Firms Team Up On Hybrid Electric Plane Technology (bbc.com)

An anonymous reader shares a report: Airbus, Rolls-Royce and Siemens are to develop hybrid electric engine plane technology as part of a push towards cleaner aviation. The E-Fan X programme will first put an electric engine with three jet engines on a BAe 146 aircraft. The firms want to fly a demonstrator version of the plane by 2020, with a commercial application by 2030. Firms are racing to develop electric engines for planes after pressure from the EU to cut aviation pollution. Each of the partners in the programme will be investing tens of millions of pounds, they said on a press call. The firms are developing hybrid technology because fully electric commercial flights are currently out of reach, a spokeswoman said.

Comments

Diminishing returns

[Dan East]

It's good to invest in research in this area, but the laws of diminishing returns are pretty harsh with aviation. Having a turbine powered generator to provide power for an electric turboprop is a lot of extra complexity (and components to fail) just to pick up a very small amount of efficiency (IE burning less jet fuel).

While it is certainly good to have figured out the technology involved in electric engines, it will require a revolutionary new battery technology that has vastly better energy density than what we have now to make this practical.

Also, I found this part a bit odd:

The weight of batteries coupled with the weight of equipment to cool electric engines are two limiting factors at present, she said.

It's really, really cold up at cruising altitudes (-70 F), so it seems odd they need cooling equipment. I guess maybe that's just for take offs?

Re:Diminishing returns

[MightyYar]

so it seems odd they need cooling equipment.

You still need a way to transfer the heat from where it is generated to the nice, cold heat sink. As a simple thought experiment, a motor operating in a thermos isn't really going to care much about the outside temperature - you need a way to get the heat from the motor to the air outside the thermos. Obviously you won't purposely insulate the aircraft motor, but the principle is the same.

Think about the amount of power dissipated... a 2 MW motor - even if 99% efficient - is going to dissipate 20 kW of heat. Think about the heatsink for your ~100W CPU and scale it up by 200x. Not an impossible task but definitely an engineering challenge.

Re:Diminishing returns

[plague911]

Not sure. I am not an airplane doctor. But the thinning air I can imagine would reduce the ability of the air to cool the engine. Additionally ambient heat dissipation would also seem to be insufficient to cool an engine going a bajillion RPM/MPH.

Re:Diminishing returns

[aaarrrgggh]

There are things it could be useful for-- added takeoff thrust, taxiing, regenerative drag rather than just using flaps, etc. The added takeoff thrust could reduce engine wear significantly, and by extension near-airport pollution.

Diminishing returns for sure, but a few well selected points could be worthwhile with today's battery technology.

Re:Diminishing returns

[Rei]

It's an awful lot of different benefits. Your generator always runs in an optimal power band. You can add more, smaller electric motors without sacrificing efficiency - to the contrary, they increase efficiency and can be used to significantly boost lift for takeoff / landing by pushing more air across the wing. The article discusses how quieter operation means that they can fly more, bigger planes into cities, especially at night. Same goes with lower pollution at takeoff/landing (airports tend to be big point sources of pollution). It's a lot of individual advantages.

Pure electric flight will come, but "not yet". Yes, you can make electric planes, but they're far from economic for ferrying passengers and cargo. Once you start getting closer to li-air energy densities, however, things start looking a lot more interesting; the much touted "solid state" batteries have some potential in this regard, in that they have potential to reduce or eliminate damage from dendrite formation. I know Musk really wants to be the first to build a pure electric aircraft to break the sound barrier. From that, I imagine he's thinking of something like a high-bypass arcjet rather than props, which would be really fascinating, although I'd expect it to have big problems with ozone generation (if that is in fact the approach he's thinking of). A high bypass engine involving microwave plasma heating might be another way to get to high speeds with decent efficiency, possibly with lower ozone concerns. Either way, you're constrained by not wanting your "exhaust" to be moving much faster than the aircraft if you want your efficiency to be good (a critical concern if you're going for battery propulsion).

BTW, I find it interesting that people don't talk nearly as much about electrifying the other elephant in the room: shipping. Where I am, the fishing fleet is our biggest fuel consumer (although cargo shipping is another huge consumer). A fishing boat goes out with a sizeable chunk of its net weight comprised of diesel, and returns with a sizeable chunk of its net weight comprised of fish. Not an easy challenge either - but it too will eventually happen.

Re:Diminishing returns

[MightyYar]

A fishing boat goes out with a sizeable chunk of its net weight comprised of diesel, and returns with a sizeable chunk of its net weight comprised of fish. Not an easy challenge either - but it too will eventually happen.

Planes are in a similar situation, with their landing weight being a fraction of their takeoff weight. Battery-powered planes will need to haul around the takeoff weight the whole time, putting them at a serious disadvantage.

I think for niche applications like fishing boats and airplanes, the key to sustainability will be in cost-effectively producing a fuel from renewable resources, not from trying to pound a round peg into a square hole. When oil was over $100/barrel, there was a lot of movement in biofuels, hydrogen, ethanol, etc. I expect this will still be the way forward for applications where a consumable fuel simply makes more engineering sense.

Re: Diminishing returns

[MightyYar]

Finding the area on an airplane should not be difficult (wings, anyone?). Moving the heat from a very concentrated spot in the middle of a moving high-speed 2MW fan assembly into the heat dissipation area is the trick.

Re:Diminishing returns

[Rei]

Heaters have trouble reaching very high temperatures, but higher temperatures yield higher expansion efficiencies. As for props: great for lower speeds, not great for high subsonic speeds, terrible for supersonic speeds.

Re:Diminishing returns

[Type44Q]

electric engines

(insert Samuel Jackson voice) "Ain't no electric engines, motherfucker!!!"

Re:Diminishing returns

[Marxist Hacker 42]

As an asside, I wonder if we could build a smaller, more efficient fishing boat by having rubber fuel tanks at the bottom of the fish holds? As you consume fuel, you gain room to put fish.....

Re:Diminishing returns

[bws111]

So I take it you don't consider price when purchasing a flight (or anything else)?

Re:Diminishing returns

[Rei]

What's the ratio of ship/cargo/fuel mass on a big container ship? I've only ever dug into fishing vessels.

Part of the problem you get into is that the fuel consumption of a ship isn't so much to do with its physical size, but its mass. The more mass, the more volume you have under the water as buoyancy counteracting that mass; they're directly related, and the latter is directly related with drag and thus energy consumption. On the other hand, it means that ships gain a lot from improved construction methods and materials in order to reduce mass. Most large ships are still just objects made of geometrically simple pieces of mild steel welded / bolted together (very different from how airplanes and cars are made); more complicated part geometries (with advanced steel alloys used in key places) can significantly reduce mass. Scale is the reason for the difference, of course (container ships are *huge*), but scaleup of more mass-efficient construction methods would go a long way toward reducing energy demand - at least as far as the ship's own mass goes.

One of the core issues for hydrogen in cars is storing sufficient quantities of it, high pressure vessel storage are heavy, but as you get larger in size the storage vessel the less of the weight of the fuel storage system the vessel takes up compared to what can be stored.

Unfortunately, that's not actually true when it comes to pressure vessels. The volume to surface area grows linearly with the radius, yes, but the thickness also grows with size to maintain a given level of stress And dear YHVH I don't want to picture the result of a container-ship-sized hydrogen tank failure in a port. At atmospheric pressure, hydrogen burns at 4-75% mixing ratios and can detonate (which natural gas can't do at all) between something like 18-56%. And takes less than 1/10th the ignition energy of natural gas (almost anything will set it off). Combine that with pressures higher than a scuba tank.... Also, liquid hydrogen is even worse. Air in contact with liquid hydrogen freezes out into a high-explosive slush. As for all hydrogen, while it doesn't pool at the surface, it pools under overhangs (which ships tend to have in abundance), embrittles metals, leaks through almost anything, and even does weird things like leak into pipes, follow them to their destination, then pool there.

Re:Diminishing returns

[RightwingNutjob]

Morality like having reliable and safe aircraft engines? Low maintenance means less taking things apart and putting them back together, which means less opportunity to make silly but very consequential mistakes, no matter how consumate of a professional the mechanic is. The fewer chances for human error, the safer the plane. The safer the plane, the fewer people who die horrible deaths from silly mistakes.

Adulthood is understanding that many good things are in direct conflict with one another and it is not possible to have all of both. Clean air and clean water are good, but so is reliable and safe transportation, heated dwellings, and modern medicine which relies on both of those and a dozen more benefits of industrial capitalism.

Re:Diminishing returns

[bws111]

Engine: a machine with moving parts that converts power into motion.

Re:Diminishing returns

[Solandri]

While it is certainly good to have figured out the technology involved in electric engines, it will require a revolutionary new battery technology that has vastly better energy density than what we have now to make this practical.

Planes are extremely weight-sensitive. If a stewardess accidentally loses a sugar packet in a crevice somewhere, it ends up making the plane burn something like an extra half pound of fuel each year. Batteries suffer a double-whammy because the weight of fuel decreases as you burn it off. But you have to carry the full weight of batteries the entire trip, whether or not they're holding any charge.

I suspect the intent here is to carry just enough batteries to power the plane through the (low power) descent phase of a flight. That's when the engines are currently operating at their lowest efficiency. Apparently there's enough engine inefficiency at this stage to warrant seriously considering carrying around the extra weight of batteries and electric motors. (Yes idling on the taxiway would burn more fuel per distance traveled since you aren't moving. But it doesn't really cost much fuel since no thrust is required.)

Re:Diminishing returns

[vtcodger]

I dunno. I used to use arguments similar to yours about the dangers of Hydrogen as a fuel. Then someone pointed out to me (correctly. I checked) that "Town Gas" -- a noxious mixture of gases generated from coal -- which was widely used prior to the widespread availability of Natural Gas -- was often half or more Hydrogen and it was really no more catastrophe-prone in practice than NG.

Re:Diminishing returns

[AmiMoJo]

One of the main uses for hybrid aircraft engines is reducing noise and pollution at airports. Air quality is a real problem in those areas and aircraft use a lot of power getting up to speed and off the ground. Many places charge them for this to prevent them simply externalizing the cost onto people living and working in the area.

Re:Diminishing returns

[MightyYar]

That would be awesome :)

Re:Diminishing returns

[Rei]

Hydrogen is about 50% by volume in town gas, not by mass. See Ullmann's Encyclopedia, "Gas Production", p4. Also 5% N2, 5% CO2, 40% CO. That's about 6% by mass. Town gas is mostly (~70%) carbon monoxide by mass.

Re:Diminishing returns

[PoopJuggler]

Once again, Random Internet Dude who spends all his time posting crap on internet forums thinks he knows more than Professional Industry People who spend their lives on actual engineering.

Re:Diminishing returns

[HornWumpus]

AC...supergenius...or not.

Re:Diminishing returns

[BasilBrush]

The slightest puncture means leaking fuel into the area where you are going to store the fish.

Re:Diminishing returns

[Guspaz]

I don't know how much of it is the artist's impression, but it looks more like they just want to take a high-bypass turbofan and replace the turbine with an electric motor, rather than a using a more traditional ducted fan or a propeller. They're planning to replace just one of the four engines on a BAe 146 with the electric motor, so it makes sense that they'd want the airflow and thrust to be relatively similar to the other four engines. The engine on those planes is relatively high bypass (5.7:1) so I guess they'd just run the other three engines at lower thrust to match the electric engine (which would effectively have a 100% bypass).

Re:Diminishing returns

[Marxist Hacker 42]

That's why you use Prius style gas tanks- double walled, with liquid silicone seal in between the walls and 1" thick rubber.

Re:Diminishing returns

[Shotgun]

At that point, what is the advantage over the current tanking system?

Re: Diminishing returns

[blindseer]

Finding the area on an airplane should not be difficult (wings, anyone?).

The wings are already full of fuel tanks and control surfaces. Perhaps the fuel itself could be used as the fluid to transfer the heat but that still has challenges. One issue that comes to mind is that the heat of the batteries and such that needs to be cooled could vaporize the fuel. Could it get hot enough to breakdown the fuel or ignite it? What if the cooling is "too good" and the fuel gels?

Moving the heat from a very concentrated spot in the middle of a moving high-speed 2MW fan assembly into the heat dissipation area is the trick.

No doubt. The equipment to move this heat will have some mass that will need to be accounted for in considering if this is feasible.

Considering the plan to use these batteries for take-off and landing it would seem to me that the feasibility of this might be limited to short run aircraft. If the batteries are used for maybe 1 hour on the 15 hour flight then those batteries are effectively dead weight. These aircraft already have large batteries as backups in case of engine failure to keep the radios and such running. I suspect these new batteries might serve double duty, maybe not. They already served double duty on aircraft to balance out the plane, the batteries would be somewhat movable in the original design to balance weight front to back. This meant putting the batteries in the tail usually to keep the nose up without needing down force from the elevators.

Re:Diminishing returns

[blindseer]

One thing I recall reading, and I could be wrong, what that hydrogen "dissolved" in another gas is not near as corrosive on pipes or as much of a leak risk. The chemistry is something like with another gas, like methane, the hydrogen has an affinity to "bind" or "attack" the other gas than the metal pipes. This was the theory behind another kind of "Town Gas" which was using synthesized fuels from trash and sewage to create a modern mix of gases that would be a direct replacement for natural gas. If the energy of the mix got too high, that it went outside the safe energy per volume range, then they'd simply add an inert gas like nitrogen, carbon dioxide, or argon. If for some reason the mix was less energetic than natural gas then more hydrogen would be mixed in.

This modern variation on "town gas" was, again as I recall, called "hythane". This might be a trademark or something but it's generally a mix of methane and hydrogen as a replacement for natural gas and other gaseous fuels. I wonder how far this "dissolving" or hydrogen in the methane goes, can this gas be liquefied? I also wonder how far this mix of hydrogen with other gasses can go, can a mix of just hydrogen and an inert gas work as a natural gas replacement? I suspect the presence of a hydrocarbon is important to the chemistry.

Oh, one thing that was important about the composition of the town gas, going from memory again, is that the carbon monoxide made the flame bright. A pure hydrogen flame is almost invisible. A pure CO flame is blue, I think. Mixing the two, with the other gasses, produced a yellow flame.

Re:Diminishing returns

[jcr]

At typical commercial flight altitudes and speeds, there's a massive heat sink available at all times. The atmosphere is very cold, and it's going past the aircraft at very high speed.

-jcr

Re:Diminishing returns

[serviscope_minor]

terrible for supersonic speeds.

You misspelled "awesome":

https://en.wikipedia.org/wiki/...

* the outer 24-30 inches (61-76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards.

* The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run.

Re:Diminishing returns

[MightyYar]

I was trying to illustrate with my thermos example of how the difficult part is not the heat sink, but getting the heat to where it can be sunk. 2MW is an enormous amount of power, and it will generate an enormous amount of heat - all localized in the middle of the busy stuff where pipes, fins, and whatnot are all in the way.

Re:Diminishing returns

[jbengt]

. . . regenerative drag rather than just using flaps, etc.

You need to use flaps in order to maintain a high angle of attack that provides sufficient lift at low speeds without stalling. The increased drag is just a side effect that hurts on takeoff and maybe helps a little on descent.

Re:Diminishing returns

[mjwx]

so it seems odd they need cooling equipment.

Think about the amount of power dissipated... a 2 MW motor - even if 99% efficient - is going to dissipate 20 kW of heat. Think about the heatsink for your ~100W CPU and scale it up by 200x. Not an impossible task but definitely an engineering challenge.

I have.

First I thought about why I would use such an inefficient cooling solution as a heatsink and fan. Then I thought why is an electric motor putting out as much heat per watt as CPU?

The Toyota Prius has a 60KW electric engine as well as a traditional ICE. I've never even heard of one overheating (I'm sure they can, but it's a rarity). I dare say that any overheating issues have been solved. HSF assemblies are terrible for heat dissipation, but they're cheap and reliable with few moving parts or liquids. Given we don't need to cool CPU's that much they're fine for that purpose. For a motor, we'd use active cooling, in fact given the temperatures at the height these aircraft are going to be at for most of their service, we may need to think about how to the engine warm.

For cooling electric motors, I'm sure you could give your mate Elon a call (he's everyone's mate) as I'm sure he'd have a few ideas on the subject.

Re:Diminishing returns

[MightyYar]

First I thought about why I would use such an inefficient cooling solution as a heatsink and fan

Presumably, they wouldn't. Presumably they would use a liquid coolant circulated through the motor and a heat exchanger somewhere else. You still need to sink at least 20kW of power, though, so it doesn't change the size of the required heatsink - it just moves it somewhere.

Then I thought why is an electric motor putting out as much heat per watt as CPU?

It isn't. The most efficient motors are in the 99% range. It is realistic to assume a 97+% efficiency. So a 2MW motor has at least 20kW of waste energy to dissipate as heat. This is opposed to a CPU, where nearly 100% of the power is dissipated as heat. That's why the heatsink only needs to be 200x larger and not 20,000x larger.

The Toyota Prius has a 60KW electric engine as well as a traditional ICE.

The Prius does not have the same weight constraints as an airplane, nor is the motor spinning as fast. But the electric motors are cooled by the automatic transmission fluid, which has a radiator. I believe the inverter coolant also circulates through the transmission, further cooling the motors. Which reminds me - the plane will also have a 2MW inverter that will range from 95-99% efficient, requiring even more cooling... that seems pretty straightforward, though, since at least the inverter isn't moving. The batteries themselves will also require cooling.

For cooling electric motors, I'm sure you could give your mate Elon a call

Tesla patented their cooling design, so we know exactly how that works. It looks like a bullshit patent - they use the only known good way to keep fluid from leaking out of a spinning thing - centrifugal force. It is highly likely that the airplane motor will use exactly this type of cooling. But again, weight is a much bigger problem than on a car and the parts are spinning much faster. You also don't need to worry about your cooling system impeding airflow through the engine on a car.

And I'm not saying it is impossible - simply that it's a very challenging engineering problem, and it is likely to have significant trade-offs.

Re:Diminishing returns

[Marxist Hacker 42]

Being able to replace a good part of the volume of the tank with fish hold space, once the tank is empty. A five foot deep tank would collapse to less than 6 inches.

Re:Diminishing returns

[HornWumpus]

Name one commercial aviation example? It's a _dumb_ idea.

Jets aren't going away

[sjbe]

The firms are developing hybrid technology because fully electric commercial flights are currently out of reach.

And sadly likely to remain so. Two problems. One is that the energy and power density of current battery tech simply isn't there. Batteries are much too heavy currently. The other is that there is no current way to fly a plane at speeds comparable to a jet engine without throwing some material out the back of the aircraft. This means some form of fossil fuel based propulsion for the foreseeable future. While we might be able to get to a propeller driven electric plane for some commercial applications, I don't see any reasonable way to replace jets with electric motors across the industry. But it's perfectly reasonable that we might be able to use electric motors and batteries to make jets more efficient and that is still a good thing just like with automobiles.

Re:Jets aren't going away

[MightyYar]

How important is the impulse from the exhaust on modern passenger jet engines? I was under the impression that the giant fan was responsible for far more thrust. Lazy Googling seems to indicate an 80:20 bypass fan:core thrust ratio.

Re: Jets aren't going away

[HornWumpus]

The impeller part perhaps. The heat engine and impeller together, not even close.

Re:Jets aren't going away

[Shotgun]

Conceptually, a jet sucks air, heats it, then blows it out the back. A hair dryer is a jet. . . a crappy, low thrust, and inefficient one, but a jet nonetheless. All a high-bypass system does is suck more air which it doesn't heat quite as much. The bypass is just MORE exhaust. It is still all F=ma, with the bypass air being weighted to more 'm' and the "exhaust" air being weighted to more 'a'.

Re:Jets aren't going away

[MightyYar]

Yes, that is the point I was trying to make. The combustion process will also expel hot matter and create an impulse as the matter is ejected, but I don't think that is a significant source of propulsion in a modern high-bypass airliner engine... most of the thrust is coming from the ducted fan. If this were a rocket, combustion would be responsible for 100% of the thrust :)

I don't see how this will be worth it

[Viol8]

"The turbine powering the generator will run on jet fuel and provide power for the electric engine."

Ok, but with the inherent loses in that cycle why not just put the turbine directly on the wing and , err , call it a jet engine?

Hybrid cars are good in cities compared to ICE engines where's there's lot of stop start and fuel isn't wasted idling. They utterly suck on long journeys at a constant speed which is essentially what aircraft do. I really don't get the point of this unless its just to test the systems for a fully electric plane or perhaps simply to reduce pollution when taxying by using electric only (however there is another system powering the nosewheel that already does that), because otherwise a hybrid plane IMO is a nonsense.

Re:I don't see how this will be worth it

[jeff4747]

They should get an improvement during idling and taxiing, but that's not that large a part of most flights.

They may be able to do an efficiency-of-scale thing with one generator powering multiple thrust engines. That seems to me the most likely way they could boost efficiency.

Re:I don't see how this will be worth it

[careysub]

How about providing extra power for climbing, allowing a smaller engine just for cruising? Should get better fuel efficiency that way. Also electric motors would be great to reduce noise on take-off and landing at urban airports.

https://tech.slashdot.org/story/17/11/28/148213/firms-team-up-on-hybrid-electric-plane-technology#

Re:I don't see how this will be worth it

[Anonymous Coward]

Ok, but with the inherent loses in that cycle why not just put the turbine directly on the wing and , err , call it a jet engine?

Maybe if you read the article you'd see the reasons are for less noise pollution and greater fuel efficency. You could have the turbine towards the rear of the fuselage of the plane, like the 727 and DC10 and MD11 jets. The turbine you'd use would be optimized for electric generation. You'd avoid the complexity of having the fan attached to the turbine, with needing bypass airflow for the fan etc. You would also have less weight on the wings due to the electric fan motor being much lighter. Which in theory means you can put more fuel in the wings and increase flight range further as well.

Also you have other things that are bonuses, like a lack of lag and spool up time for throttle adjustments. Also if there are some batteries, those could be charged from utility power before takeoff.

There are pros and cons to this idea, but unless you actually TRY doing it, you have absolutely not idea.

Next you'll tell me that hybrid electric locomotives don't make sense either.

Re:I don't see how this will be worth it

[Viol8]

"Maybe if you read the article you'd see the reasons are for less noise pollution and greater fuel efficency"

Except the noise from an engine comes from the 500mph stream of air out the back, not burning of fuel and it won't be more efficient.

"Next you'll tell me that hybrid electric locomotives don't make sense either."

There arn't any. There are diesel electrics which are used instead of pure diesel because its mechanically simpler to have 4 or 6 electric motors on the axles with some cables linking them to a central generator than it is to have 4 or 6 diffs and the associated hugely complex mechanical linkages.

Re:I don't see how this will be worth it

[Solandri]

The efficiency of any engine (even electric motors) varies with how much power it's producing. Gas turbines hit their highest efficiency at highest load. Since as you point out the majority of a plane's time is spent at cruise speed, you want the engines to be tuned for optimum efficiency at cruise speed.

That's not possible though because the ~15 minute ascent phase of the flight requires more power than cruise. So this forces cruise to operate at a lower than optimum efficiency. In theory an electric motor boost could obviate this need, and allow jet engines to cruise more efficiently. I'm not sure there's much to be gained here though because modern twin-engine airliners are required by regulation to operate (both cruise and ascent) with one engine out. So cruise efficiency is already pretty far down the curve.

The approx 20-30 min descent phase of the flight requires running the engines at low power, far from their optimum efficiency point. This is where a lot of fuel could potentially be saved. Both the ascent and descent phases of the flight run the engines outside this max-efficiency range. The question is whether the fuel saved can offset the extra fuel burned carrying around the electric motors and batteries.

Re:I don't see how this will be worth it

[vtcodger]

"Maybe they need to be towed from the ramp to the runway, by electric tugs" ... or sails. imagine the photo impact of a big passenger jet being hauled toward a distant runway entrance by a ballooning spinnaker.

Re:I don't see how this will be worth it

[HornWumpus]

Diesel electrics are about the low speed torque. Getting a half mile long train started is just a tough problem.

Re:I don't see how this will be worth it

[HornWumpus]

Engine out issues. Long term, two generators, two fans, almost no batteries. Runs on one generator at cruise and has takeoff capability on one gen or one fan.

The whole stinking deal is just added complexity if the hybrid setup isn't operating at significantly better efficiency. 4 engine small planes like this testbed are commercial non-starters.

Re:I don't see how this will be worth it

[Viol8]

Fab size is limited by where the engines can be mounted. The fans on an A380 are already pretty much at the practical limit.

Re:I don't see how this will be worth it

[jeff4747]

Concorde used turbojet engines. They're terrible at fuel efficiency, but good at making the plane go fast.

Modern airliners use high-bypass turbofan engines. So you're going to have a lot less fuel used while taxiing and other idle/near idle situations.

Also, 500kg is not an awful lot of fuel when your flight is going to burn 10,000kg (roughly what a 737 burns on a cross-country flight).

Re:I don't see how this will be worth it

[jeff4747]

Most of what you were saying is what I was saying about economy-of-scale. But spooling up would still be a problem.

The generator in a hybrid plane would be a turbine engine. You're going to have to spool that turbine up to get the power to spool up the electrically-driven fans. Batteries are going to be too heavy to carry along to "buffer" that sort of transition.

Re:Let's solve this problem, once and for all...

[amalcolm]

Helium is in short supply - hydrogen? No thanks!

Lighter than air craft won't work

[sjbe]

More use of lighter than air craft. Blimps, zeppelins, etc.

We tried that. It didn't end well. It's a romantic idea but not a practical one for mass transportation. They have some niche uses but they aren't the answer you are looking for.

Re:Lighter than air craft won't work

[Type44Q]

News-fucking-flash: materials and propulsion technologies may have improved just a bit in the past eighty years.

Re:Lighter than air craft won't work

[vtcodger]

While the Hindenburg and some of its competitors didn't work out so well, the Graf Zeppelin made a round the world flight, then was successfully used for transatlantic commercial flights for several years. What ended its career was World War II, not poor economics or poor performance.

Whether a modern zeppelin could compete for passenger traffic is dubious. Lighter than air vehicles are never likely to be very fast.

OTOH, perhaps they'd be competitive for hauling freight from East Asia to the world's consumers.

Re:Lighter than air craft won't work

[Guspaz]

If you need it fast, you can put it on an aircraft. If you need it cheap, you can put it on a container ship. Is there really a market for something that is a bit faster than a container ship with a bit more capacity than an aircraft?

Re:Lighter than air craft won't work

[vtcodger]

I honestly don't know. Wikipedia leads me to believe that a large airliner has a payload around 20 metric tons and a cruise speed a bit below 1000 km/h. So let's assume a modern LTA with a payload of 100 metric tons and a cruise speed of 200 km/h (125mph). That gives a transit time from Shanghai to LA of 52hr, Shanghai to Buenos Aires = 97hr, Shangahi to Paris = 45 hr. Bit slow for business travel, but maybe OK for a drink and gamble cruise that doesn't put 15 kilos on the traveller. For cargo -- might be economically OK for electronics and other high value stuff. And, unlike a container ship, the terminals could be inland.

I don't think I'd invest in a Zeppelin company even (or maybe especially) if Elon Musk was backing it. But seems like a plausible investment for the sort of folks who have pushed Toronto real estate and Bitcoin prices to preposterous levels.

Re:Lighter than air craft won't work

[blindseer]

A container ship can only travel on water, meaning it sails from one coast to another. An aircraft still needs facilities to land but these airports can be just about anywhere, some even floating on water. An airship can also go anywhere to anywhere, presumably with minimal facilities.

I've seen proposals for hybrid lift aircraft that have a lighter than air gas envelope shaped like a wing. These can land on short runways, on water, or perhaps even vertically, depending on the design.

A modern airship isn't nearly as slow as the old ones, especially if it is a lifting body hybrid design. Not something like 0.8 to 0.9 mach like a modern jet but still not poking along at maybe 20 knots like a container ship. A common propeller craft would do about 70 knots on the low end, basically highway cruising speed, to a few hundred knots. I assume that a lifting body hybrid could also do speeds like any propeller craft but do it point to point over great distances.

The US military has been toying with the idea of hybrid lift craft for a long time. Maybe we'll see this happen soon enough. Imagine an aircraft that can carry a fully capable main battle tank, at speeds faster than any ship at sea, land on a spot no bigger than the aircraft itself, and fly halfway around the world without refueling. Such an aircraft would be huge and expensive, but then so is a C-5 Galaxy.

Re:Lighter than air craft won't work

[Guspaz]

I think you might be a bit off on the cargo capacity of commercial aircraft. On the extreme end is the unique An-225 with 254 tonnes, the 747F is more common at 124 tonnes, and then you get into the really common ones like the 757F (40 tonnes), 767F (53 tonnes), A300F (48 tonnes), MD-11F (91 tonnes), etc. Apart from the Antonov, I'm just reading off the most common aircraft in UPS' fleet, basically.

Military capacity is similar, the C-5M super galaxy basically has a similar capacity to the 747, although it's obviously specialized for things that you'd never do in a 747.

Like it or not, it's the future

[mykepredko]

Looking at the initial comments there are a lot of naysayers, but just like electric cars (and trucks) are becoming important market segments, electric aircraft will become a significant part of the market. Fuel cost continues to be a big uncertainty and is the major cost item of each flight - reducing this cost by any kind of double digits (ie going to electrical) would be a big win for airlines.

For some reason, the immediate response is that they will not replace the big iron, like B-777s or A-330s but that's not what the initial targets are - I wouldn't be surprised seeing the first electrically powered regional aircraft by 2025 with many flying in the 2030s. Going either further down, light aircraft fuel costs are major detriments for flying schools and air taxi services.

With the experience gained with regional aircraft, improvements in technology (ie battery energy density being the big one) will mean that the big iron aircraft will start going electric in the 2040s.

Re:Like it or not, it's the future

[Solandri]

Electric cars aren't becoming an important market segment because of fuel cost. They're becoming an important market segment because CARB (the California agency which sets pollution regulations) is requiring a certain percentage of an automaker's car sales to be EVs, otherwise they'll be prohibited from selling cars in California. If they can't hit the required percentage, they have to buy EV credits from a company which has extra (which is what keeps Tesla afloat). Since about a dozen states automatically adopt CARB's rules, this would force the automaker out of about 1/3 of the U.S. by population. So they comply with CARB's rules whether or not they make financial or environmental sense.

I'm not saying this is a bad thing. Just understand that the EVs you see on the road are there entirely because of regulatory pressure. Not because they make economic sense.

Re:Like it or not, it's the future

[mykepredko]

The problem with your argument is that only a quarter of the US states have CARB laws and other countries (like Canada) don't have them at all.

I think that Mr. Musk was brilliant in targeting the high end first where snob appeal generated interest/buzz/sales helping to build the company while developing the technology for the Model 3. Similarly for the Semi business - get in there and develop the technology and market acceptance.

The same thing with aircraft - start with smaller platforms and build/learn/develop from there.

Re:Like it or not, it's the future

[vtcodger]

"this would force the automaker out of about 1/3 of the U.S. by population."

More like 1/8th. There are a lot of people in California, but they only add up to 37 million plus no small number of illegals who are not to be found when the census folks drop by. Still 37,000,00 is more than the population of Canada or Australia, and few auto mongers want to be locked out of that market.

oh the humanity

[Joe_Dragon]

oh the humanity

Not about the bypass

[sjbe]

A majority of the thrust is produced by accelerating a large mass of unburned air to a speed just slightly higher than the airspeed of the aircraft.

You miss the point. The ONLY technology we have that can fly as fast as a jet engine (high or low bypass) is a rocket which involves throwing mass out the back of the craft. Electric motors combined with batteries lack the power density to drive any sort of fan or propeller sufficient to enable commercial applications. They are simply too heavy for the amount of power they can store right now. It might be possible to do a hybrid system similar to locomotives where the fossil fuels are used to power the electric motors for added efficiency but we currently have no batteries nor any near term likely batteries that can replace fossil fuels in that task.

Re:Not about the bypass

[HornWumpus]

To be fair, this is only a flying testbed. Commercial applications are, optimistically, decades off.

Doesn't appear to carry many batteries, rather an oversized APU to drive the electric engine(s).

Jets vs rockets vs heavy batteries

[sjbe]

How important is the impulse from the exhaust on modern passenger jet engines? I was under the impression that the giant fan was responsible for far more thrust. Lazy Googling seems to indicate an 80:20 bypass fan:core thrust ratio.

Doesn't matter. The problem isn't the specific impulse - the problem is energy/power density. The problem is that batteries are too heavy to replace fossil fuels as the store of energy while also still allowing passengers/cargo. The only alternative technology we currently have to jet engines is rockets which work by throwing mass out the back of the craft and rockets aren't efficient at all because they need to carry oxygen. A hybrid system (think locomotives) might enable some efficiency gains but wholesale replacement is currently just not feasible.

Re:Jets vs rockets vs heavy batteries

[MightyYar]

the problem is energy/power density.

Ah, I misread your comment. I agree completely. Even if the electric system's available energy density were equivalent to that of expendable fuel, it would still be a tremendous disadvantage to lug around the entire takeoff weight of the aircraft for the duration of the journey. The aircraft would even need to be structurally beefed up to handle the extra landing weight!

Zeppelins! Air travel of the future?

[Geoffrey.landis]

More use of lighter than air craft. Blimps, zeppelins, etc.

We tried that. It didn't end well. It's a romantic idea but not a practical one for mass transportation. They have some niche uses but they aren't the answer you are looking for.

Partly true. But the serious problem with Zeppelins was weather: they are inherently large and slow, so storms absolutely kill them. Forget the Hindenburg: overwhelmingly, the cause of dirigible crashes was thunderstorms.

But in the 1930s we couldn't really predict weather, and we couldn't really look at what the weather was like far away. Today we have satellites and weather prediction. If there's a thunderstorm, we know about it. We don't have to fly the dirigibles through it because we didn't know it was there. So, the main cause of dirigible crashes is, today, a solvable problem.

Still-- today people really don't want to spend a few days crossing the Atlantic, and people expect their flights to take off whether or not it's raining: people won't take "oh, come back tomorrow, weather's bad" for a trip.

So, no, probably not mass transportation. You're right that they could be useful for other niches, though.

Physics is a harsh mistress

[sjbe]

News-fucking-flash: materials and propulsion technologies may have improved just a bit in the past eighty years.

News fucking flash: physics of airships has not. They are slow, bulky, cannot fly in inclement weather, require huge and expensive hangars, are expensive to operate, and no technological advance in the last 100 years has made them an economically viable replacement for jet/propeller driven aircraft. Airships had their day for transporting people and that day has passed. There are better and more sensible options in close to every circumstance you can think of for transporting both people and cargo.

Re:Physics is a harsh mistress

[Type44Q]

Your post is full of generalizations and blanket/redundant statements ("physics," blah blah blah). The physics cancels out on both sides of the equals sign, so-to-speak; the challenges relate to engineering and materials science.

I'd have said that time will tell if your arguments have merit - except as lighter and more rigid materials - among other things - continue to be developed, time is already showing us that your arguments are steadily ceasing to relevant.

Re:Physics is a harsh mistress

[Guspaz]

Modern technology isn't going to make an airship move at speeds similar to an aircraft, and most people don't have any interest in taking four times as long to get where they want to go.

Re:Physics is a harsh mistress

[WheezyJoe]

So, your point is light and more rigid materials. You haven't answered sjbe's point of slow, bulky, and cannot fly in inclement weather. No matter how light you make your airframe, an airship is always going to be bulky because of how buoyancy works; to float, it must be lighter than an equal volume of the surrounding fluid. But being less weight is awful in view of winds and storms, and being bulky sucks for achieving any appreciable speed.

So, at best, you're offering the public a mode of transport that is slower than airplanes, takes up more room at an airport, and flights must be canceled if wind gusts along the route get too high, winds that a 777 can punch through with barely a bump. And yet still your airship must slurp tons of fuel to fight wind-resistance and air currents. Who's gonna buy a ticket for that? You wanna get somewhere, you're better off walking or taking a bus.

The nail in the coffin is the lighter-than-air substance. Hydrogen? Expensive and burns, see Hindenburg. Helium? Expensive, planet Earth is running out of the stuff, and retrieving what there is often comes as a byproduct of dirty fossil fuel drilling. And they both leak like mad from whatever container you put it in, especially something lightweight for floating, consequence of being such tiny atoms. Worse, you got to bleed even more of it right out into the atmosphere in order to land. Lighter, more rigid materials don't do shit for this. Dirigibles suck. Own it.

Economically cannot work

[sjbe]

We really didn't.

Yes we really did. Heck we still fly blimps today so it's not as if the economics or performance characteristics of them are a mystery. Every decade or two someone seems to think the laws of physics and economics have been repealed and they take another run at it with predictable results. They have a few uses but passenger transport isn't going to be among them.

If you mean the lack of LTA craft was replaced by the conventional airplanes, you're right. If you mean anything else, like a certain overwrought tragedy, you're missing a lot of the actual harm because of a bright and shiny light.

The Hindenberg was merely the most celebrated of the crashes but there is no lack of others. The Shenandoah, Akron and Macon all were lost to accidents, particularly weather and there are many many more. They cannot fly at all in a stiff breeze, they a slow, they are expensive, and there quite simply are better options both aerial and terrestrial in nearly all circumstances.

Well, you won't let us do trains anymore, so what else is there?

When did I say anything about trains? Trains are demonstrably practical in a wide variety of circumstances, especially for freight but also for passengers. Airships are not practical for either passengers or freight. They have a few niche uses and that is all they will likely ever have.

Re:Economically cannot work

[Anonymous Coward]

We really didn't.

Yes we really did.

Nope! Count how many there were. Worldwide. Hardly a pittance.

Heck we still fly blimps today so it's not as if the economics or performance characteristics of them are a mystery.

We barely bother with them, it's a token effort that's even smaller than the people using kerosene engines.

Every decade or two someone seems to think the laws of physics and economics have been repealed and they take another run at it with predictable results. They have a few uses but passenger transport isn't going to be among them.

Of course not, there's a whole wasteful airplane industry sucking up all the resources, it's like competing with Windows, you can't make headway.

If you mean the lack of LTA craft was replaced by the conventional airplanes, you're right. If you mean anything else, like a certain overwrought tragedy, you're missing a lot of the actual harm because of a bright and shiny light.

The Hindenberg was merely the most celebrated of the crashes but there is no lack of others.

Actually, there is a lack of others. Quite a lot lacking. That's the problem.

The Shenandoah, Akron and Macon all were lost to accidents, particularly weather and there are many many more.

The Shenandoah's crash was not as certainly due to an accident, so much as improper handling, in fact, much of it reached the ground safely, so it's not entirely what you believe it to be, though admittedly due to the wreck being stripped by looters, it is hard to be certain.

The Akron's major cause for a loss of life was a lack of lifejackets, an easily resolved safety issue, and the weather issues could have been addressed with greater understanding of instruments.

The Macon was improperly repaired after operating outside of its design requirements to clear a higher altitude, a problem that could and does occur regularly with airplanes enough that it's hardly news. And it had very low losses due to...lifejackets.

Sorry, you're stuck with your fervent beliefs enough that they contaminate your perceptions, so you don't bother to inform your statements.

They cannot fly at all in a stiff breeze, they a slow, they are expensive, and there quite simply are better options both aerial and terrestrial in nearly all circumstances.

In some circumstances, but not nearly all. Well, unless you count how it's simply better not to travel in nearly all circumstances.

Well, you won't let us do trains anymore, so what else is there?

When did I say anything about trains?

Pretty much every time somebody tries to do it. You go on a weekly rant. Haven't you noticed?

Trains are demonstrably practical in a wide variety of circumstances, especially for freight but also for passengers.

Yet you keep poo-pooing them. Why is that? Why do you denounce the mere idea? Heck, you won't even let us have buses. Or bicycle lanes.

Airships are not practical for either passengers or freight. They have a few niche uses and that is all they will likely ever have.

Airships are practical for a variety of passengers and freight, they certainly won't work for every use, but then, what will?

However, it's just not done. It's anathema to even think about or attempt it. That's why you are so dogmatic in your beliefs, you take it as unthinkable and inconceivable that you are wrong, and when challenged, you retrench your beliefs, because you can't have them challenged.

Re:What about when they need to drop weight

[vtcodger]

Given the mass of the average American, ejecting them downward with sufficient force should allow for a significant altitude gain.

Re:How is this even plausible?

[Guspaz]

They're hybrids, not pure electrics. They're not storing all of their energy in batteries, only enough to avoid having to run the gas turbine electric generator at anything but the most efficient speed. That is, you need more power during ascent and less power during descent, but you want to run the turbine at max speed at all times. That means you draw from the batteries to supplement power on takeoff, and dump into the batteries to recoup on descent.

You'd only be drawing from the batteries for maybe 15 minutes of the flight, and the batteries would not be supplying all the power, only the power beyond what the generator can supply.

Why hybrid - its not a car

[joe_frisch]

For automobiles, hybrid engines make sense. The batteries can store energy from deceleration and downhill and release it when needed. They can also buffer the large changes in power required for normal driving, allowing the engine to operate at its maximum efficiency power - and allow the use of engines optimized for single power operation. This outweighs the small extra drag from the battery weight.

Airplanes are different. They already store energy as potential and kinetic energy: the energy spent in climbing is largely recovered in descent, the energy of accelerating is recovered in decelerating. Aircraft engines spend most of their time operating at near maximum-efficiency power already. OTOH, battery weight directly adds to induced drag and reduces efficiency. Aircraft do sometimes use drag devices, and running a fan as a generator would reduce that loss, but it is usually only for a small fraction of the flight.

  I don't see how a hybrid engine in an aircraft helps. I must be missing something.

I could see adding small electric traction motors for ground operations to reduce engine idle fuel consumption and pollution. Presumably so far the weight of batteries and motors is too much to make this a net efficiency win - but I could imagine it being useful in some cases.

Zippy Zeppelins

[Geoffrey.landis]

They still can't outrun thunderstorms.

Indeed. You would either not fly in thunderstorms, or you would choose a route that doesn't fly through them.

But at least now we know where the thunderstorms are, and have moderately good predictions as to where they're going. In the 1930s they didn't.

They're inherently slow, wallowing creatures. They're only "efficient" because they're so incredibly slow compared to bicycles

Well, Hindenburg's top speed was 84 miles per hour, with a cruising speed of 76 mph. You'd be hard pressed to hit that on a bicycle.

http://www.airships.net/hinden...

...

Turn off one or two jet engines during crusing?

[knorthern knight]

> That's not possible though because the ~15 minute ascent phase of the
> flight requires more power than cruise. So this forces cruise to operate at a
> lower than optimum efficiency. In theory an electric motor boost could obviate
> this need, and allow jet engines to cruise more efficiently. I'm not sure there's
> much to be gained here though because modern twin-engine airliners are
> required by regulation to operate (both cruise and ascent) with one engine
> out. So cruise efficiency is already pretty far down the curve.

It would obviously be hairy, not to mention stressfull on the wings, to consistently run a twin-engine jet with one engine turned off. But things would be different with a triple-engined plane like the DC10 or L1011. Would it be possible to use 3 engines for takeoffs and landings, and turn the middle engine off during cruising, or at least idle it to reduce fuel consumption? Then the remaining 2 engines would operate at closer to full thrust during cruise.

On a 4-engine jet, you might look at turning off or idling one engine on each wing, i.e. cruising on 2 engines. Then the remaining 2 engines would operate at closer to full thrust during cruise.