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#11
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Well, some research group is claiming to have come up with a new way to
store hydrogen, which may make it more feasible as a vehicular fuel: http://www.sciencedaily.com/releases...0907102549.htm http://denmark.dk/portal/page?_pagei..._schema=PORTAL http://www.amminex.com/ http://www.thewatt.com/modules.php?n...rticle&sid=763 http://www.investindk.com/visNyhed.asp?artikelID=13670 But admittedly, it's very new and as yet untried in the marketplace. |
#12
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Richard Riley wrote:
On Mon, 03 Oct 2005 10:52:49 +1300, Frank van der Hulst wrote: wrote: : And hydrogen is a lightweight fuel too, for lower fuel load. : But suppose you want some extra juice sometimes, for more : maneuvering/lifting power. : :Hydrogen is only a lightweight fuel in its uncompressed, gaseous form. :In fact, in terms of energy per Kg, hydrogen is not a good fuel. Storing :hydrogen in sufficient density to be useful requires strong (read heavy) :tanks. Liquid hydrogen has the most energy per pound of any chemical fuel. It has 39,000 Wh/kg, gasoline only has 12,200 Wh/kg. Unfortunately it is also not very dense - even in it's liquid form. Liquid hydrogen has a density of 0.07 grams per cubic centimeter, whereas water has a density of 1.0 g/cc and gasoline about 0.75 g/cc. Oops, yes, you're right. It was in terms of energy/volume that hydrogen is poor, NOT energy/mass. Therefore the container to hold your liquid hydrogen needs to be large. It also needs to be strong, and therefore heavy. Therefore, as Richard said, hydrogen won't be a practical aircraft fuel unless the storage issue can be solved. |
#13
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"Frank van der Hulst" wrote It *might* be possible that diesel-electric system would be lighter than pure electric or pure diesel. I'm from Oklahoma. Show me! A small diesel could be optimised to run continuously at its most economical RPM, It would already have to have a gearbox for a heli, so it can run whatever RPM you want. An electric motor would also have a gearbox. Yes I know, there are low speed electric motors, but they are huge and heavy. producing only a little more electricity than needed to drive the rotor in level flight. There will always be losses, driving a generator, then a motor. You will have to have at least 10% more power output by the diesel motor, just to break even, and more than that to charge batteries. So lets see, we have to have a gearbox both ways, no change in weight between the two. We will have to have a bigger diesel to take care of losses, so penalty goes to electric. We would have to have batteries for electric, so more penalty for electric. Since our electric has gotten heavier, we will have to have a bigger engine, and more fuel, so BIG penalty for electric. For additional power, electricity from the battery would also drive the rotor. When descending, the battery gets charged faster. What you are talking about is like an autorotation. The blades in an autorotation have to go to negative pitch, just to make the blades maintain RPM, and to get more power to generate electricity than a plain autorotation, they would have to be at even more negative pitch. You would have to descend so fast to get the rotor to produce electricity, your passengers would freak! -- Jim in NC |
#14
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Morgans wrote:
"Frank van der Hulst" wrote A small diesel could be optimised to run continuously at its most economical RPM, It would already have to have a gearbox for a heli, so it can run whatever RPM you want. An electric motor would also have a gearbox. Yes I know, there are low speed electric motors, but they are huge and heavy. The whole point of these wheelmotors is that they are smaller than equivalent DC motors, and turn at low speeds. The numbers I've seen are 110-150rpm. See http://www.smartmotor.no/products/quiet_traction/ -- this talks about wheelmotors in relation to wheelchairs, and claims twice the efficiency over traditional DC+gearbox systems. You could think of the generator/motor combination as an electrical rather than mechanical gearbox. Another interesting site is http://www.killacycle.com/ -- an electrically powered drag bike that gets 9.450 seconds @152.07 mph over the 1/4 mile. Still a long way from the 5.895 @ 238.22 nitro powered world record though. producing only a little more electricity than needed to drive the rotor in level flight. There will always be losses, driving a generator, then a motor. You will have to have at least 10% more power output by the diesel motor, just to break even, and more than that to charge batteries. So lets see, we have to have a gearbox both ways, no change in weight between the two. We will have to have a bigger diesel to take care of losses, so penalty goes to electric. We would have to have batteries for electric, so more penalty for electric. Since our electric has gotten heavier, we will have to have a bigger engine, and more fuel, so BIG penalty for electric. But the diesel only ever runs at one speed... it's most economical. I'm assuming that there will be significant weight savings in that. I may be wrong in that assumption. I do know that having a car petrol engine which can potentially deliver a lot more horsepower means that it uses more fuel at lower horsepower output. Maybe this relationship doesn't apply to diesels. For additional power, electricity from the battery would also drive the rotor. When descending, the battery gets charged faster. What you are talking about is like an autorotation. No. I'm saying that when descending, less power from the engine/generator goes to the rotor, leaving more to go to the battery. |
#15
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manofsan,
Differential rotor speeds -will- rotate the aircraft, but will that turn the aircraft, in level flight, or just rotate the aircraft in yaw? The hard part about differential rotor speeds is not in yawing the aircraft. The hard part is NOT yawing the aircraft, constantly. Gyros might do the job of balancing rotor speeds for you (with *more* expense and complexity), but you would still lose the safety advantages of simplicity, and maintaining control if one motor fails. The spider gears and one motor might not maintain altitude, but you could still move forward and steer as you descend slowly, to select a good place for the BRS deployment. In a deployment situation, one motor could still be used for a last-minute burst of power, to soften the parachute landing. Recovering energy by auto-rotation would mean a lot of weight and complexity for very small gains. Aircraft are like boats, always fighting drag, and if aircraft could get anything back on descent, they would have to expend a lot more energy to do the climb, first. You can never win against drag, so at best, we just try to cut our losses, up front. I hear Boeing is working on a single-engine plane using a fuel cell and an electric motor to provide propellor thrust, so that technology seems realistic. New hydrogen storage systems can derive their hydrogen "fuel" from other liquids, rather than highly pressurized hydrogen gas, which would need strong and heavy tanks. The WaveCrest motor idea looks good, too. -- (Replies *will* bounce, unless you delete the letter A from my email address) Cheers, Red wrote: Hi red, thanks for the great ideas. Hmm, I read about how a coax design can use differential rotation speed between the 2 rotors for the purpose of turning the aircraft. That'd be pretty easy to do with a wheelmotor for each rotor. Here's a link to a new kind of wheelmotor which is attracting attention: http://www.wavecrestlabs.com The company is headed by General Wesley Clark, former NATO commander. Regarding portable fuel cell for propulsion, here's another link: http://www.intelligent-energy.com/in...6&artID=3 709 And hydrogen is a lightweight fuel too, for lower fuel load. But suppose you want some extra juice sometimes, for more maneuvering/lifting power. Then use the new Toshiba battery: http://www.dpreview.com/news/0503/05...sh1minbatt.asp It can apparently discharge and absorb energy at a very high rate. This might be useful for using regenerative braking to recover energy from your rotor when you're reducing airspeed/altitude, since a wheelmotor can convert torque/rpm back into electricity. Once you've landed, regenerative braking would allow you to quickly bring the rotors to a stop while recovering energy from them. I'd also imagine the electric motors would be quieter too, so your eardrums don't take a beating. |
#16
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Richard Riley wrote:
So you build your aircraft engine so it's best fuel economy is at full throttle. If it's not getting it's best economy during decent and landing, that's fine, it's at idle anyway. You must be thinking of fixed-wings Richard. A helo's engine only goes to idle during and auto not during decent nor landing. Actually during landing a helo uses a whole lot of power, more than while flying (due to loss of translational lift). Bryan "The Monk" Chaisone |
#17
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Richard Riley wrote: Believe me, I've been doing the trade studies for the last 3 years. You can't buy a COTS fuel cell, and the volume required to store H2 (not to mention the handling difficulties) mean it won't be used as a fuel for anything but very high end, special purpose machines for a very long time to come. How does liquified methane (at high pressure, ambient temperature) look to power a conventional internal combustion engine, or perhaps even a methane fuel cell? I think that methane requires somewhere around 3700 psi to compress it into a liquid at normal temperature, surely there's got to be some carbon-fibre reinforced, aluminum polyester-lined composite tank technology available nowadays that can handle the pressures necessary to handle non-cryo liquified methane, without being prohibitively heavy for an aircraft. Methane has a motor octane rating of around 130 in a piston engine too, and you certainly won't be needing a fuel pump, just a good strong pressure regulator / phase change heat exchanger/gassifier at the tank's output valve to feed a direct fuel injection metering system for the engine. You could probably employ the phase change heat exchanger as a clever way to air-condition the cabin too! (just make damn sure of no leaks) |
#18
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Richard Riley wrote:
What percentage of a helicopter's flying lifecycle is spent at or near it's rated power output, and what percentage is spent at a small fraction of that rated power output? About 100% of the time Richard, more power to fly higher, less to fly lower. It only goes into idle while NOT flying. Bryan "The Monk" Chaisone |
#19
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Here is yet another interesting design from that same website:
http://www.gizmag.com/go/3107/ I wonder if this could be converted into a gyroplane? Here's how I imagine it. sorry, my ascii art isn't good enough to reproduce the chassis, so I just drew the tires (which of course have the electric wheelmotors in them): ========== | | ( o----------------+ ======== | | =========== Note that the "o-------------+" is supposed to be the rotor mast folded back along the longitudinal axis of the craft. Okay, I guess that would require the craft to have some kind of upper fuselage canopy for the mast to attach to. The "o" is the base of the mast which attaches to the upper fuselage canopy, while the "+" is where the rotor head would be. But the rotor mast wouldn't have to be very long, since it doesn't need much height for its rotors to clear the rest of the craft. The rotors themselves would be bent forward in V-shape from the rotorhead, with their tips clipped to the sides of the fuselage/chassis. So the wheelmotors roll the craft along the ground until it picks up lots of speed. Then the rotor mast pops upright, the rotors are freed and start spinning overhead. The craft then takes off like a gyroplane, and once airborn the front tires swivel to face frontwards to act as fan-props: || ||____ || | || | ( + ======= || | ||___|__ || || Heh, very James Bond-ish, huh? ;P |
#20
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Frank van der Hulst wrote:
wrote: And hydrogen is a lightweight fuel too, for lower fuel load. But suppose you want some extra juice sometimes, for more maneuvering/lifting power. Hydrogen is only a lightweight fuel in its uncompressed, gaseous form. In fact, in terms of energy per Kg, hydrogen is not a good fuel. Storing hydrogen in sufficient density to be useful requires strong (read heavy) tanks. Unless you are driving an anti-static engineered lifting body shaped dirigible, in which case, compressing or decompressing a little of the surplus fuel / bouyancy medium using a "bouyancy bladder" device allows ascent and descent without actual fuel expenditure, except that required to compress the gas when descending. Quite the inverse of a normal flying vehicle, where energy is expended to ascend. Has anybody analyzed that in terms of fuel efficincy? Terry K |
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