So you argue that instead it's worthwhile to lug around an extra electric engine plus a significant amount of batteries for the duration of the flight, just to get a little oomph during take-off?

Don't get me wrong. IF we can get energy storage (batteries) sorted and IF we can get the grid updated so that it is able to deliver the power required to charge our batteries relatively quickly, I think 100% electric is the future. First for cars, later on for aircraft.

But hybrid aircraft, sort of like a Cessna Prius? I don't think so, particularly not if the electric bit has to be charged at some point from the fossil fuel bit of the aircraft somehow. Aircraft normally don't brake (so no regenerative braking possible) and they don't crawl along in traffic jams or city traffic - the places where hybrid cars can achieve the most fuel savings.

A hybrid car on a constant highway speed uses almost exactly the same amount of fuel as a normal non-hybrid car. And that scenario is by far the best comparison to an aircraft in flight. Minus one thing: The weight penalty for aircraft is much higher than for cars. So carrying around all these batteries will have more impact on energy required in airplanes than in cars.

That assumes that the efficiency at 100% max rated power is any better. It won't be.
This changes a lot once one takes into account the theoretical maximum 40% efficiency of the steam cycle used to generate electricity (except a gas turbine driving a generator directly).

I don't think a hybrid plane makes any sense because the whole case for it in cars hangs on a) a car using little power most of the time and b) energy recovery from braking. Neither of these apply to planes.

I reckon hybrid will make sense in all forms of transport when

a) power density increases. LiPo is getting there, but the high density stuff is still in research labs, and a way off yet, and

b) when power generation comes from something much smaller than an engine, such as a fuel cell, whether methanol, hydrogen or lpg powered

I think pure battery power is a way off, partly due to the energy density mentioned, but more specifically due to the recharge capabilities. Even where batteries have been designed that can take a huge charge current to recharge quickly without boiling, the power infrastructure to get it to the charging point is not there. National grid would have to redig everyone's driveway and build new substations to make it possible!

Having said all that, I can imagine a day where a polymer based battery is used as structural components to the aircraft, as well as power. At that point, mass and power density take on a whole new meaning, as you are replacing more than just a power plant.

As for regenerative braking, it really isnt all that worth it! It helps a little, but I cant see it ever being of true value flying. It works for cars since they spend most of the time with very light loads, need a little push from the electric motors sometimes, and spend a lot of time coasting downhill. For boats, they are worth it since the wind is moving the boat, so you might as well tow a generator and get the water flow to work for you, but we are talking tens of watts, not hundreds or thousands.

From my limited experience of aircraft so far, except for gliders, when you turn the engine off or to idle, the thing heads down pretty darn quick. Even if you could generate hundreds of watts of power during that time, what you going to use it for?

Interesting discussion though!

Going off topic a tiny bit here but who an earth would fly an electric aeroplane, I personally couldn't think of anything worse... changing batteries like a bloody torch, humming along with an engine which feels like a fan. I agree it would be environmentally friendly but take all of the fun and what we know out of flying. :(

Well, other than a reduced noise level I don't think there's a lot of difference between flying electric or flying on fossile fuel. Especially if you fly FADEC equipped aircraft today already.

Yes, you only have one "load" lever instead of throttle, mixture, prop, carb heat, ignition and maybe a few other knobs and dials but I personally have never found those to be an integral part of the "fun" of flying.

Not to mention getting your hands dirty when refueling. Especially the smell of Jet-A can linger for hours.

(And electric aircraft can be turned upside down without needing inverted fuel/oil systems, header tanks and whatnot, so they're great for aerobatics - apart from the weight issue of the batteries.)

Point taken and I agree flying is flying wheather it be by glider, microlight, jet or even balloon, but I suppose people (including myself) fear change and disapprove in things they do not yet have knowledge about. But fossil fuel aeroplanes will always be needed surely to teach CPL students in complex singles and for ATPL training? Do you think fossil fuel engines/planes will one day be a thing of the past?
:E

Yup, given that one day, fossil fuels will be a thing of the past too.

Other factors when considering electric propulsion are instant availability, simple controls, lack of altitude effects, no icing or fuel contamination issues, very accurate range/endurance information and superior reliability. Also, not being surrounded by large amounts of flammable liquid in an accident is a bonus.

At the moment, as pointed out in this thread, battery tech. hasn't advanced to the stage where it is close to fuel in terms of energy density but the form factor is much better, i.e. you can put batteries anywhere, like the wings, whereas an engine is a big lump with aerodynamic and/or balance problems, wherever you put it.

It's very simple really.

An electric plane is trivial to do.

You could replace an IO540 with a brushless motor, a speed controller, and a load of bricks to make up the W&B, all off the shelf.

I reckon it would take under a week to do it all.

Might have to get a custom motor made, with a thick shaft, a prop flange, and a strong case, with IO-540-compatible mounting points.

Stick an "Experimental" sticker on it and off you go.

There's no contest.

The only issue are ................... the batteries ;)

I dont know, just do away with the pilot and pax and transfer to the model flying thread. ;)

You're approaching a flying hybrid too traditionally. I'm not talking about adding a slightly larger starter that can "help" out during takeoff on a Rotax or Lycoming. No, the combustion engine has to go completely. I'm talking about a brushless electric motor in the front, nothing else. A battery and a turbine APU in the tail running a genset. Just like in the airlines.

The battery in this case made smaller and less heavy as it's only designed to be an energy storage device and be able to propel for maybe 30mins on its own. And the APU wouldn't have to be designed to excruciating standards as if it fails - you still have the battery that can execute a safe landing.

That would be lighter than a combustion setup and have all the benefits of electric and fossil. And even if it's the same weight, it's still much more desirable as it eliminates all the crap you to deal with with reciprocating engines.

As a side, and I say this owning two ancient Lycoming GO-435's on my AC520 (and I love they way the sound), but the problem is the combustion engine and the people that make them. They are the most traditionalist bunch I have ever come across and they've set aviation back 50 years. Let's talk some examples:

1. Why isn't the starter and generator combined to save weight? Ah, dunno, it works, don't mess with it...

2. Why are there still carburettors when the rest of the world moved to fuel injection years ago? Ah, dunno, it works, don't mess with it...

3. Fadec? Ah, dunno, it works, don't mess with it...

4. Will disintegrate if not fed ancient and eco unfriendly Avgas? Ah, dunno, it works, don't mess with it...

5. Magnetos that break mid flight when the rest of the world has had electronic ignition that doesn't brake ever for 20 years? Ah, dunno, it works, don't mess with it...

6. Exhaust Turbo that run the generator instead so you're not siphoning power from the engine? Ah, dunno, it works, don't mess with it...

The list just goes on and on. They're dinosaurs made by people why have had it far too comfortable and have not had to innovate. This is the drawback with type certification - once you're on paper as the engine that a type cert aircraft can use, they have you over a barrel. They don't need to do anything after that except cash your checks.

It's not so simple

They do exist, on jets and turboprops. They are quite pricey... not your $300 starter and your $300 alternator. You are looking at $10k (TBM850)

You do have the choice of FI so nobody has to fly with a carb anymore. I wouldn't if you paid me for it.

FADEC is fairly complex, requires sensors, electronics which have a poor history of reliability in GA (largely because there are very few competent electronics people in GA) and it would not deliver more MPG in cruise than a correctly leaned engine.

Engine efficiency is strongly dependent on the compression ratio...

Again, electronics reliability. A poor excuse, sure. But if you had electronic ignition it would need its own alternator. Unlike a car whose engine stops when the battery goes flat.

That has been done, many years ago, but the energy recovery is tiny, for all the hassle you get. Also, making a generator which runs at tens of thousands of RPM is non-trivial. It has been done in recent years, for small turbine engines (look up Bladon Jets for example).

The new Skycatcher has a carb and carb heat. Don't think there's a FI option. This is on an aircraft that hasn't even been released yet - the newest of the new!

My dinosaur Aero Commander from 1953 has an autolean function - you never touch the mixtures as it leans itself by barometric pressure. This is 60 years ago and they still want me to believe it can't be done in this day and age electronically? They're just cheap and complacent, as simple as that.

Oh well, it was built to be cheap and light (flimsy) and I would not fly one anyway. Carbs are a little bit cheaper than fuel servos.

Firstly, that system uses a diaphragm which is known to burst, and the resulting rich cut stops the engine (if at altitude) unless you are really on the ball and pull the red lever fast.

Secondly, the system might do a general form of altitude compensation but it won't do any kind of thermal engine management for say a climb from SL to the aircraft ceiling (constant EGT all the way up). It also won't give you the choice between best economy (peak EGT or slightly LOP) and best power (about 130F ROP); this is very relevant if trying to fly anywhere near the operating ceiling, and requires (in your case) a manual mixture control all the same.

Altitude compensated carbs have been around for yonks but they do only half the job, and in any case leaning manually is no hardship. It is a trivial non-event, if you have EGT and CHT instrumentation.

If there was some kind of magic bullet which would bring a dramatic improvement to the old engines, it would have been done long ago.

Sure one can do small improvements but the adoption would have been small.

An oxygen sensor in the exhaust would give you the potential for accurate peak-EGT control but it would not deal with the need to fly ~ 150F ROP during climb, for thermal management of an engine which for weight reasons cannot deliver 100% of max rated power while at peak EGT because it cannot dissipate the heat which would be thus generated.

Nothing short of a full FADEC is worth having, and the history of those working reliably is hardly good. In aviation electronics, one is kind of grateful to have a good working radio!

I drive a nice old 1995 Toyota import and while it is built like a tank, I have had two engine failures through alternator failures. In this case, you have maybe 10 mins (at night) before it stops. A bit like a DA40TDi then ;) Would I buy one of those? What do you think?

Technically, nothing keeps us from having engine electronics with a degree of reliability acceptable for light/general/recreational aviation. And that would be a great improvement. Yet there is none on the market today, the development would be expensive and there is but little sales volume to make up for it.
For lack of anything better, we make do with automotive electronics, which have good reliability when compared to traditional automotive electrical systems, but aren't really good enough for us fliers.
For one example, I understand Rotax 4-strokers are often (or even as a standard?) equipped with electronic ignition from Ducati motorbikes.

You might be surprised how small that difference actually is. I was much surprised on seeing an electrically powered trike demo'ed, and finding it quite as noisy as the others. The greater part of noise obviously comes from the prop.

Yeah, but you do have to be careful in case you dont hear them coming and they reverse into you....erm ?:confused:

Not any product that was made in 2011 and has a Cessna label on it is neccesarily good. Using the Continental O-200 instead of Lycoming IO-233 (which isn't yet certified) was one of the major mistakes in the design of Skycatcher. Using carbureted Lycontinental engines on new trainer in 21st century is just bad, you can't even lean them properly. OK, they do 100°F ROP without any problems, but if you want to get near optimum BSFC, most of them needs full throttle (well actually it's usually better to close it just a bit to create some turbulent airflow, which distributes fuel more evenly between cylinders), but for using full throttle at normal cruise powers (75% or below), you would need to climb to 5-6 thousand feet. As IO540 states, the altitude compensating carbs or fuel pumps do simplify things, but you lack the control over what kind of mixture do you want to have - best power for fastest cruise, deep LOP for maximum endurance, ... And using FADEC and "new" technology, such as diesel engines, the old engines remain competitive when comparing SFC, if you understand aircraft piston engine management and know how to lean properly. Besides, it's very difficult to destroy low-powered engines with leaning, especially if they are running a fixed-pitch prop: unless you don't see a problem with CHTs over 420-430°F.

Agreed, but even then it's dependant on how much load you put on the engine. Thielert's Centurion 2.0 has a compression ratio of 18:1, but provides very little advantage in SFC over C172's "default" engine O320-D2J, which has a compression ratio of 8.5:1. I think the only really notable differences between the engines are: ability to use Diesel/Jet A-1 and constant-speed propeller, which gives a few knots increase in cruise speed, but FADEC has a very strange way of setting propeller RPM dependant on the load. I think if you set load below 20%, the RPM starts increasing (contrary to normal CSP), which actually means blades' pitch is going to very very fine and can indeed be felt with the aircraft slowing down significantly. Well speaking of electronics, Centurion 2.0 (one of the rare certified FADEC aircraft piston engines) doesn't have really the brightest history with clutch issues (although that was more of a problem on 1.7), the FADEC sometimes can't really decide on the RPM, especially when using somewhat medium loads with medium speeds on a C172 (say 45% load at 75 knots) and then it ends up by changing pitch and your passengers wondering (as well as you) what is going on :)

Basically, as was written lots of times: if there were any magic formula for creating mass of energy from nothing, it's likely that it would have already been developed, at least in some sorts of experimental version :)

My question goes beyond that: why do I have to lean at all? I should be able to just push a button that says LOP or GOP and automation takes care of everything else. Or there should be an Economy setting or a Sport setting, just like in my car;)...

The reasons for leaning the existing aero engines are not necessarily obvious. I have some notes here.

What you want could be achieved with a full FADEC box.

Adam

I am sorry but I have not waded through this thread but (and I hope I have the jist from the last page or two)

Your ideas are of course sound. Almost everyone that pilot's light aircraft wants FADEC and a host of other innovations; doubtless many are technically possible BUT you must appreciate aviation is one of the most conservative of industries which stems from its (understandable) fixation with safety. Combine those two facets with a market place that is really small in commercial terms and you start to understand why it is so expensive (and commercially not viable) to be innovative.

GA has almost no commercial market. No one is trying to make money out of fly piston aircraft these days and the number of private pilots that fly is probably dwindling. Without doubt in the name of safety the regulatory pressures ever increase.

You will see that there is little commercial incentive for manufacturers to invest in the huge R and D costs associated with developing new technology, in the knowledge that if they get it wrong it will destroy the company. (Diamond being a recent example, albeit they managed the Pheonix, but probably only just).

Compare and contrast that with commercial AT, the motor trade, and the computer business to give a few examples. Huge numbers of units are developed, the R and D costs can be spread thin, the commercial incentive to innovate and steal a lead on the opposition is attractive. That is why if we still flew piston aircraft around the world as the only means of commercial passenger transport piston engines would have evolved beyond your wildest dreams - and in fact they did, they turned themselves into turbines because that was the obvious cost effective solution.

The green revolution is interesting. At the moment it is fueled more by politics and government grants and incentives than by the goals it seeks to achieve. We have only just begun to count the cost of so many of the so called green technologies. Do we account for the enviromental cost of batteries, the impact of shipping the component parts half way around the world, the enviromental damage that ensues from their relatively short life, and the cost of producing the electricity with which we fill them. We dont, or at least we like to pretend we dont. That doesnt mean that the technology will not mature, and it doesnt mean that it is not a worthy cause, but the time will come when we must assess whether it is the best or only solution to the carbon power of today that we have fallen in love with assuming of course there is any other alternative. Ultimately there is not because fossil fuels are finite and regardless of the means we use to carry energy down stream we must find a source of producing energy that does not rely on fossil fuels.

I suspect the trick of how you pour energy into a vehicle that can get off the ground, travel at useful speeds and carry a useful load will be as great a challenge as was our efforts to get off the ground in the first place.

Electricity is most definitely not the solution unless you can find away of packing it at a density beyond our current wildest dreams or to be fanciful find a way of using electricity to counter act gravity in which case you have at least overcome the biggest energy cost of getting an object off the ground. Neither are close to being on the drawing board.

For that reason electric powered aircraft are a wonderful notion, and doubtless we will see electric powered gliders and other small and very light aircraft that can move personal loads over short distances at relatively slow speeds but that is as good as it gets at the moment.

I wonder if we will see electric power in airships first?

Weight is less of an issue (you add buoyancy, ie make them bigger), and there is plenty of space on top for solar panels!

My profession is electronic engineering and also being a mechanical engineer I was originally horrified at the lack of innovation when I started flying.

Now, 11 years later, I can see good reasons for a lot of it.

A lot could be improved but the thing which is holding back those bits is not "certification costs" as we are all repeatedly told. In fact any big player is perfectly capable of getting some new widget certified. It doesn't even have to be reliable to get certified - Thielert showed that one pretty well... The reason things are held back is partly a widespread ineptitude in the industry, where the big players are packed with old fogies counting the days to their pension, and partly the fact that "the market" is the USA where you cannot afford to screw up. If you "did a Thielert" out there you would be dead and buried for a hundred years. That's why Diamond sold the avgas DA40 out there (with a SE you don't want a dodgy motor) while "market testing" ;) the DA40TDi over here.

Thread drift, but I'll bite; there's a fundamental flaw in the certification system. The FAA and EASA certification is based on known entities and if you bring something new to the market that hasn't been proven, however trivial, they will bury you under certification requests. This favors not only big players with big pockets who have less inclination to renew as they have vested interest likely already in the marketplace. And as I mentioned earlier, once you've gone through the rigmarole of having a certain, say, engine in the type cert for an aircraft, they have you by the b***s.

Ultimately, this will in the end create unsafe scenarios, or let me put it this way; sticking with older, more unsafe solutions rather than replacing them with newer, safer options, simply because it's cost and legislatively prohibitive to do so.

Let me give you a real world example. My AC520 has old, 50's seats with really low back rests. No support for the head and a real whiplash feast should you ever bump into anything. All you've got is a two point lap belt. I wanted to change the seats (not the support or attachment, just the seat) for one of those new, snug, racing carbon fibre seats and add a 5 point harness. Can't be done legally. You are not allowed to change or even alter the seats without an STC. You're not even allowed to add a 5-point harness to the existing one without a STC or at the very least a 337 FSDO approval.

How does this benefit safety?

There are thousand examples like this where clearly the safety is of no concern, but bureaucracy is.

That's not a problem if you are a big company with full time people doing this stuff. They know how to tick the boxes.

Very hard for a startup with no expertise (I have looked into this and even a PMA is a lot of hassle).

Of course, but that is "business".

That is what business is about. Your objective is to put yourself in a position where competitors face large barriers to entry. You can do this by a lot of R&D spending resulting in a heavy rate of innovation (hardly the case in GA :) ), by patenting every stupid thing you do, by using various (often illegal) techniques to maintain dealer/reseller loyalty, and by other legal and illegal methods.

The certification process supports this, but not really intentionally. I think EASA (which is basically a load of gravy train riders) does support Part 21 firms actively, however, by refusing to accept FAA AML STCs and more generally in other ways.

Adam yeah i know been there a few times and it is frustrating.

But think it through. It seems simple enough but you would be amazed how easy it is to change the seats (incorrectly) and create even greater problems. Ate the seats designed for an aircraft, will they burn, will the runners latch properly (you really dont want the seat sliding backwards on the climb out), can the rear pax still fold the seat forward readily in an emergency, what about the fixing points etc.

In other words allowing changes to the design would be a recipe for all sorts of ill thought through bodge jobs. Now you and i would think it through thoroughly of course but you would be surprised how many wouldnt. So minor mods and stc provide a design mechanism to overcome these concerns. Is the process too costly and overly complicated - yes almost certainly but you can blame the lawyers for that as much as anyone.

The best way is for half a dozen of you to get together as we did, share the cost and then it is not too bad - morever you own the stc and if it is a good one others will follow and doubtless be happy to make further contributions.

Don't know about EASA but in FAA-land you can do a Major Alteration (337) for just about anything.

The only time you would do an STC is to acquire intellectual property in the design if you want to sell it.

This had passed me by. An electric Cri-Cri set the electric speed record almost a year ago at 163mph. Cool!

ELECTRAVIA concept : electrix planes, electrical motorizations for aircraft and optimized propellers

I was just seeing and reading a lot of interviews with Elon Musk, the CEO and founder of Tesla. Specifically about the imminent release of their Model S with 300 mile range and a start price of $57K, which is rather competitive.

He broached the subject on how long it would take before most cars sold would be electric, and he mentioned 20 years. I agree with this and I can see the next couple of years being an avalanche in this regard. Old companies not willing to change will be going out of business. It's going to be interesting.

But what's most interesting is that if that happens, then the only way big oil and the old guard can fight back is to lower the cost of fuel. And because it's going to take dinosaurs and troglodytes in aviation much longer to see the benefits of electric, we as pilots will enjoy lower fuel prices as well.

So if you fly, buy an electric or hybrid car next time. It's in your best interest.

http://www.thetorquereport.com/tesla_model_s.jpg

One factor which may affect the viability of electric flight is taxation.

If taxation on Avgas was reduced to the same level as the tax on the electricity used to charge batteries, then the economics of electric aircraft would fall away.

Hybrid cars exploit the use of batteries to smooth out the peaks and troughs in energy demand in a car. This is not really possible in an aircraft (gliders excepted).

If significant proportions of aircraft and cars start to use untaxed electricity (or lowly taxed), then governments will find a way to tax them.

So, we have the situation where a Kg of Avgas has 50p of Avgas plus £1.30 tax. If this is replaced with 44 MJ of electricity costing 30p the real saving is only 20p plus a tax saving of £1.30. Thus the technology to deliver electric power is really a tax avoidance scheme and governments can quickly close these loopholes down.

You are absolutely right in that governments will not quietly stand by to see their multi billion revenue from carbon fuel taxation go away. If someone made a car that runs on air tomorrow, they will find a way of taxing that. But electricity is also harder to earmark and keep track of, and there will be plenty of opportunities for ways around that taxation. Which is good - the less they have us in their pockets with no options, the better.

A few thoughts whilst reading through the thread...

At least in the radio-control world, where my experience lies, large electric setups running at up to 5 horsepower or so are now quite common. A typical setup for an electric helicopter may have a 500g motor putting out about 4 kW. Over the past year or two they suddenly came of age. They're clean, reliable, quiet... last time I showed up at a flying field there were no IC engines in sight. The only maintainence they need is to lubricate the bearings - though motors to drive large propellers may be lighter and more efficient if they also incorporate a gearbox, which would obviously increase complexity. The main failure modes are for the bearings to give up, to shed rare-earth magnets which are epoxied into place, or if they're overheated then the magnets weaken.

Brushless motors from reputable brands are very reliable - unfortunately the same can't be said for the speed controllers (ESCs) that drive them. If they go wrong, they have a nasty habit of starting battery fires and burning out expensive motors. They often cost more than the motors they drive, and judging by the number of product recalls, designing a reliable one can't be nearly as easy as it looks. The basic circuit involves bridges - i.e. two switches in series which, if both turned on at the same time, will short circuit the battery.

Cooling is a perfectly tractable problem. One of the great advantages of an 85% efficient motor is that it generates much less waste heat than an ic engine of equivalent power output - you don't need to remove 100kW of heat from a 100kW motor as someone mentioned previously. Most model aircraft motors incorporate centrifugal fans, though I'd wonder whether these would still be effective on a propeller driven aircraft operating at a much lower RPM.

Rare-earth scarcity is going to be an issue in the short term. It's already pushing the prices of brushless motors up quite considerably. Prices for small motors have just about doubled over the past 5 years. However, new mines will come on line in the next few years, and there are research projects to develop magnets based on the commoner rare earths. My guess is that this will be a much bigger issue for cars than aircraft where cost will be less of an issue, and weight more important. At present, a 5KW motor costs about £150. Lithium scarcity (for the batteries) is another potential problem.

I don't really know enough to comment on whether electric aircraft will cause problems for electricity grids. I suspect not - for pleasure flying, overnight charging will probably be practical. Airfields could have on-site generators. Batteries in aircraft that had been charged overnight but were not currently in operation could be used to charge other aircraft by day. Microlights that only get used once a week for an hour of pleasure flying could possibly get by with a big solar panel.

Electric motors are different from IC engines. They're physically smaller for the same power output. After a certain size, big motors aren't much more efficient than small motors, and two smallish motors aren't much more expensive than a single bigger motor because a lot of the cost is in the materials - they're mechanically much simpler than IC engines of any variety.

Batteries are also different from fuel. They don't get lighter as you run them down. On the upside, this means that their center of gravity doesn't change and their placement in a new-design aircraft can be more flexible. We've talked a lot about energy density, but something that has only been touched on is that power density for an electric aircraft is potentially much greater than for an IC one - even a jet. My model helicopter's batteries can supply 60C at 36v at a weight of 1kg and a total capacity of 4 amp hours. In other words, about 10 horsepower per kilogram... for a whole minute. A 10 horsepower motor will weigh another kilogram... so all in all we get about 5 horsepower/kilo. 200 kg of batteries and motor... 1000 horses, instantly available at practically any altitude. This might not be sensible, but in between this hypothetical aircraft and the electric motor gliders currently being built, there may be some rather interesting compromises.

So, whilst in many cases it might be straightforward to bolt them on to existing airframes, aircraft designed for electric power from the outset will probably look quite different from existing models. You could build a twin or triple with very minimalist engine pods that cost very little more than a single. You could perhaps build a 500kg ducted fan aircraft that would outfly most military aircraft, for a while minute. An electric VTOL jump-jet. A simpler gyrocopter with one motor to do the pre-spin, and a separate motor for the propeller. With regenerative charging of the batteries, you could slope soar for an hour or two and generate enough power to do a long cross country flight.

Batteries, unfortunately, are the key. Lithium polymer batteries only last a few hundred charges, even when you take good care of them. A123 lithium-Fe batteries are much better and can last thousands of charges, but weigh about 20% more per unit of usable energy (if you discharge LiPo past 85% of rated capacity their lifetimes are shortened considerably - LiFe are much more forgiving). Lithium polymer also burst into a ball of flames if you puncture them, but you can drive a nail through an A123 battery and it just gets mildly unhappy. The last I heard, Lithium air batteries had the capacity, but not the discharge rates required for sustained flight, but I haven't looked into it for a while. Anyway, if we ever do get a battery with the capacity of Li-air and the robustness and safety of A123, then things could get quite exciting, though I agree it's likely to take a little while for the changes to percolate through.

abgd, Hi. I read your posting with great interest.

Please see your pm inbox. Chris N.

Thanks Abgd for giving such detailed insights into the RC world which I only had spurious knowledge of.

Thank you very much for that fascinating and informative review Abgd.

You refer to the short cycle life of LiPo cells. It fascinates me that if you ask almost any so-called 'engineer' in the electric car business "how long does the battery last?" they immediately start telling you about the capacity. You have to say "no, how many cycles does it last" to get to the real operating cost. And very few of them will answer the question head on.

Even then, a characteristic not picked up on by commentators is that capacity doesn't just fall off a cliff after x cycles (though it might) ; it degrades progressively, every time you cycle the battery. This means that a car that could just about do x to y last week might not make the same trip next month quite so easily, and probably won't do it all next year. Inconvenient for a car driver stuck on the hard shoulder of the M6 and a bit of a concern for a pilot of an electric aircraft.

My experience with models leads me to completely endorse what Abgd says about multiple motors and designs being completely different from traditional aircraft. The motors (and batteries) scale so well that I don't see why you would stop at 2 or 3 motors: 10 or 20 might offer almost as much efficiency while protecting you from the great danger of controller failure, as has been pointed out.

Motors and batteries are best combined in compact pods, reducing heavy and wasteful cable runs to an absolute minimum. That's what a model aircraft is, and one of the main reasons that they work so well. Multiple pod mounted motor/battery combinations might aid maintenance and also be designed to burn off the wing without destroying the aircraft when the inevitable Lipo battery fireball develops. (Petrol seems really safe after exposure to a burning LiPo cell!).

All this is well within the reach of amateur developers and we can expect to see numerous examples of the multi motor aircraft appear in the years to come (except in over-regulated UK, of which Wherner Von Braun once said "The history of spaceflight might have followed a different course if amateur rocketry had not been made illegal (in the 1920's) in that inventive country").

Will full-size electric aircraft ever surpass petrol ones? The secret to all of these new technologies is economy of scale and scale has become quite significant in the model aircraft sector, enough to attract serious Chinese manufacturers. Todays 'ready to fly' model, straight out of the box, not only outperforms it's IC engined counterpart of 20 years ago but comes at an FOB China price of maybe 10% of the traditional model in real terms. Nothing like that can ever occur for conventional IC engined light aircraft.

So a future electric lightplane might be vastly economic in comparisom with it's traditional counterpart, especially as low utilisation (compared with a car) would favour the limited cycle life of the batteries. None of that makes up for lack of energy density compared with petrol, but the 4/5 Hours safe cruising endurance of our petrol powered spamcans probably doesn't fit in with the future shape of hobby aviation either. So on the whole, I'm a believer.

If you have been, thanks for reading!

abgd -

Right on the mark. My son is RC mad and I have seen the stuff he flies. The problem is that while the motor has been a non-issue for years (a 250HP motor, with enough poles to not need a gearbox, would be probably under 50kg) and similarly for the electronics, the battery technology does not scale, or at least not economically. A decent size RC LIPO battery retails for £100, and while RC stuff is IMHO way way overpriced, you are looking at £100k for the battery to make a viable long distance car.

The current energy density comparison between petrol and LIPO is about 40:1.

Recently I went to a presentation by a specialist in the field and while ebullient he accepted that there are unresolved long term issues like the loss of petrol tax revenue, so maybe there will be an increase in road taxes, perhaps by having a mileage based tax. Otherwise, domestic electricity is far too cheap relative to petrol.

David

Yes this is an unresolved issue and nobody wants to talk about it. I put that to the speaker and he agreed :)

If the £5k LIPO battery makes 200 cycles rather than the claimed 1000, the case collapses.

I wish electric aircraft were feasible, but if the electricity is only cheap because there is no tax then it is somewhat pointless exercise.
I wonder what would happen if we started using central heating fuel at 53p/litre in modified diesel engines.
With the extra economy of diesel this would seem to be a much more available technology than batteries today and probably cheaper than the cost of electricity plus batteries.

How long do you think we could get away with it? (assuming the LAA/CAA approvals were available).

But even so, fossil fuel makes so very little sense from an efficiency standpoint:

1. A diesel engine has at best 30-40% efficiency. Electric has 90%. Even if all your electricity comes from coal fired power plants, it's still environmentally better than extracting oil, refining it, trucking it, burning it in an inefficient gas engine.

2. Trucking fuel out to gas/fill up stations is very inefficient compared to using the infrastructure we've already got for electric - your outlet. Doesn't cost a penny to transport it.

3. The reason countries and states can control the petrol prices to the degree they do is that laymen could never refine petrol in the backyard and take control of production. They had us by the balls. Electricity can't be controlled like that - there is solar power, wind power and plain old water powered solutions readily available for anyone. Who's going to stop you from charging your aircraft or car from your farms stream?

No doubt this Government will find a way.
I have said before that if it were possible to run an engine on water the Government would fence off the beaches & charge fuel tax for flushing the toilet.

Time is money these days.

Normal EU outlet with normal current limiters (230V, 20A), gives you 4,6 kWh in a single hour (P = U * I = 230 V * 20 A = 4600W), which equals 16,56 MJ/h. Diesel fuel has an energy density of 37,3 MJ/l. Assuming a normal fuel pump can provide a fuel flow of 3 liters/s, which is no biggie, you get an energy flow of 111,9 MJ/s. Multiply this with 3600 seconds in an hour, and you get 402840 MJ/h. This effectively means you need a little over 24000-times longer to transfer the same amount of energy via electric outlet than if you would fill your car at a gas station. Very inefficient if you ask me - even if you reduce it by a factor of 3, to count for the better efficiency of electric engine. Plus, as IO540 points out - where will you store a comparable amount of electric energy. 200 liters of Avgas is a lot of energy, believe it or not.

What efficiency does a nucler power plant have? Just to give it a thought...