Siemens and Airbus To Push Electric Aviation Engines (networkworld.com)

coondoggie quotes a report from Networkworld: Siemens and Airbus teamed up today to develop electric and hybrid electric/combustion engines for commercial and private aircraft. The companies said they would amass a joint development team of about 200 employees that would jointly develop prototypes for various propulsion systems with power classes ranging from a few 100 kilowatts up to 10 and more megawatts, for short, local trips with aircraft below 100 seats, helicopters or unmanned aircraft up to classic short and medium-range flights. Hybrid-electric propulsion systems can significantly reduce fuel consumption of aircraft and reduce noise. European emissions targets aim for a 75% reduction of CO2 emissions by 2050. These ambitious goals cannot be achieved by conventional technologies, the companies stated. Airbus has developed a 2-seat electrically powered aircraft, known as the E-Fan. Siemens too has been developing an electric aircraft engine.

Comments

Energy density per kg

[NotInHere]

Is the energy density per kg of batteries really that much better than the energy density of methane gas, or liquid hydrogen?

Re:Energy density per kg

[Sam36]

Freakin heck no

Re:Energy density per kg

[R3d M3rcury]

I would imagine not. On the other hand, there are other ways of storing energy than batteries (like hydrogen fuel cells).

Get the electric airplane engine working. Let someone else worry about storing the electricity to power it.

Re:Energy density per kg

[blindseer]

If the hydrogen is from a carbon neutral source, which I assume it must or it's a waste of time, then would it not be more efficient to just burn the hydrogen in a traditional jet engine? Looking to Rube Goldberg for hints on aircraft design does not sound like a good idea to me.

Re:Energy density per kg

[rmdingler]

You basically charge your car batteries with methane, unless you live in a district that primitively burns thermal coal.

The fact that a preponderance of people cannot do long-term loss calculation precludes the likelihood Nuclear is an option for you and yours.

Tesla3 (pre)sales estimates alone seem to suggest a couple million less barrels of oil per year... what are we going to be creating the additional electricity with?

Re:Energy density per kg

[thinkwaitfast]

LH2 = 142MJ/kg

LiPo = 0.95MJ/kg

Re:Energy density per kg

[rmdingler]

For values of year, in the context of this single post, we mean day.

Trust us, it's for your own good.

Re:Energy density per kg

[Anonymous Coward]

Quite the opposite, but that's okay; the sun and wind are free! Slap some solar panels on the body and a windmill on the nose, and the plane will have all the energy it could ever use, while providing lots of jobs. It will never actually leave the runway, but that is a minor point, right? /s

Many of the "green" ideas are attractive, and superficially plausible to the layman. Ultimately though, reality has the final word, and the numbers just don't work. At a small scale, obscene subsides can partially compensate, but those technologies have no hope of achieving their ideals. Energy density is a real thing, and it matters. Scale also matters. Batteries are not even remotely capable enough for aviation applications, much less providing backup for a "renewable" grid.

The only practical technology at scale is the one that the crusaders are so eager to dismiss. Nuclear has an amazing energy density, with a very small environmental footprint in terms of land and resources. Also things which matter, but that the so-called "greens" are happy to sacrifice in enormous quantities in pursuit of their ideology. (Obviously, we aren't putting reactors on planes, but the heat can be used to produce synthetic fuels for planes and other transportation.)

Re:Energy density per kg

[dbIII]

what are we going to be creating the additional electricity with?

A mixture of different electricity generation methods, including a small number of 1970s style nuclear AP1000 units currently planned or under construction. Not having a monoculture means not being held hostage by a single industry with a small number of major players among a range of other benefits, which is one reason why some in the oil industry are pushing hard against windmills and anything else they see as a threat to their influence.
Also demand has been dropping so the "additional electricity" is not going to be very hard to plan for at all - there is already spare capacity so if demand starts ramping up again there's a bit of time to build more stuff before it exceeds what's already available or under construction.

Re: Energy density per kg

[Anonymous Coward]

No, but think of this. The military, and all passenger jets have a wind turbine generator that can power all the systems on that bird. Use a fuel powered generator to power electric engines till number 1engine is stable in operation, usually having a generator to power the aircraft, where the onboard generator can be shutdown. Or use the ground apu to start the craft.

Re: Energy density per kg

[Anonymous Coward]

Only problem with the Tesla, no one is going back to the basics, you need good roads, power supplies, and pencil pushers. We are not producing any more liberally trained thinkers to move forward. So as like Rome, we start with the circuises?
I've driven a Tesla coup. Nice, but four inches separated me from the concrete, that's the bottom of the car. Potholes are getting bigger then that.

Re:Energy density per kg

[Anonymous Coward]

Do we know what the energy density of graphene supercapicitors could be, based on low-scale tests? With 2-3 groups in the pre-production stage of graphene (MIT for example is apparently doing a vapor deposit method, others have developed spray-on methods) in larger and more reliable lots, coupling that with carefully-prepped nonene (monolayer tin) circuits that have room temperature superconductivity might be a viable method of storage. With the base material and non-conductive backing at worst the thickness of a sheet of paper, you could put together multi-ply segments fitted to the airframe (encased in carbon fiber? Aluminimum Lithium Alloys? Inconel?), essentially making the body of the fuselage one huge supercapicitor with quick charge capabilities.

Further, there are groups working to turn our glut of atmospheric carbon into usable materials before it gets absorbed into the ocean, as well as teams working on pulling what we've missed so far out of the ocean. Granted, it's a minuscule effort so far with our current pollution rates, but the tech could be used to turn our biggest global problem into innovative manufacturing resources an ubiquitous energy storage. And give future electric plane designs the capacity to approach current flights.

Re:Energy density per kg

[ChrisMaple]

Use hydrocarbons for takeoff and landing, and battery power when cruising. This will provide many jobs - for morticians.

Re:Energy density per kg

[Brett Buck]

Not at all. Kerosene is a very good fuel.

    The problem with methane, or even worse, liquid hydrogen, is that while the energy content per pound is good, the energy content per unit volume it terrible. That means very large fuel tanks, meaning more drag and more airframe mass, which leads you to making the wings bigger, which leads to you needing and even bigger tank, which leads to more drag, etc. Liquid hydrogen is one of the worst fuels imaginable for an airplane.

      Liquid hydrogen is only about 4.4 lbs/ cu ft and lerosene is something like 55 lb/cu ft. You simply can't make the airplane big enough.

Re:Energy density per kg

[Solandri]

If I remember from last time an article about these showed up, they're not planning to power the aircraft with 100% electric. It's a hybrid. During ascent it can run the engines at full fuel burn like is done now. During cruise, instead of throttling back, it continues to run the engines at full burn for a while, partly to move the plane forward, partly to charge the batteries. Then it switches the fuel off and runs the engines off the batteries for a while. When the batteries are depleted, run off fuel at full burn again. Repeat.

Run this way, the engines can be optimized for maximum efficiency at just a single RPM (max thrust), instead of having to be optimized across a wide range of RPM. The fuel you save from the higher efficiency of optimizing for a single RPM can more than makes up for the extra weight of the batteries. The point of this project is to figure out what combination of battery size and RPM optimization profile yields the greatest overall fuel savings.

Re:Energy density per kg

[Lisandro]

The engine is the easy part. We already have plenty options for efficient electric engines on any power range you'd like. I recall a group called "Bye Electric" fitting a C172 with a 200hp electric engine with little issues.

Power storage is everything. Every single option to store electric energy onboard an aircraft is orders of magniture less power-density efficient than gas.

Re:Energy density per kg

[Lisandro]

This was actually tried in the past: both the USA and the ex-USSR experimented with nuclear powered engines. Instead of electric engines they used regular jet engines, with the combustion chamber using heat from the reactor instead of burning fuel. It worked fine, the problem was they were unable to properly shield the crew from the reactor's radiation without adding too much weight.

Re:Energy density per kg

[jcr]

If the hydrogen is from a carbon neutral source, which I assume it must or it's a waste of time,

There are other advantages to hydrogen as a transport fuel besides the tree-hugger appeal.

would it not be more efficient to just burn the hydrogen in a traditional jet engine?

Nope. When you burn anything in an internal combustion engine, more than half of the energy from the reaction is lost as exhaust heat. If hydrogen fuel cells can be made with a similar power to weight ratio, then the ability to capture 70% or more of the chemical energy of the 2H2+O2 -> 2H20 reaction beats jet engines all to hell. A fuel cell/electric fan drive train would be far cheaper, require less maintenance, and much lower noise than today's aircraft.

-jcr

Re:Energy density per kg

[DigiShaman]

Modern GE and RR engines are incredibly efficient as they are already. And if I'm not mistaken, they all use variable stator vanes too. The conversion loss in converting KE into EE has to be substantial, yes? Obviously brighter minds will try and crack this nut, but I just don't see it being cost effective to do so with the added complexity.

Re:Energy density per kg

[Anonymous Coward]

I think the idea is exactly the opposite of that, you use the battery to boost power during takeoff. For takeoff the airplane needs more power than at cruise, so for most of the flight the engines are running at reduced power. A hybrid system would allow an aircraft to have smaller engines that run more efficiently at cruise speed.

The other deal I've read about is modern turbo-fan engines get their efficiency by having a high bypass ratio. Basically they are fan powered. The higher the ratio the more efficient the engine. The problem is the designed are topping out mechanically just because of the diameter needed for the fan itself. However with a hybrid system you could have two fans per engine. Which allows for a higher bypass ratio.

Yet another advantage noise. The fans on a jet engine are relatively quiet. It's the exhaust from the turbine that is noisy. So hybrid systems should be quieter. In thoery for landing you may be able to throttle the engines way down.

The other thing I haven't seen mentioned but I think is important, gas turbines have really poor throttle control. Means that when a jet airplane needs extra power, for instance when the pilot decides to abort landing due to wind shear the engines take vital seconds to ramp up. The throttle response of a hybrid should be very fast, a second or two. That should make these aircraft safer.

And finally if you lose an engine on a twin engines aircraft flying becomes tricky, you have half the thrust and it's unbalanced. Makes flying tricky. However with a hybrid mean only losing partial thrust on one side. This also would make these designs safer.

Re:Energy density per kg

[Harlequin80]

Energy density for liquid hydrogen needs to be measure in MJ/L for you to really see why it sucks to use. LH2 is 5.6MJ/L and a LiPo is 2.28 MJ/L.

While batteries are probably a long way from being capable of driving aircraft liquid hydrogen is a non starter because it takes up too much space. Standard Kerosene jet fuel has an energy density of 37MJ/L and has none of the painful storage or explosive risks of hydrogen.

Re:Energy density per kg

[blindseer]

There are other advantages to hydrogen as a transport fuel besides the tree-hugger appeal.

There are also many disadvantages. Hydrogen eats steel and aluminum. It has a much poorer energy density by weight and volume than jet fuel. I could come up with more if I wasn't so tired right now but those two alone really kills hydrogen as aviation fuel, especially if derived from a very useful fuel like natural gas (which is mostly just methane) or propane.

Since the entire goal of using this system is to improve the efficiency of burning the jet fuel then producing hydrogen from a fossil fuel sounds like you'd be going backwards. Part of the energy of the fuel is in the carbon hydrogen bonds, if you break those bonds on the ground to make the hydrogen then it is not contributing to the movement of the plane in the air.

Unless you can show me where I've gone wrong, or something I missed, I still think that hydrogen fuel for airplanes is a very bad idea with the possible exception of hydrogen derived from cracking water with power derived from nuclear fission. I won't even consider wind, solar, or geothermal good alternatives since they currently cost more than nuclear power.

Nope. When you burn anything in an internal combustion engine, more than half of the energy from the reaction is lost as exhaust heat.

That would be relevant if the aircraft in question did not have an internal combustion engine. What they want to do is run a generator with an internal combustion engine, then use that electricity to run a motor that drives a ducted fan. While you caught me on the thermal efficiency angle since they claim to reduce fuel consumption by 25% with this system they also hope to gain on efficiency by having batteries be part of the airplane structure. That is not a simple task and they know it.

Their claim of these efficiency gains comes from the hope that they can develop an electric storage system suited to power an aircraft. Since we have not even found a suitable storage system for the much simpler problem of electric cars and trains I believe they are not going to find that solution soon. If they do then perhaps we can see internal combustion cars get beat out by pure electric and electric hybrid cars on every price point, not just luxury cars and tree hugger magnets.

If I use the definition of efficiency to refer to it's cost and complexity, and not it's ability to convert fuel to forward motion, then a common jet engine is more efficient than the hybrid. For an airline this is a make or break matter, they run on total cost of ownership. For a personal vehicle this might not be so critical since a hybrid might offer other advantages such as comfort, performance, or just bragging rights, that a common jet engine would not have.

Re:Energy density per kg

[thinkwaitfast]

Yes, volumetric density is bad, but mass density is more important.

Re:Energy density per kg

[Harlequin80]

They are both equally important. Especially in things like aircraft. To carry the amount of energy required the size of the hydrogen tanks would be stupidly large. So large that it you wouldn't have any room for anything else. The 777s cary 181,300 L of fuel, this is 6,708,100 MJ of energy. If you assume the same efficiency for a hydrogen burning engine you will need 1,197,875L of liquid hydrogen fuel.

When you then consider that the 777 is 73.9m long and has a cabin diameter of 5.87m which, if treated as a cylinder is 1,362,000 L you start to see the problem. Even if you assume that all 181k of jet fuel is carried in the wings, you have cut your cabin space down to just 345m3 from the original 1362m3 just to hold the extra fuel volume. And this would be an over estimate as it is based on the plane being a tube.

Re:Energy density per kg

[Lisandro]

The very best supercapacitors are in the neighbour of 20 Wh/kg. For reference, petrol is 12,300 Wh/kg.

Re: Energy density per kg

[gargleblast]

Mmm. Perpetual motion.

Re:Energy density per kg

[Anonymous Coward]

Liquid Hydrogen would work well in Commercial jets - massive reduction in fuel mass reduces structure weights. It doesn't matter much that have to store fuel in fuselage tanks (just make a bigger fuselage), because so much of plane power use is to lift 1/3rd of takeoff mass in kerosene and bigger engines to accelerate it at takeoff.

EG 787-8 takeoff kerosene is 130tonnes dry, 100tonnes out of total 230tonnes needing about 125m for average mission weight of 180 tonnes.
LH2 would be about 140 tonnes for 25% power or energy saving, needing about 24 tonnes of fuel (engine and landing gear and structure would be lightened) and needing about 350m (tanks about 3.5 tonnes) in a fuselage length of 14m (which is roughly difference between the 787-8 and the 787-10).

If necessary you can just make your jet fly higher to reduce relative size of fuselage compared to larger wings, gives benefit of more internal volume for comfort.

Liquid Hydrogen is probably the best fuel for supersonic use - as it cuts fuel weight by about 75% (about 40-50% of takeoff weight) lowering structural loads and weights, lowering thrust needed proportionally and lowering boom noise by up to half (perhaps more if flying higher), and can easily give global range (eg see lapcat). Also possible advantages in improving gas turbine efficiency through pre or intercooling or using a superheated rankine cycle on the LH2 for even bigger fuel savings. Can also cool passengers.

LH2 would also be fine in Trucks and Ships. What it really sucks at is intermittent small applications like cars motorbikes etc where small scale long term storage issues and close proximity to humans make it dangerous. Fortunately batteries are good enough for that.

So in a post fossil fuel world LH2 is pretty attractive for all sorts of transport, as long as we can find cheap methods of manufacture (ideally nuclear or perhaps southern ocean floating wind turbines or around Antartica to use collosal power available in katabatic winds there.)

Re:Energy density per kg

[Hognoxious]

Not currently (sorry). Maybe that's why they're targeting short haul flights - it's limited by the length of the cable.

Re:Energy density per kg

[jcr]

It has a much poorer energy density by weight and volume than jet fuel.

Volume yes, weight no. There's a reason why hydrogen was used in the first stage of the Saturn V.

-jcr

Re:Energy density per kg

[Hognoxious]

Low density is a good thing. You could use the fuel tank's buoyancy to generate lift. Maybe you could do away with wings completely.

I'm amazed that in all humanity, nobody's tried it.

Re:Energy density per kg

[jenningsthecat]

...making the body of the fuselage one huge supercapicitor with quick charge capabilities.

Aside from the very poor energy density of supercaps, (even when compared with liquid hydrogen), there's also the problem of even minor fuselage damage seriously compromising or destroying your energy source.

Re:Energy density per kg

[thegarbz]

Part of the energy of the fuel is in the carbon hydrogen bonds, if you break those bonds on the ground to make the hydrogen then it is not contributing to the movement of the plane in the air.

Unless you can show me where I've gone wrong, or something I missed, I still think that hydrogen fuel for airplanes is a very bad idea with the possible exception of hydrogen derived from cracking water with power derived from nuclear fission. I won't even consider wind, solar, or geothermal good alternatives since they currently cost more than nuclear power.

That depends if you're a lone source then it's energy inefficient. But there's more energy in a H-H bond than a H-C bond so Hydrogen itself is quite a viable fuel. The question of how to make it is more interesting. Yes building a plant to produce just hydrogen is wasteful. However Hydrogen is a by product of many other processes and at least one refinery I know of generates enough waste hydrogen that they can't actually export it all with the facilities they have... so they just send it to the flare.

That said fueling the worlds supply of hydrogen powered planes unlikely can be done from "waste gas streams".

Re:Energy density per kg

[dabadab]

Instead of electric engines they used regular jet engines, with the combustion chamber using heat from the reactor instead of burning fuel.

Actually what they have managed to do (both the USA and the russians) is to put a working nuclear reactor on a aircrafts using conventional engines - the reactors had nothing to do with moving the aircrafts. After that point, the projects were abandoned because there were too many problems (radiation shielding was a big one).

Re:Energy density per kg

[phayes]

Aircraft are only now beginning to use turbines to generate electricity which is then used in electric motors but is is a very widely used technology in many ships -- especially large warships.

A first application for adding an electric engine to the tail end of an airliner to re-energize the fuselage boundary layer airflow. As the plane flies through the air it slows down some of the air which ends up as drag. By putting a ring around the end of the fuselage directing the boundary layer airflow to an electric engine powered from the main turbines, drag goes down to the point that smaller diameter engines are needed (also diminishing drag). The major design change needed is that with the ring and engine, the horizontal stabilizers must be moved to a T tail.

Both NASA & Airbus are studying this for future designs: see here.

Re:Energy density per kg

[Anonymous Coward]

Liquid hydrogen is heavier than air, you can't use it to make a blimp.

Re:Energy density per kg

[Harlequin80]

Ummmmmm. Liquid hydrogen is heavier than air.... So for the purposes of an aircraft it actually makes you fall....

Re:Energy density per kg

[Hognoxious]

Don't liquefy it then. Do I have to do all the thinking round here?

Re:Energy density per kg

[AmiMoJo]

This is a hybrid, it still uses liquid fuel.

TFA doesn't have specifics but it seems that they have a set up similar to diesel electric trains. A liquid fuel combustion engine drives a generator that produces electricity, and that electricity is used to drive electric motors that provide propulsion. The advantage is that you only need one combustion engine and it can be run at the most efficient speed.

You can then add a battery pack so you don't need to run the combustion engine all the time. Great for cutting down pollution and noise at airports. You can charge it on the ground too, using renewable energy from the solar panels on the airport's roof rather than fossil fuels.

Re:Energy density per kg

[Rei]

Fuel cells are not all that great either. One of the biggest problems is that they're low power density. And the more power you try to get out of them, the lower their efficiency gets. Plus, aircraft jet engines - when operating at high throttle - are actually pretty efficient to begin with.

A hydrogen fuel cycle - between electrolysis losses and fuel cell losses is much less efficient than an electric cycle. When it comes to cars, usually 1/4 to 1/2 the system efficiency; for aircraft it'd be in the ballpark of 1/2. It also represents far higher capital costs (if you think batteries are expensive, try pricing fuel cells some time) and shorter lifespans (yes, fuel cell lifespans are generally pretty terrible - even in passenger car usage). Fuel cells also demand very high purity fuel, which means that you can rule out the cheapest hydrogen (NG-reformed) - it has to be (extremely expensive) electrolysis H2. Electricity, by contrast, is extremely cheap - much cheaper than jet fuel.

The biggest advantages for switching to electricity for an aircraft come on the ground and during landing. While jet engines are very efficient at high throttle, they're very inefficient at low throttle, and burn a lot of fuel when idling, too. So there's already a lot of work on electrifying the landing gear for taxi, for example.

When it comes to hybrid engines, there's two big targets. One is an electric fan feeding the engine. The other is direct electric drive of the compressor, with the nacelle as the stator and the compressor as the rotor. The latter option lets you entirely eliminate the turbine, which is an expensive piece of hardware that adds significant parasitic drag and reduces combustion efficiency. So moving energy consumption to electric not only lets you save on fuel - one of the biggest costs of an airline - but also engine purchase cost and maintenance. This of course comes at the cost of batteries, but their prices keep dropping (and with how much Tesla is going to need to scale up to meet their orders, they're going to drop even more than expected)

Re:Energy density per kg

[Anonymous Coward]

Hydrogen [...] has a much poorer energy density by weight and volume than jet fuel.

Hydrogen has better energy density by weight than jet fuel. What kills it is that energy density by volume is, as you say, lower, which means the tanks are unreasonably large - and, worse, they need to be insulated and pressurised to keep it liquid, whereas jet fuel stays liquid at room temperature.

A handy chart: the energy density by weight (horizontal axis) is about three times better for hydrogen than for kerosene and other hydrocarbons.

Re:Energy density per kg

[Anonymous Coward]

It's not quite that bad. Fuel mass is a significant fraction of the aircraft mass, so a lot of fuel gets burned to move the rest of the fuel, rather than to move the dry mass of the aircraft. If your fuel has better energy-density-by-mass, you can manage with less mass of fuel, so your total mass is decreased, which means you don't need as much total stored energy.

You could also increase the diameter of the aircraft fueslage to carry more fuel, although this increases your drag, and hence your fuel requirements.

The biggest problem might be that, unlike jet fuel tanks, hydrogen tanks need to be insulated and pressurised, which makes them heavy.

Re:Energy density per kg

[religionofpeas]

Don't liquefy it then. Do I have to do all the thinking round here?

Good idea. Let's put all the fuel in a big cigar shaped tank that you carry on top of the plane. By virtue of being so light, it also helps to create extra lift.

Re:Energy density per kg

[jafiwam]

Aircraft are only now beginning to use turbines to generate electricity which is then used in electric motors but is is a very widely used technology in many ships -- especially large warships.

A first application for adding an electric engine to the tail end of an airliner to re-energize the fuselage boundary layer airflow. As the plane flies through the air it slows down some of the air which ends up as drag. By putting a ring around the end of the fuselage directing the boundary layer airflow to an electric engine powered from the main turbines, drag goes down to the point that smaller diameter engines are needed (also diminishing drag). The major design change needed is that with the ring and engine, the horizontal stabilizers must be moved to a T tail.

Both NASA & Airbus are studying this for future designs: see here.

Do you ever fly?

APUs have been in aircraft in various forms since World War 1. Modern APUs are turbines that burn jet fuel.

Next time you are close to a big plane, look for a small-ish vent on the wing or the tip of the fuselage. Large planes (and lighter than air aircraft) have had these for a century already.

Your article does have some interesting ideas about using drag envelopes to gain an efficiency advantage, but the idea there haven't been separately powered generators on aircraft before is false.

Re:Energy density per kg

[bev_tech_rob]

Ummmm.....I thought the first stage of Saturn V burned kerosene and LOX. Second and third stages burned liquid hydrogen and oxygen.

Re:Energy density per kg

[plover]

The previous poster was referring to a motor-generator system, where turbine engines are used to generate electricity to power electric motors that drive the propellers. The APUs you confused them with are "Auxiliary" Power Units, and have never been used to make the plane move.

What I wonder about in such a system is the cost of converting the power to electricity before creating thrust. You have to carry around heavy coils of wire in each motor and generator, whereas the turbofan only has to carry a drive shaft (or transmission) between the turbine and the fan. Plus, electric conversion is not perfectly efficient, some losses are introduced. I have to assume the engineers have minimized most of those impacts. On the other hand, decoupling the motors from the generators would allow for extra margins of safety: a flameout of one turbine would result in an overall loss of power, but it would not necessarily be an unbalanced loss of thrust.

Re:Energy density per kg

[plover]

I'm amazed that in all humanity, nobody's tried it.

"Oh, all the humanity!"

Re: Energy density per kg

[manu144x]

The electricity is already there of you charge at night. All the wasted energy at night time would simply be used to charge ev's. Also since the price of the wasted energy will no longer need to be included in the price of the daytime used energy it might actual get cheaper. I know it's not a 100% fix since we still have electricity generates from fossil fuel but think of the 80% energy in fossil fuel that is wasted in ICE engines. Nobody talks about that. I know electricity transport has losses too, but not 80%. Plus, fossil fuel needs to be transported too, and required massive infrastructure to be cheap, and if something goes wrong, it's really bad. I think electricity is the best option we have, but yes, the battery technology is nowhere near mass market yet compared to fossil fuels. But it will reach the good enough point soon, where charging 20 mins for 200 mile range is livable.

Re:Energy density per kg

[Anonymous Coward]

Yes, I'm sure being armed means he is a child who likes poking gun barrels up his ass.

What the fuck is wrong with you?

Re:Energy density per kg

[Agent0013]

I won't even consider wind, solar, or geothermal good alternatives since they currently cost more than nuclear power.

Are you sure that nuclear costs less. Just the other day I heard a radio program talking about how there are many nuclear plants in the US shutting down because they can't compete on price with the newer renewable energy plants like solar and wind. http://www.npr.org/2016/04/07/...

Re:Energy density per kg

[i41Overlord]

>Get the electric airplane engine working. Let someone else worry about storing the electricity to power it. They've had electric motors for more than a century. The motors were never the technical hurdle. That's like saying "Pack your things for a camping trip on Pluto. We'll let someone else worry about how to get there"

Re:Energy density per kg

[brambus]

A liquid fuel combustion engine drives a generator that produces electricity, and that electricity is used to drive electric motors that provide propulsion.

In that case, job done. You're basically describing the thermodynamic cycle of a high-bypass turbofan or turboprop engine, minus all the electrical efficiency losses in between. Gas generator driving a turbine which produces mechanical power to drive a bypass fan or prop. And you're misunderstanding the reason why we have multiple engines on passenger aircraft. It isn't because we can't build em large enough. It's because everything fails. That's why you have two of everything in aircraft. Two engines, two fully independent electrical systems, two sets of flight control actuators, yes even the two pilots. Heck, it's also the reason why landing gear has least two sets of wheels on each axle.

Re:Energy density per kg

[blind biker]

Hydrogen eats steel and aluminum.

I noticed there is a strong groupthink on Slashdot that is against hydrogen fuel cell technology. And one of the (blatantly incorrect) statements is that hydrogen is impossible to store. And yet, there are multiple car manufacturers that make viable hydrogen-powered cars, and the hydrogen storage is not the problem at all. The problem is the current common methods of producing hydrogen, and the (non) availability of gas stations.

I swear that the collective Slashdot IQ falls through the floor when fuel cells, especially hydrogen fuel cells, are the topic. The dumbest, least researched statements, get the most upvotes. It's embarrassing to watch.

Re:Energy density per kg

[blind biker]

Energy density for liquid hydrogen needs to be measure in MJ/L for you to really see why it sucks to use. LH2 is 5.6MJ/L and a LiPo is 2.28 MJ/L.

While that is the metric you would use to conform to the Slashodt groupthink, you might want to consider the specific energy, i.e. energy per mass (MJ/kg). There, hydrogen beats Li+ batteries by two orders of magnitude.
I am not denying that volumetric energy density is important, but gravimetric density is even more important in aviation technology.

Re:Energy density per kg

[blind biker]

Don't liquefy it then. Do I have to do all the thinking round here?

Good idea. Let's put all the fuel in a big cigar shaped tank that you carry on top of the plane. By virtue of being so light, it also helps to create extra lift.

Actually, compressed hydrogen can be made to have higher volumetric density than liquid hydrogen. I know, mind-blowing.

Re:Energy density per kg

[GuB-42]

Making electric engines is easy, storing energy to power them is hard.
That's why we started with electric trains, then we moved on to electric cars, and we still don't have commercial electric planes.

Re:Energy density per kg

[brambus]

instead of having to be optimized across a wide range of RPM

But that's not how turbine engines work. This isn't your car. Typically turbine engines operate 85-100% of their rated rpm and in cruise it's closer to 95-100%. Oh and continually stopping and starting turbine engines is one of the worst things you can do to them, because that's when they experience most of their wear.

Re:Energy density per kg

[Grishnakh]

Is the energy density per kg of batteries really that much better than the energy density of methane gas, or liquid hydrogen?

No, but it doesn't have to be. When you burn (oxidize) fuel to run an engine and create rotational energy, you're only getting somewhere between 30-60% efficiency, and the rest is simply wasted as heat. (The 60% number is for really big power plant turbines, you won't see that on any vehicle; it's more like 40% or so there in the best case.)

With an electric motor, it's very different. Instead of wasting most of the energy as heat, almost all of it is used for rotational force: good electric motors are 98% efficient or more. Of course, you also lose a bit of efficiency in the batteries when you discharge them, but that's still probably in the 90+% range.

So to equal fossil-fuel-powered engines, you just need to get a little less than half the energy density per kg.

As for liquid hydrogen, that isn't a practical fuel. To make that work, you have to carry liquid oxygen with you and use a rocket engine. The storage requirements are pretty ridiculous. It works OK on spacecraft because they need an insanely-high thrust-to-weight ratio for a short time and can afford the ridiculous costs in both money and safety factor that are inherent in using it. Aircraft don't work that way: fuels have to be relatively safe and relatively cheap. Liquid hydrogen is neither.

And methane gas? When has anyone ever used that in any kind of engine? Methanol != methane.

Re:Energy density per kg

[Rei]

I assumed they meant to say "wasn't" ;)

Indeed, to sum up:

Mass density: excellent
Volumetric density: horrible
Thrust: poor (though probably not an issue for passenger jets)
Ease of ignition: easy. Burns aggressively in almost any fuel-air mixture, requires only a trivial spark to ignite, and burns can accelerate from deflagrations to detonations in many circumstances.
Ease of accidental ignition: likewise, easy.
Liquid storage: very difficult. High boiloff rate (liquefies air outside its tank), lots of energy goes into creation (incl. ortho/para conversion), entrained air freezes out as a highly explosive ice, subpar compatibility with composites, metal embrittlement over long periods. Boiloff gases pool under overhangs / enters pipes & follow them to their destinations.
Gas storage: difficult. Requires very high pressures for even low densities; high leakage rate and metal embrittlement over long periods. Leaked gas pools under overhangs / enters pipes & follows them to their destinations.
Airflow required for stoichiometric burn: high (~17kg air per kg kerosene, ~40kg air per kg H2)

Basically: as a fuel, hydrogen is both wonderful and terrible.

Re:Energy density per kg

[phayes]

Do you start all your posts with a stupid question?

Can you point out where I stated that airplanes do not have "separately powered generators"?

Did you attempt to understand what I said and the URL I gave that make it clear that I was referring to hybrid turbine-electric propulsion & not just housekeeping/emergency power for control surfaces?

From where I am standing the answers to these questions are maybe, hell no and clearly no.

The next time you sit down in front of a keyboard, like you probably are as you are reading this, you might want to engage your brain so that you understand what I said before posting a reply in which you attempt to put words in my mouth and end up invalidating a theory that's only in your mind.

Re:Energy density per kg

[phayes]

From what I have read, yes, the diminution of drag from the re-energized boundary flow and smaller main engines does indeed make enough of a difference that the added weight and drag from the hybrid propulsion system should bring efficiency up by low 2 digit numbers.

The changes to the turbines were claimed to be minor and given how common turbine-electric is in power plants, locomotives and ships, well mastered.

Do note that while there are other studies on going much further and replacing the turbine's direct role in propulsion with electric motors much more, that wasn't what I was referring to here. This should give big gains for relatively minor tweaks in current platforms.

Losing a turbine/generator on liftoff would still be very bad news because you'd lose both the engine's thrust and all power from that side - diminishing thrust from the electric motor in the tail too. Pushing the remaining engine to make up for the loss in power still makes for asymmetric thrust. You would have to move the engines closer to the centerline as is being mooted for blended wing-body designs but those are massively different designs from what is flying today.

Re:Energy density per kg

[Grishnakh]

You're forgetting how inefficient turbofan engines are at part-throttle conditions. You're assuming they run at full throttle all the time, and that isn't true. They run at full throttle on takeoff only, and then part throttle for cruising, but the worst is when they're idling on the runway: airlines waste a huge amount of fuel at that time.

Re:Energy density per kg

[Grishnakh]

Don't forget electric boats and electric dump trucks and construction equipment.

Many boats now are electric; cruise ships are a good example here. They use things called "azipods" for propulsion, which are giant pods on the bottom of the ship which have a giant motor and a propeller, and which can rotate a full 360 degrees for maneuvering. The motor of course is driven by electricity generated by diesel generators on the ship.

Extremely large construction equipment (like dump trucks) are the same: they have motors driving the wheels, powered by a diesel engine/generator.

The main reason we use motors for trains and dump trucks is because of torque: motors generate peak torque at stall, which is great for moving huge loads. It's actually rather curious that we haven't moved to this for semi-tractors yet, because those also need huge torque and not so much horsepower. By contrast, fossil-fuel-burning ICEs generate peak torque at rather high speeds, which isn't all that useful when the engine is coupled to the drive wheels and you need the most torque to get the load moving.

Trains and dump trucks and ships don't need really high power-to-weight ratios because they aren't trying to fly, so the extra weight penalty of serial hybrid powertrains isn't much of a disadvantage compared to their advantages.

Re:Energy density per kg

[Ranbot]

Power storage is everything. Every single option to store electric energy onboard an aircraft is orders of magniture less power-density efficient than gas.

Could power storage needs be reduced by regenerating some electricity during flight? Rudders, elevators, and ailerons steer a plane by creating airflow disturbances and drag, but if the drag forces could also spin a turbine to generate electricity in flight, then less [heavy] battery space would be needed. Like regenerative breaking in hybrid/electric cars.

Re:Energy density per kg

[brambus]

You're forgetting how inefficient turbofan engines are at part-throttle conditions.

Proportions matter here. Turbine engines run in cruise at around 95% of rated RPM and about 3/4 to 4/5 of maximum thrust. In those regions, they are pretty much at the efficiency plateau. Those things aren't designed by idiots.
As for idling, yeah, they're inefficient. Everybody knows this, which is why partial-engine taxis are common nowadays and even so the overhead isn't so bad. I just did a quick calculation with my dispatch tool and a 737-800 on a relatively short hop of ~1.5 hours (only about 1 hour actual air time). A 20 minute taxi-out and 8-minute taxi-in (all engines running) comes to only about 9% of the trip fuel (6000 lbs trip, 500 lbs taxi). Would airlines be happy to reduce it? Definitely. But is it some huge environmental saving? Not really. And keep in mind, this is short-haul, so about as high as it gets. On longer routes the taxi falls quite dramatically. On a transatlantic route it's only about 2% of the trip fuel and transatlantic is quite short by long-haul standards (only ~6 hrs flight time).

Re:Energy density per kg

[Lisandro]

I'm not an aerodynamicist, but from what i understand this would not be efficient at all: you cannot tap into induced drag without introducing other surfaces. At best, you'd be trading induced drag (vortex related) for parasite drag (related to shape, construction and materials).

Re:Energy density per kg

[Ranbot]

From one non-aerodynamicist to another, that sounds like a reasonably good point. :-)

Re:Energy density per kg

[Anonymous Coward]

This. All the hydro and hybrid solutions discussed add significant weight that would severely cut or eliminate any advantage over traditional designs. No way H2 could be stored in fuel talks designed for liquid jet fuel without substantial, heavy reinforcement. Fuel cells and batteries are not exactly lightweight either, and this extra gear is added in addition to the power plant itself. Perhaps the electric propulsion fans would be lighter than the jets they replace, but the rest of the trade-off is a lot less clear.

In land uses, the weight of electrics has been put to good use. Heavy is actually a good thing for diesel-electric locomotives, as the weight serves to increase the grip on the tracks. In cars, the weight of the battery has been put to good use by shifting down the center of gravity, which provides better road performance. But added weight is simply no good for aircraft.

Re:Energy density per kg

[Anonymous Coward]

This is exactly how hybrid cars work.

Internal Cumbustion Engines (ICE) have a very narrow efficiency band. They perform terribly under load (During acceleration from stop, for example - F=MA)

DC motors don't have this issue. (Well they do but it's several orders of magnitude less severe)

In a hybrid the electric drive system provides power when the ICE is less efficient, letting you get away with a smaller engine optimized for running efficiently. The electric drive system also runs in reverse, storing extra energy int the event that the optimal ICE power band is providing more energy than you need.

Ford's next gen hybrid engine is a tiny 3 cylinder turbo charged engine. Why turbo? Turbo engines can be ridiculously efficient (and powerful) but their bands are even more narrow.

Re:Energy density per kg

[Anonymous Coward]

And methane gas? When has anyone ever used that in any kind of engine? Methanol != methane.

Um, all the time? CNG/LNG engines are well-known.

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

Re:Energy density per kg

[LWATCDR]

"There are other advantages to hydrogen as a transport fuel besides the tree-hugger appeal."
For subsonic aircraft not really. It has a very low energy density by volume, it is hard to store and transport, and it is expensive. It is good for the upper stages but not so much for aircraft.
". When you burn anything in an internal combustion engine, more than half of the energy from the reaction is lost as exhaust heat"
Very few multi-engine commercial aircraft use internal combustion engines any longer they are mostly turbofans and turboprops.
  " A fuel cell/electric fan drive train would be far cheaper, require less maintenance, and much lower noise than today's aircraft."
Maybe but today they are not. Once you push them to match the performance of a gas turbine I doubt they will be cheap or low maintenance in comparison. A modern turbofan has a TBO in the tens of thousands of hours. Noise is another issue but the truth is that most of the noise from a modern turbofan or turboprop is from the fan/prop. It will not make a lot of difference if they are driven by a gas turbine or by an electric motor.

To me the real place that they need to look at is the brakes. If you could replace the brakes on an airliner with electric motors/generators then you may have something. If they could keep the engines off until they got on the runway you could save a lot of fuel and emissions. Maybe large super caps and an apu to top them up if you have a long delay.

Re:Energy density per kg

[Anonymous Coward]

whooosh... over poster's head like a led zeppelin.

Re:Energy density per kg

[Anonymous Coward]

...and then, light up a cigar to celebrate! Oh, the humanity!

Re:Energy density per kg

[Anonymous Coward]

Are you really that ignorant?

Re:Energy density per kg

[blindseer]

I'd think that comparing 40+ year old nuclear reactors to brand new wind and solar is not a fair fight. That's also one nuclear reactor out of nearly 100 in the USA. Many of those are also 40+ years old and recently got 20 year renewals on their operation license. That means the utility believes the reactor will produce power at a competitive price for another two decades.

I've seen presentations from nuclear engineers that say the materials, labor, and engineering for a modern nuclear power plant is the same or lower than that of a coal fired plant. The problem with costs in the USA is largely regulatory. If nuclear power was regulated like any other power source, including it's radiation output, then we'd be building nuclear power almost exclusively. The radioactive waste that coal produces alone would shut them down if they were a nuclear power plant.

So what we see are nuclear reactor designers in the USA going overseas to build reactors because the USA has insane restrictions on getting them built.

Re:Energy density per kg

[Areyoukiddingme]

I noticed there is a strong groupthink on Slashdot that is against hydrogen fuel cell technology. And one of the (blatantly incorrect) statements is that hydrogen is impossible to store.

Storing highly compressed hydrogen is, in fact, very difficult. The VentureStar/X-33 program failed specifically because of how difficult it is to store hydrogen. This is not a theoretical problem. Lockheed-Martin spent millions trying to make it behave safely, and failed. In a car, you can get away with things that are far too dangerous in an aircraft. In an aircraft, fuel tanks are also structural. The stresses on parts directly exposed to hydrogen are far higher.

Re:Energy density per kg

[Agent0013]

From the article I linked to: "But right from the start, people in the nuclear industry struggled with a big problem: cost. Making nuclear power cheap was the Holy Grail." That does not sound like a recent problem.

Also in the article: "Entergy has already taken one unprofitable reactor offline in Vermont and plans to close two more plants that are losing money in upstate New York and Massachusetts. In all, 19 nuclear reactors are undergoing decommissioning, of which five have been shut down in the past decade, according to the U.S. Nuclear Regulatory Commission." It does not look like you read this at all. You said it was one plant when it is many being shut down.

Do I just need to post all the text of the article right in here for the idiot pro-nukes to understand what it says? "The main reason behind the wave of closures is a new generation of cheap, gas-fired power plants that has pushed the wholesale price of electricity into the basement. But Mycle Schneider, a nuclear industry analyst, says nuclear also faces growing price pressure from wind and solar. Renewable energy is so cheap in some parts of the U.S. that it's even undercutting coal and natural gas." That is a nuclear industry analyst saying that. And the wind and solar is even undercutting coal and natural gas. It isn't just a nuclear problem.

It also states that the average age of the nuclear reactors in the US is only 35 years old. The pro-nuke fan boys always talk about how they are all over 60 years old or something ridiculous. That is the reason it stood out as such an interesting fact to me, because it was counter to what I keep hearing here an /. about how we should be building new nuke plants because they are all so old. I guess if the lies help push your wold view, it's all ok in the end, right?

Re:Energy density per kg

[Tough Love]

Batteries are not even remotely capable enough for aviation applications...

The skies are already full of battery powered drones, so that claim is wildly wrong. Perhaps you meant to say "for many aviation applications".

Nuclear has an amazing energy density, with a very small environmental footprint in terms of land and resources.

How are you going to build a rector light enough to put in an airplane? Consider coming back down to earth.

Re:Energy density per kg

[delt0r]

Hydrogen is a very hard substance to store. In its most dense, weight/mass efficient form, liquid hydrogen is only 70kg per m3. Ten times less than A1 jet fuel. It is not just cold, at 20K it is about 4 times colder than liquid nitrogen and will instantly freeze air! So tanks are Huge and require a lot of heavy insulation. All other forms of hydrogen storage are just too heavy for aircraft.

Consider that for a long haul flight, a 747/A380 are about half fuel by weight. Finding 10x more fuel tank + insulation is a much bigger aircraft with a lot more drag.

Liquid methane is however much more practical. Liquid at about liquid nitrogen temp is really a lot easier to deal with and it about 300kg/m3 IIRC. It only halves the CO2 however compared to A1.

Both are better than batteries. But then A1 jet fuel is working now.

Re:Energy density per kg

[delt0r]

As a rocket propellant it is very good for other reasons than energy density. Though it is quite high. It is the low molecular weight of the exhaust which means a much higher exhaust velocity and higher specific impulse. Note that many belive that hydrogen is not the best propellant to use from earth because this doesn't tell the whole story with vehicle performance.

Re:Energy density per kg

[delt0r]

Very well summed up.

Re:Energy density per kg

[delt0r]

You cannot change the laws of physics. Hydrogen embritlement is a fact. The very low energy density of hydrogen is a fact. The very very cold temperatures of liquid hydrogen is a fact. The high energy cost and complexity of liquefying hydrogen is a fact (It has to do with the magnetic states of the molecule, its cool physics). The very high diffusion rates of hydrogen through a lot of common materials is a fact. The very high ignition range (flash point? i never remeber) in hydrogen is a fact (5%-90% IIRC).

There are no commercially successful hydrogen vehicles, so you don't even have a point.

Re:Energy density per kg

[delt0r]

But the sheer power required is huge. 747 engines are in the MW range and that is going to a battery bigger than an airplane!

Re:Energy density per kg

[delt0r]

200HP or less than 200kW is a toy compared to modern airliners. You need to be well into the MW range to be relevant.

Re:Energy density per kg

[delt0r]

It really doesn't work that way. Also 20K is soo freeking cold you need lots of heavy insulation. It really doesn't work well in practice, and is very expensive to even try.

Re:Energy density per kg

[delt0r]

technically they don't need to be pressurized. But insulated is a requirement. Heavy insulation. Also hydrogen really has a long list of other problems. Hope this is a link to a comment further up. Someone summed up better than me.

Re:Energy density per kg

[Lisandro]

Again, easily achievable. ABB sells electric motors in the 10 MW range with an efficiency of ~96%. And thats pretty much off the shelf offerings.

Re: Energy density per kg

[Anonymous Coward]

Ah, you mean that Mao, Stalin, Pol Poth and Hitler killed too little number of people?
Or will you start the purging with your own family? I can send you some money for bullets.

Re:Energy density per kg

[Grishnakh]

Whoops, you got me there.

However, LNG vehicles are land-based, not aircraft. I've never heard of anyone using CNG or LNG for aircraft. CNG would probably be pretty hard because it's a gas; the tank would be huge and heavy. LNG wouldn't be much better: the tank would be really heavy to keep it compressed and keep it from gasifying.

Re:Energy density per kg

[Anonymous Coward]

gas isn't renewable

Re: Energy density per kg

[rmdingler]

I know electricity transport has losses

6% is the percentage lost most often referenced on these united internets. That seems like an incredibly small number just considering the ubiquitous transmission lines you can observe as you travel pretty much everywhere.

The electricity is already there of you charge at night.

If you're correct, and the energy for reinvigorating the electric vehicles is available at night, I assume that must be in some places during some parts of the year. But. Even if we grant that the energy is generally available at night, there will be some number of procrastinators (or all night partiers) who still need daylight charging. People are a difficult lot to plan for.

Re:Energy density per kg

[Anonymous Coward]

It's not been widespread, but it has been done:

http://naturalgasnow.org/natural-gas-airplanes-take/

And NASA has:

http://www.nasa.gov/centers/marshall/news/releases/2015/nasa-tests-methane-powered-engine-components-for-next-generation-landers.html

Re:Energy density per kg

[Harlequin80]

Groupthink? Volumetric energy density lets you know the volume that your required energy store will take up. Per weight hydrogen is fantastic, per volume it sucks.

Have you ever sent anything via air freight? Do you know why they have a volumetric AND a weight calculation? Because sometimes the volume is more important than the weight.

The fuel tanks that a 777 would require to fly on hydrogen cuts your internal capacity by over 75%. Mass is NOT the only consideration when it comes to fuel.

Re:Energy density per kg

[blind biker]

You cannot change the laws of physics. Hydrogen embritlement is a fact. The very low energy density of hydrogen is a fact. The very very cold temperatures of liquid hydrogen is a fact. The high energy cost and complexity of liquefying hydrogen is a fact (It has to do with the magnetic states of the molecule, its cool physics). The very high diffusion rates of hydrogen through a lot of common materials is a fact. The very high ignition range (flash point? i never remeber) in hydrogen is a fact (5%-90% IIRC).

There are lining materials that solve the issue - surprisingly enough, they do that using "the laws of physics".
Hydrogen is not stored in liquid form - it's compressed at 700 bars.

There are no commercially successful hydrogen vehicles, so you don't even have a point.

Straw man argument.

Did they elect you the captain of Slashdot groupthink? You're not doing too well.

Re:Energy density per kg

[Rei]

Power density is far better in batteries than fuel cells. I think you're confusing energy density and power density.

Re:Energy density per kg

[delt0r]

Not in flight weight configurations. Trains, boats and buildings don't care much about mass. Aircraft do.

Re:Energy density per kg

[delt0r]

No i am not. Even LiPoly is huge and cooling is a massive problem. Even then you have almost no range at all. Power density is fine for a drone with a 10-20min flight time. That is not going to cut it even for the shortest short haul flight because by law you need a longer loiter time than that. Power density for a 1 hour flight time already looks rather poor.

Re:Energy density per kg

[delt0r]

What a moron. 700bars and you think that is a flight weight tank. You don't understand the very basics of anything.

Re:Energy density per kg

[Rei]

. Even then you have almost no range at all. Power density is fine for a drone with a 10-20min flight time.

You ARE mixing up energy and power density. Power has nothing to do with time. Energy is power times time. A joule (energy) is a watt(power)-second.

Please at least get your terms correct before you start discussing an issue.

Re:Energy density per kg

[Lisandro]

You're seriously underestimating how lightweight electric engines are for a given power output - it all boils down to the fact that they're mechanically very simple.

A state of the art GENx aircraft turbofan engine (as the ones powering the 787 dreamliner) has a dry weight of 12,400 lbs. A marine 10MW electric engine weights 9,000lbs, and that is with a fully enclosed, liquid cooled, waterproof casing around it. Make it air cooled (these already exists too) and you'll halve that weight.

Granted, you still need to worry about control electronics and power but, again, the actual motors were never an obstacle to have an electric airplane. IIf anything, electric engines are a great idea because they're powerful, small, lightweight and have basically zero maintenance. It is all about the power storage.

Re:Energy density per kg

[delt0r]

holy shit that is impressive. Ok yea there are probably technical details that matter for an air cooled flight motor, but in marine applications there is no way it was highly optimized for weight, so very doable. Power storage it is then (as the outstanding problem).

Re:Energy density per kg

[delt0r]

Yes time matters and of course it affects total effective power density. If i want my drone to fly 2x longer. I need 2x the mass of batteries when consuming the *same power* (and now i am heaver so i need more power to stay aloft).

So if i want 1kW for 6 min, i can get away with a battery 10x lighter than if i need 1kW for an hour. Right now batteries are still just shit if you want to do anything that is not a toy for flying.

Re:Energy density per kg

[Lisandro]

It is :) Last year Siemens demonstrated an electric motor for aircrafts with a power-to-weight ratio of 5000 W/Kg. The modified C172 i mentioned before used an off the shelf tri-phase motor and they had to place batteries on the front because the aircraft was all of the sudden tail heavy. On top of add, they needed ballast to keep the CG within specs.

I just wish someone came up with an usable power storage solution. Electric engines are a dream come true for aircrafts.

Re:Energy density per kg

[Rei]

Yes time matters and of course it affects total effective power density

No, by the DEFINITION OF POWER, time is not a component of it.

consuming the *same power*

You don't consume "power", you consume energy.

So if i want 1kW for 6 min, i can get away with a battery 10x lighter than if i need 1kW for an hour

Because 1kW *6 minutes = 6 kW-minutes (360J = 6kW-minutes = 0,1kWh), while 1kWh*1h = 1kWh (3600J = 1kWh). Joules and kilowatt hours are measures of ENERGY, not power.

I'm done here, I'm not going to waste my time with an idiot.

Re:Energy density per kg

[Anonymous Coward]

** 1kW * 1h = 1kWh (typo)

Re:Energy density per kg

[jcr]

Gun grabbers have a tendency to be snotty, since they can't make cogent arguments for disarming crime victims.

-jcr

Re:Energy density per kg

[delt0r]

Man i thought you where one of the good ones. Guess not.

Re:Energy density per kg

[Coren22]

Gasoline may not be renewable, but Methane is.

Re:Energy density per kg

[Coren22]

I wonder what the efficiency of the fuel cell would be at altitude though where Oxygen is in lower supply. Would it be enough to cause the efficiency to drop?

CO2 emissions

[110010001000]

The EU has been increasing CO2 output year after year since the 1700s. How are they suddenly going to start REDUCING Co2 emissions? They even increased them this year! What a joke.

Re:CO2 emissions

[Trachman]

If they will reduce CO2 output, it will come at significant cost, significant expense.

Significant expense for consumer is, at the same time, significant revenue to the counter party. Extracting revenues is the main point of all the initiatives.

Re:CO2 emissions

[blindseer]

How are they suddenly going to start REDUCING Co2 emissions?

Nuclear fission?

No, wait, that should not have been a question...

Nuclear fission. The answer is nuclear fission.

Re:CO2 emissions

[ShadowRangerRIT]

Inability to completely solve the problem means we should not even attempt to reduce the scale of the problem? That's your argument? Really?

Re:CO2 emissions

[ArylAkamov]

Good luck convincing the public to support nuclear energy. For some reason they would much rather rely on ancient designs instead of replacing them with vastly superior and safer modern designs.

It's okay though, cold fusion soon, right? r-right?

Re:CO2 emissions

[dbIII]

There has not been the R&D to make those "safer modern designs" into physical objects and ensure that a prototype works as designed and can be altered to produce something good enough to go into production.
Software models don't quite match up to reality in a lot of areas guys. The real world has turbulent flow and other stuff that doesn't model well.

Re:CO2 emissions

[FlyHelicopters]

Inability to completely solve the problem means we should not even attempt to reduce the scale of the problem? That's your argument? Really?

Yes, quite possibly, yes...

We only have so much money and so many resources. Would they best be put to use reducing the scale of the problem, or planning for and mitigating the problem as it arrives?

It is possible that all the efforts to reduce the core problem will leave us unable to actually deal with it when it arrives.

Imagine that you're on the Titanic. Sure, bailing out water and trying to stop the flooding are all noble goals, but is that the best way to use the time you have left? Had the Captain accepted the loss of the ship more quickly, once you are ok with the idea that the ship is not going to survive, then the question becomes, how do we mitigate the damage?

They had hours before the ship sank? Why wasn't it all hands on deck, ripping up the decks to form makeshift lifeboats? Why not ram the ship into the iceburg and try and put people onto it? Crazy, but better than death.

Re:CO2 emissions

[blindseer]

Good luck convincing the public to support nuclear energy.

At least I'm trying. I bring it up here on Slashdot and on other forums I subscribe to. When politicians call me or knock on my door I ask them about nuclear energy. I've e-mailed politicians, not just the ones I voted for. What have you done?

I'd like to do more but I must still work and go to school.

Re:CO2 emissions

[Anonymous Coward]

You are denying the existens of modern nuclear power stations?

Re:CO2 emissions

[Blaskowicz]

If that idea holds, then the extracted revenues may be cause high CO2 output or need high CO2 output for them to be.
E.g. consumer buys a hybrid car, saves 18% CO2 per mile, gets paid by the government for buying the car, drives it 10% more since it's so much "green" and better ; that still results in a 10% CO2 savings at use. But making the car and batteries released twice the CO2 than making the non-hybrid car.
So, the hybrid car is more expensive and worse for the environment.

Other example, Germany runs a terrible energy policy. CO2 emissions increase. But has lots of solar panels and/or wind to show off (not that they're necessarily bad in themselves..)

In both cases the problem does NOT come from wanting to reduce CO2, rather it's because of PRETENDING to. That's fake environmentalism, "green" capitalism a.k.a. greenwashing which is a bit like asking the tobacco industry for health advice.

Re:CO2 emissions

[Anonymous Coward]

"existens "

Hey Cronenberg, how about a spell checker?

Re:CO2 emissions

[Viol8]

"Imagine that you're on the Titanic."

Seriously, you're going with that analogy?

Ok genius, so we bugger up the climate and are metaphorially all bobbing around in the ocean slowly dying. Do tell us where in your analogy where the rescue ship comes from?

Re:CO2 emissions

[dbIII]

Yes. The AP1000 is not modern by any definition applying beyond 1980.

Re:CO2 emissions

[pnutjam]

ugh.. A single issue voter...?

Re:CO2 emissions

[dave420]

You keep stating this when it's patently false. In fact, in 2015 the EU had its lowest CO2 emissions since 1990.

It might help you to stay abreast of that which you use to condemn. It will help you to avoid situations like this, where you make an argument drenched in drama, based on something you, or someone you trust, made up.

Re:CO2 emissions

[religionofpeas]

But making the car and batteries released twice the CO2 than making the non-hybrid car.

Citation required.

In both cases the problem does NOT come from wanting to reduce CO2, rather it's because of PRETENDING to.

Easily solved by taxing CO2 across the board, so that any CO2 used for manufacturing the car is also counted.

Re:CO2 emissions

[religionofpeas]

We only have so much money and so many resources. Would they best be put to use reducing the scale of the problem, or planning for and mitigating the problem as it arrives?

We'll still have to deal with phasing out fossil fuels when they run out, so why not start earlier ? The cost will be less.

Re:CO2 emissions

[religionofpeas]

What do you mean it's sinking ? My end is sticking 200 feet in the air.

Re:CO2 emissions

[FlyHelicopters]

We'll still have to deal with phasing out fossil fuels when they run out, so why not start earlier ? The cost will be less.

Of course, I have no problems with starting now.

The question is, how hard do we push for it?

To keep CO2 below 500 PPM would require massive and dramatic changes, that would likely crush the world economy and put us into recession. It is possible that we couldn't avoid 500 PPM no matter what we do, because of the existing CO2 and existing emissions, but if we could, it would require that we more or less turn off all our coal plants tomorrow, half our cars, half our natural gas, etc.

Since we aren't going to do that, we're going to pass 500 PPM.

---

Let me put it this way. We can slowly move towards a fossil free world, with perhaps a 100 year plan to get there. But we also have to accept that a 100 year plan takes too long to stop the CO2 rise from going through the roof.

In other words, the ship is going to sink, she's made of iron, fill her with water and she'll drop to the bottom of the ocean. Are we going to ignore that fact, or start ripping up the decks to build lifeboats?

---

http://400.350.org/

It all sounds very scary when you read stuff like that sight. Clearly they are a propaganda site, but I accept that they also might be right, or right enough.

But what they DON'T do is explain what it would take, what it would ACTUALLY take, to get CO2 back down to 350 PPM. Why? Because if they did, everyone would promptly ignore them.

http://www.globalwarming.org/2...

That is 7 years old, but it is even more true today than when it was published.

"Absent revolutionary changes in energy production, distribution, conversion, and storageâ"Nobel-caliber breakthroughs that nobody can plan or predictâ"lowering CO2 emissions to 350 ppm is impossible without draconian cutbacks in population, economic output, or both. Whether they realize it or not, the Climate 350 Club is asking us to go back to the caves."

---

http://sustainabilityadvantage...

This is an example of what happens when someone attempts to put it into an actual plan for action. First, there are a ton of flaws with that plan and some outright errors. #8 for example assumes that 67% of power is lost in transmission. No it isn't, the real number is about 7%.

It just isn't going to happen, it is the sort of list you come up with when someone is daydreaming about "if I could magically just change the world, what would I do?"

Re:CO2 emissions

[FlyHelicopters]

Ok genius, so we bugger up the climate and are metaphorially all bobbing around in the ocean slowly dying. Do tell us where in your analogy where the rescue ship comes from?

Moving 25 miles inland and 100 miles north.

Re:CO2 emissions

[Anonymous Coward]

We only have so much money and so many resources. Would they best be put to use reducing the scale of the problem, or planning for and mitigating the problem as it arrives?

It is possible that all the efforts to reduce the core problem will leave us unable to actually deal with it when it arrives.

If you are going to declare hand-waved possibilities, then it's also possible a lack of effort to reduce the core problem will leave us unable to actually deal with it when it arrives.

Try to at least get some specifics behind you, not mere platitudes.

Imagine that you're on the Titanic. Sure, bailing out water and trying to stop the flooding are all noble goals, but is that the best way to use the time you have left? Had the Captain accepted the loss of the ship more quickly, once you are ok with the idea that the ship is not going to survive, then the question becomes, how do we mitigate the damage?

They had hours before the ship sank? Why wasn't it all hands on deck, ripping up the decks to form makeshift lifeboats? Why not ram the ship into the iceburg and try and put people onto it? Crazy, but better than death.

Not really, no. Among the Titanic's problems was that they didn't load the lifeboats properly, doing that right would have saved more lives than a haphazard measure that wouldn't have been feasible with their lack of tools let alone training to do it. Those deck planks were very securely bolted down, and the ship's carpenter was not that well supplied. And I'm genuinely unsure how buoyant they would have been. But in three-hours? I doubt you could have managed it.

Of course, the even better measure would have been to load even more lifeboats before setting out, then train the passengers and crew in using them. This would have been an almost inconsequential cost.

Your example thus does not bear up as demonstrating your point very well.

Re:CO2 emissions

[Anonymous Coward]

And what will the taxing solve?
Is the money magically withdraving the CO2 from the atmosphere? Last I heard, that wast the business of plants (they grow and "eat" CO2 to grow).

Use the US Navy seawater to jet fuel tech instead

[blindseer]

The US Navy has been experimenting with the technology that can extract carbon and hydrogen from seawater, connect those elements together in long hydrocarbon chains, with heat and electricity from nuclear fission. They've shown it works. This technology makes aircraft carbon neutral without any modifications to the aircraft itself.

The use of an electric hybrid aircraft would still require hydrocarbon fuels. If that fuel is dug from the ground then it is still adding carbon to the air. I suppose we could combine the two technologies, synthetic hydrocarbons and hybrid planes, but it would still require that we invest in synthetic hydrocarbons.

These electric planes are interesting I suppose but they would not solve the problem like synthesized fuels would.

not going to work

[supernova87a]

I will be happy to be proven wrong, but I do not believe fundamentally the chemistry of batteries will ever be able to allow for profitable or sustainable passenger aircraft, because batteries do not even come close to approaching the energy density afforded by liquid fuels. If this were anything other than flight, where weight is paramount, it might be workable (and obviously is in land transport).

Liquid fuels like kerosene have energy densities on the order of 40-50 MJ/kg, while batteries (of any type available) right now range from 0.5-1.0 MJ/kg.

You simply cannot overcome this large a performance gap if you're talking about these categories of fuels, especially since the weight of fuel dominates the mass of any large / long distance aircraft. We're not talking about a factor of a few here, this is a factor of 100x missing energy density.

Part of the benefit of hybrids in cars, too, is that the idle time they spend can be turned into electric consumption at much lower energy usage than keeping a gas engine spinning. Airplanes spend very little time idling.

Ok, if somehow the on-demand flight services industry takes off (Uber for airplanes, short distance, personal travel), then maybe small battery/hybrid aircraft might be viable, but we will simply not find a battery-chemistry-based improvement on liquid fuels. The compressed energy of millions of years of dinosaurs and plants cannot be beaten, and there's a reason for it...

Re:not going to work

[MightyYar]

Not to mention that the hydrocarbon-fueled aircraft gets lighter and more efficient as it burns fuel, while batteries stay the same weight that they were at takeoff.

Re:not going to work

[fnj]

You nailed it. IDIOTS are pushing this. Void of any comprehension of engineering realities.

There is a REASON why hybrid cars give benefits. IC automotive engines are HEAVY. Adding two intermediate conversion steps (mechanical -> electrical, then electrical back to mechanical) does not add a crippling amount of weight. And the IC engines in straight-IC cars operate at abominably inefficient settings. Most of the time that 250 hp engine is putting out not over 25 hp, and it has ghastly thermal efficiency at 10% power. In a hybrid, you can arrange it so the engine is operating either not at all (batteries filling in), or at an efficient cruise power setting (charging the batteries AND running the car, whether purely mechanically or mechanical->electric->mechanical does not make a huge difference in efficiency under these conditions).

Aircraft are completely different beasts. Their IC engines are much lighter in kg/kW (lb/hp) than are automotive engines, which is a good thing because they have to be vastly more powerful. And they operate all the time at pretty much the optimum efficiency setting. A little higher on takeoff but only for a very brief time, and around 75% of full power during cruise. Never at 10%. There is no efficiency gain from going hybrid, and there is a crippling weight penalty from the batteries, and a not at all inconsiderable weight penalty from the mechanical->electric and electric->mechanical steps.

Re:not going to work

[Anonymous Coward]

There you go again.....applying common sense to an engineering problem........ :)

Re:not going to work

[glitch!]

Yes. I have been a pilot for almost three decades and I have followed the two interesting improvements: one is diesel aircraft engines, the other is called operating "lean of peak". The diesel engines seemed promising, but it seems that they just fizzled out. Maybe they were just too expensive for the cost savings. The "lean of peak" idea made a lot of sense, but only for aircraft with fuel injection and when the injectors were carefully matched. It's a great idea, but can it help us car users when we change our throttle many times per minute? Maybe not.

Re:not going to work

[SirSlud]

I'm sure this is all new information to them.

Re:not going to work

[Lisandro]

"Lean of peak" is common on modern piston-engine aircrafts; you trade off a little power for a significant fuel economy. John Deakin wrote a fantastic piece on the subject.

Re:not going to work

[Lisandro]

On the other hand, the efficiency of regular aircraft engines vary wildly with altitude. Electric engines don't have that issue.

Re:not going to work

[Harlequin80]

No question that liquid fuel is more energy dense then batteries. But what is the conversion ratio of that stored energy to thrust. From here, http://www.ipcc.ch/ipccreports..., I get average efficiency of 30-37%.

If it is 37% though you are down to an effective energy store of 14 MJ/KG. Electric engines can be in the 98%+ efficiency level. So while it is still a huge distance to span it's not as big as the pure fuel density implies.

Also when you compare energy density per litre vs per kg batteries do better. Kero is 37 MJ/L and Lipoly is up to 2.25MJ/L. Given that you are now down to a difference of 13.69 vs 2.2ish. Potentially you are in the vicinity of batteries allowing different air frame designs that the higher weight can be, to some degree, compensated.

There is a long way to go before we are replacing jets but I don't think it is quite as insurmountable as you put it.

Re:not going to work

[Anonymous Coward]

The diesel engines seemed promising, but it seems that they just fizzled out. Maybe they were just too expensive for the cost savings.

The Aircraft diesel engine has always been a bit hard. I know, I've been involved in two separate developments of it. The development of it has suffered from 1) the fact that current Leaded gasoline aircraft engines very nicely fulfill a niche market (I.E. the aviation aircraft market) and 2) Diesels have only recently become powerful enough and light enough to power a Light General aviation aircraft. Basically, the light general aviation aircraft field is the only market for them. Once you go above a certain HP rating, you might as well use a turboprop engine. The light general aviation aircraft market is relatively small, so you don't really get the economies of scale. And the power of light aircraft diesel engines have only relatively recently (I.E. in the last 10 years) become powerful enough for General Aviation use.

So combine a small market with the fact that they have only recently become technically feasible that means that they just fizzled out.

Gordon

Re:not going to work

[Michael Woodhams]

Picking the only named engineer in the article (actually the in the Sugarvolt video), Marty Bradley has a PhD in aerospace engineering and a high profile career at one of the worlds best aerospace companies, with a whole bunch of other super smart engineers looking over his shoulder to ensure he doesn't waste company money. He has studied the idea in detail, and thinks it might work. You've read a pop-engineering article, and on that basis you call Dr Bradley an idiot.

It looks like a hard problem. I don't see how it could work. But my degrees in maths and physics are nothing to his education and experience in this field. If you happen to be an experienced aerospace engineer who has looked in detail at the proposals, you've earned the right to call him an idiot (if the proposals are, in fact, idiotic.) Otherwise acknowledge your own ignorance, and be a whole lot more humble.
 

Re:not going to work

[jcr]

Electric engines don't have that issue.

Actually, they do. Not the motors so much as the fans, but there's still a tradeoff.

-jcr

Re:not going to work

[Lisandro]

Yeah, but to a much lesser degree. Aircraft engines are usually optimized for a given altitude range - normal piston engines decrease power with altitude. Turbochargers improved on this, but they suffer the same issue. Turbofan engines used on airliners have peak efficiency at cruise altitude but suck when flying low.

In general, air density is the main factor impacting aircraft performance, because it impacts on three separate thing: how the engine runs, how much lift can the wings generate and how much air can a propeller push or a jet can suck. Of those, the first one is by far the most important, as it in it can compensate (to a degree) for the rest.

Re:not going to work

[Anonymous Coward]

"Electric engines can be in the 98%+ efficiency"

But here you are not comparing to thrust...

Re:not going to work

[shawn2772]

You nailed it. IDIOTS are pushing this. Void of any comprehension of engineering realities.

Yeah, Siemens and Airbus aerospace engineering teams tend to contain lots of idiots.

Well, either that or slashdot tends to contain lots of arrogant blowhards.

Which is the case here is left as an exercise for the reader.

Re:not going to work

[Harlequin80]

I thought the whole point of the efficiency measure was the conversion of stored energy to thrust. If thats not what it's measure what is it?

Re:not going to work

[Gussington]

You nailed it. IDIOTS are pushing this. Void of any comprehension of engineering realities.

Either that or the best aeronautical Engineers in the world know maybe know more about this than you.

Re:not going to work

[Anonymous Coward]

You nailed it. IDIOTS are pushing this. Void of any comprehension of engineering realities.

There is a REASON why hybrid cars give benefits. IC automotive engines are HEAVY. Adding two intermediate conversion steps (mechanical -> electrical, then electrical back to mechanical) does not add a crippling amount of weight. And the IC engines in straight-IC cars operate at abominably inefficient settings. Most of the time that 250 hp engine is putting out not over 25 hp, and it has ghastly thermal efficiency at 10% power. In a hybrid, you can arrange it so the engine is operating either not at all (batteries filling in), or at an efficient cruise power setting (charging the batteries AND running the car, whether purely mechanically or mechanical->electric->mechanical does not make a huge difference in efficiency under these conditions).

Aircraft are completely different beasts. Their IC engines are much lighter in kg/kW (lb/hp) than are automotive engines, which is a good thing because they have to be vastly more powerful. And they operate all the time at pretty much the optimum efficiency setting. A little higher on takeoff but only for a very brief time, and around 75% of full power during cruise. Never at 10%. There is no efficiency gain from going hybrid, and there is a crippling weight penalty from the batteries, and a not at all inconsiderable weight penalty from the mechanical->electric and electric->mechanical steps.

You're RIGHT, random Slashdot reader! I'm sure you know better than they do! Thanks for setting us all straight. Good thing YOU were here. Whew.

Re:not going to work

[evilviper]

the hydrocarbon-fueled aircraft gets lighter and more efficient as it burns fuel, while batteries stay the same weight

But the batteries just need wires and switches to move the power around, where explosive liquid fuel needs fuel tanks, fire suppression systems, redundant electric boost pump and mechanical pumps, valves, cross-feed, filters, drainage, filling connectors, thermometers and heating, bleed-air pressurizing system, and let's not forget the ENGINE, where the fuel is burned, as well as a big starter battery/APU, exhaust system, and more. Note that (like batteries) NONE of that disappears, or gets any lighter, as the fuel is burned, and almost all of it, both maintenance complexity and weight, could be eliminated in a fully-electric system.

Re: not going to work

[WarJolt]

A random Slashdot user with the crudest understanding of a hybrid I've ever read. Electric motors have low end torque, so you don't have to Rev up to get moving and they recover power instead of wasting braking energy as heat.

Re:not going to work

[evilviper]

they operate all the time at pretty much the optimum efficiency setting.

Actually: "Compared to advanced piston engine airliners of the 1950s, current jet airliners are only marginally more efficient per passenger-mile."

weight penalty from the mechanical->electric and electric->mechanical steps.

Fuel cells are more thermodynamically efficient than even the best turbines at converting hydrocarbons into work, and they conveniently happen to output electricity, directly.

Fuel cells are being developed that can run directly on common liquid hydrocarbon fuels, not just hydrogen.

At lower-speeds, props are much more efficient than turbofans, and props can of course be easily driven by electric motors.

The lower speeds of prop-driven planes gives additional added efficiency in lower aerodynamic drag, as well.

Instead of retrofitting such a system onto current jets, combine electric propulsion with "blended wing" aircraft, and the future of passenger air travel could be vastly quieter and more fuel efficient, albeit slower.

And electrically-driven aircraft is incredibly simplified, to the point that airlines would want them for their lower maintenance costs and less downtime, even if the efficiency wasn't substantially better... See my quote above, as airlines previously embraced inefficient turbines for just this reason.

Re:not going to work

[hcs_$reboot]

Yes but maybe the electric engines powered planes would transport only a handful of passengers on shorter distances.

Re:not going to work

[AmiMoJo]

It's actually more like the BMW i3 with range extender. A small, efficient petrol engine generates electricity to recharge the batteries. It's light weight because it's not mechanically coupled to the wheels and no complex gearing is required like in a Prius.

They appear to be planning to have a combustion engine to generate electricity, and a small battery pack to allow that engine to run at a constant, maximum efficient speed. It's a great idea, and entirely feasible.

Re:not going to work

[MightyYar]

Yes, that is a huge bonus for electric - it is mechanically simpler.

Even so, the fuel weight of a plane is enormous compared to the mechanicals. An additional trick that you can play with an expendable-fuel plane is to weaken the aircraft such that its landing weight is lower than its takeoff weight. An all-electric plane will need a beefed-up structure to land at full-weight. This is why some planes need to dump fuel before an emergency or earlier than expected landing.

Re:not going to work

[MightyYar]

Aren't these electric engines meant to replace turboprops, though? Those do quite well for the lower-altitude regional flights we are talking about.

Re:not going to work

[brambus]

A turboprop is basically a very high bypass turbofan with a lower exhaust velocity. The means its propulsive efficiency is best at lower air speeds. Maximizing propulsive efficiency, in the simplest terms, is simply about using as much of the energy provided by an engine to displace the aircraft forward and as little to displace the surrounding air backward - you want to get the aircraft from point A to point B, not the static air in reverse. Hence, propulsive efficiency is best when effective exhaust velocity is as close to true airspeed as possible. Propeller effective exhaust velocity is lower than for turbofans, so they work better at lower speeds than turbofans do. It actually has relatively little to do with altitude and fairly little to do with how the mechanical power to drive a prop/fan is generated.

Re:not going to work

[Anonymous Coward]

but think of the planes we could power with blowhard engines

Re:not going to work

[Anonymous Coward]

Ya but maybe they'll power them with disposable batteries - the plane could leave a contrail of AA batteries falling out the back.

Re:not going to work

[MightyYar]

I like it! There might even be a cottage industry of battery salvagers/home repairers.

Re:not going to work

[fnj]

Half-wit morons have effectively censored my post. They can eat shit.

Here it is reproduced so people can see it.

You nailed it. IDIOTS are pushing this. Void of any comprehension of engineering realities.

There is a REASON why hybrid cars give benefits. IC automotive engines are HEAVY. Adding two intermediate conversion steps (mechanical -> electrical, then electrical back to mechanical) does not add a crippling amount of weight. And the IC engines in straight-IC cars operate at abominably inefficient settings. Most of the time that 250 hp engine is putting out not over 25 hp, and it has ghastly thermal efficiency at 10% power. In a hybrid, you can arrange it so the engine is operating either not at all (batteries filling in), or at an efficient cruise power setting (charging the batteries AND running the car, whether purely mechanically or mechanical->electric->mechanical does not make a huge difference in efficiency under these conditions).

Aircraft are completely different beasts. Their IC engines are much lighter in kg/kW (lb/hp) than are automotive engines, which is a good thing because they have to be vastly more powerful. And they operate all the time at pretty much the optimum efficiency setting. A little higher on takeoff but only for a very brief time, and around 75% of full power during cruise. Never at 10%. There is no efficiency gain from going hybrid, and there is a crippling weight penalty from the batteries, and a not at all inconsiderable weight penalty from the mechanical->electric and electric->mechanical steps.

Re:not going to work

[fnj]

I'm sure this is all new information to them.

Quite evidently.

Re: not going to work

[fnj]

understanding of a hybrid I've ever read

Orders of magnitude more understanding than you. Look, I don't mind people being ignorant, but arrogant denial of one's own ignorance ticks me off.

Alternate applications...

[fuzzyfuzzyfungus]

These seem like the perfect tool for producing an impressively dense(and very conducive to lights-out management, if only because the alternative would be absolutely brutal) free-air datacenter cooling mechanism.

You server OEM types use enough underfill to keep the forced air cooling from lifting the ICs off the logic boards, right?

Sure, why not?

[50000BTU_barbecue]

The first time, we built full-size planes, then we built models that look like them. Now, we are building model planes with these:

http://www.hobbyking.com/hobby...

...now we just need to build bigger ones!

Re:Sure, why not?

[Anonymous Coward]

Because an EDF big enough to power a 787 would not only be much louder than an actual jet engine (to humans at least, and dogs might actually be killed, too), but the battery required to power it for even a short jump between neighbouring cities would be so large you couldn't fit nay passengers in the plane.

Those things are freakishly noisy on model planes compared to model electric props or even small-scale jet engines.

Also that thing you linked it an absolute brick. It must be the crash-happy durable option of the EDF family.

Re:Sure, why not?

[50000BTU_barbecue]

You think that's noisy? I guess you missed out on the first ones powered by two stroke engines? Or the pulsejets?

Re:Sure, why not?

[Anonymous Coward]

Had a couple of two-stroke boat engines (another application where power-to-weight is massively important, hence 4-strokes not being mainstream until much later), but at least their exhaust is underwater so it's not THAT bad. Still pretty bad though.

But if we're going pulse engines, go big or go home sonny jim

https://www.youtube.com/watch?v=vwrLR2kv5KA

Pilots say NO

[Anonymous Coward]

No no no, I am a pilot and this is a threat to my way of life like drones so my lobbying group opposes it.

How short range?

[Anonymous Coward]

The Tesla Model S has a range over 200 miles, and it has a pretty big battery. Air travel is several times less efficient than road travel. Airplanes are reasonably efficient by squeezing people like sardines, and being flimsy enough for a coke can explosive to destroy a 200 person aircraft. So, let Airbus have that market. Synthetic fossil fuels, and more high speed rail for me.

The cylinder is heavy, not the gas, but where from

[raymorris]

Why use liquid hydrogen? Does it have some magical property? Given the weight of the cylinder, it's not a particularly efficient way to store energy, though it may be better than batteries.

At larger sizes, hybrid, multi-stage systems can work. The typical locomotive is a great example. The diesel engine turns a generator which powers the electric motors that propel the train.

Not a single data point situation

[dbIII]

No but electric motors have improved a great deal.

Re:Not a single data point situation

[thinkwaitfast]

The electric motor used in the solar car at my university was measured at 97% in the early 1990's.

Re:Use the US Navy seawater to jet fuel tech inste

[rossdee]

Thars fine for the Navy, it lands its planes on carriers to refuel them.
I don't think airline passengers are going to be too happy to do that.

Entire system

[dbIII]

Comparing fuel to batteries totally ignores that they are not feeding the same types of engines. You have to compare entire systems to each other, thus jet engine plus fuel and electric motor plus batteries.

It's like the mistake with the all ceramic engine project - fantastic performance on a test rig but as soon as you wanted the thing to move the extra weight of the cooling system exceeded the benefits.

In other news..

[JustNiz]

Siemens and Airbus just formed a partnership to develop a 4000 mile long power cord.

Re:In other news..

[Eloking]

Siemens and Airbus just formed a partnership to develop a 4000 mile long power cord.

Ha rats.....I was hoping they''ll be shooting power laser at it...

Re:In other news..

[Anonymous Coward]

Or as scientists call it: a "space elevator".

Re:In other news..

[tlhIngan]

Why bother? Siemens admitted their electric motors for aircraft are unsafe and unsuitable for flights over water.

So you can use it over land only, and you don't need a big extension cord when you can land and charge right up again...

Re:In other news..

[Anonymous Coward]

Never forget Airbus is the 'aviation' company that directly and physically tied their onboard entertainment system into their critical avionics systems.

Yes indeed. It was, of course, done so that hackers could more easily hack the avionics. Sure why not, right. And it was hacked more than once, whether you heard about it or not.

Critical systems should always, repeat, always be 'air gapped.' But this so-called Aircraft company didn't know that. Nope, not with this "brilliant" company of government funded idiots

So when I hear or read about Airbus and anything electric or electronic I find what they do beyond dubious.

Re:In other news..

[ebvwfbw]

It's on a retractable reel. Just stay out of the way when it rewinds.

Re:In other news..

[JustNiz]

What do you mean? Thats how cattle class get their return flight.

Re:The cylinder is heavy, not the gas, but where f

[ChrisMaple]

Due to traction limitations of steel-on-steel, locomotives are heavy by design and the diesel-electric weight is not a disadvantage. The same does not apply to airplanes.

As a pilot, i wish them the very best

[Lisandro]

I'd love a reliable, commercial electric airplane to become available. Sadly, we're very far away from that - electric engines can be made to be very efficient but you still need batteries to power them, which weight a lot. Either that, or a gas based poweplant, which beats the point entirely.

I wish someone started looking into nuclear powered jet engines again. Unlike electric this technology really did show some future.

Re: As a pilot, i wish them the very best

[Anonymous Coward]

How do you make nuclear engines crash proof? Or disassembly to dirty bomb after hijacking proof?
Is it possible to design an efficient reactor that only carries enough fuel for one flight, and/or can deplete it completely into safe products on command?

Re: As a pilot, i wish them the very best

[Lisandro]

From what i've read, the main issue they had was not safety but (surprise surprise) weight. It took a lot of shielding to protect the crew from the reactor's radiation.

Re:As a pilot, i wish them the very best

[EmagGeek]

Since when do you need batteries to power an electric motor?

Re:As a pilot, i wish them the very best

[Lisandro]

Well, i imagine you could power them using a regular gas engine. This would mean that you could (theoretically) run the petrol engine at its optimum power settings to decrease fuel consumption, but you're still left with a myriad of problems - increased mechanical complexity, loss of power with altitude, etc. I don't know if this is the intent of the project.

A "true" electric airplane would use an electric motor and batteries as a power plant. This setup would be orders of magnitude more efficient and reliable than regular petrol engines, but we're unable to figure out how to store power without adding too much weight.

Who said it was battery powered?

[WoTG]

This sounds a lot like the diesel-electric "hybrids" that power trains. Diesel generators generate electricity to power electric propellers. It makes sense to me... of course I know nothing about this stuff. If my assumption is correct, a nice benefit would be that aircraft could use cheaper fuel rather than jet fuel (which I assume costs more per litre... I think it does, if only because of lower volumes).

Re:Who said it was battery powered?

[fnj]

Diesel-electric trains have no batteries and are not hybrids. A hybrid is not the same thing as an electric transmission. Sheesh.

What makes sense to you may not make sense to anyone with a modicum of engineering knowledge.

BTW, diesel fuel is most assuredly NOT cheaper than jet fuel. Jet fuel is just kerosene.

Re:Who said it was battery powered?

[drinkypoo]

Diesel-electric trains have no batteries and are not hybrids. A hybrid is not the same thing as an electric transmission. Sheesh.

No, they are hybrids. Their drive system is part ICE, part electric. What they aren't is parallel hybrids, and what they don't have is power storage beyond what it takes to start the diesels. The former will probably never come (why bother) and the latter will only come when all trains adopt active bogeys rather than using dedicated engines in the first place. Such a train might have battery cars specifically for power storage interlaced throughout the load, as well as generator cars. You could cut arbitrary pieces of the train away without even stopping, which would be quite handy.

Re:Who said it was battery powered?

[Anonymous Coward]

Diesel-electric trains have no batteries and are not hybrids. A hybrid is not the same thing as an electric transmission. Sheesh.

No, they are hybrids. Their drive system is part ICE, part electric. What they aren't is parallel hybrids, and what they don't have is power storage beyond what it takes to start the diesels. The former will probably never come (why bother) and the latter will only come when all trains adopt active bogeys rather than using dedicated engines in the first place. Such a train might have battery cars specifically for power storage interlaced throughout the load, as well as generator cars. You could cut arbitrary pieces of the train away without even stopping, which would be quite handy.

Actually, full on "parallel hybrid" locomotives have been with us for some time:

https://en.wikipedia.org/wiki/Railpower_GG20B

In general, these have been most successful in switching (or shunting, for those outside North America) applications, where such locomotives tend to stand around idling much of the time.

Re:Who said it was battery powered?

[drinkypoo]

Actually, full on "parallel hybrid" locomotives have been with us for some time:
[...]
In general, these have been most successful in switching

Yes, they are worse than worthless for long-haul because they don't have enough battery capacity to be useful, and because you cannot recapture significant power from regen because only the engines can do it. That's why you need active bogeys.

Re:Use the US Navy seawater to jet fuel tech inste

[Anonymous Coward]

And you failed to understand what a Hybrid Electric System is. It's a Combination of Internal Combustion engine with an Electric Drive Motor - The Fucking Chevy Volt uses such a setup. Locomotives are also Hybrids - Diesel/Electric and many of the latest cruise ships are using the same tech so why in hell can't you get it through your tiny little mind that Hybrid does not mean Fuel Cells and Batteries.

Seriously, take a god damn Turbine and hook it to a Generator (we're talking fairly large generator) that provides all of the power an aircraft needs. This is everything from the A/C systems when on the Ground to Propulsion. What fuel do they use? JP4 or existing Jet Fuels. The Colaboration between Siemens and Airbus is a deliberate Misdirection as this is pretty god damn common in the Aviation industry. Hell no company has all of the skills to design a modern Jet liner today. They're too complex so companies colaborate on designs all the time. All that this announcement means is that someone feels that an Electric Propulsion System may be viable for smaller aircraft such as your common commuter (turboprop) puddle jumper. Hell you can even do a turbo prop on a 707 instead of jets if speed isn't of the essence.

Re:Use the US Navy seawater to jet fuel tech inste

[Anonymous Coward]

"This technology makes aircraft carbon neutral..." I don't think you know what carbon neutral means. Refining carbon out of the ocean and burning it on a plane to make CO2 does not get rid of the CO2 you generated

Re:Use the US Navy seawater to jet fuel tech inste

[FrankSchwab]

I'd pay for that experience...

Arresting wire landing in a 737...
Catapult takeoff in a 737...

It'd be far more entertaining than the normal takeoff/landing.

Re:Use the US Navy seawater to jet fuel tech inste

[blindseer]

And you failed to understand what a Hybrid Electric System is. It's a Combination of Internal Combustion engine with an Electric Drive Motor

A true hybrid allows for power from more than one energy source. An internal combustion engine driving a generator, and the generator driving a motor, is not a hybrid. That would make an electric drive train.

The Fucking Chevy Volt uses such a setup.

No the fucking Chevy Volt has a battery pack and a mechanical transmission. While it might not be able to go in reverse or slow speeds without the electric drive train it is capable of going highway speeds without it. These proposed aircraft do not claim to have a mechanical link from the on board internal combustion engine to the ducted fans. If they did then I might be impressed since that would be an engineering feat.

Locomotives are also Hybrids

Very few trains are true hybrids. Some are capable of using a "third rail" for power, those are hybrids. Even using capacitors or batteries on board would not make them hybrids since all the energy to drive the train comes from the fuel oil.

many of the latest cruise ships are using the same tech

Yes they do, but unless those ships use under water extension cables to power the ship at sea they are still just diesel powered with electric drives.

so why in hell can't you get it through your tiny little mind that Hybrid does not mean Fuel Cells and Batteries.

Because I actually looked up what "hybrid" means.

Re:Use the US Navy seawater to jet fuel tech inste

[blindseer]

Carbon neutral means that they don't add carbon to the atmosphere. Since the carbon they emit comes from the air and is returned to the air after being burned it is carbon neutral. If that is not carbon neutral then bio-fuels are not carbon neutral.

Perhaps you don't understand how the carbon gets in the water, it dissolves in the water from contact with the air.

Endgame is turboelectric distributed propulsion

[Anonymous Coward]

Distributed propulsion for aircraft is theoretically a superior propulsion system, especially if it can suck in boundary layer air or otherwise turbulent air. The problem is, the preferred embodiment is a line of tiny fans all down the wing, which if implemented traditionally is either inefficient (tiny turbofans turbines generally do poorly for efficiency) or heavy (having a long transmission line from a large turbine engine to all those little fans). Making all the fans electric mostly solves the weight issue with the transmissions, but then you have cable weight and fan motor weight issues, then efficiency issues of the generator attached to your large turbine.

But distributed turboelectric will happen eventually. NASA is currently working on LEAPtech/SPECTER that will clearly demonstrate distributed electric propulsion, though the generator will not be a gas turbine on that prototype.

Not a single metric situation

[dbIII]

How much did it weigh?

Translation

[Anonymous Coward]

Raise the price of our ticket to fund it....

Then keep that high price once these super efficient engines are available.

Enjoy raping us from both ends....

Profit?

Re: Endgame is turboelectric distributed propulsio

[Anonymous Coward]

The nice thing here is that when/if there's a breakthrough or breakeven in electric generation or storage, the turbine can easily be replaced by the new technology without altering the rest of the aircraft much.

Re: The cylinder is heavy, not the gas, but where

[Anonymous Coward]

Put the airplanes on rails, problem solved.

Pushing an engine?

[Anonymous Coward]

In Soviet Russia, aviation engine pushes you.

Re:Use the US Navy seawater to jet fuel tech inste

[Anonymous Coward]

The P8 is a modified 737, and it does carrier takeoffs and landings.

Re:The cylinder is heavy, not the gas, but where f

[Anonymous Coward]

> The typical locomotive is a great example. The diesel engine turns a generator which powers the electric motors that propel the train.

Diesel locomotives are only typical in the USA, where nobody dares to build overhead wires, because the next management board would sell it off for the price of copper contained in the cables, because premiums are paid for outstanding quarterly profit...

In other parts of the world, like Europe, Japan, ex-USSR, India, locomotives run on electricity supplied via the catenary. The running cost is half of diesel (that assuming absolutely honest personnel, who do not steal a barrels' worth of diesel here and there to fuel a tractor or truck for private profit. Let me say, that assumption is a brave assumption!)

Honestly said, there is no need for airlines within Europe at all. The money Airbus burns should better be spent on the high-speed train (HST) network. Legacy catenary systems should be re-tuned to the 25kV/50Hz UIC world standard. The patchwork of railway safety systems should be unified on the ETCS platform. That way electric pulled trains could travel quickly across the continent, without stopping and replacing locomotives. Door to door time is better with HST in Europe, compared to air travel, because of the airport security nightmare and the large distance of noisy landing strips from cities.

Ah, how cool :-)

[jandersen]

I know - this is about turboprop and that sort of things, but I can't help imagining a jet-engine with an almighty bolt of lightning coming out of the rear end.

It's about Bypass Ratio Improvement

[monkeyxpress]

Wow, all the comments on this article have completely missed the point of this. IDIOTS are not pushing this - the concept offers very real efficiency improvements.

The primary constraint in modern jet aircraft efficiency is the propulsive efficiency - turning the mechanical shaft power into forward thrust. This is fundamentally limited by the size of your fan for a given airspeed. If you make the fan swept area a little bit bigger, you can get major improvements in the overall efficiency of the aircraft. This is why newer airplanes always have bigger and bigger engines (787 vs 767, 737NG, A320NEO).

However there are limits to how big you can go. One problem is physically fitting a large diameter engine into existing airframe designs. On the 737NG they had to raise the nose landing gear to accommodate the new engines. There are practical limits to how much you can keep doing this sort of thing without having to create a completely new airframe (the 737 is a 1960s airframe). The other problem with larger fan blades is that the tip speed increases with diameter, which means the fan RPM must reduce to prevent supersonic airflow. This then creates a compromise on the turbine section of the engine. The newest generation of engines are now using gearboxes so that the turbine can run at a higher speed than the fan, which lets them go to larger bypass ratios. The cost, however, is in weight and complexity.

The big benefit that hybrid electric could offer is being able to effectively increase the fan area by distributing fans along the wing. This could create massive efficiency gains, and bring jet aircraft closer to the efficiency of turboprops. Imagine a 737 with two large electric fans next to each other. This could double the swept area on the same fuselage. Further, the concpept could make boundary layer ingestion designs practical, and these also offer big advantages in terms of efficiency for future airframe designs.

This is not about making battery powered aircraft. It is about re-arrangement of the aircraft systems to provide better propulsive efficiency.

Re:It's about Bypass Ratio Improvement

[brambus]

to prevent supersonic airflow

Actually, supersonic airflow at the fan tip is pretty common. Has been for at least 30 years.
RB211-535E4:

• Fan diameter: 1.88m
• Fan RPM at 100% N1: 4500
• Tip speed: 443 m/s

Re:The cylinder is heavy, not the gas, but where f

[Anonymous Coward]

However the power to weigh ratio of an electric motor and a turbine engine is ball park comparable.

Hydrogen just works

[Kant_resistor]

Hydrogen has proven advantages in air transportation. Let's start by citing the quiet, luxurious staterooms on the Hindenburg.

Re:Hydrogen just works

[ebvwfbw]

I'm hoping we can get by that. Especially for balloons because we're running out of HE. Once it's gone, it's gone and we're running out.
H is safe for fuels. After all, people would be bitching up a storm if we introduced gasoline today. It can blow up, it can burn us, etc. Ambulance chaser lawyers would be all over that.

But jets are faster

[Anonymous Coward]

Parent said jet engines are only marginally more fuel efficient per pssenger mile than reciprocating piston engine aircraft. Maybe, but jets sure get you A HELL OF A LOT FASTER to your destination!

Re:But jets are faster

[evilviper]

jets sure get you A HELL OF A LOT FASTER to your destination!

Speeds are only double, at best. That matters a lot on longer, intercontinental routes, but not too much on short routes. Going through airport check-in and security screening often take longer than the actual flight. There are several other potential ways an electric-prop craft could trim some time off your travel...

Turbine about a third the weight

[raymorris]

Two example turbines:

The Lycoming T53, first produced in 1955, produces 1400 horsepower and weighs 688 pounds. So just over 2 horsepower per pound.

The turbines in on the Boeing 777 produce over 8 horsepower per pound.

Electric motors:
The Prius motor produces 0.8 HP per pound.
The Tesla motors are better, but still not as good as a 1950s era turbine, if memory serves.

Re:Turbine about a third the weight

[Grishnakh]

A lot of the weight of motors comes from the copper windings.

It makes me wonder what kind of motor you could make if you used superconducting wire for the windings. Of course, the liquid nitrogen cooling could be a bit of a problem, but on a large aircraft that's probably doable.

Re:Use the US Navy seawater to jet fuel tech inste

[jafiwam]

The P8 is a modified 737, and it does carrier takeoffs and landings.

Hahahah ... no.

Re:Use the US Navy seawater to jet fuel tech inste

[John Allsup]

In taking carbon from the ocean and dumping it into the air as CO2, without a corresponding step to move it back to the ocean when used, it is not carbon neutral.

A modest proposal

[cellocgw]

How about instead of arguing about how to reduce carbon emission per flight by X% (X generally being dang small), we stop insisting that every vacation has to be a long air-flight away? And stop thinking that every business meeting has to be face-to-face when high-quality realtime video chat is available?
Without even building up ground transportation (busses, trains), we could cut air-related emissions in half by just changing our insistence on long-distance travel.

And best of all, how about "It Absolutely, Positively, Does NOT Need to Get There Overnight," and kill off 90% of airborne freight in favor of ground transportation. Trucks are wildly more efficient (fuel per kg-km) than air, and trains are incredibly more efficient than trucks.
   

Re:A modest proposal

[Moof123]

You sir have apparently never been in a typical meeting with overseas colleagues/customers. My typical experience is that it can takes months of weekly calls to make half the progress of just being in the same room with someone and a whiteboard. It is stupid, but I have dealt with it multiple times.

What I think you are arguing for is a way to discourage un-needed travel. Usually that means putting a higher price on it, which logically leads to a carbon tax. While that works for me, it is DOA with the public at large.

lithium ion batteries can't melt steel beams

[Thud457]

Yes, they can build an airplane with electric motors, but will it fly?


Frankly, I don't see how this advancement would alter the balance for "would you rather fight 100 duck-sized horses or 1 horse-sized duck" or "which would win an a space battle between a imperial star destroyer and the USS Enterprise"

Re:The cylinder is heavy, not the gas, but where f

[Anne Thwacks]

Door to door time is better with HST in Europe,

And we don't have to face endless queues and stupid pat-downs for the security theatre.

I am not sure about your "retuning" - here in London, trains are made to switch between 33kV AC overhead and 700V DC third rail invisibly to passengers, while the train is at a station. (Where trains operate underground, they mostly use 700V DC or similar). I am sure lesser compatibility isses are no problem.

Having said that, I believe Airbus is quite profitable, and I suspect Glasgow to Athens by train would take a wee while longer than a flight, and the planning permission for HST compatible track from Glasgow to London would take at least 100 years, with time off for good behaviour. Meanwhile we probably have enough working steam locos to handle the expected volume of traffic on that route (sod the carbon emissions).

think more differenter

[Thud457]

Surely we can build a powertrain with solar cells that power an electric motor that stores kinetic energy in a rubber band that drives the propellers.
Plug in the motor into the mains when on the ground to preload the rubber band before takeoff.

Re: The cylinder is heavy, not the gas, but where

[Anonymous Coward]

You speak in jest, but Elon Musk calls it Hyperloop

Joint development team

[The-Ixian]

That's gotta be one hell of a joint

Sounds fantastic!

[Anonymous Coward]

Dead battery at 8 km altitude? Not so much.

Hope that kite has a hell of a glide path profile.

Re:Sounds fantastic!

[ebvwfbw]

There's a thing called a power meter. It's like a fuel gauge. So same problem as a normal fuel. Make sure you have enough to get there. Watch it on the way.

Charging?

[Anonymous Coward]

Given the current turn around for planes in an airport terminal, how would they deal with he time it takes to charge these planes?

Airports wont adopt until the battery tech and charging rates catch up

Energy savings

[Moof123]

In RTFA I failed to find a decent breakdown of where the huge energy savings were exactly coming from.

The new wing style should be usable without the electric drive aspect, so how much is the hybrid aspect actually contributing, or is that just a way to score Buzzword Bingo points?

Timescales are everything

[GPS Pilot]

The critical question is, over what timescale does the ocean re-absorb the carbon that the Navy just moved into the atmosphere?

If it takes like a week, I think it's safe to call this process carbon-neutral.

If it takes 10 years, not so much.

High Speed Rail

[Anonymous Coward]

Thread over!

Can it go faster than the Speed of Sound?

[Anonymous Coward]

I thought propeller airplanes stopped working at higher speeds because at the tip of the propeller, it reached the speed of sound and beyond that, the propeller didn't work. Jets have expanding gas like rocket engines, thus the thrust isn't from manipulating the working fluid (air), it's from expanding gases.

Somebody that knows should weight in here now.

How to accommodate that much H2 fuel

[GPS Pilot]

First of all, we need to correct a math error. A cylinder with diameter 5.87 m and length 73.9 m has a volume of 1,999,910 liters, not 1,362,000.

Now, how big does the aircraft have to be if you want to meet the following criteria?
1. Can carry 1,197,875 L of H2 fuel (for simplicity, all in the fuselage)
2. Has 1,999,910 L of volume in the fuselage available for other-than-fuel (same as the 777)
3. Keep the same proportions as the 777 (diameter/length ratio is 0.0794)

Answer: you only have to make the aircraft 16.9% longer. Then you will have
Diameter = 6.86 m
Length = 86.4 m
Fuselage volume = 3,197,785 liters (1,197,875 for H2 fuel + 1,999,910 for other-than-fuel)

A 16.9% longer aircraft is not a dealbreaker.

Re:How to accommodate that much H2 fuel

[Harlequin80]

Please tell me where my maths is wrong. Volume of a cylinder is area of the base times the height. Area of the base is piD, 3.14 x 5.87m = 18.0864m2 times the height, 73.9 is 1336m3. There are 1000l per cubic metre so 1,336,000 litres.

Where did I go wrong?

Even leaving that out. Increasing the length of the aircraft by 16% is a massive deal breaker for no additional carrying capacity! The expense would be astronomical and the entire thing would have to be designed from scratch. It would have crappier flight characteristics, higher drag, require significantly more structural support due to the additional length and weight.

Re:How to accommodate that much H2 fuel

[GPS Pilot]

Circumference of the base is pi*D.

Area of the base is pi*r^2 = 27.06 m^2.

I agree with you that you'd have to redesign the entire aircraft to convert it to H2 fuel, and that the dry weight would be heavier.

But given that jet fuel weighs 0.81 kg/liter, while liquid H2 weighs 0.0708 kg/liter, the takeoff weight (with a full load of fuel) of the larger aircraft is potentially less than that of the smaller, conventionally-fueled aircraft. I haven't done that math.

Re:How to accommodate that much H2 fuel

[Harlequin80]

Oh shit Maths Fail. Now I want to find a hole to crawl into. Thanks for correcting.

Take off fuel weight would be lower. Considerably so. Hydrogen is up over the 140Mj/kg where as Kero is aroun 37/kg. So for the same amount of energy you need a lot less mass. The only question around mass would be how heavy a pressure vessel able to hold that much hydrogen would be.

Re:How to accommodate that much H2 fuel

[GPS Pilot]

In theory, if the vessel is well insulated, it doesn't need to be a pressure vessel (the liquid H2 will stay liquid). Maybe just have a relief valve to vent gaseous H2 in case the insulation gets degraded.

Re:The cylinder is heavy, not the gas, but where f

[evilviper]

Due to traction limitations of steel-on-steel, locomotives are heavy by design

Locomotives are heavy, because they need to haul the equivalent of a MOUNTAIN behind them. As far as I know, no intentional attempt to add extra ballast is involved in the design. There certainly aren't any big blocks of lead included in the chassis; the most common method to add weight.

Steel-on-steel traction isn't an issue... Locomotives carry loads of sand, which can be dropped onto the tracks in front of the wheels, as needed: https://en.wikipedia.org/wiki/...

If traction was a significant issue, locomotives could easily include more bogeys/trucks, or alternative designs with higher friction.

Confusing headline

[von Stalhein]

Why? Wont they go by themselves?