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#142
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Electrically Powered Ultralight Aircraft
wrote Unless the added weight is enough to deform the tires, the increase in rolling resistance in the total energy expediture can't be found. Bull hockey. Just because it is not noticeable, or measurable by the lack of sensitivity with the instrument you are currently not using, does not mean that it does not exist. More weight on the bearings will cause more rolling resistance. That is fact, not open to dispute. If you say it is, I want to buy the rights to the bearings you are using, so I can patent them and make a fortune. -- Jim in NC |
#143
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Electrically Powered Ultralight Aircraft
In rec.aviation.piloting Charles Vincent wrote:
wrote: In rec.aviation.piloting cavelamb himself wrote: wrote: To carry more weight at the same speed and altitude takes more power, so you have to account for the energy expended kiting you deadweight electric takeoff system around the sky as well. Sizing an engine for cruise has been done, if only backwards. Think JATO. Most JATO's are actually RATO (rocket assisted takeoff). I expect RATO would beat an electric system based on energy density and the fact that when it is done you have reduced your weight by the fuel. I also suspect for a given amount of thrust the rocket will be lighter than an electric motor and associated clutches and gearing. In my opinion, at this point in time it is just as practical for a homebuilt as well as in not. Well, that's true enough, but the above was about hybrid cars. No, it's not true enough. To carry more weight at the same speed and altitude requires more LIFT. A higher CL - and/or more wing area. THEN, to overcome the increased drag, THEN you need more power. But more power by itself won't satisfy the constraints... So if I add 1 pound to a 2400 pound gross aircraft loaded to 2300 pounds, it would be impossible to cruise at the same speed and altitude without the 1 pound unless I added wing area? How about 50 pounds? No. You can increase the angle of attack, which increases the lift ( to a limit) and also increases the drag, which must be overcome with more power. If your speed drops, so does the lift. If you could increase your aspect ratio, you could get more lift at the same speed at the same power I think. So I guess Richard is flying a swing wing texas parasol.;') For the rest of us, we have to add power to carry more weight at the same speed and altitude. Since most planes lose weight while in flight in the real world, you actually have the opposite issue. Gee, you mean all I gotta do is tweek the trim and throttle a bit? Who'd have guessed it? :-) -- Jim Pennino Remove .spam.sux to reply. |
#144
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Electrically Powered Ultralight Aircraft
On Aug 15, 8:18 am, Larry Dighera wrote:
On Wed, 15 Aug 2007 12:23:00 GMT, CanalBuilder wrote in : How much of a fire hazard would a paper battery be? http://www.energy-daily.com/reports/...oring_Power_In... That is an interesting device indeed. Given these quotes from the article: Rensselaer researchers infused this paper with aligned carbon nanotubes, which give the device its black color. The nanotubes act as electrodes and allow the storage devices to conduct electricity. The device, engineered to function as both a lithium-ion battery and a supercapacitor, can provide the long, steady power output comparable to a conventional battery, as well as a supercapacitor's quick burst of high energy. ... Along with use in small handheld electronics, the paper batteries' light weight could make them ideal for use in automobiles, aircraft, and even boats. The paper also could be molded into different shapes, such as a car door, which would enable important new engineering innovations. IF these can be made practical, they sound ideal for use in an airplane. They are light, and they can be shaped in just about any way to fit inside the airframe. Suppose they were integrated into the airframe and wings such that a large percentage of the airplane consisted of battery. It might be possible to get enough capacity there for a practical general aviation electric plane. |
#145
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Electrically Powered Ultralight Aircraft
Charles Vincent wrote:
No. You can increase the angle of attack, which increases the lift ( to a limit) and also increases the drag, which must be overcome with more power. If your speed drops, so does the lift. If you could increase your aspect ratio, you could get more lift at the same speed at the same power I think. So I guess Richard is flying a swing wing texas parasol.;') For the rest of us, we have to add power to carry more weight at the same speed and altitude. Since most planes lose weight while in flight in the real world, you actually have the opposite issue. Charles Don't be snotty, Charles. Since the subject is an electrically powered aircraft, the weight issue is not trivial. That's been my issue with this thread from the start. The constraints given here were to fly at the same speed and altitude but at a higher weright. You can increase lift via increased angle of attack only as far as CLmax. No Farther. (You seem to have that part right) Beyond that any increased weight will require increased wing area. Aspect ratio alone won't answer is most cases. And - an electric powered plane would NOT lose weight in flight. No electrons are "consumed" - no change in battery weight. |
#146
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Electrically Powered Ultralight Aircraft
"Phil" wrote IF these can be made practical, they sound ideal for use in an airplane. They are light, and they can be shaped in just about any way to fit inside the airframe. Suppose they were integrated into the airframe and wings such that a large percentage of the airplane consisted of battery. It might be possible to get enough capacity there for a practical general aviation electric plane. I can see the headlines, now. Plane (or car) crashes, and the car's structure electrocutes the occupants. g -- Jim in NC |
#147
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Electrically Powered Ultralight Aircraft
On Fri, 17 Aug 2007 11:28:06 -0700, Phil wrote
in .com: It might be possible to get enough capacity there for a practical general aviation electric plane. It might indeed. But I'd have to know more about the paper battery specifications before I could render any sort of judgment. I guess we'll have to wait until more information is disclosed. Let's see ..... http://www.eetimes.com/news/semi/rss...etimes_semiRSS Paper battery is rechargeable R. Colin Johnson EE Times (08/14/2007 9:42 AM EDT) PORTLAND, Ore. — Rensselaer Polytechnic Institute researchers said they have developed a paper-thin battery by immersing a carpet of vertical nanotubes in an ionic liquid electrolyte. The result is a cellulose paper that stores electrical energy. The RPI team produced a supercapacitor by placing a second nanotube electrode on the other side of the paper. They then added a lithium electrode atop the paper, creating what they claim is a paper-thin rechargeable battery. "The carbon nanotubes are embedded in the paper, and the electrolyte is soaked into the paper, so it really looks, feels and weighs about the same as paper," said RPI professor Robert Linhardt. The supercapcitor and rechargeable battery are the result of a year and half of collaborative research among three RPI labs. One lab was making carbon nanotube-based structures, which were adapted to serve as a battery electrode. By growing the nanotubes vertically on a sheet, liquid cellulose was poured between the "forest of nanotubes" to form the battery. Another lab added a lithium-based top electrode to create either a rechargeable battery or a supercapacitor by adding a second nanotube electrode. Ionic liquids first dissolved the cellulose, turning it into a gel. The fluids also serve as the battery electrolyte, carrying ions from one side of the paper battery to the other. Each sheet of battery-paper generated about 2.4 volts with a power density of about 0.6 milliamps/cm2. For higher voltages, paper can be stacked. For more current, the sheets can be expanded to larger areas. The battery-paper operates from minus 100 degrees up to 300 degrees Fahrenheit, and can deliver quick surges of current, the RPI researchers claim. It can also be rolled twisted or cut into many shapes. So far, the RPI researchers have only cycled their paper batteries through 100 rechargings. But they claim no deterioration in performance has been detected after recharging. Next, they plan long-term testing of the batteries to determine the maximum number of rechargings, and to optimize the design for higher power densities. ... http://www.uberreview.com/2007/08/fl...-institute.htm It does not function better than existing batteries on the market and at present it is extremely expensive to produce. http://news.rpi.edu/update.do?artcenterkey=2280 Contact: Michael Mullaney Phone: (518) 276-6161 E-mail: “We’re not putting pieces together – it’s a single, integrated device,” he said. “The components are molecularly attached to each other: the carbon nanotube print is embedded in the paper, and the electrolyte is soaked into the paper. The end result is a device that looks, feels, and weighs the same as paper.” Can someone make the necessary conversions to compare the power density of about 0.6 milliamps/cm2 for the paper battery to secondary lithium-ion Polymer batteries at 130 - 1200 Wh/kg*? * http://xtronics.com/reference/energy_density.htm |
#148
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Electrically Powered Ultralight Aircraft
The original paper battery article is available on-line:
http://www.pnas.org/cgi/content/abst...urcetype=HWCIT Proceedings of the National Academy of Sciences of the United States of America Published online before print August 15, 2007 Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0706508104 This Article Full Text (PDF) Articles by Pushparaj, V. L. Articles by Ajayan, P. M. Engineering Flexible energy storage devices based on nanocomposite paper To whom correspondence should be addressed. Pulickel M. Ajayan, E-mail: |
#149
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Electrically Powered Ultralight Aircraft
Morgans wrote:
"Phil" wrote IF these can be made practical, they sound ideal for use in an airplane. They are light, and they can be shaped in just about any way to fit inside the airframe. Suppose they were integrated into the airframe and wings such that a large percentage of the airplane consisted of battery. It might be possible to get enough capacity there for a practical general aviation electric plane. I can see the headlines, now. Plane (or car) crashes, and the car's structure electrocutes the occupants. g LOL! These paper batterise are light because they are so small. By the time they make a battery will a few megawatts capacity, it's NOT going to be all that light. Lighter than Lead/Acid? Probably. But light enough to fly? It might be a while... |
#150
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Electrically Powered Ultralight Aircraft
cavelamb himself wrote:
Don't be snotty, Charles. Since the subject is an electrically powered aircraft, the weight issue is not trivial. That's been my issue with this thread from the start. The constraints given here were to fly at the same speed and altitude but at a higher weright. You can increase lift via increased angle of attack only as far as CLmax. No Farther. (You seem to have that part right) Beyond that any increased weight will require increased wing area. Aspect ratio alone won't answer is most cases. And - an electric powered plane would NOT lose weight in flight. No electrons are "consumed" - no change in battery weight. Not really being snotty at all. Frankly, I was in the process of deleting screenfulls of messages on the topic of electric powered airplanes being as the subject really holds no interest for me. For some reason I happened to read "The advantage from the electric engine at cruise is that it uses zero energy" on one message just as I deleted it. Pulling it back from the trash, I felt compelled to respond to it. My mistake. For some reason you are in turn compelled to nit pick my correct assertion because it did not completely cover the relevant aerodynamic theory. In my opinion, it covered enough, but not following the thread, I have no idea what sort of debate has been raging. As I stated elsewhere, I just didn't expect that information required for even the most basic pilot ticket would be the subject of any debate here. In the end, to fly at the same speed and altitude but at a higher weight requires more power be applied, whether you use that power to drag the same wing at a higher angle of attack or a bigger wing doesn't change that. Or you could use more power to drag the wing at a higher speed to generate the lift you needed. All of this ignores the fact that for internal combustion aircraft powerplants, the weight per HP goes down as the power goes up. Last time I looked at it, the opposite is true of electric motors. I don't think an electric assist for an IC engine is going to be viable for aircraft in the near future. Charles |
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