Notional passenger electric aircraft from EADS: Ceiling?

[mheslep]

EADS had a pseudo model of an electric passenger aircraft at the Paris airshow. Apparently they like a hybrid approach: six electric motor driven ducted fans, a battery, and a single traditional jet turbine that assists on take off and generates electric power for the fans/battery.

I'm curious as to what would drive a practical upper limit to ceiling for such commercial e-aircraft? Wing stall? Passenger compartment pressurization?

https://www.youtube.com/watch?v=GlqX4m0R6E8

Also appears the above-wing mounted fans allow a return to fuselage quite a bit lower to the ground on take off and landing, avoiding these kinds of ground standoffs driven by current jet turbo fans.

 

[256bits]

The mock up is only for promotional purposes to inspire awe and fascination to the public. No doubt everyome seeing the styrofoam/wood model left with a good feeling that the future is in good hands and that the European aerospace industry is at the forefront of new technology to make the planet greener and healthier for their sons and daughters and grandchildren, and will be thus part with some of their own income willingly in support.

While that is somewhat editoriialized, the theme is that to get a grand idea off the ground what better way to start than through public support. Perhaps it is a great idea and will bear fruit, perhaps not. Once they have a functioning prototype several years down the road a better assessment of its viability can be made, ( Actually sometime before that when the engineering calculations are more fine-tuned so to speak )

The electric powered aircraft suffer from power/weight ratio, maximum speed, maximum ceiling, range - probably more. The consortium that decides to research and build this thing has quite a lot of juggling and tradeoffs to do. The electric motors will need cyrogenics for cooling and maybe superconducting. How will that extra system add or subtract from the passenger load? Has something like that been done before so it will be safe at 20,000 feet?

So to answer your question, it is not the old ( by old I mean mature ) technology and systems that will set the functioning parameters such as ceiling of this aircraft, but the incorporated new technology. We know how airplane shells function in low atmosphere conditions, as well as wings and fans, so that is not an issue.

The issue is whether something like this mock up be constructed - I would say yes.
Can it be constructed to have performance features similar to existing jet airplanes - maybe.
Can it constucted similar to say a 737 and have a payload to carry 100 passengers or only 2 - the big maybe.

 

[mheslep]

The mock up is only for promotional purposes to inspire awe and fascination to the public. "

Sure, that's one aspect, the PR, which is a part of everything on display at an airshow. However I suggest the mock up also shows some non-trivial engineering design has already taken place.
...

The electric powered aircraft suffer from power/weight ratio, maximum speed, maximum ceiling, range - probably more. "

Of those I think range is the only one that is necessarily a true limitation given current technology. Electric motors haven built with power well into the hundreds of megawatts. The problem is sustaining the power from a fixed energy supply, and doing so with a low mass profile. Certainly a propulsion system that requires no oxygen (in cruise) has distinct ceiling advantages.

... electric motors will need cyrogenics for cooling and maybe superconducting. ... Has something like that been done before so it will be safe at 20,000 feet?

Shuttling Jet-A around an aircraft has been done for some time, and in commercial aircraft it has somehow been considered acceptable to do so for decades without nitrogen to inert the fuel supply, and largely still is. Such a system is considered "mature", when I think it more accurate to call it accepted even though inerting would have clearly spared some fuel related aviation disasters. By comparison I suspect cryogenics will be less dangerous.

So to answer your question, it is not the old ( by old I mean mature ) technology and systems that will set the functioning parameters such as ceiling of this aircraft, but the incorporated new technology.

Anything particular come to mind? I can not think of anything dependent on breathing atmosphere or atmospheric pressure in such propulsion system.

The issue is whether something like this mock up be constructed - I would say yes.
Can it be constructed to have performance features similar to existing jet airplanes - maybe.

I think doubtful the electric hybrid will be similar to existing aircraft in terms of range. But in many other areas - energy costs, acoustic signature allowing late night operations - I see some clear advantages.

 

[AlephZero]

However I suggest the mock up also shows some non-trivial engineering design has already taken place.

That depends what you call "non trivial". If you set up a team of say three people with more than 100 person years combined experience on real propulsion systems, you can get plenty of "non trivial engineering design" done in a week - and that's the way these sort of projects are often handled. Given the number of paper aircraft that arrive in an engine manufacturer's inbox each year, a week is about as long as most of them are worth thinking about, unless somebody is prepared to pay an interestingly large amount of money to think for longer, of course.

And the team doing the thinking won't have any delusions that somebody might actually start real work on the project!

Things like how to pressurize the cabin are just details. You know from experience how much energy input it takes, and that's probably all that goes into this level of modeling.

I can not think of anything dependent on breathing atmosphere or atmospheric pressure in such propulsion system.

An electric powered fan is no different from any other sort of fan, in converting power into thrust.

But in many other areas - energy costs, acoustic signature allowing late night operations - I see some clear advantages.

And when you contemplate the cost of even figuring out how convince the FAA that something like this could be certified for real-world use (let alone actually dong the certification), those advantages had better be worth billions of dollars...

 

[mheslep]

...
And when you contemplate the cost of even figuring out how convince the FAA that something like this could be certified for real-world use (let alone actually dong the certification), those advantages had better be worth billions of dollars...

<Shrug> Not an engineering issue. We might as well shutdown all major technology innovation under regulation by the government (e.g. gen iv nuclear) if the engineers must wait for a "by your leave" from the government to get started.

 

[mheslep]

Like most such projects, the first design is not a design that would attempt totally replace all prior passenger aviation, but would likely first show up in dozens of niche applications - low acoustic and low thermal signature aircraft for the military, extremely high ceiling missions (80k+ feet), short range and inexpensive to fly training aircraft, etc, etc.

Given the ample applications, it's no surprise that drawings have already left the drawing board:

 

[AlephZero]

You seem to have changed the thread subject from "passenger (i.e. commercial) electric aircraft" to niche markets applications.

But it you think aircraft certification and regulation is "not an engineering issue", I guess you are happy to let 787s crash and burn...

Whatever, if you want to see some serious research rather than a pop-sci video, go to http://www.eurtd.com/moet/ and look at the "final public technical report" for an overview of the project, and the "forum" (= public conference proceedings, not an internet chat forum) for more on your original topic.

(Most of the reports in the "publications" section are only the abstracts).

 

[mheslep]

You seem to have changed the thread subject from "passenger (i.e. commercial) electric aircraft" to niche markets applications.

There are some quarter million aircraft registered in the US. Passenger aviation consists of more than 2-400 seat jumbos.

 

[mheslep]

Yif you want to see some serious research rather than a pop-sci video, go to http://www.eurtd.com/moet/

Thanks for the link, but MOET is about aircraft auxiliary electrical systems - APUs, methods of taking electric power off convention jet turbines, etc. There is no analysis of electric or of hybrid electric propulsion.

 

[256bits]

I think doubtful the electric hybrid will be similar to existing aircraft in terms of range. But in many other areas - energy costs, acoustic signature allowing late night operations - I see some clear advantages.

Definitely advantageous. The aviation industry is also attempting to reduce their carbon footprint, so this would be an area for them to investigate to see what is possible.

Of those I think range is the only one that is necessarily a true limitation given current technology. Electric motors haven built with power well into the hundreds of megawatts. The problem is sustaining the power from a fixed energy supply, and doing so with a low mass profile. Certainly a propulsion system that requires no oxygen (in cruise) has distinct ceiling advantages

The power/load in the main limitation and all other limitations follow from that.

One other aspect of the electric hybrid is that the pilots will be more restricted in juggling fuel load with cargo load and range. The battery weight is always there whether fully charged or not. An emply plane may have to take on as much aviation fuel ( for the turbine ) as a plane fully loaded with cargo and/or passengers.

I would be interesting to see how the international aviation bodies, as alluded to by AlphaZero, come to terms with this. There are regulations for presernt day aircraft on amount of aviation fuel needed for taxiing to the runway, takeoff, alternative airport in case destination is unavailable, and landing reserve. Would the amount of energy within the battery be part of that, or only the liquid aviation fuel brought on board? That is an engineering issue as the plane will have to follow within the certain guidlines and regulations that governing bodies will adopt.

 

[mheslep]

One other aspect of the electric hybrid is that the pilots will be more restricted in juggling fuel load with cargo load and range. The battery weight is always there whether fully charged or not.

More restricted or freed from yet another task? I've never flown anything more than small single engine single tank aircraft so I don't know, but I would think a fixed mass and CG battery frees the pilot (and aircraft designer) from having to manage a changing mass with a changing CG (liquid fuel) in level flight, never mind acrobatic maneuvers.

 

[mheslep]

Also on the subject of CG advances, on re-watching the EADS promo film, I notice that they fairly clearly call out the e-motor fans as producing the thrust, I think they mean all the thrust, and that the single large combustion turbine is only for generating electrical power and no thrust.

Some reasons that come to mind for forgoing thrust on the turbine:
1. CG. A center mounted jet turbine for thrust pretty much has to be an absolute rear mounted turbine. In the notional promo, they show the turbine mounted perhaps 10-15% forward of the stern along the roll axis.
2. Full thrust power is available at high ceiling (any elevation) when on batteries alone.

 

[256bits]

I think the turbine in this EADS configuration utilizes all shaft HP as a means to charge the batteries and to provide more electrical power to the motors when needed such as during takeoff.
Pilot checks CG on the ground with cockpit instrumentation and the autopilot will take care of that in the air on cruise.

 

[Enthalpy]

Eads' concept gets power from the gas turbine and transmits it electrically to the fans. Batteries serve for short thrust increase at take-off, and to store regenerative "braking" (descent).

Its ceiling is hence the same as other jets, resulting from the gas turbine and the wing.

Getting the thrust mainly from electric fans is a means to increase the blown area and distribute the thrust. This improves the efficiency, as a step beyond by-passing.

As for mass and size of electric motors and generators, don't be fooled by a common misconception. If an electric machine runs at the speed of a turbine or fan, then it's smaller and as light as a turbine. In an electric plant for instance, the alternator is much smaller than the turbines, despite optimizing efficiency.

For some computed sketches, google "quick electric machines". Absolutely no need for superconductors nor cryogenics.

I also suggested the electric transmission of turbine powered aeroplanes elsewhere a few years ago. Though, hydrogen becomes slowly feasible as the car industry develops good fuel cells.

 

[mheslep]

Eads' concept gets power from the gas turbine and transmits it electrically to the fans. Batteries serve for short thrust increase at take-off, and to store regenerative "braking" (descent).

Its ceiling is hence the same as other jets, resulting from the gas turbine and the wing.

Yes, on review I see that is the current EADs concept - battery is never the sole energy source for the e-fans, so the ceiling has the same limitations. I'm curious as to what multiple of battery capacity would be required to also support cruise per unit range, at a higher ceiling w/ lower drag.

Getting the thrust mainly from electric fans is a means to increase the blown area and distribute the thrust. This improves the efficiency, as a step beyond by-passing.

Thanks.

 

[mheslep]

As for mass and size of electric motors and generators, don't be fooled by a common misconception. If an electric machine runs at the speed of a turbine or fan, then it's smaller and as light as a turbine. In an electric plant for instance, the alternator is much smaller than the turbines, despite optimizing efficiency.

For some computed sketches, google "quick electric machines". Absolutely no need for superconductors nor cryogenics.

I also suggested the electric transmission of turbine powered aeroplanes elsewhere a few years ago. Though, hydrogen becomes slowly feasible as the car industry develops good fuel cells.

I could see smaller perhaps, but I don't see how a path to higher specific power for an e-motor versus a gas turbine. Some work has been done in this area. See this reference for instance, slides 17 and 18. Paper http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4275231&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D4275231.

Gas turbines per the reference have a specific power of 3-8 kW/kg (and rising I suspect). The highest specific power non HTS e-motor I'm aware of is the 3-phase induction motor designed by Tesla Motors: 288HP (214kW) in 115 lbs (53 kg), or 4.1 kW/kg. A given B field in a rotor requires a proportional copper winding mass (or H field in a stator), which limits the power density. I'm unaware of anyway to avoid that problem, aside from replacing the copper with HTS. Apparently EADS assumes similarly, given their cryo plans.

Thanks for the pointers to your nice motor designs, though I note aviation has long had a need for lightweight auxillary e-motors without anything ever being produced at very high specific powers.

 

[256bits]

From where did I get my info - I dug this up about the E-thrust, although not the original place.

To make the E-Thrust system viable, superconducting technology would be required to reduce the size of the electrical components, combined with next-generation electrical storage technology (EADS has its eye on Lithium-air batteries) capable of energy densities over 1,000 Wh/kg.

E-Thrust falls under EADS' Distributed Electrical Aerospace Propulsion (DEAP) project, which seeks to meet the targets set out in the European Commission's report Flightpath 2050 – Europe's Vision for Aviation. Specifically, the report calls for a 75 percent reduction in C02 emissions, 90 percent reductions in NOx emissions, and 65 percent reduction in noise levels by 2050, compared to the year 200.

http://www.gizmag.com/eads-concepts-paris/27979/
( year 200 is in their text )

Eads also had a concept all electric airplane at the 2011 airshow called the VoltAir.
http://www.gizmag.com/eads-voltair-electric-airliner/18988/
I wonder how far along in design that one went.

 

[Aero_UoP]

Look at that : http://www.rolls-royce.com/paris_airshow/news_airshow/18062013_power_concept.jsp

Sorry, 256bits said it above... I just provided the link :)

 

[256bits]

Look at that : http://www.rolls-royce.com/paris_airshow/news_airshow/18062013_power_concept.jsp

Sorry, 256bits said it above... I just provided the link :)

Hey, super great! I did not think of looking at RR. EADS did not, al least nothing I could find, on the E-Thrust.

 

[Aero_UoP]

I had read this article a couple of weeks ago that's why I knew it was in RR's website ;)

 

[mheslep]

Airbus has the electric trainer in the air (referenced in the OP).

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

and claims it has plans for production of the trainer as early as 2017. They're also talking about a regional passenger aircraft, 70-90 people, 15-20 years.