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On Tue, 15 Apr 2008 22:35:03 GMT, wrote in
: Larry Dighera wrote: On Tue, 15 Apr 2008 17:45:04 GMT, wrote in : Another limitation is that for something the size of a C-172, your battery has to deliver around 120 kW to get off the ground and climb to altitude. I don't see that fact as being too limiting. Why do you feel that's an issue? Big wires your battery has to deliver that much power without going up in flames, yet be light enough to carry on an airplane. If the electric motor, controller, battery, and fuel-cell are sited in close proximity to each other (al la Sonex), the connecting bus can be kept reasonably short. As in IC engine powered aircraft, there is the necessity to dump waste heat to the atmosphere. The electric motor, controller, and Li-ion battery are quite efficient, but they do generate considerable heat at the power level you chose as an example (C-172; ~166 HP). Here's John Monnett describing the system: http://www.youtube.com/watch?v=P8Pb_psj1A8 Sonex Electric Powered Flight, EAA AirVenture Oshkosh 2007 John Monnett Of course there is always the potential for fire when dealing with volatile or reactive fuels as we've been discussing. Engineers have been reasonably successful in designing systems that minimize the probability of that hazard. That would, of course, part of the development goal. As a "back of the envelope" hack at the practicability of an hydrogen (/oxygen) fuel-cell powered electric aircraft employing present day technology, I'd say it looks worth an effort if for no other reason than to be ready to exploit future technical discoveries as they are made. [snip] However according to the articles below, hydrogen embrittlement doesn't seem to be an issue with carbon fiber composite cylinders: http://en.wikipedia.org/wiki/Hydrogen_tank A Hydrogen tank (other names- cartridge or canister) is used for hydrogen storage, most tanks are made of composite material because of hydrogen embrittlement. Some tanks are used for fixed storage others are exchangeable for refueling at a hydrogen station[1]. http://www1.eere.energy.gov/hydrogen...s/32405b27.pdf The 5,000 and 10,000 psi tanks developed by QUANTUM Technologies have been validated to meet the requirements of DOT FMVSS304, NGV2-2000 (both modified for 10,000 psi hydrogen) and draft E.I.H.P standard. Typical safety tests completed, in order to ensure safety and reliability in an automotive service environment included: Burst Tests (2.35 safety margin), Fatigue, Extreme Temperature, Hydrogen Cycling, Bonfire, Severe Drop Impact Test, Flaw Tolerance, Acid Environment, Gunfire Penetration, Accelerated Stress, Permeation and Material Tests. And nowhere does it say anything about the actual tank weight. It was the best information I could find quickly. Over the course of our discussion, I believe I've provided enough information to show that the weight of the electrical equipment would be at least in the same order of magnitude as that it would be replacing if not reasonably close to equaling it, not only in weight, but power and runtime. There will be differences to be sure. The very last thing you would want to do is put it in a wing spar. Why do you believe that is true? Hydrogen embrittlement. Not that I'm sincerely proposing it, but if spar/cylinder of a carbon fiber composite tube could be successfully developed, it might be feasible, as it appears the that material is not affected by hydrogen embrittlement. At least that's what the information I found implies. Personally, I don't see why it would be, as it would seem that hydrogen could as easily migrate through composite as metal. Of course these rough theoretical calculations are predicated on existing technologies, and don't consider the inevitable future technical advancements. Which are no better than a wish and a hope in the real world. You've got to start somewhere, right? Why? At this time in the history of civilization, with the planet's finite petroleum reserves being pumped at ever higher volume, and the onset of climate change, it would seem prudent to have the power to produce a non-polluting, renewable-energy powered aircraft (in the event anti-gravity technology doesn't become practicable BG) before the use of our present fuel becomes impractical. Diesel airplanes sound like a lot better idea than electric or hydrogen airplanes to me, plus the technology to do it exists now. It not only exists, you can currently purchase diesel converted Cessnas. I'm not considering becoming involved in an electric project, but it does look like electric may actually be achievable. Diesel airplanes need some refinement to be generally usefull. Electric and hydrogen airplanes need new and major basic science breakthroughs which may not ever occur and right now are nothing more than a pipe dream. I believe Boeing's recent effort has demonstrated that electric fuel cell aircraft motive power is achievable with current technology. Hopefully Boeing's demonstration will provide some impetus toward improvement and refinement. |
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Larry Dighera wrote:
On Tue, 15 Apr 2008 22:35:03 GMT, wrote in : Larry Dighera wrote: On Tue, 15 Apr 2008 17:45:04 GMT, wrote in : Another limitation is that for something the size of a C-172, your battery has to deliver around 120 kW to get off the ground and climb to altitude. I don't see that fact as being too limiting. Why do you feel that's an issue? Big wires your battery has to deliver that much power without going up in flames, yet be light enough to carry on an airplane. If the electric motor, controller, battery, and fuel-cell are sited in close proximity to each other (al la Sonex), the connecting bus can be kept reasonably short. As in IC engine powered aircraft, there is the necessity to dump waste heat to the atmosphere. The electric motor, controller, and Li-ion battery are quite efficient, but they do generate considerable heat at the power level you chose as an example (C-172; ~166 HP). Here's John Monnett describing the system: Why in the world would you have a battery and a fuel cell, ignoring for the moment that neither is practical for aircraft use? Any waste heat just makes the problem worse. Neither batteries nor fuel cells have the energy density required with 100% efficiency, much less with energy ****ed away as heat. The big wires have to be IN the battery. You think nano wires are going to carry 120 kW? http://www.youtube.com/watch?v=P8Pb_psj1A8 Sonex Electric Powered Flight, EAA AirVenture Oshkosh 2007 John Monnett Of course there is always the potential for fire when dealing with volatile or reactive fuels as we've been discussing. Engineers have been reasonably successful in designing systems that minimize the probability of that hazard. That would, of course, part of the development goal. As a "back of the envelope" hack at the practicability of an hydrogen (/oxygen) fuel-cell powered electric aircraft employing present day technology, I'd say it looks worth an effort if for no other reason than to be ready to exploit future technical discoveries as they are made. A lab toy and press release fodder, nothing else for the forseeable future. snip You've got to start somewhere, right? Why? At this time in the history of civilization, with the planet's finite petroleum reserves being pumped at ever higher volume, and the onset of climate change, it would seem prudent to have the power to produce a non-polluting, renewable-energy powered aircraft (in the event anti-gravity technology doesn't become practicable BG) before the use of our present fuel becomes impractical. Why? It makes more sense to put the effort into producing cheap electricity on the ground, which has a much better chance of sucess, then synthesize engine fuel with it. Diesel airplanes sound like a lot better idea than electric or hydrogen airplanes to me, plus the technology to do it exists now. It not only exists, you can currently purchase diesel converted Cessnas. I'm not considering becoming involved in an electric project, but it does look like electric may actually be achievable. Not a chance. The electric airplane, not the diesel. Diesel airplanes need some refinement to be generally usefull. Electric and hydrogen airplanes need new and major basic science breakthroughs which may not ever occur and right now are nothing more than a pipe dream. I believe Boeing's recent effort has demonstrated that electric fuel cell aircraft motive power is achievable with current technology. Hopefully Boeing's demonstration will provide some impetus toward improvement and refinement. Well, sure, if you goal is to spend a huge pile of money to get a motor glider up 3000 feet. The Boeing demo was PR for military products, pure and simple. -- Jim Pennino Remove .spam.sux to reply. |
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