both lithium polymer/lithium ion cells are much more temperature sensitive when compared to most liquid fuels. When flying fpv quadcopters in cold weather, (speaking from a anecdotal hobbyist experience here), I get a much lower maximum current for the first minute or so until the individual cells warm up due to the internal resistances. This translates to less total raw wattage. Total battery capacity is reduced as well. I imagine a big challenge would be keeping the batteries at a happy temperature. A quick google search shows the Solar Impulse team ran into this problem: (https://www.theverge.com/2015/7/11/8933295/solar-impulse-sustains-battery-damage-after-record-flight https://www.theverge.com/2015/7/11/8933295/solar-impulse-sus...) Edit: The above in regards to providing reliable electric power. Disregarding this, the main downside by far is energy density of currently available batteries. From https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density, a kilogram of gasoline has about 53x as much energy as a comparable 1 kilogram lithium ion battery. Gasoline 46.4 Lithium-ion battery 0.36–0.875 (MJ/Kg)

sowbug 8y ago

These are some differences that I can think of after mentally running through a C172SP checklist. In a gas plane, checking fuel level during preflight is a matter of direct observation. It's at a certain level, it's the right color, and it doesn't have any gunk in it. In an electric plane, you can't directly observe a battery's state of charge; rather, you can measure the voltage using a device of some kind, and then extrapolate range/capacity from that. That's not hard to do correctly, but it does involve more moving parts than just looking at the gas. Batteries don't change their weight based on state of charge, which is nice for flight planning that normally has to take into account a heavier plane at takeoff than landing. But it is nice to be able to trade off range for performance by fueling to different levels in a gas plane, and you can't do that in an electric one. Batteries perform worse in the cold. Gas engines don't (though normally aspirated/carbureted engines do). The eFlyer is a pretty small plane, though, and it probably won't go high enough to reach altitudes that are consistently very cold. If your gas engine catches fire, there are a bunch of things you can do to put it out without killing yourself. But I'm not sure what you do if your batteries catch fire, except hope you're very close to a surface you can land on.

cmurf 8y ago

Cold weather operations might differ. It's not uncommon to heat a fuel powered engine in the winter, whereas with battery it might be mandatory. Also, cabin heat affect on range will need to be well understood and incorporated in performance and endurance charts for flight planning purposes. For pressurized airplanes, the power cost of pressurizing and cooling. I'm not sure what that cost to endurance would be, but it would need to be accounted for.