E-Fan X: R-R/Airbus electric drive demonstrator
 

Airbus, Rolls-Royce, and Siemens team up for electric future ? Rolls-Royce

This looks interesting. Airbus, R-R, and Siemens developing an electric demonstrator aircraft. Specifically, the airframe is a BAe 146 with one engine replaced with a ducted electric fan. The power comes from a 2MW turboshaft generator in the tail - like a big APU (IIRC that's in the same ball park as the 787's electrics). Once that's working they'll swap a second engine.

Questions I have about this:

1) Is the efficiency gain that good it's still worthwhile when the power is coming from a gas turbine?
2) Or is the idea to prove the power electronics and the fan, with a view to getting the power from something else?
3) Are they thinking of a duty cycle change - take-off on turbofan and cruise on turboelectric?

A bit more detail: https://www.siemens.com/innovation/e...y-e-fan-x.html

The key seems to be that the on-board generator is designed only to provide enough power for cruise. Take-off and climb will have this generator's power supplemented by LiIon batteries. This means that because the generator will always operate at full capacity, it can be much more weight-efficient than one that is required to handle the peak loads associated with take-off and climb.

That makes a lot of sense.

Before one can run, it must crawl, stand, walk and then maybe take a few running steps. This maybe just a start, but at least some are experimenting with new innovations. Lets, let them start with a slow crawl or even belly drag.

Fascinating. This could be the future of more efficient fan-based propulsion.

The real challenge is commercial aviation moving away from fossil fuels, but for the time being, the potential power to weight ratio (not to mention cost) of a gallon of kerosene is hard to beat.

Assuming the batteries are rechargeable, what's the cost of joules per hour compared to gallons per hour in a fan drive?

Interesting question, Lomapaseo. I do not have an exact answer, but I do know that kerosene contains 100 times the energy by weight compared to electric storage batteries. We all know weight is of primary importance when considering things airborne.

I can tell you current (Tesla) battery manufacturing prices are around $200 per kilowatt hour. Consider the current price of kerosene, and the fact that one gallon is equivalent to around 40 kilowatt hours of energy and the scope of the challenge becomes more apparent.

Consider it takes around 90 megawatts to get a typical 747 in the air, the cost of batteries powering the original jumbo, if we set aside the enormous weight penalty, is quite staggering - $200x90,000 = a very large figure - and that's just to get airborne.

Of course those batteries are rechargeable, but the initial capital cost buys a lot of liquid fuel and thus we remain plying the skies on carbon based fuels for the foreseeable future, again leaving aside the weight problem.

Not trying to be a totally negative Nancy, as I feel renewable power is our best bet for the future, but consider this: An operational reality that is often left out of discussions involving battery powered aircraft is weight. A lesser, yet consequential aspect of that weight is how a conventionally powered aircraft gets lighter and more efficient as the fuel is consumed, while battery powered aircraft land at nearly the same weight that they took off - after power is depleted, the battery dead weight remains the same.

I imagine much useful data will be gained with this test bed. But for the most part...Greenwashing.

When much of the charge for takeoff N comes from descent N-1, that joules per hour cost (negating capital costs) looks great. That it also set's you up nicely for a go-around is just icing on the cake.

vapilot2004

No disagreement from me, but I do think that you also need to take into account losses. The thermal efficiency of an aircraft turbofan is pretty poor compared with an electric motor....empirically stated a 100kWh Tesla can easily drive 300 miles. Try that on 2.5 gallons of Kerosene or gas.

An electric 146
 

Good grief, an electric 146 !
Having witnessed the project from start to finish, it continues to surprise with the range of new uses; met research, firefighting, etc.
The wing - engine pylon geometry is ideal for this type of testing, which together with the aircraft’s twin hyd/elect systems and a four engining configuration should minimise problems and maximise opportunity. It should also be possible to test a range of different motor/fan sizes with the same installation as well as relatively large size open-rotor configuration.

As for the weight - cost debate, the reduced complexities of the power plant - optimisation of the gas path, no high temp metals, turbine containment, lower overall weight, could offset a considerable part of a battery installation.
Then there could be many advantages from not requiring a ‘wet wing’, reduced weight, ease of manufacture, fuel piping, pumps, and system integrity and isolation, ...

No wonder that the big players have made a significant move in the testing of future systems.
And perhaps an even quieter, quiet 146.

Well, the batteries only need to supply that 90 MW during climb (and climb power is lower than take-off power), so you can drain the batteries with 90 MW in about 10 minutes, requiring a 15.000 kwh battery, which would cost about 3 million dollar at your quoted price. Not that much compared to the list price of a 747.

Translation.... "I havent a clue what i am talking about!"

thats megawatthours? megawhatseconds? megawhattheforknanoseconds?

he quotes time and power.
multiply that and you get the energy of the 15 MWh he sized the battery at.

now how much does this 15 MWh battery weigh is a interesting question.

now the wording might not be perfect but it's quite clear.
on the other hand people saying this windmill prodcues 1 MW per year now that is stupid.

oh and Translation:
"reading comprehension: not so good"

you are referring to a later post where the value is estimated as 90megawatt for 10 minutes .... exactly the point I was making! not that i agree with that estimation, the get off the ground value will be significantly greater than the climb away value.

But there are several other possible gains
1 fan speed can be optimum without gears
2 contra rotating fans also can be achieved very simply without gears
3 and finally for getting off the ground "ludicrous" amount of power available for short bursts and this power is instantly available without any turbine lag which is a good thing for a go around.

still an hour worth of power to get "airborne" is still reasonable if you want to include the climb :)

but yeah you are right i misunderstood because the quoted part was put in a better context in another post.

anyway estimating the cost of the batteries is the wrong approach.
especially because you are assuming power needed to get the plane off the ground with the current powerplant+fuel. with all the heavy batteries you have significantly lower useful load.

weight of a 15 MWh lithium ion battery assuming 300 Wh/kg:
a whopping 50 000 kg or 110 000 lbs
payload of 747 freighters is around 120 000 kg.

this should make it clear how ridiculous the idea is with current batteries sometimes i think people just don't get that. or maybe they do what do i know :)

Most of this "green" :mad: is just marketing, sounding eco-friendly to the gullible.

I don't think wet wings are gone just yet. A big benefit of this is the ability to move away for standard design. The fan would basically be an overgrown hairdryer (Wasn't there a joke about 146s being powered by 4 hairdryers or was that 4oil leaks connected by an electrical fault?).
You could put the generator anywhere in the aircraft's structure to optimise design. For a 146 you could potentially power 4 fans from 1 big generator or two smaller generators to allow for redundancy. I think batteries should only be carried for the power plant to reduce lag for quick spool-up times.

Unless you're suggesting that it's a perpetual motion machine, the fuel to power the turbine generators is still going to have to be accommodated somewhere.

Agreed, unless they plan to recharge the "take off" batteries on the ground the total fuel onboard will be about the same as current technology. Ground recharge would likely not save much.

This is similar to diesel railroad engines that drive a generator which in turn powers electric motors to actually drive the wheels.
Although there is some loss in the conversion it has become standard rather than a direct mechanical drive as was used on steam engines.

As others have mentioned a major potential advantage of the system is being able to size the turbine for average rather than peak load. In addition to weight savings (likely negated by the batteries) this should also significantly reduce stress and prolong the time to overhaul.

The fans of course would need to cover the full range but would not be as sensitive to operation at peak load so less need for reduced performance take offs.

Of course one last consideration is the size of the fire if the batteries ever go off, would make the Dreamliner fires seem like a small spark :E

I agree, but once we get to our cruising altitude, how about a destination?

Agreed, Ion_B. I believe it's around ~90% for our best electric motors, ~40% for the best we have in turbo fans.

Say, 2 to 1 to keep it simple, and we are left with perhaps a 20 to 1 ratio on the delta between aviation fuel and battery power, with the efficiency factored in, regarding energy to weight ratios.

True again, although add two or three stone's worth of go juice and we get the same range using current tech on the ground. Put it in the air however and the mission at hand becomes all about the weight, yes?

Replacing the 120 metric tonnes of fuel at 20X the weight for a long range flight seems truly unreachable even on a massive aircraft. A short haul sector for a narrow body works out to around 160 tonnes of batteries in an aircraft designed for a max fuel load of well under a quarter of that weight with a MTOW of half, let alone trip fuel where we get the same energy out of a mere 8 tonnes of kerosene.

With batteries being currently impractical, for cost and weight reasons, leaving aside energy management and replenishment times and costs, hybrid-electric propulsion seems like a great place to start...as demonstrated in our conversation starter, which has a cousin under development in the US as well.

There are people who are trying to sequester hydrogen without the high compression and heavy steel tanks. That would be the magic bullet for aircraft hybrids like the subject of our discussion. H2 > Fuel Cell > Ducted Electric Fans would be brilliant.

So why not just use nuclear power to generate the electricity needed on board instead of heavy batteries or beyond huge hydrogen tanks?
https://www.scientificamerican.com/a...ered-aircraft/

Brilliant....ly funny! :ok:

I was blissfully unaware of the nuclear powered B-36 here in the states. Good grief!, as Charlie Brown might say.

There also seems to be an assumption that electric motors are "light".
I am sure that there is room for lightening, but I can not imagine any motor of the required size being lighter than its equivalent gas turbine.

As for variable speed and contra-rotating fans, only with the penalty of (currently) heavy inverters and IGBT's.

Why the extra complication and weight of a fuel cell/electric motor? Just burn the H2 in a gas turbine.
While the electric propulsion is interesting, I just don't see it being practical unless there is a massive breakthrough in battery technology resulting in much lighter batteries.

Indeed. The Common Motor/Starter Controllers on the 787 are huge and weigh about 400lbs each. The only drive small motors like Engine Starters or Hydraulic pumps.

Each generator is rated at about 250KvA. Two on each engine and similar on the APU. So thereabouts 1.5MvA. Ok, a lot of that is redundancy power in case an engine fails but you get the gist.

I think it's a lot of nonsense...real jets are better to focus talent on

You're going to need a lot of copper to transmit power from a tail generator to wing mounted electric motors. I guess that could lead to the re-emergence of tail mounted engines.

I'll believe this when Slebs stop lecturing us deplorables and actually cut back on their lifestyles. Not holding my breath. Greenwash.

Quite true, TD. Even the best fuel cells are beaten by a GE-90 in power to weight ratio.

That is the current dilemma. Meanwhile, I do wonder how a hybrid electric fan would stack up against conventional turbofan power. Maintenance would certainly be less and I would imagine somewhat lower emissions.

True enough, Ken. I feel sure there would be a net weight savings in swapping some copper conductors for pneumatic plumbing.

Electric motors have 100% torque available from 1 rpm to max rpm.
Turbine engines are very efficient at a max continuous power.

Connect the two (or three or four) and you end up with new performance dynamics (so long as battery storage doesn't literally become the driver).

I would have thought most of the recharging would have to be done by running the generator at full power during descent and diverting the surplus power generated to the battery, otherwise where does power for a go-around come from?

I am probably missing something, but in top level view of the architecture;

• The Generator and battery pack will be sizeable.
• The architecture shows 1 Gen = 1 Fan.

Even if we assume future development (Economics aside) allows 1Gen = 2 Fans, then how do ETOPS apply? Obviously a modified version of ETOPS, but principally you would only have 1 power source, so by default, does this technology only lend itself to Multi Engined aircraft? Or perhaps with 1 Gen = 2 Engines, a regional pax aircraft or cargo drone?

:confused:

It seems like it compares to running out of fuel today in ETOPS (common cause type of failure)

Correct on rechaging, that is part of having the generator handle the average load while running continuously.
Your comment does bring up an interesting point of how many go-around peak loads would need to be handled by the battery and time to recharge battery for next takeoff etc.

Worst case would need to at least accommodate a couple of go arounds followed by climb to cruise to alternate arriving with sufficiently charged battery for at least one more go around. Next take off can likely handled by running the generator on the ground.

Not at all an expert on aircraft energy state, seems a go around would require less energy than full take off but no idea how much less, since also need to account for climb as well as initial acceleration.
Good exam question for the right advanced physics course :)