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What Use Is An Electric Airplane?

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Does NASA's $1.35 million prize for Pipistrel's ultra-efficient electric airplane signal a new chapter in aviation, or is it just a sideshow? I tend to think it's the first step down a long and bumpy road that could take general aviation in new directions.

For people who fly for fun -- presuming there are many of those left, it seems to be one of the fastest-shrinking segments of GA -- electric airplanes are sure to appeal. They are easier to deal with, and quieter, with less vibration. A few years ago at Oshkosh one of the Yuneec executives said that when model aircraft switched over from messy little gas engines to electric motors, the hobby grew dramatically. He hoped the same would happen with real airplanes, and I think that makes sense. A nice clean battery-powered airplane just seems more modern, more reliable, simpler, cleaner, and more manageable to a new aviation prospect. A motorglider with a quiet little electric motor can take one or two hobby flyers aloft for hours, and lunch probably would cost more than the power used. An electric trike could take sport flyers on epic flying adventures, without the tiresome noise and rattle from a gas engine.

For flight schools, the technology is just about perfect. Since most flights only last an hour or two, the limited lifespan of current technology is not a problem. The savings in maintenance and fuel costs are likely to be significant.

But is it really any "greener"? Electric motors recharge off the power grid, which is supplied mainly by coal-burning power plants, not exactly emissions-free or squeaky clean. But since the efficiency is so high, electrics still come out ahead. Pipistrel's winner, for example, carries up to four people and averaged out at equivalent to about 100 miles per gallon of gas. Even a Prius gets only about 50 mpg. Another advantage of battery power is that if managed properly, it doesn't impose extra stress on the grid. Since powerplants can't be shut down and restarted every day, there is always excess power on the grid at night. Batteries provide a way to store that energy and use it later. So lots of batteries could be powered by existing powerplants, using energy that is now just going to waste, before any excess demand would be created.

All these efficiencies multiply to make battery power superior to gasoline. There are other issues, with some of the materials that are needed for batteries, for example, and how to dispose of them once they're dead, and how long before they have to be replaced. But the technology is evolving fast, and the more we find good uses for it, the more incentive there is to improve.

Is it economically feasible, over the lifetime equivalent of a gas vs. electric airplane? I don't know if anyone has done that study in detail, but in any case the answers today might be different in a year or two, or five or ten. Add in the grim geopolitical costs of our current fuel system, the problems with leaded gas, the trillions of dollars in government subsidies, the cost of oil spills, ad infinitum, and the scales tip even farther toward investing in an electric future for flight.

Comments (136)

I was lucky enough to attend the Green Flight Expo Monday and had a few thoughts about this.

I was expecting to be "bowled over" by really unusual technology (take a look at Pipistrel's winning entry, for example), but what I walked away with was the fundamental impression that most of the nuts and bolts of these entries were based on technologies which are not that "new". Sure, the details of the batteries and motors were pretty cutting-edge, but the airplanes themselves were essentially modified gliders, the instrumentation was, largely, conventional.

My point: The "feasibility" question has been answered, period. The outlook for these devices is no longer an issue of "if" but "when". The argument...
"... is it really any "greener"? Electric motors recharge off the power grid, which is supplied mainly by coal-burning power plants..."
raises a valid question, but the sporatic use of an electric aircraft by a recreational flyer like me seems especially well-suited to off-grid electric sources (solar, wind) - a fact which was not emphasized in Grady's editorial.

Evolution is inevitable. We are no longer in a position to wring our hands and ask if this step should be taken. We are watching the birth of a new, beautiful species. I can't wait to see more of these marvelous machines become available.

Tony Nasr

Posted by: ANTHONY NASR | October 5, 2011 7:19 PM    Report this comment

The internal combustion engine wasn't viable for a long time, and that was competing against horses. Electric engines may become competitive someday, but probably not for a decade or two minimum.

Posted by: Jesse Derks | October 5, 2011 7:58 PM    Report this comment

It does seem as if electric and training, with their one-hour typical flights, could be a good match.

Probably more so for the reduced maintenance factor than anything else because I question the overall efficiency figures people bandy about. There is a heck of a lot of system inefficiency in all the energy conversion & transmission steps from power plant heat source to turning propeller.

One other consideration is the problem with turn-around time at a busy flight school operation; if you use the same batteries they must be charged REALLY fast or else you must have a plane in which they could be swapped out. Each approach has problems.

Ditto for the concept of spreading the load; except in the case of having banks of swappable spare batteries, you have to recharge when you need it, not park the plane and and wait for off-peak power.

Bottom line, electric airplanes can only be a niche product. Self-launched sailplanes, OK. Training, maybe.

Posted by: John Wilson | October 5, 2011 8:39 PM    Report this comment

Seems impractical and the application limited. I guarantee because of those two things, the govt will subsidize it. Not great.

Posted by: David Schultz | October 6, 2011 3:11 AM    Report this comment

I believe electric aircraft do indeed have a bright future. And I don't believe that future to be too far off. The greatest hurdles, in my opinion, will be "refueling" and turning petrol-heads (such as myself, though I am an open minded one) into volt-brains (that needs work).

One advantage gasoline burning AC now have is that when their tank runs dry, a fill up is fairly quick. Filling up the batteries in an EV is still considerable longer. I believe the Electric Aircraft Council will have to push for some standards to allow for an infrastructure capable of swapping out charged batteries for empty ones.

Turning the petrol heads will be the same issue Jesse Derks brings up. In addition to competing with the ponies, steam engine manufacturers referred to IC engines as "explosion" engines to turn people off of making the switch. EVs will have the same resistance (pardon the pun) from the gassers.

Posted by: Jason McGloin | October 6, 2011 3:45 AM    Report this comment

I have been seriously considering building an electric powered sport plane for several years. When I first started working on this idea I set an arbitrary benchmark for a practical airplane. It needed to go 100 mph and cruise for a minimum of 2 hours. This turned out to be exactly the same requirement for the award recently given to Pipistrel.

I don't think the demonstration shows the technology is ready for wide spread use yet. However, this is a big deal. It can't be too far in the future when this same benchmark can be met with a conventional design airplane rather than a glider. This should probably be 2 seats with wing loading in the 10 to 20 pounds per square foot range.

Current electric airplane costs are high but this is offset by much lower fuel costs. The biggest problem is batteries, and automobile manufacturers are all over this issue. I think we will see much better batteries in just a couple of years.

I refuse to worry about recharging time or methodology. These problems will solve themselves when there is a real demand.

For electric airplanes, the future is here.

Posted by: PAUL MULWITZ | October 6, 2011 5:48 AM    Report this comment

GO ELECTRIC! Cleaner, more reliable, more efficient, less(no) vibration....WOW. I can't wait, and I think it can dramatically revive GA. As a private pilot who has 200 hours but has battled against the high cost but also the complexity of flying SAFELY, I believe electric powered aircraft will prove to be a major step towards creating more PROFICIENT, SAFE GA pilots.

Posted by: Joe Goebel | October 6, 2011 5:57 AM    Report this comment

It's a huge step backward and the result is very limiting(the same with clothes lines, bicycles, and windmills). Electric cars are a much easier but WHERE are electric cars (beyond the quiet and short roads of a golf course)?

The fact is that batteries are heavier and less energy dense than liquid fuel. That is the reason that electric power is not an Aviation winner.

Posted by: Mark Fraser | October 6, 2011 7:10 AM    Report this comment


I think you would be wiser to look forward rather than backward.

I agree with you that hydrocarbon fuels are a lot more energy dense in today's technology. The problem is that internal combustion engines are very inefficient while electric motors are almost perfect in efficiency. That means that each improvement in battery technology (or other electric source technologies from fuel cells to small fission/fusion devices in the distant future) will be directly realized in airplane performance.

The demonstration just completed shows electric flight is possible. It just doesn't require much more improvement to make it really practical for everyday use by a large segment of general aviation.

I have heard many people (including you?) complain that the cost of recreational aviation is too high. Electric power has the potential to greatly reduce costs for just that segment of GA most recreational pilots occupy.

Posted by: PAUL MULWITZ | October 6, 2011 7:39 AM    Report this comment

This is a fantastic acievement-- the two electric teams did a great job doubling the specified performance at 100 +mph. The concept of electric powered flight is 40 years old this year. I know-- i hold the only patent which was granted in 1976 It expired 23 year ago. My first public demonstration was in april 1971 with a scale model of a Fournier RF4. within a year i flew an electric model over one hour at 60 mph on a closed course. A practical two place trainer can be designed today with near 300 mile range within the cost parameters of gasoline powered planes. the operating cost can be expected to be about 1/10 of gas powered planes and the annual inspection of the power plant to be basically non existant. Want to know more visit my web site www.projectsunrise.info
this discusss the first solar powered plane which flew in 1975 and at the end discusss the design cosniderations of a two place electric plane

Roland Boucher Irvine CA

Posted by: Roland Boucher | October 6, 2011 8:03 AM    Report this comment

This is a fantastic acievement-- the two electric teams did a great job doubling the specified performance at 100 +mph. The concept of electric powered flight is 40 years old this year. I know-- i hold the only patent which was granted in 1976 It expired 23 year ago. My first public demonstration was in april 1971 with a scale model of a Fournier RF4. within a year i flew an electric model over one hour at 60 mph on a closed course. A practical two place trainer can be designed today with near 300 mile range within the cost parameters of gasoline powered planes. the operating cost can be expected to be about 1/10 of gas powered planes and the annual inspection of the power plant to be basically non existant. Want to know more visit my web site www.projectsunrise.info
this discusss the first solar powered plane which flew in 1975 and at the end discusss the design cosniderations of a two place electric plane

Roland Boucher Irvine CA

Posted by: Roland Boucher | October 6, 2011 8:04 AM    Report this comment

My hope is that Pipenstrel takes the money and invests it in bringing a product to market so that we can start flying these machines in real world environments. I believe you are right, Mary. If the initial price-point is spot-on, flight schools will buy them and put them on the line. If people train in them, they will want them. As for battery recharge time? That's easy. Just swap batteries for a charged-up set and go again. That way batteries, in integral packs, are charging while the machines are up making the flight school money. Better yet, you can remove the batteries for charging each evening and it would become very difficult to steal the airplane off the line overnight.

Posted by: Amy Laboda | October 6, 2011 8:19 AM    Report this comment

I think Mary is correct. This could be a real boon to recreational flying. I typically fly only 1 to 1.5 hrs at a time, sightseeing close to home, with only one other person.

I prefer open-air flying to being stuck inside a can, so ultralight type aircraft are suitable for me. A quiet, simple, 2-seat aircraft that can remain aloft for an hour or two at Cub-like speeds would be very enjoyable, especially for a new person to aviation. The sheer reduction in noise will greatly improve the experience of flying like a bird.

Smaller light aircraft would also be perfect for removeable battery packs to allow a quick turnaround. There is already a single-seat trike that flies with such a concept in Europe - why do they out-invent us?
I am still waiting for a 2-seat version of such a thing before I consider a switch.

Let's not fall into the trap as thinking of aviation as transportation only. It will never compete cost-wise with cars or commercial carriers. If we make it fun and convienient, we can keep General aviation's demise as slow as possible.

Posted by: Scott Thomason | October 6, 2011 8:20 AM    Report this comment

Batteries, batteries and batteries.
Renault and Nissan, have invested over €2 billion on all electric vehicles, only just hitting the showrooms after three years. They may not be a success right away because in real life driving the range is 100km, about 60 miles.
But some of that money has gone to the battery people and suddenly, after years when only the military was interested in new battery technology (field GPS and radio units have gone from two hours use to two weeks in 10 years) transport applications are getting a look in. Expect the next big car battery advance in four years, followed two seconds later by someone putting it in an aircraft.
Then hopefully, prices might start to fall, and the electric recreational market will take off.
It is not really a green argument -- even the most basic electric car is so nice to drive compared to any gas powered one costing less than $80,000 because of the lack of noise and vibration, that I am sure the same will be true of aircraft.
Mind you, while there are nuclear power stations, which you cannot turn down at night, you might as well use the juice to charge a battery or two.

Posted by: Brian McCulloch | October 6, 2011 8:32 AM    Report this comment

"The problem is that internal combustion engines are very inefficient while electric motors are almost perfect in efficiency."

Who cares about efficiency when there is NO WAY that electric will power an airliner, a fighter aircraft, MedEvac helicopters, or even a long distance private flight with a family of 4? As said, POWER DENSITY makes liquid fuel the choice in Aviation.

Sure, powered gliders with one or two aboard for short flights are kinda cute. Electric is just not the future for PRACTICAL aviation. You'll never see a 787 or an F35 or a Piper Lance class aircraft running electric. Power density trumps efficiency every time.

Posted by: Mark Fraser | October 6, 2011 8:54 AM    Report this comment

I'm a die-hard internal combustion fan but bring on the electrics! Seems to me, initially, they would be ideal for the recreational flyer. Simple to fuel, smooth, quiet, reliable, much more user friendly than internal combustion, no pre-heat, no plug fouling, no mixture, no oil changes, no mags. As the technologies improve so will the practicallity and utilty of electrics.

Posted by: Richard Montague | October 6, 2011 9:31 AM    Report this comment

I suggest readers review Consumer Reports articles on Electric cars. You need a driveway or garage and expensive 220v charger to revive the batteries in a night. The 110v units require two days - one 'tester' wrote of needing a backup car every other day to get to work until the maker made 220v chargers available for $1000 or so. A Prius battery pack runs about $3500 installed. Like all batteries plane on a periodic replacement. If you have a backup plane and plan to fly one sortie every other day then battery power is for you.

Valclav Smil wrote in his book "Energy Myths and Realities' of Thomas Edison's push for electric cars and how he got a series of charging stations spaced out between D.C. and Philadelphia. The time spent charging the lead acid batteries exceeded the time to take the trip in a De Dion steamer. Edison hired a kid named Henry ford to work on the electric car, but Ford had a better idea that killed the electric car.

Posted by: THOMAS M CONNOR | October 6, 2011 9:31 AM    Report this comment

The advantage of hydrocarbon propulsion is the first ounce has the same amount of power as the last ounce with the benefit of losing weight along the way. Batteries decline rapidly, so the last ounce of battery produces less power than the first ounce, and there is no weight loss with power decline. So the strategy is to install far more battery than necessary and regulate it so the last minute seems as powerful as the first. As one test driver of the Chevy Volt commented: That works until you need lights and heat - also battery powered. Then the last minute arrives quickly.

Many hope for and others promise a magic battery, affordable fuel cells, cheap hydrogen or efficient compressed air engines while ignoring the cost of production. Lithium batteries seem to offer the best solution. This is the same technology that requires hazmat shipping because of a history of catching fire.

Finally, Smil addresses the efficiencies of converting from hydro/coal/nuclear or natural gas to AC power, then convert to DC power to charge the batteries and convert again to mechanical power to run the prop or wheels. From a thermodynamic point of view, hydrocarbon power is still more efficient and will likely stay that way until a miracle in battery technology occurs.

Posted by: THOMAS M CONNOR | October 6, 2011 9:32 AM    Report this comment

Electric flight is a fantastic idea. The technology is getting there. Though, moving forward, making this feasible for wide scale use does beg a few questions. Some things I have thought of: 1. Why not create a self sustaining power source from an alternator hooked up directly on the shaft? Apply power to the coils on one end for the power to the prop, and draw power from the spinning magnet on the other part of the shaft (similar to a magneto, but much stronger). Now I am no engineer, just a CFI, but I think when the technology advances this could be feasible. 2. When they start putting these setups into faster, high altitude singles, how are they going to combat the problem of electrical arcing within the motor. Pressurizing the electrical motor, akin to PMag, sounds more complex than need be. It would be interesting to how they combat these issues, if they ever arise.

Posted by: Benjamin Crow | October 6, 2011 9:52 AM    Report this comment


The motor-running an alternator-charging a battery-running the motor is called perpetual motion. Google it for a fun read. The first law of thermodynamics essentially says you don't get something for nothing - which kills perpetual motion in the cradle. The second law essentially says that you will pay dearly for what you do get - meaning efficiencies are frustratingly low on a good day and abysmal on a bad day.

Posted by: THOMAS M CONNOR | October 6, 2011 10:14 AM    Report this comment

Feasible = Yes, Practical = No.

The extent to which electric powered aircraft will change general aviation will be driven by flight hour economics and nothing else. Consider that the current high hourly costs associated with Avgas and engine overhauls that are the primary factor for driving out recreational pilots (those who fly purely for pleasure, not necessarily the LSA types) and limiting new pilot starts. If electric GA aircraft can substantially reduce those costs, the market will respond appropriately. Like alternatives to 100LL, there is also a huge infrastructure issue to overcome, like a standardized recharging station at the FBO when you arrive at your non-home airport. Battery technology will continue to improve with higher energy densities (KW/Kg) and reduced manufacturing costs as time goes on and eventually the ‘five-years-from-now’ economically optimal price point will arrive. Hopefully the transformation will occur before recreational GA becomes a memory of a bygone era.

Posted by: John Salak | October 6, 2011 10:17 AM    Report this comment

Let's not forget the difference between an invention and a product. An invention looks great in a demonstration. A product has to look great when used and maintained by the clueless.

I'm skeptical that the efficiency of the Pipstrel can be duplicated in an airplane you could sell to Joe Private Pilot. Experimental aircraft have had both great speed and great efficiency for half a century now, and they also have cramped interiors and quirky handling qualities that send many pilots rushing back to their crude-but-safe Skyhawks.

In any event, propulsion efficiency and power source are mostly a different issue from airframe efficiency (save some interlinked factors like cowling shape and cooling drag). Conflating the two just makes it harder to understand what has and hasn't been accomplished in these inventions.

I'm waiting for someone to report on some simple core questions. Number one: what is the battery weight of the energy production equivalent of 10 gallons of gas? Compare 100 horsepower of electric motor with its Lycoming/Continental/Rotax equivalents. Small GA aircraft are all about weight limitations, so knowing these facts -- and knowing how much experts expect battery weight to improve over the next decade or two -- is key to our understanding of the extent to which electric aircraft might make sense.

Posted by: John Schubert | October 6, 2011 10:50 AM    Report this comment

Electric power is at the very beginning, there are many problems yet to be solved. The battery or fuel cell has a long way to go. Weight,recharging,usuable life and cost of replacement to name a few. These will be solved in the future, hopefully soon, but for now it is not ready for general use

Posted by: Chuck Buzbee | October 6, 2011 12:21 PM    Report this comment

One thing that I don't think has been mentioned is, considering a two hour flight in your newly electric-modified 172 arriving at the destination airport, looking forward to a break but at the same takeoff weight, as tom explained the battery power is now diminished to very low, how does that affect a necessary go-around safely? Max weight but least available power at that critical time is a bit unnerving to me.

Also for this non-engineer, how is torque affected if at all on an aircraft with electric? My neighbor's Tesla Model S snaps my neck on takeoff, could a 172 get airborne in 50'? That could be a safety feature at takeoff but not upon landing!

Posted by: David Miller | October 6, 2011 12:33 PM    Report this comment

The Teslamotors*com web site claims their Lion battery power density at 160Wh/Kg claiming about 4x the energy density of lead-acid batteries. Note that's watts/kg.

Mogas energy density is 73.5KwH/Kg, (note that's Kilowatts/kg, aka 73,500 watts/kg) If my math is right, 73,500/160 = 459 times more energy per kg in gasoline than a Kg of Tesla's high density/high price lithium battery. Of course you get to use the battery again, but there are hidden costs.

According to a study done in Europe, a 100% conversion to electric passenger vehicles would require a 15% increase in electric grid capacity assuming an unrealistic zero increase in other demands. Solar, wind, geothermal and recycled iPads have gained a few hundredths of a percent a year while some consider decommissioning nuclear power plants out of simple fear, so a 15% increase in capacity would mean more coal plants. What was the goal again?

A discussion of miles per gallon equivalent and the formula is here: en*wikipedia*org/wiki/Miles_per_gallon_gasoline_equivalent

Posted by: THOMAS M CONNOR | October 6, 2011 12:40 PM    Report this comment

John Schubert’s questions regarding batteries v.s. gasoline go to the heart of the electric airplane concept.

The EPA standard is that one gallon of gasoline equals 33.7 kilowatt-hours (kWh) of electric energy.

Current real-world battery technology for a battery capable of performing for several thousand cycles is represented by the Chevrolet Volt’s Li-ion battery pack, which weighs 435 pounds (which I don’t think includes the thermal control stuff) and can repeatedly deliver 10.4 kWh of power per charge, or about the equivalent energy of 40 ounces of gasoline.

Let’s consider a practical training aircraft that is used day in and day out for one hour flights. As we know, these aircraft generally end up needing a motor in the 100-hp range.

If we assume a 100-hp electric motor with it’s controller is 90% efficient at full power, then at full throttle the motor would drain a bit over 82 kWh from the battery every hour. Make a further assumption that you have an airplane-optimized Li-ion battery good for one hour of full-throttle flight time on a repeatable basis that is 45% lighter than the Chevrolet Volt’s and you still end up with a 1,886 pound battery.

It doesn’t take a genius to see that there are real problems in creating an electrical aircraft that can actually perform as a commercially practical tool.

It is important not to let the hype that abounds throughout the “alternative energy” field blind us to the real problems that exist.

Posted by: John Wilson | October 6, 2011 12:50 PM    Report this comment

---- I'm waiting for someone to report on some simple core questions. Number one: what is the battery weight of the energy production equivalent of 10 gallons of gas? Compare 100 horsepower of electric motor with its Lycoming/Continental/Rotax equivalents. ----

My search for products for use in electric airplanes has given some approximate answers to these questions.

A Rotax/Jabiru 100 hp engine weighs about 180 pounds including firewall forward needs. Lyc/Cont weighs about 100 lbs more. 80 KW electric motor (roughly the same power) and controller electronics weigh around 40 pounds (mostly a guess on my part, but the right scale). The problem is the batteries.

According to a vendor who actually sells this stuff (Yuneec, China) battery packs to meet my 2 hour cruise requirement with this motor would weigh around 200 lbs, take up the space a passenger uses, and cost around $20K. This means I could convert a 2 seat LSA to a single seat electric meeting my 100+ mph and 2 hour cruise today.

I want more than that, so I am waiting for the next jump in battery density and cost. I am hopeful the intense worldwide effort to achieve that will give fruit in a small number of years.

Posted by: PAUL MULWITZ | October 6, 2011 1:00 PM    Report this comment

---- how is torque affected if at all on an aircraft with electric? ----

Piston engines develop increased torque as the RPM increases. Electric motors are the other way around. They have maximum torque at zero rpm.

This torque would be applied to the propeller rather than the wheels of a car that don't slip on the pavement. It wouldn't be as noticeable in a plane as it is in the car.

This could be a problem for executing a go around if it was a surprise to the pilot, airframe designer, and power plant designer, but it shouldn't surprise them. Merely applying power gently could get around this real potential problem.

Posted by: PAUL MULWITZ | October 6, 2011 1:05 PM    Report this comment

We should all remind ourselves that while Lithium Batteries are combustible and are therefore shipped as Hazmat, so are lead-acid batteries, which can explode and/or drip battery acid in inconvenient locations.

As can be seen from this discussion, the success or failure of the Electric Airplane is going to rely on improvements in battery performance/technology.

The only realistic approach is to get on with it. Exactly how “getting on with it” is going to be financed, designed, certificated, produced and marketed is the real question.

Posted by: THOMAS OLSEN | October 6, 2011 1:08 PM    Report this comment

Electric power in "model" aviation has definitely increased the popularity of the sport as Mary stated. The technology improvements in both motors and batteries have been tremendous and it is used for fixed wing, rotary and ducted fan applications with great success. Essentially a whole new segment of scale aviation enthusiasts were born complete with electric only tournaments. The improvements in capacity of lithium battery chemistries, especially lithium polymers, make a day at the airfield enjoyable with a reasonable recharge time. Unfortunately, polymers have a flammability issue probably not suitable for manned flight. But, other lithium combinations are much, much safer. Some very promising technology in lithium is at the doorstep. When scaled-up, the current power/weight ratio of batteries to AVAGAS (energy density) is still an issue. If battery weight is an issue for cars now, then it is definitely an issue for aircraft!

Given the efficiency of electric motors, however, small, continuous incremental steps forward in battery capacity to weight ratios will quickly make more and more economic sense to a broader range of full-scale aviation applications. FBO recharging stations will be the next hurdle because standard 110 VAC/15-20 AMP house current is just not going to be sufficient to recharge any known battery chemistry in a reasonable time.

Posted by: Brian Kough | October 6, 2011 1:10 PM    Report this comment

It’s hard to imagine powering an airliner with batteries, but some limited GA applications are definitely in sight for the near term if technology continues to improve. Perhaps it will spark a new generation or at least additional segment of electric pilots (hopefully!)
BTW, those flying “model” airplanes prefer the term "scale" airplanes or “remote controlled airplanes” because they are “real” airplanes using Bernoulli’s Principle and Newton’s Third Law – just different sizes. Confession: I love flying “gas” powered RC airplanes BECAUSE OF the noise and vibration!

- “Real” Commercial Pilot

Posted by: Brian Kough | October 6, 2011 1:10 PM    Report this comment

> 1. Why not create a self sustaining power source from an alternator hooked up directly on the shaft? Apply power to the coils on one end for the power to the prop, and draw power from the spinning magnet on the other part of the shaft (similar to a magneto, but much stronger).


You joking, right?

Posted by: Gary Dikkers | October 6, 2011 1:11 PM    Report this comment

John Wilson,

Your assumptions prove the Pipistrel couldn't possibly have accomplished the feat it just got awarded over a million dollars for. Obviously you have missed something someplace.

I don't know exactly where your numbers go wrong, but I suspect a big part is the notion that the battery pack needed for a Volt are the same as the needs for an airplane. There are a zillion different battery chemistries and most of them are variations on Li-ion.

Still, I believe the demonstration just performed is great but not quite enough to make it possible to go downtown and buy an electric airplane off your local used car (airplane?) lot. We still need a little patience.

Posted by: PAUL MULWITZ | October 6, 2011 1:13 PM    Report this comment

Electric cars have been around since about the 1850s, so it's anything but infant technology. Despite lavish funding, state mandates and hippie appeal it has not caught on except for those with too much money. A short accounting is here: en*wikipedia*org/wiki/History_of_the_electric_vehicle

An electric cars can be fun because an electric traction motor develops max torque at stall, so hole-shots are stunning, but at the end of a quarter mile run it may have to be towed back to the pits because the battery needs recharge.

Just for grins lets consider a 12 volt, 100 amp/hour battery. For the unaware, watts is volts times amps, so our hypothetical battery is also rated at 1200 watts. When new and properly charged it should produce 100 amps for one hour, or one amp for 100 hours or any combination in between. It's also possible to draw 200 amps for a few minutes. that over-current might damage the battery, and is why most electric cars, golf carts, airplanes and other electric contraptions have power management systems that prevent the operator from abusing the battery. Power management is part of the key to longer battery life. the other is weight reduction. The conundrum I see is how to install hundreds of lb of batteries in an airframe and maintain crash-worthiness, ie, crash survivability.

Posted by: THOMAS M CONNOR | October 6, 2011 1:14 PM    Report this comment

Interesting point of views... but I notice that only a few are dialoging with each other, so here goes:

Ben Crow: Tom Conner is right, you discribed a perpetual motion machine. Were you pulling our leg?

Dave Miller: Just because engineers at Tesla provided a sportscar with super acceration is no reason to expect that the same would happen in a prop driven aircraft. The prop is limited by tip speed near Mach One.

Posted by: Candice Brown Elliott | October 6, 2011 1:21 PM    Report this comment

Mark Fraser: Who cares if airliners or military aircraft will continue to use liquid fuel for their turbines. We are talking about recreational, propeller driven, aircraft.

Battery technology is improving... as are ultra-capacitors. twenty years ago, a one Farad capacitor filled a room. Today, a one Farad capacitor is about the size of a AA battery. In the lab, a one Farad capacitor is the size of a very small hearing aid battery. Care to guess where they will be in 20 years? It is indeed all about energy density. But it need not be as dense as the raw energy of liquid fuel when combined with atmospheric oxygen... it only needs to equal the energy available through to the shaft... and an ultra-capacitor to electric motor is far higher efficiency than that of a IC engine.

Jessy Derks: Agreed, it may indeed be a decade or two before we see electric aircraft becoming the dominant technology. All technology adoption follows a classic differential equation that results in an "S" curve, where-in very little seems to be happening at first, then all at once more and more folks are switching, intil it slows down as the hold-outs slowly adopt it. It took sixty years from the first introduction of the sewing machine to full adoption by the garment industry. Improvements occured continously along the way. I fully expect the same for electric aircraft.

Posted by: Candice Brown Elliott | October 6, 2011 1:23 PM    Report this comment

----- remind ourselves that while Lithium Batteries are combustible -----

There's Lithium metal batteries (small coin cells) and Lithium ion batteries. The Lithium metal batteries are hazardous. Lithium Ion batteries are not. (Well, at least Li-ion batteries are no more hazardous than any other concentrated power source.)

I was confused by this issue until attending the electric aircraft symposium at Oshkosh last Summer. It turns out Lithium Ion batteries often have no solid metal at all in them. Through some sort of magic I can't follow they use composite plastic and carbon fiber electrodes - at least in some cases. It is the pure Lithium metal in the coin cells that is flammable and hazardous in transport.

Posted by: PAUL MULWITZ | October 6, 2011 1:30 PM    Report this comment

Mea Culpa. I mixed gallons and kilos in my calculations. John Wilson is right: Mogas has an energy density of 33.41 KwH/Gallon, not Kg as I said. Converting a 6 lb gallon of gas to Kg I get 2.73 Kg/gallon. 33.41/2.73 = 12.24 KwH/Kg. 12240 watts/160 watts = only 76.5 times more energy in a Kg of mogas vs a Kg of Tesla battery.

Posted by: THOMAS M CONNOR | October 6, 2011 1:39 PM    Report this comment

What we really need are "bridge" products. I recently got a Chevy Volt. It has a "range extender" engine which only powers a generator, for use when the battery charge depletes. This retains the practical use of the car while taking advantage of the electric power for short range commutes. The implications of this technology are enormous. While I get the electric advantage, the battery technology advances through mass production, and I still have a vehicle which is extremely practical. So far, I haven't saved any money, but I have the satisfaction of knowing that I'm not contributing to some sheik's platinum plated Audi. I have become a big fan of electric powered vehicles.

Posted by: Dennis Vied | October 6, 2011 1:53 PM    Report this comment

“Your assumptions prove the Pipistrel couldn't possibly have accomplished the feat it just got awarded over a million dollars for. Obviously you have missed something someplace. “

Paul, I given the 1500-character limitation I had to condense a lot of thoughts into a small space.

My point was not that you can’t build a battery-powered airplane that will fly one or two hours, but that in a PRACTICAL airplane you have to consider things like depth of discharge (the 10.4 kWh Volt car battery is actually a 16 kWh unit limited to a practical 65% discharge). You can build an experimental like Pipistrel with a super light battery that you don’t care if you discharge to a killer 90% or so because you aren’t going to need it to last several years of daily cycling.

Ditto on the weight issue, both for the plane and the battery; what works for an experimental probably won’t cut it on a training aircraft that gets beat up every day and must have crashworthiness too.

Then there’s aerodynamic qualities & performance; what works for a super-efficient custom CAFÉ racer likely would be a bummer for training or even general flying.

I think my problem was that in my productive days I worked as a systems engineer and had to consider every factor that influenced the system, from concept all the way to overall life-cost. Makes you prone to look under the chrome plate & shiny paint, so to speak.

Posted by: John Wilson | October 6, 2011 2:01 PM    Report this comment

Thielert Centurion diesel engines cannot use composite props because of the pounding from the diesel despite an elaborate gearbox and shock absorber system designed to absorb the power pulses. That makes me wonder if the sudden acceleration of an electric motor requires similar considerations, or do present designs have a 'soft start' feature?

Posted by: THOMAS M CONNOR | October 6, 2011 2:01 PM    Report this comment

@ Candice Brown Elliott, WE are talking about "practical" flight. John Schubert nailed it when he said that electrics are impractical because they are cramped and quirky. If you want a small electric powered glider(Pipistrel) then you have to accept that it preforms no better than a small gas powered glider.

Posted by: Mark Fraser | October 6, 2011 2:17 PM    Report this comment

Any modern motor controller will have a "soft start" feature simply to protect itself. Very high starting torque needs very high current which would damage reasonable sized power semiconductor devices. Limiting the current to a value safe for the propeller (and the controller) would be quite trivial.

Posted by: Mark Spellman | October 6, 2011 2:18 PM    Report this comment

Safety has only been addressed as a negative factor here. If I am not mistaken gasoline is also very combustible and very often results in a fire in a crash. Hot exhaust components, carbon monoxide gas,vibration and more are safety issues not mentioned in this blog so far. It s not just batteries that can pose a danger in flight.

Posted by: Ronald Moss | October 6, 2011 2:20 PM    Report this comment

Dennis Vied

Thanks for having the courage to tell us you own a Volt. I thought only Govt agencies could afford to buy and operate them. Do you mind sharing your experiences, such as what made you chose the Volt? what climate you live in and how far can you go on battery before the gasoline engine takes over? Do you use the AC and cabin heat on battery? Do you use a 110 or 220 charger and were they included or extra cost? When the battery is exhausted and he gasoline engine gets ou home, how long does it take to bulk charge and top off the battery?

Posted by: THOMAS M CONNOR | October 6, 2011 2:22 PM    Report this comment

Paul Bertorelli over on the 100LL alternatives blog made a sage observation, paraphrasing: Pilots are a funny bunch, complaining about the 1940s technology under the hood and drooling over the latest widget and fob,indicating there might be a market. But when a vendor finally gets a widget thru the FAA wickets the infatuation disappears and the cheerleaders walk away, choosing to stay with what they know. Granted there are the early adopters, glad to do the beta testing, but the hoi polloi stay away in droves.

Posted by: THOMAS M CONNOR | October 6, 2011 2:37 PM    Report this comment


TOM,PAUL,BRIAN all good questions and comments

we will hear more in the future but practical two and four place planes are in the design phase now and planed for production.

you wont find an electric cessna 172 sorry

electric aircraft have to be designed with care to maximize efficiency after all out energy density is no where near that of gasoline BUT



Today an electric plane that is 50% motor & battery could fly 300 miles and if it did not have to meet LSA landing requirements would probably do 150 mph.

I did this with models and RPV's for DARPA a long time ago

within one year i flew over 60 miles at 60 mph with an 8 pound model.

the next year i clocked a 6 pound model at 98 mph - on nicad batteries

the following year 60 mph for 60 miles on a 25 pound RPV carrying a five pound payload, the next year a solar powered plane deigned to climb to over 70,000 feet. The equations are the same for a 1/6 or 1/4 scale model as they are for the real thing. The reynolds number favor the larger aircraft,

what was proven this past week is the the equations don't lie and that some real talent in design and construction was displayed in santa Rosa.



Posted by: Roland Boucher | October 6, 2011 2:44 PM    Report this comment

Brian, the charge time issue CANNOT be solved through battery chemistry or super capacitors or whatever. Lets say you have a 10kW-hr battery. Charging it up with 120V/20 amps = 2.4kW (like my hangar)would take a minimum of 4hrs 10 min assuming 100% efficiency (and that I unplug the refrigerator and let the beer get warm). Charging in a more reasonable 15 minutes requires a 40kW supply, such as 240V at 167 amps! The only improvement battery chemistry could do is allow the battery to withstand a fast charge without being destroyed; the problem of how to supply multiple 40kW charging stations at the local FBO remains.

Posted by: Mark Spellman | October 6, 2011 2:50 PM    Report this comment

As Ronald Moss mentioned, there aren't many comments here about safety in favor of electrics. What about carb icing? or cylinder head blow-outs? Loss of oil pressure? All of those issues seem to be much safer on the electric side. And no one will ever have to argue over lean-of-peak anymore, either! Also, with the increased efficiency, how much additional weight do electrics SAVE because of no need for cooling, oil pumps, heavy gear boxes, etc.? As John Wilson said, a complete systems engineering approach is needed. When the change is so fundamental, every system has to be thought out.

Then again, what about hybrids? Use of a small engine to keep charging while in flight would minimize the need for full recharges on the ground. (Although I know it starts to break the weight issue having two sets of engines.)

Posted by: William Barto | October 6, 2011 2:52 PM    Report this comment

How many early adopters are out there with checkbook in hand ready to break the surly bonds of earth in an electric plane that requires different care and feeding and limited range? I was an early adopter of the Unison Slick Lasar mags. I'm pretty handy with a meter and schematic which is good because I never found a mechanic who would work on it. Imagine coasting up to the Moosebreath Montana FBO in an electric plane looking for an electrician/mechanic. I can hear the laughter now . . .

Posted by: THOMAS M CONNOR | October 6, 2011 2:53 PM    Report this comment

I don't have time to read all the comments, so my apologies if this was mentioned by others already.

There's a great article on the futility of electric cars. Maybe small GA airplanes would still be able to work out under the premise of that article given there's about 3 orders of magnitude more cars, but I think it's still instructive.

www dot altenergystocks dot com/archives/2011/08/its_time_to_kill_the_electric_car_drive_a_stake_through_its_heart_and_burn_the_corpse_1 dot html

Replace " dot " with "." for the link.

There's a ton of info in that article but the gist is that there's simply not enough of the metals necessary for the high-density batteries to go around to support large scale EV adoption. That aspect will drive battery cost through the roof and destroy any likely economic advantage. Additionally the curve for battery energy density improvements is far too shallow for any expectation of sufficient increases in the foreseeable future.

Bottom line - Electric is great for niche markets, but stinks as a mass transportation energy source, and is not practical for long distance uses.

Posted by: Andrew Upson | October 6, 2011 3:00 PM    Report this comment

From the few articles I've read of the electric planes they are lightly-built gossamer-winged contraptions built for a specific purpose and wouldn't survive a head-on crash with a mosquito. A certified electric spam-can would have to prove crash survivability in testing. I must admit, the auto industry has come a long way since my 1957 Chevy: It was guaranteed to pop the doors open in a crash so I could run alongside if I wasn't already impaled on the steering column. That doesn't happen any more, and the cars are lighter to boot. Those design features in a modern airplane should enhance survival.

Posted by: THOMAS M CONNOR | October 6, 2011 3:02 PM    Report this comment

Thank You Ronald.

I was growing tired of the one-sided discussion of how dangerous batteries were because they were flammable but no mention of how inherently dangerous handling liquid fuel is. Yet we have made explosive gasoline a (relatively) safe power source.

There is nothing about batteries that makes them inherently more dangerous than liquid fuels.

My question is what is the cost per cycle of the battery? Batteries are VERY expensive and have limited lifespan. While the cost of the electricity is relatively low, what is the cost of the battery expressed in terms of it being a consumable like liquid fuel or kilowatt hours of electricity?

Posted by: KRIS LARSON | October 6, 2011 3:11 PM    Report this comment

Part of the problem with the instant information age is that experimental designs seem to look like the real thing. These aircraft were designed to meet a specific goal, not real life.

It will likely take at least an order of magnitude or two for battery density to be sufficient for multi-purpose flight. To that you have to get the cost/weight to reasonable levels.

It's a good path to explore, but don't get your checkbook out yet. The electric car is a much easier problem to solve, and it is far from being practical to date.

Posted by: RAY DAMIJONAITIS | October 6, 2011 3:15 PM    Report this comment

Tom, modern cars are NOT lighter for a comparable size. A 1957 Chev Belair weighs in at about 3300lbs while a 2011 Impala is 3555lbs. Stronger/safer, definitely. Lighter, no way.

Posted by: Mark Spellman | October 6, 2011 3:19 PM    Report this comment

@Tom Conner

"Mogas has an energy density of 33.41 KwH/Gallon, not Kg as I said. Converting a 6 lb gallon of gas to Kg I get 2.73 Kg/gallon. 33.41/2.73 = 12.24 KwH/Kg. 12240 watts/160 watts = only 76.5 times more energy in a Kg of mogas vs a Kg of Tesla battery."

But we must also take into account the lower efficiency of the IC engine, with its Carnot Cycle Thermodynamic efficiency limits. Consider that a 180HP horse power engine running at 75% power burns 10Ga typically... and produces 100KwH of power. Thus, the *available* energy is only 10KwH/Ga. Thus, present battery tech is only 25 times lower specific energy density. Again, given the time course that we can envision, I fully expect that in 20 years, ultra-capacitor tech will improve that much.

About the charging issue... yes, trying to use low voltage/high current charging won't be practical. But, I imagine high voltage/moderate current will be. And yes, it will mean taxi-ing up to a special charging station for quick charge.

Posted by: Candice Brown Elliott | October 6, 2011 3:59 PM    Report this comment

OOPS...the weblink was removed but you can search RC Groups for "100% scale, Electric Lazair". There are also some Youtube videos of this project as well.

Posted by: Randal Dallas | October 6, 2011 4:10 PM    Report this comment

@Kris Larson

"My question is what is the cost per cycle of the battery? Batteries are VERY expensive and have limited lifespan. While the cost of the electricity is relatively low, what is the cost of the battery expressed in terms of it being a consumable like liquid fuel or kilowatt hours of electricity?"

Kris, today's Li ion battery is probably good for a thousand moderately deep 'cycles'. At two hours flight per cycle, that gives it a 2000 hour TBO, similar to the engines we fly behind today. If those batteries cost the same as a rebuild, then it is a wash. But, I fully expect that price to come down. And of course, as one can see from my earlier comments, I'm betting on ultra-capacitors to improve even faster.

Posted by: Candice Brown Elliott | October 6, 2011 4:13 PM    Report this comment

Here's a simpler url to Andrew Upson's link regarding electric vehicles.


Scroll down a bit. It's the second article.

It's worth a read because it looks at the 'rare earths'required by electric vehicles, windmills and solar panels to achieve their efficiencies. They are called rare earths because they are - um- rare, and the author claims the rising price of these metals is changing 'green' (ptui) plans to save us from ourselves. Specific to this discussion is the "M" in MiMH batteries. The M is the rare metal Lanthanum.

when compared to hydrocarbons he describes electric vehicles thus: "When batteries are used as fuel tank replacements, a single kWh of capacity can only save 19 gallons of fuel per year and most of the fuel savings at the vehicle level will be offset by increased fuel consumption in power plants."

The author also addresses the hopefullness noted in this blog that 'someday battery technology will improve.' Data: Over the 160 years of storage battery design, energy densities have improved a factor of six. Hardly Moore's law where we expect micro-electronics to double in capacity at half the price in 18-24 months.

Posted by: THOMAS M CONNOR | October 6, 2011 4:23 PM    Report this comment

Quit wasting my tax money only silly things like this. It is no where near a reality.

Posted by: Stuart Baxter | October 6, 2011 4:39 PM    Report this comment

Candice Brown Elliott

"given the time course that we can envision, I fully expect that in 20 years, ultra-capacitor tech will improve that much."

I have a fair amount of experience with industrial start and run capacitors and know they need to be sized to the desired phase shift/torque/load requirements. Hence I wonder at the advantage of a super-capacitor on a motor. Do you have a URL to share or make your thinking more transparent?

Posted by: THOMAS M CONNOR | October 6, 2011 4:52 PM    Report this comment

@Tom Conner

You said: "Thielert Centurion diesel engines cannot use composite props because of the pounding from the diesel despite an elaborate gearbox and shock absorber system designed to absorb the power pulses."

Better notify Diamond Aircraft. Every
Thielert powered TwinStar I've flow or
looked at has an MT Composite prop.

Posted by: Ric Lee | October 6, 2011 5:20 PM    Report this comment

Battery cycle life

The IO360-C1C6 in my arrow went 2200 hrs and cost $24,000 to rebuild.
a battery to power a similar 4 place plane would probably cost no more but the fuel (electricity) would cost a lot less than the 25000 gal of avgas thai i bought in those 2200 hours. 1000 to 2000 cycle battries seem reasonable with preformance degrading somewhat during the life of the battery. In any case the two place trainer and sport plane are likely to be the most popular electrics.

Posted by: Roland Boucher | October 6, 2011 5:47 PM    Report this comment

Ric Lee
Ric Lee:
I swear I read several accounts of M-T props delaminating on the Diesel but after an hour of search I cannot find anything about it, so I must have been on drugs. Thanks for correcting me!

Posted by: THOMAS M CONNOR | October 6, 2011 7:48 PM    Report this comment

"Now get this...the gas used to recharge the batteries was substantially less than what the gas motors he used on the plane, prior to switching to electric, would have used for equal flight time."

Perhaps he should have gotten rid of the gas engine on the generator, replaced it with one of his electric motors, got the whole system spinning,and scooped up all of the excess electricity.

Posted by: Richard Helm | October 6, 2011 8:10 PM    Report this comment

I'm enjoying this thread because it brings out how prevalent is the tendency to gloss over or even better totally ignore hard truths.

By way of example, many posters appear to at least acknowledge that although a battery of adequate capacity may currently be far too heavy to power an airplane, they embrace without reservation the notion that all we have to do is wait a few years, technology will improve them by a factor of 10 or so, and bingo, we will fly!

Doubtless this tendency is, as others have noted, related to the success of the computer industry in keeping pace with Moore’s Law, which holds the relative complexity of micro-electronic circuits will double every two years.

Unfortunately, Moore’s Law won’t work with devices like batteries, where advances are circumscribed by the physics of chemical reaction. Unlike micro-circuits, you can’t miniaturize molecules. This puts the improvement of any given battery type into the same category as jet engines where progress is measured not by predictable jumps of 50% per year but in a painful steps of few percent each.

Posted by: John Wilson | October 6, 2011 8:19 PM    Report this comment

John Wilson

Batteries have been flying planes for over 40 years (april 1971 in usa) these planes carried a payload of 25 percent and more (they were called radio's) Today's batteries are good for over 2hr flight time and up to 300 mile range
this is not just a theory it was proven last week

The job of desiging and building a comercial product can now begin--in the case off the wnning team a very attractive four place plane is under development-

Today I am retired and just an observer- take a look at their web site
Roland Boucher

Posted by: Roland Boucher | October 6, 2011 8:43 PM    Report this comment

Has anyone seen a price tag for an electric plane? We have electric cars to compare with- with $3500 for a prius battery pack but no clue about motor, prop and controller costs. What does an unsubsidized Volt go for, $50k? What's the automotive to aviation cost conversion rate these days?

Then there is the cost of certification. Oh my.

The feds have certification procedures for spam can jet, gas and diesel. What are the cert requirements for an electric propulsion system? They would have to be all new, created by the risk averse bureaucrats at the FAA. Just as a thought experiment, what are the redundancies and software certification a bureaucrat might dream up? In my feeble mind that relegates electric planes to the experimental camp.

Posted by: THOMAS M CONNOR | October 6, 2011 8:56 PM    Report this comment

There is a basic concept that should be understood. When taken from the grid and used to power an aircraft or car for that matter, electricity is merely a power transmission and storage system, and not an energy source in itself. Since fossil fuels are by far the greatest source of energy for electrical power generation worldwide, it is essential to use the well-researched and documented efficiencies for these plants as the basis for the derived fuel efficiencies of (grid powered) electrically driven vehicles. If one takes the efficiency at the power station as 37%, the transmission efficiency to the domestic socket or outlet as 83%, the combined efficiency at the outlet will be around 31%. Now, assuming a combined transforming and rectification efficiency of 95%, no battery storage losses, and a combined controller and electric motor efficiency of 95%, the total system efficiency would be around 28%.

This is, of course rather less efficient than a modern, optimally operated gasoline engine, and very much less than a modern turbocharged common-rail automotive diesel power plant.

I’m enthusiastic about developments that reduce non-renewable fuel usage. But we have to be careful not to be misled by industrial and media hype that electric vehicles fuelled from the grid, are magically more efficient than contemporary internal combustion engines, aren’t using fossil fuels and don’t pollute or emit CO2 - when in fact, they are demonstrably worse!

Roy Venton-Walters

Posted by: Roy Venton-Walters | October 6, 2011 9:01 PM    Report this comment


I am afraid your grid power efficiency is more of a political comment than a technical one. It doesn't matter to an electric airplane whether the power came originally from evil coal or nearly as evil oil or gas. It is still a very efficient use of the power once it enters the airplane.

You may be correct about world wide power being derived primarily by fossil fuel, but where I live it is all derived from renewable energy - hydroelectric dams. There is also a lot of use of nuclear power - a completely pollution free source of energy. In some parts of Europe (particularly France) nearly all electricity comes from nuclear reactors.

Posted by: PAUL MULWITZ | October 6, 2011 10:26 PM    Report this comment


As you know there are no commercially available sport planes yet. There is a lot of talk about products in development, but you can't go to the local dealer and buy one.

The motor and controller I saw on display at Oshkosh from Yuneec cost around $10,000 total. Batteries must be added to this cost.

Certification for FAA part 23 planes is in the works, but ASTM standards are already approved for LSA with electric power. That means it could be feasible for a factory built LSA sport plane - fully certified - as soon as the factories can produce them. I would guess there was little difference for a manufacturer to certify an LSA with electric power than one with gasoline power.

The ASTM standards aren't quite enough since the FAA still has to agree to issue airworthiness certificates. They have promised that when the planes are ready they will also be ready. The FAA guys that hang out with ASTM F37 committee are very enthusiastic about electric power for light planes.

Posted by: PAUL MULWITZ | October 6, 2011 10:34 PM    Report this comment

John Wilson,

I agree with you that Moore's law doesn't apply to battery chemistry. Fortunately that is not the only way for technology to advance.

If it was only airplanes that needed better batteries then I would not be optimistic about big developments in the near future. The truth is that cars are in the same boat. There are a lot of car manufacturers and government labs that support them that really really want better batteries to replace the thirst for petroleum we all experience now. It is the effort of all these people and the huge amount of research money spent for this purpose that aviation can piggy back on. It is this thrust that makes me think it will be very soon when we get big gains in battery energy density.

Posted by: PAUL MULWITZ | October 6, 2011 10:41 PM    Report this comment

There have been a few references to 'wasted' or unused power on the commercial power grid. I don't have first-hand knowledge of how the load vs supply is managed, but I've been an unwilling participant in many local discussions as the greens killed a coal plant my coop claimed was needed to provide 'base' power. In the end, the greens let them build a gas-powered plant that the coop managers say can only provide 'firming' power and they still need to find a source of base power. The need arose because their Bonneville power contracts expire in a few years. Apparently, firming power can start quickly and assume 'new' or sporadic loads on the grid that exceeds the base power capacity. Other sources, such as hydro-power were referred to as 'spinning reserve', able to increase output quickly because the dynamo is already rotating as water goes down the spillways to satisfy fish needs, but it might not be producing power until an exciter current is applied. Said another way, some power sources appear to be throttleable, others not so much, resulting in less 'wasted' power than some may think.

Posted by: THOMAS M CONNOR | October 6, 2011 11:27 PM    Report this comment


A little girl attending primary school was absolutely horrified when her teacher mentioned that milk came from cows. “No it DOES NOT” she protested, in tears and in firm denial; “My mom gets it in plastic cartons from the supermarket shelf!” Do her words and demeanor remind you of someone, Paul?

Roy Venton-Walters

Posted by: Roy Venton-Walters | October 6, 2011 11:45 PM    Report this comment

Good one Roy. I am glad someone has a technical grasp on the subject.

It doesn't matter if you live where there is a hydroelectric plant. The whole electric airplane contest was touted as the "green" solution, and it is not. They even equated electrical power used in the aircraft to miles per gallon of fossil fuel. Roy I think you hit the point of the whole thing right on the head.

It simply floors me that people seam to think that electricity is a power source. I have heard people on the internet state that electricity is one of the solutions to the energy crisis. They don't seam to get that it has to be generated from something.

These guys, in the competition, were using extremely efficient aircraft with low power motors. I dare say that a small gas engine, of the same power, on any of those planes, flown in the same way, would have been more efficient, if you measure the energy as the fuel being used not the electricity as the transmission system.

Posted by: Richard Helm | October 6, 2011 11:52 PM    Report this comment


Sorry first link seem to have been eliminated. Let me try again.


Roy Venton-Walters

Posted by: Roy Venton-Walters | October 7, 2011 12:13 AM    Report this comment


Try this... If it doesn't work, I'm giving up.


Roy Venton-Walters

Posted by: Roy Venton-Walters | October 7, 2011 12:19 AM    Report this comment

I don't know if electric power for airplanes is green, blue or purple. I also don't care.

On an economic level (hopefully politically neutral) the world has a big problem with petroleum addiction. This shows up more in transportation than anyplace else. We can substitute all sorts of power sources for most energy demands, but only petroleum seems to work for transportation. Malthus got it wrong. Overpopulation doesn't seem to result in starvation from lack of food. It seems the world economy is choking from lack of oil. Crude oil is ten times more expensive in US Dollars than it was just a few years ago and there is no reason to think the supply imbalance won't raise the prices by another factor of 10 in coming years.

For recreational fliers the cost of fuel is a show stopper. As technology stands now it is almost practical to fly electric airplanes with an hourly price rate that is a very small fraction of light planes with IC engines. Planes powered by electricity instead of 100LL will save at least 90 percent on fuel and probably a lot more on maintenance costs and reserves. The price of a new plane with electric power is just slightly above the IC plane today and I believe battery improvements will make it considerably smaller in the near future.

I know only a few recreational pilots can afford to buy a new plane - even a new LSA. Flight schools will find the business case for electric trainers much easier with much lower hourly rates than current trainers.

Posted by: PAUL MULWITZ | October 7, 2011 12:43 AM    Report this comment

This is all very exciting to me. I believe the impossible is possible, and I particularly appreciated on of the team membersprophetic comment that we'll see supersonic electric flight within a decade! I experienced the contagious enthusiasm of the space race, and have long looked forward to the day when we could collectively enjoy the evolution and birth of a new possibility born out of a seemingly impossible objective. Kudos to Google and others who encourage and inspire innovation.

Posted by: Chase Snodgrass | October 7, 2011 1:21 AM    Report this comment


Now we have something that we both absolutely agree on, our addiction and overdependence on oil. As demand necessitates, the line between oil and the other fossil fuels is rapidly becoming less well defined. In fact only a few months ago the US military cleared a bill permitting coal to be synthesized into liquid fuel for military purposes. In addition Natural Gas is increasingly being used in vast quantities to help convert tar sands into liquid fuel: An extremely wasteful and polluting way of effectively converting Natural Gas to oil. So, nowadays, you can’t really distinguish between the misuse of oil and the misuse of other fossil fuels. It’s all out the same damn bucket.

But Paul: Where I disagree with you is over the priorities that you appear to be placing on fossil fuel wastage. Price; cost; dollars; appears to be your only criterion of fuel usage. If it’s cheaper to use electricity and thereby waste fossil fuels as a by-product of that action, then you will do so. This is what you are saying when you say “Planes powered by electricity instead of 100LL will save at least 90 percent on fuel…” You can’t mean save 90% on energy usage, because one can clearly show fossil fuel usage will actually be greater. Ok, now I see it; let’s waste energy to save you some loot. Fair enough. But please don’t do it under the false name of conservation and saving the world.

Roy Venton-Walters

Posted by: Roy Venton-Walters | October 7, 2011 1:59 AM    Report this comment


Actually, electrically powered supersonic flight has already been demonstrated by the military. It’s called a Rail Gun. However, I imagine a manned version might be a tad hard on the eyeballs, though!

Roy Venton-Walters

Posted by: Roy Venton-Walters | October 7, 2011 2:31 AM    Report this comment

"On an economic level (hopefully politically neutral) the world has a big problem with petroleum addiction."

This is kind of a silly statement. To understand how silly, I would recommend for you several books: Vaclav Smil's Energy Myths and Realities and his companion volume, Energy at the Crossroads, also Huber and Mills' Bottomless Well and Robert Bryce's Power Hungry. To that reading list, add a new volume: Daniel Yergin's The Quest.

Taken together, these books will give you a well-rounded view of primary energy theory and the history of primary energy sources. Reams of supporting data, graphs and so on.

You would then view the word "addiction" used in the same sentence as oil for exactly what it is: The product of a general press that's too shallow and unsophisticated to write on this subject intelligently, much less with enough sophistication to inform a public used to thinking in 10-second sound bites.

Posted by: Paul Bertorelli | October 7, 2011 4:47 AM    Report this comment

I really didn't want to change the subject of this discussion to energy policy and politics, but I can try once more to clear this up.

Price is the way a free economy measures value. The crude oil price increase proves there is a shortage of this stuff. This is not a wild theory about saving the world from carbon or some 10-second sound bite. It is simple reality disclosed by the free economy.

The only energy source that really works today for transportation is petroleum. It can be gasoline for cars, diesel fuel for trucks and ships, or jet fuel and it always comes right back to crude oil.

The world produces around 80 million barrels of crude oil per day. It also consumes that much. Demand for oil is rapidly rising. Movement of the two most populous countries in the world, China and India, into the industrial age places a lot more demand on all sources of energy than the world can supply. This is focused heavily on oil because of the transportation energy monopoly it enjoys.

So, any legitimate movement of transportation energy use from oil to anything else really helps out the world economy. This shows up in prices. The cost savings for light plane use of electricity is a clear and unbiased sign that this is a good thing to do. It will also increase demand for light aviation due to lower prices.

Posted by: PAUL MULWITZ | October 7, 2011 5:59 AM    Report this comment

There are already two applications where electric is a better solution: the self-launching sailplane, and the ultralight. I could argue that aerobatics may be a third. For sailplanes, the advantage of reliable starting dominates other considerations. In a sailplane, when you need your cold-soaked (from altitude), rarely-run motor to start, you need it to start. Now. Other features, such as relative quietness, and the lack of fuel smells inside the aircraft, and the ease of maintenance, are (very) nice to have, but have to be traded off with the much-superior range of gasoline-powered motors. For ultralights, range isn't that important anyway, but reliability and low noise are huge. And, for aerobatics, range isn't that important either, but throttle response (and even the ability to reverse the prop) may be quite interesting.

The application of electric to training fleets is interesting. I'm not sure it makes sense, but I'm not sure it doesn't.

Posted by: Thomas Boyle | October 7, 2011 7:55 AM    Report this comment

For "go-places" airplanes - even for "$100 hamburger" applications - we're not there yet. There is a "Moore's Law" of sorts for batteries, but it involves performance doubling every 9 years, not every 18 months. With all the money going into research that rate may improve some. So, an airplane with 4 hours' cruise at 100+kt could be feasible in a decade. Sure, it would need charging, but that's still approaching useful.

To me, reliability and operational simplicity are the appeal of electric motors. The electric motor is a vastly simpler piece of kit than either a piston engine or a turbine. It has one rotating part (and possibly a gearbox, which is relatively easy to build when you don't have to deal with the impulses from a piston engine). You're looking at reliability comparable to turbine engines (potentially better) in GA airplanes, with almost nothing to do on the annual inspection. Add to that, you have single lever control, no density altitude issues, low noise (just the fan noise from the prop) with benefits for the occupants and for community acceptance of airports, minimal vibration (prop pulses on the airframe), and a much greater degree of flexibility in airframe/propulsion layout.

Now we need a major jump (approx. 5x would be good) in battery storage or a breakthrough in fuel cells that can consume avgas or Jet A. Unfortunately, it is likely to be a decade-long (or longer) wait for either.

Unless, of course, you want to fly a sailplane or an ultralight.

Posted by: Thomas Boyle | October 7, 2011 7:59 AM    Report this comment


I agree with most of your comment and analysis. However, I think you are asking for a little bit too much for electric power to work. Perhaps you are considering current IC plane capability of 4 hours rather than my choice of 2 hours cruise range.

For recreational flight (my sole interest) and for training flight a one to two hour flight is all you really want. After this length of time a student is over worked and an old guy like me is really ready for a pit stop. It is only when you are trying to do "Commerce" that you want longer range to cover lots of miles in a relatively short time.

Also, I think "Stepper Motor" technology will win out for the electric motor. This moves the "Gear box" requirement back to the electronic controller. This kind of motor is also called "DC Brushless" which means there really is only one moving part (not counting bearings).

Posted by: PAUL MULWITZ | October 7, 2011 8:12 AM    Report this comment

One of our participants wrote:

> I prefer open-air flying to being stuck
> inside a can, ............

Unfortunately an open-cockpit aircraft like the Stearman biplane has higher aerodynamic drag than a plane such as the Van Grunsven RV-6 (See page 59, October 2011 Flying magazine). So if you are going to use electric propulsion, it would be more necessary than ever to use the latter kind of airframe design. I am in favor of research on electric propulsion systems for airplanes for the following reasons: 1. If one utilizes wing tip vortex energy recovery systems (essentially a small propeller in reverse mounted on the end of a wing so as to recover wing tip vortex energy), the electric power thus generated will replace some of the power normally supplied by an engine-driven alternator. 2. If it is possible to mount solar cells on an upper wing or fuselage surface without increasing skin drag, that too would supply power for which you would otherwise have to burn fuel. So even if a pure electric airplane isn't to one's liking, the technology being developed for such could be applied to reducing fuel consumption of the aircraft we presently have.

Posted by: Alex Kovnat | October 7, 2011 8:27 AM    Report this comment

Has anyone considered the down falls of these sort of batteries ie. the thermal runaway fire hazard (inherent in NiCad) which can be dealt with using a thermostat to shut off the battery supply and what about the battery at the end of it's charge suddenly dropping to low or 0 volts? I guess that would be like running out of gas but this is a variable, my understanding is that these batteries have a shelf life with ever shortening life spans so the idea that you could trade batteries at the nearest FBO may have to be based on the battery's age or better on amount of recharges.

Posted by: Luke Vanworkum | October 7, 2011 8:44 AM    Report this comment

"The crude oil price increase proves there is a shortage of this stuff. This is not a wild theory about saving the world from carbon or some 10-second sound bite. It is simple reality disclosed by the free economy."

No, it doesn't. It proves there are distribution interruptions, not an inherent supply shortage based on dwindling resources. You seem to be suggesting we're running out of oil, hence the addiction comment. We aren't running out of oil. (See Yergin, Huber, et al.)

You probably know about the Hubbert pimple and other peak oil predictions. There's now a cottage industry in debunking these, given that proven reserver are higher than ever and new resources or being found.

The point is, if you say "addicted to oil" you might just as well say addicted to prosperity, or driving, or flying, because oil (and gas) is the dominant primary energy sources. As Smil points out, primary energy source transitions have typically taken decades and we are in the middle of the age of oil.

The transitions occurred because market sources made alternatives more viable; wood replaced carbohydrates, coal replaced wood, oil replaced coal. The replacement for oil is hardly in sight because alternatives aren't even close to being viable primary energy sources, but rather niches.

Posted by: Paul Bertorelli | October 7, 2011 10:20 AM    Report this comment

How this relates to electric airplanes is this: I think they will fail to potentiate in any meaningful way that moves the market. They'll find niches alright, early adopters and the curious and dedicated environmentalists. Just enough to garner sales in exactly the same way the LSA segment has. A lukewarm dribble of market activity. No cigar. I wouldn't be surprised to see them fail entirely.

That's because oil and the internal combustion engine will remain dominant for several decades, if not longer. Improving engine efficiency will outstrip the phony Moore's laws claims being made for battery development.

Hybrids will and are making great market gains in surface transportation, but the duty cycle means they make no sense for airplanes. There's nothing on the horizon that suggests this will change.

Except for one thing: If the body politic gets serious about restricting carbon emissions. That could change things radically.

Posted by: Paul Bertorelli | October 7, 2011 10:33 AM    Report this comment

Paul B,

I agree with you about hybrids. I love my Camry Hybrid automobile, but I'm convinced it is the intermittent duty cycle inherent in local driving that makes this work. Airplanes, farm tractors, and long haul truckers won't gain much from this elegant technology.

I also agree that any transition away from oil as the dominant transportation energy source will take decades or longer. Even if a new technology were free to use the capital needed to replace all the cars, trucks, planes, and ships would guarantee a slow transition.

Still, if light plane manufacturers can offer a moderately priced airplane that needs only a few dollars per hour for fuel and maintenance this would find a welcome market in the primary flight training industry. It would also encourage a lot of people to take up recreational flying. This is the outcome I hope to see before I am too old to enjoy the change.

I don't see a need to convince you that it is supply vs. demand for crude oil above the ground, not buried two miles into the earth, that controls the price. If you prefer to believe it is all a big conspiracy and speculators that is your privilege. I don't think we will run out of oil soon. I do think the supply cannot keep up with the rapidly growing demand.

Posted by: PAUL MULWITZ | October 7, 2011 10:52 AM    Report this comment

Paul M.,

For your application I agree, feasibility is reached sooner. But - most people like an hour in the tanks when they land, and the $100 hamburger is likely to be an hour away, so you need closer to 3 hours before even the recreational market looks promising.

Separately, on the motor: direct drive is appealing but you get lower motor weight by driving up the RPM and putting in a gearbox - same as with internal combustion! (Again, a gearbox on an electric motor is much easier: what tears gearboxes apart on airplanes is the hammering from the power impulses in piston engines.)


Posted by: Thomas Boyle | October 7, 2011 11:40 AM    Report this comment

Whether is it ground based or airborne, the discussion of the economics of alternative fuels always seem to forget one major issue; TAXES. This discussion is no different.

Those who promote alternative fuel for ground transportation always compare the cost of "fuels" like used doughnut oil and electricity to the fully taxed cost of gasoline. The resulting comparisons are skewed by the tax subsidy of not paying road tax. The same happens with aviation.

Fuel taxes are an efficient and fair way to collect revenue to support transportation infrastructure. How are they going to tax electrons?

User fees anyone?

Posted by: KRIS LARSON | October 7, 2011 11:44 AM    Report this comment

Mary Grady's original question was 1. Is it green, whatever that is, and 2. Is it practical? I'll add a third that many have addressed in an oblique manner: 3. Is it convenient, at least more so than IC power.

I think Roy Venton-Walters did a marvelous job of describing the efficiencies of converting coal into prop wash, and from a systems point of view, IC does better and I cannot improve on it.

Apparently practicality is in the eye of the beholder. Electric and hybrid car owners speak of worrying about range, $2500 battery chargers, 480 Volt batteries and deciding between defrosting or locomotion, but they still love their Leaf/Prius/Volt/Tesla, so why wouldn't they love an electric plane? I have a friend who loves his '90 Fiat Ppyder. He's even had it running a few times. Like love, there's no explaining it, and madison Avenue depends on it. Think about the Marlboro man ad campaign, one of the most successful of all time. What do horses and chaps have to do with cigarettes? Who knows but it sells butts.

Are electric aircraft convenient, I.E., easier to maintain and cheaper than IC? We don't know. Aviation Consumer hasn't gotten owner feedback yet, yet writers write as if they have one in the hanger with lots of hours on it. A bit of horsies and chaps perhaps?

Posted by: THOMAS M CONNOR | October 7, 2011 11:56 AM    Report this comment

There seems to be a lot of me-too-ism and wishfull thinking. "If only batteries had 100x more energy density and cost a buck two ninety eight per ton I'd buy one". That thinking is the huckster's playground, so beware. There is a reason the US Patent Office will not accept patent applications for perpetual motion machines without a working model. You shouldn't either.

A good antidote is Robert Park's book "VooDoo Science" in which the author describes how quickly people flock to widgets that defy the laws of physics and thermodynamics. No working model either. It's a testament to the lack of science education in this country, but I won't go there except to say the green movement depends on ignorance and non-critical thinking to expand it's flock. Please learn to ask the hard intelligent questions. Be skeptical.

Finally, Mom said never buy the first version if anything. V2.0 almost always works better. "airworthy' stuff seems to be the poster child for stuff rushed to market.

Posted by: THOMAS M CONNOR | October 7, 2011 12:16 PM    Report this comment

Anyone that thinks parallel hybrids, e.g. Prius, are a good idea from an efficiency or environmental standpoint must have failed thermodynamics (FTR that was one class I was proud of the C I earned - but I passed the first time and still maintain a basic understanding).

Series hybrids (e.g. diesel-electric submarines and freight trains) have their place, and in a car make more sense than a parallel hybrid. But unless the aspects of electric propulsion are a major requirement for a given application (low noise, super high torque at low RPM, etc) they still loose out in the overall cost and efficiency perspective.

Posted by: Andrew Upson | October 7, 2011 12:47 PM    Report this comment

On the side issue of the cost of oil: A reasonable measure of the value of the dollar is the price of oil, gold and US postage. In inflation-adjusted dollars oil is a bargain, and that's despite increased demand from India and China.

Another way to look at it is the market price of dollars, reflected in it's cost to borrow. Treasury is presently 'lending' dollars at zero interest to banks who are lending it to home buyers at less than 4%, which means dollars are cheap compared to gold, postage and oil, so it only makes sense that the cost in dollars goes up: Dollars are worth less.

The dollar also enjoys an advantage as the currency of oil - so far oil is priced in dollars, not rials, kroner, drachma or euros for reasons I won't go into. That could change. If it does, expect a big jump in the price of oil.

Posted by: THOMAS M CONNOR | October 7, 2011 1:24 PM    Report this comment

"If you prefer to believe it is all a big conspiracy and speculators that is your privilege. "

I'm the last guy to believe in conspiracies, by the oil companies or anyone else. No, it's just the way the oil business works. Demand has proven wildly spikey and production can run in fits and starts. For example, U.S. gasoline demand is off the peak of 2007 and some say it will be a long time recovering because of people switching to hybrids like you are driving.

Eight times in the last 20 years, the price of gasoline has fallen below the inflation-adusted 80 year average. Will it again? Don't bet that it won't. Big price swings like that play havoc with consumer behavior and don't bode well for electric transportation. The oil industry has and is undergoing massive evolution that most of us don't see or understand. Yergin's book treats it.

So along comes the budding electric airplane idea in a market that volatile. Forget the battery endurance, cost and all the rest of it. Think about market acceptance sufficient for businesses to survive. Good technology does not a marketable product make.

Posted by: Paul Bertorelli | October 7, 2011 1:39 PM    Report this comment

There are a few people with electric aircraft in the hangar, with at least some hours on them. Commercial aircraft, not experimental ones.

Dick VanGrunsven is one of them. He's written about his experience - good and not so good - and perspective on the future at vansaircraft*/RVator/2009/4-2009-RVator**P (replace the * with .com and replace **P with .pdf).

On the subject of whether batteries will ever compete with internal combustion, I'm inclined to think it's quite likely we'll see the energy stored in hydrocarbons, with a fuel cell to convert that to electricity, that then goes to the motor. The gain would not be in efficiency, so much, but in reliability and the various other advantages of electric power. That's likely to be a long way off. I expect that batteries, as we now conceive of them, are quite likely to never break out of the niche applications.

Some of those niche applications look fun, though!

Posted by: Thomas Boyle | October 7, 2011 1:42 PM    Report this comment

"I agree with you about hybrids. I love my Camry Hybrid automobile"

Yet the new VW Passat TDI is lighter, roomier, cheaper, simpler, and more efficient all at the same time. The VW's 800 mi range on a tank is also a bonus. Point being is that the best hybrid is actually worse than old technologies.

Electric flight will also be second class on roominess, range, simplicity, and flexibility. I seriously doubt if flight schools would accept a 2-4 hour down time between rentals.

Posted by: Mark Fraser | October 7, 2011 1:42 PM    Report this comment

oops... the link disappeared. That really is annoying AVweb !!!!


replace the ** with http//

Posted by: Candice Brown Elliott | October 7, 2011 2:38 PM    Report this comment

oops... the link disappeared. That really is annoying AVweb !!!!

That may be, Candice. But it's a hell of a lot more annoying to see 20 spam messages for Rolex watches and ladies fashions, which is what you'll get if we turn the link option back on.

Sorry. Just don't have the time to patrol it for spam.

Posted by: Paul Bertorelli | October 7, 2011 3:08 PM    Report this comment

"I seriously doubt if flight schools would accept a 2-4 hour down time between rentals."

Of course they wouldn't, which is why the winning technology will be a modular battery unit on a little cart. Yank the depleted battery out, put the fresh one in, then plug in the cart.

It's an easy solution already being discussed. Doesn't mean it's economical, but it's not a technical show stopper.

Posted by: Paul Bertorelli | October 7, 2011 3:17 PM    Report this comment


Thanks for the link but it was not helpful unless I pay 32 lb sterling for an article that may or may not be informative, so the lack of data about advances in super-capacitors continues. You seem reluctant to say anything concrete. How about some words on how the super capacitor enhances motor operation?

Glad there are optimists. As a pilot closing in on 10,000 hrs I've become a skeptic bordering cynic. Some say I've crossed that line and gaining speed as others try to kill me while claiming to save me. From what they can't specify.

After 160 years of storage batteries and 110 years of electric motors making incremental improvements and a long history of failed revolutions in the marketplace it must take a stiff upper lip to stay positive.

I grew up on a farm with a pitcher pump, icehouse, outhouse and a state of the art 32 VDC windmill, battery bank and a few light bulbs. We could not wait to get on the grid and install an electric water pump, toilet, Frigidaire and burn the outhouse. Oh, and add an Easy washing machine with the open spinners that could rip a curious kid's arm off and keep on rinsing. At least we skipped over the gasoline-powered model. Entertainment tended toward hoeing corn or tending to the fruit orchard with a 'pop-n-johnny' powered sprayer. Or 4H electrical projects.

Posted by: THOMAS M CONNOR | October 7, 2011 3:50 PM    Report this comment

I included that because I tend toward the practical, labor saving and cheap. Spending big bucks to do what my $10k 42 year old Cessna does better is a hard sell. Buying into vaporware and conceptual hardware takes effort on my part. Help me understand your enthusiasm about super-capacitors?

Posted by: THOMAS M CONNOR | October 7, 2011 3:50 PM    Report this comment

Tom and Candice,

There are a lot of enthusiasts over super capacitors. This subject came up several times in the Oshkosh electric symposium, and the experts said the capacitors just don't hold enough energy compared to batteries. I forget the details, but there is one or two orders of magnitude difference in energy density to overcome.

Super capacitors are another energy storage device that includes some very exciting charge and discharge speeds compared to batteries. However both technologies are slowly progressing and the batteries seem like they will maintain the advantage for a long time.

Now if you are talking laser weapons or something else that benefits from very high current discharge then the capacitors do seem like an exciting technology.

Posted by: PAUL MULWITZ | October 7, 2011 4:41 PM    Report this comment

Paul m

So the supercapacitor is being touted as a battery replacement and not a phase shift device?

Posted by: THOMAS M CONNOR | October 7, 2011 4:48 PM    Report this comment

Thomas Boyle

Thanks for the vans article. Finally, someone with practical experience!

Posted by: THOMAS M CONNOR | October 7, 2011 4:51 PM    Report this comment

Just read the Van's article and have some comments

but first lets talk Super Capacitor

the are used in indoor free flight plabes and have been sugested for the Science Olympiad midle school competition. they work great

Posted by: Roland Boucher | October 7, 2011 4:59 PM    Report this comment

OK lets try again
but first lets talk Super Capacitor

the are used in indoor free flight planes and have been sugested for the Science Olympiad midle school competition. they work great BECAUSE THEY DO NOT HAVE ANY WHERE NEAR THE ENERGY OF A LIPO BATTERY. No one wants to watch a free flight plane cruise for hours in a gym...the Super cap maked 90 sec a challange

Now to the Van Article

His plane is a self launched Saiplane... the operating mode is power-off

his battery was less than 20% of his gross weight and his prop was small for the job it had to do.

A SERIOUS ELECTRIC DESIGN SHOULD ALLOCATE 50% OF GROSS WEIGHT TO THE MOTOR, BATTERY AND PROP. Electric model avaition fans like me have been doing this for over 30 years. Just think like you are designing a gas powered light plane
with 3000 mile range. Dont worry about take off power --short bursts at 400 percent cruise power are no problem.

This is a structural and aerodynmic problem, it is not a battery problem. the only electrical problems have been reliable high power motor controllers but the winning plane had a 200 HP motor and controller so they solved the problem. If you are technically oriented feel free to visit my website www.projectsunrise.info

Posted by: Roland Boucher | October 7, 2011 5:23 PM    Report this comment


Yes, I think proponents of capacitor use in electric planes is as a primary power storage device. The technology isn't competitive in energy density with batteries, but that doesn't stop people from being interested.

Phase shift is not an issue when using stepper motor technology. There are multiple coils in the outer band of the motor casing and a permanent magnet mounted across the axis on a rotating core. You energize one set of coils and the magnet tries to line up with them, but before it gets there you switch which coils are energized so the rotating magnet keeps going. This takes some fancy timing and powerful switching devices but all of that is within current state-of-the-art for electronic power control. I imagine the timing to get the RPM and torque you desire is a relatively simple piece of software in a trivial microprocessor. This controller is high tech but not outside current capabilities. The motors use technology that has been in use in industry for decades. It is only the battery cost and energy density that prevent this whole power plant from being on the shelf today.

Posted by: PAUL MULWITZ | October 7, 2011 7:15 PM    Report this comment


I have not used the simple weight formula you presented, but I like the way you do this for scale models. Let me try to apply this approach to an LSA format.

For an LSA to work properly with two heavy people (400 lbs) the empty weight with fuel added must be around 800 lbs. Current empty weight for IC designs without fuel rarely get below 700 lbs. The most popular engine (Rotax 912 ULS) weighs in at around 200 lbs with all the extra stuff you need to support it. In the Rotax case this is mostly an engine mount and oil cooler along with some hoses and maybe a fuel pump or two. Fancy installations include an extra alternator.

Adding, subtracting, and doing a few jumping jacks that leaves you some 200 lbs for batteries and $10K in purchase price to get an equivalent electric powered LSA. Unfortunately, today that $10k will only get you about an hour of cruise time with something around the right weight. To get to my 2 hour cruise benchmark will take another $10k and another 200 lbs. This is more than 50% weight in the batteries but not a lot more. To hit my goal the batteries need to be around twice as dense and half the price of today's offerings. That is either a 2:1 or 4:1 improvement depending on how you hold your head.

When will that happen? I don't know, but with all the current effort I think it will be only a few years rather than the 10 or so other writers here have guessed.

Posted by: PAUL MULWITZ | October 7, 2011 7:27 PM    Report this comment

Every day a new interesting sub-subject in this thread :-)

Let’s see, today I’ll select “well, they do electric in models, therefore there is no problem in building a big electric, right?” Wrong, I would say.

The problem in comparing model airplanes with “real” ones involves what happens when you increase the scale.

We need to bring in Peter Garrison to properly explain why this is so, but I am comfortable in stating that in the same way a flying insect somehow blown up to cow-size would not have a prayer of flying, you can’t simply expand a good-performing scale model C-182 with an electric propulsion system into a full-size electric C182 look-alike that will fly 165 mph and safely pull a few G’s with four people and baggage on board.

Consider that the wing loading on a 1/7 scale RC model of a light production airplane might be something on the order of 1 pound per square foot (PSF), while the “real” plane would be maybe 7 or 8 PSF. This allows the model’s basic structure to be proportionally much lighter, which in turn leaves plenty of spare payload for the heavy electric batteries. Scaled up, it simply doesn’t work.

Posted by: John Wilson | October 7, 2011 9:08 PM    Report this comment

OK... yes there was some confusion that Paul M. cleared. The link that I posted was regarding a new material for the capacitor dialectic that allows 0.2 Farads/cm^2 of plate. Capacitors of that magnitude once (and not so long ago, certainly when I was a young electrical engineer...) were the size of a car. With this stuff, it is the size of a dime and the thinness of a sheet of paper. Improvements have been on orders of magnitude in recent years, and will be orders of magnitude in the near future.

My position is that such energy storage capacitors will exceed the energy density of batteries in the very near future. Further, yes, they can be charged very, very fast. Thus, a high voltage/ moderate current charging station may someday charge electric aircraft in as little as half an hour or even less.

Posted by: Candice Brown Elliott | October 7, 2011 9:14 PM    Report this comment


you cant do it with an LSA weight limit today

400 lb payload
400 lb structure
800 lbs battery ,motor,prop
1600 lb gross weight ( the four place entry weighed 3300 pounds)

the 25% structure wont be easy but it will give you over 250 miles range with today's batteries and motors

by the way dynamic scaling requires weight be varied directly with volume or scale cubed. this way the dynamic handeling of the plane will be similar to the full scale plane. I have done this and it works, so has NACA. I usually start with empty weight just to be safe on early flights


Posted by: Roland Boucher | October 7, 2011 9:43 PM    Report this comment

John W,

I'm sure your concept is correct but your numbers are a little bit off. There is an excellent wiki on wing loading that anyone can find through google.

Gliders (and apparently model planes) have wing loading in the 1 to 5 pounds per square foot (PPSF)range .

LSA nearly all have 10 PPSF loading. This isn't mentioned in the spec. but it is the only one that works for the stall speed and still gets you a decent cruise speed.

Cessna singles run about 15 to 20 PPSF.

Fighter jets are around 100 PPSF. The monster Airbus 780 runs around 200.

Each increase in wing loading gives you better tolerance of turbulence. It also increases your stall speed and runway length requirement.

Posted by: PAUL MULWITZ | October 7, 2011 10:42 PM    Report this comment


wing loading for indoor rubber powered models is measured in grams per sq ft to oz pe sq ft for outdor rubber

wing loading specification s for OLD TIMER RC was 8oz per sq ft until the 90,s when it wa raised to 10oz per sq ft

These planes are flown for durarion like gliders

For dynamic scaling the wing loading is inversly a function of scale factor

1/4 scale = 1/4 wing loading your 20 psf cessna would scale to 5 lb/ftsq at 1/4 scale

most model planes are lighter than this because ther is no need to burden them with this weight. By the way in the 1980's i produced a kit of the American R eaglet which was an exact dynamic scale and powered by an 05 size electric motor

scale weight, scale size , scale prop, scale pitch, almost scale RPM --i gave it an extra 10% to account for reynolds number

some customers loved it, most hated it-too hard to build-- the balsa Zeekly engine had hundereds of parts

you are right-- the stall speed sets the wing loading

Posted by: Roland Boucher | October 8, 2011 8:24 AM    Report this comment


Pau there is an error in my scaling table the power requirements at 1/4 scale is indeed 1/128 ( 64 x2) but the equation should be 1/ ( S cubed x square root S)

this stuff was done in 1970 when I was designing my first electric and first published in 1975 in the NATIONAL FREE FLIGHT SOCIETY SYMPOSIUM

Posted by: Roland Boucher | October 8, 2011 8:41 AM    Report this comment

"I'm sure your concept is correct but your numbers are a little bit off."

The numbers were just intended as ball-park examples, I wasn't citing any specific aircraft.

The point I wanted to make is that the apparently marvelous performance of a electric-powered model airplane is not valid as evidence that such performance could be obtained in a practical full-size traveling machine. Sounds like there is general agreement on that.

I also have some comments for the capacitor-powered airplane crowd, but that'll have to wait because it's time to take my non-electric Bonanza out for a run.

Posted by: John Wilson | October 8, 2011 10:16 AM    Report this comment


an airplane ia an airplane and numbers are numbers

the equations are the same only the reynolds numbers change

I ran my analysis on a two place aircraft with 400 pound payload

Enjoy your flight

It is a beautiful day to fly, I just go back from a flight in my 1980 Arrow IV

I wish i still had my Marquart Charger. I would have n been a great day to fly an open cockpit biplane


Posted by: Roland Boucher | October 8, 2011 2:42 PM    Report this comment

Wow - ten Farads in a 10 gram package is a lot in the capacitor world. While impressive, that's only 27 watts for a few minutes. Just for comparison, The Concorde RG35AXC engine start battery makes 33 Ah at 12V, or 396 watts for an hour. Of course it weighs 32 lb. I don't know how to make an apples to apples comparison of power to weight for an hour's worth of power, but the results might be revealing.

Posted by: THOMAS M CONNOR | October 8, 2011 6:16 PM    Report this comment

super-capacitors and lasers: I happen to have some experience with the Airborne laser test bed, a B747 with a turret mounted laser. It has been funded on again and off again and I lost contact with the project office in the mid 2000s, but at the time, it used - drumroll please - chemical fuel. Google "Boeing YAL-1" for details. At the time chemistry easily out performed electronics when it comes to brute horsepower.

Posted by: THOMAS M CONNOR | October 8, 2011 6:28 PM    Report this comment

Supercapacitors have the ability to be charged and discharged rapidly with no effect on their durability. However, compared with batteries, their energy storage capacity is, minimal.

What does this mean in reality? Well, If one were to take a heavy military series diesel-electric hybrid truck, using several office-desk-sized banks of supercapacitors weighing several hundreds of pounds to absorb and discharge regenerative braking energy back into the trucks electrical driving system, how much energy is that worth in terms of something that we understand such as diesel fuel? 10 gallons? 5 gallons? Maybe one gallon.

No, none of the above. Actually, these massive banks of supercapacitors, fully charged, amount to less than a cup-full of diesel fuel!

However, the extra power given by just cup of diesel fuel when you need to accelerate a 35,000 lb military truck up to speed in a dire situation is invaluable.

Now, all I have to say to you is don’t just talk about it – do the arithmetic. Want to go flying on less than a cup full of diesel?

Roy Venton-Walters

Posted by: Roy Venton-Walters | October 8, 2011 8:58 PM    Report this comment

Enough with the vague generalities and wishful thinking about super capacitors. Here's a wiki article with references and links to papers. en*wikipedia*org/wiki/Electric_double-layer_capacitor

Posted by: THOMAS M CONNOR | October 8, 2011 10:13 PM    Report this comment

I see Roy Venton-Walters has already hit much of this, but since I promised to inflict my take on supercaps on everyone, here it is anyway:

The so-called “supercapacitors”, or EDLCs, were an incredible advance over conventional capacitors in terms of energy storage per unit weight, something like two full orders of magnitude.

It appears to me that this sudden leap in capacitor technology dazzled many people into an expectation that advances of similar magnitude would continue. This isn’t going to happen, because the leap was the result of a single radical change in the way the capacitive layers were electrically separated from each other. Improvements from this point on will be incremental (a caution that also covers advances we can expect in battery technology).

The worst handicap the EDLC has when compared to a battery is energy density. The best Li-ion batteries available can deliver around 113 watt-hours per pound of weight, while even in the laboratory supercaps have at best shown around 39 watt-hours/pound. Given that battery weight is what is keeping truly practical full-scale electric airplanes from taking off (pun intended), it is obvious that for powering airplanes capacitors are far from becoming a contender. This disadvantage is of course not nearly so significant in earth-bound applications.


Posted by: John Wilson | October 9, 2011 12:30 AM    Report this comment


There are other disadvantages, although they are less severe. An individual EDLC can only store about 5 volts, requiring large series strings of capacitors to handle the higher voltages needed for practical motor drives. This requires some sort of voltage distribution control in order to prevent breakdown of the individual capacitor cells. Also, unlike a battery the voltage supplied by the capacitor starts to drop immediately upon loading and this drop continues right down to zero as the power is recovered from the capacitor. An electric motor doesn’t like this and additional high-power electronics elements are needed to compensate, which decreases system efficiency by a fairly significant percentage.

EDLCs do have some great advantages over batteries. They don’t wear out and therefore the ultimate lifetime cost per charge/discharge cycle can become very low. They have very low internal resistance, allowing them to accept rapid charge/discharge rates without significant heating and (over short cycle periods) show well over 90% cycle efficiency.

Bottom line, you can pray for another orders-of-magnitude rabbit to pop out of the hat, but while you are praying, I recommend putting your electric airplane bets on a different power source.

Posted by: John Wilson | October 9, 2011 12:32 AM    Report this comment

Whatever became of fuel cells? That was the 'next big thing' 20 years ago. It seems to have disappeared without a trace.

Posted by: THOMAS M CONNOR | October 9, 2011 10:20 AM    Report this comment

“Whatever became of fuel cells?”

Interesting question. You do see fuel cell stationary power units here & there, and there are small fleets of demonstration vehicles like busses running. I understand one of the best markets is in materials handling equipment (forklifts, etc.) that are used inside buildings where emissions are a problem & the time-consuming recharge of battery-powered units is a big operational disadvantage.

The most common (i.e. most practical) fuel cell types for mobile applications have conversion efficiencies in the 50% range, which is approximately double that of an internal combustion engine. However although in principal a fuel cell can be designed to use nearly any hydrocarbon fuel, the higher efficiency units need hydrogen, bringing in hydrogen’s big cost, supply & distribution problems.

Several companies market various types of fuel cell so they are readily available to anyone wishing to incorporate them in some system or other, but it is probably significant that - reportedly at least - no fuel cell division or company has yet become profitable overall.

My impression is that mobile fuel cell improvements have reached sort of a plateau where technological advances have bumped up against the high cost of materials like platinum and the inherent difficulties of working with hydrogen. As always, the devil is in the details.

Posted by: John Wilson | October 9, 2011 12:10 PM    Report this comment

"My impression is that mobile fuel cell improvements have reached sort of a plateau where technological advances have bumped up against the high cost of materials like platinum and the inherent difficulties of working with hydrogen. As always, the devil is in the details."

I get an SAE newsletter that covers this occasionally. There are some commercially viable fuel cell designs out there apparently being marketed by about five companies. The majority use PEM catalysts requiring platinum, but the emerging technology, says SAE, is carbon-cobalt-iron. Still at the bench research phase.

On a per watt basis, fuel cells are still awfully pricey. I wouldn't be surprised if designers considering them tilt toward more efficient internal combustion engines or parallel hybrids.
I think electric airplanes have and will have exactly the same problem.

Posted by: Paul Bertorelli | October 9, 2011 1:55 PM    Report this comment

Eight years ago I owned an experimental one-seat electric car called a Corbin Sparrow. It was a whole lot of fun. It's partly why I'm looking forward to buying or sharing an electric aircraft for recreational flying.

I learned from the Sparrow that designing a good car is hard, and that designing a good battery and charging system is hard. The door handles broke. The batteries were damaged by bad charging. Electric aircraft will have to overcome similar hurdles.

I also learned from the Sparrow that it's possible, and perhaps better, to have specialised vehicles instead of general-purpose vehicles. Petrol power makes it easier to build a car that can carry four people, run errands around town, drive at 120 km/h on the freeway, and drive 500km with one refueling. The Sparrow could only carry one person, run around town, and drive at 120 km/h for a 30km commute. But this was enough for some of my driving.

By the same token, don't look for a single electric aircraft to do everything a 172 does. And don't look for electric power to displace petroleum fuel for all aviation missions and types. But I can imagine that, as several have pointed out, a two-seater training and one-hour flight aircraft, with swappable batteries or some other fast charging system, might be quite compelling.

Also: I expect the price of petroleum to rise. I expect the price of carbon emissions to become non-zero. This will change the economic balance between power options, for a given aviation mission.

Posted by: James DeLaHunt | October 10, 2011 4:41 AM    Report this comment

"But I can imagine...a two-seater training and one-hour flight aircraft, with swappable batteries"

Swappable batteries double the expense, are very heavy(need a trolly & lift system), and would need a 6G complex mounting structure in the aircraft. The FBO would also need the expense of contracting for massive new wiring to (and inside) the building. Add to that the need for ground-based inverter/chargers and it gets really expensive.

Point being is that primary training is hardly a money-maker. Massive investment to support a limited aircraft is not a good business model.

Posted by: Mark Fraser | October 10, 2011 7:34 AM    Report this comment

Swaping out battries after every flight/ drive wont work for cars or airplanes.

with 300 mile range it wont be necessary if charge times are reasonable

NI-cad batteries can be charged to 100 percent capacity in 15 minutes

This is where the battery improvements will best help make electrics popular

In any case after a few thousand are flying any limitations will become obvious

an annual electric contest for distance, speed, etc would speed things up.

average speed over a 200 mile course should work out fine

Posted by: Roland Boucher | October 10, 2011 9:46 AM    Report this comment

Fascinating discussions in systems engineering, economics and politics. Obviously, the technology is not quite advanced enough to make economic sense on a large scale for individuals or large businesses, yet. From a business/marketing perspective, though, it is getting close. Should the technology in battery energy density continue to improve, I think we will see a turning point with “early adopters” moving to a tipping point of a viable market. As Mary pointed out, the RC/scale market saw an entire new segment of customers grow out of nothing.
Why? Because it was new, it was exciting, it was clean, it used the latest technology, it created new communities of interests, it created new events to attend and it re-energized a marketplace (pun intended). Did it make logical, physical and engineering sense – no. Why dismiss +70-years of proven engine technology? The marketing folks targeted aviation oriented people who were interested in working with and tweaking the latest technology – made it cool. (Electric scale airplanes can even fly backwards!) The best, most efficient technology doesn’t always win. (Beta-max vs. VHS, etc.) Does Joe pilot care if IC is more efficient in converting energy into prop wash? Or, does Joe Pilot care that his 2-hour flight cost him less in electricity than a comparable 22 gallons of AVGAS AND he’s sitting in a TAA cockpit with XM WX/radio, PFD screens...

Posted by: Brian Kough | October 11, 2011 12:24 PM    Report this comment


electric took off in 1981 after about 10 years because the average builder learned to use them--- there was no improvement in technology except fo lighter radios which made the inexpensive 05 class fun to fly and compete with.

also no noise meant new flying fields could be found and powered flyers could fly at most glider fields for most but no all days of the week.

Technology of electric powere is there now. the aircraft designers have ALMOST learned to use electric power but not quite,

When designers buckle down and design a plane that is 50 percent electricity, that is the weight of prop,motor, controller,and battrey at 50% of the gross weignt of the aircraft, the the QUIET REVOLUTION WILL START

Posted by: Roland Boucher | October 11, 2011 4:36 PM    Report this comment

Here's a benefit of partial electrification of aircraft propulsion using ultra (or, if you prefer, super) capacitors: If it doesn't add too much to gross weight or take up too much volume to have the required ultracapacitors, and if an aircraft alternator can be devised that will work in both directions (i.e. electric --> mechanical as well as mechanical --> electric), and if said machine can work as a highly productive motor for a few seconds during takeoff, and if the ultracapacitor is charged up on the ground, the pilot can arrange for said capacitor's charge to be dumped into the motor/alternator during takeoff. This would improve takeoff performance, especially if the engine is not developing its full rated takeoff power owing to high density altitude.

Posted by: Alex Kovnat | October 12, 2011 8:53 AM    Report this comment

I would like to thank you for the efforts you have made in writing this article. I am hoping the same best work from you in the future as well.

Posted by: rc bazaar | July 23, 2015 3:44 AM    Report this comment

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