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#62
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Electrically Powered Ultralight Aircraft
George wrote:
Just a wild guess, but wouldn't this make for a very, very safe airplane?? George None would be safer, though you might find some people who would have a problem with calling it an airplane if it couldn't get off the ground. |
#63
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Electrically Powered Ultralight Aircraft
wrote Well, to be fair, there is solar cell research that if it becomes practical and cheap enough would work on sail planes with lithium batteries. Are you sure about that? I think I recall seeing someone do the calculations of how much solar energy hits the top surface of a sailplane and wing, and it was still not enough to motor without thermals, if it was all converted to electrical energy. Anyone better in math, than me, want to take on that supposition? -- Jim in NC |
#64
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Electrically Powered Ultralight Aircraft
On Tue, 07 Aug 2007 20:54:59 GMT, wrote in
: In rec.aviation.piloting Larry Dighera wrote: On Tue, 07 Aug 2007 19:14:59 GMT, wrote in : If you go to http://xtronics.com/reference/energy_density.htm you find the energy densities of a lot of things. Propane (liquid) 13,900 Wh/kg Diesel 13,762 Wh/kg gasoline 12,200 Wh/kg Ethanol 7,850 Wh/kg Methanol 6,400 Wh/kg Secondary Lithium - ion Polymer 130 - 1200 Wh/kg Primary Zinc-Air 300 Wh/kg Lead Acid Battery 25 Wh/kg So batteries have to improve by a factor of 10 to match gasoline. When you compare the efficiency of internal combustion Otto Cycle engines (30% - 40%) against electric motors (80% - 95%), it appears that a factor of five might be a more realistic comparison of their relative merits. Then there is the issue of power plant weight... Well, you have to look at total system weight. Agreed. A 100 HP electric motor is not going to be particularly light The ~100 HP Continental O-200 is about 170 lbs. If you look at the motors offered by AstroFlight, it looks like they weigh about one pound per horsepower, but that doesn't include the controller, charger, etc. and the power cables are going to weigh a whole lot more than fuel lines for example. True, but there are several trade offs: No oil cooler nor oil, No gascolator nor fuel pump, etc... But the electric motor will require a controller, a charging system, wiring, etc. It's difficult to speculate about the weight without more specific information. When you look at the total installed system, assuming you have batteries 5 times better than you have now, I doubt the total weight difference will be all that much. It's difficult to say. Electric motors don't lose power in thin air either. With regard to reliability, electric motors have only one moving part compared to scores of moving parts for IC engines, their failure rate should be substantially greater than IC engines. AC motors have only one moving part but would require a beefy inverter to generate (and induce more system loss) the AC. But the controller has no moving parts either except perhaps a cooling fan and contractor. I would guess the electrical propulsion system to be potentially more reliable than an IC system, but there is the Sony LI battery recall issue ... DC motors have brushes but motor control is simpler. If the DC motor was designed for easy inspection and replacement of the brushes, then the failure rate should be much lower than a gas engine. Today, brushless DC motors, or even three-phase induction motors, are used. Sonex mentions a brushless DC motor: http://www.greencarcongress.com/2007...aft-.html#more Using a purpose-built AeroConversions brushless DC cobalt motor, controller, and highly efficient battery ... ... the design team, in collaboration with Bob Boucher of Astro Flight, Inc. (http://www.astroflight.com/), has designed and built a completely new AeroConversions motor. This motor is the most powerful, lightest-weight, and efficient unit of this type ever produced. It is a 3 phase, 270 volt, 200 amp motor that will be over 90 percent efficient. This works out to about 75 continuous HP by my calculations. It will be interesting to see what the future brings. |
#65
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Electrically Powered Ultralight Aircraft
Gig 601XL Builder wrote:
George wrote: Just a wild guess, but wouldn't this make for a very, very safe airplane?? George None would be safer, though you might find some people who would have a problem with calling it an airplane if it couldn't get off the ground. That was my point, if it can't fly, how can it crash?? vbg George |
#66
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Electrically Powered Ultralight Aircraft
James Sleeman opined
On Aug 7, 3:39 am, Larry Dighera wrote: Are external combustion engines as efficient as internal combustion engines? Stirling engines are great for converting waste heat to mechanical energy, but I'm not sure how appropriate they would be for aircraft propulsion. In theory, I think that stirling engines are quite well suited to aircraft, all it needs is a source of "hot" and a source of "cold", the cold is in abundance (stick a heatsink in the wind, higher you go, colder it gets, more power the engine can deliver, directly the opposite of IC), the hot could be provided with any number of combustables (and some oxygen delivery system). I found yesterday after writing my initial post an article about exactly this - http://www.qrmc.com/fourpartstirling.html "Why Aviation Needs the Stirling Engine by Darryl Phillips" from 1993/1994. Given what was said in the article, I'm kind of surprised that nobody has come up with a working protoype actually. I see 2 problems. First is that although the temperature at 30,000' is low, so is the air density, so the size of the heat sink is smaller than one might think. Second is heat generated by compression of airby the high true airspeeds at altitude. -ash Cthulhu in 2007! Why wait for nature? |
#67
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Electrically Powered Ultralight Aircraft
In rec.aviation.piloting Larry Dighera wrote:
Today, brushless DC motors, or even three-phase induction motors, are used. Sonex mentions a brushless DC motor: http://www.greencarcongress.com/2007...aft-.html#more Using a purpose-built AeroConversions brushless DC cobalt motor, controller, and highly efficient battery ... ... the design team, in collaboration with Bob Boucher of Astro Flight, Inc. (http://www.astroflight.com/), has designed and built a completely new AeroConversions motor. This motor is the most powerful, lightest-weight, and efficient unit of this type ever produced. It is a 3 phase, 270 volt, 200 amp motor that will be over 90 percent efficient. This works out to about 75 continuous HP by my calculations. It will be interesting to see what the future brings. I'm not totally convinced the internal controllers electronics for a brushless DC motor are going to be that reliable at these power and heat levels. Time will tell. The Civic hybrid uses a brushless DC motor, so there's a test bed for that level of power. -- Jim Pennino Remove .spam.sux to reply. |
#68
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Electrically Powered Ultralight Aircraft
In rec.aviation.piloting Morgans wrote:
wrote Well, to be fair, there is solar cell research that if it becomes practical and cheap enough would work on sail planes with lithium batteries. Are you sure about that? I think I recall seeing someone do the calculations of how much solar energy hits the top surface of a sailplane and wing, and it was still not enough to motor without thermals, if it was all converted to electrical energy. Anyone better in math, than me, want to take on that supposition? In rough numbers, you get about 1 kW/m^2 of energy from the sun on a clear day. Current conversion technology is about 22% at best. Technologies in the works are promising 50-60% (the check is in the mail and I will respect you in the morning). One presumes a sailplane is going to spend most of its time sailing and only using the motor (with batteries) to get off the ground and occassionaly cruise between thermals. So most of the time you are just charging the batteries. -- Jim Pennino Remove .spam.sux to reply. |
#69
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Electrically Powered Ultralight Aircraft
On Tue, 7 Aug 2007 16:12:16 -0500, "Gig 601XL Builder"
wrDOTgiaconaATsuddenlink.net wrote in : Here is a 100hp electric motor. I don't know if it is typical for an electric motor but damn the thing weighs over half a ton. I might make the 601XL a little nose heavy. But it's priced right up there with a Lyc of equal power. http://www.baldor.com/products/detai...neralPur pose Catalog Number: D50100P Description: STOCK MOTOR,368AT,100HP,1750/2000RPM,DPFG Ship Weight: 1,118 lbs. List Price: $21,195 Multiplier Symbol: N2 Right. Those are the type I used to install in the early '70; that was about forty years ago. Today the situation is a bit different. Here's a small electric motor manufactured by the same fellow, Bob Boucher, who designed the Sonex motor: http://www.astroflight.com/store/sto...y3CKHwWtA02470 Cobalt 90 Direct Drive Motor Cobalt 90 Direct Drive Motor, 30 to 40 cells, 1500W Astro 90 Cobalt Motor p/n 690 Model No. p/n 690 Name 90 Cobalt Armature Winding 10 turns Armature Resistance 0.111 ohms Magnet Type Sm Cobalt Bearings Ball Bearings Motor Speed /volt 256 rpm/volt Motor Torque/amp 5.3 in-oz /amp Voltage Range 24 to 48 volts No Load Currrent 3 amps Maximum Continuous Current 35 amps Maximum Continuous Power 1200 watts Motor Length 3.7 inches Motor Diameter 2.1 inches Motor Shaft Diameter 0.25 inches Prop Shaft Diameter 5/16 inch Motor Weight 32 oz Expected Performance of Cobalt 90 Battery Prop Amps Watts Rpm 36 Nicads 14x7 20 amps 800 watts 9,000 rpm 36 Nicads 14x10 25 amps 1000 watts 8,500 pm 36 Nicads 15x10 30 amps 1200 watts 8,000 rpm 36 Nicads 16x10 35 amps 1400 watts 7,500 rpm This is a small motor, as you can see, but it uses ~1,500 watts, so at 720 watts per horsepower, that's about two horsepower, and it weighs 32 oz, or about two pounds. That works out to about one horsepower per pound for this type of motor. I have no idea if a one hundred horsepower motor of this type would weigh 100 lbs or not, but it seems reasonable. |
#70
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Electrically Powered Ultralight Aircraft
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