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#41
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Electriflying
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#42
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Electriflying
In article ,
"vaughn" wrote: wrote in message ... How many light planes are actually used for transportation? All of them that fly unless they are remotely controlled. The trip may be as short as 3 turns around the pattern to maintain currency, but a person is still being moved. Sorry, but that's stretching a point beyond nonsense. You could also argue that a pogo stick is a transportation device, but few would take you seriously. "Three turns around the pattern" may actually be either recreation or training, but hardly transportation. Most light planes are used for training and recreation, not transportation. Regardless of the owner's intentions when they buy them, few light planes are actually used for serious transportation. This thread started with a post about a 2-place training aircraft with a 90- minute endurance. Fact is, that plane (if it really exists) could handle many, (possibly most) of the missions I see flown out of my local airport. If available as a rental, it could handle about 70% of my own flights. Vaughn That all depends on turnaround time. If it takes 8 to 12 hours to recharge the batteries, the plane will be sitting idle for most of the operating day -- not a good return on investment! |
#43
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Electriflying
Orval Fairbairn wrote:
In article , "vaughn" wrote: wrote in message ... How many light planes are actually used for transportation? All of them that fly unless they are remotely controlled. The trip may be as short as 3 turns around the pattern to maintain currency, but a person is still being moved. Sorry, but that's stretching a point beyond nonsense. You could also argue that a pogo stick is a transportation device, but few would take you seriously. "Three turns around the pattern" may actually be either recreation or training, but hardly transportation. Most light planes are used for training and recreation, not transportation. Regardless of the owner's intentions when they buy them, few light planes are actually used for serious transportation. This thread started with a post about a 2-place training aircraft with a 90- minute endurance. Fact is, that plane (if it really exists) could handle many, (possibly most) of the missions I see flown out of my local airport. If available as a rental, it could handle about 70% of my own flights. Vaughn That all depends on turnaround time. If it takes 8 to 12 hours to recharge the batteries, the plane will be sitting idle for most of the operating day -- not a good return on investment! The current crop of electric cars "quick charge" times run from about 3 hours to 6 hours with 240V/48A service and 2 to 3 times that for standard 110V service. So allowing 1.5 hours to get the airplane in the air, do training, get the airplane back on the ground, do the paperwork, hook up to the charging station, then 4 hours of charge, you could get 2 flights per day in an eleven hour day. Cut the charge time in half to 2 hours and you can get 3 flights per day. -- Jim Pennino Remove .spam.sux to reply. |
#44
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Electriflying
"Orval Fairbairn" wrote in message news That all depends on turnaround time. If it takes 8 to 12 hours to recharge the batteries, the plane will be sitting idle for most of the operating day -- not a good return on investment! Yep. I actually agree 100%. We discussed that very point a few days ago. That, along with the amortized hourly price of battery use are potential deal killers, and are up to the manufacturers to solve if electric planes are ever to make a dent in the training market. Vaughn |
#45
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Electriflying
On Jun 22, 10:17*am, Gatt wrote:
A few years ago when people were discussing the possibility of electric-powered flight, you'd get hacked on pretty hard for suggesting such a thing would be practical or possible in our lifetime. Obviously if you knew anything about physics or electrical engineering, why, you'd know it was totally impossible. Buddy of mine has a Tesla. It'll make Seattle on a charge, he says. You couldn't have done that with an electric car even a few years ago. It's amazing what they've been able to do, and it only gets better. Curt |
#46
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#47
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Electriflying
On 2011-06-27, Orval Fairbairn wrote:
Hextane? I don't think so! Don't you mean octane (C8H18)? It doesn't matter for this calculation, the numbers work nearly the same for any alkane. C8H18 + 25 O = 8 CO2 + 9 H2O Molar weight of C8H18 = 114 Molar weight of O = 16 So for each 114g of C8H18 we need 400g oxygen. Or around 3.5 parts oxidiser to each part fuel. Pretty much the same. I stand by my analogy in that, even though the nitrogen does not participate in the chemical reaction, it still plays an important role in the propulsion equation, by providing a working medium to receive heat and expand to push pistons or to turn turbines. But it cannot be used to compare with chemicals required in batteries, because batteries do not need this at all! If you want to compare against the mass that must be included in a battery, how can you include the nitrogen? It doesn't make sense, because batteries do not need the equivalent of nitrogen carried along with them. Batteries are not heat engines, they don't need a working medium to transfer heat or turn turbines. So a comparison involving nitrogen is just not valid, so I would reconsider standing by that particular analogy because it's just incorrect. |
#48
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Electriflying
Dylan Smith wrote:
On 2011-06-27, wrote: 1kWh per kilogram is 3.6 MJ/kg. But it is an order of magnitude (more or less) better than what we have now, and would certainly be useful for electric ground transportation. That depends on what you mean by "what we have now". The only chemistry seriously concidered for vehicle use these days is lithium. battery MJ/kg fraction of 3.6 MJ/kg lithium sulphur 1.8 2 lithium ion .72 5 lithium manganse 1.01 3.6 lithium thionyl chloride 2.5 1.4 lithium ion nanowire 2.54 1.4 lead acid .14 25.7 So yeah, a 3.6 MJ/kg battery would be more than an order of magnitude better than a lead acid battery, but nowhere near an order of magnitude better than existing lithium technology as it is only 1.4 times better than the best of the chemistries currently being developed. -- Jim Pennino Remove .spam.sux to reply. |
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#50
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Jim Logajan wrote:
wrote: 100LL Avgas is 44 MJ/kg. Batteries need to be able to produce better than 20 MJ/kg to be generally usefull for transportation. The Avgas energy density is not comparable to battery energy density because it doesn't factor in thermal to mechanical conversion. Current automobile engines extract only about 20% of that 44 MJ/kg. Electric motors are anywhere from 75% to 95% efficient in converting electrical power to mechanical power. So a battery with ~11 MJ/kg powering an 80% efficient electric motor has the same usable energy density as Avgas powering an internal combustion engine. Setting the goal for battery energy density at 20 MJ/kg would simply be wrong because it uses the wrong numbers. There is a difference between the theoretical efficiency of a motor of any type and the obtainable efficiency of a real world motor. The 20 MJ/kg assumes that a real electric airplane motor would be about twice as energy efficient as a real gasoline airplane motor. We can quibble about exactly what that number is, but a factor of 2 seems to me to be a realistic number. And since airplane engines spend most of their time operating at a single point in their power curve by design, while automobiles spend a lot of time at different points in their power curve by necessity, the overall real efficiency of an airplane engine is a bit better than an automobile engine. -- Jim Pennino Remove .spam.sux to reply. |
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