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I can't wait for electric/hybrid aircraft.
Half of the threads here pertain to safety and high workload related issues connected to the antiquated way modern aircrafts are made and propelled.
Just below is a thread about a C152 engine quitting because of either a rich cut or carb ice, depending on who's answering. Not even injection engines are commonplace even though the offer more security. Cessnas new 162 Skycatcher? Carb - check. Just imagine if the above aircraft were hybrids. Until the new nanowire batteries get powerful enough in the meantime a hybrid solution with a small turbine APU would recharge a LiPo battery (like they've had and broken all records with in the R/C world for the best part of 20 years now). The battery runs a brushless electrical motor with 90% efficiency compared to the 20% efficiency of the combustion engine. Just imagine all the benefits: 1. No carb ice. 2. No need for complicated constant speed props (as electrical motors have linear power output and no sweet spot). 3. No TBO - only limited by bearing life. 4. No CO poisoning. 5. No shock cooling. 6. No rich cut. 7. No degradation at altitude, no need for turbos etc. 8. Built in Fadec (brushless motors you set a RPM setting and it keeps it through the controller, no matter what). 9. No need to check oil. 10. Much less weight - 15Kw (21hp) R/C brushless weighs less than 2kg. That means that a O-200 replacement would weigh about 10kg. That leaves a lot of weight for a battery.. 11. No dirt. 12. No vibrations. 13. No noise. 14. No leaning at altitude. I want to enjoy flying and the view, not manage a steam driven 100 year old system just looking to screw me up. I can't friggin' wait. |
The Moni is available now with electric power.They are getting over an hr from a 40 min charge. OK not much use for cross country, but as a motor glider you can thermal all day and go home on power for less than $6 (they say).
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There was an article in one of the magazines (I think Flyer) about a year ago where they did the calculation for a two-seater. From memory, a Twister. Based on the latest technology, particularly battery, they calculated that they could rip out all the fossile fuel stuff, add in electric motors, controllers and so forth, and fit sufficient batteries in the aircraft, remaining within MTOW, for 40 minutes of flight. And they made some very generous assumptions to get to that number anyway. So, not enough for any meaningful x-country plus VFR reserves. Battery technology has to improve dramatically for this to work.
Gliders need only a few minutes of power to get to a height sufficiently for thermaling. I'd never heard of that Moni, but that sounds like a fair application. As far as hybrids are concerned, well, they're nice for stop-and-go traffic, where kinetic energy can be converted into electricity and stored in the battery when the lights turn red, to become available again when the lights turn green. But this is not a typical usage scenario in an aircraft. Aircraft typically need continuous power and converting/storing that in an intermediate form is going to lead to efficiency losses in any case, and weight addition for no gain. If you want to use a light-weight turbine APU, just run the electric power from that APU directly to the propellor motor. Or even better, connect the propellor directly to the APU shaft. |
Interesting idea, although I suspect a truely electrical tourer is a while away.
On the hybrid idea, whilst an electric motor maybe 90% efficient, a small APU is not going to get any where near 20% efficient, so you would still be better off with a good old fashioned donk. If want rid of the nasty bits of a piston engine, forget the batteries, put a small APU in the aircraft, wire it up to an electric motor bolted to the prop and off you go. It won't be quiet, but you get around most of the problems with the old Lycoming. Plus you would have all the electrical power in the world for all the modern fancy nav kit. Mind you I wouldn't like to buy or maintain the APU, nor would I like to share a small airframe with one. 60,000rpm spinning just behind/infront of you? no thanks. |
I agree, while the hybrid thing makes a lot of sense on a car where weight is less of an issue, I would not want to carry two engines in an airplane (unless it's a twin)
I do however agree that the GA industry is hopelessly behind the curve and I find it hard to understand why we are still sticking to carbs and aircooling (even Porsche had to move on). There are a couple of promising developments going on though, Rotax abviously being one well proven and quiet solution. Another (less quiet) are the new generation of small turbines such as this: PBS Velká Bíte?, a.s. ... Turbovrtulový motor TP 100 Sonex are mounting the jet version on their new sub-sonex |
The revolution has already begun. This will be the first certified electric LSA.
YouTube - Yuneec International E430 Electric Aircraft But the beautiful thing with a hybrid is that you could take off on battery power, climb to your altitude and throttle back to economy cruise (which on an electric is probably below 50%). Now you start the APU. This ensures that the APU will be running at a higher altitude and consume less fuel. And all it needs to power is the economy cruise. It will also reduce noise considerably for take off. As you descend you windmill and generate electricity to top batteries up a bit. And should you really need to get down fast, you just regen more and make the prop/fan work as a speed brake. But sure, there are still obstacles to be overcome for a pure battery powered tourer. But they're closer than many think. Battery capacity has doubled in just 5 years. I've researched this quite extensively and what's important is power density, i.e. Wh/Kg. Newest LiPo batteries (like the R/C guys use) deliver about 400Wh/kg today. That means you could run a motor at full power of 400W for one hour. Or to put it in perspective of a C152 - a 182kg battery pack could make you cruise at 100% for one hour. In reality, you would never use 100% all the time on electric motors, so the endurance would probably be closer to 2 hrs for that weight. Not that far off - remember, you'd save not only on the weight of the fuel and the engine and that's gotta be an easy 150kg alone. Now, here's the interesting thing - nanowire batteries that have just been patented and are getting geared up for production have a potential power density of 4500Wh/kg. If they can deliver on that promise, then it's all over for the combustion engine. Bye bye. Gone. Obviously cost is also a factor for batteries, and to keep them healthy no more than 1000 charges are recommended. At the price of batteries today that would be a large sum of money, probably the equivalent to a TBO overhaul of your Lycoming. But the nanowire promise has the added benefit of dramatically reducing the price as well. It's closer than we think. I wouldn't want to be Rolls Royce, General Electric, Pratt & Whitney, Lycoming or Continental in 20 years time. |
Unless one of the snap up the innovators while they are small and use their name, presence and experience to get the hybrid certified and into the engines
Reminds me a little of the Dynacam (or axial) engine that really makes a lot of sense in an aircraft and with Piper having plans to manufacture it for the PA28 range (late seventies I think, someone might remember).....and it all stranded on an disagreement over how rich the patent holder should be allowed to get :ugh: I think these guys hold the rights now: AVEC | Axial Vector Energy Corporation | |
I find it hard to understand why we are still sticking to carbs and aircooling Air cooling: Light. Simple. Can not break (with a slight caveat for baffle seals and cooling flaps, which degrade gracefully, as opposed to a water cooling system that fails catastrophically). Sufficiently effective for a boxer engine, which happens to be the ideal shape for an engine that is to be mounted in the nose of an aircraft without a gear box or belt drive. Is the method used in engines whose development is already paid for, thus cheap. |
It's closer than we think. For experimental designs it sounds interesting. Give the EAA members and their likes a couple decades to sort it out, and then we can start discussing it. For normal category aircraft: No way this side of year 2035. We haven't even got the diesels sorted yet, despite their obvious theoretical advantages, and that technology has been around for a long time. The development costs, including getting it certified, would be astronomical considering the tiny volumes of light GA today. The days when any significant technological advance could be paid for by users of light GA engines ended when taxi, business and light airline operators went turbine. What we can hope for today is reusing some parts of what the automotive industry comes up with, but since their operating environment and requirements are entirely different, most of their technology can not produce a light GA engine that is better than an IO-360. |
What we can hope for today is reusing some parts of what the automotive industry comes up with, but since their operating environment and requirements are entirely different, most of their technology can not produce a light GA engine that is better than an IO-360. It's battery technology that needs to make a giant leap for electric power to become feasible for aviation use (and automotive use as well, BTW), but the rest of the components you need for an all-electric airplane (or car) are already available, and well proven. |
Well, the energy inefficiencies in aviation are staggering.
It's taken 50 years of jet travel and APU-equipped aicraft to come to this (Delta starts using it this year) - you'd think that'd be day one that would have been sorted out, but no: WheelTug plc Regular long taxis with all engines running, complicated non-GPS approaches following antiquated flight paths that waste millions of gallons - the list goes on and on. It's just very, very backwards and slow. I mean, the C152 I fly has 12.000hrs on it and was made in the early 70's. Only in aviation. |
BackPacker:
Good point regarding the electric motors themselves, but also regarding the batteries! And once you have the motor and the batteries, the hardest part remains: Systemization and system integration, taking that engine and those batteries along with all the other parts that will be needed and turning it into a practical, economical, reliable (both in terms of safety and dispatchability) and generally well functioning power source. Add certification standard development, certification (both aircraft and pilots; what differences training will be needed?), and so on and so forth. Those are not reasons why this isn't a good idea, but they are reasons for why it will take a good long while and be expensive. Again, in the experimental world it is a different matter entirely. This is exactly the type of thing the experimental category is intended for! Best of luck to them! :ok: AdamFrisch: Backwards and slow...? Slow, yes. Backwards, really? There is a difference between stagnation and maturity. By the 1950s (some would say the 1930s), airframe and engine technology for light aircraft had reached sufficient maturity for designs based on that technology to be "good enough" for many purposes. Once that stage is reached, a new design is not automatically much better than an old one. Taking into account aspects like reliability, maintainability, customer base, market positioning and so on, the older design can be better than the newer one. Or more commonly, the newer design is better, but not so much better that it really matters much in practice. When that happens, you will not see much progress in that particular field, but that is not stagnation, it is maturity. Stagnation would be when progress stops before the field is mature. Maturity allows one's efforts to be spent on other areas, in fields that are not yet mature and where progress really matters. The progress made in GA in the last 10 - 15 years is quite tremendous IMHO, and I think it is accelerating rather than slowing down. But the results are not seen on the outside, or in performance specifications; a C172B looks deceptively similar to a glass panel C172S, from the outside. The difference is found on the panel, and in terms of the functionality provided by the systems on that panel. As in so many other fields of technology, capability growth takes place in software, not in hardware. You may well be right that power plant technology will be an area of strong progress in a not too distant future, say the next couple decades or so. But I do not think it is fair to say that aviation in general, or GA in particular, is backwards or has been standing still in recent years. Avionics is not a mature field of engineering, and that is where most current progress is made. |
Add certification standard development, certification (both aircraft and pilots; what differences training will be needed?), and so on and so forth. Then consider that the potential savings of an electric engine over a Lycosaurus vs. the potential savings of a Rotax or diesel over a Lycosaurus are much greater, consider that once you have the basic integrated systems certification in place, you can just swap in and out larger or smaller motors, or add more batteries as desired, and consider the environmental angle. It's a great business opportunity, better than that faced by Rotax, Diamond or Thielert. For starters that means more investment money available to go through the certification process. And as for differences training: the UK CAA already has this covered by introducing the category of "Single Lever Power Control" (SLPC) aircraft, for which they indeed require differences training by a suitable instructor, but no specific exam. If Adam is right and those nanobatteries are indeed going to deliver energy densities (kWh per kg) approaching that of fossile fuels, for an interesting price from a TCO perspective, then I think the rest of the story (the other components, and the certification of the integrated system) is probably sorted in zero time flat. Oh, and then we'll probably run into the same problem that the automotive industry is already deeply aware of: where are the Amps going to come from to charge all these batteries? The power grid is going to need a serious upgrade to be able to supply even a fraction of the energy that's currently being consumed by road and aviation consumers in the form of fossile fuels. |
Apparently the power contained in aircraft fuel amounts to the equivalent of 12000Wh/kg, so even with the new batteries fuel has more energy. However, a combustion engine only turns 20-30% of that into power, whereas an electric motor will turn 85-90% of into power, so you'll never need to reach those power storage levels.
If the car industry is anything to go by, then the shift will happen pretty quick once things start getting in place. Just remember how quick the hybrids went from the car nobody wanted to the car everybody wanted. The Prius is a massive seller for Toyota and every manufacturer has some type of hybrid on the go. Fast forward 30 years. A board is going to have to be pretty convincing and persuasive if they want the shareholders to approve the costs of a gas guzzling Gulfstream G650 when they could be riding in an electric or hybrid bizjet that might not be exactly as fast or have exactly the same range, but get you there for a fraction of the cost. Imagine the badwill. Not to mention that the carbon excesses imposed by government on fossil fuels by then. They're never gonna get cheaper, that's for sure. Backwards and slow...? Slow, yes. Backwards, really? |
Carbs: Less sensitive to fuel contamination. Re electrics, as stated, the motor is not an issue. I have worked with model plane brushless motors and some bigger ones and 250HP is easy to achieve with a unit weighing perhaps 30kg i.e. ~ 1/10 of an IO-540 engine. The batteries are the problem... But even if suitable batteries are developed, you have to charge them from somewhere. We don't have the infrastructure to charge them in cars, and are not likely to have for many decades, which is why all mainstream-usage electric cars will be hybrids, perhaps with a small turbine to charge the battery. The power would all have to come from power stations and there won't be anywhere near enough of those about, for the foreseeable future. Airfields will never get the infractructure to support electric planes - who would pay for it? Most can barely afford to fill potholes in the runway... 1. No carb ice. 2. No need for complicated constant speed props (as electrical motors have linear power output and no sweet spot). 3. No TBO - only limited by bearing life. 4. No CO poisoning. 5. No shock cooling. 6. No rich cut. 7. No degradation at altitude, no need for turbos etc. 8. Built in Fadec (brushless motors you set a RPM setting and it keeps it through the controller, no matter what). 9. No need to check oil. 10. Much less weight - 15Kw (21hp) R/C brushless weighs less than 2kg. That means that a O-200 replacement would weigh about 10kg. That leaves a lot of weight for a battery.. 11. No dirt. 12. No vibrations. 13. No noise. 14. No leaning at altitude. I'd like to see electrics too (I work in electronic & mechanical engineering) but the economic case has to be present. They will also need to address battery safety issues. I know fuel is not that safe but it goes off only if you set fire to it. LIPO batteries often go off by themselves if damaged, overloaded, etc. and they release an awful lot of heat when that happens. |
Is that really the reason most planes still use carbs? I have never heard of fuel purity being an issue. Cars have had FI for many years. I fly a FI plane and would never ever buy one with a carb. I thought that carbs, with their lethal carb ice issues, are still used only due to tradition / certification inertia. |
More likely it is because of a bad fuel system layout which created many points at which water could settle, and since they had to recertify half the plane due to the FI, this was a reasonable juncture at which to implement changes which had been "pending" for many years but which they did not want to introduce alone because it would be an admission of a bad design :)
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TBH, on the car side I tend to view the current craze for the hybrid as a triumph of marketing and legislation over basic physics. At the end of the day all the power to drive the car has to come from the petrol or diesel engine. The only difference is that some of the time the power to drive from the car comes from the batteries but that pwer has to have been put into the batteries by the ICE. Just like if I pay for something with a credit card, my bank balance does not change but when the statement becomes payable my bank balance does change.
Against that the hybrid has to lug around a lot more weight, has to be more expensive to manufacture and as the batteries will have a finite life in terms of time and/or cycles will have periodic big replacemnet costs. In the case of the pure electric cars at the moment I suppose that for someone who only does short trips they might be practical but you will still need to either own or hire a different car for any longish journey. Same problem as the hybrid as regards bettery life cycle. Not emmision free as they just move the emmisions from the tailpipe of the car to the chimney of the power station except possibly in France as they have a fair bit of nuclear. But lets say that new battery technology, nanowire, ultra capaciter or whatever, becomes available, and it probably will. The electric car should now be practical as should the electric light aircraft, provided enough money is thrown at it. However I can see one huge potential snag both for cars and aircraft. For it to be pracical the batteries have to have really high energy storage capacity. What happens when you do any physical damage to such a battery? That energy is going to go somewhere and not in any controlled manner. |
Have a look at this. Here's your dream come true (albeit in a Wrightish brothers kind of duration), Adam :ok:
Interesting to note that they set their record with battery power but are moving on to fuel cells. Discuss! |
Interesting to note that they set their record with battery power but are moving on to fuel cells. Discuss! I don't know what the energy density of hydrogen storage is these days (in kWh/kg) but if it's better than what batteries can deliver these days (400 Wh/kg for LiPo according to one of Adams posts, above) then it makes sense to use hydrogen as an intermediate energy storage solution, instead of batteries. You do have the added weight of the fuel cell (converting the hydrogen into electricity) but I don't think they're that heavy. And hydrogen requires more infrastructure on the ground, both for production and storage, vs. an all-electric solution. Oh, and at some point in time the general public will remember that the Hindenburg was also filled with hydrogen. That may become a significant psychological barrier to widespread adoption of hydrogen technology. |
At the end of the day all the power to drive the car has to come from the petrol or diesel engine. 1) A car spends a lot of its time at low power, which is OK with electric but a petrol engine is inefficient, and would be better used running at a higher power setting charging the batteries. In fact the efficiency situation is so poor that a small gas turbine (which is normally a lot less efficient than a piston engine) is viable, just to run more or less nonstop, as the battery charger - e.g. here. (I know the people who designed that one). 2) You can do regenerative braking 3) You can do direct drive to the wheels, which avoids gearbox (and diff) losses But I agree the technology is in its infancy; IMHO largely because nobody has yet been able to do a commercially viable design "properly" i.e. direct drive brushless motors on each driven wheel, and a turbine charging the battery. There are some major long term issues. If all current liquid fuel vehicles were suddenly charged from the mains, one would need to build many more power stations and totally overhaul the distribution grid. Especially with the steam cycle limiting PS efficiency to around 50%, it would mak sense only with nuclear fusion, which has had a great future for about 50 years now :) And, because mains electricity is currently much cheaper than petrol (per kWh), electricity would have to rise in price massively. Not sure everybody would like that. |
The fuel cell is looking a lot more like a non starter. For the huge cost (mainly due to the platinum needed in them) and difficulties with hydrogen production and storage. Very little advancement has been done recently.
I think power cells and batteries have a brighter future. Yes, the microturbine running a generator is interesting as it delivers pretty good efficiency at max rpm and at altitude. It's also lightweight. And the turbine stage that goes out to a shaft to generate power can also be made a lot more efficient than if you would just take a turboprop type solution - the turbine stage at the end that converts the hot gases to shaft power could for instance be made as a Pelton turbine. Peltons are very efficient at capturing high speed streams and converting it to shaft power. Or the free piston generator is also a very interesting development, albeit not as light or vibration free as a turbine. But probably a bit more efficient. Basically, it's just an opposed piston running in a tube, but instead of converting the linear motion to a circular motion in a crankshaft that then drives a generator (with all the losses that entails), the pistons themselves act as a magnets and travel back and forth inside a coil (AC current): Free Piston Power Home Here's a clip showing a simple free piston generator (ignore the Stirling bit): YouTube - RESONANT STIRLING ENGINE GENERATOR Or here: YouTube - Ubiquitous Electric Power Generation Devices : DigInfo |
There aren't enough rare earth elements available for the requisite magnets in DC motors. If adopted, the price would go through the roof, way beyond what the auto industry could / would pay. Similarly there is a supply problem with Lithium, if that is the battery technology employed. See the Jack Lifton Report (sign up to read part 1)
In hybrids, one of the limiting factors is that electric motors overheat, killing the magnets permanently. It's one of the principal reasons that hybrids switch back to ICE drive. Thus no point in having large battery capacity! Having hub motors might lead to serious unsprung weight issues in cars. Employing a small ICE running at constant speed / load solely powering a generator which would both power the electric motor and/or charge a battery and/or other storage technology, would provide significantly higher MPG. Wheeltug, as mentioned above, is based on the Chorus Motor which doesn't have magnets. It has automotive potential See ChorusForCars. There hasn't been much news from Wheeltug recently, but things are pretty busy on the inside. (I'm involved) |
New Battery technology
There is a new Lithium battery that is due out in under 5 years.
Lithium Air, this battery could have an energy density of up to 5kwhours/kilogram. IBM are working on it and Japan with some success. As Avgas is 12Kwh/kg but engines are only 25% efficient then it means only 3kgwh/kg is used, as electric motors are 85% then any battery about 4kwh/kg or over is about the same as Avgas. These batteries can be recharged or the lithium & electrolite with a cassette can be replaced to recharge them, 10 minute to refuel. So a rechargable or lithium fuel cell. Please forget about hydrogen it will never happen, just to difficult to implement and lower over all efficiency never mind the cost. So by 2020 nearly all cars will be direct electric drive and light weight in wheel electric motors/brakes, no mechanical brakes, will be normal, 120Kw at 66lbs. These are available to day, Volvo and Ford are building demo cars and trucks with them. So electric aircraft will be feasible, with good range and carry capability. |
There aren't enough rare earth elements available for the requisite magnets in DC motors. If adopted, the price would go through the roof, way beyond what the auto industry could / would pay |
Brushless motors are used all over industry The key issues for an electric aeroplane are likely to be energy density of power sources and airframe efficiency. Energy recovery, in-flight generation and reliability may have a part to play, but until the first two are cracked, routine powered flight of significant duration is inevitably limited (though motor-gliding is another matter). I don't agree that the noted factors afflicting light aircraft petrol engines are actually non-issues |
Some of the more interesting DC motors use masses of electronics (eg the so-called "Switched Reluctance (SR) Drive) to improve efficiency, but possibly making them difficult to get certified for aircraft use. The technology for this is several decades old and anybody could take an existing plane (my TB20 would do just fine) and stick a 250HP direct drive brushless motor in there (a suitably ruggedised version with a massive shaft and bearings because it has to carry the prop and the axial loads) and an off the shelf variable speed controller, plus a lump of concrete for W&B reasons because the assembly will be so much lighter than the old engine, and ..... sit there and stare at it because it won't be going anywhere :) The battery, and how to charge it in practice, will be the major issues. It goes without saying that certification would be a major project, regardless of what motor is used. The motor will be the easy bit. Demonstrating safety of the battery would be something else. All you need is a defect within the battery, or a short downstream, and you have a massive fire - unless the battery technology is very different to the present LIPO ones. |
You will also have to contend and design for pretty high voltages as rpm is a function of volts in these motors. There are ways around this with big outrunner motors that turn slowly or with parallel windings. But as it is with the motors now used in electric experimental flight (often adapted from r/c), they're often running around 200V or more and that is a killer should you come in contact with it.
As mentioned, the brushless motors are not the problem from a certification standpoint, but the batteries and the power distribution is. We'll see how this develops in the coming years. |
I don't think 200V per se is that big a headache - though 200V DC can get quite interesting when it comes to handling faults. I also suspect that a fuel cell - perhaps a methanol type - would not be an entirely dead duck. And it's quite conceivable that a novel fuel linked to a novel fuel cell coupled to a modern control system that manages a stock motor could be more reliable than a 40-year old LyConting. But all that new-fangled stuff requires R&D for GA application with certification on top and I suspect that there is your problem.
(It'd be one fabulous PhD project though wouldn't it!!) |
The micro APU idea has been a dream for a very long time. Nevil Shute (Norway) wrote about it in his lovely model engineering novel "Trustee from the toolroom". Isaac Asimov has a micro APU of prodigious power in "Foundation and Empire" that welds itself into a solid block of metal in the event of tampering. And Scott Crossfield writes eloquently about the tribulations of the micro turbine APU's in the X-15 that would seize solid inches away from his head in "Always another dawn". But despite this, for 50 years or more, the micro APU has remained elusive.
One reason is certainly materials science - bearing cooling being one and demagnetisation being another, both related to the immense energy density required in these hypothetical machines. Even the tiniest inefficiency, converted into heat as it must be, will push the machine past it's materials limits. Perhaps these restrictions will be overcome, but if they are, I suspect there will be many more pressing (and financially rewarding) applications than private aeroplanes. I'd love to see a successful micro APU giving perhaps 100KW for maybe 20Kg or something in place of diesels weighing 1/2 ton or more that never seem to work when needed. There would be plenty of server centres, hospitals, and so in line for that. |
Not sure. Diesels are dirt cheap and they work often enough to be useful, especially if you have more than one :)
There was a well known "innovative" company (my shares in it were down 99% when I sold them ;) ) which tried to take on this market and totally failed. They did develop some generator technology which can work at the high RPM that you get out of a turbine and are trying to sell that, AFAIK. I suspect the existing engines will see most of us out... 100kW in 20kg would, assuming a small package and even high efficiency (say 50%) mame an impressive space heater :) You'd need quite some airflow to get rid of that 100kW loss when trying to make a 100kW real output. |
Aren't DC brushless motors just normal 3 phase ac motors driven by half a variable speed drive?
If that is the case then the weight of a 100hp motor is going to be something else. We have a fair few at work and they come in at significant fractions of a tonne. Yes you could shed some weight from the casing but the copper windings are going to be a serious weight. Unless you intend to run at 400vdc then the current draw for full power will mean some pretty heavy gauge wire involved. Also aren't LiPos prone to failure or worse unless charged very carefully? So not only do you have to lug a shed load of copper into the air you then need to drag along a complex battery charger as well. I suspect that this sort of thing won't be certified anytime soon the market is far to small to recoup the cost. It may take off in a small way for permit types or more likely EAA experimentals but spam cans won't be electric without some major advancements in superconductors. |
They're very light even with all that copper winding. I can get an off the shelf 15Kw (21hp) DC brushless r/c motor that weighs 2 kg. Add the controller to that and you're looking at 3-4 kg, tops. There is no combustion engine that comes close to that, not even a turbine can deliver that kind of power-to-weight ratio.
All one has to do is look at the revolution in the r/c field. The electric aircrafts shatter everything and are not even allowed to compete with the nitro/turbine ones because they cleaned up so much - they had to create an electric class just for them. Now, naturally they don't need to take much notice of endurance, so they can use light battery packs and overpower them, but still. Electric makes sense. We just need a way to store the energy now. When that's licked, it's game over for the combustion engine. |
Aren't DC brushless motors just normal 3 phase ac motors driven by half a variable speed drive? The higher the voltage is used, the more efficient the electronic inverter can be, but they are very efficient anyway - well into the 90s % region. There really is absolutely NO issue with the motor. If not off the shelf (due to the thick shaft with a prop flange on the end :) ) it would nevertheless be trivial. The inverter would be trivial too; this is off the shelf technology made by many firms e.g. this. The battery, and charging it practically (where from???), would be the fun bit :) But the charging process is again straightforward and established technology for LIPO or whatever. In the RC model world, the funny thing is that the "poor" flyers use fuel. Electric stuff is better in every way but it is "less authentic" and most cannot afford to buy enough of the Ł100 batteries to last them the day out :) My son has had a few of these and smashed them up in the obligatory crashes. One of bis brushless motors had to be dug out from about 6" deep in the soil, but iw was fine after some cleaning up. It soon gets very expensive and now he flies mostly with the nitro engines. But the other day he blew a hole in a piston so that was his savings gone for a bit :) The thing I find more puzzling in aviation is why the hell do autopilot servos use brush motors. What you are supposed to do - and this applies to a TB20 as to a TBM850 or a King Air - is to fly until the motor (i.e. the autopilot) fails because there is nothing left of the brushes or the commutator (the two seem to have a similar life). There is no precautionary maintenance, the brushes are not replaceable, and the "motor repair" is a whole new or overhauled servo at at least $2000. This application is crying out for either brushless or microstepped stepper motors but there seems to be a total lack of imagination in the industry which keeps turning out the same old garbage. I wonder if the new Garmin autopilot uses brushless motors... |
An Interesting Thread
Some photos of the current, flyable, state of the fuel cell art for small aircraft. Not much room left for anything else! Boeing Fuel Cell Work on Flickr - Photo Sharing! Boeing Fuel Cell Work on Flickr - Photo Sharing! Boeing Fuel Cell Work on Flickr - Photo Sharing! This will not be easy or soon. Charlie |
Any idea what the fuel is ?
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The Fuel is H2O
Charlie |
My previous post was much to short!
This is a Hydrogen Fuel Cell / Lithium Ion Battery Hybrid Concept. More Information on this project can be found here. Boeing: Boeing Successfully Flies Fuel Cell-Powered Airplane Charlie |
The Fuel is H2O Hydrogen is bulky and heavy to store and perceived as dangerous but makes for quite efficient power conversion. Methanol is easier to store but poisonous. It's difficult to get good efficiency. Ethanol is easy to get hold of (ferment anything you like) and is already part of the distributed fuel chain. However, ethanol cells are in their infancy. All can be environmentally neutral, ultimately simply releasing recently stored solar energy (unlike many so-called environmentally friendly electric vehicles which for the large part just move the point of pollution further up the chain) Given the huge investment going in to fuel cells we should see some significant steps in the short and medium term. The problems (and I'm sorry to say I'm merely a bystander in this) seem to be around the catalyst that promotes reaction. |
In the end, the challenge is energy density. You can get a lot of heat out of a kilogram of avtur and rather less from a kilogram of lead-acid battery. Battery technolgy is still at the wrong end of the scale.
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