On 23/01/2014 11:32, The Natural Philosopher wrote:
On 23/01/14 08:48, Adrian wrote:
On Wed, 22 Jan 2014 21:12:18 +0000, The Natural Philosopher wrote:

And that is the point. Right now electric cars are hopeless, electric
aeroplanes are toys, but multiply battery capacity to weight by 4, and
cars work brilliantly.

Given that the battery pack in a Nissan Leaf is currently 300kg, that'll
just take the weight down to about 50% more than a full fuel tank - which
gives five or more times the range.

Give us 6 or better and aeroplanes really start to take off.

It's always helpful...

Recharge times? never more than an hour.

Sorry - can we just clarify this - you reckon you going to recharge a
5MWh
battery in one hour? Umm, how, exactly...? Multiplied by the traffic on a
summer weekend at a larger regional airfield?

As I said before this is the ONLY green idea that actually has a chance,
if they can knock out cheap safe lithium air batteries.

Boeing aren't exactly having much success as yet. And they're only tiddly
batteries. Even Elon Musk is quoted saying it's the wrong technology for
batteries on planes.

And overnight charging can only help - most commercial flights happen by
day, of the short haul sort.

We're talking about something like a Twin Otter. Not exactly the most
common size of commercial plane. A 787 has north of 300,000 litres of
fuel on board, rather than the 18,000 we've been talking about here. Care
to guesstimate the turn-around times? Or, indeed, the peak recharge
capacity that - say - Heathrow would need?

I had only just got around to a ducted fan design for a 787

300,000 litres would be around hmm 100,000 x 10Kwh, so a GWh or so. 160
tonnes of battery.

No reason not to recharge that in an hour, or have a whole airport full
of the things plugged in on a 10 hour overnight charge.

Given the incentive, they could all use standard battery packs, and they
could be swapped as quickly as they currently swap freight containers.
so the plane would only need to hang about as long as it does now, using
multiple battery packs on charge at all times.

Also, when using electrical power, it may pay to look at the old
propeller driven planes, as a lot of the trade offs that make jets
currently the most efficient means of flying may become invalid. Didn't
someone write on this group not long ago that it's only recent
improvements in battery technolgy that have made electric ducted fans
possible for models?

The total energy needed for an airport is the problem. Heathrow, for
instance, needs a two foot diameter pipeline just to supply fuel to one
terminal's fuelling points. I'm having trouble finding details, but I
suspect that the pipeline from Buncefield to Luton is about the same
diameter. A Boeing 737 travelling to Paris uses about 3.5 tonnes of fuel
at roughly 27 megajoules per kilogramme. So one short flight would need
something like the entire output of Sizewell for many minutes, and that
assumes that the battery is no heavier than the fuel load, as most
getting the weight up to cruising height requires a *lot* of energy, it
takes roughly 1200 kg of fuel for a 737-400 to get to cruising height,
then it's about 3000kg per hour cruising, and 300 kg while dropping from
cruising height to landing. The current average flight requency for
Luton is roughly one flight departure every twenty minutes, averaged
over 24 hours. So, you'd need rather more power than one Sizewell B to
run it, according to my envelope. Heathrow would need more than 25 times
that amount of energy. at current traffic levels.



--
Tciao for Now!

John.