Electric Airplane?

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Posted by Overmod on Tuesday, October 31, 2017 10:27 PM

erikem
As for dealing with batteries, I would put them in pods mounted on hard points under the wing.

Even with the fire hazard and optimized cooling systems required, I think Zunum's approach (which is to put the modules inside the wing structure between the spars, much as the fuel load is actually positioned on an airliner, preserving as much of the streamlining and proper wing geometry as possible) is better than external battery 'pods'.  They point out that the modules are explicitly designed for gang replacement (probably with automated equipment) to allow rapid turnaround with effective full takeoff charge.

I do not expect 'pure' electric airliners to be nearly as successful as designs using full-parallel combustion engines as 'thrust augmentors' for the straight-electric motors.  I am highly interested in seeing the 'propfan' geometry that is actually used on these, as opposed to the 'generic' ducted fan shown in the publicity materials...

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Posted by BLS53 on Wednesday, November 01, 2017 4:53 AM

Alternative fuels for jets, are far more likely than a completely new form of propulsion.

I think the decades are numbered for the short to medium haul airliner anyway. Too many current unresolvable issues. Ripe for the pickings of a new transporation break through.

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Posted by gregc on Wednesday, November 01, 2017 6:41 AM

the other problem with batteries is that their full weight must be carried the entire flight while the weight of liquid fuel diminishes.   

In other words the average weight of liquid fuel over the course of the flight is half.   It takes less fuel to fly the aircraft near the end of the flight.   And for safety purposes, the aircraft landing weight is much less than it's take-off weight.

Maybe hanging batteries from jettisonable pods would be of value if there were an engine failure and the aircraft must glide (10:1) or during an emergency landing.

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Posted by 54light15 on Wednesday, November 01, 2017 9:29 AM

Miningman, I've seen stuff about highways in the air. It looked legitimate but it was on "The Jetsons." 

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Posted by Overmod on Wednesday, November 01, 2017 10:09 AM

gregc
the other problem with batteries is that their full weight must be carried the entire flight while the weight of liquid fuel diminishes.[

That is of course correct; I would observe though that for 'single hops' the primary effect of the fuel load (as with rockets) is in the initial climb to altitude, where there would still be considerable fuel mass present, so the functional effect of the added 'structural' weight is more significant only as it applies to cruise, particularly last-half cruise where some gravitational energy is assisting with glide, and so I think the effect is less troublesome than you indicate.  There is also less concern with 'having' to shift fuel between tanks to maintain attitude or balance as the fuel load is consumed.  A concern you didn't raise explicitly is the implication of the additional mass and its distribution in recovery from something like high-CAT, and while it is possible that the larger polar moment, etc. of the wing-mounted batteries might help keep the aircraft from prompt attitude change, it is also possible that the added mass would impede necessary recovery actions or perhaps even contribute toward a (deadly) combination of low airspeed and nose-high attitude.

There has been some discussion of the 'optimal' battery capacity vs. liquid-fuel tankage for hybrid airliners in places like the Intelligent Aerospace group, in part looking at this precise concern.  My own feeling at this point (much of the required high-energy-density battery work not being fully commercialized) is that the provision of the 'boostable' electric engines and adequate reserve to accomplish prompt climbout without unacceptable battery cycling is more important than 'being able to make the trip fully on Electricity Fairy power'.  I also suspect that in a 'green' world, it will still be better to use biorenewable liquid fuel, even if it is blatantly a 'carrier fuel' when full energy analysis is done, in preference to fully renewable electricity recharge.  I suspect much of the present 'cost bias' in favor of electricity over hydrocarbon vehicle fuel will likely not apply to a generating infrastructure heavily weighted toward 'renewable energy', at least as I see those trends developing in practical electricity-utility implementation with the current thinking about tradable 'green energy' credits.

It takes less fuel to fly the aircraft near the end of the flight.   And for safety purposes, the aircraft landing weight is much less than its take-off weight.

I am not sure that it is near the end of the flight that is the principal concern of the battery deadweight, as the aircraft will be predominantly in glide or in a known holding pattern then, and I do presume that using 'regionals' as destinations will facilitate a more direct, short, and safe approach.  The concern I have is that on landing the full additional mass has to be handled with reversers and brakes, perhaps just at the time the battery requires heavy draw because of voltage conversion at low capacity.  Clever application of some kind of spoilers or speedbrakes, or moving the wing to get higher effective drag, might get around some of this, but I think you'd be right to be concerned.

Maybe hanging batteries from jettisonable pods would be of value if there were an engine failure and the aircraft must glide (10:1) or during an emergency landing.

I saw at least one proposal ... I confess I ridiculed it, but it had a certain queer logic ... to use demountable pods or even additional boost motors to get a large electric aircraft airborne reliably, and then either drop them in a 'known safe' location for recovery or 'fly' them back to base similar to an autonomous version of the early WS110 vehicles (or the 'mother ship' for two-stage TAV).

The big, awful problem is the idea that you're bombing civilians indiscriminately if you do that.  These pods would have tremendous chemical energy in them, and as with non-degassed Bakken crude in tankcars it will take far less shock or stress to breach them to failure than perhaps even a parachute-assisted pod landing may provide.  Just one of these that causes even property damage will have the lawyers all over you ... let alone the result of setting a house on fire or killing people on the ground.  There is also the fun that would ensue if one side didn't drop when the other did -- a relatively common issue with both ordnance and drop tanks -- and while any modern 'autonomous' autopilot could probably deal with the effect (could it be worse than turning into the dead engine on a light twin?) I think it would be wiser to avoid the whole idea if possible.

Having the batteries between spars and structures assures consistent glide ratio and other measures of wing performance reliably, and it 'might' be possible to jettison some of the cells (in pairs for balance) through the equivalent of bomb-bay doors were they to show imminent signs of catastrophic failure or fire.  I have to confess that when I first saw the Zunum configuration I wondered what arrangements were being made for caustic release and/or fire in a confined space adjacent both to key wing structure and aerodynamically-significant skin.  There are some ways to 'recover' from having to drop internal battery modules that would not degrade aerodynamics severely, and I think there would be at least a reasonable presumption that the 'remaining' capacity plus the sustainer engine would get the aircraft reliably to an alternate safe landing area and provide reasonable control authority through landing.

My own thinking about 'quick exchange' batteries was to have them packaged much like laptop batteries, dropping through doors in the lower wing surface and at least semi-automatically disengaging and engaging the electrical contacts, cooling means, etc. and on installation running a proper BITE routine to assure complete systems operation.  That has proceeded at least as far as specific support-vehicle designs for various scales of "FBO" at regionals.

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Posted by gregc on Wednesday, November 01, 2017 10:31 AM

another benfit of dismountable batteries hung from wings is that they could be replaced quickly to get the plane back in flight and recharge the spare packs while the plane is in flight.

greg - Philadelphia & Reading / Reading

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Posted by Overmod on Wednesday, November 01, 2017 12:57 PM

gregc
another benefit of dismountable batteries hung from wings is that they could be replaced quickly to get the plane back in flight and recharge the spare packs while the plane is in flight.

At zunum.aero (under ‘technology - wing-mounted batteries’) they indicate their arrangement is ‘modular’ and suitable for ‘swap or recharge’; this without the potential drag and induction of turbulence associated with external pods or bays.

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Posted by erikem on Wednesday, November 01, 2017 11:01 PM

One additional advantage of wing mounted batteries is that the thermal management system might be usable as a means of de-icing. The downside is that there may not be enough heat available to be effective.

Hybrid electric/combustion propulsion starts to get interesting with VTOL/STOL.

Which brings up another question, what kind of range could we get out of an electric multiple unit running with Li-ion batteries. Would be kind of fun seeing the DMU's on NCTD's Sprinter service replaced with EMU's. A historical note: 100 year old battery powered streetcars could do 80-100 miles on a charge.

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Posted by Overmod on Thursday, November 02, 2017 5:01 AM

erikem
One additional advantage of wing mounted batteries is that the thermal management system might be usable as a means of de-icing. The downside is that there may not be enough heat available to be effective.

I am tempted to note that the provision of appropriate resistive elements along the leading edge, combined with proper routing of the active TMS of the battery cells, would with relative ease assure 'enough heat available to be effective'.  I would take more than usual care to assure that no part of the system could produce enough current draw to cause thermal runaway to start in any part of the battery system, though. 

Hybrid electric/combustion propulsion starts to get interesting with VTOL/STOL.

Or STOVL, which is something that has increased attractiveness with 'expert system' autopilots.  Suspect there will be adequate space at most "regional" facilities to allow horizontal acceleration to aerodynamic lift, using less power at a lower peak rate, instead of VTO with drone-like propulsion or Agusta-Westland-like tilt-rotors, although I think most of the dynamic stability issues have been solved.  But it might be nice to have quick and clean descent reasonably close to an 'intermodal' transfer point, and in theory you could avoid much of the wheel braking/spoiler/thrust reverse and active wing-lift 'enhancement' concerns with an aerodynamically 'clean' envelope that would have to land conventionally at high relative stall speed.  (I was commenting recently that an expert-system autopilot can take measures at landing that few if any human pilots could achieve safely, like using the sailplane 'trick' of walking the rudder to preclude wing stall and falloff at low final speed...)

Which brings up another question, what kind of range could we get out of an electric multiple unit running with Li-ion batteries. Would be kind of fun seeing the DMU's on NCTD's Sprinter service replaced with EMU's.

I think we are about to see a spate of proposals for this very thing, probably enabled by large commercial battery suppliers to the rail industry making and warrantying the necessary elements (which is starting for Siemens' primary battery supplier right about now).  I do think that here, too, the correct design would be a hybrid and not 'straight electric', but it shouldn't be difficult to adapt current forms of 'wayside assistance' and some of those streetcar charging proposals to provide at least reasonable energy 'replenishment', perhaps inductively, at the many stops, in which case the 'combustion engine' would become much more an 'emergency' device ... perhaps included in some kind of hi-rail vehicle that would be driven to a stalled consist and quickly connected to run it on some of its own motors and start recharging it rather than 'tow' it.

A historical note: 100 year old battery powered streetcars could do 80-100 miles on a charge.

But I would have to wonder how many of those miles would have been with orange-dim lighting and very slow golf-cart-on-the-35th-hole motor performance...  of course, as noted, modern voltage-to-voltage conversion solves much of these but at the 'cost' of somewhat shorter range and more potential degradation of the battery array near the end of its practical discharge.  These are all things that you know well, so mentioned for completeness and context only.

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Posted by Overmod on Thursday, November 02, 2017 5:11 AM

Miningman
So if everyone has one of these drone type versions how on earth do you control the airspaces...roadways in the air?

Now that we've established a legitimate railroad tie-in for this topic, we can tolerate a little drift...

The easiest way is to incorporate the 3D regions of potential danger from wires, overhead structures, towers, etc. into the 'haptic space' in which the autopilot works.  This solves, for example, the potential problem (seen in using older-generation light amplification for nighttime military flight) of wires being below the resolution of key sensor systems and hence undetectable until 'too late' in pure sensor-fusion autonomous operation.  I will not go into the complexities of who would manage this space, keep it uncorrupted, etc. etc. etc.

Yeah, security is going to be an interesting implementation.  But most of it would be much more interesting than a typical cop or Government-agency kind of 'enforcement'...

Meanwhile, there was this; while I agree with the premise, I find I can't let the statement pass without comment.

Analog TV 7 years ago with all the snow will never get better.  Now HD TV.

Right!  Replacing snow and ghosting with macroblock artifacts and freezing!  In a nutshell, ATSC was a crap idea and imnsho still is; we should have gone with some version of COFDM, even if it was by then 'European'.  I find somewhat to my surprise that this can still get me riled these, now, decades later.

 

 

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Posted by erikem on Thursday, November 02, 2017 10:38 PM

Overmod

 

 
erikem
Which brings up another question, what kind of range could we get out of an electric multiple unit running with Li-ion batteries. Would be kind of fun seeing the DMU's on NCTD's Sprinter service replaced with EMU's.

 

I think we are about to see a spate of proposals for this very thing, probably enabled by large commercial battery suppliers to the rail industry making and warrantying the necessary elements (which is starting for Siemens' primary battery supplier right about now).  I do think that here, too, the correct design would be a hybrid and not 'straight electric', but it shouldn't be difficult to adapt current forms of 'wayside assistance' and some of those streetcar charging proposals to provide at least reasonable energy 'replenishment', perhaps inductively, at the many stops, in which case the 'combustion engine' would become much more an 'emergency' device ... perhaps included in some kind of hi-rail vehicle that would be driven to a stalled consist and quickly connected to run it on some of its own motors and start recharging it rather than 'tow' it.

 

I did some quick estimates for possible range for a rail car with Li-ion batteries, and the limiting range assuming all weight in the battery and 12 pounds per ton (24 w-hr per ton mile) of total train resistance and 200w-hr/kg for the battery. Results comes out to be 7,000 or so miles. This implies that a few hundred miles of range with battery weight less than 10% of total.

Taking the future of electric power in a large portion of the US, the cheapest rates will be in the middle of the night and mid morning to early afternoon (solar surplus). This suggests enough battery capacity to run the whole morning commute on a charge, with cars recharging from say 10AM to 2PM, then doing the evening commute.

Battery operated EMU's would be a better deal than battery locomotives as having motors on most of the axles will a lot of the kinetic energy to be regenerated during braking. Having batteries being somewhat larger than the bare minimum needed would help with energy efficiency - more batteries in parallel will reduce equivalent series resistance for both discharge and charge cycles. Other advantage of regenerative braking is reducing brake wear - the NCTD Sprinter cars had serious problems with brake wear.

For quick recharging at stops, it would be pretty simple to put a short section of wire, say the length of platform, and power the car directly.

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Posted by Overmod on Friday, November 03, 2017 2:17 AM

I think a better estimate would be to start with something like an FRA-compliant EMU car/married pair’s mass, then add the prospective battery pack and environmental ‘shielding’ mass to that, and then look at acceleration and deceleration at some “accepted” performance rate (istr 1.5 f/s^2 but that may be too old-fashioned) for the number of stops and starts.

I’ve been figuring on some ‘charge buffering’ to get extended dynamic braking while soft-charging the battery arrays at all times; there may be some economic advantage in throwing away some of the peak decel in grids with makeup from the electricity fairy (I hate waste, but I like non-friction braking more...). Of course we still need enough tread braking or wiping or whatever to assure good tread cleanliness and signal contact, don’t we, even with PTC ubiquitous? but blended braking isn’t difficult to ‘program in’.

It’s funny how few of the ‘asynchronous charge’ proposals I remember seeing use the short-length-of-wire approach (many give ‘reasoning’; it is a comparative eyesore, contact hazard, requires comparatively expensive equipment on the car, etc.) but I agree with you that it is a good technical approach.  I suspect at this point that either inductive charge or an updated version of the old GE approach with pins coming up and only energizing when they ‘handshake’ with the car would be “politically preferable” alternatives when selling the idea — but I may well be confusing light rail with heavy.

The other piece of the analysis is whether cars (or, indeed, perhaps locomotives) like this begin to make sense even for systems like MARC that already operate partly under wire but don’t like the economics as provided to them.  Might even be worthwhile to divide the traction battery into reserve and ‘cycling’ portions, as good electric car designs do, so that you get all the benefits of regenerative brake without all the wayside storage modules with KERS and so forth or having to do full regeneration to high-voltage catenary...

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Posted by erikem on Saturday, November 04, 2017 5:19 PM

Overmod

I think a better estimate would be to start with something like an FRA-compliant EMU car/married pair’s mass, then add the prospective battery pack and environmental ‘shielding’ mass to that, and then look at acceleration and deceleration at some “accepted” performance rate (istr 1.5 f/s^2 but that may be too old-fashioned) for the number of stops and starts.

A somehwat more real-world estimate of energy requirements comes from Doane's "Electric Railway Engineering" from 1915. The measured energy consumption for a local interurban run with a scheduled speed of 22 MPH came out to 76.6w-hr/ton-mile. Bear in mind that this is with motor/controller efficiency of 75% at running speed and 60% when accelerating with no regeneration. Modern motor/controller efficiency would be on the order of 90% and it would be safe to assume that at least a 10% reduction in total consumption from regeneration.

Let's assume a 50 on articulated pair (e.g. original Siemens car for the San Diego trolley at 68,000 lb, +10,000 lb battery pack, + 22,000 lb for passengers and structural stengthening) and a 80w-hr/ton-mile (to allow for HVAC) energy consumption. Reports about the standard and long range versions of the Tesla Model 3 suggest that 1 kwhr of battery pack will weigh in about 11 lb, say 180 kwhr/ton. With 900 kwhr (5 tons X 180kwhr/ton) and 4 kwhr/car-mile, we have a range of 225 miles. Actual enrgy consumption is likely less than 4 kwhr/car-mile and battery capacity could be increased if additional range is needed.

The NCTD Sprinters travel about 22 miles between Oceanside and Escondido, with trains scheduled for 53 minutes with 15 stops (basically interurban local service). A full charge would get through about 10 trips. The currently scheduled layovers at the endpoints are 7 minutes, which would be enough put one run's worth of charge into the battery. My impression is that NCTD runs single pair trains during off peak times and multiple car trains during rush hours, so it would be possible to schedule car usage to allow recharging from late morning to early afternoon such that each car only does 6 or 7 runs between recharging.

The Tesla Model 3 is priced assuming $190/kwhr, so the 900kwhr wort of batteries enioned above would run under $200,000.

I’ve been figuring on some ‘charge buffering’ to get extended dynamic braking while soft-charging the battery arrays at all times; there may be some economic advantage in throwing away some of the peak decel in grids with makeup from the electricity fairy (I hate waste, but I like non-friction braking more...). Of course we still need enough tread braking or wiping or whatever to assure good tread cleanliness and signal contact, don’t we, even with PTC ubiquitous? but blended braking isn’t difficult to ‘program in’.

In the example of a 900kwhr battery above, the battery should be capable of handling all of the normal decel, with friction brakes used for emergencies. The improved acceleration available should allow for more relaxed braking rates while still maintaining schedule. A 900 kwhr battery should have no problem supporting 2,000HP for short periods.

As for lineside batteries... There are a few cases for implementation. One is smoothing out demand peaks (perhaps best served with ultracaps?), another is reducing utility power consumption at peak demand times and providing back-up during power outages.

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Posted by erikem on Thursday, November 16, 2017 1:09 AM

An email on from Texas Instruments brought up some pertinent data for the discusion on this thread. One of the titems mnetioned was charge rates for Li-ion batteries, specifically severely discharged, normally discharged and top 20% of charge. A severely discharged battery has to have a slow initial charge to prevent damage, fast charge can start after a certain point is reached (implication was 20% charged) and charging needs to slow down past 80%.

The implication is that fast charge will only work over ~60% of the battery capacity, i.e. from 20% to 80% charged. This also means that electric airliners will need to have quickly replaceable batteries to allow for the final 20% of charge. The same may hold true for electric semis. It also means that an electric car with a 300 mile range will translate into stops every 180 to somewhat over 200 miles for recharging.

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Posted by Overmod on Thursday, November 16, 2017 7:01 AM

I think it is much more likely that the current approach to battery management will be continued with the new chemistries and the proportional ‘weight penalty’ accepted.  There is no reason whatsoever on an electric aircraft to run into deep discharge except perhaps incidentally by a few percent in the last use of reverse thrust for landing and in taxiing.  Likewise the margin from 80% to 100% is not critical for short-period takeoff  in a hybrid aircraft where even optimized ‘trickle charge’  of the last 20% can be easily arranged during cruise even if fancy charge-management schemes are in use.

I had thought the principal reason for quick swap was less related to pure charge-rate considerations than to using nominally cheap or political-credit-favored Electricity Fairy renewable green etc. power for as great a proportion of flight as practical.  As with road vehicles even a small sustainer engine can have dramatic practical advantages even with ‘pure’ electric transmission and its assumed conversion losses.

Modular swap outs of EV ‘battery packs’ are of course a very old idea ... similarly very old are the practical objections to the idea.  Some of these are lessened by technical details of newer construction, or if you go to more of an autonomous rental-in-demand model for the vehicle use itself.  But frankly I would no more drive into some random supercharger station and swap my expensive actively-cooled battery array out for Hobson’s next choice ... or one of an actively-promoted-like-cell-phone array of Blue Rhino-type options, all replete with hidden charges and ‘gotchas’ and surly Bangalore customer service that tells you any problem was your fault ... to get extra 20% per stop?  I would not buy it for a quarter and neither should you.

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Posted by erikem on Thursday, November 16, 2017 2:00 PM

FWIW, I have the same objections to swap out batteries in cars that you do. My comment with respect to cars was aimed at the claim of 300 mile battery range spells the end of internal combustion powered cars. A 300 mile rage does make for a much more useful battery electric car than one with a sub 100 mile range.

Heavy duty trucks may be another matter, where the swap-outs may be done by the trucking company or a vetted service company.

The probem with fast charging is the amount of electric power involved. Even without renewable electric generation, the price of electricity will vary a lot between minimum demand and peak load times, so thee is a strong incentive to average out charging and avoiding certain times of day.

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