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#31
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Electrically Powered Ultralight Aircraft
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#33
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Electrically Powered Ultralight Aircraft
"Michael Ash" wrote The extra drag caused by the extra weight of the batteries and the rest of the hybrid system would probably outweigh any efficiency gain. Probably? You are being far too kind. A redundant power system, only helping at takeoff is GOING to waste efficiency. There is no way to avoid that fact unless then cruise speed is going to be painfully slow. -- Jim in NC |
#34
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Electrically Powered Ultralight Aircraft
In rec.aviation.soaring Morgans wrote:
"Michael Ash" wrote The extra drag caused by the extra weight of the batteries and the rest of the hybrid system would probably outweigh any efficiency gain. Probably? You are being far too kind. A redundant power system, only helping at takeoff is GOING to waste efficiency. There is no way to avoid that fact unless then cruise speed is going to be painfully slow. I don't doubt you in any way, and in fact my general feeling is in complete agreement with you. But I'm not speaking from a position of great knowledge so I used a weasel word to indicate that. -- Michael Ash Rogue Amoeba Software |
#35
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Electrically Powered Ultralight Aircraft
In rec.aviation.piloting Michael Ash wrote:
In rec.aviation.soaring wrote: In rec.aviation.piloting Phil wrote: I wonder if anyone has done any experiments with a hybrid drive system for an aircraft. I am thinking of something like a 3-cylinder diesel engine providing enough power for cruise, supplemented with a battery pack and motor for takeoff and climb. The advantage for hybrids comes from stop and go driving where the battery is charged by regenerative braking. There isn't much stop and go flying. There is also an advantage which comes from only needing to size the engine for cruise, not for acceleration, since you can suppliment the smaller engine with the batteries during acceleration. Smaller engines are generally more efficient than larger ones when putting out the same amount of power. If you are trying to say it takes less power to maintain speed than to accelerate, yes that is true. The advantage from the electric engine at cruise is that it uses zero energy. There were attempts to increase mileage of gas engines by turning off uneeded cylinders at cruise. They didn't work that well and you still had to move the pistons, the big crank, and all the rest of the stuff. The other advantage is that the engine can stay in the engine's efficiency band even when the RPM demanded of it is higher (acceleration) or lower (initial start). The transmission keeps the engine RPM within a limited range. Hybrids have no effect on that. However, these also don't help nearly as much on aircraft as on cars. The difference between acceleration and cruise power on an aircraft is much less than in a car, and aircraft engines tend to spend most of their time in the efficiency band anyway, especially if there's a constant-speed prop affixed. The extra drag caused by the extra weight of the batteries and the rest of the hybrid system would probably outweigh any efficiency gain. It doesn't help at all on airplanes. The advantage to hybrids is they get better gas mileage. They do that by using the deceleration to charge batteries which recovers some of the kinetic energy instead of using it all to heat the brake linings. -- Jim Pennino Remove .spam.sux to reply. |
#36
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Electrically Powered Ultralight Aircraft
James Sleeman wrote:
stick a heatsink in the wind, higher you go, colder it gets, more power the engine can deliver, directly the opposite of IC What I didn't get from the article: Where does the "hot" come from? A fuel burner, probably, which would have the same problems with altitude as an IC engine, wouldn't it? Ad- -- The mail address works, but please notify me via usenet of any mail you send to it, as it has a retention period of just a few hours. |
#37
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Electrically Powered Ultralight Aircraft
Gattman wrote:
"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in message ... Come on, it's not like there isn't sufficient motivation out there now and it isn't coming from battlebots. If anyone comes up with a battery that can power and automobile for 4 hours at highway speeds and is affordable to produce they will be very wealthy. If they can make one that is as efficient as a tank of gasoline they will shortly become very, very wealthy. I agree. It's on the way. Wasn't too long ago that terms like "lithium ion" and "nickle metal hydride" were unheard of to the common consumer. Five or six years ago your choices were Hawker Genesis-style Sealed Lead Acid or custom-built NiCad battery arrays which is what we used. NiMH and lithium ion weren't available or affordable but the proliferation of power chairs, stuff like the Segway, electric scooters and so forth have really pushed the demand for lightweigh, high performance batteries. -c Do me a favor Gattman. What is the weight of the most effeicent battery that could power an automobile at highway speed and how long will it do so and how long to recharge? |
#38
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Electrically Powered Ultralight Aircraft
wrote in message ... The advantage from the electric engine at cruise is that it uses zero energy. Snippage -- Jim Pennino Remove .spam.sux to reply. You want to support this, somehow? Tim Ward |
#39
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Electrically Powered Ultralight Aircraft
On Mon, 06 Aug 2007 18:22:41 -0700, James Sleeman
wrote in .com: 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 see what you mean. Unfortunately, the highest power requirements of aircraft engines are during the takeoff and climb phases of flight. Power requirements are even greater when the ambient temperature rises resulting in less air density or a higher density altitude. That is when the most power is required for takeoff, but that would be a situation where the Stirling engine would have its minimum power production. I would also like to see a comparison of the efficiencies of IC and EC engines and their relative weight and size per horsepower compared. Unlike electrical motors, that must be constructed with heavy iron, IC and EC engines can be constructed of lighter materials like aluminum, but electrical motors are usually 80% to 95% efficient. With the Stirling aircraft engine there is a requirement for what I would imagine would be a large heat sink or heat exchanger located in the slip stream. The weight of this heat exchanger and its drag penalty must also be considered. 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. The article is interesting; thank you for mentioning it. I am e-mailing a copy of this followup article to the author Darryl Phillips. There might be one advantage to using Sterling external combustion engines for aviation: the use of atomic energy as a fuel source if the weight of the lead shielding were not too great. Imagine an aircraft that effectively never runs out of fuel! There'd be no more fuel exhaustion mishaps. |
#40
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Electrically Powered Ultralight Aircraft
On Mon, 6 Aug 2007 20:43:47 -0500, "Maxwell" wrote
in : "Larry Dighera" wrote in message .. . Personally, I'd like to see an electrically powered parachute (http://skyhighflying.com/homepage.html) design attempted. Surly the lighter weight would require less power. It would seem that lithium-ion polymer batteries are a potential enabling technology. They might be lightweight and strong, but I think they would be far too inefficent. All the canopies I have been around have had a very poor L/D when compared to something like a sailplane. The web site below mentions an L/D of four to one. I always assumed they were so popular because they were so strong, portable and quick to set-up. But I'm thinking their fuel mileage would be very poor. I would be more interested in the specific horsepower required to operate powered parachutes than their efficiency. This web site mentions 50 HP to 65 HP: http://www.all-about-powered-parachutes.com/faq.htm There is a 14 HP Powered Paraglider (PPG) engine offered he http://www.poweredparasports.com/Par...#Jet%20Details They also state that the weight of their engines ranges from 46 lbs. to 68 lbs. If a 14 HP electric propulsion system weighing 46 lbs could be constructed, apparently it would permit the use of PPGs by pilots up to 180 lbs. |
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