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NoEnzLefttoSplit
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Posted: Dec 28, 2017 - 12:22pm

 Lazy8 wrote:
 NoEnzLefttoSplit wrote:
While we are at it, what are you views of the ReactionEngine air breathing rocket engine I posted a link to below? Is it possible to store / handle the hydrogen/kerosene mix this thing runs on? 
Presuming we get a cheap supply of clean electricity, does it make sense to use pure hydrogen engines or are the handling problems still too difficult to solve?

The handling problems are the least of it, but those problems are severe. We measure the utility of rocket fuels by specific impulse: thrust/unit mass. Liquid hydrogen/liquid oxygen is hard to beat by that metric. Unfortunately they are very fluffy; the tanks required are huge. Remember the space shuttle, with that enormous external tank? Remember its boosters? the boosters were solid fuel, very dense. They fit into the package much better. The Saturn V used liquid kerosene/liquid oxygen for a better mas/size tradeoff.

Hydrogen doesn't keep or store or transport very well. While it's not as dangerous as it has been made out to be in some quarters it's a pain in the ass, all things considered.

This engine is going to be terribly inefficient as a subsonic power source, so it's never going to be practical for ordinary air travel. If you want to build a Firefly-style atmo-to-low-orbit craft or an around-the-world-by-lunch transport it might be just the ticket, but the Concorde proved there just isn't enough demand for that to pay for it.

 
hmm. so it looks like liquid fuels will be with us for a while then. damn. Thx for your input. Appreciate it. 
Lazy8
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Posted: Dec 28, 2017 - 12:10pm

 NoEnzLefttoSplit wrote:
While we are at it, what are you views of the ReactionEngine air breathing rocket engine I posted a link to below? Is it possible to store / handle the hydrogen/kerosene mix this thing runs on? 
Presuming we get a cheap supply of clean electricity, does it make sense to use pure hydrogen engines or are the handling problems still too difficult to solve?

The handling problems are the least of it, but those problems are severe. We measure the utility of rocket fuels by specific impulse: thrust/unit mass. Liquid hydrogen/liquid oxygen is hard to beat by that metric. Unfortunately they are very fluffy; the tanks required are huge. Remember the space shuttle, with that enormous external tank? Remember its boosters? the boosters were solid fuel, very dense. They fit into the package much better. The Saturn V used liquid kerosene/liquid oxygen for a better mas/size tradeoff.

Hydrogen doesn't keep or store or transport very well. While it's not as dangerous as it has been made out to be in some quarters it's a pain in the ass, all things considered.

This engine is going to be terribly inefficient as a subsonic power source, so it's never going to be practical for ordinary air travel. If you want to build a Firefly-style atmo-to-low-orbit craft or an around-the-world-by-lunch transport it might be just the ticket, but the Concorde proved there just isn't enough demand for that to pay for it.
haresfur
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Posted: Dec 28, 2017 - 12:07pm

 NoEnzLefttoSplit wrote:

well I guess that's progress. The above system is merely a testbed. It's not out to be efficient or "sensible" at this stage. The one engine idea is merely to see how the thing performs on a moderately large plane. Once it works, they'll install two fans and test that. I doubt whether this hybrid system described was ever intended as a working solution, given the weight it would entail.

I fully realise electrically powered planes will only make sense when the power to weight ratio of battery storage reaches something approaching that of liquid fuel (which I believe still means something like a 50-fold improvement!!). But if it gets close enough, economic and environmental considerations will come into play (and yes I live near an airport and would like quieter planes). They are only talking of short hops. Nothing more.

 
On my recent trip westward across the Pacific, they didn't let the standby passengers on because there were headwinds and needed to cut the weight. One of the standby geeks was explaining how needing to carry some extra fuel for the headwinds meant that they needed a lot more fuel to take off.  Then we sat on the ground for 10 minutes burning off excess fuel. I was happy about the open seat next to me but not about the carbon footprint. So the calculations get complicated when you get into the details. But it does seem to be a point that you are likely to get the biggest gain from just enough battery power to take off. And if you factor in the difficult to monetize lower GHG and social benefit of quieter conditions surrounding the airports...
NoEnzLefttoSplit
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Posted: Dec 28, 2017 - 11:21am

While we are at it, what are you views of the ReactionEngine air breathing rocket engine I posted a link to below? Is it possible to store / handle the hydrogen/kerosene mix this thing runs on? 
Presuming we get a cheap supply of clean electricity, does it make sense to use pure hydrogen engines or are the handling problems still too difficult to solve?
Lazy8
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Posted: Dec 28, 2017 - 11:12am

 NoEnzLefttoSplit wrote:
sure. And it's not new. 20 years ago a mate of mine was involved in an aviation project using fuel cells that also um, stalled. But I think you are being overly pessimistic. Forget the hybrid concept. The whole thing with electric planes hinges on how much power a battery can store for given weight. The rest of it is purely economics, how much will fuel cost in future compared to electricity? Other considerations are the time spent refuelling as compared to just plugging in new batteries, etc. 
The noise thing is not quite correct. The noise is from the violent expansion of gas (which admittedly comes rushing out the arse end of the machine) but a fan doesn't push air using thermal expansion like that. They will definitely be quieter. Siemens tested this and unless they are fudging their figures big time, the e-fan has about half the noise emission of a comparable combustion-powered machine.

As for the battery issue...exactly. Get us a battery that makes sense for a passenger airplane and you can make electric airplanes that compete with combustion airplanes. We don't have them. We don't have anything within an order of magnitude of what we need. Electric airplanes are a waste of time and effort until we do.

As for comparing an electric motor to a piston engine...sure, electric motors are quieter. Compared to a turbine? If there's a difference it will be small. There are small (<=20 passenger) piston-powered airliners still flying but they represent a tiny portion of the fleet. They just aren't as efficient (or—surprise!—as quiet) as turboprops. Turbine engines don't go "bang"*, they go "whoosh".

Refueling time is under 15 minutes for most commercial airplanes (it takes about 45 for a 747). Servicing the cabin and getting passengers in and out takes longer. Removing a battery (a not-insignificant amount of weight, and weight that can't share structural duties like a fuel tank if it has to be removable) and reconnecting is going to take significant time. The airplane's safety depends on that connection and attachment so it's not going to be like popping a new AA in your flashlight. Fuel loads are also spread all over the non-passenger areas of airplanes—like the wings. You can do that with batteries as well but they aren't coming off to swap out if you do. Turn-around time for battery-powered airplanes will be a disadvantage to overcome, not an advantage to exploit.

*Unless something goes very very wrong.
NoEnzLefttoSplit
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Posted: Dec 28, 2017 - 10:16am

 Lazy8 wrote:

The goal of the project is to build an electric-powered airplane. That's it.

Not we want to build an electric-powered airplane because it will do X better than what we have but build an electric airplane.

Can we turn a fan with an electric motor? Of course. Can we mount electric motors on airplanes? Of course. No breakthrus here. As a next step in this development I have a suggestion: Instead of burning jet fuel to turn a generator to turn electric motors to spin fans, burn jet fuel to turn the fans directly and haul the generator and electric motor around in the cargo bay, strapped down and inert. Efficiency will go up and they can herald it as a milestone in electric airplane development.

If you think this is going to be quieter you're in for a rude surprise. The noise doesn't come from combustion (which, in this case, goes on regardless) but from all that air rushing out the ass end of the propulsion device. You want to make airplanes quieter? Make them lighter so they don't have to move so much air. Of course that will require more airplanes taking off to carry the same passenger load, but hey.

The electric airplane, at present, is a ginormous virtue signal. Look at us being all green! This is Potemkin Village technology, like building  a teleportation subway station. We'll just use trains until the actual teleportation is practical. But look! Proof of concept.

 
sure. And it's not new. 20 years ago a mate of mine was involved in an aviation project using fuel cells that also um, stalled. But I think you are being overly pessimistic. Forget the hybrid concept. The whole thing with electric planes hinges on how much power a battery can store for given weight. The rest of it is purely economics, how much will fuel cost in future compared to electricity? Other considerations are the time spent refuelling as compared to just plugging in new batteries, etc. 
The noise thing is not quite correct. The noise is from the violent expansion of gas (which admittedly comes rushing out the arse end of the machine) but a fan doesn't push air using thermal expansion like that. They will definitely be quieter. Siemens tested this and unless they are fudging their figures big time, the e-fan has about half the noise emission of a comparable combustion-powered machine. 

 


aflanigan
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Posted: Dec 28, 2017 - 9:58am

 NoEnzLefttoSplit wrote:

well I guess that's progress. The above system is merely a testbed. It's not out to be efficient or "sensible" at this stage. The one engine idea is merely to see how the thing performs on a moderately large plane. Once it works, they'll install two fans and test that. I doubt whether this hybrid system described was ever intended as a working solution, given the weight it would entail.

I fully realise electrically powered planes will only make sense when the power to weight ratio of battery storage reaches something approaching that of liquid fuel (which I believe still means something like a 50-fold improvement!!). But if it gets close enough, economic and environmental considerations will come into play (and yes I live near an airport and would like quieter planes). They are only talking of short hops. Nothing more.

 
Or to put it more prosaically, you could probably throw a frisbee® as far as the Wright brothers' utterly impractical prototype flying machine went in 1913 on its maiden voyage.
Lazy8
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Location: The Gallatin Valley of Montana
Gender: Male


Posted: Dec 28, 2017 - 9:58am

 NoEnzLefttoSplit wrote:
well I guess that's progress. The above system is merely a testbed. It's not out to be efficient or "sensible" at this stage. The one engine idea is merely to see how the thing performs on a moderately large plane. Once it works, they'll install two fans and test that. I doubt whether this hybrid system described was ever intended as a working solution, given the weight it would entail.

I fully realise electrically powered planes will only make sense when the power to weight ratio of battery storage reaches something approaching that of liquid fuel (which I believe still means something like a 50-fold improvement!!). But if it gets close enough, economic and environmental considerations will come into play (and yes I live near an airport and would like quieter planes). They are only talking of short hops. Nothing more.

The goal of the project is to build an electric-powered airplane. That's it.

Not we want to build an electric-powered airplane because it will do X better than what we have but build an electric airplane.

Can we turn a fan with an electric motor? Of course. Can we mount electric motors on airplanes? Of course. No breakthrus here. As a next step in this development I have a suggestion: Instead of burning jet fuel to turn a generator to turn electric motors to spin fans, burn jet fuel to turn the fans directly and haul the generator and electric motor around in the cargo bay, strapped down and inert. Efficiency will go up and they can herald it as a milestone in electric airplane development.

If you think this is going to be quieter you're in for a rude surprise. The noise doesn't come from combustion (which, in this case, goes on regardless) but from all that air rushing out the ass end of the propulsion device. You want to make airplanes quieter? Make them lighter so they don't have to move so much air. Of course that will require more airplanes taking off to carry the same passenger load, but hey.

The electric airplane, at present, is a ginormous virtue signal. Look at us being all green! This is Potemkin Village technology, like building  a teleportation subway station. We'll just use trains until the actual teleportation is practical. But look! Proof of concept.
NoEnzLefttoSplit
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Posted: Dec 28, 2017 - 9:31am

 Lazy8 wrote:

"The BAE 146 demo aircraft, a jet that seats up to 100 people, will at first have one of its four gas turbine engines replaced with the hybrid engine. This engine will be powered by batteries and an onboard generator using jet fuel."

This is not the silliest idea I've ever heard but it's in the top ten.

 
well I guess that's progress. The above system is merely a testbed. It's not out to be efficient or "sensible" at this stage. The one engine idea is merely to see how the thing performs on a moderately large plane. Once it works, they'll install two fans and test that. I doubt whether this hybrid system described was ever intended as a working solution, given the weight it would entail.

I fully realise electrically powered planes will only make sense when the power to weight ratio of battery storage reaches something approaching that of liquid fuel (which I believe still means something like a 50-fold improvement!!). But if it gets close enough, economic and environmental considerations will come into play (and yes I live near an airport and would like quieter planes). They are only talking of short hops. Nothing more.


Lazy8
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Posted: Dec 28, 2017 - 8:56am

 NoEnzLefttoSplit wrote: 
"The BAE 146 demo aircraft, a jet that seats up to 100 people, will at first have one of its four gas turbine engines replaced with the hybrid engine. This engine will be powered by batteries and an onboard generator using jet fuel."

This is not the silliest idea I've ever heard but it's in the top ten.
NoEnzLefttoSplit
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Posted: Dec 28, 2017 - 12:20am

ha, and this just in.. 
NoEnzLefttoSplit
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Posted: Dec 27, 2017 - 11:07pm

 haresfur wrote:

Well in that case, just use a really long extension cord that will pop unplugged after takeoff. Put it on a reel on the ground, wind it back up and plug into the next plane.

Oh wait, you should never yank on a cord to unplug. nvm

 
I like the way you think.. and actually that is not such a dumb idea. patent it!
haresfur
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Posted: Dec 27, 2017 - 11:00pm

 NoEnzLefttoSplit wrote:

exactly, that is the crux.. one idea is to create a hybrid system with a small turbine/generator at the back of the plane. Given that most energy is expended at take-off I could imagine that working too.

 
Well in that case, just use a really long extension cord that will pop unplugged after takeoff. Put it on a reel on the ground, wind it back up and plug into the next plane.

Oh wait, you should never yank on a cord to unplug. nvm
NoEnzLefttoSplit
Being Norwegian is over-rated.
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Posted: Dec 27, 2017 - 10:56pm


NoEnzLefttoSplit
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Posted: Dec 27, 2017 - 10:07pm

 haresfur wrote:

I suppose you need to consider the drive train plus the battery weight for longer flights and you need low-carbon footprint electricity.

 
exactly, that is the crux.. one idea is to create a hybrid system with a small turbine/generator at the back of the plane. Given that most energy is expended at take-off I could imagine that working too.
NoEnzLefttoSplit
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Posted: Dec 27, 2017 - 10:06pm

 ScottFromWyoming wrote:

Cool. Fixed your link tho.

 
thx!
haresfur
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Posted: Dec 27, 2017 - 10:03pm

 NoEnzLefttoSplit wrote:
And electric engines for short-haul flights are looking increasingly viable.

 
I suppose you need to consider the drive train plus the battery weight for longer flights and you need low-carbon footprint electricity.
ScottFromWyoming
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Posted: Dec 27, 2017 - 10:00pm

 NoEnzLefttoSplit wrote:
And electric engines for short-haul flights are looking increasingly viable.

 
Cool. Fixed your link tho.
NoEnzLefttoSplit
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Posted: Dec 27, 2017 - 9:39pm

And electric engines for short-haul flights are looking increasingly viable.


NoEnzLefttoSplit
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Posted: Dec 27, 2017 - 9:30pm

I have started feeling a lot more optimistic about the future lately, what with fusion looking increasingly likely (difficult as hell, but more and more likely). 

Then new propulsion systems like this one from Reaction Engines make me think, maybe we can have our cake and eat it too..  
..as far as I understand it, they run on a combination of hydrogen and refined kerosene.. does anyone know how much kerosene? Pure hydrogen would be cool, particularly if we got a virtually limitless source of electricity.


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