Is it time for Three Engine Hybrid Aircraft?

morrisond · Fri Jan 12, 2018 3:03 pm

Just thinking out loud and to give us something to debate.

Given current battery technology how efficient could a 787 sized aircraft be with 35K GTF's (or less as you have three supplies and can get away with less for engine out situations) under the wings and a 40-45K electric Motor in the tail for Takeoff and Climb? Batteries sized to support just takeoff and climb plus a few TOGA's in case of a missed approach. Batteries to be charged on ground before takeoff.

The Electric Motor in the tail could have Torpedo Tube like Doors in the sides of the tail to supply the fan fresh air that would be closed in cruise when not in use for better Aero.

You would also have Electric Motors in the bogies for taxi supplied by the batteries. No need for an APU as you would have the batteries.

I'm guessing that you could save a lot of weight going from 80K engines to 35K engines.

How much more efficient in cruise would 35K engines be?

Is there a better way to do a hybrid aircraft?

Has battery technology progressed enough (or will have by 2025) that Boeing should be considering something similar for MOM or any new program?

JustSomeDood · Fri Jan 12, 2018 3:30 pm

A big problem with such an aircraft, at least with battery tech that is even close to what is feasible today, is the massive size of the battery that is inevitably needed just for take-off, which then becomes dead weight through the rest of the trip.

Just some back of the envelope calculation here, in order to provide enough energy for a 45lbf electric motor to run at max for an hour-ish. You'd need ~1/2*200KN*268m/s=26.8MWH of battery, if we use a Tesla Model S's battery pack density as a reference (~170WH/kg), you end up needing 157 tons of battery, no amount of downsizing engines or reduced fuel requirements can compensate for that. To even think about a hybrid aircraft battery energy density will have to triple from that figure, then there's the question of charging such ludicrously sized batteries in the 1-2hr turnaround times that such planes will inevitably operate in.

lightsaber · Fri Jan 12, 2018 3:35 pm

morrisond wrote:
Given current battery technology how efficient could a 787 sized aircraft be with 35K GTF's (or less as you have three supplies and can get away with less for engine out situations) under the wings and a 40-45K electric Motor in the tail for Takeoff and Climb? Batteries sized to support just takeoff and climb plus a few TOGA's in case of a missed approach. Batteries to be charged on ground before takeoff.

The Electric Motor in the tail could have Torpedo Tube like Doors in the sides of the tail to supply the fan fresh air that would be closed in cruise when not in use for better Aero.

You would also have Electric Motors in the bogies for taxi supplied by the batteries. No need for an APU as you would have the batteries.

I'm guessing that you could save a lot of weight going from 80K engines to 35K engines

Your concept would only be viable for short missions where the 3rd hybrid motor is sufficient for diversions. Your concept would have the airframe short of thrust to cruise at the faster speeds of widebodies.

80k engines are much more fuel efficient than 35k. For long missions the wing will be sized large enough to have the two engines larger engines at the right loading. A larger thrust engine has less internal area per pound of thrust and thus better efficiency. It also has less leak area at the blade tips to cross sectional area increasing compressor and to a lesser degree turbine efficiency. This results in a free higher pressure ratio that helps efficiency.

Lightsaber

morrisond · Fri Jan 12, 2018 5:42 pm

JustSomeDood wrote:
A big problem with such an aircraft, at least with battery tech that is even close to what is feasible today, is the massive size of the battery that is inevitably needed just for take-off, which then becomes dead weight through the rest of the trip.

Just some back of the envelope calculation here, in order to provide enough energy for a 45lbf electric motor to run at max for an hour-ish. You'd need ~1/2*200KN*268m/s=26.8MWH of battery, if we use a Tesla Model S's battery pack density as a reference (~170WH/kg), you end up needing 157 tons of battery, no amount of downsizing engines or reduced fuel requirements can compensate for that. To even think about a hybrid aircraft battery energy density will have to triple from that figure, then there's the question of charging such ludicrously sized batteries in the 1-2hr turnaround times that such planes will inevitably operate in.

Thanks - 157 tons is way too much - that's why I was asking. I had no idea if it was 10 tons or 200 tons.

Slug71 · Fri Jan 12, 2018 7:47 pm

I'm sure it will happen at some point. But that some point is still a very long ways away. I would think that at least the APU would still have to run on fuel though.
I think a quad (possibly VLA) with 2 electric hybrids may come first. But even that would still be a long ways away.

OA940 · Fri Jan 12, 2018 8:17 pm

A 787-sized hybrid is pure fiction right now. Maybe not in 10 years, but now it's just not possible.

vahancrazy · Fri Jan 12, 2018 9:59 pm

It is always a matter of fuel saving and cost: if the Power provided during the needed time + the saving on fuel is greater then the cost of operating a traditional twin, it will happen.
Unfortunately, next to this variabile cost, you should add the purchase price and maintenance cost for the electric engine.
All in all, considering current situation in car industry, if I was to make a bet, I would say the first hybrid airliner will fly only after 2030. Not from the 797 or same generation airliners.

Armadillo1 · Fri Jan 12, 2018 10:30 pm

i think cessna caravan size can be more useful for hybrid and solar panels

Elementalism · Fri Jan 12, 2018 10:35 pm

Batteries are not an ideal source of power in an airplane. Where weight is a major contributor to cost. Energy density is not there. Not sure if it ever will given we have had 100 years of battery advancement and density has barely advanced over that time.

Armadillo1 · Fri Jan 12, 2018 10:42 pm

solar panel on wings, than small electric Motor for use this power time to time.
it will be a first step

next question is how we can improve jet turbine using small extra power. anything for better fuel mix or better fuel burn? may be a small lightning inside chamber can do something)
or somehow electrostatic can improve flow?

Slug71 · Fri Jan 12, 2018 11:11 pm

Elementalism wrote:
Batteries are not an ideal source of power in an airplane. Where weight is a major contributor to cost. Energy density is not there. Not sure if it ever will given we have had 100 years of battery advancement and density has barely advanced over that time.

Battery technology has vastly improved over the last decade though. There are also a number of newer technologies currently being studied. Graphene will probably be in use soon. More electric cars will soon be coming to market too. Fisker claims they have a new "revolutionary" battery that will be released/announced soon. Formula 1 and Formula E will also greatly help over the next decade. Nano technology will make a big impact over the next decade.

I still don't think we'll see a hybrid electric commercial airliner within the next 30 years at minimum though.

Waterbomber · Fri Jan 12, 2018 11:27 pm

There are many engineers and inventors thinking about such concepts already today.
Batteries as we know them today are not efficient at carrying any form of energy.

The problem with hybrid technology as we know it today is that on land vehicles it's based on reducing waste, ie charging during deceleration.
On aircraft this is not really an option since aircraft rarely need to decelerate.

Solar panels limit the operational schedule. Even if in theory they seem to be a viable option, it's not convenient for many reasons.

I predict that within 2 generations of commercial aircraft, we'll no longer be flying on jet fuel.

Lockheed Martin is for instance working on nuclear fusion technology.
lockheedmartin.com/us/products/compact-fusion.html

Then there is a lot of research being conducted in producing liquid fuels from electricity and CO2.
The concept works already in lab settings, the next step will be industrialisation and commercial application.

NameOmitted · Fri Jan 12, 2018 11:36 pm

One of the technical threads somewhere mentions that there was discussion about giving the larger 777 a third engine which would essentially be an APU on steroids. The third engine would not be needed for cruise, but would also allow for a larger aircraft than could (at the time) be powered by one engine.

The idea obviously did not get off the drawing board, but as twins get larger it still might.

JustSomeDood · Fri Jan 12, 2018 11:57 pm

Armadillo1 wrote:
solar panel on wings, than small electric Motor for use this power time to time.
it will be a first step

next question is how we can improve jet turbine using small extra power. anything for better fuel mix or better fuel burn? may be a small lightning inside chamber can do something)
or somehow electrostatic can improve flow?

F1 teams try to get leaner overall burn out of their engines by having a locally rich small pre-ignition chamber which shoots out flames to ignite the main (lean) ignition chamber. Modern turbofans have rather similar combustion chamber AFRs to high performance piston engines so this tech could work, instead of trying to make it higher bypass ratio with ever bigger fans...

RJMAZ · Sat Jan 13, 2018 12:28 am

Electric and hybrid is definitely coming soon. Obviously not for long haul as pointed out.

Electric will first come to the under 50 seat short haul regional market. The low noise will allow for smaller existing airports in very convenient locations to open up to commercial aviation. London city is a perfect example noise curfews will be relaxed or eliminated.

We'll see more air traffic completely avoid mega hubs and fly point to point to these smaller secondary airports. One of the most time consuming parts of air travel is travelling too and from the airport at both ends. Traveling to a closer regional airport nearby will significantly reduce the total travel times.

As battery tech improves we might see 1000nm range which would cover most narrowbody routes.

I predict a design that has an optional small range extender. Not to generate enough electricity to maintain flight but one to simply reduce the rate that the battery discharges. This range extender can be fitted to some of the fleet that fly longer routes.

This is the tech Airbus is testing on the BAe146. A fuel generator, battery pack and electric engine as a hybrid with a central power management system.

Armadillo1 · Sat Jan 13, 2018 9:08 am

JustSomeDood wrote:
F1 teams try to get leaner overall burn out of their engines by having a locally rich small pre-ignition chamber which shoots out flames to ignite the main (lean) ignition chamber. Modern turbofans have rather similar combustion chamber AFRs to high performance piston engines so this tech could work, instead of trying to make it higher bypass ratio with ever bigger fans...

thank you
Mercedes says their f1 engine efficiency more than 50%

Phoenix9 · Sat Jan 13, 2018 9:58 am

Has there ever been a proposal / experimental for nuclear powered aircraft? I know nuclear is a big boogeyman in public's mind and would likely not gain any traction. But, on a pure technical point, is it feasible?

Armadillo1 · Sat Jan 13, 2018 10:08 am

it can pe possible at 1960x. demo flew on common vehicles (Tu-95 and B-36)
some rumors about USA studied for global hawk

it is absolutely no reason for this.

VSMUT · Sat Jan 13, 2018 11:08 am

Phoenix9 wrote:
Has there ever been a proposal / experimental for nuclear powered aircraft? I know nuclear is a big boogeyman in public's mind and would likely not gain any traction. But, on a pure technical point, is it feasible?

Yes, it has been tested. The flying prototypes only tested the feasibility of carrying a nuclear reactor and shielding the crew. The reactors didn't actually power the aircraft, and both were cancelled before that stage was reached.

One big problem with nuclear power is that it requires highly skilled nuclear engineers to operate. The US Navy ran into this issue too. You can use a simple mechanic to fix, run and maintain a conventional engine, but nuclear power requires highly intelligent people who studied for years in a university, and who have no problem getting highly paid and attractive positions on the ground.

Elementalism · Sat Jan 13, 2018 2:15 pm

Slug71 wrote:
Elementalism wrote:
Batteries are not an ideal source of power in an airplane. Where weight is a major contributor to cost. Energy density is not there. Not sure if it ever will given we have had 100 years of battery advancement and density has barely advanced over that time.

Battery technology has vastly improved over the last decade though. There are also a number of newer technologies currently being studied. Graphene will probably be in use soon. More electric cars will soon be coming to market too. Fisker claims they have a new "revolutionary" battery that will be released/announced soon. Formula 1 and Formula E will also greatly help over the next decade. Nano technology will make a big impact over the next decade.

I still don't think we'll see a hybrid electric commercial airliner within the next 30 years at minimum though.

Has it? Yes Lithium Ion technology came out in the 70s. But 40 years later we still require a 157 ton battery to power a mythical aircraft in this thread. Are we expecting a 10x increase in battery energy density soon? Get that down to something more manageble like 16-20 tons?

There is also a safety issue. Batterys burn regardless of an oxidizer. Jet fuel, gasoline, kerosene are very safe energy source due to requiring an oxidizer to burn. When batteries burn, they burn hot and will continue to burn even if starved of oxygen. Increase the energy density of a battery 10x, and when it goes, it will go bright.

We will see more electric cars because they are not revenue generating. The hot topic right now is Teslas semi-truck. Will it be profitable due to the weight of the batteries? Semi-trucks in the US have a max weight. If more of that weight is the stored energy used for propulsion. It will cut into profits as the truck has to carry less product.

Elementalism · Sat Jan 13, 2018 2:20 pm

Phoenix9 wrote:
Has there ever been a proposal / experimental for nuclear powered aircraft? I know nuclear is a big boogeyman in public's mind and would likely not gain any traction. But, on a pure technical point, is it feasible?

Yes the B36 was retrofitted with a nuclear power plant. Though it didnt power the craft during testing. But it was deemed infeasible. It required 12 tons of lead to shield the pilots. If this was used through the entire aircraft probably weigh 120 tons

ikramerica · Sat Jan 13, 2018 2:22 pm

I read an interesting critique of the Tesla big rig proposal and how simplybcharging it would overload the local grid, require massive gage charging equipment, and require so much heat dissipation during charge that it renders the whole concept infeasible even if battery tech were to improve.

I'd imagine for an aircraft, it's even worse.

BREECH · Sat Jan 13, 2018 3:39 pm

morrisond wrote:
Just thinking out loud and to give us something to debate.
How much more efficient in cruise would 35K engines be?
Is there a better way to do a hybrid aircraft?
Has battery technology progressed enough (or will have by 2025) that Boeing should be considering something similar for MOM or any new program?

First and foremost, "MOM" will never happen. 797 will NOT be a "MOM". That settled, let's talk about "hybrid aircraft".

The biggest problem in your question is terminology. "Hybrid" means it should use some source of "wasted" energy to charge the batteries. In cars and locomotives it's the recuperative braking. How can an aircraft accumulate energy. The only way I see is put some kind of an energy harvesting device on the engines. Powerplants use water boilers to extract energy from exhaust. Scania had (maybe still does) "turbo-compound" engines that... did something to use the exhaust energy through an extra turbine. I can't quite picture a similar installation on an aircraft.

Another problem with batteries is that they have to not only store energy but also give it away on demand. And, as we recently learned, that's a much bigger problem than fast charging. Batteries simply can't supply energy fast enough even to accelerate an automobile. Where did I read something about Tesla cars not being able to accelerate fast enough because of that? And that's just a car, where power consumption is relatively low, a few hundred kW. An aircraft would need A LOT more energy and it'll need it at MUCH shorter notice. In a TOGA situation an engine goes from 10% idle thrust to full power in a matter of seconds (correct me if I'm wrong with the numbers). A battery would need to go from zero to thousands of kilowatts consumption in a blink of an eye. I don't think there is a battery that can do that. Using capacitors is not an option, either; they, on the contrary, discharge way too quickly. And don't forget that airplanes sometimes do more than one go-around in a matter of minutes. Batteries won't have enough time to recharge.

BREECH · Sat Jan 13, 2018 3:44 pm

JustSomeDood wrote:
You'd need ~1/2*200KN*268m/s=26.8MWH of battery.

Could you expain this formula, please? How did you convert kN to Wh? I always wanted to do that but had no idea how.

BREECH · Sat Jan 13, 2018 3:59 pm

VSMUT wrote:
Yes, it has been tested. The flying prototypes only tested the feasibility of carrying a nuclear reactor and shielding the crew. The reactors didn't actually power the aircraft, and both were cancelled before that stage was reached.

Just to make it extra clear, unlike its American counterpart, the Tu-95 did NOT carry an actual nuclear reactor. It was carrying what in the USSR was called a "mass-dimensional mockup".

NeBaNi · Sat Jan 13, 2018 10:12 pm

Interesting that this topic is brought up. NASA has a concept plane the size of a 737-800 called the STARC-ABL, short for Single-aisle Turboelectric AiRCraft with Aft Boundary Layer ingestion, see image:

The two underwing turbofans provide thrust, as well as power a generator that powers the electric fan at the aft fuselage, so this design is not hybrid electric (no onboard electrical energy storage in, for example, batteries), but turboelectric, where you generate electrical power from non-electrical energy sources. The benefit is that the thrust is split equally among the three propulsors, which leads to the underwing engines being smaller, saving weight there. The aft propulsor also ingests a portion of the fuselage boundary layer, which reduces the fuel burn by reducing drag. See this NASA presentation for the latest version of the STARC-ABL:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170005612.pdf

I agree with the comments made above about battery energy density, it's going to have to improve by a LOT to have a 787-sized hybrid electric aircraft. However, electric propulsion is enabled by distributed propulsion and boundary layer ingestion, and even at the battery energy densities of today. Hence, you have companies like Zunum trying to build a 12 pax regional commuter jet (backed by Boeing and jetBlue), and Airbus with its e-Fan X demonstrator, pictures below:
Zunum:

Airbus e-Fan X (based on the BAe 146):

So, while battery energy density needs to improve, electric propulsion does hold promises and I believe the future is bright!

RJMAZ · Sun Jan 14, 2018 4:20 am

BREECH wrote:
And that's just a car, where power consumption is relatively low, a few hundred kW. An aircraft would need A LOT more energy and it'll need it at MUCH shorter notice. In a TOGA situation an engine goes from 10% idle thrust to full power in a matter of seconds (correct me if I'm wrong with the numbers). A battery would need to go from zero to thousands of kilowatts consumption in a blink of an eye. I don't think there is a battery that can do that.

I have to disagree with all of this.

Adding more batteries in parallel allows the instant power output to increase to whatever level you want.

A Tesla on a race track would be going from 0 to maximum power draw in fractions of a second. An aircraft even in a TOGA situation doesnt need such quick response. A second or two is still faster than a conventional turbine aircraft.

A 500kg 100kwh battery pack on a Tesla will easily produce 500kw of continuous power in the model S. A 5,000kg battery could then produce 5,000kw of power. In terms of usage in the ATR-72 it has a fuel capacity of 5000kg with around 4000kw of power. So current battery tech would have no issue powering any aircraft, range would simply be fairly low.

The ATR would have a 1000kwh battery that weighs 5000kg. That means it can produce 1000kw for 1 hour. So in practice that means the ATR could fly for 30 minutes at 500km/h with current battery tech. Not bad and a surprisingly high number of ATR flights are under 30 minutes.

I can see battery tech doubling in power to weight in the next 10 years which would make a ATR sized full electric aircraft fly for an hour. Now that would sell like hot cakes.

BREECH · Sun Jan 14, 2018 6:02 am

RJMAZ wrote:
The ATR would have a 1000kwh battery that weighs 5000kg. That means it can produce 1000kw for 1 hour. So in practice that means the ATR could fly for 30 minutes at 500km/h with current battery tech. Not bad and a surprisingly high number of ATR flights are under 30 minutes.

One, there are no 1000 kWh batteries yet. The largest battery packs are 500-600 kWh. Two, planes don't operate like that. You need reserves for both diversion and, much more importantly, for taxiing and waiting for your turn for take off. If I remember correctly, the diversion reserve should be 45 minutes. And waiting time for take off can be up to an hour in some airports. Three, even a 10kWh "energy storage system" touted by Tesla is PROJECTED to be $3,000. I can only imagine the cost of 1 MWh thing. And last but definitely not the least, charging. How do you suggest to charge the 1MWh monster? And how long is it going to take? And how many cycles will it provide before it starts to deteriorate? Oh, and there's four. 5,000kg of fuel will get you A LOT more than 30 minutes of flying. In fact 10 times more. And they don't have to take extra 5 tons of weight on every flight.

RJMAZ wrote:
I can see battery tech doubling in power to weight in the next 10 years which would make a ATR sized full electric aircraft fly for an hour. Now that would sell like hot cakes.

Yes, you can see that. On TED. In the real world, however, there are no indications that "battery tech" will double in power-to-weight ratio in the next 10 years. There isn't even any scientific grounds for that. Hundreds of VERY eager companies have been working on it for quite some time but with very little success. In fact, with no success at all. No amount of Bill Gates's and Elon Musk's dollars will overcome the laws of physics. Which, btw, neither of them know or understand.

BREECH · Sun Jan 14, 2018 6:07 am

Actually, there is an area where progress could be done. Does anyone know where we are in wireless power transmission? Now THAT would be a cool thing for airplanes.

Waterbomber · Sun Jan 14, 2018 10:54 am

I think that batteries can give the necessary output in terms of power, just that their capacity is too limited. Tesla uses packs of 18650 batteries which weigh about 50 grams each and have a theoretical capacity of about 15Wh. So basically 300Wh/kg energy density.
JET A has an energy density of about 10kW/kg, ie 30 times more. Ie, on an A380 with 15 hour range plus reserves, you would have 0 hour range plus reserves.

Waterbomber · Sun Jan 14, 2018 11:33 am

Continuing on the argument of shifting to all-electric aircraft running solely on batteries.

Now in practice, one could argue that electric motors have a much higher efficiency than Brayton cycle engines, as there is less heat and friction loss, etc... However you also have to keep in mind that most battery types don't do well in low temperature environmments, and in the typical operating environment of aircraft, ie well below freezing, they will need heating, resulting in losing a lot of that advantage.

So if we take the previous example of the ATR72 doing 30 minute runs.
It will require about 3500kW of total engine power for take-off, but it won't need to maintain it, so let's say that a 30 minute run will require about 1500kWh of battery capacity. That's a 5000kg battery pack that you need just to fly from A to B.
HOWEVER, you will need another 7000kg of battery capacity just to guarantee the safe operations, ie reserves. Yes, safety is still a higher priority than whatever excuse you have to use electricty instead of jet fuel. The ATR72 has a useful load of about 10.000kg, so the most you can get is 15 minutes without carrying any payload or passengers, but with the necessary reserves.

Next problem, is safety. High capacity batteries tend to be unstable and present a safety risk for aircraft. I think that I don't need to explain the risks associated with putting hundreds of thousands of self-combusting li-ion batteries in an aircraft's wing.

Next problem is cost. Everyone is assuming that electricity is cheaper than jet fuel. It's not cheaper.
Electricity costs about 0.10-0.20 USD per kWh in developped countries while jet fuel costs about 0.05 USD per kwh.
You will ask: Then why is it less expensive to drive on electricity? As said before, electric motors are more efficient, but the biggest factor is how your government taxes the fuel you pump into your tank. Excise taxes, VAT, sales taxes, etc...Remove the taxes, and at today's oil prices, it would be cheaper to drive on fossil fuels for sure. If everybody starts driving electric, you can bet that there will be an excise tax on electricity.

Next problem is charging. Charging batteries takes forever and aircraft have high capital cost, so they can't sit idle on the ramp. The only solution is to swap the batteries but this will result in heavier aircraft.

Final problem: worldwide, electricty is still for a big part generated by non-renewable forms of energy. More than half of the worldwide electricity generation is done from burning coal and natural gas, ie fossil fuels that emit greenhouse gases. This while viable power generation methods exist using solely the power provided by the sun, whether it's directly with solar or indirectly, ie wind or biomass or hydric.
Once all electricity generation has shifted to "green" methods of power generation, we can talk about electricity as "green" power.
Until then, there is no reason to substitute jet fuel by electricty generated with gas or coal, is there?

Waterbomber · Sun Jan 14, 2018 11:56 am

I want to respond to the turboelectric concept.
It has an essential flaw and that is with regards to take-off and climb power requirements in engine failure scenario's.
The concept indicates that smaller engines can be installed as the electric fan in the back will provide additional power for take-off. That looks like something written by a university student as an internship paper.
The size of the engines is determined by engine failure scenario's and the number of engines that you have available.
However, in this concept, the fan in the back is driven by the engines under the wings. So if one engine fails, the fan in the back will lose 50% of available power. So basically, you will running on a smaller engine that also has to give a lot of power away to run the fan in the back, so you actually can't make the engine smaller.
From an engine failure standpoint, it's still a twin engine aircraft, only with the remaining engine having to transfer part of its power to a fan in the back instead of entirely to its own turbofan, with the aditional risk that the fan in the back could fail as well after ingesting debris from the failed engine in the front, unless placed higher up like in previous 3-engine designs.

Ruscoe · Sun Jan 14, 2018 12:19 pm

I thought the manufacturers were talking about H2 powered fuel cells to generate the electricity not stored charge.
Ruscoe

BREECH · Sun Jan 14, 2018 3:52 pm

Ruscoe wrote:
I thought the manufacturers were talking about H2 powered fuel cells to generate the electricity not stored charge.
Ruscoe

Fuel cells is no go. We don't have any feasible means to extract hydrogen. Once (if ever) that problem is solved, fuel cells are not actually the only way to use hydrogen. Many years ago Soviets experimented with "cryogenic fuel". They built Tu-155 and Tu-156 (based on Tu-154 of course) which ran on LNG and LPG respectively. Why not use hydrogen like that. BMW experimented with internal combustion engines fueled by hydrogen. I wonder what came out of all those experiments. What is a better way of using hydrogen, fuel cells or internal combustion?

drgmobile · Sun Jan 14, 2018 4:58 pm

NeBaNi wrote:
Interesting that this topic is brought up. NASA has a concept plane the size of a 737-800 called the STARC-ABL, short for Single-aisle Turboelectric AiRCraft with Aft Boundary Layer ingestion, see image:

The two underwing turbofans provide thrust, as well as power a generator that powers the electric fan at the aft fuselage, so this design is not hybrid electric (no onboard electrical energy storage in, for example, batteries), but turboelectric, where you generate electrical power from non-electrical energy sources. The benefit is that the thrust is split equally among the three propulsors, which leads to the underwing engines being smaller, saving weight there. The aft propulsor also ingests a portion of the fuselage boundary layer, which reduces the fuel burn by reducing drag. See this NASA presentation for the latest version of the STARC-ABL:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170005612.pdf

I agree with the comments made above about battery energy density, it's going to have to improve by a LOT to have a 787-sized hybrid electric aircraft. However, electric propulsion is enabled by distributed propulsion and boundary layer ingestion, and even at the battery energy densities of today. Hence, you have companies like Zunum trying to build a 12 pax regional commuter jet (backed by Boeing and jetBlue), and Airbus with its e-Fan X demonstrator, pictures below:
Zunum:

Airbus e-Fan X (based on the BAe 146):

So, while battery energy density needs to improve, electric propulsion does hold promises and I believe the future is bright!

Zunum's chief technology officer addressed delegates at a conference I was at in October. They are working on all of the technologies involved in getting their initial aircraft up and flying in the next couple of years, but then have larger models in mind as battery technology comes along. I got the sense they believe the technology is within reach within the next decade.

NeBaNi · Sun Jan 14, 2018 6:17 pm

Waterbomber wrote:
I want to respond to the turboelectric concept.
It has an essential flaw and that is with regards to take-off and climb power requirements in engine failure scenario's.
The concept indicates that smaller engines can be installed as the electric fan in the back will provide additional power for take-off. That looks like something written by a university student as an internship paper.
The size of the engines is determined by engine failure scenario's and the number of engines that you have available.
However, in this concept, the fan in the back is driven by the engines under the wings. So if one engine fails, the fan in the back will lose 50% of available power. So basically, you will running on a smaller engine that also has to give a lot of power away to run the fan in the back, so you actually can't make the engine smaller.
From an engine failure standpoint, it's still a twin engine aircraft, only with the remaining engine having to transfer part of its power to a fan in the back instead of entirely to its own turbofan, with the aditional risk that the fan in the back could fail as well after ingesting debris from the failed engine in the front, unless placed higher up like in previous 3-engine designs.

Yes, a valid point about the one-engine out takeoff scenario, but the presentation isn't the only thing out there - that was just the latest revision of an ongoing concept I could find. If you want a more detailed read, they have a journal paper out on the older Rev A model:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160007674.pdf
Not exactly a university student internship paper I'm afraid. AFAIK, there is a team of full-time research engineers at NASA Langley and NASA Glenn working on this project.

drgmobile wrote:
Zunum's chief technology officer addressed delegates at a conference I was at in October. They are working on all of the technologies involved in getting their initial aircraft up and flying in the next couple of years, but then have larger models in mind as battery technology comes along. I got the sense they believe the technology is within reach within the next decade.

Yes, I read about that too. The Zunum CTO must know something I don't, but the optimism and the buzz encourage me. Battery technology is improving faster than it used to, especially since Li-ion batteries are now used in cars and consumer electronics. Both of those are large, weight sensitive industries and they throw a lot of money at battery research. Signs are encouraging!

kalvado · Sun Jan 14, 2018 7:03 pm

NeBaNi wrote:
Battery technology is improving faster than it used to, especially since Li-ion batteries are now used in cars and consumer electronics. Both of those are large, weight sensitive industries and they throw a lot of money at battery research. Signs are encouraging!

Andre3K · Sun Jan 14, 2018 7:05 pm

Very interesting topic. But if the electric motor is mainly for takeoff, wouldn't it be more economical to either: 1. Use an EMAL system and launch everything carrier style or 2. Use rocket assisted takeoff's or. 3. Use aircraft towing where you have a high powered low weight aircraft with only 30 minutes of fuel onboard helping to drag a heavy laden aircraft up to about 10,000 and then breaking off.

I know some of these idea's might be ridiculous, but who knows one day. Hell I'm surprised we don't have self driving aircraft tug's or train like rail pulling tug's yet.

Ruscoe · Sun Jan 14, 2018 8:31 pm

I'm pretty sure Boeing have already flown an electric aircraft powered by both battery and H2 fuel cell.
The battery was used to provide extra power during take off but cruising used only the fuel cell.

I expect we will see fuel cells providing the electrical power to a kerosene powered aircraft in the first instance.

Ruscoe

frmrCapCadet · Sun Jan 14, 2018 8:45 pm

We are at the beginning of hybrid planes, and I don't think anyone knows what the first commercial application may be. Well, actually drones will be the first beneficiary. Then again, autonomous cars looked serious only a couple years ago, and GM already is prepared for the first model without steering wheel or brakes next year.

Slug71 · Sun Jan 14, 2018 9:01 pm

While not "aviation grade", this article has a good summary of the current technologies being explored for future batteries.

https://www.pocket-lint.com/gadgets/new ... ir.amphtml

A lot of advancement coming and the next decade will be interesting. A lot to keep an eye on.

RJMAZ · Sun Jan 14, 2018 10:02 pm

BREECH wrote:
[ In the real world, however, there are no indications that "battery tech" will double in power-to-weight ratio in the next 10 years. There isn't even any scientific grounds for that. Hundreds of VERY eager companies have been working on it for quite some time but with very little success. In fact, with no success at all. No amount of Bill Gates's and Elon Musk's dollars will overcome the laws of physics. Which, btw, neither of them know or understand.

Kalvado just posted a graph that shows there has been a constant improvement in battery density every year.

The tesla's latest model has 18650 battery cells wired in series/parallel to allow the electric motors to produce 500kw. This can be scaled up to any power level you like.

BREECH wrote:
One, there are no 1000 kWh batteries yet. The largest battery packs are 500-600 kWh.

The Tesla truck prototype has a 1000kwh for its long range model. There are also hundreds of batteries over 1mwh.

Tesla just installed a 100megawatt hour battery in Australia that weighs more than a fully loaded A380.

NeBaNi · Mon Jan 15, 2018 2:40 am

kalvado wrote:
NeBaNi wrote:
Battery technology is improving faster than it used to, especially since Li-ion batteries are now used in cars and consumer electronics. Both of those are large, weight sensitive industries and they throw a lot of money at battery research. Signs are encouraging!

Nice graph. You know how there is a jump from Ni-Cd/Ni-MH to Li-ion? Expect a similar jump if new lithium chemistries like Li-S or Li-air work out. At the moment, these new chemistries are just proven on lab test benches, but with continued funding, we might have commercial batteries soon with a jump in energy density.

Slug71 wrote:
While not "aviation grade", this article has a good summary of the current technologies being explored for future batteries.

https://www.pocket-lint.com/gadgets/new ... ir.amphtml

A lot of advancement coming and the next decade will be interesting. A lot to keep an eye on.

Interesting article. It talks a little bit about the Li-S chemistry I mentioned above. Other non-lithium chemistries like Zn-air, Al-air, Sodium, etc. will not make their way into aircraft, IMO. For such a weight sensitive application, the fact that lithium is the lightest metal does wonders for energy density of Li-ion batteries.

RJMAZ wrote:
BREECH wrote:
[ In the real world, however, there are no indications that "battery tech" will double in power-to-weight ratio in the next 10 years. There isn't even any scientific grounds for that. Hundreds of VERY eager companies have been working on it for quite some time but with very little success. In fact, with no success at all. No amount of Bill Gates's and Elon Musk's dollars will overcome the laws of physics. Which, btw, neither of them know or understand.

Kalvado just posted a graph that shows there has been a constant improvement in battery density every year.

The tesla's latest model has 18650 battery cells wired in series/parallel to allow the electric motors to produce 500kw. This can be scaled up to any power level you like.
BREECH wrote:
One, there are no 1000 kWh batteries yet. The largest battery packs are 500-600 kWh.

The Tesla truck prototype has a 1000kwh for its long range model. There are also hundreds of batteries over 1mwh.

Tesla just installed a 100megawatt hour battery in Australia that weighs more than a fully loaded A380.

I must emphasize here that no one doing research envisions these technologies for the near future. NASA/Boeing expect these technologies to be mature around the mid 2030s. It is not unreasonable to expect such an improvement in 20 years, especially driven by the increasingly green auto industry. The case for Zunum is a bit different - the battery technology of today or the next 5 years should be enough to power regional aircraft for sub-1000km missions. Think CapeAir from Boston to New England regional airports. Think multitudes of DHC-6/ Viking Twin Otter operators around the world. Aircraft applications will start from small, commuter aircraft and move on to larger jets as battery technology improves.

Waterbomber · Mon Jan 15, 2018 3:59 am

NeBaNi wrote:
I must emphasize here that no one doing research envisions these technologies for the near future. NASA/Boeing expect these technologies to be mature around the mid 2030s. It is not unreasonable to expect such an improvement in 20 years, especially driven by the increasingly green auto industry. The case for Zunum is a bit different - the battery technology of today or the next 5 years should be enough to power regional aircraft for sub-1000km missions. Think CapeAir from Boston to New England regional airports. Think multitudes of DHC-6/ Viking Twin Otter operators around the world. Aircraft applications will start from small, commuter aircraft and move on to larger jets as battery technology improves.

No. The battery technology of today or the next 5 years is not enough, not safe, not affordable, not environment friendly for anything.
Not even for a sub-10km mission.
See my previous posts.

Also, what's viable for small aircraft isn't necessarily for larger aircraft.

CARST · Mon Jan 15, 2018 5:46 am

kalvado wrote:
NeBaNi wrote:
Battery technology is improving faster than it used to, especially since Li-ion batteries are now used in cars and consumer electronics. Both of those are large, weight sensitive industries and they throw a lot of money at battery research. Signs are encouraging!

RJMAZ wrote:
Kalvado just posted a graph that shows there has been a constant improvement in battery density every year.

The interesting point about this graphic is that we see that battery power for Li-ion cells has trippled over 20 years. Who now expects it to go 10-fold over 10 years must be an idiot. We might see new battery technology, based on new materials, give us these options, but so far, no project came that far.

And there are huge teams working on battery tech. Every car manufacturer has massive development teams on this, there are the classical battery companies who do research into this. You have start-ups, you have teams at universities, you have NASA and other government-funded agencies all over the world looking into this topic. But I don't see a battery powered, commercial plane within the next 20 or 30 years.

Especialyl if we consider that planes must be flown not only for an hour, but three, six, twelve, 15 or 18 hours. That is reality. And BTW, we are facing the same hurdle for cars. People don't go for electric cars for three reasons: price, range and most importantly because they have no place available to charge it.

Just imagine, all cars being electric cars tomorrow. We would need hundredths of millions of charging stations. Not only for the private house / home owner. No, for every frickin' car. In the city centers, in front of social housings, skyscrapers, in parking garages. And even if we would build them (totally unlikely) our power grid is not able to charge all these cars. We would need to DOUBLE or TRIPPLE the number of power plants. We would need this millions of charging stations. REAL numbers: we have over one billion cars registered worldwide. Alone the USA has over 130 million registered cars.

But now back to airplanes:
We don't have the technology and won't have it in the next 20-30 years, we don't have the required quick-charging possibilities, we don't have the power-grid and power-plants to make all this possible, battery energy is not evolving in any way as fast as some people want to believe it, these ideas and plans are all wet dreams.

Personally I see much more future in technologies like hydrogen or any other energy-storage material. The material we need is not allowed to be flamable. And it should store energy as good or better than fossil fuel. And it must have the same or better energy output as fossil fuels. That means we either need to find a way to produce fossil fuels from renewable energies (without taking up all our fields we need to grow the stuff we eat) or find an alternative like hydrogen.

I say find an alternative, because currently producing hydrogen is no problem, but we still have to put more energy into it, than we can take out of it. Here fossil fuels are still leading. But there might be solutions in the future. In Germany, they started a new fusion-reactor two years ago. It's still in a trial stage and only rather small, because it's used for research. But it's the largest Stellarator worldwide, where liquid plasma, controlled my magnetic fields, is used to sustain and control a nuclear fusion of atoms. It's called "Wendelstein 7-X". But even for such a real world project, which does not only exist in wet dreams, but is a reality, they don't expect the technology to be usable for the next 30 years. It's a long-term project. The idea behind the project is described by the leading engineer with the words "when this reactor reaches it's final stages, four buckets of water, should deliver as much energy as 40 tons of coal, but don't expect that to happen before 2040". But once this is achieved, or only 50% of this target, we will have the option to produce energy so cheap, that we could produce hydrogen or any other energy-storing material so cheap and efficient, that it will be a real alternative to fossil fuels.

But if this project goes along as planned, we could produce hydrogen cheap enough to be used as a fossil fuel replacement. And our airplanes and cars would just put out energy and water-vapor.

frmrCapCadet · Mon Jan 15, 2018 2:24 pm

Just imagine, all cars being electric cars tomorrow. We would need hundredths of millions of charging stations. Not only for the private house / home owner. No, for every frickin' car. In the city centers, in front of social housings, skyscrapers, in parking garages. And even if we would build them (totally unlikely) our power grid is not able to charge all these cars. We would need to DOUBLE or TRIPPLE the number of power plants. We would need this millions of charging stations. REAL numbers: we have over one billion cars registered worldwide. Alone the USA has over 130 million registered cars.

Can't imagine seeing more errors in a simple paragraph. Even five years ago it was determined that merely changing all lighting to LED could power half the need if all cars were electric. And battery charging time is getting faster all of the time. Cars won't become all electric in a year or in a decade, meantime power consumption is the US is DECLINING. Efficiency in motors, heating, and industrial processes is having a huge impact on the amount of electricity we are using.

Any number of major electrical utility companies are more worried about the economics of projected decline in consumption that the other way around. Third world countries do have a shortage of power, but most suspect that between wind, solar, and efficiency it is a solvable problem.

kalvado · Mon Jan 15, 2018 4:21 pm

frmrCapCadet wrote:
meantime power consumption is the US is DECLINING.

Flattened out at best - mostly due to decline of industrial consumption. I suspect specifically because of Aluminum production being more efficient elsewhere.
https://www.eia.gov/electricity/annual/ ... 01_02.html

UpNAWAy · Mon Jan 15, 2018 4:30 pm

A little off topic but does a Ram Air generator loose more energy than it generates? If not you could have electric APUs, that are charged in flight.

kalvado · Mon Jan 15, 2018 4:43 pm

UpNAWAy wrote:
A little off topic but does a Ram Air generator loose more energy than it generates? If not you could have electric APUs, that are charged in flight.

Of course it looses energy - drag it creates requires more thrust to overcome by increased fuel burn. That is exactly why RAT is the very last resort in terms of aircraft operations..

frmrCapCadet · Mon Jan 15, 2018 5:11 pm

Aluminum production pretty much ended in the Bonneville system about 20 years ago, maybe even 35 years ago. Population is up - nuclear plant and 2 coal plants are closed/scheduled to close, we are talking about dismantling 4 Snake River dams - and no one is talking about a power shortage. My old home town has a medium sized natural gas plant, and they can't begin to sell their power on a regular basis.

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