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

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

Old 30th Nov 2017, 16:49
  #21 (permalink)  
 
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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
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Old 2nd Dec 2017, 10:38
  #22 (permalink)  
 
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Originally Posted by MathFox View Post
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.
I agree, but once we get to our cruising altitude, how about a destination?

Originally Posted by ion_berkley View Post
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....
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.

empirically stated a 100kWh Tesla can easily drive 300 miles. Try that on 2.5 gallons of Kerosene or gas.
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.

Last edited by vapilot2004; 2nd Dec 2017 at 10:52.
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Old 2nd Dec 2017, 11:16
  #23 (permalink)  
 
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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/
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Old 2nd Dec 2017, 11:34
  #24 (permalink)  
 
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Brilliant....ly funny!

"The risk of reactors cracking open in a crash could be reduced by jettisoning them before impact and bringing them down with parachutes,"
I was blissfully unaware of the nuclear powered B-36 here in the states. Good grief!, as Charlie Brown might say.
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Old 3rd Dec 2017, 00:17
  #25 (permalink)  
 
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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.
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Old 3rd Dec 2017, 00:21
  #26 (permalink)  
 
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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.
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.
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Old 3rd Dec 2017, 01:10
  #27 (permalink)  
 
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Originally Posted by WingNut60 View Post
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.
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.
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Old 3rd Dec 2017, 21:18
  #28 (permalink)  
 
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I think it's a lot of nonsense...real jets are better to focus talent on
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Old 4th Dec 2017, 08:46
  #29 (permalink)  
 
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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.
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Old 4th Dec 2017, 09:38
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Originally Posted by tdracer View Post
Why the extra complication and weight of a fuel cell/electric motor? Just burn the H2 in a gas turbine.
Quite true, TD. Even the best fuel cells are beaten by a GE-90 in power to weight ratio.

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.
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.

You're going to need a lot of copper to transmit power from a tail generator to wing mounted electric motors.
True enough, Ken. I feel sure there would be a net weight savings in swapping some copper conductors for pneumatic plumbing.
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Old 4th Dec 2017, 11:11
  #31 (permalink)  
 
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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).
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Old 4th Dec 2017, 12:47
  #32 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
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.
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?
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Old 4th Dec 2017, 14:05
  #33 (permalink)  
 
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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?

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Old 4th Dec 2017, 15:25
  #34 (permalink)  
 
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It seems like it compares to running out of fuel today in ETOPS (common cause type of failure)
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Old 4th Dec 2017, 15:25
  #35 (permalink)  
 
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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

Last edited by MurphyWasRight; 4th Dec 2017 at 15:28. Reason: Added note on recharging
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