If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#61
|
|||
|
|||
The new Electric Cessna 172
On Jan 1, 1:24*pm, wrote:
wrote: http://nextbigfuture.com/2009/12/sup...enable-electri... -- Mark Practical, manufacturable high temperature superconductors would enable a whole bunch of neat things and would be as spectacular as a cure for the common cold, lasting peace in the Middle East, and controlled fusion, and is just as likely to happen in the near future. I recently read up on some work being done with graphene supercapacitors. I IRC, it was at Caltech. What was interesting is how they performed at lower temperatures (e.g. room temp.). Also, charging times were impressive. Still in the realm of research, so it wasn't clear to me how well it would scale beyond smaller applications (consumer electronics, for example. |
#63
|
|||
|
|||
The new Electric Cessna 172
On Feb 1, 12:25*pm, wrote:
wrote: On Jan 1, 1:24*pm, wrote: wrote: http://nextbigfuture.com/2009/12/sup...enable-electri.... -- Mark Practical, manufacturable high temperature superconductors would enable a whole bunch of neat things and would be as spectacular as a cure for the common cold, lasting peace in the Middle East, and controlled fusion, and is just as likely to happen in the near future. I recently read up on some work being done with graphene supercapacitors. I IRC, it was at Caltech. What was interesting is how they performed at lower temperatures (e.g. room temp.). Also, charging times were impressive. Still in the realm of research, so it wasn't clear to me how well it would scale beyond smaller applications (consumer electronics, for example. Supercapacitors are great for things like keeping your clock from flashing on every minor power failure, but not that great for real power application. The basic physics of capacitors says the energy density can never be as good as existing batteries. Graphene makes them better but it will take yet to be invented materials to match batteries. Capacitors are also a poor choice for running something like a motor because of their discharge curve. While a battery's discharge curve is basically flat until it gets close to full discharge, then takes a big dive, a capacitor discharge curve is a straight line between fully charged and zero. Motors operate over a narrow voltage range. Electric motor speed control is done by pulsing the motor voltage on and off, not by varying a constant voltage. Now it is possible to build a thing that will take in a lower voltage and output some constant higher voltage to keep a motor happy. The problem with that is it is more complexity subject to failure, not good with airplanes, and it would require big, heavy, high current transformers, which ups the weight a good bit. My wild assed guess is that if electric airplanes ever become practical without Star Trek technology, it will likely be through a fuel cell that is yet to be invented. Most of what I was reading didn't seem to indicate that the goal is to replace, but rather to compliment existing technologies, e.g. charging applications. http://phys.org/news/2012-10-sponge-...ectrodes..html - Graphene http://phys.org/news/2011-08-energy-...-electric.html - SMC I'm not saying it will (ever) power an airplane. Just looked interesting and sometimes there are great discoveries that come out of research, often in applications that were never part of the planned research itself. Peace. |
#64
|
|||
|
|||
The new Electric Cessna 172
wrote:
snip old stuff Most of what I was reading didn't seem to indicate that the goal is to replace, but rather to compliment existing technologies, e.g. charging applications. http://phys.org/news/2012-10-sponge-...lectrodes.html - Graphene http://phys.org/news/2011-08-energy-...-electric.html - SMC Lot's of little techical problems in both of those articles. The biggest is talking about recharging in minutes. It is a rather simple calculation to calculate the current requirments to recharge a device (doesn't matter battery or capacitor) to the full energy level in a few minutes. When you do that you discover that the size of the cable required so that it will not vaporize due to the current density is as big around as your leg with matching connectors. Energy sources are rated in KWh and is equivalent to 1000 x V x A x h. A typical electric car battery is around 30 KWh and 100 volts and 6 minutes is 0.1 hours so: 30,000 / (100 x .1) = 3,000 Amps To put the wire required in perspective, those big heavy cables on an arc welder are good for a current of around 100 Amps so your charging cable would have to be about 30 times bigger than arc welder cables. I'm not saying it will (ever) power an airplane. Just looked interesting and sometimes there are great discoveries that come out of research, often in applications that were never part of the planned research itself. Yeah, that is usually the case. Peace. |
#65
|
|||
|
|||
The new Electric Cessna 172
|
#66
|
|||
|
|||
The new Electric Cessna 172
Dylan Smith wrote:
On 2013-02-01, wrote: To put the wire required in perspective, those big heavy cables on an arc welder are good for a current of around 100 Amps so your charging cable would have to be about 30 times bigger than arc welder cables. To be precise for an interconnect of 10m, two cables of 30mm diameter would suffice. It would give the line boy a bit of a work out but isn't impossible. Size-wise it's a bit like two fuel hoses but *considerably* heavier. I think you dropped a decimal point there. 4/0 AWG wire is about 12mm in diameter and rated for about 300 A. Keep in mind any real world implementation would have to follow existing regulations such as NEC and while a 30mm copper wire isn't going to vaporize, it certainly isn't going to be cool. Also there can be a great difference between "possible" and "practical". However, the price and other installation details of getting the 300kW feed to the FBO is left as an exercise for the reader... And that is if you only do one at a time. |
#67
|
|||
|
|||
The new Electric Cessna 172
|
#68
|
|||
|
|||
The new Electric Cessna 172
|
#69
|
|||
|
|||
The new Electric Cessna 172
Dylan Smith wrote:
On 2013-02-04, wrote: To be precise for an interconnect of 10m, two cables of 30mm diameter would suffice. It would give the line boy a bit of a work out but isn't impossible. Size-wise it's a bit like two fuel hoses but *considerably* heavier. I think you dropped a decimal point there. 4/0 AWG wire is about 12mm in diameter and rated for about 300 A. No decimal point dropped. Don't forget the DC current carrying capacity is not determined by the radius, but the cross section area of the cable. So you wouldn't need 120mm dia. cable. A 12mm dia cable has an area of 113mm^2. Multiplying by 10 we have a cable with a 1130mm^2 cross section, or a radius of sqrt(1130/pi), or a 38mm diameter by just making it ten times larger than a 300A cable (and not far off my initial guesstimate of 30mm dia). Sounds about right. That wire has about 1.5e-5 ohm resistance per meter (or 1.5e-4 ohm for 10 meters). Applying V=IR to find the voltage drop, we have V=3000*0.00015, or a 0.45v drop over this cable. So we'd have to dissipate about 1.4kW of heat over this 10 meter length during the charge. So yes, pretty toasty but it wouldn't melt the insulation. It's the poor line boy who gets a bit of a work out though, he'd have to drag about 200kg of cable out to the plane. Even lifting the last 2m up off the ground to connect to the aircraft would be lifting 40kg of copper. The health and safety police certainly would frown on that. Minor nit: There are two wires so shouldn't that be 2.8kW and 400 kg of cable? Note I'm not saying it's *practical*, where I live the final distribution circuits are only 180kW or so, which is less than the power that this thing would need to transfer, so the FBO which probably have just a pretty standard commercial office type electricity supply would need upgrading to something that could power a factory (in other words, eyewateringly expensive given that most GA FBOs are marginally profitable and live hand-to-mouth). I also suspect that 10m of 38mm dia cable will be a bit expensive too and a prime target for copper thieves. So even before we get as far as thinking "will a 38mm dia cable with a suitable protection device meet regulations?" the whole thing would be stymied by the astronomical cost of supplying such a large amount of power to an operation that at the best of times can just about cover the wage bill. Totally agree here. This is why no electric vehicle of any kind is ever going to "refuel" as quickly as a gasoline vehicle no matter what the storage device other than a fuel cell and for most people a refuel time of hours is not acceptable. One would think the research money for big electrical sources would be better spent on fuel cells (not that they don't have problems of their own like generating a lot of heat) than on batteries and capacitors. |
#70
|
|||
|
|||
The new Electric Cessna 172
Vaughn wrote:
On 2/4/2013 12:54 PM, wrote: would have to follow existing regulations such as NEC You would be surprised at the places where the NEC doesn't apply, and I wouldn't bet money that it would apply here. Still, the laws of physics always apply and any such installation where people must handle energized conductors would certainly need to be built to some stringent safety standard. As a general rule of thumb, the NEC applies to things connected to the electrical grid, so my guess is that it would apply. Not that it matters in the slightest as this will never become reality. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Electric jets where are You? | nrepeb | General Aviation | 5 | March 13th 11 08:56 PM |
FS: Electric tow | Bug Dout | General Aviation | 0 | October 16th 10 06:27 PM |
6CH Electric RC Helicopter for $169 | GTY | Rotorcraft | 0 | October 27th 05 08:59 PM |
Electric RC Helicopter for $83 | NYPT Man | Home Built | 0 | October 24th 05 06:47 PM |
Electric DG | Robbie S. | Owning | 0 | March 19th 05 03:20 AM |