Electric Aircraft
- Thread starter adk
- Start date
ColoradoPilot
New Member
Please no flaming if someone doesn't like Rush Limbuagh, but he made a comment about as soon as AF One is electric, he'll be willing to get on an electric plane (started off as an electric car debate segment). Kind of a funny "safety and reliability" thought.
Minuteman
I HAVE STRONG OPINIONS ABOUT AUTOMOTIVE LIGHTING!
Just doing some cocktail napkin figuring...
The specific power of avgas is around 11.9 kWh/kg. The best Lithium-polymer batteries are are achieving about 7 kWh/kg (so you have to carry more weight to have the same amount of portable power when comparing avgas and batteries). This is a heeeeyoge improvement over lead-acid batteries (0.18 kWh/kg) or Lithium-Ion batteries (0.3 kWh/kg).
However, the competition "heats" up when you consider efficiencies:
A typical O-360 application at 75% power will burn about 45 lb/hr. That works out to an effective specific power of 4.9 kWh/kg (an end-to-end efficiency of about 41%).
In an electric airplane, they need to achieve an end-to-end efficiency of 70% to have a specific power comparable to avgas. For electric motors in this power class it is reasonably expected to have efficiencies in the low-to-mid 90's (so there may be a net improvement in performance possible).
There are some additional implications to weigh:
The specific power of avgas is around 11.9 kWh/kg. The best Lithium-polymer batteries are are achieving about 7 kWh/kg (so you have to carry more weight to have the same amount of portable power when comparing avgas and batteries). This is a heeeeyoge improvement over lead-acid batteries (0.18 kWh/kg) or Lithium-Ion batteries (0.3 kWh/kg).
However, the competition "heats" up when you consider efficiencies:
A typical O-360 application at 75% power will burn about 45 lb/hr. That works out to an effective specific power of 4.9 kWh/kg (an end-to-end efficiency of about 41%).
In an electric airplane, they need to achieve an end-to-end efficiency of 70% to have a specific power comparable to avgas. For electric motors in this power class it is reasonably expected to have efficiencies in the low-to-mid 90's (so there may be a net improvement in performance possible).
There are some additional implications to weigh:
- The power source mass doesn't decrease as it is used (which reduces range).
- There is no need for turbo-normalization to have sea-level motor performance.
- Prop speeds might be more like large turboprops than recips. (800-1200 rpm).
- The rule-of-thumb for charging a battery is to do it at a rate no faster than 10% of it's energy capacity (i.e., 10 hours for a full charge). Quick charging Li-Po batteries is possible, but it reduces battery life.
- No more Janitrol!
anic:
jynxyjoe
Queso King
Just doing some cocktail napkin figuring...
The specific power of avgas is around 11.9 kWh/kg. The best Lithium-polymer batteries are are achieving about 7 kWh/kg (so you have to carry more weight to have the same amount of portable power when comparing avgas and batteries). This is a heeeeyoge improvement over lead-acid batteries (0.18 kWh/kg) or Lithium-Ion batteries (0.3 kWh/kg).
However, the competition "heats" up when you consider efficiencies:
A typical O-360 application at 75% power will burn about 45 lb/hr. That works out to an effective specific power of 4.9 kWh/kg (an end-to-end efficiency of about 41%).
In an electric airplane, they need to achieve an end-to-end efficiency of 70% to have a specific power comparable to avgas. For electric motors in this power class it is reasonably expected to have efficiencies in the low-to-mid 90's (so there may be a net improvement in performance possible).
There are some additional implications to weigh:
- The power source mass doesn't decrease as it is used (which reduces range).
- There is no need for turbo-normalization to have sea-level motor performance.
- Prop speeds might be more like large turboprops than recips. (800-1200 rpm).
- The rule-of-thumb for charging a battery is to do it at a rate no faster than 10% of it's energy capacity (i.e., 10 hours for a full charge). Quick charging Li-Po batteries is possible, but it reduces battery life.
- No more Janitrol!
You did the math? God I love it.
Well done!
Great points all.
R
Roger, Roger
Guest
That's fascinating! I had no idea that a battery/electric motor combination could come that close to competing with Avgas/recip engine in power density.Just doing some cocktail napkin figuring...
The specific power of avgas is around 11.9 kWh/kg. The best Lithium-polymer batteries are are achieving about 7 kWh/kg (so you have to carry more weight to have the same amount of portable power when comparing avgas and batteries). This is a heeeeyoge improvement over lead-acid batteries (0.18 kWh/kg) or Lithium-Ion batteries (0.3 kWh/kg).
However, the competition "heats" up when you consider efficiencies:
A typical O-360 application at 75% power will burn about 45 lb/hr. That works out to an effective specific power of 4.9 kWh/kg (an end-to-end efficiency of about 41%).
In an electric airplane, they need to achieve an end-to-end efficiency of 70% to have a specific power comparable to avgas. For electric motors in this power class it is reasonably expected to have efficiencies in the low-to-mid 90's (so there may be a net improvement in performance possible).
There are some additional implications to weigh:
- The power source mass doesn't decrease as it is used (which reduces range).
- There is no need for turbo-normalization to have sea-level motor performance.
- Prop speeds might be more like large turboprops than recips. (800-1200 rpm).
- The rule-of-thumb for charging a battery is to do it at a rate no faster than 10% of it's energy capacity (i.e., 10 hours for a full charge). Quick charging Li-Po batteries is possible, but it reduces battery life.
- No more Janitrol!
ProudPilot
Aeronautics Geek
:yeahthat:
For those of you not systems inclined:
Electric motors don't have as many moving parts or as much shear volume which reduces many of the inefficiencies of petrol motors. You lose a lot of power to noise, motion, heat and light. Only a small portion of the stored energy in petroleum actually makes it to turning the propeller. While battery capacity is lower than gas, depending on the motor, you can get very close to the same efficiency as a reciprocating engine.
For those of you asking, well what happens if the battery shorts out?
then I ask...
What if you have a gas leak or your fuel pump fails? We fly with a limited amount of energy now. It's a calculated risk.
For those of you not systems inclined:
Electric motors don't have as many moving parts or as much shear volume which reduces many of the inefficiencies of petrol motors. You lose a lot of power to noise, motion, heat and light. Only a small portion of the stored energy in petroleum actually makes it to turning the propeller. While battery capacity is lower than gas, depending on the motor, you can get very close to the same efficiency as a reciprocating engine.
For those of you asking, well what happens if the battery shorts out?
then I ask...
What if you have a gas leak or your fuel pump fails? We fly with a limited amount of energy now. It's a calculated risk.
R
Roger, Roger
Guest
Yeah, I know that aircraft recip motors do a horrible job at turning chemical energy into torque- most of it goes out the exhaust as heat. The part that really surprised me is the power density of newer batteries.
ColoradoPilot
New Member
The weight can be crippling though...
fish314
Well-Known Member
The recharging issue would be an awful lot easier for an airline or cargo mover to deal with than a GA guy. It would just require multiple batteries per aircraft, and the ability to change them out at each stop relatively quickly. In fact, the same system would work at FBO's for GA, now that I think of it. It would just require some kind of industry standard in battery types. Then, each FBO would just have to keep a sufficient number of each type of battery so that as airplanes flew in, you'd swap out the spent batteries for charged ones, and put the spent ones on the charger for the next guy. There might be times when it was difficult to keep up with demand, and the FBO might go down to his last charged battery... but in the quiet hours he would have all of the spent ones on chargers, too.
Airlines would probably use the same kind of system, except that they would own all the batteries themselves, and they would have to manage the total battery inventory and match that up to the routes they flew.
In fact, I've kind of wondered why no one has done that with trucks yet. Trucking companies probably have trucks driving the same routes day after day and week after week. I'm surprised no one has worked out an all electric trucking company with a number of battery weigh-stations along the companies' major routes. Each truck would cost a lot more because of the new expensive technology... but over time you would save a lot of money on fuel (of course still paying for Watts, but a lot cheaper for the same amount of energy), and you'd probably save money on maintenance, since electric motors have far fewer moving parts. Not to mention, it ought to be easy to offset some of that cost with a government tax break.
Airlines would probably use the same kind of system, except that they would own all the batteries themselves, and they would have to manage the total battery inventory and match that up to the routes they flew.
In fact, I've kind of wondered why no one has done that with trucks yet. Trucking companies probably have trucks driving the same routes day after day and week after week. I'm surprised no one has worked out an all electric trucking company with a number of battery weigh-stations along the companies' major routes. Each truck would cost a lot more because of the new expensive technology... but over time you would save a lot of money on fuel (of course still paying for Watts, but a lot cheaper for the same amount of energy), and you'd probably save money on maintenance, since electric motors have far fewer moving parts. Not to mention, it ought to be easy to offset some of that cost with a government tax break.
z987k
Well-Known Member
With trucks I would think they'd at least try diesel electric hybrid just like trains. You'd have all the torque in the world for going up steep grades, great braking through the motors and conventional brakes, and fuel economy would be considerably higher. The only thing I would think that would keep them from going all electric is the cost of Li-po(or Li-ion) batteries right now.
I also can't believe someone hasn't taken a tractor and trailer and put them in a wind tunnel and done testing until the aerodynamics are as good as physically possible. I bet there's 5+mpg to be picked up there alone.
darthpanda
New Member
They're already doing this. The big truck manufacturers all have hybrids, including Kenworth and Peterbilt. They also are moving towards more aerodynamic designs over the conventional square designs.
(I want to "retire" one day and go be a truck driver :hiya
Minuteman
I HAVE STRONG OPINIONS ABOUT AUTOMOTIVE LIGHTING!
Are you my old man?
He says the same thing, verbatim.It turns out they have been playing in the wind. From a 2005 Kenworth Press Release celebrating the 20th anniversary of the T600 (i.e., 1985):
fish314
Well-Known Member
Are you my old man?
It turns out they have been playing in the wind. From a 2005 Kenworth Press Release celebrating the 20th anniversary of the T600 (i.e., 1985):
Wow, that's a heck of a percentage change. Like comparing 20 MPG to almost 25!
fish314
Well-Known Member
Wouldn't it be the same as helicopters now? They lose engines, but that is why they practice autorotation. Auto-rotating, they can glide a few miles, too. I don't think it would be any different if the helicopter were electric.
ColoradoPilot
New Member
*I withdraw my comment on grounds that it is incorrect*
z987k
Well-Known Member
Are you my old man?
It turns out they have been playing in the wind. From a 2005 Kenworth Press Release celebrating the 20th anniversary of the T600 (i.e., 1985):
Haha, it's not just the Truck though, the trailer needs a major overhaul as well... can we say boundary layer separation. And then every trailer out there needs to be like this.
Also as to the hybrids, I do not mean a hybrid like these retarded battery and gas things are. I mean a small diesel motor powering a large generator, running electric motors that drive the wheels. Just like trains work. No part of the IC engine provides movement. That is a terrible design(which is probably why they went with that for cars).
KSCessnaDriver
Well-Known Member
I don't know. You ever tried to turn an electric motor without any current on it. Takes a ton of torque. Not saying that it isn't possible, just something that would also have to be taken into design consideration.