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Future air transport
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stumuzz



Joined: 17 Nov 2009
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Location: Anglesey, North Wales

PostPosted: Sun Feb 28, 2010 11:33 am    Post subject: Future air transport Reply with quote

What does everyone think of this?

http://news.bbc.co.uk/today/hi/today/newsid_8540000/8540375.stm

Low carbon air transport will allow food miles to become acceptable?
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clv101
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Joined: 24 Nov 2005
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PostPosted: Sun Feb 28, 2010 12:05 pm    Post subject: Reply with quote

I looked at airships a while ago. I concluded that lift is pretty irrelevant (cf planes), it's all about speed and drag. Airships are large and as such have huge drag. Not convinced they are much more efficient that planes unless being blown along by the wind. This loses the "straight line" advantage King mentioned.

Fact they don't need much ground infrastructure is a very good point though.
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contadino



Joined: 05 Apr 2007
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PostPosted: Sun Feb 28, 2010 12:10 pm    Post subject: Reply with quote

An airship that can carry 1,000 tonnes? I'd like to see that, but as it's David King, I doubt I ever will. The bloke is full of shit.

Laws of physics don't really help add any credibility either. Surely it takes the same amount of energy to lift 1,000 tonnes and transport it at 100-odd mph whether it's by plane or airship.
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clv101
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PostPosted: Sun Feb 28, 2010 1:06 pm    Post subject: Reply with quote

contadino wrote:
Laws of physics don't really help add any credibility either. Surely it takes the same amount of energy to lift 1,000 tonnes and transport it at 100-odd mph whether it's by plane or airship.


No it doesn't work like that at all. As I said above, it's not about lift. The airship lifts for free as it's lighter than air! The difference is that to for the plane to generate the lift it needs to be travelling fast, and overcome drag. Planes use almost all their energy overcoming drag (the reason they fly at 10km up rather than 1km up is to find thinner air, otherwise why waste all that energy going so high?).

The airship doesn't need speed to generate lift, (that's free as it's lighter than air). Just like the plane it uses its energy to overcome drag. The plane is small and fast, the air ship is big and slow. To a first approximation the drag is similar and airships aren't better than planes.
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stumuzz



Joined: 17 Nov 2009
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PostPosted: Sun Feb 28, 2010 1:12 pm    Post subject: Reply with quote

I think it was RalphW who posted a couple of years ago that 80% of the fuel used by a cargo/passenger plane was in take off. When it was at height and the descent to land it was very fuel efficient.

If these airships can just ‘ float up’ then the big use of fuel can be avoided?
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PS_RalphW



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PostPosted: Sun Feb 28, 2010 7:26 pm    Post subject: Reply with quote

On short haul flights 80% sounds about right. I used to fly Stanstead to Paris, and the plane never got to cruise altitude. It went straight up to 25,000, cut the engines to idle, and began its descent glide to Paris.

I used to write aircraft engine simulation software, but that was 20 years ago.
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adam2
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PostPosted: Thu Apr 15, 2010 3:18 pm    Post subject: Reply with quote

Airships can be very useful for delivering bulky cargo to remote places, and for other specialist purposes but I cant see them replacing conventional aircraft on a large scale.
Not fast enough to compete with rail on shorter trips, and would take 24+ hours for intercontintental trips, this would need sleeping berths which would add substantialy to the costs.

The main problem though, is with what is it proposed to fill all these airships ?
Hydrogen is far too flammable as the Hindenburg tragedy showed.
Helium is safe being inert, but is available only in small qauntities, and is a byproduct of natural gas production.
Peak natural gas=peak helium. Although the helium is not consumed like fuel, it will assuredly leak out and require topping up.
Helium use could be slightly reduced by use of a mixture of hydrogen and helium, hydrogen being used in the greatest percentage that gives a non flammable mixture. I still doubt that enough helium could be found for a large fleet though.
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Grizzly Mouse



Joined: 24 Mar 2008
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PostPosted: Fri Apr 16, 2010 4:05 am    Post subject: Reply with quote

Airships have the advantage that they can be powered by solar power. Which if high tech can survive the depletion of oil would be an advantage as no practical plane that can carry anything has been made that runs on anything over than refined oil.

Drag increases exponentially with speed, so as well as having lower power needs they could have less total energy consumption despite the longer journey time and wider body. Most of the drag comes from the wings, a plane needs to continuously spend energy to stay up in the air, while an airship stays at the same altitude when it is idling like a ground vehicle.

I wont be doing all the equations you need to do to figure out which is actually more efficient for all the different scenarios though.
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PS_RalphW



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PostPosted: Thu Jul 01, 2010 9:43 am    Post subject: Reply with quote

RyanAir are ahead of the pack again.

This will be the only way to fly when oil hits $200.

Ryanair to sell tickets for standing-room only flights
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clv101
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PostPosted: Thu Jul 01, 2010 9:57 am    Post subject: Reply with quote

RalphW wrote:
RyanAir are ahead of the pack again.

This will be the only way to fly when oil hits $200.

Ryanair to sell tickets for standing-room only flights


It's just PR! Every year he mentions paying to use the loo and standing and gets articles in all the papers for free.
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DominicJ



Joined: 18 Nov 2008
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PostPosted: Thu Jul 01, 2010 1:27 pm    Post subject: Reply with quote

Quote:
An airship that can carry 1,000 tonnes? I'd like to see that, but as it's David King, I doubt I ever will. The bloke is full of shit.

http://en.wikipedia.org/wiki/WALRUS_HULA

The US considers the concept worth looking into.

http://www.hybridairvehicles.net/products_skycat200.html
Theres already an airship with a 200t lift capacity.
Theres a plane with a greater cargo payload, but the thing can barely move when filled to the brim.

The US is, or was, quite heavily funding airships, they are much faster and much more mobile than ships and much cheaper than aircraft.
Not sure how they stack up against trains, but trains need tracks.

They're not going to make much impact on mass human transit, although people seem to manage to spend three days on a train without a berth in move of the world, but for mass cargo, they could be very useful.[/quote]
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clv101
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PostPosted: Thu Jul 01, 2010 3:03 pm    Post subject: Reply with quote

DominicJ wrote:
...and much cheaper than aircraft.

Are they really though? If so, why were they not developed in the 50s, 60s, 70s 80s, 90s etc?
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stumuzz



Joined: 17 Nov 2009
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PostPosted: Thu Jul 01, 2010 4:23 pm    Post subject: Reply with quote

But, they do not have to carry heavy weights.

A very large proportion of cargo is very light( think crisps) but has the same density as heavier objects. So transporting 24 m3 of crisps weighing 1t to another country will cost about the same as transporting 24t of heavy cargo. The cost of the lorry-ferry-lorry will be the same whatever the cargo the difference will be the amount of fuel used by the heavier load.

If the airship could carry the crisps at a rate of 20 lorry loads at a time, it would stop a lot of fuel being used,take the lorries out of towns, reduce or remove concrete/mining/tarmac for road infrastructure,give the existing roads a new lease of life, healthier environments, less photochemical smog, green gases, acid rain.

There has got to be a physical reason why no one is doing it, because I cannot think of a commercial one.

Any physicists out there wanting to give it a go?
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clv101
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PostPosted: Thu Jul 01, 2010 5:44 pm    Post subject: Reply with quote

stumuzz wrote:
There has got to be a physical reason why no one is doing it, because I cannot think of a commercial one.

Any physicists out there wanting to give it a go?


See my February posts above.
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DominicJ



Joined: 18 Nov 2008
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PostPosted: Thu Jul 01, 2010 6:04 pm    Post subject: Reply with quote

clv101 wrote:
DominicJ wrote:
...and much cheaper than aircraft.

Are they really though? If so, why were they not developed in the 50s, 60s, 70s 80s, 90s etc?


Fair point, it is relient on them actuly being as cost effective as people claim.

Why were they never developed, has there ever been a market for them?
Cargo ships had a history, Jets were the new thing after the war.
Now, airfreight is pretty limited, even the armed forces cant afford much of it, if the US decides another Afghanistan is likely, they could funnel billions into the idea.

Its unlikely it will ever be commerical to airship coal, but Cars, Machine Tools, who knows what else.
It would certainly be handy to move a dozen heavy tanks across the world in less than a week, a task that would currently take a C17, half a dozen forward positioned refuelers and a small fortune, to move just one.
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